Network Working Group Magnus Westerlund
INTERNET-DRAFT Per Frojdh
Expires: August 2005 Ericsson
February 14, 2005
SDP and RTSP extensions defined for 3GPP Packet-switched Streaming
Service
<draft-westerlund-mmusic-3gpp-sdp-rtsp-00.txt>
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Abstract
3GPP has defined a packet-switched streaming service that uses SDP
and RTSP with some extensions. This document provides information
about these extensions and registers the SDP extensions with IANA.
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TABLE OF CONTENTS
1. Definitions.....................................................3
1.1. Glossary...................................................3
2. Introduction....................................................3
3. SDP Extensions..................................................3
3.1. Video Buffering attributes.................................3
3.2. Video Frame Size attribute.................................4
3.3. Integrity Protection Configuration Attributes..............4
3.4. The alternative attributes.................................4
3.5. Adaptation Attribute.......................................5
3.6. Quality of Experience Attribute............................5
3.7. Asset Information Attribute................................5
4. RTSP Extensions.................................................5
4.1. 3GPP-Link-Char Header......................................5
4.2. 3GPP-Adaptation Header.....................................6
4.3. 3GPP-QoE-Metrics Header....................................6
4.4. 3GPP-QoE-Feedback Header...................................6
4.5. Video buffer Headers.......................................6
4.6. Integrity Protection.......................................7
4.7. RTSP URI extension.........................................7
5. IANA Considerations.............................................7
6. Informative References.........................................11
7. Authors' Addresses.............................................11
8. IPR Notice.....................................................12
9. Copyright Notice...............................................12
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1. Definitions
1.1. Glossary
3GPP - Third Generation Partnership Project
PSS - Packet-switched Streaming Service
QoE - Quality of Experience
QoS - Quality of Service
2. Introduction
3GPP has specified a packet-switched streaming service (PSS) that
uses both RTSP and SDP. The service is specified in technical
specifications 26.233 [2] and 26.234 [1] in Release 4 and later
releases. The basic service defined in Release 4 is enhanced in
Release 5 with capability exchange and in Release 6 with a number of
features, such as adaptation, digital rights management, progressive
download and a streaming server file-format.
In the process of defining this service, there has occasionally been
the need to extend both RTSP [3] and SDP [5] functionality. These
extensions have mostly been in the form of SDP attributes and RTSP
headers. The purpose of this informational document is to register
the SDP extensions, in order to avoid future conflict, and also to
raise the awareness of their existence within IETF.
The document begins with two chapters presenting the different
extensions of SDP and RTSP, respectively. The subsequent chapter
contains the IANA registration of SDP attributes. The registration
of the RTSP extensions will occur when the rules are established by
the updated RTSP specification [3]. The normative description of all
SDP and RTSP extensions is given by TS 26.234 [1].
3. SDP Extensions
The PSS specification [1] defines a number of different SDP
attributes for different purposes. They are informatively listed
below grouped together by purpose.
3.1. Video Buffring attributs
The following attributes are used to provide parameters for the
video buffer model provided in Annex G and Section 5.3.3.2 of [1].
The attributes were defined in Release 5 as "X-" attributes and were
at the time not considered for registration. In hindsight, however,
they should not have been "X-" attributes, and they should have been
registered, as SDP's [5] registration rules points out. Changing
their names today is impossible due to the deployed base of millions
of mobile handsets supporting PSS, and therefore they are registered
in their current form.
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The attributes are all media level.
- The "a=X-predecbufsize" attribute provides the size of the pre-
decoder buffer.
- The "a=X-initpredecbufperiod" attribute provides the time during
which a receiver should initially buffer before starting to
consume the data in the buffer in order to ensure that underflow
does not occur, assuming correct data delivery.
- The "a=X-initpostdecbufperiod" attribute provides the initial
buffering period for the post-decoder buffer present in H.263 and
MPEG-4 Visual.
- The "a=X-decbyterate" attribute indicates the maximum peak byte-
decoding rate used in the verification of the Annex G buffer
model.
- The "a=3gpp-videopostdecbufsize" attribute is used to indicate
the size of the H.264 video post-decoder buffer.
3.2. Video Frame Size attribute
This media-level attribute provides the receiver with the largest
picture size a specific H.263 payload type will carry within the
session. The attribute has the following form (see 5.3.3.2 of [1]):
"a=framesize:<payload type number> <width>-<height>"
3.3. Integrity Protection Configuration Attributes
These attributes are all used to configure the integrity-protection
mechanism defined in Annex K.2 of [1].
- The session-level attribute "a=3GPP-Integrity-Key" carries the
integrity key used to derive SRTP master keys for integrity
protection. They key is protected in different ways depending on
a method identifier.
- The media-level attribute "a=3GPP-SRTP-Config" is used to
configure SRTP for integrity protection and contains an integrity
nonce, a key salt used in deriving the SRTP master key from the
integrity key, and any SRTP configuration parameters, such as the
integrity tag length.
- The session-level attribute "a=3GPP-SDP-Auth" is used to carry an
authentication tag calculated over certain parts of the SDP to
prevent manipulation of the security attributes.
3.4. The alternative attributes
Two media and one session-level attributes are used in a mechanism
for providing alternative SDP lines. One or more SDP lines at media
level can be replaced, if desired, by alternatives. The mechanism is
backwards compatible in the way that a receiver that does not
support the attributes will get the default configuration. The
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different alternatives can be grouped using different attributes
that can be specified hierarchical with a top and a lower level.
3GPP Release 6 supports grouping based on bit-rate, according to the
SDP bandwidth modifiers AS and TIAS, and language.
The SDP attributes (see 5.3.3.3 and 5.3.3.4 of [1]) are:
- The media-level attribute "a=alt:<id>:<SDP-Line>" carries any SDP
line and an alternative identifier.
- The media-level attribute "a=alt-default-id:<id>" identifies the
default configuration to be used in groupings.
- The session-level attribute "a=alt-group" is used to group
different recommended media alternatives together.
3.5. Adaptation Attribute
The media-level SDP attribute "a=3GPP-Adaptation-Support" (see
5.3.3.5 of [1]) is defined as part of the negotiation procedure for
the use of the PSS adaptation mechanism. The adaptation mechanism
provides the server with information to determine available
transmission bit-rate and receiver buffer status.
3.6. Quality of Experience Attribute
The session and media-level attribute "a=3GPP-QoE-Metrics:" (see
5.3.3.6 of [1]) is used to negotiate the usage of the quality of
experience metrics. The included parameters indicate which metrics
and parameters that are desirable to use.
3.7. Asset Information Attribute
The session and media-level attribute "a=3GPP-Asset-Information"
(see 5.3.3.7 of [1]) can exist in multiple instances in a
description and describes different types of asset information. The
different asset classes that is defined in Release 6 are; Title,
Description, Copyright, Performer, Author, Genre, Rating,
Classification, Keywords, and Location. The different assets are
described with a BASE64-encoded asset box from the 3GP file format
[4].
4. RTSP Extensions
The RTSP extensions for PSS consist of a number of new RTSP headers
and a narrowing of URI usage in regards to 3GP files. The new
headers are registered by the new RTSP specification [3] that also
specifies the IANA rules for registering headers. The headers are
informatively described here, see [1] for the normative declaration.
4.1. 3GPP-Link-Char Header
The 3GPP-Link-Char header (see 5.3.2.1 of [1]) is used by clients to
provide the server with QoS information about the wireless link it
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is currently using. The header can be used to provide the server
with three different QoS parameters:
- Guaranteed Bandwidth
- Maximum Bandwidth
- Maximum Transfer Delay
The header may be included in RTSP request using either of the
methods SETUP, PLAY, OPTIONS and SET_PARAMETER.
4.2. 3GPP-Adaptation Header
The 3GPP-Adaptation header (see 5.3.2.2 of [1]) is used by the
client to provide the server with adaptation-related parameters and
to indicate support of the adaptation function. The header carries
the resource identification as a URI, the client's buffer size, and
the desired target time.
The header may be included in requests using the methods SETUP,
PLAY, OPTIONS and SET_PARAMETER. The response to a request using
this method shall include this header.
4.3. 3GPP-QoE-Metrics Header
The 3GPP-QoE-Metrics header (see 5.3.2.3.1 of [1]) is used to
negotiate the usage of the quality of experience (QoE) metrics (see
Section 11 of [1]).
The header may be included in requests and responses using the
SETUP, SET_PARAMTER, OPTIONS or PLAY method.
4.4. 3GPP-QoE-Feedback Header
The 3GPP-QoE-Feedback header (see 5.3.2.3.2 of [1]) is used to carry
QoE metrics from the client to the server when it performs reports,
which happens either during or at the end of the media delivery.
The header may be included in requests using the SET_PARAMETER,
PAUSE, or TEARDOWN method.
4.5. Video buffer Headers
PSS uses several headers to provide the client with the different
buffer parameters. They provide the buffer status at the point of a
stream that a PLAY request plays from. These headers may only be
used in PLAY responses. See Section 5.3.2.4 and Annex G of [1] for
normative definitions.
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The three "x-" headers were defined in 3GPP Release 5. When it was
realized that they should not have been given "x-" names it was too
late rename them due to deployment.
The RTSP headers are:
- x-predecbufsize
- x-initpredecbufperiod
- x-initpostdecbufperiod
- 3gpp-videopostdecbufsize
4.6. Integrity Protection
The integrity-protection mechanism defined in PSS Annex K uses the
"3GPP-Freshness-Token" (See Annex K.2.2.4 of [1]) RTSP header to
carry a freshness token in DESCRIBE requests.
4.7. RTSP URI extension
The PSS specification also defines syntax for referencing tracks
within the "3GP" file format [4]. The 3GP format is based on the ISO
base media file format and defined in several different profiles,
including a streaming-server profile, in Release 6.
To identify a track within a 3GP file the last URI segment shall
contain a structure that is <alpha string>=<track nr>.
5. IANA Considerations
IANA is requested to register the SDP attributes listed below. The
contact person for this registration is Magnus Westerlund
(magnus.westerlund@ericsson.com) Phone number +46 8 719 0000.
SDP Attribute ("att-field"):
Attribute name: X-predecbufsize
Long form: Pre-decoder buffer size
Type of name: att-field
Type of attribute: Media level only
Subject to charset: No
Purpose: See Section 3.1
Reference: 3GPP TS 26.234, Section 5.3.3.2
Values: See Reference
Attribute name: X-initpredecbufperiod
Long form: Pre-decoder initial buffering period
Type of name: att-field
Type of attribute: Media level only
Subject to charset: No
Purpose: See Section 3.1
Reference: 3GPP TS 26.234, Section 5.3.3.2
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Values: See Reference
Attribute name: X-initpostdecbufperiod
Long form: Post-decoder initial buffering period
Type of name: att-field
Type of attribute: Media level only
Subject to charset: No
Purpose: See Section 3.1
Reference: 3GPP TS 26.234, Section 5.3.3.2
Values: See Reference
Attribute name: X-decbyterate
Long form: Peak decoding rate in bytes per second
Type of name: att-field
Type of attribute: Media level only
Subject to charset: No
Purpose: See Section 3.1
Reference: 3GPP TS 26.234, Section 5.3.3.2
Values: See Reference
Attribute name: 3gpp-videopostdecbufsize
Long form: Post decoder buffer size
Type of name: att-field
Type of attribute: Media level only
Subject to charset: No
Purpose: See Section 3.1
Reference: 3GPP TS 26.234, Section 5.3.3.2
Values: See Reference
Attribute name: framesize
Long form: Maximum Video Frame Size
Type of name: att-field
Type of attribute: Media level only
Subject to charset: No
Purpose: See Section 3.2
Reference: 3GPP TS 26.234, Section 5.3.3.2
Values: See Reference
Attribute name: 3GPP-Integrity-Key
Long form: 3GPP DRM Integrity Key
Type of name: att-field
Type of attribute: Session level only
Subject to charset: No
Purpose: See Section 3.3
Reference: 3GPP TS 26.234, Section 5.3.3.2
Values: See Reference
Attribute name: 3GPP-SRTP-Config
Long form: 3GPP DRM SRTP Configuration
Type of name: att-field
Type of attribute: Media level only
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Subject to charset: No
Purpose: See Section 3.3
Reference: 3GPP TS 26.234, Section 5.3.3.2
Values: See Reference
Attribute name: 3GPP-SDP-Auth
Long form: 3GPP DRM Integrity SDP Authentication
Type of name: att-field
Type of attribute: Session level only
Subject to charset: No
Purpose: See Section 3.3
Reference: 3GPP TS 26.234, Section 5.3.3.2
Values: See Reference
Attribute name: alt
Long form: Alternative SDP line
Type of name: att-field
Type of attribute: Media level only
Subject to charset: No
Purpose: See Section 3.4
Reference: 3GPP TS 26.234, Section 5.3.3.3
Values: See Reference
Attribute name: alt-default-id
Long form: Default alternative ID
Type of name: att-field
Type of attribute: Media level only
Subject to charset: No
Purpose: See Section 3.4
Reference: 3GPP TS 26.234, Section 5.3.3.3
Values: See Reference
Attribute name: alt-group
Long form: Grouping of SDP Line alternatives
Type of name: att-field
Type of attribute: Session level only
Subject to charset: No
Purpose: See Section 3.4
Reference: 3GPP TS 26.234, Section 5.3.3.4
Values: See Reference
Attribute name: 3GPP-Adaptation-Support
Long form: 3GPP Adaptation Support
Type of name: att-field
Type of attribute: Media level only
Subject to charset: No
Purpose: See Section 3.5
Reference: 3GPP TS 26.234, Section 5.3.3.5
Values: See Reference
Attribute name: 3GPP-QoE-Metrics
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Long form: 3GPP Quality of Experience Metrics
Type of name: att-field
Type of attribute: Session and Media level
Subject to charset: No
Purpose: See Section 3.6
Reference: 3GPP TS 26.234, Section 5.3.3.6
Values: See Reference
Attribute name: 3GPP-Asset-Information
Long form: 3GPP Asset Information
Type of name: att-field
Type of attribute: Session and Media level
Subject to charset: No
Purpose: See Section 3.7
Reference: 3GPP TS 26.234, Section 5.3.3.7
Values: See Reference
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6. Informative References
[1] 3GPP TS 26.234, "Transparent end-to-end Packet-switched
Streaming Service (PSS); Protocols and codecs", version 6.2.0
(2004-12), 3rd Generation Partnership Project (3GPP).
[2] 3GPP TS 26.233, "Packet Switched Streaming service", version
6.0.0 (2004-09), 3rd Generation Partnership Project (3GPP).
[3] H. Schulzrinne, A. Rao, R. Lanphier, M. Westerlund, A.
Narasimhan , "Real Time Streaming Protocol (RTSP)", draft-ietf-
mmusic-rfc2326bis-09.txt, work in progress
[4] 3GPP TS 26.244, "Transparent end-to-end packet switched
streaming service (PSS); 3GPP file format (3GP)", version 6.2.0
(2004-12), 3rd Generation Partnership Project (3GPP).
[5] M. Handley, V. Jacobson, C Perkins, "SDP: Session Description
Protocol," draft-ietf-mmusic-sdp-new-23.txt, Dec 10 2004, work
in progress.
Any 3GPP document can be downloaded from the 3GPP webserver,
"http://www.3gpp.org/", see specifications.
7. Authors' Addresses
Magnus Westerlund
Ericsson Research
Ericsson AB
SE-164 80 Stockholm
SWEDEN
Phone: +46 8 7190000
EMail: Magnus.Westerlund@ericsson.com
Per Frojdh
Ericsson Research
Ericsson AB
SE-164 80 Stockholm
SWEDEN
Phone: +46 8 7190000
EMail: Per.Frojdh@ericsson.com
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