FEC Framework Working Group M. Watson
Internet-Draft Qualcomm Inc.
Intended status: Standards Track March 6, 2009
Expires: September 7, 2009
RTP Payload Format for Raptor FEC
draft-ietf-fecframe-rtp-raptor-01
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Abstract
This document specifies an RTP Payload Format for Forward Error
Correction repair data produced by the Raptor FEC Schemes. Raptor
FEC Schemes are specified for use with the IETF FEC Framework which
supports transport of repair data over both UDP and RTP. This
document specifies the Payload Format which is required for the use
of RTP to carry Raptor repair flows.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions, Definitions and Acronyms . . . . . . . . . . . . 4
3. Media Format Background . . . . . . . . . . . . . . . . . . . 5
4. Payload Format . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. RTP Header Usage . . . . . . . . . . . . . . . . . . . . . 6
4.2. Payload Header . . . . . . . . . . . . . . . . . . . . . . 6
4.3. Payload Data . . . . . . . . . . . . . . . . . . . . . . . 6
5. Congestion Control Considerations . . . . . . . . . . . . . . 7
6. Media Types . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Registration of the application/raptorfec media type . . . 8
6.1.1. Media Type Definition . . . . . . . . . . . . . . . . 8
6.2. Registration of the video/raptorfec media type . . . . . . 9
6.2.1. Media Type Definition . . . . . . . . . . . . . . . . 9
6.3. Registration of the audio/raptorfec media type . . . . . . 10
6.3.1. Media Type Definition . . . . . . . . . . . . . . . . 10
6.4. Registration of the text/raptorfec media type . . . . . . 12
6.4.1. Media Type Definition . . . . . . . . . . . . . . . . 12
7. Mapping to SDP . . . . . . . . . . . . . . . . . . . . . . . . 14
8. Offer/Answer considerations . . . . . . . . . . . . . . . . . 15
9. Declarative SDP Considerations . . . . . . . . . . . . . . . . 16
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
11. Security Considerations . . . . . . . . . . . . . . . . . . . 18
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Introduction
The FEC Framework [I-D.ietf-fecframe-framework] defines a general
framework for the use of Forward Error Correction in association with
arbitrary packet flows, including flows over UDP and RTP. Forward
Error Corrections operates by generating redundant data packets
("repair data") which can be sent independently from the original
flow. At a receiver the original flow can be reconstructed provided
a sufficient set of redundant data packets and possibly original data
packets are received.
The FEC Framework provides for independence between application
protocols and FEC codes. The use of a particular FEC code within the
framework is defined by means of an FEC Scheme which may then be used
with any application protocol compliant to the framework.
Repair data flows may be sent directly over a transport protocol such
as UDP, or they may be encapsulated within RTP. In the latter case,
an RTP Payload Format must be defined for each FEC Scheme.
This document defines the RTP Payload Format for the Raptor FEC
Schemes defined in [I-D.ietf-fecframe-raptor].
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2. Conventions, Definitions and Acronyms
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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3. Media Format Background
The Raptor code is an efficient XOR-based block-based fountain code,
meaning that from any group of source packets (or 'source block') an
arbitrary number of repair packets may be generated. The Raptor code
has the property that the original group of source packets can be
recovered with very high probability from any set of packets (source
and repair) only slightly greater in number than the original number
of source packets.
[I-D.ietf-fecframe-raptor] defines three FEC Schemes for the use of
the Raptor code with arbitary packet flows: the first scheme is fully
applicable to arbitary packet flows. The second scheme is a slightly
optimised version of the first scheme which is applicable in
applications with relatively small block sizes. The third scheme is
a variant of the second scheme which is applicable to a single source
flow which already has some kind of identifiable sequence number.
The presence of a sequence number in the source flow allows for
backwards compatible operation (the source flows do not need to be
modified in order to apply FEC). In this case, in the language of
the FEC Framework, there is no explicit FEC Source Payload Id.
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4. Payload Format
The RTP Payload contains a FEC Repair Payload as defined in
[I-D.ietf-fecframe-raptor].
4.1. RTP Header Usage
The rules SHALL be followed for the RTP header used with FEC repair
packets:
o Marker bit: The marker bit shall be set 1 for the last protection
RTP packet sent for each source block, and otherwise set to 0
o Timestamp: The timestamp SHALL be set to a time corresponding to
the packet's transmission time. The timestamp value has no use in
the actual FEC protection process. It may be used for packet
arrival timing and jitter calculations.
4.2. Payload Header
There is no Payload Header in this Payload Format
4.3. Payload Data
The RTP Payload contains a FEC Repair Payload as defined in
[I-D.ietf-fecframe-framework] and [I-D.ietf-fecframe-raptor].
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5. Congestion Control Considerations
See [I-D.ietf-fecframe-framework].
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6. Media Types
6.1. Registration of the application/raptorfec media type
This RTP payload format is identified using the application/raptorfec
media type which is registered in accordance with [RFC4855] and using
the template of [RFC4288].
6.1.1. Media Type Definition
Type name: application
Subtype name: raptorfec
Required parameters:
raptor-scheme-id: The value of this parameter is the FEC Scheme Id
for the specific Raptor FEC Scheme that will be used as defined in
[I-D.ietf-fecframe-raptor].
max-sbl: The value of this parameter is the FEC Object
Transmission Information element "Maximum Source Block Length" as
defined in [I-D.ietf-fecframe-raptor] encoded as a decimal
integer.
symbol-size: The value of this parameter is the FEC Object
Transmission Information element "Encoding Symbol Size" as
definedf in [I-D.ietf-fecframe-raptor] encoded as a decimal
integer.
Optional parameters: none
Encoding considerations: This media type is framed and binary, see
section 4.8 in [RFC4288]
Security considerations: Please see security consideration in
[I-D.ietf-fecframe-framework]
Interoperability considerations:
Published specification: [I-D.ietf-fecframe-raptor]
Applications that use this media type:
Additional information:
Magic number(s): <none defined>
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File extension(s): <none defined>
Macintosh file type code(s): <none defined>
Person & email address to contact for further information: Mark
Watson, watson@qualcomm.com
Intended usage: COMMON
Restrictions on usage: This media type depends on RTP framing, and
hence is only defined for transfer via RTP [[RFC3550]]. Transport
within other framing protocols is not defined at this time.
Author: Mark Watson, Qualcomm Inc.
Change controller: IETF Audio/Video Transport working group delegated
from the IESG.
6.2. Registration of the video/raptorfec media type
This RTP payload format is identified using the video/raptorfec media
type which is registered in accordance with [RFC4855] and using the
template of [RFC4288].
6.2.1. Media Type Definition
Type name: video
Subtype name: raptorfec
Required parameters:
raptor-scheme-id: The value of this parameter is the FEC Scheme Id
for the specific Raptor FEC Scheme that will be used as defined in
[I-D.ietf-fecframe-raptor]
max-sbl: The value of this parameter is the FEC Object
Transmission Information element "Maximum Source Block Length" as
defined in [I-D.ietf-fecframe-raptor] encoded as a decimal
integer.
symbol-size: The value of this parameter is the FEC Object
Transmission Information element "Encoding Symbol Size" as
definedf in [I-D.ietf-fecframe-raptor] encoded as a decimal
integer.
Optional parameters: none
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Encoding considerations: This media type is framed and binary, see
section 4.8 in [RFC4288]
Security considerations: Please see security consideration in
[I-D.ietf-fecframe-framework]
Interoperability considerations:
Published specification: [I-D.ietf-fecframe-raptor]
Applications that use this media type:
Additional information:
Magic number(s): <none defined>
File extension(s): <none defined>
Macintosh file type code(s): <none defined>
Person & email address to contact for further information: Mark
Watson, watson@qualcomm.com
Intended usage: COMMON
Restrictions on usage: This media type depends on RTP framing, and
hence is only defined for transfer via RTP [[RFC3550]]. Transport
within other framing protocols is not defined at this time.
Author: Mark Watson, Qualcomm Inc.
Change controller: IETF Audio/Video Transport working group delegated
from the IESG.
6.3. Registration of the audio/raptorfec media type
This RTP payload format is identified using the audio/raptorfec media
type which is registered in accordance with [RFC4855] and using the
template of [RFC4288].
6.3.1. Media Type Definition
Type name: audio
Subtype name: raptorfec
Required parameters:
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raptor-scheme-id: The value of this parameter is the FEC Scheme Id
for the specific Raptor FEC Scheme that will be used as defined in
[I-D.ietf-fecframe-raptor]
max-sbl: The value of this parameter is the FEC Object
Transmission Information element "Maximum Source Block Length" as
defined in [I-D.ietf-fecframe-raptor] encoded as a decimal
integer.
symbol-size: The value of this parameter is the FEC Object
Transmission Information element "Encoding Symbol Size" as
definedf in [I-D.ietf-fecframe-raptor] encoded as a decimal
integer.
Optional parameters: none
Encoding considerations: This media type is framed and binary, see
section 4.8 in [RFC4288]
Security considerations: Please see security consideration in
[I-D.ietf-fecframe-framework]
Interoperability considerations:
Published specification: [I-D.ietf-fecframe-raptor]
Applications that use this media type:
Additional information:
Magic number(s): <none defined>
File extension(s): <none defined>
Macintosh file type code(s): <none defined>
Person & email address to contact for further information: Mark
Watson, watson@qualcomm.com
Intended usage: COMMON
Restrictions on usage: This media type depends on RTP framing, and
hence is only defined for transfer via RTP [[RFC3550]]. Transport
within other framing protocols is not defined at this time.
Author: Mark Watson, Qualcomm Inc.
Change controller: IETF Audio/Video Transport working group delegated
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from the IESG.
6.4. Registration of the text/raptorfec media type
This RTP payload format is identified using the text/raptorfec media
type which is registered in accordance with [RFC4855] and using the
template of [RFC4288].
6.4.1. Media Type Definition
Type name: text
Subtype name: raptorfec
Required parameters:
raptor-scheme-id: The value of this parameter is the FEC Scheme Id
for the specific Raptor FEC Scheme that will be used as defined in
[I-D.ietf-fecframe-raptor]
max-sbl: The value of this parameter is the FEC Object
Transmission Information element "Maximum Source Block Length" as
defined in [I-D.ietf-fecframe-raptor] encoded as a decimal
integer.
symbol-size: The value of this parameter is the FEC Object
Transmission Information element "Encoding Symbol Size" as
definedf in [I-D.ietf-fecframe-raptor] encoded as a decimal
integer.
Optional parameters: none
Encoding considerations: This media type is framed and binary, see
section 4.8 in [RFC4288]
Security considerations: Please see security consideration in
[I-D.ietf-fecframe-framework]
Interoperability considerations:
Published specification: [I-D.ietf-fecframe-raptor]
Applications that use this media type:
Additional information:
Magic number(s): <none defined>
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File extension(s): <none defined>
Macintosh file type code(s): <none defined>
Person & email address to contact for further information: Mark
Watson, watson@qualcomm.com
Intended usage: COMMON
Restrictions on usage: This media type depends on RTP framing, and
hence is only defined for transfer via RTP [[RFC3550]]. Transport
within other framing protocols is not defined at this time.
Author: Mark Watson, Qualcomm Inc.
Change controller: IETF Audio/Video Transport working group delegated
from the IESG.
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7. Mapping to SDP
The mapping of the above defined payload format media type and its
parameters SHALL be done according to Section 3 of [RFC4855]
When the RTP Payload Formats defined in this document are used, the
Media Type Parameters defined above SHALL be used to specify the FEC
Object Transmission Information in preference to the SDP attributes
specified in [I-D.ietf-fecframe-sdp-elements]
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8. Offer/Answer considerations
None.
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9. Declarative SDP Considerations
None.
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10. IANA Considerations
This memo requests that IANA registers application/raptorfec as
specified in Section 6.1.1, video/raptorfec as specified in
Section 6.2.1, audio/raptorfec as specified in Section 6.3.1 and
text/raptorfec as specified in Section 6.4.1. The media type is also
requested to be added to the IANA registry for "RTP Payload Format
MIME types" (http://www.iana.org/assignments/rtp-parameters).
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11. Security Considerations
See [I-D.ietf-fecframe-framework]
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12. References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", BCP 13, RFC 4288, December 2005.
[RFC4855] Casner, S., "Media Type Registration of RTP Payload
Formats", RFC 4855, February 2007.
[I-D.ietf-fecframe-framework]
Watson, M., "Forward Error Correction (FEC) Framework",
draft-ietf-fecframe-framework-03 (work in progress),
October 2008.
[I-D.ietf-fecframe-sdp-elements]
Begen, A., "SDP Elements for FEC Framework",
draft-ietf-fecframe-sdp-elements-02 (work in progress),
November 2008.
[I-D.ietf-fecframe-raptor]
Watson, M., "Raptor FEC Schemes for FECFRAME",
draft-ietf-fecframe-raptor-00 (work in progress),
October 2008.
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Author's Address
Mark Watson
Qualcomm Inc.
3165 Kifer Rd.
Santa Clara, CA 95051
U.S.A.
Email: watson@qualcomm.com
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