draft-ietf-avt-smpte292-video-00.txt   draft-ietf-avt-smpte292-video-01.txt 
INTERNET-DRAFT Ladan Gharai INTERNET-DRAFT Ladan Gharai
<draft-ietf-avt-smpte292-video-00.txt> USC/ISI <draft-ietf-avt-smpte292-video-01.txt> USC/ISI
Gary Goncher Gary Goncher
Tektronix Tektronix
Colin Perkins
USC/ISI
David Richardson David Richardson
University of Washington University of Washington
Allison Mankin Allison Mankin
USC/ISI USC/ISI
July 13, 2000 Nov 24, 2000
RTP Payload Format for SMPTE 292M RTP Payload Format for SMPTE 292M
<draft-ietf-avt-smpte292-video-00.txt> <draft-ietf-avt-smpte292-video-01.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
skipping to change at page 1, line 40 skipping to change at page 1, line 42
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
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The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
Abstract Abstract
This document specifies a packetization scheme for encapsulating This document specifies a packetization scheme for encapsulating
uncompressed HDTV as defined by SMPTE 292M [1] into a payload format for uncompressed HDTV as defined by SMPTE 292M into a payload format for
the Real-Time Transport Protocol (RTP). The RTP packet counter is the Real-Time Transport Protocol (RTP). The RTP packet counter is
extended to 26 bits to accommodate SMPTE 292M's 1.485Gb/s data rate, and
additional positioning information is added to the payload header. extended to 32 bits to accommodate SMPTE 292M's 1.485Gb/s data rate.
1. Introduction 1. Introduction
The serial digital interface, SMPTE 292M, defines a universal medium of The serial digital interface, SMPTE 292M[1], defines a universal medium
interchange for uncompressed HDTV between various types of video of interchange for uncompressed HDTV between various types of video
equipment (camera's, encoders, VTRs, ...) at data rates of 1.485Gb/s equipment (camera's, encoders, VTRs, ...) at data rates of 1.485Gb/s
(and 1.485/1.001 Gb/s). Source data are 10-bit words, sampled at 4:2:2. (and 1.485/1.001 Gb/s). Source formats transfered by SMPTE 292M are
In this draft we specify how to transfer SMPTE 292M over RTP. SMPTE 260M, 295M, 274M and 296M. Source data for these formats are
10-bit words, sampled at 4:2:2. In this memo we specify how to
2. A Note on Compressed HDTV over RTP transfer SMPTE 292M over RTP.
HDTV is compressed using a subset of MPEG-2 [3] as its compression This memo only addresses the transfer of uncompressed HDTV. Compressed
scheme. This subset is fully described in document A/53 [4] of the HDTV is a subset of MPEG-2 [3], which is fully described in document
Advanced Television Standards Committee. The ATSC has also adopted the A/53 [4] of the Advanced Television Standards Committee. The ATSC has
MPEG-2 transport system (ISO/IEC 13818-1) [5]. Therefore: also adopted the MPEG-2 transport system (ISO/IEC 13818-1) [5].
Therefore:
1. The HDTV transport system is a compatible subset of the MPEG-2 1. The HDTV transport system is a compatible subset of the MPEG-2
transport system. Section 2 of RFC 2250 [7] describes the RTP payload transport system. Section 2 of RFC 2250 [7] describes the RTP payload
for MPEG-2's transport system, where multiple fixed length (188 bytes) for MPEG-2's transport system, where multiple fixed length (188 bytes)
MTS packets are aggregated into a single RTP packet. MTS packets are aggregated into a single RTP packet.
2. Compressed HDTV is a subset of MPEG-2 MP@HL with some additional 2. Compressed HDTV is a subset of MPEG-2 MP@HL with some additional
restrictions. Section 3 of RFC 2250 describes a packetization scheme for restrictions. Section 3 of RFC 2250 describes a packetization scheme for
MPEG-2 elementary streams. The additional restrictions of HDTV do not MPEG-2 elementary streams. The additional restrictions of HDTV do not
have any implications for RTP packetization. have any implications for RTP packetization.
2. Conventions Used in this Document
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 RFC 2119[10].
3. Payload Design 3. Payload Design
Each video frame of SMPTE292M in packetized into a number of variable Each video frame of SMPTE 292M is packetized into a number of constant
size RTP packets. All active, vertical blanking and timing information size RTP packets. All active, vertical blanking and timing information
is packetized. The end of a frame is marked by the M bit in the RTP is packetized. The end of a frame is marked by the M bit in the RTP
header. A single packet may contain data for two consecutive scan header. A single packet may contain data for two consecutive scan
lines. The SMPTE292M decoder uses the sync info in the scan lines to lines. The SMPTE292M decoder uses the sync info in the scan lines to
detect the start of scan lines. detect the start of scan lines.
A single packet may also contain information from adjacent scan lines in A single packet may also contain information from adjacent scan lines in
two consecutive frames, or by agreement between sender and receiver the two consecutive frames, or by agreement between sender and receiver the
last packet of a video frame may be padded and the the new frame start last packet of a video frame may be padded to the full length of all
in a new packet. 292M RTP packets, in which case a new will frame start in a new packet.
The standard 16 bit RTP sequence counter is extended to 26 bits to The standard 16 bit RTP sequence counter is extended to 32 bits to
accommodate HDTV's high data rates. At 1.485Gb/s, with packet sizes of accommodate HDTV's high data rates. At 1.485Gb/s, with packet sizes of
at least 1kByte, 32bits allows for an approximate 6 hour period before
the sequence counter wraps around.
at least 1k, 26bits allows for 5minute period before the sequence A 10Mhz timestamp is used as the RTP header's timestamp. This allows the
counter wraps around. receiver to reconstruct the timing of the SMPTE 292M stream, without
knowledge of the exact type of source format (e.g. SMPTE 274M or SMPTE
The payload header includes the offset of the payload data in the video 296M).
frame. The offset is for 20-bit video words and accounts for active and
inactive samples.
Given SMPTE292M's 4:2:2 color subsampling, scan line fragmentation must Given SMPTE 292M's 4:2:2 color subsampling, scan line fragmentation MUST
occur on sample-pair boundaries, such that Y and Cb and Cr values are occur on sample-pair boundaries, such that Y and Cb and Cr values are
not split across packets. not split across packets. This means the payload section of each packet
will be a multiple of 40bits. In addition, to ensure unique timestamps,
each packet SHOULD contain more than 8 video samples (20 bytes).
4. RTP Packetization 4. RTP Packetization
The standard RTP header is followed by a 4 byte payload header, and the The standard RTP header is followed by a 4 byte payload header, and the
payload data. payload data.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| V |P|X| CC |M| PT | sequence# (low bits) | | V |P|X| CC |M| PT | sequence# (low bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| time stamp | | time stamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | ssrc |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|squence#(high bits)| offset in frame | | sequence# (high bits) | unused |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.1. The RTP Header 4.1. The RTP Header
The following fields of the RTP fixed header are used for SMPTE 292M The following fields of the RTP fixed header are used for SMPTE 292M
encapsulation: encapsulation:
Payload Type (PT): 7bits Payload Type (PT): 7bits
A dynamically allocated payload type field which designates the A dynamically allocated payload type field which designates the
payload as SMPTE 292M. payload as SMPTE 292M.
Timestamp: 32 bits Timestamp: 32 bits
The timestamp field shall be defined from a counter at 10 MHz. The The timestamp field shall be defined from a counter at 10 MHz. The
timestamp shall be defined as the arrival time of the first 20-bit timestamp shall be defined as the arrival time of the first 20-bit
video sample to be transmitted in the current packet. At an arrival video sample to be transmitted in the current packet. At an arrival
rate of 74.25 MHz for 20-bit 292M video samples with 24/30/60 Hz rate of 74.25 MHz for 20-bit SMPTE 292M video samples with
frame rates, the timestamp will be unique for packets with more 24/30/60Hz frame rates, the timestamp will be unique for packets
than 8 video samples (20 bytes). Timestamps shall increase with more than 8 video samples (20 bytes) and therefore, each
monotonically until they roll over at 32 bits. packet SHOULD contain more than 8 samples. Timestamps shall
increase monotonically until they roll over at 32 bits.
The 10 MHz timestamp clock may be obtained from a GPS (Global One possible means of deriving the 10 MHz clocks is from a GPS
Positioning System) board. These boards have a disciplined (Global Positioning System) board. These boards have a disciplined
oscillator that is synchronized to GPS time. The disciplined oscillator that is synchronized to GPS time. The disciplined
oscillator can be as accurate as 1 in 10-12, but is more typically oscillator can be as accurate as 1 in 10-12, but is more typically
1 in 10-8. Thus clocks at widely separate locations can be 1 in 10-8. Thus clocks at widely separate locations can be
synchronized with an accuracy of 100 ns for video timing recovery. synchronized with an accuracy of 100 ns for video timing recovery.
Marker bit (M): 1bit Marker bit (M): 1bit
The Marker bit denotes the end of a video frame, and is set to 1 The Marker bit denotes the end of a video frame, and is set to 1
for the last packet of the video frame and is otherwise set to 0 for the last packet of the video frame and is otherwise set to 0
for all other packets. for all other packets.
Sequence Number (low bits): 16 bits Sequence Number (low bits): 16 bits
The low order bits for RTP sequence counter. The standard 16 bit The low order bits for RTP sequence counter. The standard 16 bit
RTP sequence number is augmented by 10 bits in the payload header RTP sequence number is augmented with another 16 bits in the
in order to accommodate the 1.485Gb/s data rate of SMPTE292M. payload header in order to accommodate the 1.485Gb/s data rate of
SMPTE 292M.
4.2. Payload Header 4.2. Payload Header
Sequence Number (high bits): 10bits Sequence Number (high bits): 16bits
The high order bits for the 26bit RTP sequence counter. The high order bits for the 32bit RTP sequence counter.
Offset in Frame: 22bits Unused: 16bits
An offset for the position of 20-bit video words in the video MUST be set to zero at the sender, and ignored at the receiver.
frame. The offset includes all information in the video frame and
scan lines. Range of values are:
1. 0 to 1125*2750-1 for 1080/24p.
2. 0 to 1125*2200-1 for 1080/30i.
3. 0 to 750*1650-1 for 720/60p.
5. Payload Format 4.3. Payload Format
For 4:2:2 color subsampling Cb and Cr values are subsampled by a factor For 4:2:2 color subsampling Cb and Cr values are subsampled by a factor
of two horizontally and are co-sited with even numbered Y samples. of two horizontally and are co-sited with even numbered Y samples.
Therefore, Cb, Cr and Y samples must be arranged and transmitted in the Therefore, Cb, Cr and Y samples MUST be arranged and transmitted in the
following order: following order:
Cb, Y, Cr, Y, Cb, Y, Cr, ... Cb, Y, Cr, Y, Cb, Y, Cr, ...
where the first Cb, Y, Cr sequence refers to co-sited luminance and where the first Cb, Y, Cr sequence refers to co-sited luminance and
color-difference samples, and the next Y belongs to the next luminance color-difference samples, and the next Y belongs to the next luminance
sample. sample.
Therefore, as set forth in RFC2431, for 10-bit words, each group of four Therefore, as set forth in RFC2431 [11], for 10-bit words, each group of
samples must be encoded into a 40-bit word (five octets) prior to four samples must be encoded into a 40-bit word (five octets) prior to
transmission. The following is a representation of a 720 sample packet transmission. The following is a representation of a 720 sample packet
with 10-bit quantization: with 10-bit quantization:
0 1 2 3 0 1 2 3
0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8
+---------+---------+---------+---------+ +---------+---------+---------+---------+
| Cb0 | Y0 | Cr0 | Y1 | | Cb0 | Y0 | Cr0 | Y1 |
+---------+---------+---------+---------+ +---------+---------+---------+---------+
| Cb1 | Y2 | Cr1 | Y3 | | Cb1 | Y2 | Cr1 | Y3 |
+---------+---------+---------+---------+ +---------+---------+---------+---------+
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| Cb359 | Y718 | Cr359 | Y719 | | Cb359 | Y718 | Cr359 | Y719 |
+---------+---------+---------+---------+ +---------+---------+---------+---------+
(Note that the word width is 40 bits) (Note that the word width is 40 bits)
+-------+-------+-------+-------+-------+ +-------+-------+-------+-------+-------+
Octets: | 0 | 1 | 2 | 3 | 4 | Octets: | 0 | 1 | 2 | 3 | 4 |
+-------+-------+-------+-------+-------+ +-------+-------+-------+-------+-------+
The octets shown in these diagrams are transmitted in network bit and The octets shown in these diagrams are transmitted in network bit and
byte order, that is, left-to-right as shown. byte order, that is, left-to-right as shown.
6. Security Considerations 5. RTCP Considerations
RFC1889 recommends transmission of RTCP packets every 5 seconds or at a
reduced minimum in seconds of 360 divided by the session bandwidth in
kilobits/seconds. At 1.485Gb/s the reduced minimum interval computes to
0.2ms or 4028 packets per second.
It should be noted that the sender's octet count in SR packets wraps
around in 23 seconds, and that the cumulative number of packets lost
wraps around in 93 seconds. This means these two fields cannot
accurately represent octet count and number of packets lost since the
beginning of transmission, as defined in RFC1889. Therefore for network
monitoring purposes other means of keeping track of these variables
should be used.
6. MIME Registration
This document defines a new RTP payload name and associated MIME type,
SMPTE 292M. The registration forms for MIME type for SMPTE 292M video is
enclosed below:
MIME media type name: video
MIME subtype name: SMPTE 292M
Required parameters: None
Optional parameters: None
Encoding considerations: SMPTE 292M video can be transmitted with
RTP as specified in "draft-ietf-avt-smpte292-video-01".
Security considerations: None
Interoperability considerations: NONE
Published specification: SMPTE 292M
draft-ietf-avt-smpte292-video-01
Applications which use this media type:
Video communication.
Additional information: None
Magic number(s): None
File extension(s): DV
Macintosh File Type Code(s): None
Person & email address to contact for further information:
Ladan Gharai <ladan@isi.edu>
Intended usage: COMMON
Author/Change controller:
Ladan Gharai <ladan@isi.edu>
7. Mapping to SDP Parameters
Parameters are mapped to SDP [9] as follows:
m=video 23456 RTP/AVP 111
a=rtpmap:111 SMPTE 292M/10000000
a=fmtp:111 length=1400
In this example, a dynamic payload type 111 is assumed for SMPTE 292M,
with packet sizes of 1400bytes.
8. Security Considerations
RTP packets using the payload format defined in this specification are RTP packets using the payload format defined in this specification are
subject to the security considerations discussed in the RTP subject to the security considerations discussed in the RTP
specification [4], and any appropriate RTP profile. This implies that specification, and any appropriate RTP profile. This implies that
confidentiality of the media streams is achieved by encryption. Because confidentiality of the media streams is achieved by encryption.
the data compression used with this payload format is applied end-to-
end, encryption may be performed after compression so there is no
conflict between the two operations.
This payload type does not exhibit any significant non-uniformity in the This payload type does not exhibit any significant non-uniformity in the
receiver side computational complexity for packet processing to cause a receiver side computational complexity for packet processing to cause a
potential denial-of-service threat. potential denial-of-service threat.
It is perhaps to be noted that the bandwidth of this payload is high It is perhaps to be noted that the bandwidth of this payload is high
enough (1.5 Gbps without the RTP overhead) to cause potential for enough (1.5 Gbps without the RTP overhead) to cause potential for
denial-of-service if transmitted onto most currently available Internet denial-of-service if transmitted onto most currently available Internet
paths. In the absence from the standards track of a suitable congestion paths. In the absence from the standards track of a suitable congestion
control mechanism for flows of this sort, use of the payload should be control mechanism for flows of this sort, use of the payload should be
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This payload type does not exhibit any significant non-uniformity in the This payload type does not exhibit any significant non-uniformity in the
receiver side computational complexity for packet processing to cause a receiver side computational complexity for packet processing to cause a
potential denial-of-service threat. potential denial-of-service threat.
It is perhaps to be noted that the bandwidth of this payload is high It is perhaps to be noted that the bandwidth of this payload is high
enough (1.5 Gbps without the RTP overhead) to cause potential for enough (1.5 Gbps without the RTP overhead) to cause potential for
denial-of-service if transmitted onto most currently available Internet denial-of-service if transmitted onto most currently available Internet
paths. In the absence from the standards track of a suitable congestion paths. In the absence from the standards track of a suitable congestion
control mechanism for flows of this sort, use of the payload should be control mechanism for flows of this sort, use of the payload should be
narrowly limited to suitably connected network endpoints and great care narrowly limited to suitably connected network endpoints and great care
taken with the scope of multicast transmissions. This potential threat taken with the scope of multicast transmissions. This potential threat
is common to all high bit rate applications. is common to all high bit rate applications.
7. IANA Considerations 9. IANA Considerations
[To be done] See Section 6.
8. Full Copyright Statement 10. Full Copyright Statement
Copyright (C) The Internet Society (1999). All Rights Reserved. Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it or others, and derivative works that comment on or otherwise explain it or
assist in its implementation may be prepared, copied, published and assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind, distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are included provided that the above copyright notice and this paragraph are included
on all such copies and derivative works. on all such copies and derivative works.
However, this document itself may not be modified in any way, such as by However, this document itself may not be modified in any way, such as by
removing the copyright notice or references to the Internet Soci- ety or removing the copyright notice or references to the Internet Soci- ety or
other Internet organizations, except as needed for the purpose of other Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be fol- lowed, copyrights defined in the Internet Standards process must be fol- lowed,
or as required to translate it into languages other than English. or as required to translate it into languages other than English.
The limited permissions granted above are perpetual and will not be The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns. revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an "AS This document and the information contained herein is provided on an "AS
skipping to change at page 6, line 40 skipping to change at page 8, line 21
The limited permissions granted above are perpetual and will not be The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns. revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an "AS This document and the information contained herein is provided on an "AS
IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT
INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MER- CHANTABILITY OR INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MER- CHANTABILITY OR
FITNESS FOR A PARTICULAR PURPOSE." FITNESS FOR A PARTICULAR PURPOSE."
9. Authors' Addresses 11. Authors' Addresses
Ladan Gharai Ladan Gharai
ladan@isi.edu ladan@isi.edu
Gary Goncher Gary Goncher
ggoncher@tek.com ggoncher@tek.com
Allison Mankin
mankin@isi.edu Colin Perkins
csp@isi.edu
David Richardson David Richardson
drr@u.washington.edu drr@u.washington.edu
10. Bibliography Allison Mankin
mankin@isi.edu
12. Bibliography
[1] Society of Motion Picture and Television Engineers, [1] Society of Motion Picture and Television Engineers,
Bit-Serial Digital Interface for High-Definition Television Bit-Serial Digital Interface for High-Definition Television
Systems, SMPTE292M, 1998. Systems, SMPTE292M, 1998.
[2] Society of Motion Picture and Television Engineers, [2] Society of Motion Picture and Television Engineers,
1280*720 Scanning, Analog and Digital Representation and Analog 1280*720 Scanning, Analog and Digital Representation and Analog
Interfaces, SMPTE 296M, 1998. Interfaces, SMPTE 296M, 1998.
[3] ISO/IEC International Standard 13818-2; "Generic coding of [3] ISO/IEC International Standard 13818-2; "Generic coding of
skipping to change at line 296 skipping to change at page 9, line 23
[6] Schulzrinne, Casner, Frederick, Jacobson, "RTP: A transport [6] Schulzrinne, Casner, Frederick, Jacobson, "RTP: A transport
protocol for real time Applications", RFC 1889, IETF, protocol for real time Applications", RFC 1889, IETF,
January 1996. January 1996.
[7] Hoffman, Fernando, Goyal, Civanlar, "RTP Payload Format for [7] Hoffman, Fernando, Goyal, Civanlar, "RTP Payload Format for
MPEG1/MPEG2 Video", RFC 2250, IETF, January 1998. MPEG1/MPEG2 Video", RFC 2250, IETF, January 1998.
[8] Schulzrinne, "RTP Profile for Audio and Video Conferences with [8] Schulzrinne, "RTP Profile for Audio and Video Conferences with
Minimal Control", RFC 1890, IETF, January 1996. Minimal Control", RFC 1890, IETF, January 1996.
[9] M. Handley and V. Jacobson, "SDP: Session Description Protocol",
RFC 2327, April 1998.
[10] IETF RFC 2119, "Key words for use in RFCs to Indicate
Requirement Levels".
[11] D. Tynan, "RTP Payload Format for BT.656 Video Encoding",
RFC 2431, October 1998.
 End of changes. 

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