SIPPING J. Rosenberg
Internet-Draft dynamicsoft
Expires: December 29, 2003 H. Schulzrinne
Columbia University
June 30, 2003
A Session Initiation Protocol (SIP) Event Package for Conference
State
draft-ietf-sipping-conference-package-01
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document defines a conference event package for the Session
Initiation Protocol (SIP) Events framework, along with a data format
used in notifications for this package. The conference package allows
users to subscribe to a conference URI. Notifications are sent about
changes in the membership of this conference, the state of the
dialogs that compose the conference, and general information about
the conference.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Conference Event Package . . . . . . . . . . . . . . . . . . 5
3.1 Event Package Name . . . . . . . . . . . . . . . . . . . . . 5
3.2 Event Package Parameters . . . . . . . . . . . . . . . . . . 5
3.3 SUBSCRIBE Bodies . . . . . . . . . . . . . . . . . . . . . . 6
3.4 Subscription Duration . . . . . . . . . . . . . . . . . . . 6
3.5 NOTIFY Bodies . . . . . . . . . . . . . . . . . . . . . . . 6
3.6 Notifier Processing of SUBSCRIBE Requests . . . . . . . . . 7
3.7 Notifier Generation of NOTIFY Requests . . . . . . . . . . . 7
3.8 Subscriber Processing of NOTIFY Requests . . . . . . . . . . 7
3.9 Handling of Forked Requests . . . . . . . . . . . . . . . . 8
3.10 Rate of Notifications . . . . . . . . . . . . . . . . . . . 8
3.11 State Agents . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Conference Data Format . . . . . . . . . . . . . . . . . . . 9
4.1 Structute of the Format . . . . . . . . . . . . . . . . . . 9
4.1.1 Conferencing Service Element . . . . . . . . . . . . . . . . 9
4.1.2 User Element . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1.3 Status . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1.4 Dialog . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1.5 Media Streams . . . . . . . . . . . . . . . . . . . . . . . 11
4.2 Constructing Coherent State . . . . . . . . . . . . . . . . 12
4.3 Schema . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.4 Example . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5. Security Considerations . . . . . . . . . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . 17
6.1 conference Event Package Registration . . . . . . . . . . . 17
6.2 application/conference-info+xml MIME Registration . . . . . 17
6.3 URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:conference-info . . . . . . . . . . . 18
6.4 XML Schema Registration . . . . . . . . . . . . . . . . . . 19
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
Normative References . . . . . . . . . . . . . . . . . . . . 21
Informative References . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 23
Intellectual Property and Copyright Statements . . . . . . . 24
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1. Introduction
The Session Initiation Protocol (SIP) [3] Events framework [2]
defines general mechanisms for subscribing to, and receiving
notifications of, events within SIP networks. It introduces the
notion of a package, which is a specific "instantiation" of the
events framework for a well-defined set of events. Packages have been
defined for user presence [11], watcher information [12], and message
waiting indicators [14], amongst others. Here, we define an event
package for SIP conferences. This package provides the conference
notification service as outlined in the SIP conferencing framework
[15]. As described there, subscriptions to a conference URI are
routed to the focus that is handling the conference. It acts as the
notifer, and provides clients with updates on conference state.
The information provided by this package is broken into several
general categories:
General State: A small amount of general conference state is
provided, primarily for the purposes of bootstrapping access to
other conference services, such as media and conference policy
controls.
Membership State: The members of the conference, and their state
within the conference.
Dialog State: The state of the dialogs for users connected to the
conference.
Media State: Information about what media users in the conference are
receiving.
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2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
indicate requirement levels for compliant implementations.
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3. Conference Event Package
The conference event package allows a user to subscribe to a
conference. In SIP, conferences are represented by URIs. These URIs
route to a SIP user agent, called a focus, that is responsible for
ensuring that all users in the conference can communicate with each
other [15]. The focus has sufficient information about the state of
the conference to inform subscribers about it.
This section provides the details for defining a SIP Events package,
as specified by [2].
3.1 Event Package Name
The name of this event package is "conference". This package name is
carried in the Event and Allow-Events header, as defined in [2].
3.2 Event Package Parameters
Two Event header field parameters are defined for this package. The
first is "recurse". The parameter has no values. When present, it
informs the server that it should check whether any participants in
the conference are themselves a focus, and if so, generate a
subscription to their conference state with the "recurse" attribute.
The focus can determine whether a participant is a focus based on the
presence of the "isfocus" capability indication in the Contact header
field provided by the participant [4]. The users reported in
notifications from this recursed subscription are reported to the
original subscriber. The result is that the list of users reported to
the subscriber represents the complete user list even when cascaded
conferences are used.
The second Event header field parameter is "type". Its value is a
comma separated list of the types of conference information that are
desired. This specification defines four values - "general",
"membership", "dialog", and "basic-media". When any one of these is
present, it means that the corresponding conference information is
desired. The specific components of a conference information document
corresponding to each of these values are described below. Additional
values for this parameter MAY be defined by extensions to this
package. Such extensions are anticipated to handle membership and
media policy state.
Both of these parameters MUST have the same value in a initial
SUBSCRIBE request and any refreshes of the resulting subscription. In
other words, their values are fixed for the duration of the
subscription. The default meaning of the "type" parameter, when not
present, is that the focus should send all information it has about
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the conference. When present, the type parameter MUST have at least
one value.
The BNF for these parameters is:
recurse = "recurse"
type = "type" EQUAL SWS DQUOTE conf-info *("," conf-info)
DQUOTE
;; EQUAL, SWS, DQUOTE from RFC3261
conf-info = "general" | "membership" | "dialog" | "basic-media" |
token
Example:
Event: conference;recurse;type="membership,general"
3.3 SUBSCRIBE Bodies
A SUBSCRIBE for a dialog package MAY contain a body. This body
defines a filter to apply to the subscription. Filter documents are
not specified in this document, and at the time of writing, are
expected to be the subject of future standardization activity.
A SUBSCRIBE for a dialog package MAY be sent without a body. This
implies the default subscription filtering policy. The default policy
is:
o Notifications are generated every time there is any change in the
state of the conference, where that change is in a piece of
information that the subscriber has indicated (using the "type"
Event header field parameter) an interest in receiving.
o Notifications do not normally contain full state; rather, they
only indicate the state that has changed. The exception is a
NOTIFY sent in response to a SUBSCRIBE. These NOTIFYs contain the
full state of the information requested by the subscriber.
3.4 Subscription Duration
The default expiration time for a subscription to a conference is one
hour. Once the conference ends, all subscriptions to that particular
conference are terminated, with a reason of "noresource" [2].
3.5 NOTIFY Bodies
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As described in RFC 3265 [2], the NOTIFY message will contain bodies
that describe the state of the subscribed resource. This body is in a
format listed in the Accept header field of the SUBSCRIBE, or a
package-specific default if the Accept header field was omitted from
the SUBSCRIBE.
In this event package, the body of the notification contains a
conference information document. This document describes the state of
a conference. All subscribers and notifiers MUST support the
"application/conference-info+xml" data format described in Section 4.
The subscribe request MAY contain an Accept header field. If no such
header field is present, it has a default value of "application/
conference-info+xml". If the header field is present, it MUST include
"application/conference-info+xml", and MAY include any other types
capable of representing dialog state.
Of course, the notifications generated by the server MUST be in one
of the formats specified in the Accept header field in the SUBSCRIBE
request.
3.6 Notifier Processing of SUBSCRIBE Requests
The conference information contains very sensitive information.
Therefore, all subscriptions SHOULD be authenticated and then
authorized before approval. Authorization policy is at the discretion
of the administrator, as always. However, a few recommendations can
be made.
It is RECOMMENDED that all users in the conference be allowed to
subscribe to the conference.
3.7 Notifier Generation of NOTIFY Requests
Notifications SHOULD be generated for the conference whenever there
is a change in the state in any of the information types requested by
the subscriber. For "membership", these changes generally occur when
a new participant joins, a participant leaves, and a dial-out attempt
succeeds or fails. For "dialog", these changes occur when a dialog is
created, terminated, or updated through a target refresh request. For
"basic-media", these changes occur when the media types receive by a
participant change. For "general", these changes occur when the
conference policy protocol URIs change.
3.8 Subscriber Processing of NOTIFY Requests
The SIP Events framework expects packages to specify how a subscriber
processes NOTIFY requests in any package specific ways, and in
particular, how it uses the NOTIFY requests to contruct a coherent
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view of the state of the subscribed resource.
Typically, the NOTIFY for the conference package will only contain
information about those users whose state in the conference has
changed. To construct a coherent view of the total state of all
users, a subscriber to the dialog package will need to combine
NOTIFYs received over time.
Notifications within this package can convey partial information;
that is, they can indicate information about a subset of the state
associated with the subscription. This means that an explicit
algorithm needs to be defined in order to construct coherent and
consistent state. The details of this mechanism are specific to the
particular document type. See Section 4.2 for information on
constructing coherent information from an application/
conference-info+xml document.
3.9 Handling of Forked Requests
By their nature, the conferences supported by this package are
centralized. Therefore, SUBSCRIBE requests for a conference should
not generally fork. Users of this package MUST NOT install more than
a single subscription as a result of a single SUBSCRIBE request.
3.10 Rate of Notifications
For reasons of congestion control, it is important that the rate of
notifications not become excessive. As a result, it is RECOMMENDED
that the server not generate notifications for a single subscriber at
a rate faster than once every 5 seconds.
3.11 State Agents
Conference state is ideally maintained in the element in which the
conference resides. Therefore, the elements that maintain the
conference are the ones best suited to handle subscriptions to it.
Therefore, the usage of state agents is NOT RECOMMENDED for this
package.
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4. Conference Data Format
Conference information is an XML document [5] that MUST be
well-formed and SHOULD be valid. Dialog information documents MUST be
based on XML 1.0 and MUST be encoded using UTF-8. This specification
makes use of XML namespaces for identifying dialog information
documents and document fragments. The namespace URI for elements
defined by this specification is a URN [6], using the namespace
identifier 'ietf' defined by [7] and extended by [8]. This URN is:
urn:ietf:params:xml:ns:conference-info
A conference information document begins with the root element tag
"conference-info".
4.1 Structute of the Format
Conference information begins with the top level element
"conference-info". This element has three mandatory attributes:
version: This attribute allows the recipient of conference
information documents to properly order them. Versions start at 0,
and increment by one for each new document sent to a subscriber.
Versions are scoped within a subscription. Versions MUST be
representable using a 32 bit integer.
state: This attribute indicates whether the document contains the
full conference information, or whether it contains only the
information that has changed since the previous document
(partial).
entity: This attribute contains the conference URI that identifies
the conference being described in the document.
The "conference-info" element has zero or more "conf-service"
elements, which provide URIs for access conferencing services, such
as media policy and conference policy control. This is followed by
zero or more "user" sub-elements which contain information on the
users in the conference.
4.1.1 Conferencing Service Element
The "conf-service" element contains a URI that can be used to access
some additional conferencing service. The element contains the
following attributes:
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id: This attribute provides a unique identifier (unique within the
context of the subscription) for the service. The attribute is
mandatory.
type: This attribute contains a string which indicates the type of
service. Defined values are "conf-policy", to indicate that the
URI is for manipulating the conference policy [17][18],
"media-policy", to indicate that the URI is for manipulating the
media policy [9], and "floor-control", to indicate that the URI is
for access to floor control services [19]. The attribute is
mandatory.
There MUST only be one conf-service for each type of service.
Additional service types may be defined in the future.
OPEN ISSUE: Once a protocol becomes solidified, we will need to
add some additional content here. For example, if XCAP [16] is
used, the AUID should be provided here. We may want to move to a
model where each service type is a unique XML element; that would
allow for the schema to impose the contraint on a single URI for
each service type.
The "conf-service" element is only provided in notifications if the
subscriber included the value of "general" in its "type" Event header
field parameter.
4.1.2 User Element
Each user element has zero or one "status" elements, indicating their
status in the conference, zero or one "dialog" elements, indicating
their dialog information, and zero or one "media-streams" elements,
indicating their media reception information.
The user element has one mandatory attribute, "uri" that indicates
the URI for the user in the conference. This is a logical identifier,
not a machine specific one (i.e., its taken from the authenticated
identity of the participant). The optional attribute "display-name"
contains a display name for the user. The standard "xml:lang"
language attribute can also be present to indicate the language of
the display name.
4.1.3 Status
The status element contains the status of the user in the conference.
The following statuses are defined:
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active: The user is in an active dialog with the focus.
departed: The user sent a BYE, thus leaving the conference.
booted: The user was sent a BYE by the conference host, booting them
out of the conference.
failed: The server tried to bring the user into the conference, but
its attempt to contact the specific user resulted in a non-200
class final response.
The "status" element is only provided in notifications if the
subscriber included the value of "membership" in its "type" Event
header field parameter.
4.1.4 Dialog
The dialog element is defined in [13]. It is presented from the
viewpoint of the focus. The "dialog" element is only provided in
notifications if the subscriber included the value of "dialog" in its
"type" Event header field parameter.
4.1.5 Media Streams
The "media-streams" element indicates the media streams that the user
is currently connected to. Here, "connected to" implies that a user
has a media line in their SDP [20] which is associated with a media
stream managed by the focus (see Section 2.1 of [9]). With this
definition, a user is connected to a media stream even if they are
not sending any media.
The "media-streams" element has zero or more "media-stream"
sub-elements. The value of the "media-stream" element is an
identifier, unique within the conference, which identifies the media
stream that a user is connected to [9]. The "media-stream" element
also has a mandatory "media-type" attribute which identifies the
media type (audio, video, message and application) of the media
stream.
The "media-streams" element is only provided in notifications if the
subscriber included the value of "basic-media" in its "type" Event
header field parameter.
OPEN ISSUE: This needs to be aligned with the final media policy
mechanisms done in xcon. If we wish this draft to proceed
independently, we should probably remove any notion of media
information.
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4.2 Constructing Coherent State
The conference information subscriber maintains a table for the list
of users in the conference. The table contains a row for each user.
Each row is indexed by a URI, present in the "uri" attribute of the
"user" element. The contents of each row contain the state of that
user as conveyed in the document. The subscriber also maintains a
table for the service URIs in the conference. This table contains a
row for each service type. Each row is indexed by a token, present in
the "id" attribute of the "conf-service" element. The contents of the
row contain the URI and type of that service.
Both tables are associated with a version number. The version number
MUST be initialized with the value of the "version" attribute from
the "conference-info" element in the first document received. Each
time a new document is received, the value of the local version
number, and the "version" attribute in the new document, are
compared. If the value in the new document is one higher than the
local version number, the local version number is increased by one,
and the document is processed. If the value in the document is more
than one higher than the local version number, the local version
number is set to the value in the new document, the document is
processed, and the subscriber SHOULD generate a refresh request to
trigger a full state notification. If the value in the document is
less than the local version, the document is discarded without
processing.
The processing of the conference information document depends on
whether it contains full or partial state. If it contains full state,
indicated by the value of the "state" attribute in the
"conference-info" element, the contents of both tables are flushed.
They are repopulated from the document. A new row in the user table
is created for each "user" element, and a new row in the conferencing
services table is created for each "conf-service" element. If the
document contains partial state, as indicated by the value of the
"state" attribute in the "conference-info" element, the document is
used to update the tables. For each "user" element in the document,
the subscriber checks to see whether a row exists for that user in
the user table. This check is done by comparing the URI in the "uri"
attribute of the "user" element with the URI associated with the row.
If the user doesn't exist in the table, a row is added, and its state
is set to the information from that "user" element. If the user does
exist, its state is updated to be the information from that "user"
element. If a row is updated or created, such that its state is now
booted, failed or departed, that entry MAY be removed from the table
at any time.
Similarly, for each each "conf-service" element in the document, the
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subscriber checks to see whether a row exists for that service in the
service table. This check is done by comparing the id in the "id"
attribute of the "conf-service" element with the id associated with
the row. If the service doesn't exist in the table, a row is added,
and its URI and type are set to be the information from the
"conf-service" element. Since it is not expected that this
information will change during the lifetime of the conference, there
is no way to indicate removal of a service.
OPEN ISSUE: Is this really the right way to bootstrap these URIs?
The information really is static, and placing it in an event
package will result in a waste of bandwidth during full-state
updates.
4.3 Schema
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4.4 Example
The following is an example conference information document:
active
8hha7
active
This document describes a conference with two users, both of which
are active.
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5. Security Considerations
Subscriptions to conference state can reveal very sensitive
information. For this reason, the document recommends authentication
and authorization, and provides guidelines on sensible authorization
policies.
Since the data in notifications is sensitive as well, end-to-end SIP
encryption mechanisms using S/MIME SHOULD be used to protect it.
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6. IANA Considerations
This document registers a SIP event package, a new MIME type,
application/conference-info+xml, a new XML namespace, and a new XML
schema.
6.1 conference Event Package Registration
This specification registers an event package, based on the
registration procedures defined in RFC 3265 [2]. The following is the
information required for such a registration:
Package Name: conference
Package or Template-Package: This is a package.
Published Document: RFC XXXX (Note to RFC Editor: Please fill in XXXX
with the RFC number of this specification).
Person to Contact: Jonathan Rosenberg, jdrosen@jdrosen.net.
6.2 application/conference-info+xml MIME Registration
MIME media type name: application
MIME subtype name: conference-info+xml
Mandatory parameters: none
Optional parameters: Same as charset parameter application/xml as
specified in RFC 3023 [10].
Encoding considerations: Same as encoding considerations of
application/xml as specified in RFC 3023 [10].
Security considerations: See Section 10 of RFC 3023 [10] and Section
5 of this specification.
Interoperability considerations: none.
Published specification: This document.
Applications which use this media type: This document type has been
used to support SIP conferencing applications.
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Additional Information:
Magic Number: None
File Extension: .cif or .xml
Macintosh file type code: "TEXT"
Personal and email address for further information: Jonathan
Rosenberg,
Intended usage: COMMON
Author/Change controller: The IETF.
6.3 URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:conference-info
This section registers a new XML namespace, as per the guidelines in
[8].
URI: The URI for this namespace is
urn:ietf:params:xml:ns:conference-info.
Registrant Contact: IETF, SIPPING working group, ,
Jonathan Rosenberg .
XML:
BEGIN
Dialog Information Namespace
Namespace for Dialog Information
urn:ietf:params:xml:ns:conference-info
See RFCXXXX.