draft-ietf-mmusic-sdp-media-content-06.txt   rfc4796.txt 
MMUSIC Working Group J. Hautakorpi Network Working Group J. Hautakorpi
Internet-Draft G. Camarillo Request for Comments: 4796 G. Camarillo
Intended status: Standards Track Ericsson Category: Standards Track Ericsson
Expires: March 26, 2007 September 22, 2006 February 2007
The SDP (Session Description Protocol) Content Attribute
draft-ietf-mmusic-sdp-media-content-06.txt
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The IETF Trust (2007).
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 to a 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 or small screen) based on its content.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Related Techniques . . . . . . . . . . . . . . . . . . . . . . 3 3. Related Techniques . . . . . . . . . . . . . . . . . . . . . . 2
4. Motivation for the New Content Attribute . . . . . . . . . . . 4 4. Motivation for the New Content Attribute . . . . . . . . . . . 3
5. The Content Attribute . . . . . . . . . . . . . . . . . . . . 5 5. The Content Attribute . . . . . . . . . . . . . . . . . . . . 4
6. The Content Attribute in the Offer/Answer Model . . . . . . . 6 6. The Content Attribute in the Offer/Answer Model . . . . . . . 5
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8. Operation with SMIL . . . . . . . . . . . . . . . . . . . . . 8 8. Operation with SMIL . . . . . . . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8 9. Security Considerations . . . . . . . . . . . . . . . . . . . 7
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
12.1. Normative References . . . . . . . . . . . . . . . . . . 10 12.1. Normative References . . . . . . . . . . . . . . . . . . 9
12.2. Informational References . . . . . . . . . . . . . . . . 10 12.2. Informational References . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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 to describe multimedia sessions for the purposes of session
session announcement, session invitation, and other forms of announcement, session invitation, and other forms of multimedia
multimedia session initiation. One of the most typical use cases of session initiation. One of the most typical use cases of SDP is
SDP is the one where it is used with the Session Initiation Protocol where it is used with the Session Initiation Protocol (SIP) [5].
(SIP) [5].
There are situations where one application receives several similar There are situations where one application receives several similar
media streams which are described in an SDP session description. The media streams, which are described in an SDP session description.
media streams can be similar in the sense that their content cannot The media streams can be similar in the sense that their content
be distinguished just by examining their media description lines cannot be distinguished just by examining their media description
(e.g., two video streams). The 'content' attribute is needed so that lines (e.g., two video streams). The 'content' attribute is needed
the receiving application can treat each media stream appropriately so that the receiving application can treat each media stream
based on its content. appropriately based 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.
The main purpose of this specification is to allow applications to The main purpose of this specification is to allow applications to
take automated actions based on the 'content' attributes. However, take automated actions based on the 'content' attributes. However,
this specification does not define those actions. Consequently, two this specification does not define those actions. Consequently, two
implementations can behave completely differently when receiving the implementations can behave completely differently when receiving the
same 'content' attribute. same 'content' attribute.
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
compliant implementations. for compliant implementations.
3. Related Techniques 3. Related Techniques
The 'label' attribute [10] enables a sender to attach a pointer to a The 'label' attribute [10] 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 need for backward practice, this is not possible because of the need for backward
compatibility. Existing implementations of the 'label' attribute compatibility. Existing implementations of the 'label' attribute
already use values from that unrestricted namespace in an already use values from that unrestricted namespace in an
application-specific way. So, it is not possible to reserve portions application-specific way. So, it is not possible to reserve portions
of the 'label' attribute's namespace without possible conflict with of the 'label' attribute's namespace without possible conflict with
already-used application-specific labels. already used application-specific labels.
It is possible to assign semantics to a media stream with an external It is possible to assign semantics to a media stream with an external
document that uses the 'label' attribute as a pointer. The downside document that uses the 'label' attribute as a pointer. The downside
of this approach is that it requires an external document. of this approach is that it requires an external document.
Therefore, this kind of mechanism is only applicable to special use Therefore, this kind of mechanism is only applicable to special use
cases where such external documents are used (e.g., centralized cases where such external documents are used (e.g., centralized
conferencing). conferencing).
Yet another way to attach semantics to a media stream is to use the Yet another way to attach semantics to a media stream is to use the
'i' SDP attribute, defined in [1]. However, values of the 'i' 'i' SDP attribute, defined in [1]. However, values of 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 for describing the content
content of a media stream (e.g., speaker's image, slides, sign of a media stream (e.g., speaker's image, slides, sign language) in a
language) in a form that the application can understand. Of course, form that the application can understand. Of course, the end user
the end user can see the content of the media stream and read its can see the content of the media stream and read its title, but the
title, but the application cannot understand what the media stream 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 streams needs, in some cases, to know what the
content of those streams. This kind of situation occurs, for contents of those streams are. This kind of situation occurs, for
example, in cases where presentation slides, the speaker's image, and example, in cases where presentation slides, the speaker's image, and
sign language are transported as separate media streams. It would be sign language are transported as separate media streams. It would be
desirable that the receiving application could distinguish them in a desirable that the receiving application could distinguish them in a
way that it could handle them automatically in an appropriate manner. way that it could handle them automatically in an 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
application. The 'content' attribute makes it possible for the Figure 1 shows a screen of a typical communication application. The
application to decide where to show each media stream. From an end 'content' attribute makes it possible for the application to decide
user's perspective, it is desirable that the user does not need to where to show each media stream. From an end user's perspective, it
arrange media stream every time a new media session starts. is desirable that the user does not need to arrange each media stream
every time a new media session starts.
The 'content' attribute could also be used in more complex The 'content' attribute could also be used in more complex
situations. An example of such a complex situation is an application situations. An example of such a situation is an application
controlling equipment in an auditorium. An auditorium can have many controlling equipment in an auditorium. An auditorium can have many
different output channels for video (e.g., main screen and two different output channels for video (e.g., main screen and two
smaller screens) and audio (e.g., main speakers, headsets for the smaller screens) and audio (e.g., main speakers and headsets for the
participants). In this kind of environment, a lot of interaction participants). In this kind of environment, a lot of interaction
from the end user who operates the application would be required in from the end user who operates the application would be required in
absence of cues from a controlling application. The 'content' absence of cues from a controlling application. The 'content'
attribute would make it possible, for example, for an end user needs attribute would make it possible, for example, for an end user to
to specify, only once, which output each media stream of a given specify, only once, which output each media stream of a given session
session should use. The application could automatically apply the should use. The application could automatically apply the same media
same media layout for subsequent sessions. So, the 'content' layout for subsequent sessions. So, the 'content' attribute can help
attribute can help to reduce the amount of required end user reduce the amount of required end-user interaction considerably.
interaction considerably.
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 ABNF
[2]: (Augmented Backus-Naur Form) [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" / mediacnt-ext / "alt" / mediacnt-ext
mediacnt-ext = token mediacnt-ext = token
The 'content' attribute contains a token, which MAY be attached to a The 'content' attribute contains one or more tokens, which MAY be
media stream by a sending application. An application MAY attach a attached to a media stream by a sending application. An application
content attribute to any media stream it describes. That attribute MAY attach a 'content' attribute to any media stream it describes.
contains one or more tokens describing the content of the transmitted
media stream to the receiving application.
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: the media stream includes presentation slides. The media slides: the media stream includes presentation slides. The media
type can be, for example, a video stream or a number of instant type can be, for example, a video stream or a number of instant
messages with pictures. Typical use cases for this are online messages with pictures. Typical use cases for this are online
seminars and courses. This is similar to the 'presentation' role seminars and courses. This is similar to the 'presentation' role
in H.239 [12]. in H.239 [12].
speaker: the media stream contains the image of the speaker. The speaker: the media stream contains the image of the speaker. The
media can be, for example, a video stream or a still image. media can be, for example, a video stream or a still image.
Typical use case for this are online seminars and courses. Typical use cases for this are online seminars and courses.
sl: the media stream contains sign language. A typical use case for sl: the media stream contains sign language. A typical use case for
this is an audio stream that is translated into sign language, this is an audio stream that is translated into sign language,
which is sent over a video stream. which is sent over a video stream.
main: the media stream is taken from the main source. A typical use main: the media stream is taken from the main source. A typical use
case for this is a concert where the camera is shooting the case for this is a concert where the camera is shooting the
performer. performer.
alt: the media stream is taken from the alternative source. A alt: the media stream is taken from the alternative source. A
typical use case for this is an event where the ambient sound is typical use case for this is an event where the ambient sound is
separated from the main sound. The alternative audio stream could separated from the main sound. The alternative audio stream could
be, for example, the sound of a jungle. Another example is the be, for example, the sound of a jungle. Another example is the
video of a conference room while the main stream carries the video video of a conference room, while the main stream carries the
of the speaker. This is similar to the 'live' role in H.239. video of the speaker. This is similar to the 'live' role in
H.239.
All these values can be used with any media type. The application All these values can be used with any media type. We chose not to
can make decisions on how to handle a single media stream based on restrict each value to a particular set of media types in order not
both the media type and the value of the 'content' attribute. to prevent applications from using innovative combinations of a given
Therefore the situation where one value of 'content' attribute occurs value with different media types.
more than once in a single session descriptor is not problematic.
The application can make decisions on how to handle a single media
stream based on both the media type and the value of the 'content'
attribute. If the application does not implement any special logic
for the handling of a given media type and 'content' value
combination, it applies the application's default handling for the
media type.
Note that the same 'content' attribute value can occur more than once
in a single session description.
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 the
the peer endpoint understands the 'content' attribute because peer endpoint understands the 'content' attribute because 'content'
'content' values are just informative at the offer/answer model [8] values are just informative at the offer/answer model [8] level. The
level. The fact that the peer endpoint does not understand the fact that the peer endpoint does not understand the 'content'
'content' attribute does not keep the media session from being attribute does not keep the media session from being established.
established. The only consequence is that end user interaction on The only consequence is that end user interaction on the receiving
the receiving side may be required to direct the individual media side may be required to direct the individual media streams
streams appropriately. appropriately.
Since the 'content' attribute does not have to be understood, an SDP The 'content' attribute describes the data that the application
answer MAY contain 'content' attributes even if none were present in generating the SDP session description intends to send over a
the offer. Similarly, the answer MAY contain no 'content' attributes particular media stream. The 'content' values for both directions of
a media stream do not need to be the same. Therefore, an SDP answer
MAY contain 'content' attributes even if none were present in the
offer. Similarly, the answer MAY contain no 'content' attributes
even if they were present in the offer. Furthermore, the values of even if they were present in the offer. Furthermore, the values of
'content' attributes does not need to match in an offer and an 'content' attributes do not need to match in an offer and an answer.
answer.
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 a declarative style. For example, 'content' attributes can used in a declarative style. For example, 'content' attributes can
be used in SDP session descriptors that are distributed with Session be used in SDP session descriptors that are distributed with Session
Announcement Protocol (SAP) [9]. Announcement Protocol (SAP) [9].
7. Examples 7. Examples
There are two examples in this section. The first example, shown There are two examples in this section. The first example, shown
below, uses a single 'content' attribute value per media stream: below, uses a single 'content' attribute value per media stream:
skipping to change at page 7, line 31 skipping to change at page 6, line 39
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 The second example, below, is a case where there is more than one
'content' attribute value per media stream. The difference with the 'content' attribute value per media stream. The difference with the
previous example is that now the conferencing system might previous example is that now the conferencing system might
automatically mix the video streams from the presenter and slides: automatically mix the video streams from the presenter and slides:
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,speaker a=content:slides,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 Synchronized Multimedia Integration Language (SMIL) [11].
for describing the content of a media flow. However, this 'param' SMIL contains a 'param' element, which is used for describing the
element, like 'content' attribute, provides application specific content of a media flow. However, this 'param' element, like the
description of media content. 'content' attribute, provides an application-specific description of
the media content.
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. Depending on how an attributes from a session description. Depending on how an
implementation chooses to react to the presence or absence of a given implementation chooses to react to the presence or absence of a given
'content' attribute, this could result in an application behaving in 'content' attribute, this could result in an application behaving in
an undesirable way. So, it is strongly RECOMMENDED that integrity an undesirable way; therefore, it is strongly RECOMMENDED that
protection be applied to the SDP session descriptions. integrity protection be applied to the SDP session descriptions.
Integrity protection can be provided for session description carried Integrity protection can be provided for a session description
in SIP [5] e.g., by using S/MIME [6] or Transport Layer Security carried in an SIP [5], e.g., by using S/MIME [6] or Transport Layer
(TLS) [7]. Security (TLS) [7].
It is assumed that values of 'content' attribute do not contain data It is assumed that values of 'content' attribute do not contain data
that would be truly harmful if it is exposed to an possible attacker. that would be truly harmful if it is exposed to a possible attacker.
It must be noted that the initial set of values does not contain any It must be noted that the initial set of values does not contain any
data that would require confidentiality protection. However, S/MIME data that would require confidentiality protection. However, S/MIME
and TLS can be used to protect confidentiality, if needed. and TLS can be used to protect confidentiality, if needed.
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. Some general information defines an initial set of values for it. Some general information
regarding 'content' attribute is presented in the following: regarding the '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 attribute values: "slides", "speaker", "sl", "main", "alt",
and any other registered values. and any other registered values.
The IANA is requested to create a subregistry for 'content' attribute The IANA created a subregistry for 'content' attribute values under
values under the Session Description Protocol (SDP) Parameters the Session Description Protocol (SDP) Parameters registry. The
registry. The initial values for the subregistry are presented in initial values for the subregistry are as follows:
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 4796 Presentation slides
speaker RFC xxxx Image from the speaker speaker RFC 4796 Image from the speaker
sl RFC xxxx Sign language sl RFC 4796 Sign language
main RFC xxxx Main media stream main RFC 4796 Main media stream
alt RFC xxxx Alternative media stream alt RFC 4796 Alternative media stream
Note for the RFC Editor: 'RFC xxxx' above should be replaced by a
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'.
If new values for 'content' attribute are specified in the future, If new values for 'content' attributes are specified in the future,
they should consist of a meta description of the contents of a media they should consist of a meta description of the contents of a media
stream. New values for 'content' attribute should not describe stream. New values for 'content' attributes should not describe
things like what to do in order to handle a stream. things like what to do in order to handle a stream.
11. Acknowledgements 11. Acknowledgements
Authors would like to thank Arnoud van Wijk and Roni Even, who The 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 also thank Tom
Taylor for a thorough review. Taylor for his thorough review.
12. References 12. References
12.1. Normative References 12.1. Normative References
[1] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [1] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006. Description Protocol", RFC 4566, July 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 4234, October 2005.
[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.
skipping to change at page 10, line 44 skipping to change at page 9, line 45
[8] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with [8] 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 [9] 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 Session Description Protocol [10] Levin, O. and G. Camarillo, "The Session Description Protocol
(SDP) Label Attribute", RFC 4574, August 2006. (SDP) Label Attribute", RFC 4574, August 2006.
[11] Michel, T. and J. Ayars, "Synchronized Multimedia Integration [11] Michel, T. and J. Ayars, "Synchronized Multimedia Integration
Language (SMIL 2.0) - [Second Edition]", W3C REC REC-SMIL2- Language (SMIL 2.0) - [Second Edition]", World Wide Web
20050107, January 2005. Consortium Recommendation REC-SMIL2-20050107, January 2005,
<http://www.w3.org/TR/2005/REC-SMIL2-20050107>.
[12] ITU-T, "Infrastructure of audiovisual services - Systems [12] 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
Email: Jani.Hautakorpi@ericsson.com EMail: Jani.Hautakorpi@ericsson.com
Gonzalo Camarillo Gonzalo Camarillo
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
Jorvas 02420 Jorvas 02420
Finland Finland
Email: Gonzalo.Camarillo@ericsson.com EMail: Gonzalo.Camarillo@ericsson.com
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