SIMPLE B. Campbell
Internet-Draft dynamicsoft
Expires: August 25, 2003 S. Olson
Microsoft
J. Peterson
NeuStar, Inc.
J. Rosenberg
dynamicsoft
B. Stucker
Nortel Networks, Inc.
February 24, 2003
SIMPLE Presence Publication Mechanism
draft-ietf-simple-publish-00
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on August 25, 2003.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes an extension to the Session Initiation
Protocol (SIP) [1]. The purpose of this extension to create a means
for publishing event state used within the framework for SIP Event
Notification (RFC3265 [2]). The first application of this extension
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is targeted at the publication of presence information as defined by
the SIMPLE [7] working group.
1. Introduction
This document describes a mechanism for event publication in SIP that
satisfies the requirements set forward in the SIMPLE publication
requirements [4]. A new SIP method, the PUBLISH method, is defined
by this document.
The method described in this document allows presence 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.
1.1 Why a new SIP method?
In order to satisfy the requirements necessary for publishing event
state to an event agent, different SIP protocol elements were
evaluated, namely REGISTER and SUBSCRIBE/NOTIFY.
REGISTER solves the problem of publishing the set of contacts for a
given address of record. However, the more general requirements of
publishing event state to an event agent call for a different
solution. Event agents (consumers of published event state) may
exist anywhere in the network. With REGISTER, the sole consumer of
the data being published is the registrar. For presence publication,
there may be more than one event agent that is interested in the
published event state. The inability to fork REGISTERs prevents
this. As such, the routing requirements for published event state
(e.g. a presence document) cannot be covered by the mechanisms
available to us through the REGISTER method.
We already have a mechanism for publishing event state throughout the
network: SUBSCRIBE/NOTIFY. The subscription mechanism exists to
allow a device to assert interest in a piece of state. Typically it
is used to allow potentially multiple subscribers to watch a piece of
state, where the state agent could not be expected to know in advance
all the potential watchers for this state and where the set of
watchers changes over time. The desired publication mechanism has a
different goal: publishing event state to a small number of locations
which are known in advance. The target of the publication request is
known in advance while the source of those publication requests are
not. SUBSCRIBE/NOTIFY cannot easily solve the problem at hand.
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As such, we are left with one option, to create a new method to
support publication of event state to a set of possibly unknown (in a
routing sense) event agents, who may or may not have expressed prior
interest in receiving said data: the PUBLISH method.
1.2 Publication Classes
The sources that are publishing event state can be subdivided into
classes. These classes are a logical subdivision that allows
composition policy to treat different kinds of inputs in different
manners. In some circumstances, the classes may be arbitrary,
ephemeral and without fixed semantic value. In others, the classes
may be well defined, persistent and even standardized. Examples of
the latter might include classifications such as: geolocation
publishers, mobile devices, automatons or PDAs. The publisher will
indicate its publication class as part of the publication process.
The compositor is free to use or ignore this information in
conjunction with its local policy for compositing the many inputs it
receives.
The publication class names are completely arbitrary, and there may
be any number of inputs of any class. We envision that there will be
a number of common classes that may be standardized, as well as a
number of application specific classes. We will need a mechanism to
avoid publication class name collisions.
There is a temptation to associate the idea of class with a tuple ID
in the CPIM PIDF document. However, the tuple ID has no semantics
(although some examples in early versions of the PIDF document used
the tuple ID incorrectly in this fashion). Moreover, other
composition applications may exist where this will not work. For
example, a geolocation class might get applied across multiple
tuples.
OPEN ISSUE: Does Class overlap with work in RPIDS? Should we look
to presence formats to provide their own class identifiers for
status or tuple elements?
1.3 Correlating Publications from Multiple Sources
It is sometimes desirable to indicate the specific instance of a
publication class that is publishing event state. This instance is
intended to be a correlation identifier which is unique and
consistent across multiple publications from the same source. This
serves a similar purpose to the local or remote tag in a SIP dialog.
For example, a presentity might have multiple PUAs that act as "user"
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inputs. The compositor might have policy to combine the state from
each user PUA into the composite document. But if the same PUA
publishes again, the policy may involve replacing the previous
published state of that particular PUA. Doing so requires some
manner of correlation identifier (publisher instance). The
correlation ID is highly dynamic, and should be globally unique for
any associated group of publications.
There is a temptation too have the correlation ID derive from the
authentication credentials of a publisher. But there may be
applications where each PUA publishes using the credentials of the
presentity. This could mean that multiple PUAs would publish with
the same credentials.
The PUBLISH method looks to the presence format to provide globally-
unique identifiers for particular segments of presence that are in a
single stream of publication. In PIDF, this would be the tuple ID.
Note that presence formats must also supply a way of ordering
presence information (for example, the timestamp element in PIDF).
1.4 Publication to Multiple Destinations
Just as the publication class and publication instance are used to
categorize and differentiate the publication source, there is a need
to categorize and differentiate the publication "destination". The
compositor may then apply policy on behalf of the publisher to limit,
transform, or otherwise constrain the composite event state which
various watchers may receive from the PA. Some amount of metadata is
required that aids in the decisions about composition and
dissemination of event state.
For example, a given publisher may wish to publish geolocation
information in varying degrees of fidelity. The most trusted
watchers of that event state should receive the highest fidelity
information. Less trusted, perhaps anonymous, watchers should
receive a more restricted view of the composite state. A wide range
of authorization policies can be built around this concept. To meet
this requirement, the publisher might publish several versions of the
event state, each somehow marked with a different identifier
indicating the destination grouping of the state, or somehow instruct
a presence agent to change event state before distributing it to
various destinations.
There is work underway in the SIMPLE working group on a general way
to provide authorization instructions to a presence agent regarding
the distribution of presence information (see the SIMPLE data
manipulation [5] mechanism). Publishers should use this
authorization mechanism to manage the selective distribution of
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presence information.
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].
3. The PUBLISH method
The PUBLISH method is used to push data to a set of event agents that
may or may not consume the data being published. The method is
constructed as an OPTIONS request would be, and is allowed to fork.
The Request-URI of the PUBLISH identifies the resource for whom this
data is being published. As such, the sender of a PUBLISH may not
know all of the endpoints that processed the request successfully,
but will know if at least one endpoint accepted the request by way of
the forking rules for isomorphic requests within SIP.
A PUBLISH request MAY contain a body, using the standard MIME headers
to identify the content. The typical PUBLISH request will contain a
body with the event state to publish. The absence of a body in a
PUBLISH request may have the semantics of clearing the event state
for this publication instance depending on the policy at the
compositor.
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 SIP [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 -
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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
Class R 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 *
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
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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
3.1 Request-URI
The Request-URI, as previously stated, for a PUBLISH identifies the
resource for which the published event state is intended. For
example, if we were to take the case of presence, then the Request-
URI, and the To could begin as the well known address of the
presentity for whom we are publishing a fragment of their presence
document.
OPEN ISSUE: Is this actually what we want to do? Or is a
compositor's URI is the correct destination of a PUBLISH request?
3.2 Class (Publication Class) Header
As part of the presence publication model that PUBLISH belongs to,
the document that is being published may become part of a larger
composite document consisting of multiple parts. This is not to be
confused with multipart MIME, however. An example of this would be a
presence document that spans several devices for which each presence
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tuple could be considered a "part" of the overall presence document.
The exact definition of what entails a recognizable portion of the
overall document being published is left entirely up to the semantics
of the content type being operated on.
The reverse may also be true, in that we may wish to publish a single
piece of data, which the event agent compositor is expected to apply
to multiple components of a composite document.
Because of this, simply identifying the resource party (TO) for which
the data is intended may be insufficient in order to correctly
process the document or document fragment being published. The Class
(publication class) header is used to denote a token for which the
published content is to be applied. Multiple tokens may be denoted
in the Class header, each being separated by a comma. This is an
optional header. In the absence of a Class header, the compositor
may use local policy to determine an appropriate class to sort the
publication information into.
Class = "Class" HCOLON (token *(COMMA token))
Example:
Class: geoloc, mobile
3.3 Expires Header
The event state that is published through the PUBLISH method to a
compositor/event agent is soft-state. As such, the PUBLISH SHOULD
contain an expiration value for the event state data it is
publishing. The intention is to inform the compositor of the
expected duration of this event state. This is a separate concern
from informing the watchers of this event state of the duration of
the composite state.
The publication state expiration should be carried through the
standard Expires: header as defined in RFC3261. The value of this
expiration may be decreased by the compositor from the expiration
given by the publisher, but SHOULD NOT be increased. The final
response to the PUBLISH request MUST carry the expiration value
chosen by the compositor in an Expires: header. In the absence of an
Expires: header, the compositor is free to choose a reasonable
default. It is RECOMMENDED that a default of 3600 seconds or one
hour be used. The default expiration may vary from event package to
event package depending on the semantics of the particular package.
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When the event state expires, the publisher MAY choose to refresh the
publication state by sending another PUBLISH request. When the event
state expires, the compositor should apply local policy to determine
the new composite event state based on the removal or expiration of
this particular publication input. This will typically result in the
generation of new notifications for the watchers of the composite
event state.
3.4 Event Header
Every PUBLISH request MUST contain an Event: header indicating the
event package for which this publication is carrying event state. In
the absence of an Event: header, the compositor MUST return a 489 Bad
Event response. The publish mechanism described in this document is
only intended to be applied to state associated with an event
package. This is the rationale behind requiring the presence of an
Event: header.
When presence information is sent in a PUBLISH method, the 'presence'
event is specified. When a compositor that supports presence sends a
489 Bad Event response, it MUST indicate that it supports the
'presence' event.
3.5 PUBLISH and Presence Formats
All SIP implementations that support the PUBLISH method, and use the
'presence' event, MUST implement the Presence Information Data Format
(PIDF [6]) as a MIME body type that can be sent in a PUBLISH method.
If a compositor does not support the presence format provided by a
publisher, it MUST return a 415 Unsupported Media Type with an Accept
header listing the presence formats it does support (including
'application/cpim-pidf+xml', the media type of PIDF).
4. Examples of Use
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, and has previously subscribed
successfully.
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PUA PA WATCHER
| | |
| | <---- 1. SUBSCRIBE ---- |
| | |
| | ----- 200 OK ------> |
| | |
| | ----- 2. NOTIFY ------> |
| | |
| | <---- 200 OK ------- |
| | |
| ---- 3. PUBLISH ----> | |
| | |
| <--- 4. 200 OK ------ | |
| | |
| | ----- 5. NOTIFY ------> |
| | |
| | <---- 200 OK ------- |
| | |
Message flow:
1. The watcher initiates a new subscription to the
presentity@domain.com's presence agent.
2. The presence agent for presentity@domain.com processes the
subscription request and creates a new subscription. In order to
complete the process the presence agent sends the watcher a
NOTIFY with the current presence state of the presentity.
3. 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.
4. The presence agent receives, and accepts the presence
information. The published data is incorporated into the
presentity's presence document.
5. 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.
Messages:
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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
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:watcher@domain.com>
Expires: 3600
Content-Length: 0
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NOTIFY sip:presentity@domain.com SIP/2.0
Via: SIP/2.0/UDP presence.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="j599ab8xx">
<status>
<basic>open</basic>
</status>
</tuple>
<tuple id="pl813rt4yh">
<status>
<basic>open</basic>
</status>
</tuple>
</presence>
SIP/2.0 200 OK
Via: SIP/2.0/UDP presence.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
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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: 12345678@pua.domain.com
CSeq: 1 PUBLISH
Expires: 3600
Event: presence
Class: mobile
Stream: 1@pua.domain.com
Facet: <sip:watcher@domain.com>
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="j599ab8xx">
<status>
<basic>closed</basic>
</status>
</tuple>
</presence>
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: 12345678@pua.domain.com
CSeq: 1 PUBLISH
Expires: 1800
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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=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="j599ab8xx">
<status>
<basic>closed</basic>
</status>
</tuple>
<tuple id="pl813rt4yh">
<status>
<basic>open</basic>
</status>
</tuple>
</presence>
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
5. IANA Considerations
This document introduces no considerations for the IANA.
6. Security Considerations
Like all SIP entities, implementations of the PUBLISH method MUST
meet all of the security implementation requirements of RFC3261
26.3.1.
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A presence compositor should use the standard SIP security mechanisms
to authenticate publishing user agents, and may apply authorization
policies for the distribution of presence information (following the
model described by SIMPLE data manipulation [5]). The composition
model makes no assumptions that all input sources for a compositor
are on the same network, or in the same administrative domain.
The compositor 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 compositor can help limit
refreshes of event state. Additional throttling and debounce logic
at the compositor is advisable to further reduce the notification
traffic produced as a result of a PUBLISH method.
The Class header can factor heavily into policy at the compositor.
For this reason, it is important to protect the integrity and
potentially the privacy of the PUBLISH headers. It is recommended
that appropriate SIP integrity and privacy measures be used be
employed by publishers and compositors.
Normative References
[1] Rosenberg, J., Schulzrinne, Camarillo, Johnston, Peterson,
Sparks, Handley and 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", RFC 2119, March 1997.
[4] Campbell, B., Olson, S., Peterson, J., Rosenberg, J. and B.
Stucker, "SIP Presence Publication Mechanism Requirements",
draft-ietf-simple-publish-reqs-00 (work in progress), February
2003.
[5] Rosenberg, J. and M. Isomaki, "Requirements for Manipulation of
Data Elements in SIMPLE Systems", draft-ietf-simple-data-reqs-00
(work in progress), October 2002.
[6] 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-05 (work in
progress), May 2002.
[7] <http://www.ietf.org/html.charters/simple-charter.html>
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Authors' Addresses
Ben Campbell
dynamicsoft
5100 Tennyson Parkway
Suite 1200
Plano, TX 75025
US
EMail: bcampbell@dynamicsoft.com
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
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Brian Stucker
Nortel Networks, Inc.
2380 Performance Drive
Richardson, TX 75082
US
EMail: bstucker@nortelnetworks.com
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