A Session Initiation Protocol (SIP) Event Package for Conference State :: RFC4575
Network Working Group J. Rosenberg
Request for Comments: 4575 Cisco Systems
Category: Standards Track H. Schulzrinne
Columbia University
O. Levin, Ed.
Microsoft Corporation
August 2006
A Session Initiation Protocol (SIP)
Event Package for Conference State
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document defines a conference event package for tightly coupled
conferences using 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 Uniform Resource Identifier (URI). Notifications are sent
about changes in the membership of this conference and optionally
about changes in the state of additional conference components.
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Table of Contents
1. Introduction ....................................................4
2. Terminology .....................................................4
3. Conference Event Package ........................................4
3.1. Event Package Name .........................................5
3.2. Filtering ..................................................5
3.3. Subscription Duration ......................................5
3.4. NOTIFY Bodies ..............................................5
3.5. Notifier Processing of SUBSCRIBE Requests ..................6
3.6. Notifier Generation of NOTIFY Requests .....................6
3.7. Subscriber Processing of NOTIFY Requests ...................6
3.8. Handling of Forked Requests ................................7
3.9. Rate of Notifications ......................................7
3.10. State Agents ..............................................7
4. Conference Document .............................................7
4.1. Format .....................................................7
4.2. Namespace ..................................................7
4.3. Versioning .................................................8
4.4. Partial Notifications Mechanism ............................8
4.5. Element Keys ...............................................9
4.6. Constructing Coherent State Procedure ......................9
5. Conference Data ................................................11
5.1. Overview ..................................................11
5.2. .........................................13
5.3. ..................................14
5.3.1. ........................................14
5.3.2. .....................................15
5.3.3. ...............................16
5.3.4. ..................................16
5.4. ...............................................17
5.4.1. .....................................17
5.4.2. .........................................17
5.4.3. .............................................17
5.5. ........................................17
5.5.1. .......................................17
5.5.2. ...........................................18
5.5.3. ...........................................18
5.6. and Its Sub-elements .......................18
5.6.1. .....................................19
5.6.2. ..................................19
5.6.3. ............................................19
5.6.4. ........................................19
5.6.5. ...................................19
5.6.6. .........................................20
5.7. ................................................20
5.7.1. .....................................20
5.7.2. .........................................21
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5.7.3. ...........................................21
5.7.4. ...................................22
5.7.5. .....................................23
5.7.6. .............................23
5.7.7. ...............................23
5.7.8. ............................................24
5.7.9. ........................................24
5.8. ...................................................24
5.8.1. .....................................25
5.8.2. .............................................25
5.8.3. ............................................25
5.8.4. ...........................................25
5.8.5. ...........................................26
5.9. Sidebars ..................................................26
5.9.1. ..................................26
5.9.2. ...................................26
6. XML Schema .....................................................26
7. Examples .......................................................35
7.1. Basic Example .............................................35
7.2. Rich Example ..............................................36
8. Security Considerations ........................................40
8.1. Connection Security .......................................40
8.2. Authorization Considerations ..............................41
9. IANA Considerations ............................................41
9.1. conference Event Package Registration .....................41
9.2. application/conference-info+xml MIME Registration .........42
9.3. URN Sub-Namespace Registration for ........................43
9.4. XML Schema Registration ...................................43
9.5. URI Purposes Sub-registry Establishment ...................44
10. Acknowledgements ..............................................45
11. References ....................................................45
11.1. Normative References .....................................45
11.2. Informative References ...................................46
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1. Introduction
The Session Initiation Protocol (SIP) events framework [10] 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. Here, we define a SIP event
package for tightly coupled conferences. This package can be used by
the conference notification service as outlined in the SIP
conferencing framework [16]. As described there, subscriptions to a
conference URI are routed to the focus that is handling the
conference. It acts as the notifier and provides clients with
updates on conference state.
The information provided by this package is comprised of conference
identifier(s), conference participants (optionally with their
statuses and media description), conference sidebars, conference
service URIs, etc.
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.
This document uses the conferencing terminology defined in
Conferencing Framework [16]. In addition, the "roster" term is used
to collectively refer to participants in a conference or a sub-
conference.
3. Conference Event Package
The conference event package allows a user to subscribe to the
information relating to a conference. In SIP, conferences are
represented by URIs. These URIs identify a SIP user agent (UA),
called a focus, that is responsible for ensuring that all users in
the conference can communicate with each other, as described in
Conferencing Framework [16]. The focus has sufficient information
about the state of the conference to inform subscribers about it.
It is possible that a participant in the conference may in fact be
another focus. In order to provide a more complete participant list,
the focus MAY subscribe to the conference package of the other focus
to discover the participant list in the cascaded conference. This
information can then be included in notifications by use of the
element as specified by this package.
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This section provides the details for defining a SIP-specific event
notification package, as specified by RFC 3265 [10].
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 RFC 3265
[10].
3.2. Filtering
Filters, which can be applied to conference subscriptions, are a
desirable feature and can be considered as a subject of future
standardization activities. This document does not define the
filters for the conference package to be included in the SUBSCRIBE
body.
A SUBSCRIBE for a conference package, being sent without a body,
implies the default subscription filtering policy. The default
policy is as follows:
o Notifications are generated every time there is any change in the
state of the conference.
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.
3.3. 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" as defined
in RFC 3265 [10].
3.4. NOTIFY Bodies
According to RFC 3265 [10], 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 that describes the state of a
conference. All subscribers and notifiers MUST support the
"application/conference-info+xml" data format described in Sections 9
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and 5. By default, i.e., if no Accept header is specified to a
SUBSCRIBE request, the NOTIFY will contain a body in the
"application/conference-info+xml" data format. If the Accept header
field is present, it MUST include "application/conference-info+xml"
and MAY include any other types.
3.5. 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, it is RECOMMENDED that all users in the conference be
allowed to subscribe to the conference event package.
3.6. Notifier Generation of NOTIFY Requests
Notifications SHOULD be generated for the conference state when a new
participant joins (i.e., gets "connected" to) or a participant leaves
(i.e., gets "disconnected" from) the conference.
Subject to a local focus policy, additional changes in participants'
status, changes in their media types, and other optional information
MAY be reported by the focus.
Changes in sidebar rosters SHOULD be reported by the focus to their
participants and MAY be reported to others, subject to local policy.
Changes in conference identifiers and service URIs SHOULD be reported
by the focus to the conference package subscribers.
Changes in other conference state information MAY be reported by the
focus to the conference package subscribers.
3.7. 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 construct a coherent
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 conference package will need to combine
NOTIFYs received over time.
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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 4.6 for information on
constructing coherent information from an application/
conference-info+xml document.
3.8. 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. If forking happens in the network, subscribers
to this package MUST NOT establish more than a single SIP dialog as a
result of a single SUBSCRIBE request. In the foci cascading case,
detailed conference information can be retrieved by establishing an
individual SUBSCRIBE dialog with each participating focus.
3.9. 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 does not generate notifications for a single
subscriber at a rate faster than once every 5 seconds.
3.10. State Agents
Conference state is ideally maintained in the element in which the
conference resides. Therefore, a conference focus is the best-suited
element to handle subscriptions to it. Cascaded foci MAY implement
state agents (as defined in RFC 3265 [10]) for this package.
4. Conference Document
4.1. Format
Conference information is an XML document that MUST be well-formed
and valid. It MUST be based on Extensible Markup Language (XML) 1.0
and MUST be encoded using UTF-8 [14].
4.2. Namespace
This specification makes use of XML namespaces for identifying
conference information documents and document fragments. The
namespace URI for elements defined by this specification is a Uniform
Resource Namespace (URN) [2], using the namespace identifier 'ietf'
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defined by [6] and extended by RFC 3688 [21]. This URN is as
follows:
urn:ietf:params:xml:ns:conference-info
4.3. Versioning
The conference information is described by a hierarchical XML
structure with the root element . The root element
is the only element in the schema that carries a meaningful version
number for all the elements in the document. The whole conference
information is associated with this version number.
The 'version' attribute MUST be included in the root
element.
4.4. Partial Notifications Mechanism
This specification defines a basic partial notifications mechanism by
using a 'state' attribute as described below. This mechanism MUST be
supported by all subscribing clients. Additional general partial
notifications mechanisms can be defined and applied to this package
in the future.
All sub-elements in the hierarchical XML structure
can be classified in two groups: permissible for partial
notifications or not. Elements that carry a substantial amount of
data that is subject to frequent changes are permissible for partial
notifications and have a 'state' attribute attached to them. All
future extensions to this schema MUST define which extension elements
can also use this mechanism. All other elements can be updated as
atomic pieces of data only.
Below is the complete list of elements permissible to use the partial
notifications mechanism defined in this specification. (Note that
future partial notifications mechanisms can potentially be applicable
to additional elements.)
o Element
o Element
o Element
o Element
o Element
o Element
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The 'state' attribute value indicates whether the reported
information about the element is "full" or "partial", or whether the
element has been "deleted" from the conference state document. The
default value of any 'state' attribute is "full".
A 'state' attribute of a child element in the document MUST be
consistent with its parent 'state'. This means that if the parent's
'state' is "full", the state of its children MUST be "full". If the
parent's 'state' is "partial", the state of its children MAY be
either "partial", "full", or "deleted". A parent element with
"deleted" 'state' SHOULD NOT contain child elements. Any information
provided for child elements of a "deleted" parent MUST be ignored by
the package subscriber.
4.5. Element Keys
The defined XML schema has a property of unique identification among
sub-elements of a common parent, which makes it possible to use the
partial notifications mechanism defined in this document. This
property is achieved by defining a key to each sub-element that can
appear multiple times under the common parent.
In the context of this specification, the element key is the set of
mandatory attributes or sub-elements of an element. The key value
MUST be unique for the element among its siblings of the same type.
In the context of this specification, two keys of type xs:anyURI are
considered to be equal if the UTF-8 representations of the keys
(including all URI parameters that can be included with the URI) are
identical. Consequently, using relative URIs and lexical white space
in these keys is NOT RECOMMENDED.
Below is the list of elements (subject to partial notifications of
their parent elements) with their keys as defined by this
specification:
o Element uses as the key 'entity'
o Element uses as the key 'entity'
o Element uses as the key 'id'
o Element (child to ) uses as the key
'entity'
o Element uses as the key
4.6. Constructing Coherent State Procedure
This section describes the algorithm for constructing a coherent
conference state by a subscriber to the conference package. Using
software programming abstraction, the subscriber maintains a single
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local version number for the whole conference document and a local
element instance for each element in the schema. Also, for each
element with keys (as defined above), the subscriber maintains a
virtual table with a row for each existing key value.
The first time a NOTIFY with a "full" document is received (as
indicated by the value of the 'state' attribute in the
element), the conference package subscriber MUST
set the local 'version' number to the value of the 'version'
attribute from the received and populate local data
with the received information.
Each time a new NOTIFY is received, the value of the local version
number and the value of the 'version' attribute in the new received
document are compared. If the value in the document is equal to or
less than the local version, the document is discarded without
processing.
Otherwise, if the received NOTIFY contains a "full" or "deleted"
state, the conference package subscriber MUST set the local 'version'
number to the value of the 'version' attribute from the received
and replace the local information with the received
document. Receiving "deleted" state for the
element means that the conference has ceased to exist and the
subscriber SHOULD terminate the subscription by sending the SUBSCRIBE
with Expires = 0.
Otherwise (i.e., if the received NOTIFY contains "partial" state), if
the 'version' number in the received document is more than one number
higher than the previous local version number, the subscriber MUST
generate a subscription refresh request to trigger a full state
notification. If the 'version' number in the document is one higher
than the local version number, the local version number is updated
accordingly and the document is used to update the local content as
described below.
For each sub-element of the element in the received
document,
1. If the element contains "full" state, the whole local element
content is flushed and repopulated from the document.
2. Otherwise, if the element contains "deleted" state, the whole
element MUST be removed from the local content.
3. Otherwise, if the element contains "partial" state:
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3.1. For elements with keys, the subscriber compares the keys
received in the update with the keys in the local tables.
3.1.1. If a key does not exist in the local table, a row is
added, and its content is set to the element
information from the update.
3.1.2. Otherwise, if a key of the same value does exist, for
each sub-element in the row, the algorithm is applied
from step 3.2.
3.2. For each atomic element received in the schema, the element
is replaced with the new information as a whole. For each
non-atomic element received in the schema with either no
'state' attribute included or the state attribute is set to
"full", the element is replaced with the new information as a
whole. Also, for each element with the state attribute set
to "deleted", the whole element is removed from the local
content.
3.3. For each non-atomic element with the state attribute set to
"partial", the algorithm is applied recursively starting from
step 3.1.
5. Conference Data
5.1. Overview
The document format is designed to convey
information about the conference and about participation in the
conference. The following non-normative diagram gives an example of
the overall hierarchy used in this format. Conferences contain users
who can be represented by multiple endpoints, each of which can have
multiple media streams. Conferences can also include or reference
"sidebar conferences". When sidebar information is incorporated into
a conference information document in a element,
each element represents a sidebar and can include any
sub-elements permitted in the top-level element.
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conference-info
|
|-- conference-description
|
|-- host-info
|
|-- conference-state
|
|-- users
| |-- user
| | |-- endpoint
| | | |-- media
| | | |-- media
| | | |-- call-info
| | |
| | |-- endpoint
| | |-- media
| |-- user
| |-- endpoint
| |-- media
|
|-- sidebars-by-ref
| |-- entry
| |-- entry
|
|-- sidebars-by-val
|-- entry
| |-- users
| |-- user
| |-- user
|-- entry
|-- users
|-- user
|-- user
|-- user
In most cases, this document does not mandate how the information,
presented through the conference document to the subscribers, is
obtained by the focus. In many cases, the information can be
dynamically learned from the call signaling and can also be manually
populated by an administrator - all subject to local policies. This
document specifies what the XML elements mean in order to allow the
subscribers to appropriately interpret it. Some portions of the
information are intended for processing by automata; others are for
human consumption only. For example, the sub-elements
of elements , , ,
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, , and are intended for display to
human subscribers only.
Although in multiple places this document states that specific
information "SHOULD" be communicated to the subscribers, note that
particular conference package subscribers (e.g., representing a
moderator, an administrator, or a cascaded focus) rely on accuracy of
this information for their proper operation. Therefore, a
conferencing server MUST ensure that all critical changes (stated
as "SHOULD") are communicated to these specific subscribers;
otherwise, these changes MUST be communicated to all subscribers to
the conference information.
Following sections describe the XML schema in more detail.
5.2.
A conference information document begins with the root element tag
of conference-type.
The following attributes are defined for :
entity: This attribute contains the conference URI that identifies
the conference being described in the document. This is the SIP
URI that an interested entity needs to SUBSCRIBE to in order to
get the conference package information. Note that this URI can be
listed as one of the URIs to be used in order to access the
conference by SIP means and in accordance with Section 5.3.1
below.
state: This attribute indicates whether the document contains the
whole conference information ("full") or only the information that
has changed since the previous document ("partial"), or whether
the conference ceased to exist ("deleted"). For more detail, see
Section 4.
version: This attribute allows the recipient of conference
information documents to properly order the received
notifications, and it MUST be used with the root
element. Version number is a 32-bit monotonically increasing
integer scoped within a subscription. A server MUST increment the
version number for each notification (full, partial, and deleted)
being sent to a subscriber and reporting a change in the
conference document state. For each partial notification, the
version number MUST be increased by one. Note that a partial
notification and a subsequent full notification over the same
dialog MAY contain the same version number if no change in the
conference state occurred in between.
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The element is comprised of , , , ,
and child elements. A "full"
conference document MUST at least include the
and child elements.
Following sections describe these elements in detail. The full XML
schema is provided in Section 6.
5.3.
The element describes the conference as a
whole.
The child elements , , , and
are used to describe the conference content:
: Contains descriptive text suitable for human
consumption, for example, listing in a directory
: Contains the subject of the conference
: Contains an additional longer description of the
conference
: Contains a list of space-separated string tokens that
can be used by search engines to better classify the conference
Additional child elements and are used to
describe the conference-related URIs; and
are used to describe the overall characteristics.
This information is typically derived from the system conference
policies, is set before the conference activation, and is rarely
changed during the conference lifetime.
The following sections describe the remaining elements in more
detail. Other sub-elements can extend in
the future.
5.3.1.
This element contains a sequence of child elements - each
containing the URI to be used in order to access the conference by
different signaling means. The value of the URI MUST be unique in
the conference context and is included in the sub-element.
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Each MAY contain additional information useful to the
participant when accessing the conference.
An element MAY contain the sub-element that
provides a textual description meant for human consumption.
Each element SHOULD contain a sub-element that
describes what happens when accessing the URI. The currently defined
values to be used with the are the following:
participation: Accessing a URI with this will bring the
party into the conference.
streaming: Accessing a URI with this will commence
streaming the conference, but not allow active participation.
Examples of suitable URI schemes include sip: and sips: [8], xmpp:
[22], h323: [20], and tel: [19] URIs. The rtsp [18] URI is suitable
for streaming.
Future extensions to this schema may define new values and register
them with IANA under the registry established by this specification.
5.3.2.
This element describes auxiliary services available for the
conference. Like , this element contains a set of
child elements - each containing the URI to be used in order
to access different services available for the particular conference.
The value of the URI MUST be unique in the conference context and is
included in the sub-element.
An element MAY contain the sub-element that
provides a textual description meant for user consumption.
Each element SHOULD contain a sub-element. The
currently defined values to be used with the
are the following:
web-page: Indicates the web page containing the additional
information about the conference.
recording: Indicates the link at which the recorded conference
context can be retrieved.
event: Indicates the URI at which a subscription to the conference
event package may be requested. This would typically be the
conference URI of the main conference.
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Future extensions to this schema may define new values and register
them with IANA under the registry established by this specification.
5.3.3.
The value of this element provides a hint to the recipient of the
conference document about the number of users that can be invited to
the conference. Typically, this value represents the overall number
of users allowed to join the conference by different means as
published through the conference document in . Note that
this value is set by an administrator and can reflect any local
policies combination such as network consumption, CPU processing
power, and licensing rules.
5.3.4.
This element contains a sequence of child elements of
conference-medium-type, each being indexed by the attribute 'label'.
The 'label' attribute is the media stream identifier assigned by the
conferencing server: its value will be unique in the
context. The value of this attribute will
typically correspond to the Session Description Protocol (SDP)
"label" media attribute defined in [17].
Each describes a single media stream available to the
participants in the conference and contains the following
information:
: This element contains the display text for the media
stream.
: This element contains the media type of the media stream.
The value of this element MUST be one of the values registered for
"media" of SDP [3] and its later revision(s), for example,
"audio", "video", "text", and "message".
: This element indicates the available status of the media
stream available to the conference participants. For example,
this would be the status of the media stream, which would be
offered by the focus, in a 'dial-out' scenario. Using normal SIP
offer/answer mechanisms (being defined in RFC 3264 [9]) in both
dial-in and dial-out scenarios, a participant can of course
establish only a subset of the available stream (i.e., request or
accept the stream in one direction only, if both directions are
available). The valid values are "sendrecv", "sendonly",
"recvonly", or "inactive" as defined in SDP [3] and its later
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revision(s). (Note that the value specifies the direction from
the participants' point of view.)
5.4.
This element contains information about the entity hosting the
conference. This information is set before the conference
activation, and it is rarely changed during the conference lifetime,
unless the whole conference is moved to be hosted by another entity.
The host information is comprised of the following elements:
5.4.1.
This element contains display text describing the entity hosting the
conference.
5.4.2.
This element contains HTTP: or HTTPS: URI of a web page describing
either the conference service or the user hosting the conference.
5.4.3.
This element contains a set of child elements, each
containing the URI value and optionally its description.
5.5.
By including this element in the conference document, the server can
inform the subscribers about the changes in the overall conference
information. The child elements are described
below.
5.5.1.
The value of this element tells the recipient of the conference
document the overall number of users participating in the conference
at a certain moment. Typically, this value represents the overall
number of users who joined the conference by different means as
published through the conference document in . Note that
this number does not necessarily need to match and MAY exceed the
number of the entries in the container. For example, in a
lecturing scenario, large conference notifications may not include
every participant in the element, but instead report only the
panelists or the speakers.
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5.5.2.
This Boolean element indicates whether the conference is currently
active. A conference is active if calling one of the by
an authorized client results in successful establishment of a
signaling session between the client and the focus and a successful
joining of the conference.
5.5.3.
This Boolean element says whether the conference is currently locked.
In this context, "locked" means that the conference roster cannot be
added to (although participants may leave or be removed from the
conference).
5.6. and Its Sub-elements
The element is a container of child elements, each
describing a single participant in the conference.
The following attributes are defined for element:
entity: This attribute contains the URI for the user in the
conference. This is a logical identifier, which corresponds to
the call signaling authenticated identity of the participant. The
'entity' value MUST be unique among all participants in the
conference. If, for some participants, the focus decides not to
reveal this information (e.g., due to local policies or security
reasons), the host portion of the user URI MUST use the .invalid
top level domain (TLD) according to definitions of RFC 2606 [5].
The focus also MUST construct the user portion of the URI so that
the URI is unique among all participants of the same domain. For
example, the convention
"AnonymousX"
SHOULD be used for a participant requesting privacy in accordance
with the guidelines for generating anonymous URIs of RFC 3323 [11].
Note that in a different case, such as when used in conjunction with
Enhancements for Authenticated Identity Management in SIP [25], the
following convention can be used:
"AnonymousX"
state: This attribute indicates whether the document contains the
whole user information ("full") or only the information that has
changed since the previous document ("partial"), or whether the
user was removed from the conference ("deleted").
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The following child elements are defined for element:
5.6.1.
This element is used to display the user-friendly name in the
conference.
5.6.2.
This element contains additional (to the 'entity') URIs being
associated with the . Typically, this information will be
manually provided by an administrator showing the logical association
between signaling entities otherwise independent. For example, if
the 'entity' of a contains a Globally Routable User URI (GRUU)
[24] or tel: URI RFC 3966 [19], it would be useful to populate this
field with the Address of Record (AOR) of the person who uses these
devices, each represented as an independent .
5.6.3.
This element MAY contain a set of human-readable strings describing
the roles of the user in the conference. Note that this information
is applicable for human consumption only. This specification does
not define the set of possible conferencing roles or the semantics
associated with each. It is expected that future conferencing
specifications will define these and the corresponding schema
extensions, as appropriate.
5.6.4.
This element contains a list of tokens, separated by spaces, each
containing a language understood by the user. This information can
be automatically learned via call signaling or be manually set per
participant.
5.6.5.
This element contains a conference URI (different from the main
conference URI) for users that are connected to the main conference
as a result of focus cascading. In accordance with the SIP
Conferencing Framework [16], this package allows for representation
of peer-to-peer (i.e., "flat") focus cascading only. The actual
cascading graph cannot be deduced from the information provided in
the package alone. Advanced applications can construct the graph by
subscribing to both this package and the Dialog Package [23] of each
cascaded focus and correlating the relevant information.
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5.6.6.
By including one or more elements under a parent
element, the server can provide the desired level of detail
(including the state, media streams, and access information) about
the user's devices and signaling sessions taking part in the
conference.
In a conferencing system where authentication is performed per
endpoint (rather than per user), the focus can be unaware of the
logical association of multiple endpoints under a common user. In
this case, each endpoint will appear as a separate with its
own sub-element(s) in the conference document.
In a different case, the focus may choose to shield the information
about the participant's multiple endpoints and signaling sessions
from other subscribers altogether (e.g., due to privacy policies).
To do so, the focus MAY aggregate the multiple signaling sessions'
information under a single element. Note that in this
case, the detailed call signaling information (represented by
sub-element) will not be included.
5.7.
This section describes the element in more detail.
The following attributes are defined for the element:
entity: The server MUST generate the 'entity' key for each
element included under the parent , such that its
value is unique in the user context. In SIP terms, this can be
the Contact URI, GRUU, etc.
state: This attribute indicates whether the element contains the
whole endpoint information ("full") or only the information that
has changed since the previous document ("partial"), or whether
the endpoint has been removed from the conference ("deleted").
The following child elements are defined for the element:
5.7.1.
This element contains the display text for the endpoint.
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5.7.2.
This element contains information about the user whose action
resulted in this endpoint being brought into the conference (e.g.,
the SIP user identified by this URI sent a REFER to the focus). It
MAY contain the following sub-elements:
when: This element of the XML dateTime type contains the date and
time that the endpoint was referred to the conference and SHOULD
be expressed in Coordinated Universal Time (UTC) format. For
example,
2005-03-04T20:00:00Z
reason: This element contains the reason the endpoint was referred
to the conference. Including the information in the format
defined by RFC 3326 [12] is RECOMMENDED. For example,
Reason: SIP;text="Ad-hoc Invitation"
by: This element contains the URI of the entity that caused the
endpoint to be referred to the conference. In the case of SIP, it
will be populated from the Referred-By header defined in RFC 3892
[15].
5.7.3.
This element contains the status of the endpoint and can assume the
following values:
connected: The endpoint is a participant in the conference.
Depending on the media policies, he/she can send and receive media
to and from other participants.
disconnected: The endpoint is not a participant in the conference,
and no active dialog exists between the endpoint and the focus.
on-hold: Active signaling dialog exists between an endpoint and a
focus, but endpoint is "on-hold" for this conference, i.e., he/she
is neither "hearing" the conference mix nor is his/her media being
mixed in the conference. As an example, the endpoint has asked to
join the conference using SIP, but his/her participation is
pending based on moderator approval. In the meantime, he/she is
hearing music-on-hold or some other kind of related content.
muted-via-focus: Active signaling dialog exists between an endpoint
and a focus and the endpoint can "listen" to the conference, but
the endpoint's media is not being mixed into the conference. Note
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that sometimes a subset of endpoint media streams can be muted by
focus (such as poor-quality video) while others (such as voice or
IM) can still be active. In this case, it is RECOMMENDED that the
"aggregated" endpoint connectivity reflects the status of
the most active media.
pending: Endpoint is not yet in the session, but it is anticipated
that he/she will join in the near future.
alerting: A Public Switched Telephone Network (PSTN) ALERTING or SIP
180 Ringing was returned for the outbound call; endpoint is being
alerted.
dialing-in: Endpoint is dialing into the conference, not yet in the
roster (probably being authenticated).
dialing-out: Focus has dialed out to connect the endpoint to the
conference, but the endpoint is not yet in the roster (probably
being authenticated).
disconnecting: Focus is in the process of disconnecting the endpoint
(e.g., in SIP a DISCONNECT or BYE was sent to the endpoint).
Note that the defined transient statuses (e.g., disconnecting,
alerting, etc.) could generate a lot of traffic. Therefore,
implementations MAY choose to generate notifications on these
statuses to certain participants only or not generate them at all,
subject to local policy.
5.7.4.
This element contains the method by which the endpoint joined the
conference and can assume the following values:
dialed-in: The endpoint dialed into the conference (e.g., in a SIP
sent INVITE to the focus), which resulted in successful dialog
establishment.
dialed-out: The focus has brought the endpoint into the conference
(e.g., in SIP, the focus sent a successful INVITE to the
endpoint).
focus-owner: The endpoint is the focus for this conference. This
status is used only when a participant's UA acts as a conference
focus.
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5.7.5.
This element contains information about how the endpoint joined and
MAY contain the following sub-elements:
when: This element of the XML dateTime type contains the date and
time that the endpoint joined the conference and SHOULD be
expressed in Coordinated Universal Time (UTC).
reason: This element contains the reason the endpoint joined the
conference. Including the information in the format defined by
RFC 3326 [12] is RECOMMENDED. For example,
Reason: SIP;text="Ad-hoc Invitation"
by: This element contains the URI of the entity that caused the
endpoint to join the conference.
5.7.6.
This element contains the method by which the endpoint departed the
conference and can assume the following values:
departed: In SIP, the endpoint sent a BYE, thus leaving the
conference.
booted: In SIP, the endpoint was sent a BYE by the focus, ejecting
him/her out of the conference. Alternatively, the endpoint tried
to dial into the conference but was rejected by the focus due to
local policy.
failed: In SIP, the server tried to bring the endpoint into the
conference, but its attempt to contact the specific endpoint
resulted in a non-200 class final response. Alternatively, the
endpoint tried to dial into the conference without success due to
technical reasons.
busy: In SIP, the server tried to bring the endpoint into the
conference, but its attempt to contact the specific endpoint
resulted in a 486 "Busy Here" final response. Alternatively, the
endpoint tried to dial into the conference but the focus responded
with 486 response.
5.7.7.
This element contains information about the endpoint's departure from
the conference and MAY contain the following sub-elements:
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when: This element of the XML dateTime type contains the date and
time that the endpoint departed the conference and SHOULD be
expressed in Coordinated Universal Time (UTC).
reason: This element contains the reason the endpoint departed the
conference. When known and meaningful, including the information
as conveyed/reported by the call signaling in the format defined
by RFC 3326 [12] is RECOMMENDED. For example,
Reason: SIP;cause=415;text="Unsupported Media Type"
by: This element contains the URI of the entity that caused the
endpoint to depart the conference.
5.7.8.
This element contains information about a single media stream and is
included for each media stream being established between the focus
and the . The media stream definition can be found in SDP
[3].
Note that if the sub-element of the endpoint is not
included in the document by the server, it is possible that the media
streams listed under the common were established by
separate signaling sessions.
5.7.9.
The element provides detailed call signaling information
for a call being maintained between the participant and the focus.
Privacy policies MUST be consulted before revealing this information
to other participants.
The sub-element contains the SIP dialog identifier of the
endpoint's dialog with the focus. The element includes sub-elements
, , , .
In future, the element can be expanded to include call
signaling protocol information for other protocols besides SIP.
5.8.
This section describes the element in more detail.
A single 'id' attribute is defined for this element. This is the
media stream identifier being generated by the server such that its
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value is unique in the endpoint context. This attribute is the key
to refer to a particular media stream in the conference document.
The following child elements are defined for :
5.8.1.
This element contains the display text for the media stream. The
value of this element corresponds to the SDP description media
attribute ("i") defined in SDP [3].
5.8.2.
This element contains the media type for the media stream. The value
of this element MUST be one of the values registered for "media" of
SDP [3] and its later revision(s).
5.8.3.
The element carries a unique identifier for this stream among
all streams in the conference and is assigned by the focus. The
value of this element will typically correspond to the SDP "label"
media attribute defined in [17] and is exchanged between a
participant and a focus over the signaling connection between them.
If the information (described in Section 5.3.4) is
included in the conference document, the value of this element MUST
be equal to the 'label' value of the corresponding media stream
in the container.
5.8.4.
The element, if applicable, carries the information about
the actual source of the media. For example, for Real-time Transport
Protocol (RTP) / RTP Control Protocol (RTCP) [13] media streams, the
value MUST contain the synchronization source (SSRC) identifier value
generated by the endpoint for the stream it sends.
When an RTP mixer generates a contributing source (CSRC) identifiers'
list according to RTP/RTCP [13], it inserts a list of the SSRC
identifiers of the sources that contributed to the generation of a
particular packet into the RTP header of that packet. A quote from
RFC 3550 [13] explains as follows: "An example application is audio
conferencing where a mixer indicates all the talkers whose speech was
combined to produce the outgoing packet, allowing the receiver to
indicate the current talker, even though all the audio packets
contain the same SSRC identifier (that of the mixer)."
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If an RTP mixer compliant to the above is used, participants can
perform an SSRC to user mapping and identify "a current speaker".
5.8.5.
The element indicates the status in both directions of the
media stream and has the values "sendrecv", "sendonly", "recvonly",
or "inactive" as defined in SDP [3] and its later revision(s). Note
that value specifies the direction from the participant's point of
view. For example, a muted participant's stream will have the value
of "recvonly".
5.9. Sidebars
If a participant in the main conference joins a sidebar, a new
element representing the user is created either as a part of a
separate sub-conference referenced from the element
or under one of the elements as described below.
Note that the in the main roster is not being deleted, but its
media statuses can be updated to reflect the effect being caused by
his/her participation in the sidebar. The display of this
information can vary among subscribers to the same conference
information, subject to local policies and to the subscriber role
both in the sidebar and in the main conference.
5.9.1.
This element contains a set of child elements, each
containing a sidebar conference URI. The recipient of the
information can then subscribe to sidebar information independently
from the main conference package subscription.
5.9.2.
This element contains a set of child elements, each
containing information about a single sidebar. By using this element
of conference-type, the server can include a full or partial
description of each sidebar (as a sub-conference) in the body of the
main conference document.
6. XML Schema
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7. Examples
7.1. Basic Example
The following is an example of a full conference information
document:
Agenda: This month's goals
http://sharepoint/salesgroup/
web-page
33
Bob Hoskins
Bob's Laptop
disconnected
departed
2005-03-04T20:00:00Z
bad voice quality
sip:mike@example.com
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main audio
audio
34567
432424
sendrecv
Alice
connected
dialed-out
2005-03-04T20:00:00Z
sip:mike@example.com
main audio
audio
34567
534232
sendrecv
7.2. Rich Example
The following is an example of a partial conference information
document. In this example, there are 32 participants in a voice
conference. The user Bob has been ejected from the conference by
Mike due to bad voice quality. Note that there are three sidebars in
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the conference; two are referenced just by their sidebar URIs, and
information about the third sidebar is included in this notification.
Also note that while this conference offers both audio and video
capabilities, only audio is currently in use.
Weekly Sales Meeting
Agenda: This month's goals
We will start strict on time
sales meeting weekly
tel:+18005671234
TTI Bridge
participation
h323:conf545@h323.example.com
participation
http://real.streaming.com/54634/live.ram
streaming
http://sharepoint/salesgroup/
web-page
http://quicktime.com/54634/recording.mov
Quicktime
recording
100
main audio
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audio
sendrecv
main video
video
inactive
Sales Host
http://sharepoint/salesgroup/hosts/
sip:sales@example.com
32
true
false
Bob Hoskins
mailto:bob@example.com
email
participant
en
Bob's Laptop
2005-03-04T20:00:00Z
expert required
sip:mike@example.com
disconnecting
dialed-out
2005-03-04T20:00:00Z
invitation
sip:mike@example.com
booted
2005-03-04T20:00:00Z
bad voice quality
sip:mike@example.com
main audio
audio
34567
432424
sendrecv
full info
hsjh8980vhsb78
vav738dvbs
8954jgjg8432
sips:conf233@example.com;grid=45
sidebar with Carol
sips:conf233@example.com;grid=21
private with Peter
8. Security Considerations
Subscriptions to conference state information can reveal very
sensitive information. For this reason, it is RECOMMENDED that a
focus use a strong means for authentication and conference
information protection and that it apply comprehensive authorization
rules when using the conference notification mechanism defined in
this document. The following sections will discuss each of these
aspects in more detail.
8.1. Connection Security
It is RECOMMENDED that a focus authenticate a conference package
subscriber using the normal SIP authentication mechanisms, such as
Digest as defined in Section 22 of RFC 3261 [8].
The mechanism used for conveying the conference information MUST
ensure integrity and SHOULD ensure confidentially of the information.
In order to achieve these, an end-to-end SIP encryption mechanism,
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such as S/MIME described in Section 26.2.4 of RFC 3261 [8], SHOULD be
used.
If a strong end-to-end security means (such as above) is not
available, it is RECOMMENDED that a focus use mutual hop-by-hop
Transport Layer Security (TLS) authentication and encryption
mechanisms described in Section 26.2.2 "SIPS URI Scheme" and Section
26.3.2.2 "Interdomain Requests" of RFC 3261 [8].
8.2. Authorization Considerations
Generally speaking, conference applications are very concerned about
authorization decisions. Mechanisms for establishing and enforcing
such authorization rules are a central concept throughout the SIP
Conferencing Framework [16]. Because most of the information about a
conference can be presented using the conference package, many of the
authorization rules directly apply to this specification. As a
result, a notification server MUST be capable of generating distinct
conference information views to different subscribers, subject to a
subscriber's role in a conference, personal access rights, etc. - all
subject to local authorization policies and rules.
Since a focus provides participant identity information using this
event package, participant privacy needs to be taken into account. A
focus MUST support requests by participants for privacy. Privacy can
be indicated by the conference policy - for every participant or
select participants. It can also be indicated in the session
signaling. In SIP, this can be done using the Privacy header field
described in RFC 3323 [11]. For a participant requesting privacy, no
identity information SHOULD be revealed by the focus in any included
URI (e.g., the Address of Record, Contact, or GRUU). For these
cases, the anonymous URI generation method outlined in Section 5.6 of
this document MUST be followed.
9. 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, and creates a sub-registry "URI purposes" under the existing
registry: http://www.iana.org/assignments/sip-parameters.
9.1. conference Event Package Registration
This specification registers an event package, based on the
registration procedures defined in RFC 3265 [10]. The following is
the information required for such a registration:
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Package Name: conference
Package or Template-Package: This is a package.
Published Document: RFC 4575
Person to Contact: IETF SIPPING Working Group , as
designated by the IESG
9.2. 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 [7]
Encoding considerations: Same as encoding considerations of
application/xml as specified in RFC 3023 [7]
Security considerations: See Section 10 of RFC 3023 [7] and
Section 8 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
Additional Information:
Magic Number: None
File Extension: .xml
Macintosh file type code: "TEXT"
Personal and email address for further information: IETF SIPPING
Working Group , as designated by the IESG
Intended usage: COMMON
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Author/Change controller: IETF SIPPING Working Group
, as designated by the IESG
9.3. URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:conference-info
This section registers a new XML namespace, as per the guidelines in
RFC 3688 [21].
URI: The URI for this namespace is
urn:ietf:params:xml:ns:conference-info
Registrant Contact: IETF SIPPING Working Group ,
as designated by the IESG
XML:
BEGIN
Conference Information Namespace
Namespace for Conference Information
urn:ietf:params:xml:ns:conference-info
See
RFC4575 .
