SIMPLE WG A. Niemi, Ed.
Internet-Draft Nokia
Expires: December 28, 2003 June 29, 2003
Session Initiation Protocol (SIP) Extension for Presence Publication
draft-ietf-simple-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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Conventions . . . . . . . . . . . . . . . . 3
3. Overall Operation . . . . . . . . . . . . . . . . . . . . . 4
4. Prerequisites for Event Packages using PUBLISH . . . . . . . 5
4.1 PUBLISH Bodies . . . . . . . . . . . . . . . . . . . . . . . 5
4.2 PUBLISH Response Bodies . . . . . . . . . . . . . . . . . . 5
4.3 Partial Event State . . . . . . . . . . . . . . . . . . . . 6
4.4 Event State Decomposition . . . . . . . . . . . . . . . . . 6
4.5 Default Expiration of PUBLISH . . . . . . . . . . . . . . . 6
5. Constructing the PUBLISH Request . . . . . . . . . . . . . . 7
5.1 Creating Initial Publication . . . . . . . . . . . . . . . . 8
5.2 Setting the Expiration Interval . . . . . . . . . . . . . . 9
5.3 Refreshing Event State . . . . . . . . . . . . . . . . . . . 9
5.4 Modifying Event State . . . . . . . . . . . . . . . . . . . 10
5.5 Removing Event State . . . . . . . . . . . . . . . . . . . . 10
5.6 Querying the Current Event State . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . . 16
7.2.1 "412 Precondition Failed" Response Code . . . . . . . . . . 16
7.3 New Header Fields . . . . . . . . . . . . . . . . . . . . . 16
7.3.1 "ETag" Header . . . . . . . . . . . . . . . . . . . . . . . 17
7.3.2 "If-Match" Header . . . . . . . . . . . . . . . . . . . . . 17
7.4 Augmented BNF Definitions . . . . . . . . . . . . . . . . . 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 17
8.1 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.2 Response Codes . . . . . . . . . . . . . . . . . . . . . . . 18
8.3 Header Field Names . . . . . . . . . . . . . . . . . . . . . 18
9. Security Considerations . . . . . . . . . . . . . . . . . . 18
10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 19
11. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . 25
12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 26
13. Changes from "draft-ietf-simple-publish-00" . . . . . . . . 26
Normative References . . . . . . . . . . . . . . . . . . . . 27
Informative References . . . . . . . . . . . . . . . . . . . 27
Author's Address . . . . . . . . . . . . . . . . . . . . . . 28
Intellectual Property and Copyright Statements . . . . . . . 29
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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 compositing 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 to the presence agent. The
requirements and model for presence publication are documented in
[2]. 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 [7], HTTP [8],
etc.)
2. Terminology and Conventions
In addition to the terminology of RFC 3265 [1] and RFC 3261 [3], this
document introduces some new concepts:
Event State: The composition state of a resource.
Event Publication Agent (EPA): The UAC which issues a PUBLISH request
to publish event state or event state segments. For presence, this
corresponds to the PUA.
Event State Compositor (ESC): The UAS which processes PUBLISH
requests and is responsible of compositing event state or event
state segments into a complete, composite event state. For
presence, this corresponds to the PA.
Event State Segment: For some event packages, there exists a natural
decomposition of event state into event state segments. For
presence, such decomposition is the presence tuple.
Hard State: Hard state is the steady-state or default state version
of event state at the ESC, which may be used in the absence of any
other soft state publications.
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Soft State: Soft state is a version of event state at the ESC, that
is published by the EPA. Soft state has a defined lifetime and
will expire after a negotiated amount of time.
Version Identifier: A protocol element (i.e., an entity-tag) that is
used to identify a specific soft state version of published event
state at the ESC.
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 [4] and
indicate requirement levels for compliant implementations.
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
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 package discover the event state of the
other active endpoints.
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 [5]. The entity which 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
[5].
PUBLISH requests create soft state in the state agent. 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 any other soft state provided
through the PUBLISH method.
Typically, the body of a PUBLISH request carries the published event
state. In the response to a PUBLISH request, the EPA assigns a
version identifier to the published event state or event state
segment. This identifier is used by the EPA as part of a version
precondition to subsequent refreshing PUBLISH requests of that event
state. In the event that the publication refresh is to an outdated
version of event state, the versioning precondition will fail. This
enables an EPA to detect collisions between new and refresh
publications of the same event state among a set of endpoints.
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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 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 publication.
4. Prerequisites for Event Packages using PUBLISH
In order to make use of the event publication mechanism, certain
prerequisites have to be fulfilled for each specific event package.
In order to satisfy the requirements of [2], the body of the PUBLISH
request must fulfill several requirements as well.
This section outlines these prerequisites, and demonstrates how they
are fulfilled specifically for presence publication.
4.1 PUBLISH Bodies
Any application of the PUBLISH mechanism for a given event package
MUST support a content type which fulfills the requirements in [2].
Each event package MUST also describe the semantics associated with
that content 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 [6] presence
document format is used. A PUA which uses PUBLISH to publish presence
state to the PA MUST support the CPIM PIDF presence format.
4.2 PUBLISH Response Bodies
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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 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 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.
Note that sources for event state other than those using the
PUBLISH mechanism are explicitly allowed. It is beyond the scope
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 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.
4.4 Event State Decomposition
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 presence, the CPIM PIDF presence document provides a tuple-ID to
distinguish the segments of the presence document associated with the
encompassing presentity.
OPEN ISSUE: The specifics of how the tuple-ID is used to identify
specific segments of the composite state is still open. Currently,
a specific naming convention for the tuple-ID seems like a
reasonable approach. However, this naming convention is to be
defined.
4.5 Default Expiration of PUBLISH
PUBLISH establishes soft state which expires after a negotiated
amount of time. Each event package MUST provide a default expiration
value recommendation (SHOULD strength).
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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 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 [1].
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.
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 [3].
If necessary, clients may probe for the support of PUBLISH using the
OPTIONS request defined in SIP [3]. 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.
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 are 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. The
address-of-record MUST be a SIP URI or SIPS URI. Unlike the
REGISTER request, the Request-URI SHOULD contain both "userinfo"
and "@" components.
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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.
From: The From header field contains the address-of-record of the
entity responsible for the publication. The value is the same as
the To header field unless the request is a third-party
publication. This address-of-record MUST be a SIP URI or SIPS URI.
Event: PUBLISH requests MUST contain a single Event header field. The
value of this header field indicates the event package for which
this request is publishing event state.
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 EPA.
If-Match: PUBLISH requests MAY contain a single If-Match header
field. This header field SHOULD contain one or more entity-tags
provided by the ESC, to be used as a versioning precondition to a
PUBLISH refresh.
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.
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).
5.1 Creating Initial Publication
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.
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OPEN ISSUE: Atomicity of publication. How exactly is this handled?
Can an initial "full" PIDF document be split into separate tuples
later on? If the initial publication contains several tuples, do
each of them inherit the version identifier? How can the EPA
publish presentity level information, e.g., presentity note?
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.
5.2 Setting the Expiration Interval
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.
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.
5.3 Refreshing Event State
Each EPA is responsible for refreshing the publications that it has
previously established.
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.
Also, the 200 (OK) response from the state agent MUST contain an ETag
header with a single entity-tag indicating the version information of
the publication. To refresh the event state, the EPA MUST include the
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received entity-tag in an If-Match header field in a PUBLISH request.
Note that for the EPA, the entity-tag is simply an opaque string.
It carries no further semantics for the EPA.
The If-Match header field with the version identifier entity-tag
establishes a versioning precondition to the PUBLISH request. If the
version identifier matches the version maintained by the ESC, the
refresh is successful, and the EPA receives a 200 (OK) response. If
there is no matching version at the ESC, i.e., the refreshed event
state is out-of-date, the EPA receives a 412 (Precondition Failed)
response to the PUBLISH request.
If an EPA receives a 412 (Precondition Failed) response, it MUST NOT
reattempt to refresh the event state. Instead, the EPA SHOULD query a
principal for further actions.
OPEN ISSUE: This may need some more thought. It's easy to see that
in a presence system, the UA could prompt the user when a refresh
fails. But there may be systems consisting of automata only, where
such a concept does not make much sense.
Also, to recover from this error, the client MAY 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.
A PUBLISH refresh SHOULD NOT contain a body.
5.4 Modifying Event State
Modification of event state is considered a new publication similar
to the creation of initial event state. Because the modification of
event state is not a refresh publication, the EPA does not include a
versioning precondition in the PUBLISH request. Therefore, the
PUBLISH request MUST NOT include an If-Match header field, and the
EPA MUST discard any previously received version identifier for this
event state.
5.5 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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5.6 Querying the Current Event State
To query the 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.
6. 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.
A client may probe the ESC for the support of PUBLISH using the
OPTIONS request defined in SIP [3]. In the response to 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" parameter for Contact may also be used to
specifically announce support for PUBLISH messages when
registering. (See reference [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 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. Possible mechanisms for the
authentication of SIP user agents are described in Section 22 of
RFC3261.
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4. 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. Else, 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
maintained by the ESC.
5. The ESC SHOULD determine if the authenticated user is authorized
to publish for the address-of-record of the To header field. If
the authenticated user is not authorized to publish, the ESC
MUST return a 403 (Forbidden).
Note that this authorization may take into account third
party publication of event state.
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.
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
locally-configured minimum, the ESC MAY reject the
publication with a response of 423 (Interval Too Brief), and
skip the rest of 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 examines the If-Match header of the PUBLISH request. If
the If-Match header is absent, the request is a new publication;
if the request contains a version precondition in the form of an
If-Match header field, the request is a publication refresh. The
ESC extracts any entity-tags contained in the If-Match header
and then matches those entity-tags against all locally stored
entity-tags for this address-of-record and event package. If no
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match is found, the ESC MUST reject the publication with a
response of 412 (Precondition Failed), and skip the remaining
steps.
9. The ESC may then process the body of the PUBLISH request (the
actual event state). 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 the ESC, the
ESC MUST reject the request with an appropriate response.
* 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.
Note that this version information will be generated by
the ESC when receiving a new publication, and will be
present in the If-Match header field in publication
refreshes.
* For new publications, i.e., publications without a version
precondition, the ESC MUST generate a locally unique
entity-tag, and store it, replacing any existing entity-tags
stored for that particular event state. The new entity-tag
MUST be delivered to the EPA in an ETag header field of a 200
(OK) response.
Note that the exact way in which the ESC creates the
version entity-tag is a matter of local policy. One
reasonable implementation of a version entity-tag is a
counter which is incremented by one for each new version.
* 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.
10. 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
indicating the version of 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.
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7. Syntax
This section describes the syntax extensions required for event
publication in SIP. Note that the formal syntax definitions described
in this section are expressed in the Augmented BNF format used in SIP
[3], 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
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 compositing this event state.
Table 1 and Table 2 extend Tables 2 and 3 of RFC 3261 [3] 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 | proxy | PUB |
+---------------------+---------+-------+-----+
| 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 | | | * |
| 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 | PUB |
+---------------------+-----------------+-------+-----+
| 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
7.2 New Response Codes
7.2.1 "412 Precondition Failed" Response Code
The 412 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 [3], as amended by the changes in
Section 7.1.
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+--------------+-------+-------+-----+
| Header Field | where | proxy | PUB |
+--------------+-------+-------+-----+
| ETag | 2xx | | m |
| If-Match | R | | o |
+--------------+-------+-------+-----+
Table 3: Summary of header fields, A--O
7.3.1 "ETag" Header
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
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 [3]
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
* (COMMA entity-tag)
entity-tag = quoted-string
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.
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Method Name: PUBLISH
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
The state agent SHOULD authenticate the Event Publication Agent
(EPA), and SHOULD apply its authorization policies to all requests.
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.
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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,
ETag, If-Match, 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.
10. 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 ----> |
| | |
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| | <---- M12: 200 OK ----- |
| | |
| | |
|<---- M13: NOTIFY ---- | |
| | |
|----- M14: 200 OK --> | |
| | |
Message flow:
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.
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
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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.
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
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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.
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>
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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.
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
ETag: "dx200xyz"
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.
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
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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
11. Open Issues
o Atomicity of publication. 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 The exact naming convention used for the tuple-ID when publishing
tuples.
o In case a refresh publication fails, what should the EPA do?
Current suggestion is to query the principal, i.e., "prompt the
user", but this is not quite specific.
o Does end-to-end S/MIME integrity protection make sense when an
event compositor is used? Does it indicate that the segment should
be carried to the watcher intact, or is another mechanism for this
needed?
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o The examples seem a bit elaborate, and don't even cover the
publication refresh case. We should probably work on them.
o Do we need another response code (new or some existing one) for
the case when an EPA tries to refresh a publication, but the ESC
has lost all version information it has, e.g., after e reboot?
This seems a slightly different scenario from the usual
"Precondition Failed".
12. Contributors
The original contributors to this specification are:
Ben Campbell
dynamicsoft
Sean Olson
Microsoft
Jon Peterson
Neustar, Inc.
Jonathan Rosenberg
dynamicsoft
Brian Stucker
Nortel Networks, Inc.
13. Changes from "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
o Editorial corrections, restructuring of document to improve
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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] Campbell, B., "SIMPLE Presence Publication Requirements",
draft-ietf-simple-publish-reqs-00 (work in progress), February
2003.
[3] 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.
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[5] Rosenberg, J., "A Presence Event Package for the Session
Initiation Protocol (SIP)", draft-ietf-simple-presence-10 (work
in progress), January 2003.
[6] Fujimoto, S. and H. Sugano, "Common Presence and Instant
Messaging (CPIM)Presence Information Data Format",
draft-ietf-impp-cpim-pidf-07 (work in progress), January 2003.
Informative References
[7] Postel, J. and J. Reynolds, "File Transfer Protocol", STD 9,
RFC 959, October 1985.
[8] 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.
[9] Olson, S., "A Mechanism for Content Indirection in SIP
Messages", draft-olson-sip-content-indirect-mech-01 (work in
progress), August 2002.
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[10] Rosenberg, J., Schulzrinne, H. and P. Kyzivat, "Caller
Preferences and Callee Capabilities for the Session Initiation
Protocol (SIP)", draft-ietf-sip-callerprefs-08 (work in
progress), March 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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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
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Niemi Expires December 28, 2003 [Page 30]
