draft-ietf-mmusic-sdp-media-content-02.txt   draft-ietf-mmusic-sdp-media-content-03.txt 
MMUSIC Working Group J. Hautakorpi MMUSIC Working Group J. Hautakorpi
Internet-Draft G. Camarillo Internet-Draft G. Camarillo
Expires: September 7, 2006 Ericsson Expires: October 13, 2006 Ericsson
March 6, 2006 April 11, 2006
The SDP (Session Description Protocol) Content Attribute The SDP (Session Description Protocol) Content Attribute
draft-ietf-mmusic-sdp-media-content-02.txt draft-ietf-mmusic-sdp-media-content-03.txt
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document defines a new Session Description Protocol (SDP) media- This document defines a new Session Description Protocol (SDP) media-
level attribute, 'content'. The 'content' attribute defines the level attribute, 'content'. The 'content' attribute defines the
content of the media stream in more detailed level than the media content of the media stream in more detailed level than the media
description line. The sender of an SDP session description can description line. The sender of an SDP session description can
attach the 'content' attribute to one or more media streams. The attach the 'content' attribute to one or more media streams. The
receiving application can then treat each media stream differently receiving application can then treat each media stream differently
(e.g., show it on a big screen or small screen) based on their (e.g., show it on a big screen or small screen) based on its content.
content.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Related Techniques . . . . . . . . . . . . . . . . . . . . . . 3 3. Related Techniques . . . . . . . . . . . . . . . . . . . . . . 3
4. Motivation for the New Content Attribute . . . . . . . . . . . 4 4. Motivation for the New Content Attribute . . . . . . . . . . . 4
5. The Content Attribute . . . . . . . . . . . . . . . . . . . . 5 5. The Content Attribute . . . . . . . . . . . . . . . . . . . . 5
6. The Content Attribute in the Offer/Answer Model . . . . . . . 6 6. The Content Attribute in the Offer/Answer Model . . . . . . . 6
7. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Operation with SMIL . . . . . . . . . . . . . . . . . . . . . 7 8. Operation with SMIL . . . . . . . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 7 9. Security Considerations . . . . . . . . . . . . . . . . . . . 7
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
11. Acknowledges . . . . . . . . . . . . . . . . . . . . . . . . . 9 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
12.1. Normative References . . . . . . . . . . . . . . . . . . 9 12.1. Normative References . . . . . . . . . . . . . . . . . . 9
12.2. Informational References . . . . . . . . . . . . . . . . 9 12.2. Informational References . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . . . 12 Intellectual Property and Copyright Statements . . . . . . . . . . 12
1. Introduction 1. Introduction
SDP [1] is a protocol that is intended for describing multimedia The Session Description Protocol (SDP) [1] is a protocol that is
sessions for the purposes of session announcement, session intended for describing multimedia sessions for the purposes of
invitation, and other forms of multimedia session initiation. One of session announcement, session invitation, and other forms of
the most typical use cases of SDP is the one where it is used with multimedia session initiation. One of the most typical use cases of
SIP [5]. SDP is the one where it is used with the Session Initiation Protocol
(SIP) [5].
There are situations where one application receives several similar There are situations where one application receives several similar
media stream which are described in an SDP session description. The media streams which are described in an SDP session description. The
media streams can be similar in a sense that their content cannot be media streams can be similar in the sense that their content cannot
distinguished from each other just by examining the media description be distinguished just by examining the media description lines (e.g.,
lines (e.g., two video streams). The 'content' attribute is needed, two video streams). The 'content' attribute is needed, so that the
so that the receiving application can treat each media stream receiving application can treat each media stream appropriately based
appropriately based on its content. on its content.
This specification defines the SDP 'content' media-level attribute, This specification defines the SDP 'content' media-level attribute,
which provides more information about the media stream than the 'm' which provides more information about the media stream than the 'm'
line in an SDP session description. line in an SDP session description.
2. Terminology 2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [3] and indicate requirement levels for described in BCP 14, RFC 2119 [3] and indicate requirement levels for
compliant implementations. compliant implementations.
3. Related Techniques 3. Related Techniques
The 'label' attribute [10] enables a sender to attach a pointer to a The 'label' attribute [9] enables a sender to attach a pointer to a
particular media stream. The name space of the 'label' attribute particular media stream. The name space of the 'label' attribute
itself is unrestricted, so in principle it could also be used to itself is unrestricted, so in principle it could also be used to
convey information about the content of a media stream. However, in convey information about the content of a media stream. However, in
practice, this is not possible because of the backwards practice, this is not possible because of the need for backward
compatibility. Existing implementation of the 'label' attribute compatibility. Existing implementations of the 'label' attribute
already use values from that unrestricted namespace in an application already use values from that unrestricted namespace in an application
specific way. So, it is not possible to reserve parts from the specific way. So it is not possible to reserve portions of the
'label' attributes' namespace without possible conflict with an 'label' attribute's namespace without possible conflict with already
already used, application specific labels. used, application specific labels.
It is possible to assign semantics to a media stream with the It is possible to assign semantics to a media stream with an external
external document that uses the 'label' attribute as a pointer. The document that uses the 'label' attribute as a pointer. The downside
downside of this approach is that it requires external document. of this approach is that it requires external document. Typically
Typically this kind of mechanism would be defined for some particular this kind of mechanism would be defined for some particular use case,
use case, for example centralized conferencing. for example centralized conferencing.
Yet another way to attach semantics to a media stream is by using the Yet another way to attach semantics to a media stream is by using the
'i' SDP attribute, defined in RFC 2327 [6]. Nevertheless, values of 'i' SDP attribute, defined in [1]. However, values of the 'i'
the 'i' attribute are intended for human users and not for automata. attribute are intended for human users and not for automata.
4. Motivation for the New Content Attribute 4. Motivation for the New Content Attribute
Currently, SDP does not provide any means to describe what is the Currently, SDP does not provide any means to describe what is the
content of a media stream (e.g., speaker's image, slides, sign content of a media stream (e.g., speaker's image, slides, sign
language) in a form that the application can understand. Of course language) in a form that the application can understand. Of course
the end user can see the content of the media stream, and read its the end user can see the content of the media stream and read its
title, but the application cannot understand what the media stream title, but the application cannot understand what the media stream
contains. contains.
The application that is receiving multiple similar (e.g., same type The application that is receiving multiple similar (e.g., same type
and format) media stream needs, in some cases, to know what is the and format) media stream needs, in some cases, to know what is the
content of those streams. This kind of situation occurs for example content of those streams. This kind of situation occurs, for
in cases where presentation slides, speakers image and sign language example, in cases where presentation slides, the speaker's image and
are transported as separate media streams. It would be desirable sign language are transported as separate media streams. It would be
that the receiving application could distinguish them in a way that desirable that the receiving application could distinguish them in a
it could handle them automatically in appropriate manner. way that it could handle them automatically in appropriate manner.
+--------------------------------------+ +--------------------------------------+
|+------------++----------------------+| |+------------++----------------------+|
|| || || || || ||
|| speaker's || || || speaker's || ||
|| image || || || image || ||
|| || || || || ||
|+------------+| presentation || |+------------+| presentation ||
|+------------+| slides || |+------------+| slides ||
|| || || || || ||
|| sign || || || sign || ||
|| language || || || language || ||
|| || || || || ||
|+------------++----------------------+| |+------------++----------------------+|
+--------------------------------------+ +--------------------------------------+
Figure 1: Application's screen Figure 1: Application's screen
The Figure 1 presents a screen of a typical communication The Figure 1 presents a screen of a typical communication
application. The 'content' attribute enables the application to make application. The 'content' attribute enables the application to make
the decision on where to show each media stream. From end user's the decision on where to show each media stream. From an end user's
perspective, it is desirable that the user does not need to arrange perspective, it is desirable that the user does not need to arrange
media stream every time the media session starts. media stream every time the media session starts.
The 'content' attribute could also be used in more complex The 'content' attribute could also be used in more complex
situations. This kind of complex situation could be e.g., an situations. This kind of complex situation could be e.g., an
application that is controlling the equipments in the auditorium. application that is controlling the equipment in an auditorium. An
auditorium can have many different output channels for the video
Auditorium can have many different output channels for the video
(main screen and two smaller screens) and the audio (main speakers, (main screen and two smaller screens) and the audio (main speakers,
headsets for the participants). In this kind of environment, a lot headsets for the participants). In this kind of environment, a lot
of interaction from the end user who is operating the application of interaction from the end user who is operating the application
would be required. So, the possibility for the application to handle would be required in absence of cues from a controlling application.
the media stream without end users input is greatly emphasized. So, the possibility for such an application to handle the media
stream without end users' input is highly desirable.
5. The Content Attribute 5. The Content Attribute
This specification defines a new media-level value attribute, This specification defines a new media-level value attribute,
'content'. Its formatting in SDP is described by the following BNF 'content'. Its formatting in SDP is described by the following BNF
[2]: [2]:
content-attribute = "a=content:" mediacnt-tag content-attribute = "a=content:" mediacnt-tag
mediacnt-tag = mediacnt *("," mediacnt) mediacnt-tag = mediacnt *("," mediacnt)
mediacnt = "slides" / "speaker" / "sl" / "main" mediacnt = "slides" / "speaker" / "sl" / "main"
/ "alt" / "user-floor" / "txp" / "alt" / "user-floor" / "txp"
/ mediacnt-ext / mediacnt-ext
mediacnt-ext = token mediacnt-ext = token
The 'content' attribute contains a token, which MAY be attached to a The 'content' attribute contains a token, which MAY be attached to a
media stream by a sending application. It describes the content of media stream by a sending application. It describes the content of
the transmitted media stream to the receiving application. Many the transmitted media stream to the receiving application. Multiple
'content' attribute values MAY be attached to a single media stream. 'content' attribute values MAY be attached to a single media stream.
There is a set of pre-defined values for the 'content' attribute. This document provides a set of pre-defined values for the 'content'
Also other values can be defined in the future. The pre-defined attribute. Other values can be defined in the future. The pre-
values are: defined values are:
slides: This is a media stream that includes presentation slides. slides: This is a media stream that includes presentation slides.
The media type can be e.g., a video stream or a set of instant The media type can be e.g., a video stream or a set of instant
message with pictures. Typical use case for this is e.g., online message with pictures. A typical use case for this is e.g.,
seminars and courses. This is similar to the 'presentation' role online seminars and courses. This is similar to the
in H.239 [12]. 'presentation' role in H.239 [11].
speaker: This is a image from the speaker. The media can be e.g., a speaker: This is a image from the speaker. The media can be e.g., a
video stream or a still image. Typical use case for this is e.g, video stream or a still image. Typical use case for this is e.g,
online seminars and courses. online seminars and courses.
sl: This means that the media stream contains sign language. The sl: This means that the media stream contains sign language. The
media type is a video stream. Typical use case for this is the media type is a video stream. A typical use case for this is one
one where the audio stream is translated into sign language. where the audio stream is translated into sign language.
main: This means that the media stream is taken from the main source. main: This means that the media stream is taken from the main source.
Typical use case for this is e.g., a concert, where the camera is A typical use case for this is a concert, where the camera is
shooting the performer. shooting the performer.
alt: This means that the media stream is taken from the alternative alt: This means that the media stream is taken from the alternative
source. Typical use case for the is e.g., an event, where there source. A typical use case for this is an event, where there is a
is a separate ambient sound and the main sound. The alternative separate ambient sound and the main sound. The alternative audio
audio stream could be e.g., a sound of a jungle. Another example stream could be e.g., the sound of a jungle. Another example is
is the video of the conference room while the main is the video of the video of the conference room while the main is the video of
the speaker. This is similar to the 'live' role in H.239. the speaker. This is similar to the 'live' role in H.239.
user-floor: This indicates that a user level floor control is user-floor: This indicates that a user level floor control is
required. In other words, this is meant for system without any required. In other words, this is meant for system without any
mechanism for floor control, and where a human needs to figure out mechanism for floor control, where a human needs to figure out
whether an act of floor control, e.g., saying 'over', is needed or whether an act of floor control, e.g., saying 'over', is needed or
not. Typical use case for this is e.g., a situation where the not. A typical use case for this is a situation where the other
other endpoint of the connection is a walkie-talkie type of endpoint of the connection is a walkie-talkie type of device.
device.
txp: This indicates that the media stream is originated from a txp: This indicates that the media stream is originated from a
textphone, and it requires special behavior from the receiving textphone, and it requires special behavior from the receiving
application. Typical use case for this is e.g., a connection application. A typical use case for this is a connection where
where one endpoint is an analog textphone of a kind that cannot one endpoint is an analog textphone of a kind that cannot handle
handle two-way simultaneous text communication, and the other one two-way simultaneous text communication, and the other one is a
is a native IP based real time text capable terminal. The human native IP based real time text capable terminal. The human users
normally needs to apply formal turntaking habits, and need to normally need to apply formal turn-taking habits, and need to
figure out to what extent it is possible to interrupt the other figure out to what extent it is possible to interrupt the other
part if needs arise. party if the need arises.
All of the values can be used with any media type. Application can All of these values can be used with any media type. The application
make decision on how to handle a single media stream based on both can make decisions on how to handle a single media stream based on
media type and the value of 'content' attribute. Therefore the both the media type and the value of the 'content' attribute.
situation, where one value of 'content' attribute occurs more than Therefore the situation where one value of 'content' attribute occurs
once in a single session descriptor, is not problematic. more than once in a single session descriptor is not problematic.
6. The Content Attribute in the Offer/Answer Model 6. The Content Attribute in the Offer/Answer Model
This specification does not define a means to discover whether or not This specification does not define a means to discover whether or not
the peer endpoint understands the 'content' attribute because the peer endpoint understands the 'content' attribute because
'content' values are informative only at the offer/answer model [8] 'content' values are informative only at the offer/answer model [7]
level. The fact that the peer endpoint does not understands the level. The fact that the peer endpoint does not understand the
'content' attribute, does not keep the media session from being 'content' attribute does not keep the media session from being
established. The only consequence is that end user interaction in established. The only consequence is that end user interaction on
the receiving side maybe required. the receiving side may be required to direct the individual media
streams appropriately.
At the offer/answer level, it means that the fact that an offer does Since the 'content' attribute does not have to be understood, an SDP
not contain 'content' attributes does not imply that the answer answer MAY contain 'content' attributes even if none were present in
should not have them. It also means that the fact that an offer the offer. Similarly, the answer MAY contain no 'content' attributes
contains 'content' attributes does not imply that the answer should even if they were present in the offer.
have them too.
The 'content' attribute can also be used in scenarios where SDP is The 'content' attribute can also be used in scenarios where SDP is
used in declarative style. For example, 'content' attributes can be used in declarative style. For example, 'content' attributes can be
used in such SDP session descriptors that are distributed with used in SDP session descriptors that are distributed with Session
Session Announcement Protocol (SAP) [9]. Announcement Protocol (SAP) [8].
7. Example 7. Example
The following is an example of the SDP session description that uses The following is an example of the SDP session description that uses
the 'content' attribute: the 'content' attribute:
v=0 v=0
o=Alice 292742730 29277831 IN IP4 131.163.72.4 o=Alice 292742730 29277831 IN IP4 131.163.72.4
s=Second lecture from information technology s=Second lecture from information technology
c=IN IP4 131.164.74.2 c=IN IP4 131.164.74.2
skipping to change at page 7, line 30 skipping to change at page 7, line 33
m=video 53334 RTP/AVP 31 m=video 53334 RTP/AVP 31
a=rtpmap:31 H261/9000 a=rtpmap:31 H261/9000
a=content:speaker a=content:speaker
m=video 54132 RTP/AVP 31 m=video 54132 RTP/AVP 31
a=rtpmap:31 H261/9000 a=rtpmap:31 H261/9000
a=content:sl a=content:sl
8. Operation with SMIL 8. Operation with SMIL
The values of 'content' attribute, defined in Section 5, can also be The values of 'content' attribute, defined in Section 5, can also be
used with SMIL [11]. SMIL contains a 'param' element, which is used used with SMIL [10]. SMIL contains a 'param' element, which is used
for describing the content of a media. However, this 'param' element for describing the content of a media flow. However, this 'param'
provides only application specific description of media content. By element provides only application specific description of media
using the values of the 'content' attribute, this 'param' element can content. By using the values of the 'content' attribute, this
also be used to describe the media content in globally interpretable 'param' element can also be used to describe the media content in
way. globally interpretable way.
Details on how to use the values of the 'content' attribute with Details on how to use the values of the 'content' attribute with
SMIL's 'param' element are outside the scope of this specification. SMIL's 'param' element are outside the scope of this specification.
9. Security Considerations 9. Security Considerations
An attacker may attempt to add, modify, or remove 'content' An attacker may attempt to add, modify, or remove 'content'
attributes from a session description. This could result in an attributes from a session description. This could result in an
application behaving in a non-desirable way. So, it is strongly application behaving in an undesirable way. So, it is strongly
RECOMMENDED that integrity protection be applied to the SDP session RECOMMENDED that integrity protection be applied to the SDP session
descriptions. For session descriptions carried in SIP [5], S/MIME descriptions. For session descriptions carried in SIP [5], S/MIME
[7] is the natural choice to provide such end-to-end integrity [6] is the natural choice to provide such end-to-end integrity
protection, as described in RFC 3261 [5]. Other applications MAY use protection, as described in RFC 3261 [5]. Other applications MAY use
a different form of integrity protection. a different form of integrity protection.
10. IANA Considerations 10. IANA Considerations
This document defines a new 'content' attribute for SDP. It also This document defines a new 'content' attribute for SDP. It also
defines initial set of values for it. defines an initial set of values for it.
Contact name: Jani Hautakorpi Jani.Hautakorpi@ericsson.com. Contact name: Jani Hautakorpi Jani.Hautakorpi@ericsson.com.
Attribute name: 'content'. Attribute name: 'content'.
Type of attribute Media level. Type of attribute Media level.
Subject to charset: Not. Subject to charset: No.
Purpose of attribute: The 'content' attribute gives information from Purpose of attribute: The 'content' attribute gives information from
the content of the media stream to the receiving application. the content of the media stream to the receiving application.
Allowed attribure values: "slides", "speaker", "sl", "main", "alt", Allowed attribure values: "slides", "speaker", "sl", "main", "alt",
"user-floor", "txp", and a token. "user-floor", "txp", and any other
registered values.
The IANA is requested to create a subregistry for the 'content' The IANA is requested to create a subregistry for 'content' attribute
attribute values under the Session Description Protocol (SDP) values under the Session Description Protocol (SDP) Parameters
Parameters registry. The following are the initial values for the registry. The following are the initial values for the subregistry:
subregistry:
Value of 'content' attribute Reference Description Value of 'content' attribute Reference Description
---------------------------- --------- ----------- ---------------------------- --------- -----------
slides RFC xxxx Presentation slides slides RFC xxxx Presentation slides
speaker RFC xxxx Image from the speaker speaker RFC xxxx Image from the speaker
sl RFC xxxx Sign language sl RFC xxxx Sign language
main RFC xxxx Main media stream main RFC xxxx Main media stream
alt RFC xxxx Alternative media stream alt RFC xxxx Alternative media stream
user-floor RFC xxxx User level floor control req. user-floor RFC xxxx User level floor control req.
txp RFC xxxx Media from a textphone txp RFC xxxx Media from a textphone
Note for the RFC Editor: The 'RFC xxxx' in the above should be a Note for the RFC Editor: The 'RFC xxxx' in the above should be a
reference to the coming RFC number of this draft. reference to the coming RFC number of this draft.
As per the terminology in RFC 2434 [4], the registration policy for As per the terminology in RFC 2434 [4], the registration policy for
new values for the 'content' parameter shall be 'Specification new values for the 'content' parameter shall be 'Specification
Required'. Required'.
11. Acknowledges 11. Acknowledgements
Arnoud van Wijk and Roni Even provided valuable ideas for this Authors would like to thank Arnoud van Wijk and Roni Even, who
document. provided valuable ideas for this document. We wish to thank also Tom
Taylor for a thorough review.
12. References 12. References
12.1. Normative References 12.1. Normative References
[1] Handley, M., "SDP: Session Description Protocol", [1] Handley, M., "SDP: Session Description Protocol",
draft-ietf-mmusic-sdp-new-26 (work in progress), January 2006. draft-ietf-mmusic-sdp-new-26 (work in progress), January 2006.
[2] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [2] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997. Specifications: ABNF", RFC 2234, November 1997.
skipping to change at page 9, line 32 skipping to change at page 9, line 33
[4] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA [4] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
12.2. Informational References 12.2. Informational References
[5] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., [5] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002. Session Initiation Protocol", RFC 3261, June 2002.
[6] Handley, M. and V. Jacobson, "SDP: Session Description [6] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
Protocol", RFC 2327, April 1998.
[7] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
(S/MIME) Version 3.1 Message Specification", RFC 3851, (S/MIME) Version 3.1 Message Specification", RFC 3851,
July 2004. July 2004.
[8] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with [7] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002. Session Description Protocol (SDP)", RFC 3264, June 2002.
[9] Handley, M., Perkins, C., and E. Whelan, "Session Announcement [8] Handley, M., Perkins, C., and E. Whelan, "Session Announcement
Protocol", RFC 2974, October 2000. Protocol", RFC 2974, October 2000.
[10] Levin, O. and G. Camarillo, "The SDP (Session Description [9] Levin, O. and G. Camarillo, "The SDP (Session Description
Protocol) Label Attribute", Protocol) Label Attribute",
draft-ietf-mmusic-sdp-media-label-01 (work in progress), draft-ietf-mmusic-sdp-media-label-01 (work in progress),
January 2005. January 2005.
[11] Michel, T. and J. Ayars, "Synchronized Multimedia Integration [10] Michel, T. and J. Ayars, "Synchronized Multimedia Integration
Language (SMIL 2.0) - [Second Edition]", W3C REC REC-SMIL2- Language (SMIL 2.0) - [Second Edition]", W3C REC REC-SMIL2-
20050107, January 2005. 20050107, January 2005.
[12] ITU-T, "Infrastructure of audiovisual services - Systems [11] ITU-T, "Infrastructure of audiovisual services - Systems
aspects; Role management and additional media channels for aspects; Role management and additional media channels for
H.300-series terminals", Series H H.239, July 2003. H.300-series terminals", Series H H.239, July 2003.
Authors' Addresses Authors' Addresses
Jani Hautakorpi Jani Hautakorpi
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
Jorvas 02420 Jorvas 02420
Finland Finland
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