draft-ietf-mmusic-sdp-media-content-03.txt   draft-ietf-mmusic-sdp-media-content-04.txt 
MMUSIC Working Group J. Hautakorpi MMUSIC Working Group J. Hautakorpi
Internet-Draft G. Camarillo Internet-Draft G. Camarillo
Expires: October 13, 2006 Ericsson Expires: January 1, 2007 Ericsson
April 11, 2006 June 30, 2006
The SDP (Session Description Protocol) Content Attribute The SDP (Session Description Protocol) Content Attribute
draft-ietf-mmusic-sdp-media-content-03.txt draft-ietf-mmusic-sdp-media-content-04.txt
Status of this Memo Status of this Memo
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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 its content. (e.g., show it on a big screen or small screen) based on its 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. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Operation with SMIL . . . . . . . . . . . . . . . . . . . . . 7 8. Operation with SMIL . . . . . . . . . . . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 7 9. Security Considerations . . . . . . . . . . . . . . . . . . 8
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 8
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
12.1. Normative References . . . . . . . . . . . . . . . . . . 9 12.1 Normative References . . . . . . . . . . . . . . . . . . 10
12.2. Informational References . . . . . . . . . . . . . . . . 9 12.2 Informational References . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . . . 12 Intellectual Property and Copyright Statements . . . . . . . 12
1. Introduction 1. Introduction
The Session Description Protocol (SDP) [1] is a protocol that is The Session Description Protocol (SDP) [1] is a protocol that is
intended for describing multimedia sessions for the purposes of intended for describing multimedia sessions for the purposes of
session announcement, session invitation, and other forms of session announcement, session invitation, and other forms of
multimedia session initiation. One of the most typical use cases of multimedia session initiation. One of the most typical use cases of
SDP is the one where it is used with the Session Initiation Protocol SDP is the one where it is used with the Session Initiation Protocol
(SIP) [5]. (SIP) [5].
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This document provides a set of pre-defined values for the 'content' This document provides a set of pre-defined values for the 'content'
attribute. Other values can be defined in the future. The pre- attribute. Other values can be defined in the future. The pre-
defined 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. A typical use case for this is e.g., message with pictures. A typical use case for this is e.g.,
online seminars and courses. This is similar to the online seminars and courses. This is similar to the
'presentation' role in H.239 [11]. '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. A typical use case for this is one media type is a video stream. A typical use case for this is 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.
A typical use case for this is 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. A typical use case for this is an event, where there is a source. A typical use case for this is an event, where there is a
separate ambient sound and the main sound. The alternative audio separate ambient sound and the main sound. The alternative audio
stream could be e.g., the sound of a jungle. Another example is stream could be e.g., the sound of a jungle. Another example 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, human users have to take care of the
mechanism for floor control, where a human needs to figure out floor control. The user interface of the receiving application
whether an act of floor control, e.g., saying 'over', is needed or must indicate the need for user level floor control to the human
not. A typical use case for this is a situation where the other user.
endpoint of the connection is a walkie-talkie type of device.
A typical use case is a situation where the other endpoint of the
connection is a walkie-talkie type of device, and human users must
say 'over' each time they stop transmitting.
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 that is incapable of handling simultaneous two-way
application. A typical use case for this is a connection where communication. This limitation requires special behavior from the
one endpoint is an analog textphone of a kind that cannot handle user of a terminal receiving the indication. The indication
two-way simultaneous text communication, and the other one is a should be used for an indication in the user interface.
native IP based real time text capable terminal. The human users
normally need to apply formal turn-taking habits, and need to A typical use case is a connection where one endpoint is an analog
figure out to what extent it is possible to interrupt the other textphone of a kind that cannot handle two-way simultaneous text
party if the need arises. communication, and the other one is a native IP based real time
text capable terminal. The human user of the IP terminal need to
change behaviour when this indication is received, and apply
formal turn-taking habits. They may also need to figure out to
what extent it is possible to interrupt the other party if the
need arises.
All of these values can be used with any media type. The application All of these values can be used with any media type. The application
can make decisions on how to handle a single media stream based on can make decisions on how to handle a single media stream based on
both the media type and the value of the 'content' attribute. both the media type and the value of the 'content' attribute.
Therefore the situation where one value of 'content' attribute occurs Therefore the situation where one value of 'content' attribute occurs
more than 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
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Since the 'content' attribute does not have to be understood, an SDP Since the 'content' attribute does not have to be understood, an SDP
answer MAY contain 'content' attributes even if none were present in answer MAY contain 'content' attributes even if none were present in
the offer. Similarly, the answer MAY contain no 'content' attributes the offer. Similarly, the answer MAY contain no 'content' attributes
even if they were present in the offer. even if they were present in the offer.
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 SDP session descriptors that are distributed with Session used in SDP session descriptors that are distributed with Session
Announcement Protocol (SAP) [8]. Announcement Protocol (SAP) [8].
7. Example 7. Examples
The following is an example of the SDP session description that uses There are two examples in this section. The first example, shown
the 'content' attribute: below, uses only one 'content' attribute value per media stream:
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
t=0 0 t=0 0
m=video 52886 RTP/AVP 31 m=video 52886 RTP/AVP 31
a=rtpmap:31 H261/9000 a=rtpmap:31 H261/9000
a=content:slides a=content:slides
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
The second example, below, shows a case where there is more than one
'content' attribute value per media stream. The difference to the
previous example is that now the conferencing system automatically
mixes the video streams from the presenter and slides:
v=0
o=Alice 292742730 29277831 IN IP4 131.163.72.4
s=Second lecture from information technology
c=IN IP4 131.164.74.2
t=0 0
m=video 52886 RTP/AVP 31
a=rtpmap:31 H261/9000
a=content:slides,speaker
m=video 54132 RTP/AVP 31
a=rtpmap:31 H261/9000
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 [10]. 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 flow. However, this 'param' for describing the content of a media flow. However, this 'param'
element provides only application specific description of media element provides only application specific description of media
content. By using the values of the 'content' attribute, this content. By using the values of the 'content' attribute, this
'param' element can also be used to describe the media content in 'param' element can also be used to describe the media content in
globally interpretable way. globally interpretable way.
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application behaving in an undesirable 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
[6] 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 an initial set of values for it. defines an initial set of values for it. Some general information
regarding 'content' attribute is presented in the following:
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: No. 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 any other "user-floor", "txp", and any other
registered values. registered values.
The IANA is requested to create a subregistry for 'content' attribute The IANA is requested to create a subregistry for 'content' attribute
values under the Session Description Protocol (SDP) Parameters values under the Session Description Protocol (SDP) Parameters
registry. The following are the initial values for the subregistry: registry. The initial values for the subregistry are presented in
the following, and IANA is requested to add them into its database:
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
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Required'. Required'.
11. Acknowledgements 11. Acknowledgements
Authors would like to thank Arnoud van Wijk and Roni Even, who Authors would like to thank Arnoud van Wijk and Roni Even, who
provided valuable ideas for this document. We wish to thank also Tom provided valuable ideas for this document. We wish to thank also Tom
Taylor for a thorough review. 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.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[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] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions [6] 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.
[7] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with [7] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
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