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Versions: 01 02 03 04 05 06 rfc2446                      Standards Track
Network Working Group                       Steve Silverberg, Microsoft
INTERNET-DRAFT                                  Steve Mansour, Netscape
Calendaring and Scheduling Working Group            Frank Dawson, Lotus
<draft-ietf-calsch-itip-06.txt>            Ross Hopson, ON Technologies
Expires six months after:                            September 15, 1998

       iCalendar Transport-Independent Interoperability Protocol
                                 (iTIP)
        Scheduling Events, BusyTime, To-dos and Journal Entries


Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, and
its working groups. Note that other groups may also distribute working
documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months.
Internet-Drafts may be updated, replaced, or made obsolete by other
documents at any time. It is not appropriate to use Internet-Drafts as
reference material or to cite them other than as a "working draft" or
"work in progress".

To view the entire list of current Internet-Drafts, please check the
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ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast).

Distribution of this document is unlimited.

Copyright (C) The Internet Society 1998. All Rights Reserved.


Abstract
This document specifies how calendaring systems use iCalendar objects to
interoperate with other calendar systems. It does so in a general way so
as to allow multiple methods of communication between systems.
Subsequent documents specify interoperable methods of communications
between systems that use this protocol.

The document outlines a model for calendar exchange that defines both
static and dynamic event, to-do, journal and free/busy objects. Static
objects are used to transmit information from one entity to another
without the expectation of continuity or referential integrity with the
original item. Dynamic objects are a superset of static objects and will
gracefully degrade to their static counterparts for clients that only
support static objects.

This document specifies an Internet protocol based on the iCalendar
object specification that provides scheduling interoperability between
different calendar systems. The Internet protocol is called the
"iCalendar Transport-Independent Interoperability Protocol (iTIP)".

iTIP complements the iCalendar object specification by adding semantics
for group scheduling methods commonly available in current calendar
systems. These scheduling methods permit two or more calendar systems to


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perform transactions such as publish, schedule, reschedule, respond to
scheduling requests, negotiation of changes or cancel iCalendar-based
calendar components.

iTIP is defined independent of the particular transport used to transmit
the scheduling information. Companion memos to iTIP provide bindings of
the interoperability protocol to a number of Internet protocols.


Table of Contents

1 INTRODUCTION.........................................................5

 1.1 FORMATTING CONVENTIONS ...........................................5
 1.2 RELATED DOCUMENTS ................................................6
 1.3 ITIP ROLES AND TRANSACTIONS ......................................6

2 INTEROPERABILITY MODELS..............................................8

 2.1 APPLICATION PROTOCOL .............................................8
   2.1.1 Calendar Entry State .........................................9
   2.1.2 Delegation ...................................................9
   2.1.3 Acting on Behalf of other Calendar Users .....................9
   2.1.4 Component Revisions ..........................................9
   2.1.5 Message Sequencing ..........................................10

3 APPLICATION PROTOCOL ELEMENTS.......................................11

 3.1 COMMON COMPONENT RESTRICTION TABLES .............................12
 3.2 METHODS FOR VEVENT CALENDAR COMPONENTS ..........................13
   3.2.1 PUBLISH .....................................................14
   3.2.2 REQUEST .....................................................15
     3.2.2.1 Rescheduling an Event....................................17
     3.2.2.2 Updating or Reconfirmation of an Event...................17
     3.2.2.3 Delegating an Event to another CU........................17
     3.2.2.4 Changing the Organizer...................................18
     3.2.2.5 Sending on Behalf of the Organizer.......................18
     3.2.2.6 Forwarding to An Uninvited CU............................18
     3.2.2.7 Updating Attendee Status.................................19
   3.2.3 REPLY .......................................................19
   3.2.4 ADD .........................................................21
   3.2.5 CANCEL ......................................................22
   3.2.6 REFRESH .....................................................24
   3.2.7 COUNTER .....................................................25
   3.2.8 DECLINECOUNTER ..............................................26
 3.3 METHODS FOR VFREEBUSY COMPONENTS ................................27
   3.3.1 PUBLISH .....................................................28
   3.3.2 REQUEST .....................................................29
   3.3.3 REPLY .......................................................30
 3.4 METHODS FOR VTODO COMPONENTS ....................................31
   3.4.1 PUBLISH .....................................................32
   3.4.2 REQUEST .....................................................33
     3.4.2.1 REQUEST for Rescheduling a VTODO.........................35
     3.4.2.2 REQUEST for Update or Reconfirmation of a VTODO..........35


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     3.4.2.3 REQUEST for Delegating a VTODO...........................36
     3.4.2.4 REQUEST Forwarded To An Uninvited Calendar User..........36
     3.4.2.5 REQUEST Updated Attendee Status..........................37
   3.4.3 REPLY .......................................................37
   3.4.4 ADD .........................................................38
   3.4.5 CANCEL ......................................................40
   3.4.6 REFRESH .....................................................41
   3.4.7 COUNTER .....................................................43
   3.4.8 DECLINECOUNTER ..............................................44
 3.5 METHODS FOR VJOURNAL COMPONENTS .................................45
   3.5.1 PUBLISH .....................................................46
   3.5.2 ADD .........................................................47
   3.5.3 CANCEL ......................................................48
 3.6 STATUS REPLIES ..................................................49
 3.7 IMPLEMENTATION CONSIDERATIONS ...................................51
   3.7.1 Working With Recurrence Instances ...........................51
   3.7.2 Attendee Property Considerations ............................52
   3.7.3 X-Tokens ....................................................53

4 EXAMPLES............................................................53

 4.1 PUBLISHED EVENT EXAMPLES ........................................53
   4.1.1 A Minimal Published Event ...................................54
   4.1.2 Changing A Published Event ..................................54
   4.1.3 Canceling A Published Event .................................55
   4.1.4 A Rich Published Event ......................................55
   4.1.5 Anniversaries or Events attached to entire days .............56
 4.2 GROUP EVENT EXAMPLES ............................................57
   4.2.1 A Group Event Request .......................................57
   4.2.2 Reply To A Group Event Request ..............................58
   4.2.3 Update An Event .............................................59
   4.2.4 Countering an Event Proposal ................................59
   4.2.5 Delegating an Event .........................................61
   4.2.6 Delegate Accepts the Meeting ................................63
   4.2.7 Delegate Declines the Meeting ...............................64
   4.2.8 Forwarding an Event Request .................................65
   4.2.9 Cancel A Group Event ........................................65
   4.2.10 Removing Attendees .........................................66
   4.2.11 Replacing the Organizer ....................................67
 4.3 BUSY TIME EXAMPLES ..............................................68
   4.3.1 Request Busy Time ...........................................69
   4.3.2 Reply To A Busy Time Request ................................69
 4.4 RECURRING EVENT AND TIME ZONE EXAMPLES ..........................69
   4.4.1 A Recurring Event Spanning Time Zones .......................69
   4.4.2 Modify A Recurring Instance .................................71
   4.4.3 Cancel an Instance ..........................................72
   4.4.4 Cancel Recurring Event ......................................73
   4.4.5 Change All Future Instances .................................73
   4.4.6 Add A New Instance To A Recurring Event .....................74
   4.4.7 Add A New Series of Instances To A Recurring Event ..........74
   4.4.8 Counter An Instance Of A Recurring Event ....................78
   4.4.9 Error Reply To A Request ....................................78
 4.5 GROUP TO-DO EXAMPLES ............................................79
   4.5.1 A VTODO Request .............................................80


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   4.5.2 A VTODO Reply ...............................................81
   4.5.3 A VTODO Request for Updated Status ..........................81
   4.5.4 A Reply: Percent-Complete ...................................82
   4.5.5 A Reply: Completed ..........................................82
   4.5.6 An Updated VTODO Request ....................................82
   4.5.7 Recurring VTODOs ............................................83
     4.5.7.1 Request for a Recurring VTODO............................83
     4.5.7.2 Calculating due dates in recurring VTODOs................84
     4.5.7.3 Replying to an instance of a recurring VTODO.............84
 4.6 JOURNAL EXAMPLES ................................................84
 4.7 OTHER EXAMPLES ..................................................85
   4.7.1 Event Refresh ...............................................85
   4.7.2 Bad RECURRENCE-ID ...........................................85

5 APPLICATION PROTOCOL FALLBACKS......................................87

 5.1 PARTIAL IMPLEMENTATION ..........................................87
   5.1.1 Event-Related Fallbacks .....................................87
   5.1.2 Free/Busy-Related Fallbacks .................................89
   5.1.3 To-Do-Related Fallbacks .....................................89
   5.1.4 Journal-Related Fallbacks ...................................91
 5.2 LATENCY ISSUES ..................................................92
   5.2.1 Cancellation of an Unknown Calendar Component. ..............92
   5.2.2 Unexpected Reply from an Unknown Delegate ...................92
 5.3 SEQUENCE NUMBER .................................................92

6 SECURITY CONSIDERATIONS.............................................93

 6.1 SECURITY THREATS ................................................93
   6.1.1 Spoofing the "Organizer" ....................................93
   6.1.2 Spoofing the "Attendee" .....................................93
   6.1.3 Unauthorized Replacement of the Organizer ...................93
   6.1.4 Eavesdropping ...............................................93
   6.1.5 Flooding a Calendar .........................................94
   6.1.6 Procedural Alarms ...........................................94
   6.1.7 Unauthorized REFRESH Requests ...............................94
 6.2 RECOMMENDATIONS .................................................94
   6.2.1 Use of [RFC-1847] to secure iTIP transactions ...............94
   6.2.2 Implementation Controls .....................................95

7 ACKNOWLEDGMENTS.....................................................95


8 BIBLIOGRAPHY........................................................95


9 AUTHORS ADDRESSES...................................................96


10 FULL COPYRIGHT STATEMENT...........................................98






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1  Introduction

This document specifies how calendaring systems use iCalendar objects to
interoperate with other calendar systems. In particular, it specifies
how to schedule events, to-dos, or daily journal entries. It further
specifies how to search for available busy time information. It does so
in a general way so as to allow multiple methods of communication
between systems. Subsequent documents specify transport bindings between
systems that use this protocol.

This protocol is based on messages sent from an originator to one or
more recipients. For certain types of messages, a recipient may reply,
in order to update their status and may also return transaction/request
status information. The protocol supports the ability for the message
originator to modify or cancel the original message. The protocol also
supports the ability for recipients to suggest changes to the originator
of a message. The elements of the protocol also define the user roles
for its transactions.


1.1 Formatting Conventions

In order to refer to elements of the calendaring and scheduling model,
core object or interoperability protocol defined in [ICMS], [iCAL] and
[iTIP] several formatting conventions have been utilized.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this
document are to be interpreted as described in [RFC-2119].

Calendaring and scheduling roles described by [ICMS] are referred to in
quoted-strings of text with the first character of each word in upper
case. For example, "Organizer" refers to a role of a "Calendar User"
(CU) within the scheduling protocol defined by [iTIP]. Calendar
components defined by [iCAL] are referred to with capitalized, quoted-
strings of text. All calendar components start with the letter "V". For
example, "VEVENT" refers to the event calendar component, "VTODO" refers
to the to-do calendar component and "VJOURNAL" refers to the daily
journal calendar component. Scheduling methods defined by [iTIP] are
referred to with capitalized, quoted-strings of text. For example,
"REQUEST" refers to the method for requesting a scheduling calendar
component be created or modified, "REPLY" refers to the method a
recipient of a request uses to update their status with the "Organizer"
of the calendar component.

Properties defined by [iCAL] are referred to with capitalized, quoted-
strings of text, followed by the word "property". For example,
"ATTENDEE" property refers to the iCalendar property used to convey the
calendar address of a "Calendar User". Property parameters defined by
this memo are referred to with lower case, quoted-strings of text,
followed by the word "parameter". For example, "value" parameter refers
to the iCalendar property parameter used to override the default data
type for a property value. Enumerated values defined by this memo are



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referred to with capitalized text, either alone or followed by the word
"value".

In tables, the quoted-string text is specified without quotes in order
to minimize the table length.


1.2 Related Documents

Implementers will need to be familiar with several other memos that,
along with this one, describe the Internet calendaring and scheduling
standards. This document, [iTIP], specifies an interoperability protocol
for scheduling between different implementations. The related documents
are:

     [ICMS] - describes the abstract model and defines common terms and
     concepts;

     [iCAL] - specifies the objects, data types, properties and property
     parameters used in the protocols, along with the methods for
     representing and encoding them;

     [iMIP] specifies an Internet email binding for [iTIP].

This memo does not attempt to repeat the specification of concepts or
definitions from these other memos. Where possible, references are made
to the memo that provides for the specification of these concepts or
definitions.


1.3 ITIP Roles and Transactions

ITIP defines methods for exchanging [iCAL] objects for the purposes of
group calendaring and scheduling between "Calendar Users" (CUs). CUs
take on one of two roles in iTIP. The CU who initiates an exchange takes
on the role of "Organizer". For example, the CU who proposes a group
meeting is the "Organizer". The CUs asked to participate in the group
meeting by the "Organizer" take on the role of "Attendee". Note that
"role" is also a descriptive parameter to the _ATTENDEE_ property. Its
use is to convey descriptive context to an "Attendee" such as "chair",
"req-participant" or "non-participant" and has nothing to do with the
calendaring workflow.

The ITIP methods are listed below and their usage and semantics are
defined in section 3 of this document.

+================+==================================================+
| Method         |  Description                                     |
|================+==================================================|
| PUBLISH        | Used to publish a calendar entry to one or more  |
|                | Calendar Users. There is no interactivity        |
|                | between the publisher and any other calendar     |
|                | user. An example might include a baseball team   |
|                | publishing its schedule to the public.           |


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|                |                                                  |
| REQUEST        | Used to schedule a calendar entry with other     |
|                | Calendar Users. Requests are interactive in that |
|                | they require the receiver to respond using       |
|                | the Reply methods. Meeting Requests, Busy        |
|                | Time requests and the assignment of VTODOs to    |
|                | other Calendar Users are all examples.           |
|                | Requests are also used by the "Organizer" to     |
|                | update the status of a calendar entry.           |
|                |                                                  |
| REPLY          | A Reply is used in response to a Request to      |
|                | convey "Attendee" status to the "Organizer".     |
|                | Replies are commonly used to respond to meeting  |
|                | and task requests.                               |
|                |                                                  |
| ADD            | Add one or more instances to an existing         |
|                | VEVENT, VTODO, or VJOURNAL.                      |
|                |                                                  |
| CANCEL         | Cancel one or more instances of an existing      |
|                | VEVENT, VTODO, or VJOURNAL.                      |
|                |                                                  |
| REFRESH        | The Refresh method is used by an "Attendee" to   |
|                | request the latest version of a calendar entry.  |
|                |                                                  |
| COUNTER        | The Counter method is used by an "Attendee" to   |
|                | negotiate a change in the calendar entry.        |
|                | Examples include the request to change a         |
|                | proposed Event time or change the due date for a |
|                | VTODO.                                           |
|                |                                                  |
| DECLINE-       | Used by the "Organizer" to decline the proposed  |
| COUNTER        | counter-proprosal.                               |
+================+==================================================+

Group scheduling in iTIP is accomplished using the set of "request" and
"response" methods described above. The following table shows the
methods broken down by who can send them.

+================+==================================================+
| Originator     | Methods                                          |
|================+==================================================|
| Organizer      | PUBLISH, REQUEST, ADD, CANCEL, DECLINECOUNTER    |
|                |                                                  |
| Attendee       | REPLY, REFRESH, COUNTER                          |
|                | REQUEST only when delegating                     |
+================+==================================================+

Note that for some calendar component types, the allowable methods are a
subset of the above set.







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2  Interoperability Models

There are two distinct protocols relevant to interoperability: an
"Application Protocol" and a "Transport Protocol". The Application
Protocol defines the content of the iCalendar objects sent between
sender and receiver to accomplish the scheduling transactions listed
above. The Transport Protocol defines how the iCalendar objects are sent
between the sender and receiver. This document focuses on the
Application Protocol. Binding documents such as [iMIP] focus on the
Transport Protocol.

The connection between Sender and Receiver in the diagram below refers
to the Application Protocol. The iCalendar objects passed from the
Sender to the Receiver are presented in Section 3, Application Protocol
Elements.

+----------+                      +----------+
|          |        iTIP          |          |
|  Sender  |<-------------------->| Receiver |
|          |                      |          |
+----------+                      +----------+

There are several variations of this diagram in which the Sender and
Receiver take on various roles of a "Calendar User Agent" (CUA) or a
"Calendar Service" (CS). These variants are detailed in the Model
document [ICMS].

The architecture of iTIP is depicted in the diagram below. An
application written to this specification may work with bindings for the
store-and-forward transport, the real time transport, or both. Also note
that iTIP could be bound to other transports.

+------------------------------------------+
|                   iTIP                   |
+------------------------------------------+
|Real-time | Store-and-Fwd | Other         |
|Transport | Transport     | Transports... |
+------------------------------------------+


2.1 Application Protocol

In the iTIP model, a calendar entry is created and managed by an
"Organizer". The "Organizer" interacts with other CUs by sending one or
more of the iTIP messages listed above. "Attendees" use the "REPLY"
method to communicate their status. "Attendees" do not make direct
changes to the master calendar entry. They can, however, use the
"COUNTER" method to suggest changes to the "Organizer". In any case, the
"Organizer" has complete control over the master calendar entry.







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2.1.1     Calendar Entry State

There are two distinct states relevant to calendar entries: the overall
state of the entry and the state associated with an "Attendee" to that
entry.

The state of an entry is defined by the "STATUS" property and is
controlled by the "Organizer." There is no default value for the
"STATUS" property. The "Organizer" sets the "STATUS" property to the
appropriate value for each calendar entry.

The state of a particular "Attendee" relative to an entry is defined by
the "partstat" parameter in the "ATTENDEE" property for each "Attendee".
When an "Organizer" issues the initial entry, "Attendee" status is
unknown. The "Organizer" specifies this by setting the "partstat"
parameter to "NEEDS-ACTION". Each "Attendee" modifies their "ATTENDEE"
property "partstat" parameter to an appropriate value as part of a
"REPLY" message sent back to the "Organizer".


2.1.2     Delegation

Delegation is defined as the process by which an "Attendee" grants
another CU (or several CUs) the right to attend on their behalf. The
"Organizer" is made aware of this change because the delegating
"Attendee" informs the "Organizer". These steps are detailed in the
REQUEST method section.

2.1.3     Acting on Behalf of other Calendar Users

In many organizations one user will act on behalf of another to organize
and/or respond to meeting requests. ITIP provides two mechanisms that
support these activities.

First, the "Organizer" is treated as a special entity, separate from
"Attendees". All responses from "Attendees" flow to the "Organizer",
making it easy to separate a calendar user organizing a meeting from
calendar users attending the meeting. Additionally, iCalendar provides
descriptive roles for each "Attendee". For instance, a role of "chair"
may be ascribed to one or more "Attendees". The "chair" and the
"Organizer" may or may not be the same calendar user. This maps well to
scenarios where an assistant may manage meeting logistics for another
individual who chairs a meeting.

Second, a "sent-by" parameter may be specified in either the "Organizer"
or "Attendee" properties. When specified, the "sent-by" parameter
indicates that the responding CU acted on behalf of the specified
"Attendee" or "Organizer".

2.1.4     Component Revisions

The "SEQUENCE" property is used by the "Organizer" to indicate revisions
to the calendar component. The rules for incrementing the "SEQUENCE"
number are defined in [iCAL]. For clarity, these rules are paraphrased


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here in terms of how they are applied in [iTIP]. For a given "UID" in a
calendar component:

. For the "PUBLISH" and "REQUEST" methods, the "SEQUENCE" property
  value is incremented according to the rules defined in [iCAL].

. The "SEQUENCE" property value MUST be incremented each time the
  "Organizer" uses the "ADD" or "CANCEL" methods.

. The "SEQUENCE" property value MUST NOT be incremented when using
  "REPLY", "REFRESH", "COUNTER", "DECLINECOUNTER", or when sending a
  delegation "REQUEST".

In some circumstances the "Organizer" may not have received responses to
the final revision sent out. In this situation, the "Organizer" may wish
to send an update "REQUEST", and set "RSVP=TRUE" for all "Attendees", so
that current responses can be collected.

The value of the "SEQUENCE" property contained in a response from an
"Attendee" may not always match the "Organizer's" revision.
Implementations may choose to have the CUA indicate to the CU that the
response is to an entry that has been revised and allow the CU to decide
whether or not to accept the response.


2.1.5     Message Sequencing

CUAs that handle the [iTIP] application protocol must often correlate a
component in a calendar store with a component received in the [iTIP]
message. For example, an event may be updated with a later revision of
the same event. To accomplish this, a CUA must correlate the version of
the event already in its calendar store with the version sent in the
[iTIP] message. In addition to this correlation, there are several
factors that can cause [iTIP] messages to arrive in an unexpected order.
That is, an "Organizer" could receive a reply to an earlier revision of
a component AFTER receiving a reply to a later revision.

To maximize interoperability and to handle messages that arrive in an
unexpected order, use the following rules:


1.   The primary key for referencing a particular iCalendar component is
  the "UID" property value. To reference an instance of a recurring
  component, the primary key is composed of the "UID" and the
  "RECURRENCE-ID" properties.

2.   The secondary key for referencing a component is the "SEQUENCE"
  property value.  For components where the "UID" is the same, the
  component with the highest numeric value for the "SEQUENCE" property
  obsoletes all other revisions of the component with lower values.

3.   "Attendees" send "REPLY" messages to the "Organizer".  For replies
  where the "UID" property value is the same, the value of the
  "SEQUENCE" property indicates the revision of the component to which


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  the "Attendee" is replying.  The reply with the highest numeric value
  for the "SEQUENCE" property obsoletes all other replies with lower
  values.

4.   In situations where the "UID" and "SEQUENCE" properties match, the
  "DTSTAMP" property is used as the tie-breaker. The component with the
  latest "DTSTAMP" overrides all others. Similarly, for "Attendee"
  responses where the "UID" property values match and the "SEQUENCE"
  property values match, the response with the latest "DTSTAMP"
  overrides all others.


Hence, CUAs must persist the following component properties: "UID",
"RECURRENCE-ID", "SEQUENCE", and "DTSTAMP".  Furthermore, for each
"ATTENDEE" property of a component CUAs must persist the "SEQUENCE" and
"DTSTAMP" property values associated with the "Attendee's" response.


3 Application Protocol Elements

ITIP messages are "text/calendar" MIME entities that contain calendaring
and scheduling information. The particular type of [iCAL] message is
referred to as the "method type". Each method type is identified by a
"METHOD" property specified as part of the "text/calendar" content type.
The table below shows various combinations of calendar components and
the method types that this memo supports.


+=================================================+
|         | VEVENT | VTODO | VJOURNAL | VFREEBUSY |
|=================================================|
|Publish  |  Yes   |  Yes  |  Yes     |   Yes     |
|Request  |  Yes   |  Yes  |  No      |   Yes     |
|Refresh  |  Yes   |  Yes  |  No      |   No      |
|Cancel   |  Yes   |  Yes  |  Yes     |   No      |
|Add      |  Yes   |  Yes  |  Yes     |   No      |
|Reply    |  Yes   |  Yes  |  No      |   Yes     |
|Counter  |  Yes   |  Yes  |  No      |   No      |
|Decline- |        |       |          |           |
|Counter  |  Yes   |  Yes  |  No      |   No      |
+=================================================+

Each method type is defined in terms of its associated components and
properties. Some components and properties are required, some are
optional and others are excluded. The restrictions are expressed in this
document using a simple "restriction table". The first column indicates
the name of a component or property. Properties of the iCalendar object
are not indented. Properties of a component are indented. The second
column contains "MUST" if the component or property must be present,
"MAY" if the component or property is optional, and "NOT" if the
component or property must not be present. Entries in the second column
sometimes contain comments for further clarification.




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3.1 Common Component Restriction Tables

The restriction table below applies to properties of the iCalendar
object. That is, the properties at the outermost scope. The presence
column uses the following values to assert whether a property is
required, is optional and the number of times it may appear in the
iCalendar object.

Presence Value       Description
--------------------------------------------------------------
1                 One instance MUST be present
1+                At least one instance MUST be present
0                 Instances of this property Must NOT be present
0+                Multiple instances MAY be present
0 or 1            Up to 1 instance of this property MAY be present
---------------------------------------------------------------

The tables also call out "X-PROPERTY" and  "X-COMPONENT" to show where
vendor-specific properties and components can appear.  The tables do not
lay out the restrictions of property parameters. Those restrictions are
defined in [iCAL].


Component/Property  Presence
------------------- ----------------------------------------------
CALSCALE            0 or 1
PRODID              1
VERSION             1       Value MUST be "2.0"
X-PROPERTY          0+


DateTime values MAY refer to a "VTIMEZONE" component. The property
restrictions in the table below apply to any "VTIMEZONE" component in an
ITIP message.

Component/Property  Presence
------------------- ----------------------------------------------
VTIMEZONE           0+      MUST be present if any date/time refers to
                            timezone
    DAYLIGHT        0+      MUST be one or more of either STANDARD or
                            DAYLIGHT
       COMMENT      0 or 1
       DTSTART      1       MUST be local time format
       RDATE        0+      if present RRULE MUST NOT be present
       RRULE        0+      if present RDATE MUST NOT be present
       TZNAME       0 or 1
       TZOFFSET     1
       TZOFFSETFROM 1
       TZOFFSETTO   1
       X-PROPERTY   0+
    LAST-MODIFIED   0 or 1
    STANDARD        0+      MUST be one or more of either STANDARD or
                            DAYLIGHT
       COMMENT      0 or 1


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       DTSTART      1       MUST be local time format
       RDATE        0+      if present RRULE MUST NOT be present
       RRULE        0+      if present RDATE MUST NOT be present
       TZNAME       0 or 1
       TZOFFSETFROM 1
       TZOFFSETTO   1
       X-PROPERTY   0+
    TZID            1
    TZURL           0 or 1
    X-PROPERTY      0+

The property restrictions in the table below apply to any "VALARM"
component in an ITIP message.

Component/Property  Presence
------------------- ----------------------------------------------
VALARM              0+
    ACTION          1
    ATTACH          0+
    DESCRIPTION     0 or 1
    DURATION        0 or 1  if present REPEAT MUST be present
    REPEAT          0 or 1  if present DURATION MUST be present
    SUMMARY         0 or 1
    TRIGGER         1
    X-PROPERTY      0+



3.2 Methods for VEVENT Calendar Components

This section defines the property set restrictions for the method types
that are applicable to the "VEVENT" calendar component. Each method is
defined using a table that clarifies the property constraints that
define the particular method.

The following summarizes the methods that are defined for the "VEVENT"
calendar component.

+================+==================================================+
| Method         |  Description                                     |
|================+==================================================|
| PUBLISH        | Post notification of an event. Used primarily as |
|                | a method of advertising the existence of an      |
|                | event.                                           |
|                |                                                  |
| REQUEST        | Make a request for an event. This is an explicit |
|                | invitation to one or more "Attendees". Event     |
|                | Requests are also used to update or change an    |
|                | existing event. Clients that cannot handle       |
|                | REQUEST may degrade the event to view it as an   |
|                | PUBLISH.                                         |
|                |                                                  |
| REPLY          | Reply to an event request. Clients may set their |
|                | status ("partstat") to ACCEPTED, DECLINED,        |


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|                | TENTATIVE, or DELEGATED.                         |
|                |                                                  |
| ADD            | Add one or more instances to an existing event.  |
|                |                                                  |
| CANCEL         | Cancel one or more instances of an existing      |
|                | event.                                           |
|                |                                                  |
| REFRESH        | A request is sent to an "Organizer" by an        |
|                | "Attendee" asking for the latest version of an   |
|                | event to be resent to the requester.             |
|                |                                                  |
| COUNTER        | Counter a REQUEST with an alternative proposal,  |
|                | Sent by an "Attendee" to the "Organizer".        |
|                |                                                  |
| DECLINECOUNTER | Decline a counter proposal. Sent to an           |
|                | "Attendee" by the "Organizer".                   |
+================+==================================================+


3.2.1     PUBLISH

The "PUBLISH" method in a "VEVENT" calendar component is an unsolicited
posting of an iCalendar object. Any CU may add published components to
their calendar. The "Organizer" MUST be present in a published iCalendar
component. "Attendees" MUST NOT be present. Its expected usage is for
encapsulating an arbitrary event as an iCalendar object. The "Organizer"
may subsequently update (with another "PUBLISH" method), add instances
to (with an "ADD" method), or cancel (with a "CANCEL" method) a
previously published "VEVENT" calendar component.

This method type is an iCalendar object that conforms to the following
property constraints:

Component/Property  Presence
------------------- ----------------------------------------------
METHOD              1       MUST equal "PUBLISH"
VEVENT              1+
     DTSTAMP        1
     DTSTART        1
     ORGANIZER      1
     SUMMARY        1       Can be null.
     UID            1
     RECURRENCE-ID  0 or 1  only if referring to an instance of a
                            recurring calendar component.  Otherwise it
                            MUST NOT be present.
     SEQUENCE       0 or 1  MUST be present if value is greater than 0,
                            MAY be present if 0
     ATTACH         0+
     CATEGORIES     0 or 1  This property may contain a list of values
     CLASS          0 or 1
     COMMENT        0 or 1
     CONTACT        0+
     CREATED        0 or 1
     DESCRIPTION    0 or 1  Can be null


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     DTEND          0 or 1  if present DURATION MUST NOT be present
     DURATION       0 or 1  if present DTEND MUST NOT be present
     EXDATE         0+
     EXRULE         0+
     GEO            0 or 1
     LAST-MODIFIED  0 or 1
     LOCATION       0 or 1
     PRIORITY       0 or 1
     RDATE          0+
     RELATED-TO     0+
     RESOURCES      0 or 1 This property MAY contain a list of values
     RRULE          0+
     STATUS         0 or 1 MAY be one of TENTATIVE/CONFIRMED/CANCELLED
     TRANSP         0 or 1
     URL            0 or 1
     X-PROPERTY     0+

     ATTENDEE       0
     REQUEST-STATUS 0

VALARM              0+
VFREEBUSY           0
VJOURNAL            0
VTODO               0
VTIMEZONE           0+    MUST be present if any date/time refers to a
                           timezone
X-COMPONENT         0+

3.2.2     REQUEST

The "REQUEST" method in a "VEVENT" component provides the following
scheduling functions:

  .  Invite "Attendees" to an event;
  .  Reschedule an existing event;
  .  Response to a REFRESH request;
  .  Update the details of an existing event, without rescheduling it;
  .  Update the status of "Attendees" of an existing event, without
     rescheduling it;
  .  Reconfirm an existing event, without rescheduling it;
  .  Forward a "VEVENT" to another uninvited CU.
  .  For an existing "VEVENT" calendar component, delegate the role of
     "Attendee" to another CU;
  .  For an existing "VEVENT" calendar component, changing the role of
     "Organizer" to another CU.


The "Organizer" originates the "REQUEST". The recipients of the
"REQUEST" method are the CUs invited to the event, the "Attendees".
"Attendees" use the "REPLY" method to convey attendance status to the
"Organizer".

The "UID" and "SEQUENCE" properties are used to distinguish the various
uses of the "REQUEST" method. If the "UID" property value in the


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"REQUEST" is not found on the recipient's calendar, then the "REQUEST"
is for a new "VEVENT" calendar component. If the "UID" property value is
found on the recipient's calendar, then the "REQUEST" is for a
rescheduling, an update, or a reconfirm of the "VEVENT" calendar
component.

For the "REQUEST" method, multiple "VEVENT" components in a single
iCalendar object are only permitted when for components with the same
"UID" property.  That is, a series of recurring events may have
instance-specific information.  In this case, multiple "VEVENT"
components are needed to express the entire series.

This method type is an iCalendar object that conforms to the following
property constraints:

Component/Property  Presence
-----------------------------------------------------------------
METHOD              1       MUST be "REQUEST"
VEVENT              1+      All components MUST have the same UID
    ATTENDEE        1+
    DTSTAMP         1
    DTSTART         1
    ORGANIZER       1
    SEQUENCE        0 or 1  MUST be present if value is greater than 0,
                            MAY be present if 0
    SUMMARY         1       Can be null
    UID             1

    ATTACH          0+
    CATEGORIES      0 or 1  This property may contain a list of values
    CLASS           0 or 1
    COMMENT         0 or 1
    CONTACT         0+
    CREATED         0 or 1
    DESCRIPTION     0 or 1  Can be null
    DTEND           0 or 1  if present DURATION MUST NOT be present
    DURATION        0 or 1  if present DTEND MUST NOT be present
    EXDATE          0+
    EXRULE          0+
    GEO             0 or 1
    LAST-MODIFIED   0 or 1
    LOCATION        0 or 1
    PRIORITY        0 or 1
    RDATE           0+
    RECURRENCE-ID   0 or 1  only if referring to an instance of a
                            recurring calendar component.  Otherwise it
                            MUST NOT be present.
    RELATED-TO      0+
    REQUEST-STATUS  0+
    RESOURCES       0 or 1  This property MAY contain a list of values
    RRULE           0+
    STATUS          0 or 1  MAY be one of TENTATIVE/CONFIRMED
    TRANSP          0 or 1
    URL             0 or 1


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    X-PROPERTY      0+

VALARM              0+
VTIMEZONE           0+      MUST be present if any date/time refers to
                            a timezone
X-COMPONENT         0+

VFREEBUSY           0
VJOURNAL            0
VTODO               0


3.2.2.1   Rescheduling an Event

The "REQUEST" method may be used to reschedule an event. A rescheduled
event involves a change to the existing event in terms of its time or
recurrence intervals and possibly the location or description. If the
recipient CUA of a "REQUEST" method finds that the "UID" property value
already exists on the calendar, but that the "SEQUENCE" (or "DTSTAMP")
property value in the "REQUEST" method is greater than the value for the
existing event, then the "REQUEST" method describes a rescheduling of
the event.


3.2.2.2   Updating or Reconfirmation of an Event

The "REQUEST" method may be used to update or reconfirm an event. An
update to an existing event does not involve changes to the time or
recurrence intervals, and might not involve a change to the location or
description for the event. If the recipient CUA of a "REQUEST" method
finds that the "UID" property value already exists on the calendar and
that the "SEQUENCE" property value in the "REQUEST" is the same as the
value for the existing event, then the "REQUEST" method describes an
update of the event details, but no rescheduling of the event.

The update "REQUEST" method is the appropriate response to a "REFRESH"
method sent from an "Attendee" to the "Organizer" of an event.

The "Organizer" of an event may also send unsolicited "REQUEST" methods.
The unsolicited "REQUEST" methods may be used to update the details of
the event without rescheduling it, to update the "partstat" parameter of
"Attendees", or to reconfirm the event.


3.2.2.3   Delegating an Event to another CU

Some calendar and scheduling systems allow "Attendees" to delegate their
presence at an event to another calendar user. ITIP supports this
concept using the following workflow. Any "Attendee" may delegate their
right to participate in a calendar VEVENT to another CU. The implication
is that the delegate participates in lieu of the original "Attendee";
NOT in addition to the "Attendee". The delegator MUST notify the
"Organizer" of this action using the steps outlined below.
Implementations may support or restrict delegation as they see fit. For


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instance, some implementations may restrict a delegate from delegating a
"REQUEST" to another CU.

The "Delegator" of an event forwards the existing "REQUEST" to the
"Delegate". The "REQUEST" method MUST include an "ATTENDEE" property
with the calendar address of the "Delegate". The "Delegator" MUST also
send a "REPLY" method to the "Organizer" with the "Delegator's"
"ATTENDEE" property "partstat" parameter value set to "delegated". In
addition, the "delegated-to" parameter MUST be included with the
calendar address of the "Delegate".

In response to the request, the "Delegate" MUST send a "REPLY" method to
the "Organizer" and optionally, to the "Delegator". The "REPLY" method "
SHOULD include the "ATTENDEE" property with the "delegated-from"
parameter value of the "Delegator's" calendar address.

The "Delegator" may continue to receive updates to the event even though
they will not be attending. This is accomplished by the "Delegator"
setting their "role" attribute to " NON-PARTICIPANT" in the "REPLY" to
the "Organizer"


3.2.2.4   Changing the Organizer

The situation may arise where the "Organizer" of a VEVENT is no longer
able to perform the "Organizer" role and abdicates without passing on
the "Organizer" role to someone else. When this occurs the "Attendees"
of the VEVENT may use out-of-band mechanisms to communicate the
situation and agree upon a new "Organizer".  The new "Organizer" should
then send out a new "REQUEST" with a modified version of the VEVENT in
which the "SEQUENCE" number has been incremented and value of the
"ORGANIZER" property has been changed to the calendar address of the new
"Organizer".


3.2.2.5   Sending on Behalf of the Organizer

There are a number of scenarios that support the need for a calendar
user to act on behalf of the "Organizer" without explicit role changing.
This might be the case if the CU designated as "Organizer" was sick or
unable to perform duties associated with that function. In these cases
iTIP supports the notion of one CU acting on behalf of another. Using
the "sent-by" parameter, a calendar user could send an updated "VEVENT"
REQUEST. In the case where one CU sends on behalf of another CU, the
"Attendee" responses are still directed back towards the CU designated
as "Organizer".


3.2.2.6   Forwarding to An Uninvited CU

An "Attendee" invited to an event may invite another uninvited CU to the
event. The invited "Attendee" accomplishes this by forwarding the
original "REQUEST" method to the uninvited CU. The "Organizer" decides
whether or not the uninvited CU is added to the attendee list. If the


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"Organizer" decides not to add the uninvited CU no further action is
required, however the "Organizer" MAY send the uninvited CU a "CANCEL"
message.  If the "Organizer" decides to add an uninvited CU, a new
"ATTENDEE" property is added for the uninvited CU with its property
parameters set as the "Organizer" deems appropriate. When forwarding a
"REQUEST" to another CU, the forwarding "Attendee" MUST NOT make changes
to the VEVENT property set.


3.2.2.7   Updating Attendee Status

The "Organizer" of an event may also request updated status from one or
more "Attendees. The "Organizer" sends a "REQUEST" method to the
"Attendee" and sets the "ATTENDEE;RSVP=TRUE" property parameter. The
"SEQUENCE" property for the event is not changed from its previous
value. A recipient will determine that the only change in the "REQUEST"
is that their "RSVP" property parameter indicates a request for updated
status. The recipient SHOULD respond with a "REPLY" method indicating
their current status with respect to the "REQUEST".


3.2.3     REPLY

The "REPLY" method in a "VEVENT" calendar component is used to respond
(e.g., accept or decline) to a "REQUEST" or to reply to a delegation
"REQUEST". When used to provide a delegation response, the "Delegator"
SHOULD include the calendar address of the "Delegate" on the "delegated-
to" property parameter  of the "Delegator's" "ATTENDEE" property. The
"Delegate" SHOULD include the calendar address of the "Delegator" on the
"delegated-from" property parameter of the "Delegate's" "ATTENDEE"
property.

The "REPLY" method may also be used to respond to an unsuccessful
"REQUEST" method. Depending on the value of the "REQUEST-STATUS"
property no scheduling action may have been performed.

The "Organizer" of an event may receive the "REPLY" method from a CU not
in the original "REQUEST". For example, a "REPLY" may be received from a
"Delegate" to an event. In addition, the "REPLY" method may be received
from an unknown CU (a "Party Crasher"). This uninvited "Attendee" may be
accepted, or the "Organizer" may cancel the event for the uninvited
"Attendee" by sending a "CANCEL" method to the uninvited "Attendee".

An "Attendee" can include a message to the "Organizer" using the
"COMMENT" property. For example, if the user indicates tentative
acceptance and wants to let the "Organizer" know why, the reason can be
expressed in the "COMMENT" property value.

The "Organizer" may also receive a "REPLY" from one CU on behalf of
another. Like the scenario enumerated above for the "Organizer",
"Attendees" may have another CU respond on their behalf. This is done
using the "sent-by" parameter.




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The optional properties listed in the table below (those listed as "0+"
or "0 or 1") MUST NOT be changed from those of the original request.  If
property changes are desired the COUNTER message must be used.

This method type is an iCalendar object that conforms to the following
property constraints:

Component/Property  Presence
------------------- ----------------------------------------------
METHOD              1       MUST be "REPLY"

VEVENT              1+      All components MUST have the same UID
    ATTENDEE        1       MUST be the address of the Attendee
                            replying.
    DTSTAMP         1
    ORGANIZER       1
    RECURRENCE-ID   0 or 1  only if referring to an instance of a
                            recurring calendar component.  Otherwise it
                            must NOT be present.
    UID             1       MUST be the UID of the original REQUEST

    SEQUENCE        0 or 1  MUST if non-zero, MUST be the sequence
                            number of the original REQUEST. MAY be
                            present if 0.

    ATTACH          0+
    CATEGORIES      0 or 1  This property may contain a list of values
    CLASS           0 or 1
    COMMENT         0 or 1
    CONTACT         0+
    CREATED         0 or 1
    DESCRIPTION     0 or 1
    DTEND           0 or 1  if present DURATION MUST NOT be present
    DTSTART         0 or 1
    DURATION        0 or 1  if present DTEND MUST NOT be present
    EXDATE          0+
    EXRULE          0+
    GEO             0 or 1
    LAST-MODIFIED   0 or 1
    LOCATION        0 or 1
    PRIORITY        0 or 1
    RDATE           0+
    RELATED-TO      0+
    RESOURCES       0 or 1  This property MAY contain a list of values
    REQUEST-STATUS  0+
    RRULE           0+
    STATUS          0 or 1
    SUMMARY         0 or 1
    TRANSP          0 or 1
    URL             0 or 1
    X-PROPERTY      0+

VTIMEZONE           0 or 1 MUST be present if any date/time refers to a
                           timezone


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X-COMPONENT         0+

VALARM              0
VFREEBUSY           0
VJOURNAL            0
VTODO               0


3.2.4     ADD

The "ADD" method in a "VEVENT" calendar component is used to add one or
more instances to an existing "VEVENT". Unlike the "REQUEST" method,
when using issuing an "ADD" method, the "Organizer" does not send the
full "VEVENT" description; only the new instance(s). The "ADD" method is
especially useful if there are instance-specific properties to be
preserved in a recurring "VEVENT". For instance, an "Organizer" may have
originally scheduled a weekly Thursday meeting. At some point, several
instances changed. Location or start time may have changed, or some
instances may have unique "DESCRIPTION" properties. The "ADD" method
allows the "Organizer" to add new instances to an existing event using a
single ITIP message without redefining the entire recurring pattern.

The "UID" must be that of the existing event. If the "UID" property
value in the "ADD" is not found on the recipient's calendar, then the
recipient SHOULD send a "REFRESH" to the "Organizer" in order to be
updated with the latest version of the "VEVENT".  If an "Attendee"
implementation does not support the "ADD" method it should respond with
a "REQUEST-STATUS" value of 3.14 and ask for a "REFRESH".

This method type is an iCalendar object that conforms to the following
property constraints:

Component/Property  Presence
------------------- ----------------------------------------------
METHOD              1      MUST be "ADD"
VEVENT              1
    DTSTAMP         1
    DTSTART         1
    ORGANIZER       1
    SEQUENCE        1      MUST be greater than 0
    SUMMARY         1      Can be null
    UID             1      MUST match that of the original event

    ATTACH          0+
    ATTENDEE        0+
    CATEGORIES      0 or 1 This property MAY contain a list of values
    CLASS           0 or 1
    COMMENT         0 or 1
    CONTACT         0+
    CREATED         0 or 1
    DESCRIPTION     0 or 1  Can be null
    DTEND           0 or 1  if present DURATION MUST NOT be present
    DURATION        0 or 1  if present DTEND MUST NOT be present
    EXDATE          0+


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    EXRULE          0+
    GEO             0 or 1
    LAST-MODIFIED   0 or 1
    LOCATION        0 or 1
    PRIORITY        0 or 1
    RDATE           0+
    RELATED-TO      0+
    RESOURCES       0 or 1  This property MAY contain a list of values
    RRULE           0+
    STATUS          0 or 1  MAY be one of TENTATIVE/CONFIRMED
    TRANSP          0 or 1
    URL             0 or 1
    X-PROPERTY      0+

    RECURRENCE-ID   0
    REQUEST-STATUS  0

VALARM              0+
VTIMEZONE           0+     MUST be present if any date/time refers to
                           a timezone
X-COMPONENT         0+

VFREEBUSY           0
VTODO               0
VJOURNAL            0


3.2.5     CANCEL

The "CANCEL" method in a "VEVENT" calendar component is used to send a
cancellation notice of an existing event request to the "Attendees". The
message is sent by the "Organizer" of the event. For a recurring event,
either the whole event or instances of an event may be cancelled. To
cancel the complete range of recurring event, the "UID" property value
for the event MUST be specified and a "RECURRENCE-ID" MUST NOT be
specified in the "CANCEL" method. In order to cancel an individual
instance of the event, the "RECURRENCE-ID" property value for the event
MUST be specified in the "CANCEL" method.

There are two options for canceling a sequence of instances of a
recurring "VEVENT" calendar component:

(a)    the "RECURRENCE-ID" property for an instance in the sequence MUST be
  specified with the "RANGE" property parameter value of THISANDPRIOR
  (or THISANDFUTURE)  to indicate cancellation of the specified
  "VEVENT" calendar component and all instances before (or after); or

(b)    individual recurrence instances may be cancelled by specifying
  multiple "RECURRENCE-ID" properties corresponding to the instances to
  be cancelled.

When a "VEVENT" is cancelled, the "SEQUENCE" property value MUST be
incremented.



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This method type is an iCalendar object that conforms to the following
property constraints:

Component/Property  Presence
------------------- ----------------------------------------------
METHOD              1      MUST be "CANCEL"

VEVENT              1+     All must have the same UID
    ATTENDEE        0+     MUST include all "Attendees" being removed
                           the event. MUST include all "Attendees" if
                           the entire event is cancelled.
    DTSTAMP         1
    ORGANIZER       1
    SEQUENCE        1
    UID             1       MUST be the UID of the original REQUEST

    COMMENT         0 or 1
    ATTACH          0+
    CATEGORIES      0 or 1  This property may contain a list of values
    CLASS           0 or 1
    CONTACT         0+
    CREATED         0 or 1
    DESCRIPTION     0 or 1
    DTEND           0 or 1 if present DURATION MUST NOT be present
    DTSTART         0 or 1
    DURATION        0 or 1 if present DTEND MUST NOT be present
    EXDATE          0+
    EXRULE          0+
    GEO             0 or 1
    LAST-MODIFIED   0 or 1
    LOCATION        0 or 1
    PRIORITY        0 or 1
    RDATE           0+
    RECURRENCE-ID   0 or 1  MUST be present if referring to one or more
                            or more recurring instances. Otherwise it
                            MUST NOT be present
    RELATED-TO      0+
    RESOURCES       0 or 1
    RRULE           0+
    STATUS          0 or 1  MUST be set to CANCELLED. If uninviting
                            specific "Attendees" then MUST NOT be
                            included.
    SUMMARY         0 or 1
    TRANSP          0 or 1
    URL             0 or 1
    X-PROPERTY      0+
    REQUEST-STATUS  0

VTIMEZONE           0+     MUST be present if any date/time refers to
                           a timezone
X-COMPONENT         0+

VTODO               0
VJOURNAL            0


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VFREEBUSY           0
VALARM              0


3.2.6     REFRESH

The "REFRESH" method in a "VEVENT" calendar component is used by
"Attendees" of an existing event to request an updated description from
the event "Organizer". The "REFRESH" method must specify the "UID"
property of the event to update. A recurrence instance of an event may
be requested by specifying the "RECURRENCE-ID" property corresponding to
the associated event. The "Organizer" responds with the latest
description and version of the event.

This method type is an iCalendar object that conforms to the following
property constraints:

Component/Property  Presence
------------------- ----------------------------------------------
METHOD              1      MUST be "REFRESH"

VEVENT              1
    ATTENDEE        1      MUST be the address of requestor
    DTSTAMP         1
    ORGANIZER       1
    UID             1      MUST be the UID associated with original
                           REQUEST
    COMMENT         0 or 1
    RECURRENCE-ID   0 or 1 MUST only if referring to an instance of a
                           recurring calendar component.  Otherwise it
                           must NOT be present.
    X-PROPERTY      0+

    ATTACH          0
    CATEGORIES      0
    CLASS           0
    CONTACT         0
    CREATED         0
    DESCRIPTION     0
    DTEND           0
    DTSTART         0
    DURATION        0
    EXDATE          0
    EXRULE          0
    GEO             0
    LAST-MODIFIED   0
    LOCATION        0
    PRIORITY        0
    RDATE           0
    RELATED-TO      0
    REQUEST-STATUS  0
    RESOURCES       0
    RRULE           0
    SEQUENCE        0


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    STATUS          0
    SUMMARY         0
    TRANSP          0
    URL             0

X-COMPONENT         0+

VTODO               0
VJOURNAL            0
VFREEBUSY           0
VTIMEZONE           0
VALARM              0


3.2.7     COUNTER

The "COUNTER" method for a "VEVENT" calendar component is used by an
"Attendee" of an existing event to submit to the "Organizer" a counter
proposal to the event description. The "Attendee" sends this message to
the "Organizer" of the event.

The counter proposal is an iCalendar object consisting of a VEVENT
calendar component describing the complete description of the alternate
event.

The "Organizer" rejects the counter proposal by sending the "Attendee" a
VEVENT "DECLINECOUNTER" method. The "Organizer" accepts the counter
proposal by rescheduling the event as described in section 3.2.2.1
     Rescheduling an Event.

This method type is an iCalendar object that conforms to the following
property constraints:

Component/Property  Presence
------------------- ----------------------------------------------
METHOD              1      MUST be "COUNTER"

VEVENT              1
    DTSTAMP         1
    DTSTART         1
    ORGANIZER       1       MUST be the "Organizer" of the original
                            event
    SEQUENCE        1       MUST be present if value is greater than 0,
                            MAY be present if 0
    SUMMARY         1       Can be null
    UID             1       MUST be the UID associated with the REQUEST
                            being countered

    ATTACH          0+
    ATTENDEE        0+      Can also  be used to propose other
                            "Attendees"
    CATEGORIES      0 or 1  This property may contain a list of values
    CLASS           0 or 1
    COMMENT         0 or 1


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    CONTACT         0+
    CREATED         0 or 1
    DESCRIPTION     0 or 1
    DTEND           0 or 1  if present DURATION MUST NOT be present
    DURATION        0 or 1  if present DTEND MUST NOT be present
    EXDATE          0+
    EXRULE          0+
    GEO             0 or 1
    LAST-MODIFIED   0 or 1
    LOCATION        0 or 1
    PRIORITY        0 or 1
    RDATE           0+
    RECURRENCE-ID   0 or 1  MUST only if referring to an instance of a
                            recurring calendar component.  Otherwise it
                            MUST NOT be present.
    RELATED-TO      0+
    REQUEST-STATUS  0+
    RESOURCES       0 or 1  This property may contain a list of values
    RRULE           0+
    STATUS          0 or 1  Value must be one of CONFIRMED/TENATIVE/
                            CANCELLED
    TRANSP          0 or 1
    URL             0 or 1
    X-PROPERTY      0+

VALARM              0+
VTIMEZONE           0+      MUST be present if any date/time refers to
                            a timezone
X-COMPONENT         0+

VTODO               0
VJOURNAL            0
VFREEBUSY           0


3.2.8     DECLINECOUNTER

The "DECLINECOUNTER" method in a "VEVENT" calendar component is used by
the "Organizer" of an event to reject a counter proposal submitted by an
"Attendee". The "Organizer" must send the "DECLINECOUNTER" message to
the "Attendee" that sent the "COUNTER" method to the "Organizer".

This method type is an iCalendar object that conforms to the following
property constraints:

Component/Property  Presence
------------------- ----------------------------------------------
METHOD              1      MUST be "DECLINECOUNTER"

VEVENT              1
    DTSTAMP         1
    ORGANIZER       1
    UID             1       MUST, same UID specified in original
                            REQUEST and subsequent COUNTER


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    COMMENT         0 or 1
    RECURRENCE-ID   0 or 1  MUST only if referring to an instance of a
                            recurring calendar component.  Otherwise it
                            MUST NOT be present.
    REQUEST-STATUS  0+
    SEQUENCE        0 OR 1  MUST be present if value is greater than 0,
                            MAY be present if 0
    X-PROPERTY      0+

    ATTACH          0
    ATTENDEE        0
    CATEGORIES      0
    CLASS           0
    CONTACT         0
    CREATED         0
    DESCRIPTION     0
    DTEND           0
    DTSTART         0
    DURATION        0
    EXDATE          0
    EXRULE          0
    GEO             0
    LAST-MODIFIED   0
    LOCATION        0
    PRIORITY        0
    RDATE           0
    RELATED-TO      0
    RESOURCES       0
    RRULE           0
    STATUS          0
    SUMMARY         0
    TRANSP          0
    URL             0

X-COMPONENT         0+
VTODO               0
VJOURNAL            0
VFREEBUSY           0
VTIMEZONE           0
VALARM              0



3.3 Methods For VFREEBUSY Components

This section defines the property set for the methods that are
applicable to the "VFREEBUSY" calendar component. Each of the methods is
defined using a restriction table.

This document only addresses the transfer of busy time information.
Applications desiring free time information MUST infer this from
available busy time information.




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The busy time information within the iCalendar object MAY be grouped
into more than one "VFREEBUSY" calendar component. This capability
allows busy time periods to be grouped according to some common
periodicity, such as a calendar week, month, or year. In this case, each
"VFREEBUSY" calendar component MUST include the "ATTENDEE", "DTSTART"
and "DTEND" properties in order to specify the source of the busy time
information and the date and time interval over which the busy time
information covers.

The "FREEBUSY" property value MAY include a list of values, separated by
the COMMA character (ASCII decimal 44). Alternately, multiple busy time
periods MAY be specified with multiple instances of the "FREEBUSY"
property. Both forms MUST be supported by implementations conforming to
this document. Duplicate busy time periods SHOULD NOT be specified in an
iCalendar object. However, two different busy time periods MAY overlap.

"FREEBUSY" properties should be sorted such that their values are in
ascending order, based on the start time, and then the end time, with
the earliest periods first. For example, today's busy time information
should appear after yesterday's busy time information. And the busy time
for this half-hour should appear after the busy time for earlier today.

Since events may span a day boundary, free busy time period may also
span a day boundary. Individual "A" requests busy time from individuals
"B", "C" and "D". Individual "B" and "C" replies with busy time data to
individual "A". Individual "D" does not support busy time requests and
does not reply with any data. If the transport binding supports
exception messages, then individual "D" returns an "unsupported
capability" message to individual "A".

The following summarizes the methods that are defined for the
"VFREEBUSY" calendar component.


|================|==================================================|
| Method         |  Description                                     |
|================|==================================================|
| PUBLISH        | Publish unsolicited busy time data.              |
| REQUEST        | Request busy time data.                          |
| REPLY          | Reply to a busy time request.                    |
|================|==================================================|


3.3.1     PUBLISH

The "PUBLISH" method in a "VFREEBUSY" calendar component is used to
publish busy time data. The method may be sent from one CU to any other.
The purpose of the method is to provide a message for sending
unsolicited busy time data. That is, the busy time data is not being
sent as a "REPLY" to the receipt of a "REQUEST" method.

The "ATTENDEE" property must be specified in the busy time information.
The value is the CU address of the originator of the busy time
information.


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This method type is an iCalendar object that conforms to the following
property constraints:

Component/Property  Presence
------------------- ----------------------------------------------
METHOD              1       MUST be "PUBLISH"

VFREEBUSY           1+
    DTSTAMP         1
    DTSTART         1       DateTime values must be in UTC
    DTEND           1       DateTime values must be in UTC
    FREEBUSY        1+      MUST be BUSYTIME. Multiple instances are
                            allowed. Multiple instances must be sorted
                            in ascending order
    ORGANIZER       1       MUST contain the address of originator of
                            busy time data.

    COMMENT         0 or 1
    CONTACT         0+
    X-PROPERTY      0+
    URL             0 or 1  Specifies busy time URL

    ATTENDEE        0
    DURATION        0
    REQUEST-STATUS  0
    UID             0

X-COMPONENT         0+

VEVENT              0
VTODO               0
VJOURNAL            0
VTIMEZONE           0
VALARM              0


3.3.2     REQUEST

The "REQUEST" method in a "VFREEBUSY" calendar component is used to ask
a "Calendar User" for their busy time information. The request may be
for a busy time information bounded by a specific date and time
interval.

This message only permits requests for busy time information. The
message is sent from a "Calendar User" requesting the busy time
information to one or more intended recipients.

If the originator of the "REQUEST" method is not authorized to make a
busy time request on the recipient's calendar system, then an exception
message SHOULD be returned in a "REPLY" method, but no busy time data
need be returned.

This method type is an iCalendar object that conforms to the following
property constraints:


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Component/Property  Presence
------------------- ----------------------------------------------
METHOD              1      MUST be "REQUEST"

VFREEBUSY           1
    ATTENDEE        1+     contain the address of the calendar store
                           for which busy time is being requested.
    DTEND           1      DateTime values must be in UTC
    DTSTAMP         1
    DTSTART         1      DateTime values must be in UTC
    ORGANIZER       1      MUST be the request originator's address
    UID             1
    COMMENT         0 or 1
    CONTACT         0+
    X-PROPERTY      0+

    FREEBUSY        0
    DURATION        0
    REQUEST-STATUS  0
    URL             0

X-COMPONENT         0+
VALARM              0
VEVENT              0
VTODO               0
VJOURNAL            0
VTIMEZONE           0


3.3.3     REPLY

The "REPLY" method in a "VFREEBUSY" calendar component is used to
respond to a busy time request. The method is sent by the recipient of a
busy time request to the originator of the request.

The "REPLY" method may also be used to respond to an unsuccessful
"REQUEST" method. Depending on the "REQUEST-STATUS" value, no busy time
information may be returned.

This method type is an iCalendar object that conforms to the following
property constraints:


Component/Property  Presence
------------------- ----------------------------------------------
METHOD              1      MUST be "REPLY"

VFREEBUSY           1
    ATTENDEE        1      (address of recipient replying)
    DTSTAMP         1
    DTEND           1      DateTime values must be in UTC
    DTSTART         1      DateTime values must be in UTC
    FREEBUSY        1+      (values MUST all be of the same data


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                            type. Multiple instances are allowed.
                            Multiple instances MUST be sorted in
                            ascending order. Values MAY NOT overlap)
    ORGANIZER       1       MUST be the request originator's address
    UID             1

    COMMENT         0 or 1
    CONTACT         0+
    REQUEST-STATUS  0+
    URL             0 or 1  (specifies busy time URL)
    X-PROPERTY      0+
    DURATION        0
    SEQUENCE        0

X-COMPONENT         0+
VALARM              0
VEVENT              0
VTODO               0
VJOURNAL            0
VTIMEZONE           0


3.4 Methods For VTODO Components

This section defines the property set for the methods that are
applicable to the "VTODO" calendar component. Each of the methods is
defined using a restriction table that specifies the property
constraints that define the particular method.

The following summarizes the methods that are defined for the "VTODO"
calendar component.


+================+==================================================+
| Method         |  Description                                     |
|================+==================================================|
| PUBLISH        | Post notification of a VTODO. Used primarily as  |
|                | a method of advertising the existence of a VTODO.|
|                |                                                  |
| REQUEST        | Assign a VTODO. This is an explicit assignment to|
|                | one or more Calendar Users. The REQUEST method   |
|                | is also used to update or change an existing     |
|                | VTODO. Clients that cannot handle REQUEST MAY    |
|                | degrade the method to treat it as a PUBLISH.     |
|                |                                                  |
| REPLY          | Reply to a VTODO request. Attendees MAY set      |
|                | PARTSTAT to ACCEPTED, DECLINED, TENTATIVE,       |
|                | DELEGATED, PARTIAL, and COMPLETED.               |
|                |                                                  |
| ADD            | Add one or more instances to an existing to-do.  |
|                |                                                  |
| CANCEL         | Cancel one or more instances of an existing      |
|                | to-do.                                           |
|                |                                                  |


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| REFRESH        | A request sent to a VTODO Organizer asking for   |
|                | the latest version of a VTODO.                   |
|                |                                                  |
| COUNTER        | Counter a REQUEST with an alternative proposal.  |
|                |                                                  |
| DECLINECOUNTER | Decline a counter proposal by an Attendee.       |
+================+==================================================+


3.4.1     PUBLISH

The "PUBLISH" method in a "VTODO" calendar component has no associated
response. It is simply a posting of an iCalendar object that maybe added
to a calendar. It MUST have an "Organizer".  It MUST NOT have
"Attendees". Its expected usage is for encapsulating an arbitrary
"VTODO" calendar component as an iCalendar object. The "Organizer" MAY
subsequently update (with another "PUBLISH" method), add instances to
(with an "ADD" method), or cancel (with a "CANCEL" method) a previously
published "VTODO" calendar component.

This method type is an iCalendar object that conforms to the following
property constraints:


Component/Property  Presence
------------------- ----------------------------------------------
METHOD               1       MUST be "PUBLISH"
VTODO                1+
    DTSTAMP          1
    DTSTART          1
    ORGANIZER        1
    PRIORITY         1
    SEQUENCE         0 or 1  MUST be present if value is greater than
                             0, MAY be present if 0
    SUMMARY          1       Can be null.
    UID              1

    ATTACH           0+
    CATEGORIES       0 or 1  This property may contain a list of values
    CLASS            0 or 1
    COMMENT          0 or 1
    CONTACT          0+
    CREATED          0 or 1
    DESCRIPTION      0 or 1  Can be null
    DUE              0 or 1  If present DURATION MUST NOT be present
    DURATION         0 or 1  If present DUE MUST NOT be present
    EXDATE           0+
    EXRULE           0+
    GEO              0 or 1
    LAST-MODIFIED    0 or 1
    LOCATION         0 or 1
    PERCENT-COMPLETE 0 or 1
    RDATE            0+
    RECURRENCE-ID    0 or 1  MUST only if referring to an instance of a


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                             recurring calendar component.  Otherwise
                             it MUST NOT be present.

    RELATED-TO       0+
    RESOURCES        0 or 1  This property may contain a list of values
    RRULE            0+
STATUS           0 or 1  MAY be one of COMPLETED/NEEDS ACTION/IN-
                             PROCESS/CANCELLED
    URL              0 or 1
    X-PROPERTY      0+

    ATTENDEE         0
    REQUEST-STATUS   0

VTIMEZONE            0+    MUST be present if any date/time refers to
                           a timezone
VALARM               0+
X-COMPONENT          0+

VFREEBUSY            0
VEVENT               0
VJOURNAL             0


3.4.2     REQUEST

The "REQUEST" method in a "VTODO" calendar component provides the
following scheduling functions:

  .  Assign a to-do to one or more "Calendar Users";
  .  Reschedule an existing to-do;
  .  Update the details of an existing to-do, without rescheduling it;
  .  Update the completion status of "Attendees" of an existing to-do,
     without rescheduling it;
  .  Reconfirm an existing to-do, without rescheduling it;
  .  Delegate/reassign an existing to-do to another "Calendar User".


The assigned "Calendar Users" are identified in the "VTODO" calendar
component by individual "ATTENDEE;ROLE=REQ-PARTICIPANT" property value
sequences.

The originator of a "REQUEST" is the "Organizer" of the to-do. The
recipient of a "REQUEST" is the "Calendar User" assigned the to-do. The
"Attendee" uses the "REPLY" method to convey their acceptance and
completion status to the "Organizer" of the "REQUEST".

The "UID", "SEQUENCE", and "DTSTAMP" properties are used to distinguish
the various uses of the "REQUEST" method. If the "UID" property value in
the "REQUEST" is not found on the recipient's calendar, then the
"REQUEST" is for a new to-do. If the "UID" property value is found on
the recipient's calendar, then the "REQUEST" is a rescheduling, an
update, or a reconfirm of the "VTODO" calendar object.



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If the "Organizer" of the "REQUEST" method is not authorized to make a
to-do request on the "Attendee's" calendar system, then an exception is
returned in the "REQUEST-STATUS" property of a subsequent "REPLY"
method, but no scheduling action is performed.

For the "REQUEST" method, multiple "VTODO" components in a single
iCalendar object are only permitted when for components with the same
"UID" property.  That is, a series of recurring events may have
instance-specific information.  In this case, multiple "VTODO"
components are needed to express the entire series.

This method type is an iCalendar object that conforms to the following
property constraints:


Component/Property  Presence
------------------- ----------------------------------------------
METHOD                1       MUST be "REQUEST"
VTODO                 1+      All components must have the same UID
    ATTENDEE          1+
    DTSTAMP           1
    DTSTART           1
    ORGANIZER         1
    PRIORITY          1
    SEQUENCE          0 or 1  MUST be present if value is greater than
                              0, MAY be present if 0
    SUMMARY           1       Can be null.
    UID               1

    ATTACH            0+
    CATEGORIES        0 or 1   This property may contain a list of
                               values
    CLASS             0 or 1
    COMMENT           0 or 1
    CONTACT           0+
    CREATED           0 or 1
    DESCRIPTION       0 or 1  Can be null
    DUE               0 or 1  If present DURATION MUST NOT be present
    DURATION          0 or 1  If present DUE MUST NOT be present
    EXDATE            0+
    EXRULE            0+
    GEO               0 or 1
    LAST-MODIFIED     0 or 1
    LOCATION          0 or 1
    PERCENT-COMPLETE  0 or 1
    RDATE             0+
    RECURRENCE-ID     0 or 1  present if referring to an instance of a
                              recurring calendar component.  Otherwise
                              it MUST NOT be present.
    RELATED-TO        0+
    RESOURCES         0 or 1  This property may contain a list of
                              values
    RRULE             0+
    STATUS            0 or 1  MAY be one of COMPLETED/NEEDS ACTION/IN-


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                              PROCESS
    URL               0 or 1
    X-PROPERTY        0+

    REQUEST-STATUS    0

VALARM                0+
VTIMEZONE             0+  MUST be present if any date/time refers
                          to a timezone
X-COMPONENT           0+

VEVENT                0
VFREEBUSY             0
VJOURNAL              0


3.4.2.1   REQUEST for Rescheduling a VTODO

The "REQUEST" method may be used to reschedule a "VTODO" calendar
component.

Rescheduling a "VTODO" calendar component involves a change to the
existing "VTODO" calendar component in terms of its start or due time or
recurrence intervals and possibly the description. If the recipient CUA
of a "REQUEST" method finds that the "UID" property value already exists
on the calendar, but that the "SEQUENCE" property value in the "REQUEST"
is greater than the value for the existing VTODO, then the "REQUEST"
method describes a rescheduling of the "VTODO" calendar component.


3.4.2.2   REQUEST for Update or Reconfirmation of a VTODO

The "REQUEST" method may be used to update or reconfirm a "VTODO"
calendar component. Reconfirmation is merely an update of "Attendee"
completion status or overall "VTODO" calendar component status.

An update to an existing "VTODO" calendar component does not involve
changes to the start or due time or recurrence intervals, nor generally
to the description for the "VTODO" calendar component. If the recipient
CUA of a "REQUEST" method finds that the "UID" property value already
exists on the calendar and that the "SEQUENCE" property value in the
"REQUEST" is the same as the value for the existing event, then the
"REQUEST" method describes an update of the "VTODO" calendar component
details, but not a rescheduling of the "VTODO" calendar component.

The update "REQUEST" is the appropriate response to a "REFRESH" method
sent from an "Attendee" to the "Organizer" of a "VTODO" calendar
component.

Unsolicited "REQUEST" methods MAY be sent by the "Organizer" of a
"VTODO" calendar component. The unsolicited "REQUEST" methods are used
to update the details of the "VTODO" (without rescheduling it or
updating the completion status of "Attendees") or the "VTODO" calendar
component itself (i.e., reconfirm the "VTODO").


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3.4.2.3   REQUEST for Delegating a VTODO

The "REQUEST" method is also used to delegate or reassign ownership of a
"VTODO" calendar component to another "Calendar User". For example, it
may be used to delegate an "Attendee's" role (i.e. "chair", or
"participant") for a "VTODO" calendar component. The "REQUEST" method is
sent by one of the "Attendees" of an existing "VTODO" calendar component
to some other individual. An "Attendee" of a "VTODO" calendar component
MUST NOT delegate to the "Organizer" of the event.

For the purposes of this description, the "Attendee" delegating the
"VTODO" calendar component is referred to as the "Delegator". The
"Attendee" receiving the delegation request is referred to as the
"Delegate".

The "Delegator" of a "VTODO" calendar component MUST forward the
existing "REQUEST" method for a "VTODO" calendar component to the
"Delegate". The "VTODO" calendar component description MUST include the
"Delegator's" up-to-date "VTODO" calendar component definition. The
"REQUEST" method MUST also include an "ATTENDEE" property with the
calendar address of the "Delegate". The "Delegator" MUST also send a
"REPLY" method back to the "Organizer" with the "Delegator's" "Attendee"
property "partstat" parameter value set to "DELEGATED". In addition, the
"delegated-to" parameter MUST be included with the calendar address of
the "Delegate". A response to the delegation "REQUEST" is sent from the
"Delegate" to the "Organizer" and optionally, to the "Delegator". The
"REPLY" method from the "Delegate" SHOULD include the "ATTENDEE"
property with their calendar address and the "delegated-from" parameter
with the value of the "Delegator's" calendar address.

The delegation "REQUEST" method MUST assign a value for the "RSVP"
property parameter associated with the "Delegator's" "Attendee" property
to that of the "Delegate's" "ATTENDEE" property. For example if the
"Delegator's" "ATTENDEE" property specifies "RSVP=TRUE", then the
"Delegate's" "ATTENDEE" property MUST specify "RSVP=TRUE".


3.4.2.4   REQUEST Forwarded To An Uninvited Calendar User

An "Attendee" assigned a "VTODO" calendar component may send the "VTODO"
calendar component to another new CU, not previously associated with the
"VTODO" calendar component. The current "Attendee" assigned the "VTODO"
calendar component does this by forwarding the original "REQUEST" method
to the new CU. The new CU can send a "REPLY" to the "Organizer" of the
"VTODO" calendar component. The reply contains an "ATTENDEE" property
for the new CU.

The "Organizer" ultimately decides whether or not the new CU becomes
part of the to-do and is not obligated to do anything with a "REPLY"
from a new (uninvited) CU. If the "Organizer" does not want the new CU
to be part of the to-do, the new "ATTENDEE" property is not added to the
"VTODO" calendar component. The "Organizer" MAY send the CU a "CANCEL"
message to indicate that they will not be added to the to-do. If the
"Organizer" decides to add the new CU, the new "ATTENDEE" property is


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added to the "VTODO" calendar component. Furthermore, the "Organizer" is
free to change any "ATTENDEE" property parameter from the values
supplied by the new CU to something the "Organizer" considers
appropriate.


3.4.2.5   REQUEST Updated Attendee Status

An "Organizer" of a "VTODO" may request an updated status from one or
more "Attendees". The "Organizer" sends a "REQUEST" method to the
"Attendee" with the "ATTENDEE;RSVP=TRUE" property sequence. The
"SEQUENCE" property for the "VTODO" is not changed from its previous
value. A recipient determines that the only change in the "REQUEST" is
that their "RSVP" property parameter indicates a request for an updated
status. The recipient SHOULD respond with a "REPLY" method indicating
their current status with respect to the "REQUEST".


3.4.3     REPLY

The "REPLY" method in a "VTODO" calendar component is used to respond
(e.g., accept or decline) to a request or to reply to a delegation
request. It is also used by an "Attendee" to update their completion
status. When used to provide a delegation response, the "Delegator" MUST
include the calendar address of the "Delegate" in the "delegated-to"
parameter of the "Delegator's" "ATTENDEE" property. The "Delegate" MUST
include the calendar address of the "Delegator" on the "delegated-from"
parameter of the "Delegate's" "ATTENDEE" property.

The "REPLY" method MAY also be used to respond to an unsuccessful
"VTODO" calendar component "REQUEST" method. Depending on the "REQUEST-
STATUS" value, no scheduling action may have been performed.

The "Organizer" of a "VTODO" calendar component MAY receive a "REPLY"
method from a "Calendar User" not in the original "REQUEST". For
example, a "REPLY" method MAY be received from a "Delegate" of a "VTODO"
calendar component. In addition, the "REPLY" method MAY be received from
an unknown "Calendar User", having been forwarded the "REQUEST" by an
original "Attendee" of the "VTODO" calendar component. This uninvited
"Attendee" MAY be accepted, or the "Organizer" MAY cancel the "VTODO"
calendar component for the uninvited "Attendee" by sending them a
"CANCEL" method.

This method type is an iCalendar object that conforms to the following
property constraints:


Component/Property   Presence
-------------------  ---------------------------------------------
METHOD               1      MUST be "REPLY"
VTODO                1+     All component MUST have the same UID
    ATTENDEE         1+
    DTSTAMP          1
    ORGANIZER        1


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    REQUEST-STATUS   1+
    UID              1      MUST must be the address of the replying
                            attendee

    ATTACH           0+
    CATEGORIES       0 or 1 This property may contain a list of values
    CLASS            0 or 1
    COMMENT          0 or 1
    CONTACT          0+
    CREATED          0 or 1
    DESCRIPTION      0 or 1
    DTSTART          0 or 1
    DUE              0 or 1  If present DURATION MUST NOT be present
    DURATION         0 or 1  If present DUE MUST NOT be present
    EXDATE           0+
    EXRULE           0+
    GEO              0 or 1
    LAST-MODIFIED    0 or 1
    LOCATION         0 or 1
    PERCENT-COMPLETE 0 or 1
    PRIORITY         0 or 1
    RDATE            0+
    RELATED-TO       0+
    RESOURCES        0 or 1  This property may contain a list of values
    RRULE            0+
    RECURRENCE-ID    0 or 1  MUST only if referring to an instance of a
                             Recurring calendar component. Otherwise it
                             MUST NOT be present
    SEQUENCE         0 or 1  MUST be the sequence number of
                             the original REQUEST if greater than 0.
                             MAY be present if 0.
    STATUS           0 or 1
    SUMMARY          0 or 1  Can be null
    URL              0 or 1
    X-PROPERTY       0+

VTIMEZONE            0 or 1  MUST be present if any date/time refers to
                             a timezone
X-COMPONENT          0+

VALARM               0
VEVENT               0
VFREEBUSY            0

3.4.4     ADD

The "ADD" method in a "VTODO" calendar component is used to add one or
more instances to an existing to-do.

If the "UID" property value in the "ADD" is not found on the recipient's
calendar, then the recipient SHOULD send a "REFRESH" to the "Organizer"
in order to be updated with the latest version of the "VTODO". If an
"Attendee" implementation does not support the "ADD" method it should
respond with a "REQUEST-STATUS" value of 5.3 and ask for a "REFRESH".


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The "SEQUENCE" property value is incremented as the sequence of to-dos
has changed.

This method type is an iCalendar object that conforms to the following
property constraints:

Component/Property  Presence
------------------- ----------------------------------------------
METHOD                1       MUST be "ADD"
VTODO                 1
    DTSTAMP           1
    ORGANIZER         1
    PRIORITY          1
    SEQUENCE          1       MUST be greater than 0
    SUMMARY           1       Can be null.
    UID               1       MUST match that of the original to-do

    ATTACH            0+
    ATTENDEE          0+
    CATEGORIES        0 or 1  This property may contain a list of
                              values
    CLASS             0 or 1
    COMMENT           0 or 1
    CONTACT           0+
    CREATED           0 or 1
    DESCRIPTION       0 or 1  Can be null
    DTSTART           0 or 1
    DUE               0 or 1  If present DURATION MUST NOT be present
    DURATION          0 or 1  If present DUE MUST NOT be present
    EXDATE            0+
    EXRULE            0+
    GEO               0 or 1
    LAST-MODIFIED     0 or 1
    LOCATION          0 or 1
    PERCENT-COMPLETE  0 or 1
    RDATE             0+
    RELATED-TO        0+
    RESOURCES         0 or 1  This property may contain a list of
                              values
    RRULE             0+
    STATUS            0 or 1  MAY be one of COMPLETED/NEEDS ACTION/IN-
                              PROCESS
    URL               0 or 1
    X-PROPERTY        0+

    RECURRENCE-ID     0
    REQUEST-STATUS    0

VALARM                0+
VTIMEZONE             0+      MUST be present if any date/time refers
                              to a timezone
X-COMPONENT           0+

VEVENT                0


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VJOURNAL              0
VFREEBUSY             0

3.4.5     CANCEL

The "CANCEL" method in a "VTODO" calendar component is used to send a
cancellation notice of an existing "VTODO" calendar request to the
"Attendees". The message is sent by the "Organizer" of a "VTODO"
calendar component to the "Attendees" of the "VTODO" calendar component.
For a recurring "VTODO" calendar component, either the whole "VTODO"
calendar component or instances of a "VTODO" calendar component may be
cancelled. To cancel the complete range of a recurring "VTODO" calendar
component, the "UID" property value for the "VTODO" calendar component
MUST be specified and a "RECURRENCE-ID" MUST NOT be specified in the
"CANCEL" method. In order to cancel an individual instance of a
recurring "VTODO" calendar component, the "RECURRENCE-ID" property value
for the "VTODO" calendar component MUST be specified in the "CANCEL"
method.

There are two options for canceling a sequence of instances of a
recurring "VTODO" calendar component:

(a)    the "RECURRENCE-ID" property for an instance in the sequence MUST be
  specified with the "RANGE" property parameter value of THISANDPRIOR
  (or THISANDFUTURE)  to indicate cancellation of the specified "VTODO"
  calendar component and all instances before (or after); or

(b)    individual recurrence instances may be cancelled by specifying
  multiple "RECURRENCE-ID" properties corresponding to the instances to
  be cancelled.

When a "VTODO" is cancelled, the "SEQUENCE" property value MUST be
incremented.

This method type is an iCalendar object that conforms to the following
property constraints:


Component/Property   Presence
-------------------  ---------------------------------------------
METHOD               1     MUST be "CANCEL"
VTODO                1
    ATTENDEE         0+    include all "Attendees" being removed from
                           the todo. MUST include all "Attendees" if
                           the entire todo is cancelled.
    UID              1     MUST echo original UID
    DTSTAMP          1
    ORGANIZER        1
    SEQUENCE         1

    ATTACH           0+
    CATEGORIES       0 or 1 This property MAY contain a list of values
    CLASS            0 or 1
    COMMENT          0 or 1


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    CONTACT          0+
    CREATED          0 or 1
    DESCRIPTION      0 or 1
    DTSTART          0 or 1
    DUE              0 or 1  If present DURATION MUST NOT be present
    DURATION         0 or 1  If present DUE MUST NOT be present
    EXDATE           0+
    EXRULE           0+
    GEO              0 or 1
    LAST-MODIFIED    0 or 1
    LOCATION         0 or 1
    PERCENT-COMPLETE 0 or 1
    RDATE            0+
    RECURRENCE-ID    0 or 1 MUST only if referring to one or more
                            instances of a recurring calendar
                            component. Otherwise it MUST NOT be
                            present.
    RELATED-TO       0+
    RESOURCES        0 or 1 This property MAY contain a list of values
    RRULE            0+
    PRIORITY         0 or 1
    STATUS           0 or 1  If present it MUST be set to "CANCELLED".
                             MUST NOT be used if purpose is to remove
                             "ATTENDEES" rather than cancel the entire
                             VTODO.
    URL              0 or 1
    X-PROPERTY       0+

    REQUEST-STATUS   0

VTIMEZONE            0 or 1  MUST be present if any date/time refers to
                             a timezone
X-COMPONENT          0+

VALARM               0
VEVENT               0
VFREEBUSY            0


3.4.6     REFRESH

The "REFRESH" method in a "VTODO" calendar component is used by
"Attendees" of an existing "VTODO" calendar component to request an
updated description from the "Organizer" of the "VTODO" calendar
component. The "Organizer" of the "VTODO" calendar component MAY use
this method to request an updated status from the "Attendees". The
"REFRESH" method MUST specify the "UID" property corresponding to the
"VTODO" calendar component needing update.

A refresh of a recurrence instance of a "VTODO" calendar component may
be requested by specifying the "RECURRENCE-ID" property corresponding to
the associated "VTODO" calendar component. The "Organizer" responds with
the latest description and rendition of the "VTODO" calendar component.
In most cases this will be a REQUEST unless the "VTODO" has been


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cancelled, in which case the ORGANIZER MUST send a "CANCEL". This method
is intended to facilitate machine processing of requests for updates to
a "VTODO" calendar component.

This method type is an iCalendar object that conforms to the following
property constraints:


Component/Property   Presence
-------------------  ---------------------------------------------
METHOD               1      MUST be "REFRESH"
VTODO                1
    ATTENDEE         1
    DTSTAMP          1
    UID              1       MUST echo original UID

    RECURRENCE-ID    0 or 1  MUST only if referring to an instance of a
                             Recurring calendar component. Otherwise it
                             MUST NOT be present
    X-PROPERTY       0+

    ATTACH           0
    CATEGORIES       0
    CLASS            0
    COMMENT          0
    CONTACT          0
    CREATED          0
    DESCRIPTION      0
    DTSTART          0
    DUE              0
    DURATION         0
    EXDATE           0
    EXRULE           0
    GEO              0
    LAST-MODIFIED    0
    LOCATION         0
    ORGANIZER        0
    PERCENT-COMPLETE 0
    PRIORITY         0
    RDATE            0
    RELATED-TO       0
    REQUEST-STATUS   0
    RESOURCES        0
    RRULE            0
    SEQUENCE         0
    STATUS           0
    URL              0

X-COMPONENT          0+

VALARM               0
VEVENT               0
VFREEBUSY            0
VTIMEZONE            0


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3.4.7     COUNTER

The "COUNTER" method in a "VTODO" calendar component is used by an
"Attendee" of an existing "VTODO" calendar component to submit to the
"Organizer" a counter proposal for the "VTODO" calendar component. The
"Attendee" sends the message to the "Organizer" of the "VTODO" calendar
component.

The counter proposal is an iCalendar object consisting of a "VTODO"
calendar component describing the complete description of the alternate
"VTODO" calendar component.

The "Organizer" rejects the counter proposal by sending the "Attendee" a
"DECLINECOUNTER" method. The "Organizer" accepts the counter proposal by
sending all of the "Attendees" of the "VTODO" calendar component a
"REQUEST" method rescheduling the "VTODO" calendar component. In the
latter case, the "Organizer" SHOULD reset the individual "RSVP" property
parameter values to TRUE on each "ATTENDEE" property; in order to force
a response by the "Attendees".

This method type is an iCalendar object that conforms to the following
property constraints:


Component/Property  Presence
------------------- ----------------------------------------------
METHOD               1      MUST be "COUNTER"
VTODO                1
    ATTENDEE         1+
    DTSTAMP          1
    ORGANIZER        1
    PRIORITY         1
    SUMMARY          1      Can be null
    UID              1

    ATTACH           0+
    CATEGORIES       0 or 1 This property MAY contain a list of values
    CLASS            0 or 1
    COMMENT          0 or 1
    CONTACT          0+
    CREATED          0 or 1
    DESCRIPTION      0 or 1 Can be null
    DTSTART          0 or 1
    DUE              0 or 1  If present DURATION MUST NOT be present
    DURATION         0 or 1  If present DUE MUST NOT be present
    EXDATE           0+
    EXRULE           0+
    GEO              0 or 1
    LAST-MODIFIED    0 or 1
    LOCATION         0 or 1
    PERCENT-COMPLETE 0 or 1
    RDATE            0+


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    RECURRENCE-ID    0 or 1 MUST only if referring to an instance of a
                            recurring calendar component.  Otherwise it
                            MUST NOT be present.
    RELATED-TO       0+
    REQUEST-STATUS   0+
    RESOURCES        0 or 1 This property MAY contain a list of values
    RRULE            0 or 1
    SEQUENCE         0 or 1 MUST echo the original SEQUENCE number.
                            MUST be present if non-zero. MAY be present
                            if zero.
    STATUS           0 or 1 MAY be one of COMPLETED/NEEDS ACTION/IN-
                            PROCESS/CANCELLED
    URL              0 or 1
    X-PROPERTY       0+


VALARM               0+
VTIMEZONE            0 or 1  MUST be present if any date/time refers to
                             a timezone
X-COMPONENT          0+

VEVENT               0
VFREEBUSY            0

3.4.8     DECLINECOUNTER

The "DECLINECOUNTER" method in a "VTODO" calendar component is used by
an "Organizer" of "VTODO" calendar component to reject a counter
proposal offered by one of the "Attendees". The "Organizer" sends the
message to the "Attendee" that sent the "COUNTER" method to the
"Organizer".

This method type is an iCalendar object that conforms to the following
property constraints:

Component/Property   Presence
-------------------  ---------------------------------------------
METHOD               1       MUST be "DECLINECOUNTER"

VTODO                1
    ATTENDEE         1+      MUST for all attendees
    DTSTAMP          1
    ORGANIZER        1
    SEQUENCE         1       MUST echo the original SEQUENCE number
    UID              1       MUST echo original UID

    ATTACH           0+
    CATEGORIES       0 or 1  This property may contain a list of values
    CLASS            0 or 1
    COMMENT          0 or 1
    CONTACT          0+
    CREATED          0 or 1
    DESCRIPTION      0 or 1
    DTSTART          0 or 1


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    DUE              0 or 1  If present DURATION MUST NOT be present
    DURATION         0 or 1  If present DUE MUST NOT be present
    EXDATE           0+
    EXRULE           0+
    GEO              0 or 1
    LAST-MODIFIED    0 or 1
    LOCATION         0 or 1
    PERCENT-COMPLETE 0 or 1
    PRIORITY         0 or 1
    RDATE            0+
    RECURRENCE-ID    0 or 1  MUST only if referring to an instance of a
                             recurring calendar component.  Otherwise
                             it MUST NOT be present.
    RELATED-TO       0+
    REQUEST-STATUS   0+
    RESOURCES        0 or 1  This property MAY contain a list of values
    RRULE            0+
    STATUS           0 or 1  MAY be one of COMPLETED/NEEDS ACTION/IN-
                             PROCESS
    URL              0 or 1
    X-PROPERTY       0+

VTIMEZONE            0+  MUST be present if any date/time refers to
                         a timezone
X-COMPONENT          0+

VALARM               0
VEVENT               0
VFREEBUSY            0

3.5 Methods For VJOURNAL Components

This section defines the property set for the methods that are
applicable to the "VJOURNAL" calendar component.

The following summarizes the methods that are defined for the "VJOURNAL"
calendar component.

+================+==================================================+
| Method         |  Description                                     |
|================+==================================================|
| PUBLISH        | Post a journal entry. Used primarily as a method |
|                | of advertising the existence of a journal entry. |
|                |                                                  |
| ADD            | Add one or more instances to an existing journal |
|                | entry.                                           |
|                |                                                  |
| CANCEL         | Cancel one or more instances of an existing      |
|                | journal entry.                                   |
+================+==================================================+






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3.5.1     PUBLISH

The "PUBLISH" method in a "VJOURNAL" calendar component has no
associated response. It is simply a posting of an iCalendar object that
may be added to a calendar. It MUST have an "Organizer". It MUST NOT
have "Attendees". The expected usage is for encapsulating an arbitrary
journal entry as an iCalendar object. The "Organizer" MAY subsequently
update (with another "PUBLISH" method) or cancel (with a "CANCEL"
method) a previously published journal entry.

This method type is an iCalendar object that conforms to the following
property constraints:

Component/Property  Presence
------------------- ----------------------------------------------
METHOD               1       MUST be "PUBLISH"
VJOURNAL             1+
    DESCRIPTION      1       Can be null.
    DTSTAMP          1
    DTSTART          1
    ORGANIZER        1
    UID              1

    ATTACH           0+
    CATEGORIES       0 or 1  This property MAY contain a list of values
    CLASS            0 or 1
    COMMENT          0 or 1
    CONTACT          0+
    CREATED          0 or 1
    EXDATE           0+
    EXRULE           0+
    LAST-MODIFIED    0 or 1
    RDATE            0+
    RECURRENCE-ID    0 or 1  MUST only if referring to an instance of a
                             recurring calendar component.  Otherwise
                             it MUST NOT be present.
    RELATED-TO       0+
    RRULE            0+
    SEQUENCE         0 or 1  MUST echo the original SEQUENCE number.
                             MUST be present if non-zero. MAY be
                             present if zero.
    STATUS           0 or 1  MAY be one of DRAFT/FINAL/CANCELLED
    SUMMARY          0 or 1  Can be null
    URL              0 or 1
    X-PROPERTY       0+

    ATTENDEE         0

VALARM               0+
VTIMEZONE            0+      MUST be present if any date/time refers to
                             a timezone
X-COMPONENT          0+

VEVENT               0


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VFREEBUSY            0
VTODO                0


3.5.2     ADD

The "ADD" method in a "VJOURNAL" calendar component is used to add one
or more instances to an existing "VJOURNAL" entry. There is no response
to the "Organizer".

If the "UID" property value in the "ADD" is not found on the recipient's
calendar, then the recipient MAY treat the "ADD" as a "PUBLISH".

This method type is an iCalendar object that conforms to the following
property constraints:

Component/Property  Presence
------------------- ----------------------------------------------
METHOD               1      MUST be "ADD"
VJOURNAL             1
    DESCRIPTION      1      Can be null.
    DTSTAMP          1
    DTSTART          1
    ORGANIZER        1
    SEQUENCE         1      MUST be greater than 0
    UID              1      MUST match that of the original journal

    ATTACH           0+
    CATEGORIES       0 or 1 This property MAY contain a list of values
    CLASS            0 or 1
    COMMENT          0 or 1
    CONTACT          0+
    CREATED          0 or 1
    EXDATE           0+
    EXRULE           0+
    LAST-MODIFIED    0 or 1
    RDATE            0+
    RELATED-TO       0+
    RRULE            0+
    STATUS           0 or 1  MAY be one of DRAFT/FINAL/CANCELLED
    SUMMARY          0 or 1  Can be null
    URL              0 or 1
    X-PROPERTY       0+

    ATTENDEE         0
    RECURRENCE-ID    0

VALARM               0+
VTIMEZONE            0 or 1 MUST be present if any date/time refers to
                            a timezone
X-COMPONENT          0+

VEVENT               0
VFREEBUSY            0


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VTODO                0


3.5.3     CANCEL

The "CANCEL" method in a "VJOURNAL" calendar component is used to send a
cancellation notice of an existing journal entry. The message is sent by
the "Organizer" of a journal entry. For a recurring journal entry,
either the whole journal entry or instances of a journal entry may be
cancelled. To cancel the complete range of a recurring journal entry,
the "UID" property value for the journal entry MUST be specified and a
"RECURRENCE-ID" property MUST NOT be specified in the "CANCEL" method.
In order to cancel an individual instance of the journal entry, the
"RECURRENCE-ID" property value for the journal entry MUST be specified
in the "CANCEL" method.

There are two options for canceling a sequence of instances of a
recurring "VJOURNAL" calendar component:

(a)    the "RECURRENCE-ID" property for an instance in the sequence MUST be
  specified with the "RANGE" property parameter value of THISANDPRIOR
  (or THISANDFUTURE)  to indicate cancellation of the specified "VTODO"
  calendar component and all instances before (or after); or

(b)    individual recurrence instances may be cancelled by specifying
  multiple "RECURRENCE-ID" properties corresponding to the instances to
  be cancelled.

When a "VJOURNAL" is cancelled, the "SEQUENCE" property value MUST be
incremented.

This method type is an iCalendar object that conforms to the following
property constraints:


Component/Property   Presence
-------------------  ---------------------------------------------
METHOD               1       MUST be "CANCEL"
VJOURNAL             1+      All MUST have the same UID
    DTSTAMP          1
    ORGANIZER        1
    SEQUENCE         1
    UID              1       MUST be the UID of the original REQUEST

    ATTACH           0+
    ATTENDEE         0+
    CATEGORIES       0 or 1  This property MAY contain a list of values
    CLASS            0 or 1
    COMMENT          0 or 1
    CONTACT          0+
    CREATED          0 or 1
    DESCRIPTION      0 or 1
    DTSTART          0 or 1
    EXDATE           0+


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    EXRULE           0+
    LAST-MODIFIED    0 or 1
    RDATE            0+
    RECURRENCE-ID    0 or 1  only if referring to an instance of a
                             recurring calendar component.  Otherwise
                             it MUST NOT be present.
    RELATED-TO       0+
    RRULE            0+
    STATUS           0 or 1  MAY be present, must be "CANCELLED" if
                             present
    SUMMARY          0 or 1
    URL              0 or 1
    X-PROPERTY       0+

    REQUEST-STATUS   0

VTIMEZONE            0+      MUST be present if any date/time refers to
                             a timezone
X-COMPONENT          0+
VALARM               0
VEVENT               0
VFREEBUSY            0
VTODO                0


3.6 Status Replies

The "REQUEST-STATUS" property may include the following values:


|==============+============================+=========================|
| Short Return | Longer Return Status       | Offending Data          |
| Status Code  | Description                |                         |
|==============+============================+=========================|
| 2.0          | Success.                   | None.                   |
|==============+============================+=========================|
| 2.1          | Success but fallback taken | Property name and value |
|              | on one or more property    | MAY be specified.       |
|              | values.                    |                         |
|==============+============================+=========================|
| 2.2          | Success, invalid property  | Property name MAY be    |
|              | ignored.                   | specified.              |
|==============+============================+=========================|
| 2.3          | Success, invalid property  | Property parameter name |
|              | parameter ignored.         | and value MAY be        |
|              |                            | specified.              |
|==============+============================+=========================|
| 2.4          | Success, unknown non-      | Non-standard property   |
|              | standard property ignored. | name MAY be specified.  |
|==============+============================+=========================|
| 2.5          | Success, unknown non       | Property and non-       |
|              | standard property value    | standard value MAY be   |
|              | ignored.                   | specified.              |
|==============+============================+=========================|


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| 2.6          | Success, invalid calendar  | Calendar component      |
|              | component ignored.         | sentinel (e.g., BEGIN:  |
|              |                            | ALARM) MAY be           |
|              |                            | specified.              |
|==============+============================+=========================|
| 2.7          | Success, request forwarded | Original and forwarded  |
|              | to Calendar User.          | caluser addresses MAY   |
|              |                            | be specified.           |
|==============+============================+=========================|
| 2.8          | Success, repeating event   | RRULE or RDATE property |
|              | ignored. Scheduled as a    | name and value MAY be   |
|              | single component.          | specified.              |
|==============+============================+=========================|
| 2.9          | Success, truncated end date| DTEND property value    |
|              | time to date boundary.     | MAY be specified.       |
|==============+============================+=========================|
| 2.10         | Success, repeating VTODO   | RRULE or RDATE property |
|              | ignored. Scheduled as a    | name and value MAY be   |
|              | single VTODO.              | specified.              |
|==============+============================+=========================|
| 2.11         | Success, unbounded RRULE   | RRULE property name and |
|              | clipped at some finite     | value MAY be specified. |
|              | number of instances        | Number of instances MAY |
|              |                            | also be specified.      |
|==============+============================+=========================|
| 3.0          | Invalid property name.     | Property name MAY be    |
|              |                            | specified.              |
|==============+============================+=========================|
| 3.1          | Invalid property value.    | Property name and value |
|              |                            | MAY be specified.       |
|==============+============================+=========================|
| 3.2          | Invalid property parameter.| Property parameter name |
|              |                            | and value MAY be        |
|              |                            | specified.              |
|==============+============================+=========================|
| 3.3          | Invalid property parameter | Property parameter name |
|              | value.                     | and value MAY be        |
|              |                            | specified.              |
|==============+============================+=========================|
| 3.4          | Invalid calendar component | Calendar component      |
|              | sequence.                  | sentinel MAY be         |
|              |                            | specified (e.g., BEGIN: |
|              |                            | VTIMEZONE).             |
|==============+============================+=========================|
| 3.5          | Invalid date or time.      | Date/time value(s) MAY  |
|              |                            | be specified.           |
|==============+============================+=========================|
| 3.6          | Invalid rule.              | Rule value MAY be       |
|              |                            | specified.              |
|==============+============================+=========================|
| 3.7          | Invalid Calendar User.     | Attendee property value |
|              |                            |MAY be specified.        |
|==============+============================+=========================|
| 3.8          | No authority.              | METHOD and Attendee     |


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|              |                            | property values MAY be  |
|              |                            | specified.              |
|==============+============================+=========================|
| 3.9          | Unsupported version.       | VERSION property name   |
|              |                            | and value MAY be        |
|              |                            | specified.              |
|==============+============================+=========================|
| 3.10         | Request entity too large.  | None.                   |
|==============+============================+=========================|
| 3.11         | Required component or      | Component or property   |
|              | property missing.          | name MAY be specified.  |
|==============+============================+=========================|
| 3.12         | Unknown component or       | Component or property   |
|              | property found             | name MAY be specified   |
|==============+============================+=========================|
| 3.13         | Unsupported component or   | Component or property   |
|              | property found             | name MAY be specified   |
|==============+============================+=========================|
| 3.14         | Unsupported capability     | Method or action MAY    |
|              |                            | be specified            |
|==============+============================+=========================|
| 4.0          | Event conflict. Date/time  | DTSTART and DTEND       |
|              | is busy.                   | property name and values|
|              |                            | MAY be specified.       |
|==============+============================+=========================|
| 5.0          | Request MAY supported.     | Method property value   |
|              |                            | MAY be specified.       |
|==============+============================+=========================|
| 5.1          | Service unavailable.       | ATTENDEE property value |
|              |                            | MAY be specified.       |
|==============+============================+=========================|
| 5.2          | Invalid calendar service.  | ATTENDEE property value |
|              |                            | MAY be specified.       |
|==============+============================+=========================|
| 5.3          | No scheduling support for  | ATTENDEE property value |
|              | user.                      | MAY be specified.       |
|==============+============================+=========================|


3.7 Implementation Considerations


3.7.1     Working With Recurrence Instances

iCalendar includes a recurrence grammar to represent recurring events.
The benefit of such a grammar is the ability to represent a number of
events in a single object. However, while this simplifies creation of a
recurring event, meeting instances still need to be referenced. For
instance, an "Attendee" may decline the third instance of a recurring
Friday event. Similarly, the "Organizer" may change the time or location
to a single instance of the recurring event.

Since implementations may elect to store recurring events as either a
single event object or a collection of discreet, related event objects,


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the protocol is designed so that each recurring instance may be both
referenced and versioned. Hence, implementations that choose to maintain
per-instance properties (such as "ATTENDEE" property "partstat"
parameter) may do so. However, the protocol does not require per-
instance recognition unless the instance itself must be renegotiated.

The scenarios for recurrence instance referencing are listed below. For
purposes of simplification a change to an event refers to a "trigger
property."  That is, a property that has a substantive effect on the
meeting itself such as start time, location, due date (for "VTODO"
calendar component components) and possibly description.

"Organizer" initiated actions:

  .  "Organizer" deletes or changes a single instance of a recurring
     event
  .  "Organizer" makes changes that affect all future instances
  .  "Organizer" makes changes that affect all previous instances
  .  "Organizer" deletes or modifies a previously changed instance


"Attendee" initiated actions:

  .  "Attendee" changes status for a particular recurrence instance
  .  "Attendee" sends Event-Counter for a particular recurrence instance


An instance of a recurring event is assigned a unique identification,
"RECURRENCE-ID" property, when that instance is renegotiated.
Negotiation may be necessary when a substantive change to the event or
to-do has be made (such as changing the start time, end time, due date
or location). The "Organizer" can identify a specific recurrence
instance using the "RECURRENCE-ID" property. The property value is equal
to the date/time of the instance. If the "Organizer" wishes to change
the "DTSTART", the original "DTSTART" value is used for "RECURRENCE-ID"
property and the new "DTSTART" and "DTEND" values reflect the change.
Note that after the change has occurred, the "RECURRENCE-ID" has changed
to the new "DTSTART" value.


3.7.2     Attendee Property Considerations

The "ORGANIZER" property is required on published events, to-dos, and
journal entries for two reasons. First, only the "Organizer" is allowed
to update and redistribute an event or to-do component. It follows that
the "ORGANIZER" property MUST be present in the event, to-do, or journal
entry component so that the CUA has a basis for authorizing an update.
Second, it is prudent to provide a point of contact for anyone who
receives a published component in case of problems.

There are valid [RFC-822] addresses that represent groups. Sending email
to such an address results in mail being sent to multiple recipients.
Such an address may be used as the value of an "ATTENDEE" property.



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Thus, it is possible that the recipient of a "REQUEST" does not appear
explicitly in the list.

It is recommended that the general approach to finding a "Calendar User"
in an attendee list be as follows:


1.   Search for the "Calendar User" in the attendee list where
  "TYPE=INDIVIDUAL"

2.   Failing (1) look for attendees where "TYPE=GROUP" or 'TYPE=UNKNOWN".
  The CUA then determines if the "Calendar User" is a member of one of
  these groups. If so, the "REPLY" method sent to the "Organizer" MUST
  contain a new "ATTENDEE" property in which:
  .  the "type" property parameter is set to INDIVIDUAL
  .  the "member" property parameter is set to the name of the group

3.   Failing (2) the CUA MAY ignore or accept the request as the "Calendar
  User" wishes.

3.7.3     X-Tokens

To make iCalendar objects extensible, new property types MAY be inserted
into components. These properties are called X-Tokens as they are
prefixed with "X-". A client is not required to make sense of X-Tokens.
Clients are not required to save X-Tokens or use them in replies.


4  Examples


4.1 Published Event Examples

In the calendaring and scheduling context, publication refers to the one
way transfer of event information. Consumers of published events simply
incorporate the event into a calendar. No reply is expected. Individual
"A" publishes an event. Individual "B" reads the event and incorporates
it into their calendar. Events are published in several ways including:
embedding the event as an object in a web page, e-mailing the event to a
distribution list, and posting the event to a newsgroup.

The table below illustrates the sequence of events between the publisher
and the consumers of a published event.

+-------------------------------------------------------------------+
| Action                          |  "Organizer"                    |
+---------------------------------+---------------------------------+
| Publish an event                | "A" sends or posts a PUBLISH    |
|                                 | message                         |
+---------------------------------+---------------------------------+
| "B" reads a published event     |                                 |
+---------------------------------+---------------------------------+
| Publish an updated event        | "A" sends or posts a PUBLISH    |
|                                 | message                         |


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+---------------------------------+---------------------------------+
| "B" reads the updated event     |                                 |
+---------------------------------+---------------------------------+
| Cancel a published event        | "A" sends or posts a CANCEL     |
|                                 | message                         |
+---------------------------------+---------------------------------+
| "B" reads the canceled event    |                                 |
|  publication                    |                                 |
+---------------------------------+---------------------------------+


4.1.1     A Minimal Published Event

The iCalendar object below describes a single event that begins on July
1, 1997 at 20:00 UTC. This event contains the minimum set of properties
for a "PUBLISH" for a "VEVENT" calendar component.


BEGIN:VCALENDAR
METHOD:PUBLISH
PRODID:-//ACME/DesktopCalendar//EN
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:mailto:a@example.com
DTSTART:19970701T200000Z
DTSTAMP:19970611T190000Z
SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES
UID:0981234-1234234-23@example.com
END:VEVENT
END:VCALENDAR


4.1.2     Changing A Published Event

The iCalendar object below describes an update to the event described in
4.1.1, the time has been changed, an end time has been added, and the
sequence number has been adjusted.


BEGIN:VCALENDAR
METHOD:PUBLISH
VERSION:2.0
PRODID:-//ACME/DesktopCalendar//EN
BEGIN:VEVENT
ORGANIZER:mailto:a@example.com
DTSTAMP:19970612T190000Z
DTSTART:19970701T210000Z
DTEND:19970701T230000Z
SEQUENCE:1
UID:0981234-1234234-23@example.com
SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES
END:VEVENT
END:VCALENDAR



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The "UID" property is used by the client to identify the event. The
"SEQUENCE" property indicates that this is a change to the event. The
event with a matching UID and sequence number 0 is superseded by this
event.

The "SEQUENCE" property provides a reliable way to distinguish different
versions of the same event. Each time an event is published, its
sequence number is incremented. If a client receives an event with a
sequence number 5 and finds it has the same event with sequence number
2, the event SHOULD be updated. However, if the client received an event
with sequence number 2 and finds it already has sequence number 5 of the
same event, the event MUST NOT be updated.


4.1.3     Canceling A Published Event

The iCalendar object below cancels the event described in 4.1.1. This
cancels the event with "SEQUENCE" property of 0, 1, and 2.

BEGIN:VCALENDAR
METHOD:CANCEL
VERSION:2.0
PRODID:-//ACME/DesktopCalendar//EN
BEGIN:VEVENT
ORGANIZER:mailto:a@example.com
COMMENT:DUKES forfeit the game
SEQUENCE:2
UID:0981234-1234234-23@example.com
DTSTAMP:19970613T190000Z
END:VEVENT
END:VCALENDAR


4.1.4     A Rich Published Event

This example describes the same event as in 4.1.1, but in much greater
detail.

BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:PUBLISH
SCALE:GREGORIAN
VERSION:2.0
BEGIN:VTIMEZONE
TZID:America-Chicago
TZURL:http://zones.stds_r_us.net/tz/America-Chicago
BEGIN:STANDARD
DTSTART:19671029T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
TZOFFSETFROM:-0500
TZOFFSETTO:-0600
TZNAME:CST
END:STANDARD
BEGIN:DAYLIGHT


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DTSTART:19870405T020000
RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
TZOFFSETFROM:-0600
TZOFFSETTO:-0500
TZNAME:CDT
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VEVENT
ORGANIZER:mailto:a@example.com
ATTACH:http://www.dukes.com/
CATEGORIES:SPORTS EVENT,ENTERTAINMENT
CLASS:PRIVATE
DESCRIPTION:MIDWAY STADIUM\n
 Big time game. MUST see.\n
 Expected duration:2 hours\n
DTEND;TZID=America-Chicago:19970701T180000
DTSTART;TZID=America-Chicago:19970702T160000
DTSTAMP:19970614T190000Z
STATUS:CONFIRMED
LOCATION;VALUE=URI:http://www.midwaystadium.com/
PRIORITY:2
RESOURCES:SCOREBOARD
SEQUENCE:3
SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES
UID:0981234-1234234-23@example.com
RELATED-TO:0981234-1234234-14@example.com
BEGIN:VALARM
TRIGGER:-PT2H
ACTION:DISPLAY
DESCRIPTION:You should be leaving for the game now.
END:VALARM
BEGIN:VALARM
TRIGGER:-PT30M
ACTION:AUDIO
END:VALARM
END:VEVENT
END:VCALENDAR

The "RELATED-TO" field contains the "UID" property of a related calendar
event. The "SEQUENCE" property 3 indicates that this event supersedes
versions 0, 1, and 2.


4.1.5     Anniversaries or Events attached to entire days

This example demonstrates the use of the "value" parameter to tie a
"VEVENT" to day rather than a specific time.

BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:PUBLISH
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:mailto:a@example.com


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DTSTAMP:19970614T190000Z
UID:0981234-1234234-23@example.com
DTSTART;VALUE=DATE:19970714
RRULE:FREQ=YEARLY;INTERVAL=1
SUMMARY: Bastille Day
END:VEVENT
END:VCALENDAR


4.2 Group Event Examples

Group events are distinguished from published events in that they have
"Attendees" and that there is interaction between the "Attendees" and
the "Organizer" with respect to the event. Individual "A" requests a
meeting between individuals "A", "B", "C" and "D". Individual "B"
confirms attendance to the meeting. Individual "C" declines attendance.
Individual "D" tentatively confirms attendance. The following table
illustrates the the message flow between these individuals. A, the CU
scheduling the meeting, is referenced as the "Organizer".

+--------------------------------------------------------------------+
| Action             |  "Organizer"        | Attendee                |
+--------------------------------------------------------------------+
| Initiate a meeting | "A" sends a REQUEST |                         |
| request            | message to "B", "C",|                         |
|                    | and "D"             |                         |
+--------------------------------------------------------------------+
| Accept the meeting |                     | "B" sends a REPLY       |
| request            |                     | message to "A" with its |
|                    |                     | ATTENDEE "partstat" para-|
|                    |                     | set to "accepted"       |
+--------------------------------------------------------------------+
| Decline the meeting|                     | "C" sends a REPLY       |
| request            |                     | message to "A" with its |
|                    |                     | ATTENDEE "partstat" para-|
|                    |                     | set to "declined"       |
+--------------------------------------------------------------------+
| Tentatively accept |                     | "D" sends a REPLY       |
| the meeting request|                     | message to "A" with its |
|                    |                     | ATTENDEE "partstat" para-|
|                    |                     | set to "tentative"      |
+--------------------------------------------------------------------+
| Confirm meeting    | "A" sends a REQUEST |                         |
| status with        | message to "B" and  |                         |
| attendees          | "D" with updated    |                         |
|                    | information.        |                         |
+--------------------------------------------------------------------+


4.2.1     A Group Event Request

A sample meeting request is sent from "A" to "B", "C", and "D". _E_ is
also sent a copy of the request but is not expected to attend and need
not reply. "E" illustrates how CUAs might implement an "FYI" type


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feature. Note the use of the "role" parameter. The default value for the
"role" parameter is "req-participant" and it need not be enumerated. In
this case we are using the value "non-participant" to indicate "E" is a
non-attending CU. The parameter is not needed on other "Attendees" since
"participant" is the default value.


BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED;CN=BIG A:Mailto:A@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL;CN=B:Mailto:B@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL;CN=C:Mailto:C@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL;CN=Hal:Mailto:D@example.com
ATTENDEE;RSVP=FALSE;TYPE=ROOM:conf_Big@example.com
ATTENDEE;ROLE=NON-PARTICIPANT;RSVP=FALSE:Mailto:E@example.com
DTSTAMP:19970611T190000Z
DTSTART:19970701T200000Z
DTEND:19970701T2000000Z
SUMMARY:Conference
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:0
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR


4.2.2     Reply To A Group Event Request

Attendee "B" accepts the meeting.


BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REPLY
VERSION:2.0
BEGIN:VEVENT
ATTENDEE;PARTSTAT=ACCEPTED:Mailto:B@example.com
ORGANIZER:MAILTO:A@example.com
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:0
REQUEST-STATUS:2.0;Success
DTSTAMP:19970612T190000Z
END:VEVENT
END:VCALENDAR

"B" could have declined the meeting or indicated tentative acceptance by
setting the "ATTENDEE" "partstat" parameter to "declined" or
"tentative", respectively. Also, "REQUEST-STATUS" is not required in
successful transactions.



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4.2.3     Update An Event

The event is moved to a different time. The combination of the "UID"
property (unchanged) and the "SEQUENCE" (bumped to 1) properties
indicate the update.


BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:C@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL;CN=Hal:Mailto:D@example.com
ATTENDEE;ROLE=NON-PARTICIPANT;RSVP=FALSE;
 CUTYPE=ROOM:Mailto:Conf@example.com
ATTENDEE;ROLE=NON-PARTICIPANT;RSVP=FALSE:Mailto:E@example.com
DTSTART:19970701T180000Z
DTEND:19970701T190000Z
SUMMARY:Phone Conference
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:1
DTSTAMP:19970613T190000Z
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR


4.2.4     Countering an Event Proposal

"A" sends a "REQUEST" to "B" and "C". "B" makes a counter-proposal to
"A" to change the time and location.

"A" sends the following "REQUEST":


BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:C@example.com
DTSTART:19970701T190000Z
DTEND:19970701T200000Z
SUMMARY:Discuss the Merits of the election results
LOCATION:Green Conference Room
UID:calsrv.example.com-873970198738777a@example.com
SEQUENCE:0


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DTSTAMP:19970611T190000Z
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR

"B" sends "COUNTER" to "A", requesting changes to time and place. "B"
uses the "COMMENT" property to communicate a rationale for the change.
Note that the "SEQUENCE" property is NOT incremented on a "COUNTER".


BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:COUNTER
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:C@example.com
DTSTART:19970701T160000Z
DTEND:19970701T190000Z
DTSTAMP:19970612T190000Z
SUMMARY:Discuss the Merits of the election results
LOCATION:Green Conference Room
COMMENT:This time works much better and I think the big conference
  room is too big
UID:calsrv.example.com-873970198738777a@example.com
SEQUENCE:0
DTSTAMP:19970611T190000Z
END:VEVENT
END:VCALENDAR

"A" accepts the changes from "B". To accept a counter-proposal, the
"Organizer" sends a new event "REQUEST" with an incremented sequence
number.


BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:C@example.com
DTSTAMP:19970613T190000Z
DTSTART:19970701T160000Z
DTEND:19970701T190000Z
SUMMARY:Discuss the Merits of the election results - changed to
  meet B's schedule
LOCATION:Green Conference Room
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:1


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STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR

Instead, "A" rejects "B's" counter proposal

BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:DECLINECOUNTER
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
COMMENT:Sorry, I cannot change this meeting time
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:0
DTSTAMP:19970614T190000Z
END:VEVENT
END:VCALENDAR


4.2.5     Delegating an Event

When delegating an event request to another "Calendar User", the
"Delegator" must both update the "Organizer" with a "REPLY" and send a
request to the "Delegate". There is currently no protocol limitation to
delegation depth. It is possible for the original delegate to delegate
the meeting to someone else, and so on. When a request is delegated from
one CUA to another there are a number of responsibilities required of
the "Delegator". The "Delegator" MUST:

  .  Send a "REPLY" to the "Organizer" with the following updates:
  .  The "Delegator's" "ATTENDEE" property "partstat" parameter set to
     "delegated" and the "delegated-to" parameter is set to the address
     of the "Delegate"
  .  Add an additional "ATTENDEE" property for the "Delegate" with the
     "delegated-from" property parameter set to the "Delegator"
  .  Indicate whether they want to continue to receive updates when the
     "Organizer" sends out updated versions of the event.  Setting the
     "rsvp" property parameter to "TRUE" will cause the updates to be
     sent, setting it to "FALSE" causes no further updates to be sent.
     Note that in either case, if the "Delegate" declines the invitation
     the "Delegator" will be notified.
  .  The "Delegator" MUST also send a copy of the original "REQUEST"
     method to the "Delegate".


It is not required that the "Delegate" include the "Delegator" in their
"REPLY" method. However, it is strongly advised since this will inform
the "Delegator" whether the "Delegate" plans to attend the meeting.
[Editors note:  How so?] If the "Delegate" declines the meeting, the
"Delegator" may elect to delegate the "REQUEST" to another CUA. The
process is the same.



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+---------------------------------------------------------------------+
| Action             |  "Organizer"        | Attendee                 |
+---------------------------------------------------------------------+
| Initiate a meeting | "A" sends a REQUEST |                          |
| request            | message to "B" and  |                          |
|                    | "C"                 |                          |
+---------------------------------------------------------------------+
| Delegate:          |                     | "C" sends a REPLY to "A" |
| "C" delegates to   |                     | with the ATTENDEE.       |
| "E"                |                     | "partstat" parameter set  |
|                    |                     | to "delegated" and with a|
|                    |                     | new "ATTENDEE" property  |
|                    |                     | for "E". "E's" ATTENDEE  |
|                    |                     | "delegated-from" param   |
|                    |                     | is set to "C". "C's"     |
|                    |                     | ATTENDEE "delegated-to"  |
|                    |                     | param is set to "E".     |
|                    |                     | "C" sends REQUEST message|
|                    |                     | to "E" with the original |
|                    |                     | meeting request          |
|                    |                     | information. The         |
|                    |                     |  "partstat" property      |
|                    |                     | parameter for "C" is set |
|                    |                     | to "delegated" and the   |
|                    |                     |  "delegated-to"          |
|                    |                     | parameter is set to      |
|                    |                     | the address of "E". An   |
|                    |                     | "ATTENDEE" property is   |
|                    |                     | added for "E" and the    |
|                    |                     | "delegated-from"         |
|                    |                     | parameter is set to      |
|                    |                     | the address of "C".      |
+---------------------------------------------------------------------+
| Confirm meeting    |                     | "E" sends REPLY message  |
| attendance         |                     | to "A" and optionally "C"|
|                    |                     | with its "partstat"       |
|                    |                     | property parameter set   |
|                    |                     | to "ACCEPTED"            |
+---------------------------------------------------------------------+
| Optional:          | "A" sends REQUEST   |                          |
| Redistribute       | message to "B", "C" |                          |
| meeting to         | and "E".            |                          |
| attendees          |                     |                          |
+---------------------------------------------------------------------+

"C" responds to the "Organizer".

BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REPLY
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:MAILTO:A@Example.com


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ATTENDEE;PARTSTAT=DELEGATED;DELEGATED-
 TO="Mailto:E@example.com":Mailto:C@example.com
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:0
REQUEST-STATUS:2.0;Success
DTSTAMP:19970611T190000Z
END:VEVENT
END:VCALENDAR

Attendee "C" delegates presence at the meeting to "E".

BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE;PARTSTAT=DELEGATED;DELEGATED-
 TO="Mailto:E@example.com":Mailto:C@example.com
ATTENDEE;RSVP=TRUE;
 DELEGATED-FROM="Mailto:C@example.com":Mailto:E@example.com
DTSTART:19970701T180000Z
DTEND:19970701T200000Z
SUMMARY:Phone Conference
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:0
STATUS:CONFIRMED
DTSTAMP:19970611T190000Z
END:VEVENT
END:VCALENDAR


4.2.6     Delegate Accepts the Meeting

To accept a delegated meeting, the delegate, "E", sends the following
message to "A" and "C":

BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REPLY
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:MAILTO:A@Example.com
ATTENDEE;PARTSTAT=ACCEPTED;DELEGATED-
 FROM="Mailto:C@example.com":Mailto:E@example.com
ATTENDEE;PARTSTAT=DELEGATED;
 DELEGATED-TO="Mailto:E@example.com":Mailto:C@example.com
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:0
REQUEST-STATUS:2.0;Success
DTSTAMP:19970614T190000Z
END:VEVENT
END:VCALENDAR



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4.2.7     Delegate Declines the Meeting

In this example the "Delegate" declines the meeting request and sets the
"ATTENDEE" property "partstat" parameter to "DECLINED". The "Organizer"
SHOULD resend the "REQUEST" to "C" with the "partstat" parameter of the
"Delegate" set to "declined". This lets the "Delegator" know that the
"Delegate" has declined and provides an opportunity to the "Delegator"
to either accept the request or delegate it to another CU.

Response from "E" to "A" and "C". Note the use of the "COMMENT" property
"E" uses to indicate why the delegation was declined.


BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REPLY
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:MAILTO:A@Example.com
ATTENDEE;PARTSTAT=DELEGATED;
 DELEGATED-TO="Mailto:E@example.com":Mailto:C@example.com
ATTENDEE;PARTSTAT=DECLINED;
 DELEGATED-FROM="Mailto:C@example.com":Mailto:E@example.com
COMMENT:Sorry, I will be out of town at that time.
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:0
REQUEST-STATUS:2.0;Success
DTSTAMP:19970614T190000Z
END:VEVENT
END:VCALENDAR

"A" resends the "REQUEST" method to "C". "A" may also wish to express
the fact that the item was delegated in the "COMMENT" property.


BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:MAILTO:A@Example.com
ATTENDEE;PARTSTAT=DECLINED;
 DELEGATED-FROM="Mailto:C@example.com":Mailto:E@example.com
ATTENDEE;RSVP=TRUE:Mailto:C@example.com
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:0
SUMMARY:Phone Conference
DTSTART:19970701T180000Z
DTEND:19970701T200000Z
DTSTAMP:19970614T200000Z
COMMENT:DELEGATE (ATTENDEE Mailto:E@example.com) DECLINED YOUR
 INVITATION
END:VEVENT
END:VCALENDAR


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4.2.8     Forwarding an Event Request

The protocol does not prevent an "Attendee" from "forwarding" an
"VEVENT" calendar component to other "Calendar Users". Forwarding
differs from delegation in that the forwarded "Calendar User" (often
referred to as a "Party Crasher") does not replace the forwarding
"Calendar User". Implementations are not required to add the "Party
Crasher" to the "Attendee" list and hence there is no guarantee that a
"Party Crasher" will receive additional updates to the Event. The
forwarding "Calendar User" SHOULD NOT add the "Party Crasher" to the
attendee list. The "Organizer" MAY add the forwarded "Calendar User" to
the attendee list.


4.2.9     Cancel A Group Event

Individual "A" requests a meeting between individuals "A", "B", "C", and
"D". Individual "B" declines attendance to the meeting. Individual "A"
decides to cancel the meeting. The following table illustrates the
sequence of messages that would be exchanged between these individuals.

Messages related to a previously canceled event ("SEQUENCE" property
value is less than the "SEQUENCE" property value of the "CANCEL"
message) MUST be ignored.


+--------------------------------------------------------------------+
| Action             |  "Organizer"        | "Attendee"              |
+--------------------------------------------------------------------+
| Initiate a meeting | "A" sends a REQUEST |                         |
| request            | message to "B", "C",|                         |
|                    | and "D"             |                         |
+--------------------------------------------------------------------+
| Decline the meeting|                     | "B" sends a "REPLY"     |
| request            |                     | message to "A" with its |
|                    |                     | "partstat" para-         |
|                    |                     | set to "declined".      |
+--------------------------------------------------------------------+
| Cancel the meeting | "A" sends a CANCEL  |                         |
|                    | message to "B", "C" |                         |
|                    | and "D"             |                         |
+--------------------------------------------------------------------+

The example shows how "A" cancels the event.

BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:CANCEL
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE;TYPE=INDIVIDUAL;Mailto:A@example.com


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ATTENDEE;TYPE=INDIVIDUAL:Mailto:B@example.com
ATTENDEE;TYPE=INDIVIDUAL:Mailto:C@example.com
ATTENDEE;TYPE=INDIVIDUAL:Mailto:D@example.com
COMMENT:Mr. B cannot attend. It's raining. Lets cancel.
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:1
STATUS:CANCELLED
DTSTAMP:19970613T190000Z
END:VEVENT
END:VCALENDAR


4.2.10    Removing Attendees

"A" wants to remove "B" from a meeting. This is done by sending a
"CANCEL" to "B" and removing "B" from the attendee list in the master
copy of the event.

+--------------------------------------------------------------------+
| Action             |  "Organizer"        | "Attendee"              |
+--------------------------------------------------------------------+
| Remove an "B"      | "A" sends a CANCEL  |                         |
| as an "Attendee"   | message to "B"      |                         |
+--------------------------------------------------------------------+
| Update the master  | "A" sends the       |                         |
| copy of the event  | updated event to    |                         |
|                    | the remaining       |                         |
|                    | "Attendees"         |                         |
+--------------------------------------------------------------------+

The original meeting includes "A", "B", "C", and "D". The example below
shows the "CANCEL" that "A" sends to "B". Note that in the example below
the "STATUS" property is omitted. This is used when the meeting itself
is cancelled and not when the intent is to remove an "Attendee" from the
Event.

BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:CANCEL
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE:mailto:B@example.com
COMMENT:You're off the hook for this meeting
UID:calsrv.example.com-873970198738777@example.com
DTSTAMP:19970613T193000Z
SEQUENCE:1
END:VEVENT
END:VCALENDAR

The updated master copy of the event is shown below. The "Organizer" MAY
resend the updated event to the remaining "Attendees". Note that "B" has
been removed.



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BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;TYPE=INDIVIDUAL:Mailto:C@example.com
ATTENDEE;TYPE=INDIVIDUAL:Mailto:D@example.com
ATTENDEE;TYPE=ROOM:CR_Big@example.com
ATTENDEE;ROLE=NON-PARTICIPANT;
 RSVP=FALSE:Mailto:E@example.com
DTSTAMP:19970611T190000Z
DTSTART:19970701T200000Z
DTEND:19970701T203000Z
SUMMARY:Phone Conference
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:2
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR

4.2.11    Replacing the Organizer

The scenario for this example begins with "A" as the "Organizer" for a
recurring meeting with "B", "C", and "D". "A" receives a new job offer
in another country and drops out of touch.  "A" left no forwarding
address or way to be reached.  Using out-of-band communication, the
other "Attendees" eventually learn what has happened and reach an
agreement that "B" should become the new "Organizer" for the meeting. To
do this, "B" sends out a new version of the event and the other
"Attendees" agree to accept "B" as the new "Organizer". "B" also removes
"A" from the event.

When the "Organizer" is replaced, the "SEQUENCE" property value MUST be
incremented.

This is the message "B" sends to "C" and "D"

BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:B@example.com
ATTENDEE;ROLE=CHAIR;STATUS=ACCEPTED:Mailto:B@example.com
ATTENDEE;TYPE=INDIVIDUAL:Mailto:C@example.com
ATTENDEE;TYPE=INDIVIDUAL:Mailto:D@example.com
DTSTAMP:19970611T190000Z
DTSTART:19970701T200000Z
DTEND:19970701T203000Z
RRULE:FREQ=WEEKLY
SUMMARY:Phone Conference
UID:123456@example.com


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SEQUENCE:1
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR



4.3 Busy Time Examples

Busy time objects can be used in several ways. First, a CU may request
busy time from another CU for a specific range of time. That request can
be answered with a busy time Reply. Additionally, a CU may simply
publish their busy time for a given interval and point other CUs to the
published location. The following examples outline both scenarios.

Individual "A" publishes busy time for one week.

BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
VERSION:2.0
METHOD:PUBLISH
BEGIN:VFREEBUSY
DTSTAMP:19980101T124100Z
ORGANIZER:MAILTO:A@Example.com
DTSTART:19980101T124200Z
DTEND:19980107T124200Z
FREEBUSY:19980101T180000Z/19980101T190000Z
FREEBUSY:19980103T020000Z/19980103T050000Z
FREEBUSY:19980107T020000Z/19980107T050000Z
FREEBUSY:19980113T000000Z/19980113T010000Z
FREEBUSY:19980115T190000Z/19980115T200000Z
FREEBUSY:19980115T220000Z/19980115T230000Z
FREEBUSY:19980116T013000Z/19980116T043000Z
END:VFREEBUSY
END:VCALENDAR


Individual "A" requests busy time from individuals "B", "C". Individual
"B" and "C" replies with busy time data to individual "A". The following
table illustrates the sequence of messages that would be exchanged
between these individuals.

+--------------------------------------------------------------------+
| Action             |  "Organizer"        | Attendee                |
+--------------------------------------------------------------------+
| Initiate a busy    | "A" sends "REQUEST" |                         |
| time request       | message to "B" and  |                         |
|                    | and "C"             |                         |
+--------------------------------------------------------------------+
| Reply to the "BUSY"|                     | "B" sends a "REPLY"     |
| request with "BUSY"|                     | message to "A" with     |
| time data          |                     | busy time data          |
+--------------------------------------------------------------------+



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4.3.1     Request Busy Time

"A" sends a "BUSY-REQUEST" to "B" and "C" for busy time


BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VFREEBUSY
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR:Mailto:A@example.com
ATTENDEE:Mailto:B@example.com
ATTENDEE:Mailto:C@example.com
DTSTAMP:19970613T190000Z
DTSTART:19970701T080000Z
DTEND:19970701T200000
UID:calsrv.example.com-873970198738777@example.com
END:VFREEBUSY
END:VCALENDAR


4.3.2     Reply To A Busy Time Request

"B" sends a "REPLY" method type of a "VFREEBUSY" calendar component to
"A"


BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REPLY
VERSION:2.0
BEGIN:VFREEBUSY
ORGANIZER:MAILTO:A@example.com
ATTENDEE:Mailto:B@example.com
DTSTART:19970701T080000Z
DTEND:19970701T200000Z
UID:calsrv.example.com-873970198738777@example.com
FREEBUSY:19970701T090000Z/PT1H,19970701T140000Z/PT30M
DTSTAMP:19970613T190030Z
END:VFREEBUSY
END:VCALENDAR

"B" is busy from 09:00 to 10:00 and from 14:00 to 14:30.


4.4 Recurring Event and Time Zone Examples


4.4.1     A Recurring Event Spanning Time Zones

This event describes a weekly phone conference. The "Attendees" are each
in a different time zone.



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BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VTIMEZONE
TZID:America-SanJose
TZURL:http://zones.stds_r_us.net/tz/America-SanJose
BEGIN:STANDARD
DTSTART:19671029T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
TZOFFSETFROM:-0700
TZOFFSETTO:-0800
TZNAME:PST
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:19870405T020000
RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
TZOFFSETFROM:-0800
TZOFFSETTO:-0700
TZNAME:PDT
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED;TYPE=INDIVIDUAL:A@example.COM
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:B@example.fr
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:c@example.jp
DTSTAMP:19970613T190030Z
DTSTART;TZID=America-SanJose:19970701T140000
DTEND;TZID=America-SanJose:19970701T150000
RRULE:FREQ=WEEKLY;INTERVAL=20;WKST=SU;BYDAY=TU
RDATE;TZID=America-SanJose:19970910T140000
EXDATE;TZID=America-SanJose:19970909T140000
EXDATE;TZID=America-SanJose:19971028T140000
SUMMARY:Weekly Phone Conference
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:0
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR

The first two components of this iCalendar object are the time zone
components. The "DTSTART" date coincides with the first instance of the
RRULE property.

The recurring meeting is defined in a particular time zone, presumably
that of the originator. The client for each "Attendee" has the
responsibility of determining the recurrence time in the "Attendee's"
time zone.

The repeating event starts on Tuesday, July 1, 1997 at 2:00pm PDT.
"Attendee" B@example.fr is in France where the local time on this date
is 9 hours ahead of PDT or 23:00. "Attendee" C@example.jp is in Japan


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where local time is 8 hours ahead of UTC or Wednesday, July 2 at 06:00.
The event repeats weekly on Tuesdays (in PST/PDT). The "RRULE" property
results in 20 instances. The last instance falls on Tuesday, November
11, 1997 2:00pm PDT. The "RDATE" property adds another instance: WED,
10-SEP-1997 2:00 PM PST.

There are two exceptions to this recurring appointment. The first one
is:

TUE, 09-SEP-1997 23:00 GMT
TUE, 09-SEP-1997 14:00 PDT
WED, 10-SEP-1997 06:00 JST

and the second is:

TUE, 28-OCT-1997 23:00 GMT
TUE, 28-OCT-1997 14:00 PST
WED, 29-OCT-1997 06:00 JST


4.4.2     Modify A Recurring Instance

In this example the "Organizer" issues a recurring meeting. Later the
"Organizer" changes an instance of the event by changing the "DTSTART"
property. Note the use of "RECURRENCE-ID" property and "SEQUENCE"
property in the second request.

Original Request:

BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:guid-1@host1.com
SEQUENCE:0
RRULE:FREQ=MONTHLY;BYMONTHDAY=1;UNTIL=19980901T210000Z
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE:Mailto:B@example.com
ATTENDEE:Mailto:C@example.com
ATTENDEE:Mailto:D@example.com
DESCRIPTION:IETF-C&S Conference Call
CLASS:PUBLIC
SUMMARY:IETF Calendaring Working Group Meeting
DTSTART:19970601T210000Z
DTEND:19970601T220000Z
LOCATION:Conference Call
DTSTAMP:19970526T083000Z
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR




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The event request below is to change the time of a specific instance.
This changes the July 1st instance to July 3rd.

BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:guid-1@host1com
RECURRENCE-ID:19970701T210000Z
SEQUENCE:1
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE:Mailto:B@example.com
ATTENDEE:Mailto:C@example.com
ATTENDEE:Mailto:D@example.com
DESCRIPTION:IETF-C&S Conference Call
CLASS:PUBLIC
SUMMARY:IETF Calendaring Working Group Meeting
DTSTART:19970703T210000Z
DTEND:19970703T220000Z
LOCATION:Conference Call
DTSTAMP:19970626T093000Z
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR


4.4.3     Cancel an Instance

In this example the "Organizer" of a recurring event deletes the August
1st instance.


BEGIN:VCALENDAR
METHOD:CANCEL
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:guid-1@host1.com
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE:Mailto:B@example.com
ATTENDEE:Mailto:C@example.com
ATTENDEE:Mailto:D@example.com
RECURRENCE-ID:19970801T210000Z
SEQUENCE:2
STATUS:CANCELLED
DTSTAMP:19970721T093000Z
END:VEVENT
END:VCALENDAR





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4.4.4     Cancel Recurring Event

In this example the "Organizer" wishes to cancel the entire recurring
event and any exceptions.

BEGIN:VCALENDAR
METHOD:CANCEL
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:guid-1@host1.com
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE:Mailto:B@example.com
ATTENDEE:Mailto:C@example.com
ATTENDEE:Mailto:D@example.com
DTSTAMP:19970721T103000Z
STATUS:CANCELLED
SEQUENCE:3
END:VEVENT
END:VCALENDAR


4.4.5     Change All Future Instances

This example changes the meeting location from a conference call to
Seattle starting September 1 and extends to all future instances.


BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:guid-1@host1.com
RECURRENCE-ID;THISANDFUTURE:19970901T210000Z
SEQUENCE:3
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE:Mailto:B@example.com
ATTENDEE;RSVP=TRUE:Mailto:C@example.com
ATTENDEE;RSVP=TRUE:Mailto:D@example.com
DESCRIPTION:IETF-C&S Discussion
CLASS:PUBLIC
SUMMARY:IETF Calendaring Working Group Meeting
DTSTART:19970901T210000Z
DTEND:19970901T220000Z
LOCATION:Building 32, Microsoft, Seattle, WA
DTSTAMP:19970526T083000Z
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR




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4.4.6     Add A New Instance To A Recurring Event

This example adds a one-time additional instance to the recurring event.
"Organizer" adds a second July meeting on the 15th.

BEGIN:VCALENDAR
METHOD:ADD
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:123456789@host1.com
SEQUENCE:4
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE:Mailto:B@example.com
ATTENDEE;RSVP=TRUE:Mailto:C@example.com
ATTENDEE;RSVP=TRUE:Mailto:D@example.com
DESCRIPTION:IETF-C&S Conference Call
CLASS:PUBLIC
SUMMARY:IETF Calendaring Working Group Meeting
DTSTART:19970715T210000Z
DTEND:19970715T220000Z
LOCATION:Conference Call
DTSTAMP:19970629T093000Z
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR

4.4.7     Add A New Series of Instances To A Recurring Event

The scenario for this example involves an ongoing meeting, originally
set up to occur every Tuesday.  The "Organizer" later decides that the
meetings need to be on Tuesdays and Thursdays, but does not want to
reschedule the entire meeting or lose any of the per-instance
information already collected.

The original event:

BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:123456789@host1.com
SEQUENCE:0
RRULE:WKST=SU;BYDAY=TU;FREQ=WEEKLY
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE:Mailto:B@example.com
SUMMARY:Review Accounts
DTSTART:19980303T210000Z
DTEND:19980303T220000Z
LOCATION:The White Room
DTSTAMP:19980301T093000Z


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STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR


Assume that many other updates happen to this event and that a lot of
instance-specific information exists in the recurring series. The
"SEQUENCE" property value is 7 for the next update. Now the "Organizer"
wants to add Thursdays to the event:

BEGIN:VCALENDAR
METHOD:ADD
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:123456789@host1.com
SEQUENCE:7
RRULE:WKST=SU;BYDAY=TH;FREQ=WEEKLY
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE:Mailto:B@example.com
SUMMARY:Review Accounts
DTSTART:19980303T210000Z
DTEND:19980303T220000Z
DTSTAMP:19980303T193000Z
LOCATION:The Usual conference room
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR

Alternatively, if the "Organizer" is not concerned with per-instance
updates, the entire event can be rescheduled using a "REQUEST". This is
done by using the "UID" of the event to reschedule and including the
modified "RRULE". Note, that since this is an entire rescheduling of the
event, any instance-specific information will be lost.


BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:123456789@host1.com
SEQUENCE:7
RRULE:WKST=SU;BYDAY=TU,TH;FREQ=WEEKLY
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE:Mailto:B@example.com
SUMMARY:Review Accounts
DTSTART:19980303T210000Z
DTEND:19980303T220000Z
DTSTAMP:19980303T193000Z
LOCATION:The White Room
STATUS:CONFIRMED


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END:VEVENT
END:VCALENDAR

The next series of examples illustrate how an "Organizer" would respond
to a "REFRESH" submitted by an "Attendee" after a series of instance-
specific modifications. To convey all instance-specific changes, the
"Organizer" must provide the latest event description and the relevant
instances. The first three examples show the history including the
initial "VEVENT" request and subsequent instance changes and finally the
"REFRESH".

Original Request:

BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:123456789@host1.com
SEQUENCE:0
RDATE:19980304T180000Z
RDATE:19980311T180000Z
RDATE:19980318T180000Z
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE:Mailto:B@example.com
SUMMARY:Review Accounts
DTSTART:19980304T180000Z
DTEND:19980304T200000Z
DTSTAMP:19980303T193000Z
LOCATION:Conference Room A
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR

Organizer changes 2nd instance Location and Time:

BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:123456789@host1.com
SEQUENCE:1
RECURRENCE-ID:19980311T180000Z
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE:Mailto:B@example.com
SUMMARY:Review Accounts
DTSTART:19980311T160000Z
DTEND:19980311T180000Z
DTSTAMP:19980306T193000Z
LOCATION:The Small conference room
STATUS:CONFIRMED


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END:VEVENT
END:VCALENDAR

Organizer adds a 4th instance of the meeting using the "ADD" method

BEGIN:VCALENDAR
METHOD:ADD
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:123456789@host1.com
SEQUENCE:2
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE:Mailto:B@example.com
SUMMARY:Review Accounts
DTSTART:19980315T180000Z
DTEND:19980315T200000Z
DTSTAMP:19980307T193000Z
LOCATION:Conference Room A
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR

If "B" requests a "REFRESH", "A" responds with the following to capture
all instance-specific data. In this case both the initial request and an
additional "VEVENT" that specifies the instance-specific data are
included. Because these are both of the same type (they are both
"VEVENTS"), they can be conveyed in the same iCalendar object.

BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:123456789@host1.com
SEQUENCE:2
RDATE:19980304T180000Z
RDATE:19980311T160000Z
RDATE:19980315T180000Z
Error! Bookmark not defined.
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE:Mailto:B@example.com
SUMMARY:Review Accounts
DTSTART:19980304T180000Z
DTEND:19980304T200000Z
DTSTAMP:19980303T193000Z
LOCATION:Conference Room A
STATUS:CONFIRMED
END:VEVENT

BEGIN:VEVENT
Error! Bookmark not defined.


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SEQUENCE:2
RECURRENCE-ID:19980311T160000Z
Error! Bookmark not defined.
ATTENDEE;ROLE=CHAIR;Error! Bookmark not defined.
ATTENDEE;Error! Bookmark not defined.
SUMMARY:Review Accounts
DTSTART:19980311T160000Z
DTEND:19980304T180000Z
DTSTAMP:19980306T193000Z
LOCATION:The Small conference room
STATUS:CONFIRMED
END:VEVENT

END:VCALENDAR


4.4.8     Counter An Instance Of A Recurring Event

In this example one of the "Attendees" counters the "DTSTART" property
of the proposed second July meeting.


BEGIN:VCALENDAR
METHOD:COUNTER
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:guid-1@host1.com
RECURRENCE-ID:19970715T210000Z
SEQUENCE:4
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;RSVP=TRUE:Mailto:A@example.com
ATTENDEE;RSVP=TRUE:Mailto:B@example.com
ATTENDEE;RSVP=TRUE:Mailto:C@example.com
ATTENDEE;RSVP=TRUE:Mailto:D@example.com
DESCRIPTION:IETF-C&S Conference Call
CLASS:PUBLIC
SUMMARY:IETF Calendaring Working Group Meeting
DTSTART:19970715T220000Z
DTEND:19970715T230000Z
LOCATION:Conference Call
COMMENT:May we bump this by an hour? I have a conflict
DTSTAMP:19970629T094000Z
END:VEVENT
END:VCALENDAR


4.4.9     Error Reply To A Request

The following example illustrates a scenario where a meeting is proposed
containing an unsupported property and a bad property.

Original Request



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BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:guid-1@host1.com
SEQUENCE:0
RRULE:FREQ=MONTHLY;BYMONTHDAY=1
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR:Mailto:A@example.com
ATTENDEE;RSVP=TRUE:Mailto:B@example.com
ATTENDEE;RSVP=TRUE:Mailto:C@example.com
ATTENDEE;RSVP=TRUE:Mailto:D@example.com
DESCRIPTION:IETF-C&S Conference Call
CLASS:PUBLIC
SUMMARY:IETF Calendaring Working Group Meeting
DTSTART:19970601T210000Z
DTEND:19970601T220000Z
DTSTAMP:19970602T094000Z
LOCATION:Conference Call
STATUS:CONFIRMED
FOO:BAR
END:VEVENT
END:VCALENDAR

Response from "B" to indicate that RRULE is not supported and an
unrecognized property was encountered


BEGIN:VCALENDAR
PRODID:-//RDU Software//NONSGML HandCal//EN
METHOD:REPLY
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE:Mailto:B@example.com
REQUEST-STATUS:2.8;Repeating event ignored. Scheduled as a single
  event;RRULE
REQUEST-STATUS:3.0;Invalid Property Name;FOO
UID:guid-1@host1.com
SEQUENCE:0
DTSTAMP:19970603T094000Z
END:VEVENT
END:VCALENDAR


4.5 Group To-do Examples

Individual "A" creates a group task in which individuals "A", "B", "C"
and "D" will participate. Individual "B" confirms acceptance of the
task. Individual "C" declines the task. Individual "D" tentatively
accepts the task. The following table illustrates the sequence of
messages that would be exchanged between these individuals. Individual
"A" then issues a "REQUEST" method to obtain the status of the to-do


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from each participant. The response indicates the individual
"Attendee's" completion status. The table below illustrates the message
flow.


+--------------------------------------------------------------------+
| Action             |  "Organizer"        | Attendee                |
+--------------------------------------------------------------------+
| Initiate a to-do   | "A" sends a REQUEST |                         |
| request            | message to "B", "C",|                         |
|                    | and "D"             |                         |
+--------------------------------------------------------------------+
| Accept the to-do   |                     | "B" sends a "REPLY"     |
| request            |                     | message to "A" with its |
|                    |                     | "partstat" paramater     |
|                    |                     | set to "accepted".      |
+--------------------------------------------------------------------+
| Decline the to-do  |                     | "C" sends a REPLY       |
| request            |                     | message to "A" with its |
|                    |                     | "partstat" parameter     |
|                    |                     | set to "declined".      |
+--------------------------------------------------------------------+
| Tentatively accept |                     | "D" sends a REPLY       |
| the to-do request  |                     | message to "A" with its |
|                    |                     | "partstat" parameter     |
|                    |                     | set to "tentative".     |
+--------------------------------------------------------------------+
| Check attendee     | "A" sends a REQUEST |                         |
| completion status  | message to "B" and  |                         |
|                    | "D" with current    |                         |
|                    | information.        |                         |
+--------------------------------------------------------------------+
| Attendee indicates |                     | "B" sends a "REPLY"     |
| percent complete   |                     | message indicating      |
|                    |                     | percent complete        |
+--------------------------------------------------------------------+
| Attendee indicates |                     | "D" sends a "REPLY"     |
| completion         |                     | message indicating      |
|                    |                     | completion              |
+--------------------------------------------------------------------+


4.5.1     A VTODO Request

A sample "REQUEST" for a "VTODO" calendar component that "A" sends to
"B", "C", and "D".


BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VTODO
ORGANIZER:Mailto:A@example.com


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ATTENDEE;ROLE=CHAIR:Mailto:A@example.com
ATTENDEE;RSVP=TRUE:Mailto:B@example.com
ATTENDEE;RSVP=TRUE:Mailto:C@example.com
ATTENDEE;RSVP=TRUE:Mailto:D@example.com
DTSTART:19970701T170000Z
DUE:19970722T170000Z
PRIORITY:1
SUMMARY:Create the requirements document
UID:calsrv.example.com-873970198738777-00@example.com
SEQUENCE:0
DTSTAMP:19970717T200000Z
STATUS:Needs Action
END:VTODO
END:VCALENDAR


4.5.2     A VTODO Reply

"B" accepts the to-do.

BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REPLY
VERSION:2.0
BEGIN:VTODO
ORGANIZER:Mailto:A@example.com
ATTENDEE;PARTSTAT=ACCEPTED:Mailto:B@example.com
UID:calsrv.example.com-873970198738777-00@example.com
COMMENT:I'll send you my input by e-mail
SEQUENCE:0
DTSTAMP:19970717T203000Z
REQUEST-STATUS:2.0;Success
END:VTODO
END:VCALENDAR

"B" could have declined the TODO or indicated tentative acceptance by
setting the "partstat" property parameter sequence to "declined" or
"tentative", respectively.


4.5.3     A VTODO Request for Updated Status

"A" requests status from all "Attendees".


BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VTODO
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR:Mailto:A@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:D@example.com


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UID:calsrv.example.com-873970198738777-00@example.com
SUMMARY:Create the requirements document
PRIORITY:1
SEQUENCE:0
STATUS:IN-PROCESS
DTSTART:19970701T170000Z
DTSTAMP:19970717T230000Z
END:VTODO
END:VCALENDAR


4.5.4     A Reply: Percent-Complete

A reply indicating the task being worked on and that "B" is 75% complete
with "B's" part of the assignment.

BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REPLY
VERSION:2.0
BEGIN:VTODO
ORGANIZER:MAILTO:A@example.com
ATTENDEE;PARTSTAT=IN-PROCESS:Mailto:B@example.com
PERCENT-COMPLETE:75
UID:calsrv.example.com-873970198738777-00@example.com
DTSTAMP:19970717T233000Z
SEQUENCE:0
END:VTODO
END:VCALENDAR


4.5.5     A Reply: Completed

A reply indicating that "D" completed "D's" part of the assignment.


BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REPLY
VERSION:2.0
BEGIN:VTODO
ORGANIZER:MAILTO:A@example.com
ATTENDEE;PARTSTAT=COMPLETED:Mailto:D@example.com
UID:calsrv.example.com-873970198738777-00@example.com
DTSTAMP:19970717T233000Z
SEQUENCE:0
END:VTODO
END:VCALENDAR


4.5.6     An Updated VTODO Request

Organizer "A" resends the "VTODO" calendar component. "A" sets the
overall completion for the to-do at 40%.


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BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VTODO
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;PARTSTAT=ACCEPTED;TYPE=INDIVIDUAL:Mailto:B@example.com
ATTENDEE;PARTSTAT=IN-PROCESS;TYPE=INDIVIDUAL:Mailto:D@example.com
DTSTART:19970701T170000Z
DUE:19970722T170000Z
PRIORITY:1
SUMMARY:Create the requirements document
UID:calsrv.example.com-873970198738777-00@example.com
SEQUENCE:1
DTSTAMP:19970718T100000Z
STATUS:IN-PROGRESS
PERCENT-COMPLETE:40
END:VTODO
END:VCALENDAR


4.5.7     Recurring VTODOs

The following examples relate to recurring "VTODO" calendar components.


4.5.7.1   Request for a Recurring VTODO

In this example "A" sends a recurring "VTODO" calendar component to "B"
and "D".


BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VTODO
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR:Mailto:A@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:D@example.com
RRULE:FREQ=MONTHLY;COUNT=10;BYDAY=1FR
DTSTART:19980101T100000-0700
DUE:19980103T100000-0700
SUMMARY:Send Status Reports to Area Managers
UID:calsrv.example.com-873970198738777-00@example.com
SEQUENCE:0
DTSTAMP:19970717T200000Z
STATUS:NEEDS ACTION
PRIORITY:1
END:VTODO
END:VCALENDAR


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4.5.7.2   Calculating due dates in recurring VTODOs

The due date in a recurring "VTODO" calendar component is either a fixed
interval specified in the "REQUEST" method or specified using the
"RECURRENCE-ID" property. The former is calculated by applying the
difference between "DTSTART" and "DUE" properties and applying it to
each of the start of each recurring instance. Hence, if the initial
"VTODO" calendar component specifies a "DTSTART" property value of
"19970701T190000Z" and a "DUE" property value of "19970801T190000Z" the
interval of one day which is applied to each recurring instance of the
"VTODO" calendar component to determine the "DUE" date of the instance.


4.5.7.3   Replying to an instance of a recurring VTODO

In this example "B" updates "A" on a single instance of the "VTODO"
calendar component.


BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REPLY
VERSION:2.0
BEGIN:VTODO
ATTENDEE;PARTSTAT=IN-PROCESS:Mailto:B@example.com
PERCENT-COMPLETE:75
UID:calsrv.example.com-873970198738777-00@example.com
DTSTAMP:19970717T233000Z
RECURRENCE-ID:19980101T170000Z
SEQUENCE:1
END:VTODO
END:VCALENDAR


4.6 Journal Examples

The iCalendar object below describes a single journal entry for October
2, 1997. The "RELATED-TO" property references the phone conference event
for which minutes were taken.


BEGIN:VCALENDAR
METHOD:PUBLISH
PRODID:-//ACME/DesktopCalendar//EN
VERSION:2.0
BEGIN:VJOURNAL
DTSTART:19971002T200000Z
ORGANIZER:MAILTO:A@Example.com
SUMMARY:Phone conference minutes
DESCRIPTION:The editors meeting was held on October 1, 1997.
  Details are in the attached document.
UID:0981234-1234234-2410@example.com


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RELATED-TO:0981234-1234234-2402-35@example.com
ATTACH:ftp://ftp.example.com/pub/ed/minutes100197.txt
END:VJOURNAL
END:VCALENDAR


4.7 Other Examples


4.7.1     Event Refresh

Refresh the event with "UID" property value of "guid-1-12345@host1.com":


BEGIN:VCALENDAR
PRODID:-//RDU Software//NONSGML HandCal//EN
METHOD:REFRESH
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE:Mailto:B@example.com
ATTENDEE:Mailto:C@example.com
ATTENDEE:Mailto:D@example.com
UID: guid-1-12345@host1.com
DTSTAMP:19970603T094000
END:VEVENT
END:VCALENDAR

4.7.2     Bad RECURRENCE-ID

Component instances are identified by the combination of "UID",
"RECURRENCE-ID", and "SEQUENCE". When an "Organizer" sends a request to
an "Attendee", there are three cases in which an instance cannot be
found.  They are:


1.   The component with the referenced "UID" and "RECURRENCE-ID" has been
  found but the "SEQUENCE" number in the calendar store does not match
  that of the ITIP message.

2.   The component with the referenced "UID" has been found, the
  "SEQUENCE" numbers match, but the "RECURRENCE-ID" cannot be found.

3.   The "UID" and "SEQUENCE" numbers are found but the CUA does not
  support recurrences.


In case (1), two things can happen. If the "SEQUENCE" number of the
"Attendee's" instance is larger than that in the "Organizer's" message
then the "Attendee" is receiving an out-of-sequence message and MUST
ignore it.  If the "SEQUENCE" number of the "Attendee's" instance is
smaller, then the "Organizer" is sending out a newer version of the
component and the "Attendee's" version needs to be updated. Since one or


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more updates have been missed, the "Attendee" SHOULD send a "REFRESH"
message to the "Organizer" to get an updated version of the event.

In case (2), something has gone wrong.  Both the "Organizer" and the
"Attendee" should have the same instances, but the "Attendee" does not
have the referenced instance.  In this case the "Attendee" SHOULD send a
"REFRESH" to the "Organizer" to get an updated version of the event.

In case (3), the limitations of the "Attendee's" CUA makes it impossible
to match an instance other than the single instance scheduled. In this
case, the "Attendee" need not send a "REFRESH" to the "Organizer".

The example below shows a sequence in which an "Attendee" sends a
"REFRESH" to the "Organizer".

+--------------------------------------------------------------------+
| Action             |  "Organizer"        | Attendee                |
+--------------------------------------------------------------------+
| Update an instance | "A" sends  "REQUEST"|                         |
| request            | message to "B"      |                         |
+--------------------------------------------------------------------+
| Attendee requests  |                     | "B" sends a "REFRESH"   |
| refresh because    |                     | message to "A"          |
| "RECURRENCE-ID" was|                     |                         |
| not found          |                     |                         |
+--------------------------------------------------------------------+
| Refresh the entire | "A" sends the       |                         |
| Event              | latest copy of the  |                         |
|                    | Event to "B"        |                         |
+--------------------------------------------------------------------+
| Attendee handles   |                     | "B" updates to the      |
| the request and    |                     | latest copy of the      |
| updates the        |                     | meeting.                |
| instance           |                     |                         |
+--------------------------------------------------------------------+

Request from "A":


BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:acme-12345@host1.com
SEQUENCE:3
RRULE:FREQ=WEEKLY
RDATE;VALUE=PERIOD:19970819T210000Z/199700819T220000Z
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE:Mailto:B@example.com
DESCRIPTION:IETF-C&S Conference Call
SUMMARY:IETF Calendaring Working Group Meeting
DTSTART:19970801T210000Z


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DTEND:19970801T220000Z
RECURRENCE-ID:19970809T210000Z
DTSTAMP:19970726T083000
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR

"B" has the event with "UID" property "acme-12345@host1.com" but "B's"
"SEQUENCE" property value is "1" and the event does not have an instance
at the specified recurrence time. This means that "B" has missed at
least one update and needs a new copy of the event.  "B" requests the
latest copy of the event with the following refresh message:


BEGIN:VCALENDAR
PRODID:-//RDU Software//NONSGML HandCal//EN
METHOD:REFRESH
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE:Mailto:B@example.com
UID:acme-12345@host1.com
DTSTAMP:19970603T094000
END:VEVENT
END:VCALENDAR


5  Application Protocol Fallbacks


5.1 Partial Implementation

Applications that support this memo are not required to support the
entire protocol. The following describes how methods and properties
SHOULD "fallback" in applications that do not support the complete
protocol. If a method or property is not addressed in this section, it
may be ignored.


5.1.1     Event-Related Fallbacks


Method           Fallback
--------------   -----------------------------------------------------
PUBLISH          Required
REQUEST          PUBLISH
REPLY            Required
ADD              Required
CANCEL           Required
REFRESH          Required
COUNTER          Reply with Not Supported
DECLINECOUNTER   Required if EVENT-COUNTER is implemented; otherwise
                 reply with Not Supported



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iCalendar
Property         Fallback
--------------   -----------------------------------------------------
CALSCALE         Ignore; assume GREGORIAN
PRODID           Ignore
METHOD           Required as described in the Method list above
VERSION          Ignore

Event-Related
Components       Fallback
--------------   -----------------------------------------------------
VALARM           Reply with Not Supported
VTIMEZONE        Required if any DateTime value refers to a time zone.

Component
Property         Fallback
--------------   -----------------------------------------------------
ATTACH           Ignore
ATTENDEE         Required if EVENT-REQUEST is not implemented;
                 otherwise reply with Not Supported
CATEGORIES       Ignore
CLASS            Ignore
COMMENT          Ignore
COMPLETED        Ignore
CONTACT          Ignore
CREATED          Ignore
DESCRIPTION      Required
DURATION         Reply with Not Supported
DTSTAMP          Required
DTSTART          Required
DTEND            Required
EXDATE           Ignore
EXRULE           Ignore Reply with Not Supported. If implemented,
                 VTIMEZONE MUST also be implemented.
GEO              Ignore
LAST-MODIFIED    Ignore
LOCATION         Required
ORGANIZER        Ignore
PRIORITY         Ignore
RELATED-TO       Ignore
RDATE            Ignore
RRULE            Ignore. The first instance occurs on the DTStart
                 property. If implemented, VTIMEZONE MUST also be
                 implemented.
RECURRENCE-ID    Required if RRULE is implemented; otherwise Ignore
REQUEST-STATUS   Required
RESOURCES        Ignore
SEQUENCE         Required
STATUS           Ignore
SUMMARY          Ignore
TRANSP           Required if FREEBUSY is implemented; otherwise Ignore
URL              Ignore
UID              Required
X-               Ignore


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5.1.2     Free/Busy-Related Fallbacks


Method           Fallback
--------------   -----------------------------------------------------
PUBLISH          Implementations MAY ignore the METHOD type. The
                 REQUEST-STATUS "3.14;Unsupported capability" MUST be
                 returned.
REQUEST          Implementations MAY ignore the METHOD type. The
                 REQUEST-STATUS "3.14;Unsupported capability" MUST be
                 returned.
REPLY            Implementations MAY ignore the METHOD type. The
                 REQUEST-STATUS "3.14;Unsupported capability" MUST be
                 returned.


iCalendar
Property         Fallback
--------------   -----------------------------------------------------
CALSCALE         Ignore; assume GREGORIAN.
PRODID           Ignore
METHOD           Required as described in the Method list above.
VERSION          Ignore


Component
Property         Fallback
--------------   -----------------------------------------------------
COMMENT          Ignore
CONTACT          Ignore
DTEND            Required
DTSTAMP          Required
DTSTART          Required
DURATION         Required
FREEBUSY         Required
ORGANIZER        Ignore
REQUEST-STATUS   Ignore
UID              Required
URL              Ignore
X-               Ignore



5.1.3     To-Do-Related Fallbacks

Method           Fallback
--------------   -----------------------------------------------------
PUBLISH          Required
REQUEST          PUBLISH
REPLY            Required
ADD              Required
CANCEL           Required


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REFRESH          Required
COUNTER          Reply with Not Supported
DECLINECOUNTER   Required if VTODO - COUNTER is implemented; otherwise
                 reply with Not Supported

iCalendar
Property         Fallback
--------------   -----------------------------------------------------
CALSCALE         Ignore; assume GREGORIAN.
PRODID           Ignore
METHOD           Required as described in the Method list above.
VERSION          Ignore


To-Do-Related
Components       Fallback
--------------   -----------------------------------------------------
VALARM           Reply with Not Supported
VTIMEZONE        Required if any DateTime value refers to a time zone.


Component
Property         Fallback
--------------   -----------------------------------------------------
ATTACH           Ignore
ATTENDEE         Required if REQUEST is not implemented; otherwise
                 ignore
CATEGORIES       Ignore
CLASS            Ignore
COMMENT          Ignore
COMPLETED        Required
CONTACT          Ignore
CREATED          Ignore
DESCRIPTION      Required
DUE              Required
DURATION         Ignore Reply with Not Supported
DTSTAMP          Required
DTSTART          Required
EXDATE           Ignore Reply with Not Supported
EXRULE           Ignore Reply with Not Supported. If implemented,
                 VTIMEZONE MUST also be implemented.
LAST-MODIFIED    Ignore
LOCATION         Ignore
ORGANIZER        Ignore
PERCENT-COMPLETE Ignore
PRIORITY         Required
RECURRENCE-ID    Ignore
RELATED-TO       Ignore
REQUEST-STATUS   Ignore
RDATE            Ignore
RRULE            Ignore.  The first instance occurs on the DTSTART
                 property. If implemented, VTIMEZONE MUST also be
                 implemented.
RESOURCES        Ignore


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SEQUENCE         Required
STATUS           Required
SUMMARY          Ignore
URL              Ignore
UID              Required
X-               Ignore


5.1.4     Journal-Related Fallbacks


Method           Fallback
--------------   -----------------------------------------------------
PUBLISH          Implementations MAY ignore the METHOD type. The
                 REQUEST-STATUS "3.14;Unsupported capability" MUST be
                 returned.
ADD              Implementations MAY ignore the METHOD type. The
                 REQUEST-STATUS "3.14;Unsupported capability" MUST be
                 returned.
CANCEL           Implementations MAY ignore the METHOD type. The
                 REQUEST-STATUS "3.14;Unsupported capability" MUST be
                 returned.


iCalendar
Property         Fallback
--------------   -----------------------------------------------------
CALSCALE         Ignore; assume GREGORIAN.
PRODID           Ignore
METHOD           Required as described in the Method list above.
VERSION          Ignore


Journal-Related
Components       Fallback
--------------   -----------------------------------------------------
VTIMEZONE        Required if any DateTime value refers to a time zone.


Component
Property         Fallback
--------------   -----------------------------------------------------
ATTACH           Ignore
ATTENDEE         Required if JOURNAL-REQUEST is implemented; otherwise
                 ignore
CATEGORIES       Ignore
CLASS            Ignore
COMMENT          Ignore
CONTACT          Ignore
CREATED          Ignore
DESCRIPTION      Required
DTSTAMP          Required
DTSTART          Required
EXDATE           Ignore


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EXRULE           Ignore Reply with Not Supported. If implemented,
                 VTIMEZONE MUST also be implemented.
LAST-MODIFIED    Ignore
ORGANIZER        Ignore
RECURRENCE-ID    Ignore
RELATED-TO       Ignore
RDATE            Ignore.
RRULE            Ignore. The first instance occurs on the DTSTART
                 property. If implemented, VTIMEZONE MUST also be
                 implemented.
SEQUENCE         Required
STATUS           Ignore
SUMMARY          Required
URL              Ignore
UID              Required
X-               Ignore

5.2 Latency Issues

With a store-and-forward transport, it is possible for events to arrive
out of sequence. That is, a "CANCEL" method may be received prior to
receiving the associated "REQUEST" for the calendar component. This
section discusses a few of these scenarios.


5.2.1     Cancellation of an Unknown Calendar Component.

When a "CANCEL" method is received before the original "REQUEST" method
the calendar will be unable to correlate the "UID" property of the
cancellation with an existing calendar component. It is suggested that
messages that can not be correlated that also contain non-zero sequence
numbers be held and not discarded. Implementations MAY age them out if
no other messages arrive with the same "UID" property value and a lower
sequence number.


5.2.2     Unexpected Reply from an Unknown Delegate

When an "Attendee" delegates an item to another CU they MUST send a
"REPLY" method to the "Organizer" using the "ATTENDEE" properties to
indicate that the request was delegated and to whom. Hence, it is
possible for an "Organizer" to receive an "REPLY" from a CU not listed
as one of the original "Attendees". The resolution is left to the
implementation but it is expected that the calendaring software will
either accept the reply or hold it until the related "REPLY" method is
received from the "Delegator". If the version of the "REPLY" method is
out of date the "Organizer" SHOULD treat the message as a "REFRESH"
message and update the delegate with the correct version.


5.3 Sequence Number

Under some conditions, a CUA may receive requests and replies with the
same "SEQUENCE" property value. The "DTSTAMP" property is utilized as a


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tie-breaker when two items with the same "SEQUENCE" property value are
evaluated.


6  Security Considerations

ITIP is an abstract transport protocol which will be bound to a real-
time transport, a store-and-forward transport, and perhaps other
transports. The transport protocol will be responsible for providing
facilities for authentication and encryption using standard Internet
mechanisms that are mutually understood between the sender and receiver.


6.1 Security Threats


6.1.1     Spoofing the "Organizer"

In iTIP, the "Organizer" (or someone working on the "Organizer's"
behalf) is the only person authorized to make changes to an existing
"VEVENT", "VTODO", "VJOURNAL" calendar component and republish it or
redistribute updates to the "Attendees". An iCalendar object that
maliciously changes or cancels an existing "VEVENT", "VTODO" or
"VJOURNAL" calendar component may be constructed by someone other than
the "Organizer" and republished or sent to the "Attendees".


6.1.2     Spoofing the "Attendee"

In iTIP, an "Attendee" of a "VEVENT" or "VTODO" calendar component (or
someone working on the "Attendee's" behalf) is the only person
authorized to update any parameter associated with their "ATTENDEE"
property and send it to the "Organizer". An iCalendar object that
maliciously changes the "ATTENDEE" parameters may be constructed by
someone other than the real "Attendee" and sent to the "Organizer".


6.1.3     Unauthorized Replacement of the Organizer

There will be circumstances when "Attendees" of an event or to-do
decide, using out-of-band mechanisms, that the "Organizer" must be
replaced. When the new "Organizer" sends out the updated "VEVENT" or
"VTODO" the "Attendee's" CUA will detect that the "Organizer" has been
changed, but it has no way of knowing whether or not the change was
mutually agreed upon.


6.1.4     Eavesdropping

The iCalendar object is constructed with human-readable clear text. Any
information contained in an iCalendar object may be read and/or changed
by unauthorized persons while the object is in transit.




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6.1.5     Flooding a Calendar

Implementations MAY provide a means to automatically incorporate
"REQUEST" methods into a calendar. This presents the opportunity for a
calendar to be flooded with requests, which effectively block all the
calendar's free time.


6.1.6     Procedural Alarms

The "REQUEST" methods for "VEVENT" and "VTODO" calendar components MAY
contain "VALARM" calendar components. The "VALARM" calendar component
may be of type "PROCEDURE" and MAY have an attachment containing an
executable program. Implementations that incorporate these types of
alarms are subject to any virus or malicious attack that may occur as a
result of executing the attachment.


6.1.7     Unauthorized REFRESH Requests

It is possible for an "Organizer" to receive a "REFRESH" request from
someone who is not an "Attendee" of an event or to-do. Only "Attendee's"
of an event or to-do are authorized to receive replies to "REFRESH"
requests. Replying to such requests to anyone who is not an "Attendee"
may be a security problem.


6.2 Recommendations

For an application where the information is sensitive or critical and
the network is subject is subject to a high probability of attack, iTIP
transactions SHOULD be encrypted. This may be accomplished using public
key technology, specifically Security Multiparts for MIME [RFC-1847] in
the iTIP transport binding. This helps mitigate the threats of spoofing,
eavesdropping and malicious changes in transit.


6.2.1     Use of [RFC-1847] to secure iTIP transactions

iTIP transport bindings MUST provide a mechanism based on Security
Multiparts for MIME [RFC-1847] to enable authentication of the sender's
identity, and privacy and integrity of the data being transmitted. This
allows the receiver of a signed iCalendar object to verify the identity
of the sender. This sender may then be correlated to an "ATTENDEE"
property in the iCalendar object. If the correlation is made and the
sender is authorized to make the requested change or update then the
operation may proceed. It also allows the message to be encrypted to
prevent unauthorized reading of the message contents in transit. iTIP
transport binding documents describe this process in detail.

Implementations MAY provide controls for users to disable this
capability.




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6.2.2     Implementation Controls

The threat of unauthorized replacement of the "Organizer" SHOULD be
mitigated by a calendar system that uses this protocol by providing
controls or alerts that make "Calendar Users" aware of such "Organizer"
changes and allowing them to decide whether or not the request should be
honored.

The threat of flooding a calendar SHOULD be mitigated by a calendar
system that uses this protocol by providing controls that may be used to
limit the acceptable sources for iTIP transactions, and perhaps the size
of messages and volume of traffic, by source.

The threat of malicious procedural alarms SHOULD be mitigated by a
calendar system that uses this protocol by providing controls that may
be used to disallow procedural alarms in iTIP transactions and/or remove
all alarms from the object before delivery to the recipient.

The threat of unauthorized "REFRESH" requests SHOULD be mitigated by a
calendar system that uses this protocol by providing controls or alerts
that allow "Calendar User" to decide whether or not the request should
be honored.  An implementation MAY decide to maintain, for audit or
historical purposes,  "Calendar Users" who were part of an attendee list
and who were subsequently uninvited.  Similar controls or alerts should
be provided when a "REFRESH" request is received from these "Calendar
Users" as well.


7  Acknowledgments

A hearty thanks to the following individuals who have participated in
the drafting, review and discussion of this memo:

Anik Ganguly, Dan Hickman, Paul Hill, Daryl Huff, Bruce Kahn, Antoine
Leca, Bob Mahoney, John Noerenberg, Leo Parker, John Rose, Doug Royer,
Vinod Seraphin, Richard Shusterman, Derik Stenerson, John Sun, Alexander
Taler, Kevin Tsurutome.


8  Bibliography

[iCAL] "Internet Calendaring and Scheduling Core Object Specification -
iCalendar", Internet-Draft, October 1997, ftp://ftp.ietf.org/internet-
drafts/draft-ietf-calsch-ical-07.txt.

[ICMS] "Internet Calendaring Model Specification", Internet-Draft,
October 1997, ftp://ftp.ietf.org/internet-drafts/draft-ietf-calsch-mod-
03.txt.

[ID-UTF8] "UTF-8, a transformation format of Unicode and ISO 10646",
Internet-Draft, July 1996, ftp://ftp.ietf.org/internet-drafts/draft-
yergeau-utf8-01.txt.




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[iMIP] "iCalendar Message-Based Interoperability Protocol - iMIP",
Internet-Draft, October 1997, ftp://ftp.ietf.org/internet-drafts/draft-
ietf-calsch-imip-05.txt.

[ISO8601] "Data elements and interchange formats - information
interchange - Representation of dates and times", ISO 8601, 1996-06-15,
+1 (212) 642-4900 for ANSI Sales.

[VCAL] "vCalendar - The Electronic Calendaring and Scheduling Format -
Version 1.0", Versit Consortium, September 18, 1996,
http://www.imc.org/pdi/vcal-10.doc.

[VCARD] "vCard - The Electronic Business Card Exchange Format - Version
2.1", Versit Consortium, September 18, 1996,
http://www.imc.org/pdi/vcard-21.doc.

[RFC-821] Postel, "Simple Mail Transfer Protocol", RFC 821, organization
name, November 1996, http://ds.internic.net/rfc/rfc821.txt.

[RFC-1983] "Internet Users' Glossary", RFC 1983, August 1996,
http://ds.internic.net/rfc/rfc1983.txt.

[RFC-2119] "Key words for use in RFCs to Indicate Requirement Levels",
RFC 2119, March 1997, http://ds.internic.net/rfc/rfc2119.txt.

[RFC-2045] N. Freed and N. Borenstein, "Multipurpose Internet Mail
Extensions - Part One - Format of Internet Message Bodies", RFC 2045,
Innosoft, First Virtual, November 1996,
http://ds.internic.net/rfc/rfc2045.txt.

[RFC-2046] N. Freed and N. Borenstein, "Multipurpose Internet Mail
Extensions - Part Two - Media Types", RFC 2046, Innosoft, First Virtual,
November 1996, http://ds.internic.net/rfc/rfc2046.txt.

[UNICODE] The Unicode Consortium, "The Unicode Standard -Version 2.0",
Addison-Wesley Developers Press, July 1996. UTF-8 is described in
section A-2.

[US-ASCII] Coded Character Set--7-bit American Standard Code for
Information Interchange, ANSI X3.4-1986.


9  Authors Addresses

The following address information is provided in a MIME-VCARD,
Electronic Business Card, format.

The authors of this draft are:


BEGIN:VCARD
VERSION:3.0
N:Dawson;Frank
FN:Frank Dawson


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ORG:Lotus Development Corporation
ADR;WORK;POSTAL;PARCEL:;;6544 Battleford Drive;Raleigh;NC;27613-
  3502;USA
TEL;WORK;MSG:+1-919-676-9515
TEL;WORK;FAX:+1-919-676-9564
EMAIL;INTERNET:Frank_Dawson@Lotus.com
URL:http://home.earthlink.net/~fdawson
END:VCARD

BEGIN:VCARD
VERSION:3.0
N:Hopson;Ross
FN:Ross Hopson
ORG:On Technology, Inc.
ADR;WORK;POSTAL;PARCEL:Suite 1600;;434 Fayetteville St.
  Mall, Two Hannover Square;Raleigh;NC;27601
TEL;WORK;MSG:+1-919-890-4036
TEL;WORK;FAX:+1-919-890-4100
EMAIL;INTERNET:rhopson@on.com
END:VCARD

BEGIN:VCARD
VERSION:3.0
N:Mansour;Steve
FN:Steve Mansour
ORG:Netscape Communications Corporation
ADR;WORK;POSTAL;PARCEL:;;501 East Middlefield Road;Mountain
  View;CA;94043;USA
TEL;WORK;MSG:+1-650-937-2378
TEL;WORK;FAX:+1-650-937-2103
EMAIL;INTERNET:sman@netscape.com
END:VCARD

BEGIN:VCARD
VERSION:3.0
N:Silverberg;Steve
FN:Steve Silverberg
ORG:Microsoft Corporation
ADR;WORK;POSTAL;PARCEL:;;One Microsoft Way;
Redmond;WA;98052-6399;USA
TEL;WORK;MSG:+1-425-936-9277
TEL;WORK;FAX:+1-425-936-8019
EMAIL;INTERNET:stevesil@Microsoft.com
END:VCARD

The iCalendar object is a result of the work of the Internet Engineering
Task Force Calendaring and scheduling Working Group. The chairman of
that working group is:


BEGIN:VCARD
VERSION:3.0
N:Ganguly;Anik
FN:Anik Ganguly


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ORG: Open Text Inc.
ADR;WORK;POSTAL;PARCEL: 38777 West Six Mile Road;Suite 101;
 Livonia;MI; 48152;USA
TEL;WORK;MSG:+1-734-542-5955
EMAIL;INTERNET:ganguly@acm.org
END:VCARD


The co-chairman of that working group is:

BEGIN:VCARD
VERSION:3.0
N:Moskowitz;Robert
FN:Robert Moskowitz
NICKNAME:Bob
EMAIL;INTERNET:rgm-ietf@htt-consult.com
END:VCARD


10 Full Copyright Statement

"Copyright (C) The Internet Society (1998). All Rights Reserved.

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it or
assist in its implmentation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are included
on all such copies and derivative works. However, this document itself
may not be modified in any way, such as by removing the copyright notice
or references to the Internet Society or other Internet organizations,
except as needed for the purpose of developing Internet standards in
which case the procedures for copyrights defined in the Internet
Standards process must be followed, or as required to translate it into
languages other than English.

The limited permissions granted above are perpetual and will may be
revoked by the Internet Society or its successors or assigns.

THIS DOCUMENT AND THE INFORMATION CONTAINED HEREIN IS PROVIDED ON AN "AS
IS" BASIS AND THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT
INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR
FITNESS FOR A PARTICULAR PURPOSE.











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