SIMPLE B. Campbell
Internet-Draft dynamicsoft
Expires: August 28, 2003 S. Olson
Microsoft
J. Peterson
NeuStar, Inc.
J. Rosenberg
dynamicsoft
B. Stucker
Nortel Networks, Inc.
February 27, 2003
SIMPLE Presence Publication Mechanism
draft-olson-simple-publish-02
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on August 28, 2003.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes an extension to the Session Initiation
Protocol (SIP) for publishing event state used within the framework
for SIP Event Notification. The first application of this extension
is targeted at the publication of presence information.
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The method described in this document allows event information to be
published to a presence agent on behalf of a user. This method can
be extended to support publication of other event state, but it is
not intended to be a general-purpose mechanism for transport of
arbitrary data as there are better suited mechanisms for this purpose
(ftp, http, etc.) This method is intended to be a simple,
light-weight mechanism that employs SIP in order to support SIMPLE
services.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
3. Constructing the PUBLISH Request . . . . . . . . . . . . . 6
4. Requirements of the body of a PUBLISH request . . . . . . 8
5. Creating Initial Publication Soft-State . . . . . . . . . 9
6. Setting the Expiration Interval of Event State . . . . . . 10
7. Removing Event State . . . . . . . . . . . . . . . . . . . 11
8. Querying the Current Event State . . . . . . . . . . . . . 12
9. Refreshing Event State . . . . . . . . . . . . . . . . . . 13
10. Processing PUBLISH Requests . . . . . . . . . . . . . . . 14
11. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 17
11.1 New Method . . . . . . . . . . . . . . . . . . . . . . . . 17
11.2 New Response Code . . . . . . . . . . . . . . . . . . . . 18
11.2.1 "494 Out Of Sync" Response Code . . . . . . . . . . . . . 19
12. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 20
13. IANA Considerations . . . . . . . . . . . . . . . . . . . 28
14. Security Considerations . . . . . . . . . . . . . . . . . 29
15. Open Issues . . . . . . . . . . . . . . . . . . . . . . . 30
Normative References . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 31
Intellectual Property and Copyright Statements . . . . . . 33
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1. Introduction
The focus of this specification is to provide a framework for the
publication of event state from a UA to a entity that is responsible
for compositing this event state and distributing that state to
interested parties through the SUBSCRIBE/NOTIFY mechanism. This
specification fills a current gap in the event notification framework
to allow for a client to push its state to the state agent that acts
on its behalf. It is the intention of this framework to allow any
event state for which there is an appropriate event package (as
defined in RFC 3265 [2]) to be published.
The first application of this mechanism is the publication of
presence state by a PUA to a presence compositor which has a tightly
coupled relationship to the PA. The requirements and model for
presence publication are documented in [4]. This specification will
address each of these requirments.
To accomplish this task a new SIP method, PUBLISH, is defined.
PUBLISH is analogous to REGISTER in that it allows a UA to add,
modify, and remove state in another entity which manages this state
on behalf of a user. The user may in turn have multiple UAs or
endpoints. Each endpoint may publish its own unique state and
through a subscription to that event discover the event state of the
other endpoints for a user. PUBLISH is defined to create soft-state
in the state agent; this state has a defined lifetime and will expire
after a negotiated amount of time. Local policy at the compositor
may in turn define hard-state for this event package. That is, the
steady-state of this event package in the absence of any other
soft-state provided through the PUBLISH method. In the generic
sense, a UAC which publishes event state is labelled an Event
Publication Agent (EPA). For presence in particular, this is the
familiar PUA role as defined in [7]. The entity which processes the
PUBLISH request is known as a Event State Compositor (ESC). For
presence in particular, this is the familiar PA role.
Event state publication inherently involves at least two parties: the
source of the publication and the target of the publication. The
source of the publication is naturally represented as an
address-of-record (AOR). For some types of event state, namely
presence, the target of the publication may not sufficiently be
represented by an address-of-record (AOR) alone. Rather, the target
is a combination of both an AOR and a unique identifier which acts to
represent one of N possible sections of an overall event state for
that AOR. In this specification, these sections are referred to as
event state segments. In the context of presence publication, the
event state segment is nothing more than the presence tuple
associated with the presentity (AOR). It is the role of the
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compositor to aggregate these segments into a complete event state
which is presented to the subscribers of that event state. This
composition logic is a matter of local policy. For some event
packages, there is no natural decomposition of event state into these
segments and for these packages, an AOR is sufficient to identify the
target of the publish.
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [3].
In addition to the terminology of RFC 3265 [2], this document
introduces some new concepts:
Event Publication Agent (EPA): The UAC which issues a PUBLISH
request to publish event state.
Event State Compositor (ESC): The UAS which processes PUBLISH
requests and composites the event state. It is assumed that there
is a tight coupling between the ESC which receives the PUBLISH
requests and the state agent which issues appropriate NOTIFY
requests based on this change in event state. The interface
between these two components is out-of-scope for this
specification.
Event State Segment: The EPA may publish event state that is
divided into individual segments. For the presence publication
case, these segments are the individual tuples in the presence
document. In the generic case, this document will refer to these
segments as event state segments.
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3. Constructing the PUBLISH Request
PUBLISH requests create, remove, and modify event state. A PUBLISH
request can create new event state in the state agent, associating
this event state with an address-of-record and optionally with a
unique identifier for segments of event state being published.
Publication on behalf of a particular address-of-record may also be
performed by a suitably authorized third party. To determine the
current published state for a particular address-of-record, the
client MAY create a subscription for this address-of-record and event
package using the SUBSCRIBE/NOTIFY mechanism of RFC3265.
Note that in the case the event state is segmented, each segment
logically represents an independent publication that may be added,
removed, modified, and expired separately. For presence publication,
this means each tuple in the PIDF document in the PUBLISH request is
logically a separate publication that may be manipulated
independently even though they are grouped together in the same PIDF
document initially.
Except as noted, the construction of the PUBLISH request and the
behavior of clients sending a PUBLISH request is identical to the
general UAC behavior described in Section 8.1 and Section 17.1 of RFC
3261 [1].
A PUBLISH request does not establish a dialog. A UAC MAY include a
Route header field in a PUBLISH request based on a pre-existing route
set as described in Section 8.1 of RFC3261. The Record-Route header
field has no meaning in PUBLISH requests or responses, and MUST be
ignored if present. In particular, the UAC MUST NOT create a new
route set based on the presence or absence of a Record-Route header
field in any response to a PUBLISH request. The PUBLISH request MUST
NOT contain a Contact header.
The following header fields MUST be included in a PUBLISH request:
Request-URI: The Request-URI initially contains the address-of-record
whose publication is to be created, removed, or modified. Unlike
the REGISTER request, the Request-URI SHOULD contain a SIP(S) URI
with a username. The address-of-record MUST be a SIP URI or SIPS
URI.
To: The To header field contains the address of record whose
publication is to be created, removed, or modified. The To header
field and the Request-URI field are typically the same. This
address-of-record MUST be a SIP URI or SIPS URI.
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From: The From header field contains the address-of-record of the
person responsible for the publication. The value is the same as
the To header field unless the request is a third- party
publication.
Call-ID: All publications from an EPA MAY use the same Call-ID header
field value for publications sent to a particular state agent.
CSeq: An EPA MUST increment the CSeq value by one for each PUBLISH
request with the same Call-ID. Unlike REGISTER requests, the
Call-ID and CSeq are not directly used for ordering of PUBLISH
requests.
Event: PUBLISH requests MUST contain a single Event header field.
This value indicates the event package which this request is
publishing state for.
Expires: PUBLISH requests SHOULD contain a single Expires header
field. This value indicates the lifetime of the event state being
published by this request. A special value of "0" indicates the
removal of any prior soft-state established by a prior PUBLISH
request from this UAC.
The body of the PUBLISH request contains the event state that the
client wishes to publish. The content format and semantics are
dependent on the event package identified in the Event header. Any
event package which makes use of the PUBLISH mechanism MUST describe
these semantics and MUST prescribe a default, mandatory to implement
format. This document defines the semantics of the presence
publication requests (event package "presence") when the CPIM PIDF
[5] presence document format is used.
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4. Requirements of the body of a PUBLISH request
In order to satisfy the requirements of [4], the body of the PUBLISH
request must fulfill several requirements as well. Any application
of the PUBLISH mechanism for a given event package MUST support a
Content-Type which fulfills these requirements. For presence
publication, it will be demonstrated how these requirements may be
fulfilled using the CPIM PIDF presence format in [5] within a PUBLISH
request. A PUA which uses PUBLISH to publish presence state to the
PA MUST support the CPIM PIDF presence format.
The content type MUST provide a way to indicate an ordering of
publication requests. For example, the timestamp element in PIDF
provides a temporal ordering of presence state changes that allows
the Event State Compositor (ESC) to properly order PUBLISH
requests. When used as the content of a PUBLISH request, the PUA
MUST supply a timestamp element for every presence tuple present
in the PIDF document.
The content type MUST provide a way to publish partial state for
an event package. The intention is to allow each device or client
for an address-of-record to publish event state independently. To
accomplish this, the event state that is published by these
devices must be allowed to be only a portion of the complete state
that the state agent advertises for that AOR. For example, a PUA
can publish presence state for just a subset of the tuples that
may be composited into the presence document that watchers receive
in a NOTIFY. The mechanism by which the ESC aggregates this
information is a matter of local policy.
If the content type allows for event state segments to be
represented, the content type MUST provide a means to uniquely
identify each unique segment. For example, the CPIM PIDF presence
document provides a tuple ID to distinguish the segments of the
presence document associated with the encompassing presentity.
As with any other SIP message, the PUBLISH mechanism MAY use the
content indirection mechanism defined in [6]. There are no
additional requirements or restrictions on content indirection as
applied to the PUBLISH request. Content indirection is a useful
mechanism for communicating large event state information that cannot
be carried directly within the SIP signaling (PUBLISH request).
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5. Creating Initial Publication Soft-State
The PUBLISH request created by the EPA and sent to the Event State
Compositor (ESC) establishes soft-state in the state agent for the
event package indicated in the request and bound to the
address-of-record in the To header of the request. Additionally, the
PUBLISH request may publish event state that is further sub-divided
into segments of event state that may be manipulated independently.
As an example, presence publication using the CPIM PIDF format may
manipulate individual tuples related to a common presentity.
Once the initial PUBLISH request has been processed by the ESC, the
EPA MAY send subsequent PUBLISH requests to refresh, modify, or
delete the publication state established by the first PUBLISH
request. These operations will be described in subsequent sections.
EPAs MUST NOT send a new PUBLISH request (not a re-transmission)
until they have received a final response from the state agent for
the previous one or the previous PUBLISH request has timed out.
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6. Setting the Expiration Interval of Event State
When a client sends a PUBLISH request, it SHOULD suggest an
expiration interval that indicates how long the client would like the
publication to be valid. The actual duration of the soft state is
defined by local policy at the ESC. The expiration value is
presented in the Expires header of the PUBLISH request. If an
Expires header is not present, the client is indicating its desire
for the server to choose. It is RECOMMENDED that the PA use a value
of 3600 seconds (1 hour) for this default expiration value in the
case of presence publication. The default value is generally event
package specific.
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7. Removing Event State
PUBLISH establishes soft state which expires unless refreshed. This
event state may also be explicitly removed. A UA requests the
immediate removal of event state by specifying an Expires value of
"0" in the PUBLISH request. Such a request SHOULD NOT contain any
body. UAs which support PUBLISH SHOULD support this mechanism for
explicitly removing event state.
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8. Querying the Current Event State
The response to a PUBLISH request indicates whether the request was
successful or not. In general, the body of a such response will be
empty unless the event package defines explicit meaning for such a
body. There is no such meaning for a response to a presence
publication when the document format used is CPIM PIDF.
To query the event state that the state agent in fact publishes, the
client may SUBSCRIBE to the event package for which it has sent a
PUBLISH, indicating the same address-of-record in the To header. An
Expires header value of "0" may be used in this SUBSCRIBE request to
do a one-time fetch of this event state as defined in RFC3265.
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9. Refreshing Event State
Each EPA is responsible for refreshing the publications that it has
previously established. An EPA MAY choose to refresh the publication
established by another EPA for the same address-of-record. The
authorization policy of the ESC.
The 200 (OK) response from the state agent MUST contain an Expires
header indicating the expiration time interval for the publication.
The EPA then issues a PUBLISH request for each of its publications
before the expiration interval has elapsed.
If an EPA receives a 423 (Interval Too Brief) response to a PUBLISH
request, it MAY retry the publication after changing the expiration
interval in the Expires header to be equal to or greater than the
expiration interval within the Min-Expires header field of the
423(Interval Too Brief) response.
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10. Processing PUBLISH Requests
The Event State Compositor (ESC) is a UAS that responds to PUBLISH
requests and maintains a list of publications for a given
address-of-record. The ESC MUST ignore the Record-Route header field
if it is included in a PUBLISH request. The ESC MUST NOT include a
Record-Route header field in any response to a PUBLISH request.
The ESC has to know (for example, through configuration) the set of
domain(s) for which it maintains event state. PUBLISH requests MUST
be processed in the order that they are received. PUBLISH requests
MUST also be processed atomically, meaning that a particular PUBLISH
request is either processed completely or not at all.
When receiving a PUBLISH request, the ESC follows these steps:
1. The ESC inspects the Request-URI to determine whether this
request is for a domain supported by the ESC. If not, the ESC
SHOULD proxy the request to the addressed domain.
2. To guarantee that the ESC supports any necessary extensions, the
ESC MUST process the Require header field values as described for
UASs in Section 8.2.2 of RFC3261.
3. An ESC SHOULD authenticate the UAC. Mechanisms for the
authentication of SIP user agents are described in Section 22 of
RFC3261.
4. The ESC SHOULD determine if the authenticated user is authorized
to publish for this address-of-record. If the authenticated user
is not authorized to publish, the ESC MUST return a 403
(Forbidden). This authorization may take into account 3rd party
publication of event state.
5. The ESC extracts the address-of-record from the To header field
of the request. If the address-of-record is not valid for the
domain in the Request-URI, the ESC MUST send a 404 (Not Found)
response and skip the remaining steps. The URI MUST then be
converted to a canonical form. To do that, all URI parameters
MUST be removed (including the user-param), and any escaped
characters MUST be converted to their unescaped form. The result
serves as an index into the list of publications.
6. The ESC examines the Event header of the PUBLISH request. If the
Event header is missing or contains an event package which the
ESC does not support, the ESC MUST respond to the PUBLISH request
with a 489 (Bad Event) response.
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7. The ESC now processes the Expires header value from the PUBLISH
request.
* If the request has an Expires header field, that value MUST be
taken as the requested expiration.
* Else, a locally-configured default value MUST be taken as the
requested expiration.
* The ESC MAY choose an expiration less than the requested
expiration interval. If and only if the requested expiration
interval is greater than zero AND less than a ESC-configured
minimum, the ESC MAY reject the publication with a response of
423 (Interval Too Brief). This response MUST contain a
Min-Expires header field that states the minimum expiration
interval the ESC is willing to honor. It then skips the
remaining steps.
8. The ESC may then process the body of the PUBLISH request (the
actual event state)
* For each publication, the ESC will record the target of the
publication (To URI), the source of the publication (From
URI), and the version of the publication. This version
information must be present in the body of the PUBLISH
request. In the presence publication application, this
information will come from the timestamp element associated
with each presence tuple.
* If the version of the event state present in the PUBLISH
request is older than the current version known by the ESC,
the ESC MUST return a 494 (Out of Sync) response and MUST NOT
update the event state for this AOR. This is to handle
out-of-order or stale PUBLISH requests. To recover from this
error, the client SHOULD determine the current version of the
event state at the server by sending a SUBSCRIBE request to
the server and re-issue the PUBLISH request if the event state
changes again.
* The processing of the PUBLISH request must be atomic. If
internal errors (such as the inability to access a back-end
database) occur before processing is complete, no portion of
the PUBLISH document must be published and the ESC MUST fail
with a 500 (Server Error) response.
9. The ESC returns a 200 (OK) response. The response MUST contain
an Expires header indicating the expiration interval chosen by
the ESC. The state agent associated with this ESC may then issue
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appropriate NOTIFY requests to any watchers of this event state.
The timing between the receipt of the PUBLISH request and the
issuance of NOTIFY requests is implementation dependent and may
vary according to throttling policies at the state agent.
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11. Syntax
11.1 New Method
The following is the BNF definition for the PUBLISH method. As with
all other SIP methods, the method name is case sensitive.
PUBLISHm = %x50.55.42.4C.49.53.48 ; PUBLISH in caps.
Tables 1 and 2 extend Tables 2 and 3 of RFC 3261 [1] by adding an
additional column, defining the header fields that can be used in
PUBLISH requests and responses.
Header Field where proxy PUBLISH
__________________________________________
Accept R -
Accept 2xx -
Accept 415 m*
Accept-Encoding R -
Accept-Encoding 2xx -
Accept-Encoding 415 m*
Accept-Language R -
Accept-Language 2xx -
Accept-Language 415 m*
Alert-Info R -
Alert-Info 180 -
Allow R o
Allow 2xx o
Allow r o
Allow 405 m
Authentication-Info 2xx o
Authorization R o
Call-ID c r m
Call-Info ar o
Contact R -
Contact 1xx -
Contact 2xx -
Contact 3xx o
Contact 485 o
Content-Disposition o
Content-Encoding o
Content-Language o
Content-Length ar t
Content-Type *
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CSeq c r m
Date a o
Event a m
Error-Info 300-699 a o
Expires o
From c r m
In-Reply-To R o
Max-Forwards R amr m
Organization ar o
Table 1: Summary of header fields, A--O
Header Field where proxy PUBLISH
__________________________________________
Priority R ar o
Proxy-Authenticate 407 ar m
Proxy-Authenticate 401 ar o
Proxy-Authorization R dr o
Proxy-Require R ar o
Record-Route ar -
Reply-To o
Require ar c
Retry-After 404,413,480,486 o
500,503 o
600,603 o
Route R adr o
Server r o
Subject R o
Timestamp o
To c(1) r m
Unsupported 420 o
User-Agent o
Via R amr m
Via rc dr m
Warning r o
WWW-Authenticate 401 ar m
WWW-Authenticate 407 ar o
Table 2: Summary of header fields, P--Z
11.2 New Response Code
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11.2.1 "494 Out Of Sync" Response Code
The 494 event response is added to the "Client-Error" header field
definition. "494 Out of Sync" is used to indicate that the server
detected that the event state that the client is trying to publish is
out of sync (stale) relative to the event state that the server has.
The version information in the PUBLISH body is older than the version
information that the server maintains for the corresponding event and
AOR.
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12. Examples
The following section shows an example of the usage of the PUBLISH
method in the case of publishing the presence document from a
presence user agent to a presence agent. The watcher in this case is
watching the PUA's presentity. The PUA will SUBSCRIBE to its own
presence to see the composite presence state exposed by the PA. This
is an optional but likely step for the PUA.
PUA PA WATCHER
(EPA) (ESC)
| | |
| | <---- M1: SUBSCRIBE --- |
| | |
| | ----- M2: 200 OK -----> |
| | |
| | ----- M3: NOTIFY -----> |
| | |
| | <---- M4: 200 OK ------ |
| | |
| --- M5: SUBSCRIBE --> | |
| | |
|<--- M6: 200 OK --> | |
| | |
|<--- M7: NOTIFY ----- | |
| | |
| --- M8: 200 OK --> | |
| | |
| --- M9: PUBLISH ----> | |
| | |
| <-- M10: 200 OK ---- | |
| | |
| | ----- M11: NOTIFY ----> |
| | |
| | <---- M12: 200 OK ----- |
| | |
| | |
|<---- M13: NOTIFY ---- | |
| | |
|----- M14: 200 OK --> | |
| | |
Message flow:
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M1: The watcher initiates a new subscription to the
presentity@domain.com's presence agent.
SUBSCRIBE sip:presentity@domain.com SIP/2.0
Via: SIP/2.0/UDP 10.0.0.1:5060;branch=z9hG4bKnashds7
To: <sip:presentity@domain.com>
From: <sip:watcher@domain.com>;tag=12341234
Call-ID: 12345678@10.0.0.1
CSeq: 1 SUBSCRIBE
Expires: 3600
Event: presence
Contact: <sip:watcher@domain.com>
Content-Length: 0
M2: The presence agent for presentity@domain.com processes the
subscription request and creates a new subscription. A 200 (OK)
response is sent to confirm the subscription.
SIP/2.0 200 OK
Via: SIP/2.0/UDP 10.0.0.1:5060;branch=z9hG4bKnashds7
To: <sip:presentity@domain.com>;tag=abcd1234
From: <sip:watcher@domain.com>;tag=12341234
Call-ID: 12345678@10.0.0.1
CSeq: 1 SUBSCRIBE
Contact: <sip:pa@domain.com>
Expires: 3600
Content-Length: 0
M3: In order to complete the process, the presence agent sends the
watcher a NOTIFY with the current presence state of the
presentity.
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NOTIFY sip:presentity@domain.com SIP/2.0
Via: SIP/2.0/UDP pa.domain.com;branch=z9hG4bK8sdf2
To: <sip:watcher@domain.com>;tag=12341234
From: <sip:presentity@domain.com>;tag=abcd1234
Call-ID: 12345678@10.0.0.1
CSeq: 1 NOTIFY
Event: presence
Subscription-State: active; expires=3599
Content-Type: application/cpim-pidf+xml
Content-Length: ...
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
entity="pres:presentity@domain.com">
<tuple id="mobile-phone">
<status>
<basic>open</basic>
</status>
<timestamp>2003-02-01T16:49:29Z</timestamp>
</tuple>
<tuple id="desktop">
<status>
<basic>open</basic>
</status>
<timestamp>2003-02-01T12:21:29Z</timestamp>
</tuple>
</presence>
M4: The watcher confirms receipt of the NOTIFY request.
SIP/2.0 200 OK
Via: SIP/2.0/UDP pa.domain.com;branch=z9hG4bK8sdf2
To: <sip:watcher@domain.com>;tag=12341234
From: <sip:presentity@domain.com>;tag=abcd1234
Call-ID: 12345678@10.0.0.1
CSeq: 1 NOTIFY
Contact: <sip:watcher@domain.com>
M5: To view its composite presence state, the PUA issues a SUBSCRIBE
to the PA for itself.
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SUBSCRIBE sip:presentity@domain.com SIP/2.0
Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bKjjsdfj
To: <sip:presentity@domain.com>
From: <sip:presentity@domain.com>;tag=43214321
Call-ID: 87654321@10.0.0.2
CSeq: 1 SUBSCRIBE
Expires: 3600
Event: presence
Contact: <sip:pua@domain.com>
Content-Length: 0
M6: The presence agent for presentity@domain.com processes the
subscription request and creates a new subscription. A 200 (OK)
response is sent to confirm the subscription.
SIP/2.0 200 OK
Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bKjjsdfj
To: <sip:presentity@domain.com>;tag=abcd1235
From: <sip:watcher@domain.com>;tag=43214321
Call-ID: 87654321@10.0.0.2
CSeq: 1 SUBSCRIBE
Contact: <sip:pa@domain.com>
Expires: 3600
Content-Length: 0
M7: In order to complete the process, the presence agent sends the
PUA a NOTIFY with the current presence state of the presentity.
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NOTIFY sip:presentity@domain.com SIP/2.0
Via: SIP/2.0/UDP pa.domain.com;branch=z9hG4bK8sdfk
To: <sip:watcher@domain.com>;tag=abcd1235
From: <sip:presentity@domain.com>;tag=43214321
Call-ID: 87654321@10.0.0.2
CSeq: 1 NOTIFY
Event: presence
Subscription-State: active; expires=3599
Content-Type: application/cpim-pidf+xml
Content-Length: ...
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
entity="pres:presentity@domain.com">
<tuple id="mobile-phone">
<status>
<basic>open</basic>
</status>
<timestamp>2003-02-01T16:49:29Z</timestamp>
</tuple>
<tuple id="desktop">
<status>
<basic>open</basic>
</status>
<timestamp>2003-02-01T12:21:29Z</timestamp>
</tuple>
</presence>
M9: A presence user agent for the presentity detects a change in the
user's presence state. It initiates a PUBLISH to the presentity's
presence agent in order to update it with the new presence
information. The timestamp element is updated to indicate the
time of the change. The Expires header indicates the desired
duration of this soft-state. The "entity" attribute of the
presence element in the PIDF document matches the To AOR.
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PUBLISH sip:presentity@domain.com SIP/2.0
Via: SIP/2.0/UDP pua.domain.com;branch=z9hG4bK652hsge
To: <sip:presentity@domain.com>;tag=1a2b3c4d
From: <sip:presentity@domain.com>;tag=1234wxyz
Call-ID: 81818181@pua.domain.com
CSeq: 1 PUBLISH
Expires: 3600
Event: presence
Content-Type: application/cpim-pidf+xml
Content-Length: ...
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
entity="pres:presentity@domain.com">
<tuple id="mobile-phone">
<status>
<basic>closed</basic>
</status>
<timestamp>2003-02-01T17:00:19Z</timestamp>
</tuple>
</presence>
M10: The presence agent receives, and accepts the presence
information. The published data is incorporated into the
presentity's presence document. A 200 (OK) response is sent to
confirm the publication.
SIP/2.0 200 OK
Via: SIP/2.0/UDP pua.domain.com;branch=z9hG4bK652hsge
To: <sip:presentity@domain.com>;tag=1a2b3c4d
From: <sip:presentity@domain.com>;tag=1234wxyz
Call-ID: 81818181@pua.domain.com
CSeq: 1 PUBLISH
Expires: 1800
M11: The presence agent determines that a reportable change has been
made to the presentity's presence document, and sends another
notification to those watching the presentity to update their
information regarding the presentity's current presence status.
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NOTIFY sip:presentity@domain.com SIP/2.0
Via: SIP/2.0/UDP presence.domain.com;branch=z9hG4bK4cd42a
To: <sip:watcher@domain.com>;tag=12341234
From: <sip:presentity@domain.com>;tag=abcd1234
Call-ID: 12345678@10.0.0.1
CSeq: 2 NOTIFY
Event: presence
Subscription-State: active; expires=3400
Content-Type: application/cpim-pidf+xml
Content-Length: ...
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
entity="pres:presentity@domain.com">
<tuple id="mobile-phone">
<status>
<basic>closed</basic>
</status>
<timestamp>2003-02-01T17:00:19Z</timestamp>
</tuple>
<tuple id="desktop">
<status>
<basic>open</basic>
</status>
<timestamp>2003-02-01T12:21:29Z</timestamp>
</tuple>
</presence>
M12: The watcher confirms receipt of the NOTIFY request.
SIP/2.0 200 OK
Via: SIP/2.0/UDP presence.domain.com;branch=z9hG4bK4cd42a
To: <sip:watcher@domain.com>;tag=12341234
From: <sip:presentity@domain.com>;tag=abcd1234
Call-ID: 12345678@10.0.0.1
CSeq: 2 NOTIFY
Content-Length: 0
M13: The presence agent also sends a NOTIFY to the PUA.
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NOTIFY sip:presentity@domain.com SIP/2.0
Via: SIP/2.0/UDP presence.domain.com;branch=z9hG4bK4cd42b
To: <sip:watcher@domain.com>;tag=abcd1235
From: <sip:presentity@domain.com>;tag=43214321
Call-ID: 87654321@10.0.0.2
CSeq: 2 NOTIFY
Event: presence
Subscription-State: active; expires=3400
Content-Type: application/cpim-pidf+xml
Content-Length: ...
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
entity="pres:presentity@domain.com">
<tuple id="mobile-phone">
<status>
<basic>closed</basic>
</status>
<timestamp>2003-02-01T17:00:19Z</timestamp>
</tuple>
<tuple id="desktop">
<status>
<basic>open</basic>
</status>
<timestamp>2003-02-01T12:21:29Z</timestamp>
</tuple>
</presence>
M14: The PUA confirms receipt of the NOTIFY request.
SIP/2.0 200 OK
Via: SIP/2.0/UDP presence.domain.com;branch=z9hG4bK4cd42b
To: <sip:watcher@domain.com>;tag=abcd1235
From: <sip:presentity@domain.com>;tag=43214321
Call-ID: 87654321@10.0.0.2
CSeq: 2 NOTIFY
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13. IANA Considerations
This document registers a new response code. This response code is
defined by the following information, which is to be added to the
method and response-code sub-registry under http://www.iana.org/
assignments/sip-parameters. Response Code Number: 494 Default
Reason Phrase: Out Of Sync
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14. Security Considerations
The state agent SHOULD authenticate the Event Publication Agent
(EPA), and SHOULD apply authorization policies. The composition
model makes no assumptions that all input sources for a compositor
(ESC) are on the same network, or in the same administrative domain.
The ESC should throttle incoming publications and the corresponding
notifications resulting from the changes in event state. As a first
step, careful selection of default Expires: values for the supported
event packages at a ESC can help limit refreshes of event state.
Additional throttling and debounce logic at the ESC is advisable to
further reduce the notification traffic produced as a result of a
PUBLISH method.
Integrity protection and privacy of the PUBLISH requests can be
ensured using the S/MIME mechanisms outlined in section 23 of
RFC3261. Integrity protection of the To, From, Call-ID, CSeq, Event,
Route, and Expires headers should be done at a minimum.
If the ESC receives a PUBLISH request which is integrity protected
using a security association that is not with the ESC (for example,
end-to-end S/MIME integrity protection), the state agent coupled with
the ESC MUST NOT modify the event state before exposing it to the
watchers of this event state in a NOTIFY request(s). This is to
preserve the end-to-end integrity of the event state.
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15. Open Issues
o Should the version information of the publication request be
carried explicitly in a header of the request, or is sufficient to
rely on the body for this information?
o Should the segments of event state (presence tuples) be sent in
separate PUBLISH requests or is it enough to treat these as
implicitly separate publication requests?
o Should the PUBLISH mechanism be overloaded to publish
authorization information (ACLs) for the event state as well?
o Does end-to-end S/MIME integrity protection make sense when an
event compositor is used?
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Normative References
[1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[2] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[4] Campbell, Olson, Peterson, Rosenberg and Stucker, "SIMPLE
Presence Publication Requirements",
draft-ietf-simple-publish-reqs-00 (work in progress), February
2003.
[5] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A. and W. Carr,
"Common Presence and Instant Messaging (CPIM) Presence
Information Data Format", draft-ietf-impp-cpim-pidf-07 (work in
progress), May 2002.
[6] Olson, "A Mechanism for Content Indirection in SIP Messages",
draft-olson-sip-content-indirect-mech-01 (work in progress),
August 2002.
[7] Rosenberg, "A Presence Event Package for the Session Initiation
Protocol (SIP)", draft-ietf-simple-presence-10 (work in
progress), January 2003.
Authors' Addresses
Ben Campbell
dynamicsoft
5100 Tennyson Parkway
Suite 1200
Plano, TX 75025
US
EMail: bcampbell@dynamicsoft.com
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Sean Olson
Microsoft
One Microsoft Way
Redmond, WA 98052
US
Phone: +1-425-707-2846
EMail: seanol@microsoft.com
URI: http://www.microsoft.com/rtc
Jon Peterson
NeuStar, Inc.
1800 Sutter St
Suite 570
Concord, CA 94520
US
Phone: +1-925-363-8720
EMail: jon.peterson@neustar.biz
URI: http://www.neustar.biz
Jonathan Rosenberg
dynamicsoft
72 Eagle Rock Avenue
First Floor
East Hanover, NJ 07936
US
EMail: jdrosen@dynamicsoft.com
Brian Stucker
Nortel Networks, Inc.
2380 Performance Drive
Richardson, TX 75082
US
EMail: bstucker@nortelnetworks.com
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgement
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