XCON BOF R. Even
Internet-Draft Polycom
Expires: December 21, 2003 O. Levin
RADVISION
N. Ismail
Cisco Systems, Inc.
June 22, 2003
Conferencing media policy requirements
draft-even-xcon-media-policy-requirements- 00.txt
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Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document defines the requirements for Media Policy, i.e. a set
of rules associated with the media distribution of the conference.
This document presents the requirements for the media manipulations
that can be done using these rules by conference participants or
third parties using any kind of media/conference policy control
protocol. This document does not address the interface between the
focus and the media policy.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Rational . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. High Level Architecture . . . . . . . . . . . . . . . . . . . 3
5. Media Policy Data Model . . . . . . . . . . . . . . . . . . . 5
5.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Media Policy Requirements . . . . . . . . . . . . . . . . . . 6
6.1 Genera Media Policy Requirements . . . . . . . . . . . . . . . 6
6.2 Video specific requirements . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . 9
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1. Introduction
The Conferencing Framework [2] presents an overall framework and
defines the terminology for SIP [1] tightly coupled conferencing.
The conferencing framework architecture includes the media policy.
This is a set of rules that describes the media distribution of a
conference. This document presents the requirements for the media
policy data model and for the manipulations on these rules by
conference participants or third parties using any kind of media/
conference policy control protocol. This document does not address
the interface between the focus and the media policy and between the
focus and the media mixer.
2. Rational
The media policy enables a conference participant or an application
server to define and manipulate the content of the media streams
going to the conference participants. This will enable applications
like sidebars, announcement to specific participants, call centers
and panel conferences.
3. Terminology
The draft relies on the terminology defined in the conferencing
framework document[2].
4. High Level Architecture
The basic conferencing architecture used in this document is defined
in the Conferencing architecture framework [2]. This document
focuses on the media policy component and the requirements to
manipulate the media policy by authorized entities.
An authorized entity can manipulate the media policy using a supplied
application. Examples for such applications include a web
application, an interactive voice response application, an
interactive Instant Messaging (IM) base application, or an
application that uses the media policy control protocol.
The Conference policy control protocol (CPCP) provides a standard way
for an automated authorized entity to manipulate the media policy.
The requirements and definition of the CPCP protocol are out of scope
of this document.
The media policy is a set of rules that describes the media mixing or
switching required for each participant in the conference. This
includes the set of sources to be mixed or switched and the rules for
their mixing or switching. The focus uses the media policy to
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determine the proper configuration of the mixers. Authorized
entities will be notified of changes to the media policy by
subscribing to the conference event package. The information about
the current contributing sources to the mixed streams can be learned
by the information in the RTP header or by the conference event
package [4]. The data structures that include the contributing
sources of the current streams is in the focus or the mixer and is
not in the scope of the work.
The initial state of the media policy data structure is defined at
the conference creation time. It can be either provisioned or
created by using a conference policy control protocol or/and other
protocols being used to create the conference.
Typically, a focus has access to the media policy and is responsible
for translating the media policy data into the actions towards the
physical entities ("mixers").
Figure 1 describes an instance of media policy of a conference. The
figure shows a single mixer and a single type of stream for ease of
drawing but the model does not have such a restriction.
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Conference .
Policy . +-----------+ //-----\\ .
Control . | | || || .
Protocol . | Conference| \\-----// .
+------------->| Policy | | | .
| . | Server |----> |Conference .
| . | | | | .
| . +-----------+ | & | .
| . | | .
| . | Media | .
+------------+ . +-----------+ | Policy| .
| +----------++ . | | \ // .
| | || . | | \-----/ .
|Participants||<-------->| Focus | | .
| | || SIP . | | | .
| | || Dialog . | |<-----------+ .
+-+----------++ . +-----------+ .
+-----------+ . | .
^ | . | .
| | Contributing . | .
| | Streams . +-----------+ .
| +------------->. | | .
| Distributed . | Mixer | .
| Streams . | | .
+-------------------. +-----------+ .
.....................................
Conference
Functions
Figure 1: Media Policy in a Conference
5. Media Policy Data Model
5.1 General
The fundamental conferencing functionality is being able to combine
(i.e. "to mix") in a media specific manner participants' streams
that belong to a logical sub-function within a conference (such as
participant's video, left audio stream, right audio stream, video
streaming presentation, slide presentation) and are of the same media
type (such as video, audio, etc.). In the case of using
centralized-mixing the resultant stream(s) will be sent back to the
participants. In the case of end-point mixing, the original streams,
needed to produce the mixed media, will be distributed to the
participants that will perform the actual mixing.
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Typically, the maximum number of different mixers in a conference is
preconfigured as part of the media conference policy. Mixers MAY be
dynamically created and destroyed during the conference lifetime.
This document will not describe the data model itself.
6. Media Policy Requirements
All the requirements are based on having a privilege mechanism that
authorizes users to access and manipulate the media policy data. The
requirements are for the manipulations that can be done on the media
distrbution by the mixer using the CPCP protocol. The protocol
itself is not in the scope of this document. Authorization is also
part of CPCP. The requirements are not for the mixer itself.
6.1 Genera Media Policy Requirements
REQ-GP1: An authorized participant MUST be able to specify its own
unique topology.
REQ-GP2: It MUST be possible for a group of users to receive the same
mix. This mix may be a conference common mix.
REQ-GP3:It MUST be possible, using the protocol, to dynamically
modify the number of contributing streams associated with a mixer.
REQ-GP4: It MUST be possible, using the protocol, to define the
mixing function for each participant in the conference.
REQ-GP6: It SHOULD be possible to send a participant multiple streams
from one mixer. This requirement is to enable support for end- point
mixing.
REQ-GP7: It SHOULD be possible to define relationships between
different mixers. The relationships can be time synchronized such as
specifying that the audio mixer and video mixer is a pair to
establish lip-synchs.
REQ-GP8: It SHOULD be possible to define the number of different
topologies and the number of streams in each of them that will be
mixed in a mixer. For example the conference will support only one
video topology that will go to all the participants, the video
topology will support 2x2 display, or each participant will be able
to receive his own audio topology that will include up to 4
contributing sources.
REQ-GP9: It SHOULD be possible to have more then one stream from the
same type (video or audio) coming from the same user and to mix them
separatly. For example one video stream will be the video camera
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showing the speakerwhile the other may be a presntation or a second
camera showing the whole room.
6.2 Video specific requirements
Video is a bit different than audio when mixing is concerned. In
multipoint video the common mixing modes are:
Video switching where one of the contributing sources is sent to all
participants, the video source may be forced by the media policy
control protocol or may be dynamic by using for example a voice
activated video switching mode where the participants will see the
loudest speaker.
"Continuous presence" or tiled windows display where the topology is
composing one video stream that has a layout defining the shape and
position of viewing windows that will be displayed to the
participants. The layout includes N viewing windows so that in each
of the windows there is one contributing stream. Even though the
viewing windows can be of any shape we will address in this work only
rectangular windows of any size. The windows may overlap.
The section defines the specific requirements for media policy and
media policy control to enable "Continuous presence"
REQ-V1: It should be possible to define rectangular overlapping
windows in a video mix.
REQ-V2: It should be possible to map a stream to a window based on
some mode like having one window display the loudest speaker or the
floor holder while for the remaining windows fixed input streams are
used.
REQ-V3: It should be possible for authorized participants to change
the layout of the video topology.
REQ-V4: It should be possible for authorized participants to define
the mapping of a stream to a window.
7. Security Considerations
The media policy control protocol may enables unauthorized users to
manipulate the media mixing of conferences, this may enable them to
listen to conference or eject unsolicited media streams. The
protocol should provide authentication of the users. The media
policy data may include information about the sources and targets of
mixer, if this information will be transferred in the protocol in the
clear that may cause a security risk. The protocol should allow for
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encryption of the media policy transferred in the media policy
control protocol.
References
[1] 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.
[2] Rosenberg, J., "A Framework for Conferencing with the Session
Initiation Protocol", draft-
rosenberg-sipping-conferencing-framework-01 (work in progress),
February 2003.
[3] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002.
[4] Rosenberg, J. and H. Schulzrinne, "A session initiation
protocol (SIP) event package for conference state", , June 2002.
Authors' Addresses
Roni Even
Polycom
94 Derech Em Hamoshavot
Petach Tikva 49130
Israel
EMail: roni.even@polycom.co.il
Orit Levin
RADVISION
266 Harristown Road
Glen Rock
NJ USA
EMail: orit@radvision.com
Nermeen Ismail
Cisco Systems, Inc.
170 West Tasman Drive
San Jose 95134
CA USA
EMail: nismail@cisco.com
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