SIP WG A. Niemi, Ed.
Internet-Draft Nokia
Expires: April 23, 2004 October 24, 2003
Session Initiation Protocol (SIP) Extension for Event State
Publication
draft-ietf-sip-publish-01
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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.
The mechanism described in this document can be extended to support
publication of any event state, for which there exists an appropriate
event package. 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.)
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Definitions and Document Conventions . . . . . . . . . . . . 4
3. Overall Operation . . . . . . . . . . . . . . . . . . . . . 5
4. Considerations for Event Packages using PUBLISH . . . . . . 6
4.1 PUBLISH Bodies . . . . . . . . . . . . . . . . . . . . . . . 6
4.2 PUBLISH Response Bodies . . . . . . . . . . . . . . . . . . 6
4.3 Partial Event State . . . . . . . . . . . . . . . . . . . . 6
4.4 Default Expiration of PUBLISH . . . . . . . . . . . . . . . 7
5. Constructing PUBLISH Requests . . . . . . . . . . . . . . . 7
5.1 Identification of Published Event State . . . . . . . . . . 8
5.2 Creating Initial Publication . . . . . . . . . . . . . . . . 8
5.3 Setting the Expiration Interval . . . . . . . . . . . . . . 9
5.4 Refreshing Event State . . . . . . . . . . . . . . . . . . . 9
5.5 Modifying Event State . . . . . . . . . . . . . . . . . . . 10
5.6 Removing Event State . . . . . . . . . . . . . . . . . . . . 10
5.7 Querying the Current Event State . . . . . . . . . . . . . . 11
5.8 Error Responses . . . . . . . . . . . . . . . . . . . . . . 11
6. Processing PUBLISH Requests . . . . . . . . . . . . . . . . 11
7. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1 New Methods . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1.1 PUBLISH Method . . . . . . . . . . . . . . . . . . . . . . . 14
7.2 New Response Codes . . . . . . . . . . . . . . . . . . . . . 17
7.2.1 "412 Precondition Failed" Response Code . . . . . . . . . . 17
7.3 New Header Fields . . . . . . . . . . . . . . . . . . . . . 17
7.3.1 "ETag" Header Field . . . . . . . . . . . . . . . . . . . . 18
7.3.2 "If-Match" Header Field . . . . . . . . . . . . . . . . . . 18
7.4 Augmented BNF Definitions . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 18
8.1 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.2 Response Codes . . . . . . . . . . . . . . . . . . . . . . . 19
8.3 Header Field Names . . . . . . . . . . . . . . . . . . . . . 19
9. Security Considerations . . . . . . . . . . . . . . . . . . 19
9.1 Access Control . . . . . . . . . . . . . . . . . . . . . . . 19
9.2 Denial of Service Attacks . . . . . . . . . . . . . . . . . 20
9.3 Replay Attack . . . . . . . . . . . . . . . . . . . . . . . 20
9.4 Man in the Middle Attacks . . . . . . . . . . . . . . . . . 20
9.5 Confidentiality . . . . . . . . . . . . . . . . . . . . . . 21
10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 21
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 29
12. Document Change History . . . . . . . . . . . . . . . . . . 30
12.1 Changes since "draft-ietf-sip-publish-00" . . . . . . . . . 30
12.2 Changes since "draft-ietf-simple-publish-01" . . . . . . . . 30
12.3 Changes since "draft-ietf-simple-publish-00" . . . . . . . . 31
Normative References . . . . . . . . . . . . . . . . . . . . 32
Informative References . . . . . . . . . . . . . . . . . . . 32
Author's Address . . . . . . . . . . . . . . . . . . . . . . 33
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Intellectual Property and Copyright Statements . . . . . . . 34
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1. Introduction
The focus of this specification is to provide a framework for the
publication of event state from a user agent to an entity that is
responsible for composing this event state and distributing it to
interested parties through the SIP events [1] framework. This
specification fills a gap in the SIP events framework to allow for a
client to push its event state to the state agent that acts on its
behalf.
The first application of this mechanism is the publication of
presence state by a presence user agent to a presence compositor,
which has a tightly coupled relationship with the presence agent. The
requirements and model for presence publication are documented in
[4]. This specification will address each of those requirements.
The mechanism described in this document can be extended to support
publication of any event state, for which there exists an appropriate
event package as defined in [1]. 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 [5], HTTP [6],
etc.)
2. Definitions and Document Conventions
In addition to the definitions of RFC 3265 [1] and RFC 3261 [2], this
document introduces some new concepts:
Event State: State information for a resource, associated with an
event package and an address-of-record.
Event Publication Agent (EPA): The UAC that issues PUBLISH requests
to publish event state. For presence, this corresponds to the PUA.
Event State Compositor (ESC): The UAS that processes PUBLISH
requests, and is responsible of composing event state into a
complete, composite event state of a resource. For presence, this
corresponds to the PA.
Publication: The act of an EPA sending a PUBLISH message to an ESC to
publish event state.
Hard State: The steady-state or default event state of a resource,
which the ESC may use in the absence of, or in addition to, soft
state publications.
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Soft State: Event state published by an EPA using the PUBLISH
mechanism. A protocol element (i.e., an entity-tag) is used to
identify a specific soft state entity in the ESC. Soft state has a
defined lifetime and will expire after a negotiated amount of
time.
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] and
indicate requirement levels for compliant implementations.
Indented passages such as this one are used in this document to
provide additional information and clarifying text. They do not
contain normative protocol behavior.
3. Overall Operation
This document defines a new SIP method, PUBLISH, for publishing event
state. PUBLISH is analogous to REGISTER in that it allows a user to
create, modify, and remove state in another entity which manages this
state on behalf of the user. The user may in turn have multiple UAs
or endpoints. Each endpoint may publish its own unique state, out of
which the event agent generates the composite event state of the
resource. Through a subscription to that event package, the user is
able to discover the composite event state of all the active
endpoints.
In the generic sense, a UAC that publishes event state is labeled an
Event Publication Agent (EPA). For presence in particular, this is
the familiar PUA role as defined in [7]. The entity that processes
the PUBLISH request is known as an Event State Compositor (ESC). For
presence in particular, this is the familiar PA role as defined in
[7].
PUBLISH requests create soft state in the ESC. This state has a
defined lifetime and will expire after a negotiated amount of time,
requiring the publication to be refreshed by subsequent PUBLISH
requests. Local policy at the compositor may in turn define hard
state for a particular event package. That is, the steady-state of
this event package in the absence of, or in addition to, soft state
provided through the PUBLISH mechanism. Setting this hard state or
configuring the composer policy is out of the scope of this
specification.
Typically, the body of a PUBLISH request carries the published event
state. In the response to a PUBLISH request, the ESC assigns an
identifier to this event state. This identifier is then used by the
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EPA as a request precondition to point to that specific event state
in the subsequent PUBLISH requests that modify, refresh or remove
that event state. In case the PUBLISH request points to an expired
event state, this precondition will fail.
4. Considerations for Event Packages using PUBLISH
This section discusses several issues which should be taken into
consideration when applying the PUBLISH mechanism to event packages.
It also demonstrates how these issues are handled when using PUBLISH
for presence publication.
4.1 PUBLISH Bodies
The body of the PUBLISH request typically carries the published event
state. Any application of the PUBLISH mechanism for a given event
package MUST define what content type or types are expected in
PUBLISH requests. Each event package MUST also describe the semantics
associated with that content, and MUST prescribe a default, mandatory
to implement MIME type.
This document defines the semantics of the presence publication
requests (event package "presence") when the CPIM PIDF [8] presence
document format is used. A PUA that uses PUBLISH to publish presence
state to the PA MUST support the CPIM PIDF presence format. It MAY
support other formats.
4.2 PUBLISH Response Bodies
The response to a PUBLISH request indicates whether the request was
successful or not. In general, the body of such a response will be
empty unless the event package defines explicit meaning for such a
body.
There is no such meaning for the body of a response to a presence
publication when the document format used is CPIM PIDF.
4.3 Partial Event State
The content type MUST provide a way to publish partial state for an
event package. The intention is to allow each endpoint for an
address-of-record to publish event state independently. To accomplish
this, the event state that is published by these endpoints MUST be
allowed to be only a portion of the complete state that the state
agent advertises for that address-of-record.
Note that sources for event state other than those using the
PUBLISH mechanism are explicitly allowed. It is beyond the scope
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of this document to define such interfaces.
For presence in particular, a PUA can publish presence state for just
a subset of the tuples that may be composed 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 and
out of the scope of this specification.
4.4 Default Expiration of PUBLISH
PUBLISH requests establish soft state in the ESC which expires after
a negotiated amount of time. Each event package MUST provide a
default expiration value recommendation (SHOULD strength).
For presence publication, it is RECOMMENDED that the ESC use a
default value of 3600 seconds (1 hour) for this default expiration
value.
5. Constructing PUBLISH Requests
PUBLISH requests create, modify, and remove event state associated
with an address-of-record. A suitably authorized third party may also
perform publication on behalf of a particular address-of-record.
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 [2].
If necessary, clients may probe for the support of PUBLISH using the
OPTIONS request defined in SIP [2]. The presence of "PUBLISH" in the
"Allow" header field in a response to an OPTIONS request indicates
support for the PUBLISH method. In addition, the "Allow-Events"
header field indicates the supported event packages.
Note that it is possible for the OPTIONS request to fork, and
consequently return a response from a UA other than the ESC. In
that case, support for the PUBLISH method may not be appropriately
represented for that particular Request-URI.
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 RFC 3261 [2]. 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.
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EPAs MUST NOT send a new PUBLISH request (not a re-transmission)
until they have received a final response from the ESC for the
previous one or the previous PUBLISH request has timed out.
5.1 Identification of Published Event State
Identification of published events is provided by four pieces of
information: Request-URI, event type, and (optionally) an entity-tag
and the message body.
The Request-URI of a PUBLISH request contains enough information to
route the request to the appropriate entity per the request routing
procedures outlined in SIP [2]. It also contains enough information
to identify the resource whose event state is to be published, but
not enough information to determine the type of the published event
state.
For determining the type of the published event state, the EPA MUST
include a single Event header field in the PUBLISH requests. The
value of this header field indicates the event package, for which
this request is publishing event state.
To update previously published event state, PUBLISH requests MAY
contain a single If-Match header field identifying the specific
entity of event state that the request is refreshing, modifying or
removing. This header field MUST contain a single entity-tag provided
by the ESC in receipt of the initial publication.
The PUBLISH request MAY contain a body, which contains event state
that the client wishes to publish. The content format and semantics
are dependent on the event package identified in the Event header
field.
As with any other SIP message, the PUBLISH mechanism MAY use the
content indirection mechanism defined in [9]. 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 reasonably be
carried directly within the SIP signaling (PUBLISH request).
5.2 Creating Initial Publication
The PUBLISH request created by the EPA and sent to the ESC
establishes soft state for the event package indicated in the Event
header field of the request, and bound to the address-of-record in
the To header field of the request.
The published event state is typically carried in the body of the
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PUBLISH request.
The EPA MAY send subsequent PUBLISH requests to refresh, modify, or
remove the event state established by a prior publication. These
operations will be described in subsequent sections.
An initial PUBLISH request MUST not contain an If-Match header field.
However, if the EPA expects an appropriate, locally stored entity-tag
to still be valid, it SHOULD try to modify that event state as
described in Section 5.5, instead of submitting an initial
publication.
5.3 Setting the Expiration Interval
PUBLISH requests SHOULD contain a single Expires header field. This
value indicates the suggested lifetime of the event state being
published by this request. The actual duration of the soft state is
defined by local policy at the ESC.
For example, a reasonable implementation might maintain event
state over a short grace period even after the publication on
which it arrived has expired.
If an Expires header is not present, the EPA is indicating its desire
for the ESC to choose. The Expires header field in a 200 (OK)
response to PUBLISH indicates the actual duration for which the
PUBLISH will remain active, unless it is refreshed.
5.4 Refreshing Event State
Each EPA is responsible for refreshing the publications that it has
previously established.
The 200 (OK) response to a PUBLISH request from the ESC contains an
Expires header field indicating the expiration time interval for the
publication. To refresh its publications, the EPA issues a PUBLISH
request for each of its publications before the expiration interval
has elapsed.
Also, the 200 (OK) response to a PUBLISH request from the ESC
contains an ETag header field with a single entity-tag indicating an
identifier for the published event state. To refresh the event state,
the EPA includes the received entity-tag in an If-Match header field
of the PUBLISH request.
Note that for the EPA, the entity-tag is simply an opaque token
without any semantics associated with it.
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The If-Match header field containing an entity-tag preconditions the
PUBLISH request to refresh a specific instance of event state in the
ESC. If the entity-tag matches a valid event state in the ESC, the
refresh is successful, and the EPA receives a 200 (OK) response. If
there is no matching event state at the ESC, i.e., the event state to
be refreshed has already expired, the EPA receives a 412
(Precondition Failed) response to the PUBLISH request.
A PUBLISH request that refreshes event state SHOULD NOT contain a
body.
5.5 Modifying Event State
Modifying event state closely resembles the creation of initial event
state. But instead of establishing completely new event state in the
ESC, already existing event state is replaced with modified event
state. Typically, the modified event state is carried in the body of
the PUBLISH request.
The 200 (OK) response to a PUBLISH request from the ESC contains an
ETag header field with a single entity-tag indicating an identifier
for the published event state. To modify that event state, the EPA
includes the received entity-tag in an If-Match header field of the
PUBLISH request.
The If-Match header field containing an entity-tag preconditions the
PUBLISH request to modify a specific instance of event state in the
ESC. If the entity-tag matches a valid event state in the ESC, that
event state is replaced by the event state carried in the PUBLISH
request, and the EPA receives a 200 (OK) response. If there is no
matching event state at the ESC, i.e., the event state to be modified
has already expired, the EPA receives a 412 (Precondition Failed)
response to the PUBLISH request.
Note that the entity-tag will remain unchanged when modifying the
event state associated with it.
5.6 Removing Event State
Soft state established by the PUBLISH request will expire unless
periodically refreshed. This event state may also be explicitly
removed. An EPA can influence the expiration interval selected by the
ESC as described in Section 5.3.
An EPA requests the immediate removal of event state by specifying in
the PUBLISH request an Expires value of "0", and setting the If-Match
header field to contain the entity-tag of the event state to be
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removed.
Note that removing event state is effectively a publication
refresh suggesting an infinitesimal expiration interval.
Consequently, the refreshed event state expires immediately after
being refreshed.
A PUBLISH request that removes event state SHOULD NOT contain a body.
EPAs which support the PUBLISH method SHOULD support this mechanism
for explicitly removing event state.
5.7 Querying the Current Event State
To query the composite event state that the state agent in fact
delivers to the subscribers, 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 [1].
Note that a subscription to the event package will likely deliver
results of the event composition process of the state agent, which
may be a subset or a superset of the current published event
state.
5.8 Error Responses
If an EPA receives a 412 (Precondition Failed) response, it MUST NOT
reattempt the PUBLISH request. Instead, to publish event state, the
EPA SHOULD perform an initial publication, i.e., a PUBLISH request
without a request precondition, as described in Section 5.2.
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 field to be equal to or greater than
the expiration interval within the Min-Expires header field of the
423 (Interval Too Brief) response.
6. Processing PUBLISH Requests
The Event State Compositor (ESC) is a UAS that processes and responds
to PUBLISH requests, and maintains a list of publications for a given
address-of-record. The ESC has to know (e.g., through configuration)
the set of addresses for which it maintains event state.
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
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field in any response to a PUBLISH request.
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.
A client may probe the ESC for the support of PUBLISH using the
OPTIONS request defined in SIP [2]. In the response to such an
OPTIONS request, the ESC SHOULD include "PUBLISH" to the list of
allowed methods in the Allow header field. Also, it SHOULD list the
supported event packages in an Allow-Events header field.
The "methods" Contact header field parameter may also be used to
specifically announce support for PUBLISH messages when
registering. (See SIP Capabilities [10] for details on the
"methods" parameter).
When receiving a PUBLISH request, the ESC follows these steps:
1. The ESC inspects the Request-URI to determine whether this
request is targeted to a resource for which the ESC is
responsible for maintaining event state. If not, the ESC MUST
return a 404 (Not Found) response and skip the remaining steps.
2. To guarantee that it supports any necessary extensions, the ESC
MUST process the Require header field values as described for
UASs in Section 8.2.2 of RFC3261 [2].
3. An ESC SHOULD authenticate the EPA. Mechanisms for the
authentication of SIP user agents are described in Section 22 of
RFC3261 [2]. If no authentication mechanism is available, the ESC
MAY take the address-of-record of the From header field as the
asserted identity of the originator of the request.
4. The ESC SHOULD determine if the authenticated user is authorized
to perform event state publication for the identified by the
Request-URI. If the authenticated user is not authorized, the ESC
MUST return a 403 (Forbidden) response and skip the rest of the
remaining steps.
Note that this authorization may need to take into account
third-party publication of event state.
5. The ESC examines the Event header field of the PUBLISH request.
If the Event header field 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, and skip the
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remaining steps.
6. The ESC examines the If-Match header field of the PUBLISH request
for the presence of a request precondition.
* If the request has an If-Match header field, the ESC checks
whether the header field contains a single entity-tag. If not,
the request is invalid, and the ESC MUST return with a 400
(Invalid Request) response and skip the remaining steps.
* Else, the ESC extracts the entity-tag contained in the
If-Match header field and matches that entity-tag against all
locally stored entity-tags for this resource and event
package. If no match is found, the ESC MUST reject the
publication with a response of 412 (Precondition Failed), and
skip the remaining steps.
* If the request contains no If-Match header field, the ESC MUST
generate and store a locally unique entity-tag for identifying
the publication.
Note that the exact way in which the ESC creates the
entity-tag is a matter of local policy. One reasonable
implementation of an entity-tag is a counter which is
incremented by one each time a publication is allocated a
new entity-tag.
7. The ESC processes the Expires header field 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. Only if the requested expiration interval
is greater than zero and less than a locally-configured
minimum, the ESC MAY reject the publication with a response of
423 (Interval Too Brief), and skip the remaining steps. This
response MUST contain a Min-Expires header field that states
the minimum expiration interval the ESC is willing to honor.
8. The ESC processes the published event state, typically contained
in the body of the PUBLISH request. If the request contains no
body (when it should contain one), or the content type of the
request does not match the event package, or is not understood by
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the ESC, the ESC MUST reject the request with an appropriate
response and skip the remainder of the steps.
* For each publication, the ESC records the target of the
publication, the entity-tag identifying the publication, the
expiration value of the event state, and a pointer to the
actual event state.
* If present, the ESC stores the event state delivered in the
PUBLISH request and identified by the associated entity-tag.
* Else, the event state identified by the entity-tag is
refreshed, setting the expiration value to the chosen
expiration interval. If the chosen expiration interval has a
special value of "0", the event state identified by the
entity-tag MUST be immediately removed.
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, the publication MUST NOT
succeed, 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 response MUST also contain an ETag header identifying
the published event state. The state agent associated with this
ESC may then issue appropriate NOTIFY requests to any watchers of
this event state.
Note that the timing between the receipt of the PUBLISH
request and the issuance of NOTIFY requests is implementation
dependent and may also vary according to throttling policies
at the state agent.
7. Syntax
This section describes the syntax extensions required for event
publication in SIP. The formal syntax definitions described in this
section are expressed in the Augmented BNF format used in SIP [2],
and contain references to elements defined therein.
7.1 New Methods
7.1.1 PUBLISH Method
"PUBLISH" is added to the definition of the element "Method" in the
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SIP message grammar. As with all other SIP methods, the method name
is case sensitive. PUBLISH is used to publish event state to an
entity responsible for composing this event state.
Table 1 and Table 2 extend Tables 2 and 3 of RFC 3261 [2] by adding
an additional column, defining the header fields that can be used in
PUBLISH requests and responses.
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+---------------------+---------+---------+
| Header Field | where | 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 | | - |
| Allow | R | o |
| Allow | 2xx | o |
| Allow | r | o |
| Allow | 405 | m |
| Allow-Events | R | o |
| Allow-Events | 489 | m |
| Authentication-Info | 2xx | o |
| Authorization | R | o |
| Call-ID | c | m |
| Call-Info | | o |
| Contact | R | - |
| Contact | 1xx | - |
| Contact | 2xx | - |
| Contact | 3xx | o |
| Contact | 485 | o |
| Content-Disposition | | o |
| Content-Encoding | | o |
| Content-Language | | o |
| Content-Length | | t |
| Content-Type | | * |
| CSeq | c | m |
| Date | | o |
| Event | R | m |
| Error-Info | 300-699 | o |
| Expires | | o |
| Expires | 2xx | m |
| From | c | m |
| In-Reply-To | R | - |
| Max-Forwards | R | m |
| Min-Expires | 423 | m |
| MIME-Version | | o |
| Organization | | o |
+---------------------+---------+---------+
Table 1: Summary of header fields, A--O
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+---------------------+-----------------+---------+
| Header Field | where | PUBLISH |
+---------------------+-----------------+---------+
| Priority | R | o |
| Proxy-Authenticate | 407 | m |
| Proxy-Authenticate | 401 | o |
| Proxy-Authorization | R | o |
| Proxy-Require | R | o |
| Record-Route | | - |
| Reply-To | | - |
| Require | | o |
| Retry-After | 404,413,480,486 | o |
| Retry-After | 500,503 | o |
| Retry-After | 600,603 | o |
| Route | R | c |
| Server | r | o |
| Subject | R | o |
| Supported | R | o |
| Supported | 2xx | o |
| Timestamp | | o |
| To | c(1) | m |
| Unsupported | 420 | o |
| User-Agent | | o |
| Via | R | m |
| Via | rc | m |
| Warning | r | o |
| WWW-Authenticate | 401 | m |
| WWW-Authenticate | 407 | o |
+---------------------+-----------------+---------+
Table 2: Summary of header fields, P--Z
7.2 New Response Codes
7.2.1 "412 Precondition Failed" Response Code
The 412 (Precondition Failed) response is added to the "Client-Error"
header field definition. 412 (Precondition Failed) is used to
indicate that the precondition given for the request has failed.
7.3 New Header Fields
Table 3 expands on Table 2 in SIP [2], as amended by the changes in
Section 7.1.
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+--------------+-----+-----+----+----+----+----+----+----+-----+
| Header Field | whr | prx | AC | BY | CA | IN | OP | RE | PUB |
+--------------+-----+-----+----+----+----+----+----+----+-----+
| ETag | 2xx | | - | - | - | - | - | - | m |
| If-Match | R | | - | - | - | - | - | - | o |
+--------------+-----+-----+----+----+----+----+----+----+-----+
Table 3: Summary of header fields, A--O
7.3.1 "ETag" Header Field
ETag is added to the definition of the element "general-header" in
the SIP message grammar. Usage of this header is described in Section
6.
7.3.2 "If-Match" Header Field
If-Match is added to the definition of the element "general-header"
in the SIP message grammar. Usage of this header is described in
Section 5.
7.4 Augmented BNF Definitions
This section describes the Augmented BNF definitions for the various
new and modified syntax elements. The notation is as used in SIP [2]
and the documents to which it refers.
PUBLISHm = %x50.55.42.4C.49.53.48 ; PUBLISH in caps.
extension-method = PUBLISHm / token
ETag = "ETag" HCOLON entity-tag
If-Match = "If-Match" HCOLON entity-tag
entity-tag = token
8. IANA Considerations
This document registers a new method name, a new response code and
two new header field names.
8.1 Methods
This document registers a new SIP method, 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.
Method Name: PUBLISH
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Reference: [RFCYYYY]
(Note to RFC Editor: Replace YYYY with the RFC number of this
document when published).
8.2 Response Codes
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: 412
Default Reason Phrase: Precondition Failed
8.3 Header Field Names
This document registers two new SIP header field names. These headers
are defined by the following information, which is to be added to the
header sub-registry under http://www.iana.org/assignments/
sip-parameters.
Header Name: ETag
Compact Form: (none)
Header Name: If-Match
Compact Form: (none)
9. Security Considerations
9.1 Access Control
Since event state may be considered sensitive information, the ESC
should have the ability to selectively accept publications from
authorized sources only, based on the identity of the EPA.
The state agent SHOULD authenticate the EPA, and SHOULD apply its
authorization policies (e.g., based on access control lists) to all
requests. The composition model makes no assumptions that all input
sources for an ESC are on the same network, or in the same
administrative domain.
Authentication issues are discussed in SIP [2]. The exact methods for
creation and manipulation of the ESC authorization policies are
outside the scope of this document.
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9.2 Denial of Service Attacks
The creation of state at the ESC upon receipt of a PUBLISH request
can be used by attackers to consume resources on a victim's machine,
possibly rendering it unusable.
To reduce the chances of such an attack, implementations of ESCs
SHOULD require authentication of PUBLISH requests. Authentication
issues are discussed in SIP [2].
Also, 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 header
field values for the supported event packages at an 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 request.
9.3 Replay Attack
Replaying the PUBLISH request can have detrimental effects. An
attacker may be able to perform any event state publication it
witnessed being performed at some point in the past, by replaying a
PUBLISH request. Among other things, such a replay message may be
used to spoof old event state information, although a versioning
mechanism, e.g., a timestamp, in the state information may help
mitigate such an attack.
To prevent replay attacks, implementations SHOULD require
authentication with anti-replay protection. Authentication issues are
discussed in SIP [2].
9.4 Man in the Middle Attacks
Even with authentication, man-in-the-middle attacks using PUBLISH may
be used to install arbitrary event state information, modify or
remove existing event state information in publications, or even
remove event state altogether at an ESC.
To prevent such attacks, implementations SHOULD, at a minimum,
provide integrity protection across the To, From, Event, If-Match,
Route, and Expires headers and the bodies of PUBLISH messages.
If the ESC receives event state in a PUBLISH request which is
integrity protected using a security association that is not with the
ESC (e.g., integrity protection is applied end-to-end, from publisher
to subscriber), the state agent coupled with the ESC MUST NOT modify
the event state before exposing it to the subscribers of this event
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state in NOTIFY requests. This is to preserve the end-to-end
integrity of the event state.
Integrity protection of message headers and bodies is discussed in
SIP [2].
9.5 Confidentiality
The state information contained in a PUBLISH message may potentially
contain sensitive information. Implementations MAY encrypt such
information to ensure confidentiality.
The mechanisms for providing confidentiality are detailed in SIP [2].
10. Examples
This 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 may also 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, and is not shown in this
example.
TBD: replace domain.com with example.com
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PUA PA WATCHER
(EPA) (ESC)
| | |
| | <---- M1: SUBSCRIBE --- |
| | |
| | ----- M2: 200 OK -----> |
| | |
| | ----- M3: NOTIFY -----> |
| | |
| | <---- M4: 200 OK ------ |
| | |
| | |
| ---- M5: PUBLISH ---> | |
| | |
| <--- M6: 200 OK ---- | |
| | |
| | ----- M7: NOTIFY -----> |
| | |
| | <---- M8: 200 OK ------ |
| | |
| ---- M9: PUBLISH ---> | |
| | |
| <--- M10: 200 OK --- | |
| | |
| | |
| --- M11: PUBLISH ---> | |
| | |
| <-- M12: 200 OK ---- | |
| | |
| | ----- M13: NOTIFY ----> |
| | |
| | <---- M14: 200 OK ----- |
| | |
Message flow:
M1: The watcher initiates a new subscription to the
presentity@example.com's presence agent.
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SUBSCRIBE sip:presentity@example.com SIP/2.0
Via: SIP/2.0/UDP 10.0.0.1:5060;branch=z9hG4bKnashds7
To: <sip:presentity@example.com>
From: <sip:watcher@example.com>;tag=12341234
Call-ID: 12345678@10.0.0.1
CSeq: 1 SUBSCRIBE
Max-Forwards: 70
Expires: 3600
Event: presence
Contact: <sip:watcher@example.com>
Content-Length: 0
M2: The presence agent for presentity@example.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@example.com>;tag=abcd1234
From: <sip:watcher@example.com>;tag=12341234
Call-ID: 12345678@10.0.0.1
CSeq: 1 SUBSCRIBE
Contact: <sip:pa@example.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@example.com SIP/2.0
Via: SIP/2.0/UDP pa.example.com;branch=z9hG4bK8sdf2
To: <sip:watcher@example.com>;tag=12341234
From: <sip:presentity@example.com>;tag=abcd1234
Call-ID: 12345678@10.0.0.1
CSeq: 1 NOTIFY
Max-Forwards: 70
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@example.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.example.com;branch=z9hG4bK8sdf2
To: <sip:watcher@example.com>;tag=12341234
From: <sip:presentity@example.com>;tag=abcd1234
Call-ID: 12345678@10.0.0.1
CSeq: 1 NOTIFY
Contact: <sip:watcher@example.com>
M5: A presence user agent for the presentity initiates a PUBLISH to
the presentity's presence agent in order to update it with new
presence information. The Expires header indicates the desired
duration of this soft state.
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PUBLISH sip:presentity@example.com SIP/2.0
Via: SIP/2.0/UDP pua.example.com;branch=z9hG4bK652hsge
To: <sip:presentity@example.com>
From: <sip:presentity@example.com>;tag=1234wxyz
Call-ID: 81818181@pua.example.com
CSeq: 1 PUBLISH
Max-Forwards: 70
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@example.com">
<tuple id="mobile-phone">
<status>
<basic>closed</basic>
</status>
<timestamp>2003-02-01T17:00:19Z</timestamp>
</tuple>
</presence>
M6: 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. The 200 (OK) response contains an ETag
header field with an entity-tag. This is used to identify the
published event state in subsequent PUBLISH requests.
SIP/2.0 200 OK
Via: SIP/2.0/UDP pua.example.com;branch=z9hG4bK652hsge
To: <sip:presentity@example.com>;tag=1a2b3c4d
From: <sip:presentity@example.com>;tag=1234wxyz
Call-ID: 81818181@pua.example.com
CSeq: 1 PUBLISH
ETag: dx200xyz
Expires: 1800
M7: 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@example.com SIP/2.0
Via: SIP/2.0/UDP presence.example.com;branch=z9hG4bK4cd42a
To: <sip:watcher@example.com>;tag=12341234
From: <sip:presentity@example.com>;tag=abcd1234
Call-ID: 12345678@10.0.0.1
CSeq: 2 NOTIFY
Max-Forwards: 70
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@example.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>
M8: The watcher confirms receipt of the NOTIFY request.
SIP/2.0 200 OK
Via: SIP/2.0/UDP presence.example.com;branch=z9hG4bK4cd42a
To: <sip:watcher@example.com>;tag=12341234
From: <sip:presentity@example.com>;tag=abcd1234
Call-ID: 12345678@10.0.0.1
CSeq: 2 NOTIFY
Content-Length: 0
M9: The PUA determines that the event state it previously published
is about to expire, and refreshes that event state.
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PUBLISH sip:presentity@example.com SIP/2.0
Via: SIP/2.0/UDP pua.example.com;branch=z9hG4bK771ash02
To: <sip:presentity@example.com>
From: <sip:presentity@example.com>;tag=1234kljk
Call-ID: 98798798@pua.example.com
CSeq: 1 PUBLISH
Max-Forwards: 70
If-Match: dx200xyz
Expires: 3600
Event: presence
Content-Length: 0
M10: The presence agent receives, and accepts the publication
refresh. The timers regarding the expiration of the specific event
state identified by the entity-tag are updated. Note that no
actual state change has occured, so the watchers will receive no
NOTIFYs.
SIP/2.0 200 OK
Via: SIP/2.0/UDP pua.example.com;branch=z9hG4bK771ash02
To: <sip:presentity@example.com>;tag=2affde434
From: <sip:presentity@example.com>;tag=1234kljk
Call-ID: 98798798@pua.example.com
CSeq: 1 PUBLISH
ETag: dx200xyz
Expires: 1800
M11: The PUA of the presentity detects a change in the user's
presence state. It initiates a PUBLISH request to the presence
agent to modify the published presence information with the recent
change.
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PUBLISH sip:presentity@example.com SIP/2.0
Via: SIP/2.0/UDP pua.example.com;branch=z9hG4bKcdad2
To: <sip:presentity@example.com>
From: <sip:presentity@example.com>;tag=54321mm
Call-ID: 5566778@pua.example.com
CSeq: 1 PUBLISH
Max-Forwards: 70
If-Match: dx200xyz
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@example.com">
<tuple id="mobile-phone">
<status>
<basic>open</basic>
</status>
<timestamp>2003-02-01T19:15:15Z</timestamp>
</tuple>
</presence>
M12: The presence agent receives, and accepts the publication
modification. The timers regarding the expiration of the specific
event state identified by the entity-tag are updated, and the
published data is incorporated into the presentity's presence
document. Note that the document delivered in this modification
will replace the previous document.
SIP/2.0 200 OK
Via: SIP/2.0/UDP pua.example.com;branch=z9hG4bKcdad2
To: <sip:presentity@example.com>;tag=effe22aa
From: <sip:presentity@example.com>;tag=54321mm
Call-ID: 5566778@pua.example.com
CSeq: 1 PUBLISH
ETag: dx200xyz
Expires: 3600
M13: 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@example.com SIP/2.0
Via: SIP/2.0/UDP presence.example.com;branch=z9hG4bK32defd3
To: <sip:watcher@example.com>;tag=12341234
From: <sip:presentity@example.com>;tag=abcd1234
Call-ID: 12345678@10.0.0.1
CSeq: 2 NOTIFY
Max-Forwards: 70
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@example.com">
<tuple id="mobile-phone">
<status>
<basic>open</basic>
</status>
<timestamp>2003-02-01T19:15:15Z</timestamp>
</tuple>
<tuple id="desktop">
<status>
<basic>open</basic>
</status>
<timestamp>2003-02-01T12:21:29Z</timestamp>
</tuple>
</presence>
M14: The watcher confirms receipt of the NOTIFY request.
SIP/2.0 200 OK
Via: SIP/2.0/UDP presence.example.com;branch=z9hG4bK32defd3
To: <sip:watcher@example.com>;tag=12341234
From: <sip:presentity@example.com>;tag=abcd1234
Call-ID: 12345678@10.0.0.1
CSeq: 2 NOTIFY
Content-Length: 0
11. Contributors
The original contributors to this specification are:
Ben Campbell
dynamicsoft
Sean Olson
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Microsoft
Jon Peterson
Neustar, Inc.
Jonathan Rosenberg
dynamicsoft
Brian Stucker
Nortel Networks, Inc.
12. Document Change History
(Note to RFC Editor: please remove this whole section prior to
publication as an RFC.)
12.1 Changes since "draft-ietf-sip-publish-00"
The following changes were made since the last version:
o Specified the role of the Request-URI in identifying the
publication target resource. Also, clarified chapter 5 in this
regard to explicitly talk about the identification of
publications.
o Changed chapter 6 to use Request-URI in determining the
publication target resource. Also clarified language within the
processing steps of an ESC.
o Added missing header fields and removed unneeded "proxy" column in
Table 1 and Table 2. Corrected Table 3 content.
o Corrected various nits in examples and in body text.
12.2 Changes since "draft-ietf-simple-publish-01"
The following changes were made since the last version:
o Submitted as "draft-ietf-sip-publish-00".
o Changed title to better reflect the content.
o Removed event state segmentation and collision detection of
segments, and simplified usage of entity-tags.
o Rewrote Ch 4 "Considerations for Event Packages Using PUBLISH" to
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mimic the way RFC 3265 defines considerations for event packages.
Also, removed normative dependency to
"draft-ietf-simple-publish-reqs".
o Rewrote Ch 9 "Security Considerations" to now include text about
specific vulnerabilities and the security tools to counter those
attacks.
o Clarified both UAC and UAS usage of entity-tags. Moved common
error handling of UACs to a separate sub-section.
o Improved description of UAS functionality of Ch 6 "Processing
PUBLISH Requests", and alinged it with RFC 3261 Chapter 10 on
processing registrations.
o Changed entity-tag syntax from "quoted-string" to "token". This is
a deviation from RFC 2616 entity-tag syntax, but more aligned to
how similar things are expressed in SIP.
o Restricted the If-Match header syntax to only allow a single
entity-tag. Multiple entity-tags are not applicable to PUBLISH.
o Added methods other than PUBLISH to Table 3.
o Rewrote Ch 10 "Examples" to better reflect actual PUBLISH usage.
o Changed reference [10] from caller-prefs to callee-caps.
o Overall language and structure tweaking.
12.3 Changes since "draft-ietf-simple-publish-00"
The following changes were made since the last version:
o Merged with "draft-olson-simple-publish-02"
o Removed usage of Call-ID and CSeq for ordering
o Removed timestamp based versioning
o Added versioning based on entity-tag version information (ETag),
and request precondition (If-Match)
o Changed reference to content-indirection as Informative
o Added section for ABNF definitions
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o Editorial corrections, restructuring of document to improve
readability
o Moved the original authors into a new "Contributors" section
o Added new definitions in Terminology, and clarified EPA and ESC
definitions
o Strengthened the IANA considerations section.
o Added text for announcing/probing support for publish, namely
OPTIONS and "methods" parameter usage.
Normative References
[1] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[2] 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.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
Informative References
[4] Campbell, B., "SIMPLE Presence Publication Requirements",
draft-ietf-simple-publish-reqs-00 (work in progress), February
2003.
[5] Postel, J. and J. Reynolds, "File Transfer Protocol", STD 9,
RFC 959, October 1985.
[6] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L.,
Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[7] Rosenberg, J., "A Presence Event Package for the Session
Initiation Protocol (SIP)", draft-ietf-simple-presence-10 (work
in progress), January 2003.
[8] Sugano, H. and S. Fujimoto, "Presence Information Data Format
(PIDF)", draft-ietf-impp-cpim-pidf-08 (work in progress), May
2003.
[9] Olson, S., "A Mechanism for Content Indirection in SIP
Messages", draft-olson-sip-content-indirect-mech-01 (work in
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progress), August 2002.
[10] Rosenberg, J., "Indicating User Agent Capabilities in the
Session Initiation Protocol (SIP)",
draft-ietf-sip-callee-caps-00 (work in progress), June 2003.
Author's Address
Aki Niemi (editor)
Nokia
P.O. Box 321
NOKIA GROUP, FIN 00045
Finland
Phone: +358 50 389 1644
EMail: aki.niemi@nokia.com
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Full Copyright Statement
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Niemi Expires April 23, 2004 [Page 34]
Internet-Draft SIP Event State Publication October 2003
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Niemi Expires April 23, 2004 [Page 35]
