VALARM Extensions for iCalendar
draft-ietf-calext-valarm-extensions-07

Document Type Active Internet-Draft (calext WG)
Authors Cyrus Daboo  , Kenneth Murchison 
Last updated 2021-03-24 (latest revision 2021-03-03)
Replaces draft-daboo-valarm-extensions
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Network Working Group                                           C. Daboo
Internet-Draft                                                     Apple
Updates: 5545 (if approved)                            K. Murchison, Ed.
Intended status: Standards Track                                Fastmail
Expires: September 4, 2021                                 March 3, 2021

                    VALARM Extensions for iCalendar
                 draft-ietf-calext-valarm-extensions-07

Abstract

   This document defines a set of extensions to the iCalendar VALARM
   component to enhance use of alarms and improve interoperability
   between clients and servers.

   This document updates RFC5545.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 4, 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
   3.  Extensible syntax for VALARM  . . . . . . . . . . . . . . . .   3
   4.  Alarm Unique Identifier . . . . . . . . . . . . . . . . . . .   5
   5.  Alarm Related To  . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Alarm Acknowledgement . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Acknowledged Property . . . . . . . . . . . . . . . . . .   7
   7.  Snoozing Alarms . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Relationship Type Property Parameter  . . . . . . . . . .   9
     7.2.  Example . . . . . . . . . . . . . . . . . . . . . . . . .   9
   8.  Alarm Proximity Trigger . . . . . . . . . . . . . . . . . . .  13
     8.1.  Proximity Property  . . . . . . . . . . . . . . . . . . .  14
     8.2.  Example . . . . . . . . . . . . . . . . . . . . . . . . .  15
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   10. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  16
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     11.1.  Property Registrations . . . . . . . . . . . . . . . . .  17
     11.2.  Relationship Types Registry  . . . . . . . . . . . . . .  17
     11.3.  Proximity Value Registry . . . . . . . . . . . . . . . .  17
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  18
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     13.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Appendix A.  Change History (To be removed by RFC Editor before
                publication) . . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   The iCalendar [RFC5545] specification defines a set of components
   used to describe calendar data.  One of those is the "VALARM"
   component which appears as a sub-component of "VEVENT" and "VTODO"
   components.  The "VALARM" component is used to specify a reminder for
   an event or task.  Different alarm actions are possible, as are
   different ways to specify how the alarm is triggered.

   As iCalendar has become more widely used and as client-server
   protocols such as CalDAV [RFC4791] have become more prevalent,
   several issues with "VALARM" components have arisen.  Most of these
   relate to the need to extend the existing "VALARM" component with new
   properties and behaviors to allow clients and servers to accomplish
   specific tasks in an interoperable manner.  For example, clients
   typically need a way to specify that an alarm has been dismissed by a

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   calendar user, or has been "snoozed" by a set amount of time.  To
   date, this has been done through the use of custom "X-" properties
   specific to each client implementation, leading to poor
   interoperability.

   This specification defines a set of extensions to "VALARM" components
   to cover common requirements for alarms not currently addressed in
   iCalendar.  Each extension is defined in a separate section below.
   For the most part, each extension can be supported independently of
   the others, though in some cases one extension will require another.
   In addition, this specification describes mechanisms by which clients
   can interoperably implement common features such as "snoozing".

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   When XML element types in the namespaces "DAV:" and
   "urn:ietf:params:xml:ns:caldav" are referenced in this document
   outside of the context of an XML fragment, the string "DAV:" and
   "CALDAV:" will be prefixed to the element type names respectively.

3.  Extensible syntax for VALARM

   Section 3.6.6 of [RFC5545] defines the syntax for "VALARM" components
   and properties within them.  However, as written, it is hard to
   extend this by adding, e.g., a new property common to all types of
   alarm.  Since many of the extensions defined in this document need to
   extend the base syntax, an alternative form for the base syntax is
   defined here, with the goal of simplifying specification of the
   extensions while augmenting the existing functionality defined in
   [RFC5545] to allow for nested sub-components (as required by
   proximity alarm triggers (Section 8)).

   A "VALARM" calendar component is re-defined by the following
   notation:

   alarmcext  = "BEGIN" ":" "VALARM" CRLF
                *alarmprop *alarm-subcomp
                "END" ":" "VALARM" CRLF

   alarmprop  = (

                ; the following are REQUIRED,

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                ; but MUST NOT occur more than once

                action / trigger /

                ; one set of action properties MUST be
                ; present and MUST match the action specified
                ; in the ACTION property

                actionprops /

                ; the following are OPTIONAL,
                ; and MAY occur more than once

                x-prop / iana-prop

                )

   actionprops = *audiopropext / *disppropext / *emailpropext

   audiopropext  = (

                   ; 'duration' and 'repeat' are both OPTIONAL,
                   ; and MUST NOT occur more than once each,
                   ; but if one occurs, so MUST the other

                   duration / repeat /

                   ; the following is OPTIONAL,
                   ; but MUST NOT occur more than once

                   attach

                   )

   disppropext = (

                 ; the following are REQUIRED,
                 ; but MUST NOT occur more than once

                 description /

                 ; 'duration' and 'repeat' are both OPTIONAL,
                 ; and MUST NOT occur more than once each,
                 ; but if one occurs, so MUST the other

                 duration / repeat

                 )

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   emailpropext = (

                  ; the following are all REQUIRED,
                  ; but MUST NOT occur more than once

                  description / summary /

                  ; the following is REQUIRED,
                  ; and MAY occur more than once

                  attendee /

                  ; 'duration' and 'repeat' are both OPTIONAL,
                  ; and MUST NOT occur more than once each,
                  ; but if one occurs, so MUST the other

                  duration / repeat

                  ; the following is OPTIONAL,
                  ; and MAY occur more than once

                  attach

                  )

   alarm-subcomp = (

                   ; the following are OPTIONAL,
                   ; and MAY occur more than once

                   x-comp / iana-comp

                   )

4.  Alarm Unique Identifier

   This extension adds a "UID" property to "VALARM" components to allow
   a unique identifier to be specified.  The value of this property can
   then be used to refer uniquely to the "VALARM" component.

   The "UID" property defined here follows the definition in
   Section 3.8.4.7 of [RFC5545] with the security and privacy updates in
   Section 5.3 of [RFC7986].  In particular it MUST be a globally unique
   identifier that does not contain any security- or privacy-sensitive
   information.

   The "VALARM" component defined in Section 3 is extended here as:

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   alarmprop  =/ (

                 ; the following is OPTIONAL,
                 ; but MUST NOT occur more than once

                 uid

                 )

5.  Alarm Related To

   It is often convenient to relate one or more "VALARM" components to
   other "VALARM" components (e.g., see Section 7).  This can be
   accomplished if the "VALARM" components each have their own "UID"
   property (as per Section 4).

   This specification updates the usage of the "RELATED-TO" property
   defined in Section 3.8.4.5 of [RFC5545] to enable its use with
   "VALARM" components.  Specific types of relationships between
   "VALARM" components can be identified by registering new values for
   the "RELTYPE" property parameter defined in Section 3.2.15 of
   [RFC5545].

   The "VALARM" component defined in Section 3 is extended here as:

   alarmprop  =/ (

                 ; the following is OPTIONAL,
                 ; and MAY occur more than once

                 related

                 )

6.  Alarm Acknowledgement

   There is currently no way for a "VALARM" component to indicate
   whether it has been triggered and acknowledged.  With the advent of a
   standard client/server protocol for calendaring and scheduling data
   ([RFC4791]) it is quite possible for an event with an alarm to exist
   on multiple clients in addition to the server.  If each of those is
   responsible for performing the action when an alarm triggers, then
   multiple "alerts" are generated by different devices.  In such a
   situation, a calendar user would like to be able to "dismiss" the
   alarm on one device and have it automatically dismissed on the others
   too.

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   Also, with recurring events that have alarms, it is important to know
   when the last alarm in the recurring set was acknowledged, so that
   the client can determine whether past alarms have been missed.

   To address these needs, this specification adds an "ACKNOWLEDGED"
   property to "VALARM" components to indicate when the alarm was last
   acknowledged (or sent, if acknowledgement is not possible).  This is
   defined by the syntax below.

   alarmprop       =/ (

                      ; the following is OPTIONAL,
                      ; but MUST NOT occur more than once

                      acknowledged

                      )

6.1.  Acknowledged Property

   Property Name:  ACKNOWLEDGED

   Purpose:  This property specifies the UTC date and time at which the
      corresponding alarm was last sent or acknowledged.

   Value Type:  DATE-TIME

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property can be specified within "VALARM" calendar
      components.

   Description:  This property is used to specify when an alarm was last
      sent or acknowledged.  This allows clients to determine when a
      pending alarm has been acknowledged by a calendar user so that any
      alerts can be dismissed across multiple devices.  It also allows
      clients to track repeating alarms or alarms on recurring events or
      to-dos to ensure that the right number of missed alarms can be
      tracked.

      Clients SHOULD set this property to the current date-time value in
      UTC when a calendar user acknowledges a pending alarm.  Certain
      kinds of alarms, such as email-based alerts, might not provide
      feedback as to when the calendar user sees them.  For those kinds
      of alarms, the client SHOULD set this property when the alarm is
      triggered and the action successfully carried out.

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      When an alarm is triggered on a client, clients can check to see
      if an "ACKNOWLEDGED" property is present.  If it is, and the value
      of that property is greater than or equal to the computed trigger
      time for the alarm, then the client SHOULD NOT trigger the alarm.
      Similarly, if an alarm has been triggered and an "alert" presented
      to a calendar user, clients can monitor the iCalendar data to
      determine whether an "ACKNOWLEDGED" property is added or changed
      in the alarm component.  If the value of any "ACKNOWLEDGED"
      property in the alarm changes and is greater than or equal to the
      trigger time of the alarm, then clients SHOULD dismiss or cancel
      any "alert" presented to the calendar user.

   Format Definition:  This property is defined by the following
      notation:

   acknowledged = "ACKNOWLEDGED" *acknowledgedparam ":" datetime CRLF

   acknowledgedparam  = (

                        ; the following is OPTIONAL,
                        ; and MAY occur more than once

                        (";" other-param)

                        )

   Example:  The following is an example of this property:

   ACKNOWLEDGED:20090604T084500Z

7.  Snoozing Alarms

   Users often want to "snooze" an alarm, and this specification defines
   a standard approach to accomplish that.

   To "snooze" an alarm that has been triggered, clients MUST do the
   following:

   1.  Set the "ACKNOWLEDGED" property (see Section 6.1) on the
       triggered alarm.

   2.  Create a new "VALARM" component (the "snooze" alarm) within the
       parent component of the triggered alarm (i.e., as a "sibling"
       component of the triggered alarm).

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       A.  The new "snooze" alarm MUST be set to trigger at the user's
           chosen "snooze" interval after the original alarm triggered.
           Clients SHOULD use an absolute "TRIGGER" property with a
           "DATE-TIME" value specified in UTC.

       B.  The new "snooze" alarm MUST have a "RELATED-TO" property (see
           Section 5) with a value set to the "UID" property value of
           the original "VALARM" component that was triggered.  If the
           triggered "VALARM" component does not already have a "UID"
           property, the client MUST add one.  The "RELATED-TO" property
           added to the new "snooze" alarm MUST include a "RELTYPE"
           property parameter with a value set to "SNOOZE" (see
           Section 7.1).

   3.  When the "snooze" alarm is triggered, the client MUST do the
       following:

       A.  Update the "ACKNOWLEDGED" property on the original related
           alarm.

       B.  If the "snooze" alarm is itself "snoozed", the client MUST
           remove the "snooze" alarm component, and return to step 2.

           Otherwise, if the "snooze" alarm is dismissed, the client
           MUST do one of the following:

           +  Set the "ACKNOWLEDGED" property on the "snooze" alarm.

           +  Remove the "snooze" alarm component.

   Note that regardless of the final disposition of the "snooze" alarm
   when triggered, the original "VALARM" component is left unchanged
   other than updating its "ACKNOWLEDGED" property.

7.1.  Relationship Type Property Parameter

   This specification adds the "SNOOZE" relationship type for use with
   the "RELTYPE" property defined in Section 3.2.15 of [RFC5545].  This
   is used when relating a "snoozed" "VALARM" component to the original
   alarm that the "snooze" was generated for.

7.2.  Example

   The following example shows the snoozing, re-snoozing, and dismissal
   of an alarm.  Note that the encompassing VCALENDAR component has been
   omitted for brevity and that the line-breaks surrounding the VALARM
   components are for clarity only and would not be present in the
   actual iCalendar data.

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   Assume that we have the following event with an alarm set to trigger
   15 minutes before the meeting:

   BEGIN:VEVENT
   CREATED:20210302T151004Z
   UID:AC67C078-CED3-4BF5-9726-832C3749F627
   DTSTAMP:20210302T151004Z
   DTSTART;TZID=America/New_York:20210302T103000
   DTEND;TZID=America/New_York:20210302T113000
   SUMMARY:Meeting

   BEGIN:VALARM
   UID:8297C37D-BA2D-4476-91AE-C1EAA364F8E1
   TRIGGER:-PT15M
   DESCRIPTION:Event reminder
   ACTION:DISPLAY
   END:VALARM

   END:VEVENT

   When the alarm is triggered, the user decides to snooze it for 5
   minutes.  The client acknowledges the original alarm and creates a
   new "snooze" alarm as a sibling of, and relates it to, the original
   alarm (note that both VALARMs reside within the same "parent"
   VEVENT):

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   BEGIN:VEVENT
   CREATED:20210302T151004Z
   UID:AC67C078-CED3-4BF5-9726-832C3749F627
   DTSTAMP:20210302T151516Z
   DTSTART;TZID=America/New_York:20210302T103000
   DTEND;TZID=America/New_York:20210302T113000
   SUMMARY:Meeting

   BEGIN:VALARM
   UID:8297C37D-BA2D-4476-91AE-C1EAA364F8E1
   TRIGGER:-PT15M
   DESCRIPTION:Event reminder
   ACTION:DISPLAY
   ACKNOWLEDGED:20210302T151514Z
   END:VALARM

   BEGIN:VALARM
   UID:DE7B5C34-83FF-47FE-BE9E-FF41AE6DD097
   TRIGGER;VALUE=DATE-TIME:20210302T152000Z
   RELATED-TO;RELTYPE=SNOOZE:8297C37D-BA2D-4476-91AE-C1EAA364F8E1
   DESCRIPTION:Event reminder
   ACTION:DISPLAY
   END:VALARM

   END:VEVENT

   When the "snooze" alarm is triggered, the user decides to snooze it
   again for an additional 5 minutes.  The client once again
   acknowledges the original alarm, removes the triggered "snooze"
   alarm, and creates another new "snooze" alarm as a sibling of, and
   relates it to, the original alarm (note the different UID for the new
   snooze alarm):

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   BEGIN:VEVENT
   CREATED:20210302T151004Z
   UID:AC67C078-CED3-4BF5-9726-832C3749F627
   DTSTAMP:20210302T152026Z
   DTSTART;TZID=America/New_York:20210302T103000
   DTEND;TZID=America/New_York:20210302T113000
   SUMMARY:Meeting

   BEGIN:VALARM
   UID:8297C37D-BA2D-4476-91AE-C1EAA364F8E1
   TRIGGER:-PT15M
   DESCRIPTION:Event reminder
   ACTION:DISPLAY
   ACKNOWLEDGED:20210302T152024Z
   END:VALARM

   BEGIN:VALARM
   UID:87D690A7-B5E8-4EB4-8500-491F50AFE394
   TRIGGER;VALUE=DATE-TIME:20210302T152500Z
   RELATED-TO;RELTYPE=SNOOZE:8297C37D-BA2D-4476-91AE-C1EAA364F8E1
   DESCRIPTION:Event reminder
   ACTION:DISPLAY
   END:VALARM

   END:VEVENT

   When the second "snooze" alarm is triggered, the user decides to
   dismiss it.  The client acknowledges both the original alarm and the
   second "snooze" alarm:

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   BEGIN:VEVENT
   CREATED:20210302T151004Z
   UID:AC67C078-CED3-4BF5-9726-832C3749F627
   DTSTAMP:20210302T152508Z
   DTSTART;TZID=America/New_York:20210302T103000
   DTEND;TZID=America/New_York:20210302T113000
   SUMMARY:Meeting

   BEGIN:VALARM
   UID:8297C37D-BA2D-4476-91AE-C1EAA364F8E1
   TRIGGER:-PT15M
   DESCRIPTION:Event reminder
   ACTION:DISPLAY
   ACKNOWLEDGED:20210302T152507Z
   END:VALARM

   BEGIN:VALARM
   UID:87D690A7-B5E8-4EB4-8500-491F50AFE394
   TRIGGER;VALUE=DATE-TIME:20210302T152500Z
   RELATED-TO;RELTYPE=SNOOZE:8297C37D-BA2D-4476-91AE-C1EAA364F8E1
   DESCRIPTION:Event reminder
   ACTION:DISPLAY
   ACKNOWLEDGED:20210302T152507Z
   END:VALARM

   END:VEVENT

8.  Alarm Proximity Trigger

   VALARMs are currently triggered when a specific date-time is reached.
   It is also desirable to be able to trigger alarms based on location,
   e.g. when arriving at or departing from a particular location.

   This specification adds the following elements to "VALARM" components
   to indicate when an alarm can be triggered based on location.

      "PROXIMITY" property - indicates that a location based trigger is
      to be used and which action is used for the trigger

      "VLOCATION" component(s) [I-D.ietf-calext-eventpub-extensions] -
      used to indicate the actual location(s) to trigger off of,
      specified with a URL property containing a geo: URI [RFC5870]
      which allows for two or three coordinate values with an optional
      uncertainty

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   alarmprop       =/ (

                      ; the following is OPTIONAL,
                      ; but MUST NOT occur more than once

                      proximity /

                      )

   alarm-subcomp   =/ (

                      ; the following is OPTIONAL,
                      ; and MAY occur more than once, but only
                      ; when a PROXIMITY property is also present

                      locationc

                      )

   Typically, when a "PROXIMITY" property is used there is no need to
   specify a time-based trigger using the "TRIGGER" property.  However,
   since "TRIGGER" is defined as a required property for a "VALARM"
   component, for backwards compatibility it has to be present, but
   ignored.  To indicate a "TRIGGER" that is to be ignored, clients
   SHOULD use a value a long time in the past.  A value of
   "19760401T005545Z" has been commonly used for this purpose.

8.1.  Proximity Property

   Property Name:  PROXIMITY

   Purpose:  This property indicates that a location based trigger is
      applied to an alarm.

   Value Type:  TEXT

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property can be specified within "VALARM" calendar
      components.

   Description:  This property is used to indicate that an alarm has a
      location-based trigger.  Its value identifies the action that will
      trigger the alarm.

      When the property value is set to "ARRIVE", the alarm is triggered
      when the calendar user agent arrives in the vicinity of one or

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      more locations.  When set to "DEPART", the alarm is triggered when
      the calendar user agent departs from the vicinity of one or more
      locations.  Each location which MUST be specified with a
      "VLOCATION" component.  Note that the meaning of "vicinity" in
      this context is implementation defined.

      When the property value is set to "CONNECT", the alarm is
      triggered when the calendar user agent connects to a automobile to
      which is has been paired via Bluetooth(R) [BTcore].  When set to
      "DISCONNECT", the alarm is triggered when the calendar user agent
      disconnects from a automobile to which it has been paired via
      Bluetooth(R).  Note that neither current implementations of
      proximty alarms nor this document have a mechanism to target a
      particular automobile.  Such a mechanism may be specified in a
      future extension.

   Format Definition:  This property is defined by the following
      notation:

   proximity = "PROXIMITY" *proximityparam ":" proximityvalue CRLF

   proximityparam  = (

                     ; the following is OPTIONAL,
                     ; and MAY occur more than once

                     (";" other-param)

                     )

   proximityvalue  = "ARRIVE" / "DEPART" /
                     "CONNECT" / "DISCONNECT" / iana-token / x-name

8.2.  Example

   The following example shows a VALARM component with a proximity
   trigger set to trigger when the device running the calendar user
   agent leaves the vicinity defined by the URL property in the
   VLOCATION component.  Note use of the "u=" parameter with the "geo"
   URI to define the uncertainty of the location determination.

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   BEGIN:VALARM
   UID:77D80D14-906B-4257-963F-85B1E734DBB6
   ACTION:DISPLAY
   TRIGGER;VALUE=DATE-TIME:19760401T005545Z
   DESCRIPTION:Remember to buy milk
   PROXIMITY:DEPART
   BEGIN:VLOCATION
   UID:123456-abcdef-98765432
   NAME:Office
   URL:geo:40.443,-79.945;u=10
   END:VLOCATION
   END:VALARM

9.  Security Considerations

   In addition to the security properties of iCalendar (see Section 7 of
   [RFC5545]), VALARMs, if not monitored properly, can be used to
   disturb users and/or leak personal information.  For instance, an
   undesirable audio alert could cause embarassment.  An unwanted
   display alert could be considered an annoyance.  Or an email alert
   could be used to leak a user's location to a third party or to send
   unsolicited email to multiple users.  Therefore, CalDAV clients and
   servers that accept iCalendar data from a third party (e.g. via iTIP
   [RFC5546], a subscription feed, or a shared calendar) SHOULD remove
   all VALARMs from the data prior to storing in their calendar system.

   Security considerations related to unique identifiers for VALARMs are
   discussed in Section 4.

10.  Privacy Considerations

   Proximity VALARMs, if not used carefully, can leak a user's past,
   present, or future location.  For instance, storing an iCalendar
   resource containing proxmity VALARMs to a shared calendar on CalDAV
   server can expose to anyone that has access to that calendar the
   user's intent to leave from or arrive at a particular location at
   some future time.  Furthermore, if a CalDAV client updates the shared
   iCalendar resource with an ACKNOWLEDGED property when the alarm is
   triggered, will leak the exact date and time that the user left from
   or arrived at the location.  Therefore, CalDAV clients that implement
   proximity alarms SHOULD give users the option of storing and/or
   acknowledging the alarms on the local device only and not storing the
   alarm and/or acknowledgment on a remote server.

   Privacy considerations related to unique identifiers for VALARMs are
   discussed in Section 4.

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11.  IANA Considerations

11.1.  Property Registrations

   This document defines the following new iCalendar properties to be
   added to the registry defined in Section 8.2.3 of [RFC5545] and
   located here: <https://www.iana.org/assignments/icalendar#properties>

             +--------------+---------+----------------------+
             | Property     | Status  | Reference            |
             +--------------+---------+----------------------+
             | ACKNOWLEDGED | Current | RFCXXXX, Section 6.1 |
             | PROXIMITY    | Current | RFCXXXX, Section 8.1 |
             +--------------+---------+----------------------+

11.2.  Relationship Types Registry

   This document defines the following new iCalendar relationship type
   to be added to the registry defined in Section 8.3.8 of [RFC5545] and
   located here: <https://www.iana.org/assignments/
   icalendar#relationship-types>

          +-------------------+---------+----------------------+
          | Relationship Type | Status  | Reference            |
          +-------------------+---------+----------------------+
          | SNOOZE            | Current | RFCXXXX, Section 7.1 |
          +-------------------+---------+----------------------+

11.3.  Proximity Value Registry

   This document creates a new iCalendar registry for values of the
   "PROXIMITY" property located here: <https://www.iana.org/assignments/
   icalendar#proximity-values>

   Additional values MAY be used, provided the process described in
   Section 8.2.1 of [RFC5545] is used to register them, using the
   template in Section 8.2.6 of [RFC5545].

   The following table has been used to initialize the Proximity Value
   Registry.

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              +------------+---------+----------------------+
              | Value      | Status  | Reference            |
              +------------+---------+----------------------+
              | ARRIVE     | Current | RFCXXXX, Section 8.1 |
              | DEPART     | Current | RFCXXXX, Section 8.1 |
              | CONNECT    | Current | RFCXXXX, Section 8.1 |
              | DISCONNECT | Current | RFCXXXX, Section 8.1 |
              +------------+---------+----------------------+

12.  Acknowledgments

   This specification came about via discussions at the Calendaring and
   Scheduling Consortium.  Also, thanks to the following for providing
   feedback: Bernard Desruisseaux, Mike Douglass, Jacob Farkas, Jeffrey
   Harris, Ciny Joy, Barry Leiba, and Daniel Migault.

13.  References

13.1.  Normative References

   [I-D.ietf-calext-eventpub-extensions]
              Douglass, M., "Event Publishing Extensions to iCalendar",
              draft-ietf-calext-eventpub-extensions-18 (work in
              progress), January 2021.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5545]  Desruisseaux, B., Ed., "Internet Calendaring and
              Scheduling Core Object Specification (iCalendar)",
              RFC 5545, DOI 10.17487/RFC5545, September 2009,
              <https://www.rfc-editor.org/info/rfc5545>.

   [RFC5870]  Mayrhofer, A. and C. Spanring, "A Uniform Resource
              Identifier for Geographic Locations ('geo' URI)",
              RFC 5870, DOI 10.17487/RFC5870, June 2010,
              <https://www.rfc-editor.org/info/rfc5870>.

   [RFC7986]  Daboo, C., "New Properties for iCalendar", RFC 7986,
              DOI 10.17487/RFC7986, October 2016,
              <https://www.rfc-editor.org/info/rfc7986>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

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13.2.  Informative References

   [BTcore]   Bluetooth Special Interest Group, "Bluetooth Core
              Specification Version 5.0", December 2016,
              <https://www.bluetooth.com/specifications/bluetooth-core-
              specification>.

   [RFC4791]  Daboo, C., Desruisseaux, B., and L. Dusseault,
              "Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
              DOI 10.17487/RFC4791, March 2007,
              <https://www.rfc-editor.org/info/rfc4791>.

   [RFC5546]  Daboo, C., Ed., "iCalendar Transport-Independent
              Interoperability Protocol (iTIP)", RFC 5546,
              DOI 10.17487/RFC5546, December 2009,
              <https://www.rfc-editor.org/info/rfc5546>.

Appendix A.  Change History (To be removed by RFC Editor before
             publication)

   Changes in ietf-06:

   1.  Corrected timestamps in snooze example.

   2.  Editorial changes from Benjamim Kaduk.

   Changes in ietf-05:

   1.  Updated to use VLOCATION components rather than (deprecated)
       STRUCTURED-LOCATION properties for proximity alarms.

   2.  Reorganized and clarified the process of snoozing an alarm and
       added an example.

   3.  Noted that there is currently no mechanism for specifying a
       particular automobile for CONNECT/DISCONNECT proximity alarms.

   4.  Replaced the term "spam" with new wording in Security
       Considerations.

   5.  Addressed IESG comments from Benjamim Kaduk.

   6.  Addressed IESG comments from Robert Wilton.

   7.  Addressed IESG comments Alissa Cooper.

   Changes in ietf-04:

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   1.  Addressed security review comments from Valery Smyslov.

   2.  Addressed Genart review comments from Roni Even.

   3.  Added text addressing management of Proximity Value Registry.

   Changes in ietf-03:

   1.  Fixed ABNF to be properly extended.

   2.  Addressed AD review comments from Barry Leiba.

   Changes in ietf-02:

   1.  Addressed some WGLC comments from Daniel Migault.

   Changes in ietf-01:

   1.  Reintroduced the RELATED-TO property for VALARMs and the SNOOZE
       value for the RELTYPE property parameter.

   2.  Add Privacy Considerations section.

   Changes in ietf-00:

   1.  Submitted as CALEXT draft.

   Changes in daboo-05:

   1.   Added Murchison as editor.

   2.   Updated keywords boilerplate.

   3.   Added reference to UID security/privacy recommendations.

   4.   Removed default alarms.

   5.   Removed ALARM-AGENT property.

   6.   Added text about using TRIGGER value in the past in addition to
        ACTION:NONE to have a default alarm be ignored.

   7.   Removed text about related alarms.

   8.   Removed URL alarm action.

   9.   Added reference to draft-ietf-calext-eventpub-extensions for
        STRUCTURED-LOCATION.

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   10.  Added CONNECT and DISCONNECT PROXIMITY property values.

   11.  Added Security Considerations.

   12.  Editorial fixes.

   Changes in daboo-04:

   1.  Changed "ID" to "AGENT-ID".

   2.  Add more text on using "ACKNOWLEDGED" property.

   3.  Add "RELATED-TO" as a valid property for VALARMs.

   4.  Add "SNOOZE" relationship type for use with VALARMs.

   5.  State that "TRIGGER" is typically ignored in proximity alarms.

   6.  Added "PROXIMITY" value registry.

   7.  Added a lot more detail on default alarms including new action
       and property.

   Changes in daboo-03: none - resubmission of -02

   Changes in daboo-02:

   1.  Updated to 5545 reference.

   2.  Clarified use of absolute trigger in UTC in snooze alarms

   3.  Snooze alarms should be removed when completed

   4.  Removed status and replaced last-triggered by acknowledged
       property

   5.  Added location-based trigger

   6.  IANA registry tables added

   Changes in daboo-01:

   1.  Removed DESCRIPTION as an allowed property in the URI alarm.

   2.  Added statement about what to do when ALARM-AGENT is not present.

   3.  Allow multiple ALARM-AGENT properties to be present.

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   4.  Removed SNOOZE-UNTIL - snoozing now accomplished by creating a
       new VALARM.

   5.  Remove VALARM by reference section.

   6.  Added more detail to CalDAV default alarms.

Authors' Addresses

   Cyrus Daboo
   Apple Inc.
   1 Infinite Loop
   Cupertino, CA  95014
   USA

   Email: cyrus@daboo.name
   URI:   http://www.apple.com/

   Kenneth Murchison (editor)
   Fastmail US LLC
   1429 Walnut St, Suite 1201
   Philadephia, PA  19102
   USA

   Email: murch@fastmailteam.com
   URI:   http://www.fastmail.com/

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