Internet Printing Protocol WG R. Herriot
INTERNET-DRAFT consultant
<draft-ietf-ipp-notify-get-08.txt> T. Hastings
Updates: RFC 2911 and [ipp-ntfy] Xerox Corp.
[Target category: standards track] H. Lewis
Expires: April 10, 2003 IBM Corp.
October 10, 2002
Internet Printing Protocol (IPP):
The 'ippget' Delivery Method for Event Notifications
Copyright (C) The Internet Society (2002). All Rights Reserved.
Status of this Memo:
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026. Internet-Drafts are
working documents of the Internet Engineering Task Force (IETF), its
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and may be updated, replaced, or obsoleted by other documents at any
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The list of current Internet-Drafts can be accessed at
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Abstract
This document describes an extension to the Internet Printing
Protocol/1.1: Model and Semantics (RFC 2911, RFC 2910). This
document specifies the 'ippget' Pull Delivery Method for use with the
"Internet Printing Protocol (IPP): Event Notifications and
Subscriptions" specification (ipp-ntfy). This IPPGET Delivery Method
is REQUIRED for all clients and Printers that support ipp-ntfy. The
Notification Recipient, acting as a client, fetches (pulls) Event
Notifications using the Get-Notifications operation defined in this
document.
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Table of Contents
1 Introduction.....................................................4
2 Terminology......................................................4
2.1 Conformance Terminology........................................4
2.2 Other terminology..............................................5
3 Model and Operation..............................................5
4 General Information..............................................7
5 Get-Notifications operation......................................8
5.1 Get-Notifications Request.....................................10
5.1.1 notify-subscription-ids (1setOf integer(1:MAX)).............10
5.1.2 notify-sequence-numbers (1setOf integer(1:MAX)).............10
5.1.3 notify-wait (boolean).......................................11
5.2 Get-Notifications Response....................................12
5.2.1 notify-get-interval (integer(0:MAX))........................14
5.2.2 printer-up-time (integer(1:MAX))............................17
6 Additional Information about Subscription Template Attributes...21
6.1 notify-pull-method (type2 keyword)............................21
7 Subscription Description Attributes.............................21
8 Additional Printer Description Attributes.......................22
8.1 ippget-event-life (integer(15:MAX))...........................22
9 New Values for Existing Printer Description Attributes..........23
9.1 notify-pull-method-supported (1setOf type2 keyword)...........23
9.2 operations-supported (1setOf type2 enum)......................23
10 New Status Codes...............................................23
10.1 successful-ok-events-complete (0x0007).......................24
11 Encoding and Transport.........................................24
12 Conformance Requirements.......................................25
12.1 Conformance for IPP Printers.................................26
12.2 Conformance for IPP Clients..................................26
13 Normative References...........................................27
14 Informative References.........................................27
15 IANA Considerations............................................28
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15.1 Attribute Registrations......................................29
15.2 Additional keyword attribute value registrations for existing
attributes........................................................29
15.3 Additional enum attribute values.............................29
15.4 Operation Registrations......................................29
15.5 Status code Registrations....................................30
16 Internationalization Considerations............................30
17 Security Considerations........................................30
17.1 Notification Recipient client access rights..................31
17.2 Printer security threats.....................................31
17.3 Notification Recipient security threats......................31
17.4 Security requirements for Printers...........................32
17.5 Security requirements for clients............................32
18 Contributors...................................................32
19 Authors' Addresses.............................................32
20 Description of Base IPP documents (Informative)................33
21 Full Copyright Statement.......................................35
Table of Tables
Table 1 - Information about the Delivery Method....................7
Table 2 - Combinations of "notify-wait", "status-code", and "notify-
get-interval" .................................................16
Table 3 - Attributes in Event Notification Content................19
Table 4 - Additional Attributes in Event Notification Content for Job
Events ........................................................20
Table 5 - Combinations of Events and Subscribed Events for "job-
impressions-completed" ........................................20
Table 6 - Additional Attributes in Event Notification Content for
Printer Events ................................................21
Table 7 - Operation-id assignments................................23
Table 8 - The "event-notification-attributes-tag" value...........25
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1 Introduction
This document describes an extension to the Internet Printing
Protocol/1.1: Model and Semantics [RFC 2911], [RFC 2910]. This
document specifies the 'ippget' Pull Delivery Method for use with the
"Internet Printing Protocol (IPP): Event Notifications and
Subscriptions" specification [ipp-ntfy]. This IPPGET Delivery Method
is REQUIRED for all clients and Printers that support [ipp-ntfy].
The Notification Recipient, acting as a client, fetches (pulls) Event
Notifications using the Get-Notifications operation defined in this
document. For a description of the base IPP documents, see section
20 of this document. For a description of the IPP Event Notification
Model, see [ipp-ntfy].
With this Pull Delivery Method, when an Event occurs, the Printer
saves the Event Notification for a period of time called the Event
Life. The Notification Recipient fetches (pulls) the Event
Notifications using the Get-Notifications operation. This operation
causes the Printer to return all Event Notifications held for the
specified Subscription object(s). If the Notification Recipient has
selected the Event Wait Mode option to wait for additional Event
Notifications, the Printer MAY continue to return Event Notifications
to the Notification Recipient as asynchronous Get-Notification
responses as Events occur using the transaction originated by the
Notification Recipient.
The Notification Recipient can terminate Event Wait Mode (without
closing the connection) by supplying the "notify-wait" (boolean)
attribute with a 'false' value in a subsequent Get-Notifications
request. Similarly, the Printer can terminate Event Wait Mode
(without closing the connection) by returning the "notify-get-
interval" (integer) operation attribute in a Get-Notifications
response which tells the Notification Recipient how long to wait
before trying again.
2 Terminology
This section defines the following terms that are used throughout
this document:
2.1 Conformance Terminology
Capitalized terms, such as MUST, MUST NOT, REQUIRED, SHOULD, SHOULD
NOT, MAY, NEED NOT, and OPTIONAL, have special meaning relating to
conformance as defined in RFC 2119 [RFC2119] and [RFC2911] section
12.1. If an implementation supports the extension defined in this
document, then these terms apply; otherwise, they do not. These
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terms define conformance to this document only; they do not affect
conformance to other documents, unless explicitly stated otherwise.
2.2 Other terminology
This document uses the same terminology as [RFC2911], such as
"client", "Printer", "Job", "attribute", "attribute value",
"keyword", "operation", "request", "response", and "support" with the
same meanings. This document also uses terminology defined in [ipp-
ntfy], such as "Subscription (object)", "Notification Recipient",
"Event", "Event Notification", "Compound Event Notification", "Event
Life", and "Event Notification Attribute Group" with the same
meanings. In addition, this document defines the following terms for
use in this document:
Event Wait Mode: The mode requested by a Notification Recipient
client in its Get-Notifications Request and granted by a Printer
to keep the connection open while the Printer sends subsequent
Event Notifications to the Notification Recipient as they occur
as additional Get-Notification operation responses.
3 Model and Operation
In a Subscription Creation Operation, when the "notify-pull-method"
attribute is present and has the 'ippget' keyword value, the client
is requesting that the Printer use the 'ippget' Pull Delivery Method
for the Event Notifications associated with the new Subscription
Object.
When an Event occurs, the Printer MUST generate an Event Notification
and MUST assign it the Event Life. The Printer MUST hold an Event
Notification for its assigned Event Life.
When a Notification Recipient wants to receive Event Notifications
for a Subscription object, it performs the Get-Notifications
operation supplying the Subscription object's subscription-id, which
causes the Printer to return all un-expired Event Notifications held
for that Subscription object. If the Notification Recipient has
selected the Event Wait Mode option to wait for additional Event
Notifications, the response to the Get-Notifications request
continues indefinitely as the Printer continues to send Event
Notifications in the response as Events occur for that Subscription
object.
When the Notification Recipient requests Event Notifications for per-
Job Subscription Objects, the Notification Recipient typically
performs the Get-Notifications operation within a second of
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performing the Subscription Creation operation. Because the Printer
MUST save Event Notifications for at least 15 seconds (see section
8.1), the Notification Recipient is unlikely to miss any Event
Notifications that occur between the Subscription Creation and the
Get-Notifications operation.
The 'ippget' Delivery Method is designed primarily for (1) a client
that wants to get Events (from the job's per-Job Subscription object)
for a job that it has submitted and (2) for a privileged client that
wants to get all job or printer Events from a per-Printer
Subscription object.
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4 General Information
If a Printer supports this Delivery Method, the following are its
characteristics.
Table 1 - Information about the Delivery Method
Document Method Conformance Requirement Delivery Method
Realization
1. What is the URL scheme name for the 'ippget' keyword method
Push Delivery Method or the keyword name
method name for the Pull Delivery
Method?
2. Is the Delivery Method REQUIRED,
RECOMMENDED or OPTIONAL for an IPP
Printer to support? REQUIRED
3. What transport and delivery protocols IPP with one new
does the Printer use to deliver the operation.
Event Notification Content, i.e., what
is the entire network stack?
4. Can several Event Notifications be Yes.
combined into a Compound Event
Notification?
5. Is the Delivery Method initiated by This Delivery Method is
the Notification Recipient (pull), or a pull method with
by the Printer (push)? aspects of a push
method, though the
Printer does not
initiate the operation.
6. Is the Event Notification content Machine Consumable
Machine Consumable or Human
Consumable?
7. What section in this document answers Section 5
the following question? For a Machine
Consumable Event Notification, what is
the representation and encoding of
values defined in section 9.1 of [ipp-
ntfy] and the conformance requirements
thereof? For a Human Consumable Event
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thereof? For a Human Consumable Event
Notification, what is the
representation and encoding of pieces
of information defined in section 9.2
of [ipp-ntfy] and the conformance
requirements thereof?
8. What are the latency and reliability Same as IPP and the
of the transport and delivery underlying HTTP
protocol? transport
9. What are the security aspects of the Same as IPP and the
transport and delivery protocol, e.g., underlying HTTP
how it is handled in firewalls? transport and in the
same direction, so no
new firewall
considerations.
10.What are the content length None
restrictions?
11.What are the additional values or
pieces of information that a Printer
sends in an Event Notification content
and the conformance requirements
thereof? None
12.What are the additional Subscription None
Template and/or Subscription
Description attributes and the
conformance requirements thereof?
13.What are the additional Printer "ipp-event-life"
Description attributes and the (integer (15: MAX))
conformance requirements thereof?
5 Get-Notifications operation
This operation is issued by a client acting in the role of a
Notification Recipient requesting the Printer to return all Event
Notifications held for the identified Subscription object(s).
A Printer MUST support this operation, MUST accept the request in any
state (see [RFC2911] "printer-state" and "printer-state-reasons"
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attributes), and MUST remain in the same state with the same
"printer-state-reasons" values.
When a Printer performs this operation, it MUST return all and only
those Event Notifications:
1. Whose associated Subscription Object's "notify-subscription-id"
Subscription Description attribute equals one of the values of
the "notify-subscription-ids" (1setOf integer(1:MAX)) operation
attribute AND
2. Whose associated Subscription Object's contains the "notify-
pull-method" attribute and it has the 'ippget' keyword value AND
3. Whose "notify-sequence-number" is equal to or greater than the
corresponding value of the "notify-sequence-numbers (1setOf
integer(1:MAX)) operation attribute, if supplied AND
4. Whose Event Life has not yet expired AND
5. Where the Notification Recipient client has read-access rights
to the identified Subscription Object (see Access Rights
paragraph below).
The Notification Recipient client MUST either: (a) request Event Wait
Mode by supplying the "notify-wait" operation attribute with a 'true'
value or (b) suppress Event Wait Mode by omitting the "notify-wait"
operation attribute or by supplying it with a 'false' value. In
order to terminate Event Wait Mode subsequently, the Notification
Recipient client MUST close the connection. In order to terminate
Event Wait Mode, the Printer MUST either (a) return the "notify-get-
interval" operation attribute in a Get-Notifications response
(RECOMMENDED behavior) or (b) close the connection. The "notify-get-
interval" operation attributes tells the Notification Recipient how
long to wait before trying a subsequent Get-Notifications request.
Access Rights: The authenticated user (see [RFC2911] section 8.3)
performing this operation MUST be (1) the owner of each Subscription
Object identified by the "notify-subscription-ids" operation
attribute (see section 5.1.1), (2) an operator or administrator of
the Printer (see [RFC2911] Sections 1 and 8.5), or (3) be otherwise
authorized by the Printer's administrator-configured security policy
to request Event Notifications from the target Subscription
Object(s). Otherwise, the IPP Printer MUST reject the operation and
return: 'client-error-forbidden', 'client-error-not-authenticated',
or 'client-error-not-authorized' status code as appropriate.
Furthermore, the Printer's security policy MAY limit the attributes
returned by the Get-Notifications operation, in a manner similar to
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the Get-Job-Attributes operation (see [RFC2911] end of section
3.3.4.2).
5.1 Get-Notifications Request
The following groups of attributes are part of the Get-Notifications
Request:
Group 1: Operation Attributes
Natural Language and Character Set:
The "attributes-charset" and "attributes-natural-language"
attributes as described in [RFC2911] section 3.1.4.1.
Target:
The "printer-uri" (uri) operation attribute which is the target
for this operation as described in [RFC2911] section 3.1.5.
Requesting User Name:
The "requesting-user-name" (name(MAX)) attribute SHOULD be
supplied by the client as described in [RFC2911] section 8.3.
5.1.1 notify-subscription-ids (1setOf integer(1:MAX))
This attribute identifies one or more Subscription objects for
which Events are requested. The client MUST supply this
attribute with at least one value. The Printer object MUST
support this attribute with multiple values.
If no Subscription Object exists with the supplied identifier
or the identified Subscription Object does not contain the
"notify-pull-method" attribute with the 'ippget' keyword value,
the Printer MUST return the 'client-error-not-found' status
code.
Note: The name of both the "notify-subscription-ids" and
"notify-sequence-numbers" end in 's', since they are
multi-valued. However, there are other occurrences of
these attribute names without the 's' that are single
valued.
5.1.2 notify-sequence-numbers (1setOf integer(1:MAX))
This attribute specifies one or more lowest Event Notification
sequence number values for the Subscription objects identified
by the corresponding values of the "notify-subscription-ids"
operation attribute. The Notification Recipient SHOULD supply
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this attribute and the number of values SHOULD be the same as
the number of values of the "notify-subscriptions-ids"
attribute. The Printer MUST support this attribute with
multiple values.
The Printer MUST NOT return Notification Events with lower
sequence numbers for the corresponding Subscription object.
Therefore, by supplying the proper values for this attribute
the Notification Recipient can prevent getting the same Event
Notifications from a Subscription object that were returned on
a previous Get-Notifications request. The Notification
Recipient SHOULD remember the highest "notify-sequence-number"
value returned for each Subscription object requested and
SHOULD pass that value for each requested Subscription object
on the next Get-Notifications request.
If the Notification Recipient supplies fewer values for this
attribute (including omitting this attribute) than for the
"notify-subscription-ids" operation attribute, the Printer
assumes a '1' value for each missing value. A value of '1'
causes the Printer to return any un-expired Event Notification
for that Subscription object, since '1' is the lowest possible
sequence number. If the Notification Recipient supplies more
values for this attribute than the number of values for the
"notify-subscription-ids" operation attribute, the Printer
ignores the extra values.
Note: If a Notification Recipient performs two consecutive Get-
Notifications operations with the same value for "notify-
sequence-number" (or omits the attribute), the time stamp of
the first Event Notification in the second Get-Notifications
Response may be less than the time stamp of the last Event
Notification in the first Get-Notification Response. This
happens because the Printer sends all unexpired Event
Notification with a sequence number equal or higher according
to the ordering specified in [ipp-ntfy] and some Event
Notifications from the first Get-Notifications operation may
not have expired by the time the second Get-Notifications
operation occurs.
5.1.3 notify-wait (boolean)
This value indicates whether or not the Notification Recipient
wants Event Wait Mode. The client MAY supply this attribute.
The Printer object MUST support both values of this attribute.
If the client supplies the 'false' value or omits this
attribute, the client is not requesting Event Wait Mode. If
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the value is 'true', the client is requesting Event Wait Mode.
See the beginning of section 5.2 for the rules for Event Wait
Mode.
5.2 Get-Notifications Response
The Printer has the following options for responding to a Get-
Notifications Request:
1. The Printer can reject the request and return the 'server-error-
busy' status code, if the Printer is too busy to accept this
operation at this time. In this case, the Printer MUST return
the "get-notify-interval" operation attribute to indicate when
the client SHOULD try again.
2. If the Notification Recipient did not request Event Wait Mode
("notify-wait-mode" = 'false' or omitted), the Printer MUST
return immediately whatever Event Notifications it currently
holds in the requested Subscription object(s) and MUST return
the "notify-get-interval" operation attribute with number of
seconds from now at which the Notification Recipient SHOULD
repeat the Get-Notifications Request to get future Event
Notifications.
3. If the Notification Recipient requested Event Wait Mode
("notify-wait-mode" = 'true'), the Printer MUST return
immediately whatever Event Notifications it currently holds in
the requested Subscription object(s) and MUST continue to return
Event Notifications as they occur until all of the requested
Subscription Objects are canceled. A Subscription Object is
canceled either via the Cancel-Subscription operation or by the
Printer (e.g., the Subscription Object is canceled when the
associated Job completes and is no longer in the Job Retention
or Job History phase - see the "ippget-event-life
(integer(15:MAX))" attribute discussion in section 8.1).
However, the Printer MAY decide to terminate Event Wait Mode at
any time, including in the first response. In this case the
Printer MUST return the "notify-get-interval" operation
attribute. This attribute indicates that the Printer wishes to
leave Event Wait Mode and the number of seconds in the future
that the Notification Recipient SHOULD try the Get-Notifications
operation again. The Notification Recipient MUST accept this
response and MUST disconnect. If the Notification Recipient
does not disconnect, the Printer SHOULD do so.
From the Notification Recipient's view, the response appears as an
initial burst of data, which includes the Operation Attributes Group
and one Event Notification Attributes Group per Event Notification
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that the Printer is holding. After the initial burst of data, if the
Notification Recipient has selected the Event Wait Mode option to
wait for additional Event Notifications, the Notification Recipient
receives occasional Event Notification Attribute Groups. Proxy
servers may delay some Event Notifications or cause time-outs to
occur. The client MUST be prepared to perform the Get-Notifications
operation again when time-outs occur.
Each attribute is encoded using the IPP rules for encoding attributes
[RFC2910] and MAY be encoded in any order. Note: the Get-Jobs
response in [RFC2911] acts as a model for encoding multiple groups of
attributes. See section 11 for the encoding and transport rules.
The following groups of attributes are part of the Get-Notifications
Response:
Group 1: Operation Attributes
Status Message:
In addition to the REQUIRED status code returned in every
response, the response OPTIONALLY includes a "status-message"
(text(255)) and/or a "detailed-status-message" (text(MAX))
operation attribute as described in [RFC2911] sections 13 and
3.1.6.
The Printer can return any status codes defined in [RFC2911].
If the status code is not 'successful-xxx', the Printer MUST
NOT return any Event Notification Attribute groups. The
following is a description of the important status codes:
successful-ok: the response contains all Event Notification
associated with the specified subscription-ids that had
been supplied in the "notify-subscription-ids" operation
attribute in the request. If the requested Subscription
Objects have no associated Event Notification, the
response MUST contain zero Event Notifications.
successful-ok-events-complete: indicate when this return
is the last return for all Subscription objects that
match the request, whether or not there are Event
Notifications being returned. This condition occurs for
Event Wait Mode with Notification Recipients waiting for
responses when the Subscription Object is: (1) canceled
with a Cancel-Subscription operation, (2) deleted when
the Per-Printer Subscription lease time expires, or (3)
when the 'job-completed' event occurs for a Per-Job
Subscription. This condition also occurs for a Get-
Notifications request that a Notification Recipient makes
after the job completes, but before the Event Life
expires. See section 10.1.
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client-error-not-found: The Printer has no Subscription
Object's whose "notify-subscription-id" attribute equals
any of the values of the "notify-subscription-ids"
operation attribute supplied or the identified
Subscription Object does not contain the "notify-pull-
method" attribute with the 'ippget' keyword value.
server-error-busy: The Printer is too busy to accept this
operation. The Printer SHOULD return the "notify-get-
interval" operation attribute in the Operation Attributes
of the response, then the Notification Recipient SHOULD
wait for the number of seconds specified by the "notify-
get-interval" operation attribute before performing this
operation again. If the "notify-get-interval" Operation
Attribute is not present, the Notification Recipient
SHOULD use the normal network back-off algorithms for
determining when to perform this operation again.
Natural Language and Character Set:
The "attributes-charset" and "attributes-natural-language"
attributes as described in [RFC2911] section 3.1.4.2.
The Printer MUST use the values of "notify-charset" and
"notify-natural-language", respectively, from one Subscription
Object associated with the Event Notifications in this
response.
Normally, there is only one matched Subscription Object, or the
value of the "notify-charset" and "notify-natural-language"
attributes is the same in all Subscription Objects. If not,
the Printer MUST pick one Subscription Object from which to
obtain the value of these attributes. The algorithm for
picking the Subscription Object is implementation dependent.
The choice of natural language is not critical because 'text'
and 'name' values can override the "attributes-natural-
language" operation attribute. The Printer's choice of charset
is critical because a bad choice may leave it unable to send
some 'text' and 'name' values accurately.
5.2.1 notify-get-interval (integer(0:MAX))
The value of this operation attribute is the number of seconds
that the Notification Recipient SHOULD wait before trying the
Get-Notifications operation again. The Printer MUST return
this operation attribute if: (1) it is too busy to return
events, (2) the Notification Recipient client did not request
Event Wait Mode, or (3) the Printer is terminating Event Wait
Mode. The client MUST accept this attribute and SHOULD re-
issue the Get-Notifications operation (with or without "notify-
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wait" = 'true') the indicated number of seconds in the future
in order to get more Event Notifications This value is
intended to help the client be a good network citizen.
The value of this attribute MUST be at least as large as the
value of the Printer's "ippget-event-life" Printer Description
attribute (see section 8.1). The Printer MAY return a value
that is larger than the value of the "ippget-event-life"
Printer Description attribute provided that the Printer
increases the Event Life for this Subscription object, so that
Notification Recipients taking account of the larger value and
polling with a longer interval will not miss events. Note;
implementing such an algorithm requires some hidden attributes
in the Subscription object that are IMPLEMENTATION DEPENDENT.
If the Printer wants to remain in Event Wait Mode, then the
Printer MUST NOT return this attribute in the response.
Here is a complete table of combinations of "notify-wait",
"status-code", "notify-get-interval", and Event Notification
Attributes Groups for Get-Notification initial (Wait and No
Wait) Responses and subsequent Event Wait Mode Responses (which
may be staying in Event Wait Mode or may be requesting the
Notification Recipient to leave Event Wait Mode):
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Table 2 - Combinations of "notify-wait", "status-code", and "notify-
get-interval"
client sends: Printer returns: Printer Event
returns: Notification
"notify-wait" "status-code" "notify-get- Attribute
interval" Groups
1. 'false'* 'successful-ok' MUST return N maybe
2. 'false'* 'not-found' MUST NOT MUST NOT
3. 'false'* 'busy' MUST return N MUST NOT
4. 'false'* 'events- MUST NOT 'job-
complete' completed'
5. 'true' 'successful-ok' MUST NOT MUST
6. 'true' 'successful-ok' MUST return N maybe
7. 'true' 'not-found' MUST NOT MUST NOT
8. 'true' 'busy' MUST return N MUST NOT
9. 'true' 'events- MUST NOT 'job-
complete' completed' or
maybe other
* 'false' or client omits the "notify-wait" attribute.
Explanation:
1-4: client does not request Event Wait Mode
5-9: client requests Event Wait Mode
2,7: Subscription object not found, or was canceled earlier;
client should NOT try again.
3,8: server busy, tells client to try later; client should try
again in N seconds.
4: client polled after job completed, but before Event Life
expired, and got the 'job-completed' event, so the client
shouldn't bother trying again; client should NOT try again
later.
5: Printer returns one or more Event Notifications and is OK
to stay in Event Wait Mode; the client waits for more Event
Notifications to be returned.
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6: Printer wants to leave Event Wait mode. Can happen on the
first response (with or without Event Notifications) or happen
on a subsequent response with or without Event Notifications;
the client SHOULD try again in N seconds.
9: Printer either (1) returns 'job-completed' event or (2) the
Subscription Object was canceled by either a Cancel-Job or a
Per-Printer Subscription expired without being renewed. For
case (1), at least one Event Notification MUST be returned,
while for case (2), it is unlikely that any Event Notifications
are returned; the client should NOT try again.
5.2.2 printer-up-time (integer(1:MAX))
The value of this attribute is the Printer's "printer-up-time"
attribute at the time the Printer sends this response. The
Printer MUST return this attribute. Because each Event
Notification also contains the value of this attribute when the
event occurred, the value of this attribute lets a Notification
Recipient know when each Event Notification occurred relative
to the time of this response.
Group 2: Unsupported Attributes
See [RFC2911] section 3.1.7 for details on returning
Unsupported Attributes.
Group 3 through N: Event Notification Attributes
The Printer responds with one Event Notification Attributes
Group per matched Event Notification. The entire response is
considered a single Compound Event Notification (see [ipp-
ntfy]). The matched Event Notifications are all un-expired
Event Notification associated with the matched Subscription
Objects and MUST follow the "Event Notification Ordering"
requirements for Event Notifications within a Compound Event
Notification specified in [ipp-ntfy] section 9. In other
words, the Printer MUST order these Event Notification groups
in ascending time stamp (and sequence number) order for a
Subscription object. If Event Notifications for multiple
Subscription objects are being returned, the Notification
Events for the next Subscription object follow in ascending
time stamp order, etc.
Each Event Notification Group MUST contain all of attributes
specified in section 9.1 ("Content of Machine Consumable Event
Notifications") of [ipp-ntfy] with exceptions denoted by
asterisks in the tables below.
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The tables below are copies of the tables in section 9.1
("Content of Machine Consumable Event Notifications") of [ipp-
ntfy] except that each cell in the "Sends" column is a "MUST".
If more than one Event Notification is being returned and the
status of each is not the same, then the Printer MUST return a
"notify-status-code" attribute in each Event Notification
Attributes group to indicate the differing status values.
For an Event Notification for all Events, the Printer includes
the attributes shown in Table 3.
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Table 3 - Attributes in Event Notification Content
Source Value Sends Source
Object
notify-subscription-id (integer(1:MAX)) MUST Subscription
notify-printer-uri (uri) MUST Subscription
notify-subscribed-event (type2 keyword) MUST Event
Notification
printer-up-time (integer(1:MAX)) * MUST Printer
printer-current-time (dateTime) MUST ** Printer
notify-sequence-number (integer (0:MAX)) MUST Subscription
notify-charset (charset) MUST Subscription
notify-natural-language (naturalLanguage) MUST Subscription
notify-user-data (octetString(63)) MUST *** Subscription
notify-text (text) MUST Event
Notification
attributes from the "notify-attributes" MUST **** Printer
attribute
attributes from the "notify-attributes" MUST **** Job
attribute
attributes from the "notify-attributes" MUST **** Subscription
attribute
* As specified in [ipp-ntfy] section 9, the value of the
"printer-up-time" attribute sent in each Event Notification
MUST be the time at which the Event occurred, not the time at
which the Event Notification was sent.
** The Printer MUST send the "printer-current-time" attribute
if and only if it supports the "printer-current-time" attribute
on the Printer object.
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*** If the associated Subscription Object does not contain a
"notify-user-data" attribute, the Printer MUST send an octet-
string of length 0.
**** If the "notify-attributes" attribute is present on the
Subscription Object, the Printer MUST send all attributes
specified by the "notify-attributes" attribute. Note: if the
Printer doesn't support the "notify-attributes" attribute, it
is not present on the associated Subscription Object.
For Event Notifications for Job Events, the Printer includes
the additional attributes shown in Table 4.
Table 4 - Additional Attributes in Event Notification Content for
Job Events
Source Value Sends Source
Object
job-id (integer(1:MAX)) MUST Job
job-state (type1 enum) MUST Job
job-state-reasons (1setOf type2 keyword) MUST Job
job-impressions-completed (integer(0:MAX)) MUST * Job
* The Printer MUST send the "job-impressions-completed"
attribute in an Event Notification only for the combinations of
Events and Subscribed Events shown in Table 5.
Table 5 - Combinations of Events and Subscribed Events for "job-
impressions-completed"
Job Event Subscribed Job Event
'job-progress' 'job-progress'
'job-completed' 'job-completed'
'job-completed' 'job-state-changed'
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For Event Notification for Printer Events, the Printer includes
the additional attributes shown in Table 6.
Table 6 - Additional Attributes in Event Notification Content for
Printer Events
Source Value Sends Source
Object
printer-state (type1 enum) MUST Printer
printer-state-reasons (1setOf type2 keyword) MUST Printer
printer-is-accepting-jobs (boolean) MUST Printer
6 Additional Information about Subscription Template Attributes
The 'ippget' Delivery Method does not define any addition
Subscription Template attributes. The 'ippget' Delivery Method has
the same conformance requirements for Subscription Template
attributes as defined in [ipp-ntfy]. This section defines additional
information about Subscription Template attributes defined in [ipp-
ntfy].
6.1 notify-pull-method (type2 keyword)
This Subscription Template attribute identifies the Pull Delivery
Method to be used for the Subscription Object (see [ipp-ntfy]). In
order to support the 'ippget' Pull Delivery Method defined in this
document, the Printer MUST support this attribute with the following
keyword value:
'ippget': indicates that the 'ippget' Pull Delivery Method is to
be used for this Subscription Object.
7 Subscription Description Attributes
The 'ippget' Delivery Method has the same conformance requirements
for Subscription Description attributes as defined in [ipp-ntfy].
The 'ippget' Delivery Method does not define any addition
Subscription Description attributes.
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8 Additional Printer Description Attributes
This section defines additional Printer Description attributes for
use with the 'ippget' Delivery Method.
8.1 ippget-event-life (integer(15:MAX))
This Printer Description attribute specifies the Event Life value
that the Printer assigns to each Event, i.e., the number of seconds
after an Event occurs during which a Printer will return that Event
in an Event Notification in a Get-Notifications response. After the
Event Life expires for the Event, the Printer MAY no longer return an
Event Notification for that Event in a Get-Notifications response.
The Printer MUST support this attribute if it supports the 'ippget'
Delivery Method. The value MUST be 15 or more (at least 15 seconds)
and 60 (seconds) is the RECOMMENDED value to align with the PWG Job
Monitoring MIB [RFC2707] jmGeneralJobPersistence and
jmGeneralAttributePersistence objects.
For example, assume the following:
1.a client performs a Job Creation operation that creates a
Subscription Object associated with the 'ippget' Delivery
Method, AND
2.an Event associated with the new Job occurs immediately after
the Subscription Object is created, AND
3.the same client or some other client performs a Get-
Notifications operation such that the client is connected N
seconds after the Job Creation operation.
Then, if N is less than the value of this attribute, the client(s)
performing the Get-Notifications operations can expect not to miss
any Event-Notifications, barring some unforeseen lack of memory space
in the Printer. Note: The client MUST initiate the Get-
Notifications a time that is sufficiently less that N seconds to
account for network latency so that it is connected to the Printer
before N seconds elapses.
If a Printer supports the 'ippget' Delivery Method, it MUST keep
'completed', 'canceled', or 'aborted' Job objects in the Job
Retention and/or Job History phases for at least as long as this
attribute's value. The Printer MAY retain jobs longer that this
value. See [RFC2911] section 4.3.7.1 and the discussion in [ipp-
ntfy] 'job-completed' event) that explains that a Notification
Recipients can query the Job after receiving a 'job-completed' Event
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Notification in order to find out other information about the job
that is 'completed', 'aborted', or 'canceled'. However, this
attribute has no effect on the Cancel-Subscription operation which
deletes the Subscription object immediately, whether or not it
contain the "notify-pull-method" attribute with the 'ippget' keyword
value. Immediately thereafter, subsequent Get-Notifications
Responses MUST NOT contain Event Notifications associated with the
canceled Subscription object.
9 New Values for Existing Printer Description Attributes
This section defines additional values for existing Printer
Description attributes defined in [ipp-ntfy].
9.1 notify-pull-method-supported (1setOf type2 keyword)
The following keyword value for the "notify-pull-method-supported"
attribute is added in order to support the new Delivery Method
defined in this document:
'ippget' - The IPP Notification Pull Delivery Method defined in
this document.
9.2 operations-supported (1setOf type2 enum)
Table 7 lists the "operation-id" value defined in order to support
the new Get-Notifications operation defined in this document.
Table 7 - Operation-id assignments
Value Operation Name
0x001C Get-Notifications
10 New Status Codes
The following status code is defined as an extension for this
Delivery Method and is returned as the status code of the Get-
Notifications operation in Group 1 or Group 3 to N (see section 5.2).
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10.1 successful-ok-events-complete (0x0007)
The Printer MUST return the 'successful-ok-events-complete' status
code to indicate when this Get-Notifications response is the last
response for a Subscription object, whether or not there are Event
Notifications being returned. This condition occurs for Event Wait
Mode with Notification Recipients waiting for responses when the
Subscription Object is: (1) canceled with a Cancel-Subscription
operation, (2) deleted when the Per-Printer Subscription lease time
expires, or (3) when the 'job-completed' event occurs for a Per-Job
Subscription. This condition also occurs for a Get-Notifications
request that a Notification Recipient makes after the job completes,
but before the Event Life expires.
11 Encoding and Transport
This section defines the encoding and transport considerations for
this Delivery Method based on [RFC2910].
The encoding of a Get-Notifications Response is modeled the Get-Jobs
Response (see [RFC2911]). In a Get-Notifications Response, each
Event Notification Attributes Group MUST start with an 'event-
notification-attributes-tag' (see the section "Encodings of
Additional Attribute Tags" in [ipp-ntfy]), and end with an 'end-of-
attributes-tag'. In addition, for Event Wait Mode the multi-
part/related is used to separate each multiple response (in time) to
a single Get-Notifications Request.
The Printer returns Get-Notification Response as follows:
1. If the Notification Recipient client did not request Event Wait
Mode ("notify-wait" = 'false' or omitted), the Printer ends the
response with an 'end-of-attributes-tag' (see [RFC2911] Get-Jobs
encoding) as with any operation response.
2. If the Notification Recipient client requests Event Wait Mode
("notify-wait" = 'true') and the Printer wishes to honor the
request, the Printer MUST return the response as an
application/ipp part inside a multi-part/related MIME media
type. When one or more additional Events occur, the Printer
returns each as an additional Event Notification Group using a
separate application/ipp part under the multi-part/related type.
3. If the client requested Event Wait Mode ("notify-wait" =
'true'), but the Printer does not wish to honor the request in
the initial response but wants the client explicitly poll for
Event Notifications, the Printer MUST return the "notify-get-
interval" operation attribute (see section 5.2.1). The Printer
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returns the response as an application/ipp part which MAY be
inside an multi-part/related type. The client MUST accept this
response and re-issue the Get-Notifications request in the
future indicated by the value of the "notify-get-interval"
attribute value..
4. If the client requested Event Wait Mode ("notify-wait" =
'true'), and the Printer initially honored the request, but
later wishes to leave Event Wait Mode, the Printer MUST return
the "notify-get-interval" operation attribute (see section
5.2.1). The Printer returns the response as an application/ipp
part which MUST be inside an multi-part/related type.
Note: All of the above is without either the Printer or the
Notification Recipient closing the connection. In fact, the
connection SHOULD remain open for any subsequent IPP operations.
However, either the Notification Recipient or the Printer can
abnormally terminate by closing the connection. But, if the Printer
closes the connection too soon after returning the response, the
client may not receive the response.
The Printer MAY chunk the responses, but this has no significance to
the IPP semantics.
Note: While HTTP/1.1 allows a proxy to collect chunked responses
over a period of time and return them back as a single un-chunked
response (with a Content Length instead). However, in practice no
proxy wants to have an infinite buffer. Also no proxy want to hold
up responses, since user would be furious.
This notification delivery method uses the IPP transport and encoding
[RFC2910] for the Get-Notifications operation with the following
extension allocated in [ipp-ntfy]:
Table 8 - The "event-notification-attributes-tag" value
Tag Value (Hex) Meaning
0x07 "event-notification-attributes-tag"
12 Conformance Requirements
This section lists the conformance requirements for clients and
Printers.
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12.1 Conformance for IPP Printers
It is OPTIONAL for a Printer to support IPP Notifications as defined
in [ipp-ntfy]. However, if a Printer supports IPP Notifications, the
Printer MUST support the 'ippget' Delivery Method as defined in this
document as one of its Delivery Methods. IPP Printers that conform
to this specification:
1. MUST meet the conformance requirements defined in [ipp-ntfy] for
a Pull Delivery Method;
2. MUST support the Get-Notifications operation defined in section
5, including Event Wait Mode;
3. MUST support the Subscription Template object attributes as
defined in section 6;
4. MUST support the Subscription Description object attributes as
defined in section 7;
5. MUST support the "ippget-event-life" Printer Description
attribute defined in section 8.1, including retaining jobs in
the Job Retention and/or Job History phases for at least as long
as the value specified by the Printer's "ippget-event-life";
6. MUST support the additional values for IPP/1.1 Printer
Description attributes defined in section 9;
7. MUST support the 'successful-ok-events-complete' status code as
described in section 10.1;
8. MUST listen for the IPP Get-Notifications operation requests on
IANA-assigned well-known port 631, unless explicitly configured
by system administrators or site policies;
9. SHOULD NOT listen for IPP Get-Notifications operation requests
on any other port, unless explicitly configured by system
administrators or site policies.
10. MUST meet the security conformance requirements as stated in
section 17.4.
12.2 Conformance for IPP Clients
It is OPTIONAL for an IPP Client to support IPP Notifications as
defined in [ipp-ntfy]. However, if a client supports IPP
Notifications, the client MUST support the 'ippget' Delivery Method
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as defined in this document as one of its Delivery Methods. IPP
Clients that conform to this specification:
1.MUST create Subscription Objects by sending Subscription
Creation operation requests containing the "notify-pull-method"
attribute (as opposed to the "notify-recipient-uri" attribute)
using the 'ippget' keyword value (see sections 6.1 and 15.2);
2.MUST send IPP Get-Notifications operation requests (see section
5.1) via the port specified in the associated 'ipp' URL (if
present) or otherwise via IANA assigned well-known port 631;
3.MUST convert the associated 'ipp' URLs for use in IPP Get-
Notifications operation to their corresponding 'http' URL forms
for use in the HTTP layer according to the rules in section 5
"IPP URL Scheme" in [RFC2910].
4.MUST meet the security conformance requirements as stated in
section 17.5.
13 Normative References
[ipp-ntfy]
Herriot, R., and T. Hastings, "Internet Printing Protocol/1.1: IPP
Event Notifications and Subscriptions", <draft-ietf-ipp-not-spec-
10.txt>, September 10, 2002.
[RFC2119]
S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119 , March 1997
[RFC2910]
Herriot, R., Butler, S., Moore, P., and R. Tuner, "Internet
Printing Protocol/1.1: Encoding and Transport", RFC 2910, September
2000.
[RFC2911]
deBry, R., Hastings, T., Herriot, R., Isaacson, S., and P. Powell,
"Internet Printing Protocol/1.1: Model and Semantics", RFC 2911,
September 2000.
14 Informative References
[notify-req]
Hastings, T., deBry, R., and H. Lewis, "Internet Printing Protocol
(IPP): Requirements for IPP Notifications", <draft-ietf-ipp-not-
06.txt>, work in progress, July 17, 2001.
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[RFC2565]
Herriot, R., Butler, S., Moore, P., and R. Turner, "Internet
Printing Protocol/1.0: Encoding and Transport", RFC 2565, April
1999.
[RFC2566]
R. deBry, T. Hastings, R. Herriot, S. Isaacson, and P. Powell,
"Internet Printing Protocol/1.0: Model and Semantics", RFC 2566,
April 1999.
[RFC2567]
Wright, D., "Design Goals for an Internet Printing Protocol", RFC
2567, April 1999.
[RFC2568]
Zilles, S., "Rationale for the Structure and Model and Protocol for
the Internet Printing Protocol", RFC 2568, April 1999.
[RFC2569]
Herriot, R., Hastings, T., Jacobs, N., Martin, J., "Mapping between
LPD and IPP Protocols", RFC 2569, April 1999.
[RFC2616]
R. Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P.
Leach, T. Berners-Lee, "Hypertext Transfer Protocol - HTTP/1.1",
RFC 2616, June 1999.
[RFC2707]
Bergman, R., Hastings, T., Isaacson, S., and H. Lewis, "Job
Monitoring MIB - V1.0", November 1999.
[RFC3196]
Hastings, T., Manros, C., Zehler, P., Kugler, C., and H. Holst,
"Internet Printing Protocol/1.1: Implementer's Guide", RFC3196,
November 2001.
15 IANA Considerations
This section contains the exact information for IANA to add to the
IPP Registries according to the procedures defined in RFC 2911
[RFC2911] section 6. The resulting registrations will be published
in the http://www.iana.org/assignments/ipp-registrations registry.
Note to RFC Editors: Replace RFC NNNN below with the RFC number
for this document, so that it accurately reflects the content of
the information for the IANA Registry.
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15.1 Attribute Registrations
The following table lists the attributes defined in this document.
This is to be registered according to the procedures in RFC 2911
[RFC2911] section 6.2.
Printer Description attributes: Ref. Section:
ippget-event-life (integer(15:MAX)) RFC NNNN 8.1
15.2 Additional keyword attribute value registrations for existing
attributes
This section lists additional keyword attribute value registrations
for use with existing attributes defined in other documents. These
are to be registered according to the procedures in RFC 2911
[RFC2911] section 6.1.
keyword Attribute Values: Ref. Section:
notify-pull-method (type2 keyword) [ipp-ntfy] 5.3.2
notify-pull-method-supported (1setOf type2 keyword)
[ipp-ntfy] 5.3.2.1
ippget RFC NNNN 9.1
15.3 Additional enum attribute values
The following table lists the enum attribute values defined in this
document. These are to be registered according to the procedures in
RFC 2911 [RFC2911] section 6.1.
Attribute
Value Name Reference Section
------ ----------------------------- --------- -------
operations-supported (type2 enum) RFC2911 4.4.15
0x001C Get-Notifications RFC NNNN 9.2
15.4 Operation Registrations
The following table lists the operations defined in this document.
This is to be registered according to the procedures in RFC 2911
[RFC2911] section 6.4.
Operations: Ref. Section:
Get-Notifications operation RFC NNNN 5
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15.5 Status code Registrations
The following table lists the status codes defined in this document.
This is to be registered according to the procedures in RFC 2911
[RFC2911] section 6.6.
Status codes: Ref. Section:
successful-ok-events-complete (0x0007) RFC NNNN 10.1
16 Internationalization Considerations
The IPP Printer MUST localize the "notify-text" attribute as
specified in section 14 of [ipp-ntfy].
In addition, when the client receives the Get-Notifications response,
it is expected to localize the attributes that have the 'keyword'
attribute syntax according to the charset and natural language
requested in the Get-Notifications request.
17 Security Considerations
The IPP Model and Semantics document [RFC2911 section 8] discusses
high-level security requirements (Client Authentication, Server
Authentication and Operation Privacy). The IPP Transport and
Encoding document [RFC2910 section 8] discusses the security
requirements for the IPP protocol. Client Authentication is the
mechanism by which the client proves its identity to the server in a
secure manner. Server Authentication is the mechanism by which the
server proves its identity to the client in a secure manner.
Operation Privacy is defined as a mechanism for protecting operations
from eavesdropping.
The 'ippget' Delivery Method with its Get-Notifications operations
leverages the security mechanism that are used in IPP/1.1 [RFC2910
and RFC2911] without adding any additional security mechanisms in
order to maintain the same security support as IPP/1.1.
The access control model for the Get-Notifications operation defined
in this document is the same as the access control model for the Get-
Job-Attributes operation (see [RFC2911] section 3.2.6). The primary
difference is that a Get-Notifications operation is directed at
Subscription Objects rather than at Job objects, and a returned
attribute group contains Event Notification attributes rather than
Job object attributes.
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17.1 Notification Recipient client access rights
The Notification Recipient client MUST have the following access
rights to the Subscription object(s) targeted by the Get-
Notifications operation request:
The authenticated user (see [RFC2911] section 8.3) performing this
operation MUST be (1) the owner of each Subscription Object
identified by the "notify-subscription-ids" operation attribute
(see section 5.1.1), (2) an operator or administrator of the
Printer (see [RFC2911] Sections 1 and 8.5), or (3) be otherwise
authorized by the Printer's administrator-configured security
policy to request Event Notifications from the target Subscription
Object(s). Furthermore, the Printer's security policy MAY limit
the attributes returned by the Get-Notifications operation, in a
manner similar to the Get-Job-Attributes operation (see [RFC2911]
end of section 3.3.4.2).
17.2 Printer security threats
Because the Get-Notifications operation is sent in the same direction
as Job Creation operations, usually by the same client, this Event
Notification Delivery Method poses no additional authentication,
authorization, privacy, firewall, or port assignment issues above
those for the IPP Get-Job-Attributes and Get-Printer-Attributes
operations (see [RFC2911] sections 3.2.6 and 3.2.5).
17.3 Notification Recipient security threats
Unwanted Events Notifications (spam): Unlike Push Event Notification
Delivery Methods in which the IPP Printer initiates the Event
Notification, with the Pull Delivery Method defined in this document,
the Notification Recipient is the client who initiates the Get-
Notifications operation (see section 5). Therefore, there is no
chance of "spam" notifications with this method.
Note: when a client stays connected to a Printer using the Event
Wait Mode (see section 5.1.3) in order to receive Event Notifications
as they occur, such a client can close down the IPP connection at any
time, and so can avoid future unwanted Event Notifications at any
time.
It is true that client has control about whether to ask for Event
Notifications. However, if the client subscribes to an event, and
does a Get-Notifications request, the client gets all events for the
Subscription Object in the sequence number range (see section 5.1.2),
not just the ones the client wants. If a client subscribes to a Per-
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Printer Subscription job event, such as 'job-completed', and someone
then starts and cancels thousands of jobs, the client would have to
receive these events in addition to the ones the client is interested
in. A client can protect itself better by subscribing to his own
jobs using a Per-Job Subscription, rather than creating a Per-Printer
subscription whose Job events apply to all jobs.
17.4 Security requirements for Printers
For the Get-Notifications operation defined in this document, the
same Printer conformance requirements apply for supporting and using
Client Authentication, Server Authentication and Operation Privacy as
stated in [RFC2910] section 8 for all IPP operations.
17.5 Security requirements for clients
For the Get-Notifications operation defined in this document, the
same client conformance requirements apply for supporting and using
Client Authentication, Server Authentication and Operation Privacy as
stated in [RFC2910] section 8 for all IPP operations.
18 Contributors
Carl Kugler and Harry Lewis contributed the basic idea of in-band
"smart polling" coupled with multiple responses for a single
operation on the same connection, one response for each event as it
occurs. Without their continual persuasion, we would not have
arrived at this Delivery Method specification and would not have been
able to agree on a single REQUIRED Delivery Method for IPP.
Carl Kugler
IBM
P.O. Box 1900
Boulder, CO 80301-9191
Phone:
Fax:
e-mail: kugler@us.ibm.com
19 Authors' Addresses
Robert Herriot
706 Colorado Ave.
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Palo Alto, CA 94303
Phone: 650-327-4466
Fax: 650-327-4466
email: bob@herriot.com
Thomas N. Hastings
Xerox Corporation
737 Hawaii St. ESAE 231
El Segundo CA 90245
Phone: 310-333-6413
Fax: 310-333-5514
email: hastings@cp10.es.xerox.com
Harry Lewis
IBM
P.O. Box 1900
Boulder, CO 80301-9191
Phone: 303-924-5337
FAX:
e-mail: harryl@us.ibm.com
IPP Web Page: http://www.pwg.org/ipp/
IPP Mailing List: ipp@pwg.org
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Implementers of this specification document are encouraged to join
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20 Description of Base IPP documents (Informative)
The base set of IPP documents includes:
Design Goals for an Internet Printing Protocol [RFC2567]
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Rationale for the Structure and Model and Protocol for the Internet
Printing Protocol [RFC2568]
Internet Printing Protocol/1.1: Model and Semantics [RFC2911]
Internet Printing Protocol/1.1: Encoding and Transport [RFC2910]
Internet Printing Protocol/1.1: Implementer's Guide [RFC3196]
Mapping between LPD and IPP Protocols [RFC2569]
The "Design Goals for an Internet Printing Protocol" document takes a
broad look at distributed printing functionality, and it enumerates
real-life scenarios that help to clarify the features that need to be
included in a printing protocol for the Internet. It identifies
requirements for three types of users: end users, operators, and
administrators. It calls out a subset of end user requirements that
are satisfied in IPP/1.0. A few OPTIONAL operator operations have
been added to IPP/1.1.
The "Rationale for the Structure and Model and Protocol for the
Internet Printing Protocol" document describes IPP from a high level
view, defines a roadmap for the various documents that form the suite
of IPP specification documents, and gives background and rationale
for the IETF working group's major decisions.
The "Internet Printing Protocol/1.1: Model and Semantics" document
describes a simplified model with abstract objects, their attributes,
and their operations that are independent of encoding and transport.
It introduces a Printer and a Job object. The Job object optionally
supports multiple documents per Job. It also addresses security,
internationalization, and directory issues.
The "Internet Printing Protocol/1.1: Encoding and Transport" document
is a formal mapping of the abstract operations and attributes defined
in the model document onto HTTP/1.1 [RFC2616]. It defines the
encoding rules for a new Internet MIME media type called
"application/ipp". This document also defines the rules for
transporting over HTTP a message body whose Content-Type is
"application/ipp". This document defines the 'ipp' scheme for
identifying IPP printers and jobs.
The "Internet Printing Protocol/1.1: Implementer's Guide" document
gives insight and advice to implementers of IPP clients and IPP
objects. It is intended to help them understand IPP/1.1 and some of
the considerations that may assist them in the design of their client
and/or IPP object implementations. For example, a typical order of
processing requests is given, including error checking. Motivation
for some of the specification decisions is also included.
The "Mapping between LPD and IPP Protocols" document gives some
advice to implementers of gateways between IPP and LPD (Line Printer
Daemon) implementations.
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21 Full Copyright Statement
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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