path: root/doc/rfc/rfc4629.txt

Network Working Group                                             J. Ott
Request for Comments: 4629             Helsinki University of Technology
Obsoletes: 2429                                               C. Bormann
Updates: 3555                                    Universitaet Bremen TZI
Category: Standards Track                                    G. Sullivan
                                                               Microsoft
                                                               S. Wenger
                                                                   Nokia
                                                            R. Even, Ed.
                                                                 Polycom
                                                            January 2007


             RTP Payload Format for ITU-T Rec. H.263 Video

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document describes a scheme to packetize an H.263 video stream
   for transport using the Real-time Transport Protocol (RTP) with any
   of the underlying protocols that carry RTP.

   The document also describes the syntax and semantics of the Session
   Description Protocol (SDP) parameters needed to support the H.263
   video codec.

   The document obsoletes RFC 2429 and updates the H263-1998 and
   H263-2000 media type in RFC 3555.












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Table of Contents

   1. Introduction ....................................................3
      1.1. Terminology ................................................3
   2. New H.263 Features ..............................................3
   3. Usage of RTP ....................................................4
      3.1. RTP Header Usage ...........................................5
      3.2. Video Packet Structure .....................................6
   4. Design Considerations ...........................................7
   5. H.263+ Payload Header ...........................................9
      5.1. General H.263+ Payload Header ..............................9
      5.2. Video Redundancy Coding Header Extension ..................10
   6. Packetization Schemes ..........................................12
      6.1. Picture Segment Packets and Sequence Ending
           Packets (P=1) .............................................12
           6.1.1. Packets that begin with a Picture Start Code .......12
           6.1.2. Packets that begin with GBSC or SSC ................13
           6.1.3. Packets that begin with an EOS or EOSBS Code .......14
      6.2. Encapsulating Follow-on Packet (P=0) ......................15
   7. Use of this Payload Specification ..............................15
   8. Media Type Definition ..........................................17
      8.1. Media Type Registrations ..................................17
           8.1.1. Registration of Media Type video/H263-1998 .........17
           8.1.2. Registration of Media Type video/H263-2000 .........21
      8.2. SDP Usage .................................................22
           8.2.1. Usage with the SDP Offer Answer Model ..............23
   9. Backward Compatibility to RFC 2429 .............................25
      9.1. New Optional Parameters for SDP ...........................25
   10. IANA Considerations ...........................................25
   11. Security Considerations .......................................25
   12. Acknowledgments ...............................................26
   13. Changes from Previous Versions of the Documents ...............26
      13.1. Changes from RFC 2429 ....................................26
      13.2. Changes from RFC 3555 ....................................26
   14. References ....................................................26
      14.1. Normative References .....................................26
      14.2. Informative References ...................................27














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1.  Introduction

   This document specifies an RTP payload header format applicable to
   the transmission of video streams based on the 1998 and 2000 versions
   of International Telecommunication Union-Telecommunication
   Standardization Sector (ITU-T) Recommendation H.263 [H263].  Because
   the 1998 and 2000 versions of H.263 are a superset of the 1996
   syntax, this format can also be used with the 1996 version of H.263
   and is recommended for this use by new implementations.  This format
   replaces the payload format in RFC 2190 [RFC2190], which continues to
   be used by some existing implementations, and can be useful for
   backward compatibility.  New implementations supporting H.263 SHALL
   use the payload format described in this document.  RFC 2190 is moved
   to historic status [RFC4628].

   The document updates the media type registration that was previously
   in RFC 3555 [RFC3555].

   This document obsoletes RFC 2429 [RFC2429].

1.1.  Terminology

   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 [RFC2119] and
   indicate requirement levels for compliant RTP implementations.

2.  New H.263 Features

   The 1998 version of ITU-T Recommendation H.263 added numerous coding
   options to improve codec performance over the 1996 version.  In this
   document, the 1998 version is referred to as H.263+ and the 2000
   version as H.263++.

   Among the new options, the ones with the biggest impact on the RTP
   payload specification and the error resilience of the video content
   are the slice structured mode, the independent segment decoding mode,
   the reference picture selection mode, and the scalability mode.  This
   section summarizes the impact of these new coding options on
   packetization.  Refer to [H263] for more information on coding
   options.

   The slice structured mode was added to H.263+ for three purposes: to
   provide enhanced error resilience capability, to make the bitstream
   more amenable for use with an underlying packet transport such as
   RTP, and to minimize video delay.  The slice structured mode supports
   fragmentation at macroblock boundaries.




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   With the independent segment decoding (ISD) option, a video picture
   frame is broken into segments and encoded in such a way that each
   segment is independently decodable.  Utilizing ISD in a lossy network
   environment helps to prevent the propagation of errors from one
   segment of the picture to others.

   The reference picture selection mode allows the use of an older
   reference picture rather than the one immediately preceding the
   current picture.  Usually, the last transmitted frame is implicitly
   used as the reference picture for inter-frame prediction.  If the
   reference picture selection mode is used, the data stream carries
   information on what reference frame should be used, indicated by the
   temporal reference as an ID for that reference frame.  The reference
   picture selection mode may be used with or without a back channel,
   which provides information to the encoder about the internal status
   of the decoder.  However, no special provision is made herein for
   carrying back channel information.  The Extended RTP Profile for RTP
   Control Protocol (RTCP)-based Feedback [RFC4585] MAY be used as a
   back channel mechanism.

   H.263+ also includes bitstream scalability as an optional coding
   mode.  Three kinds of scalability are defined: temporal, signal-to-
   noise ratio (SNR), and spatial scalability.  Temporal scalability is
   achieved via the disposable nature of bi-directionally predicted
   frames, or B-frames.  (A low-delay form of temporal scalability known
   as P-picture temporal scalability can also be achieved by using the
   reference picture selection mode, described in the previous
   paragraph.)  SNR scalability permits refinement of encoded video
   frames, thereby improving the quality (or SNR).  Spatial scalability
   is similar to SNR scalability except that the refinement layer is
   twice the size of the base layer in the horizontal dimension,
   vertical dimension, or both.

   H.263++ added some new functionalities.  Among the new
   functionalities are support for interlace mode, specified in H.263,
   annex W.6.3.11, and the definition of profiles and levels in H.263
   annex X.

3.  Usage of RTP

   When transmitting H.263+ video streams over the Internet, the output
   of the encoder can be packetized directly.  All the bits resulting
   from the bitstream (including the fixed length codes and variable
   length codes) will be included in the packet, the only exception
   being that when the payload of a packet begins with a Picture, GOB,
   Slice, End of Sequence (EOS), or End of Sub-Bit Stream (EOSBS) start
   code, the first 2 (all-zero) bytes of the start code shall be removed
   and replaced by setting an indicator bit in the payload header.



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   For H.263+ bitstreams coded with temporal, spatial, or SNR
   scalability, each layer may be transported to a different network
   address.  More specifically, each layer may use a unique IP address
   and port number combination.  The temporal relations between layers
   shall be expressed using the RTP timestamp so that they can be
   synchronized at the receiving ends in multicast or unicast
   applications.

   The H.263+ video stream will be carried as payload data within RTP
   packets.  A new H.263+ payload header is defined in Section 5; it
   updates the one specified in RFC 2190.  This section defines the
   usage of the RTP fixed header and H.263+ video packet structure.

3.1.  RTP Header Usage

   Each RTP packet starts with a fixed RTP header.  The following fields
   of the RTP fixed header used for H.263+ video streams are further
   emphasized here.

   Marker bit (M bit): The Marker bit of the RTP header is set to 1 when
   the current packet carries the end of current frame and is 0
   otherwise.

   Payload Type (PT): The RTP profile for a particular class of
   applications will assign a payload type for this encoding, or, if
   that is not done, a payload type in the dynamic range shall be chosen
   by the sender.

   Timestamp: The RTP Timestamp encodes the sampling instance of the
   first video frame data contained in the RTP data packet.  The RTP
   timestamp shall be the same on successive packets if a video frame
   occupies more than one packet.  In a multilayer scenario, all
   pictures corresponding to the same temporal reference should use the
   same timestamp.  If temporal scalability is used (if B-frames are
   present), the timestamp may not be monotonically increasing in the
   RTP stream.  If B-frames are transmitted on a separate layer and
   address, they must be synchronized properly with the reference
   frames.  Refer to ITU-T Recommendation H.263 [H263] for information
   on required transmission order to a decoder.  For an H.263+ video
   stream, the RTP timestamp is based on a 90 kHz clock, the same as
   that of the RTP payload for H.261 stream [RFC2032].  Since both the
   H.263+ data and the RTP header contain time information, that timing
   information must run synchronously.  That is, both the RTP timestamp
   and the temporal reference (TR in the picture header of H.263) should
   carry the same relative timing information.  Any H.263+ picture clock
   frequency can be expressed as 1800000/(cd*cf) source pictures per
   second, in which cd is an integer from 1 to 127 and cf is either 1000
   or 1001.  Using the 90 kHz clock of the RTP timestamp, the time



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   increment between each coded H.263+ picture should therefore be an
   integer multiple of (cd*cf)/20.  This will always be an integer for
   any "reasonable" picture clock frequency (for example, it is 3003 for
   30/1.001 Hz NTSC; 3600 for 25 Hz PAL; 3750 for 24 Hz film; and 1500,
   1250, or 1200 for the computer display update rates of 60, 72, or 75
   Hz, respectively).  For RTP packetization of hypothetical H.263+
   bitstreams using "unreasonable" custom picture clock frequencies,
   mathematical rounding could become necessary for generating the RTP
   timestamps.

3.2.  Video Packet Structure

   A section of an H.263+ compressed bitstream is carried as a payload
   within each RTP packet.  For each RTP packet, the RTP header is
   followed by an H.263+ payload header, which is followed by a number
   of bytes of a standard H.263+ compressed bitstream.  The size of the
   H.263+ payload header is variable, depending on the payload involved,
   as detailed in the Section 4.  The layout of the RTP H.263+ video
   packet is shown as

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :    RTP Header                                                 :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :    H.263+ Payload Header                                      :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :    H.263+ Compressed Data Stream                              :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Any H.263+ start codes can be byte aligned by an encoder by using the
   stuffing mechanisms of H.263+.  As specified in H.263+, picture,
   slice, and EOSBS starts codes shall always be byte aligned, and GOB
   and EOS start codes may be byte aligned.  For packetization purposes,
   GOB start codes should be byte aligned; however, since this is not
   required in H.263+, there may be some cases where GOB start codes are
   not aligned, such as when transmitting existing content, or when
   using H.263 encoders that do not support GOB start code alignment.
   In this case, Follow-on Packets (see Section 5.2) should be used for
   packetization.

   All H.263+ start codes (Picture, GOB, Slice, EOS, and EOSBS) begin
   with 16 zero-valued bits.  If a start code is byte aligned and it
   occurs at the beginning of a packet, these two bytes shall be removed
   from the H.263+ compressed data stream in the packetization process
   and shall instead be represented by setting a bit (the P bit) in the
   payload header.






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4.  Design Considerations

   The goals of this payload format are to specify an efficient way of
   encapsulating an H.263+ standard compliant bitstream and to enhance
   the resiliency towards packet losses.  Due to the large number of
   different possible coding schemes in H.263+, a copy of the picture
   header with configuration information is inserted into the payload
   header when appropriate.  The use of that copy of the picture header
   along with the payload data can allow decoding of a received packet
   even in cases when another packet containing the original picture
   header becomes lost.

   There are a few assumptions and constraints associated with this
   H.263+ payload header design.  The purpose of this section is to
   point out various design issues and also to discuss several coding
   options provided by H.263+ that may impact the performance of
   network-based H.263+ video.

   o  The optional slice structured mode described in Annex K of [H263]
      enables more flexibility for packetization.  Similar to a picture
      segment that begins with a GOB header, the motion vector
      predictors in a slice are restricted to reside within its
      boundaries.  However, slices provide much greater freedom in the
      selection of the size and shape of the area that is represented as
      a distinct decodable region.  In particular, slices can have a
      size that is dynamically selected to allow the data for each slice
      to fit into a chosen packet size.  Slices can also be chosen to
      have a rectangular shape, which is conducive for minimizing the
      impact of errors and packet losses on motion-compensated
      prediction.  For these reasons, the use of the slice structured
      mode is strongly recommended for any applications used in
      environments where significant packet loss occurs.

   o  In non-rectangular slice structured mode, only complete slices
      SHOULD be included in a packet.  In other words, slices should not
      be fragmented across packet boundaries.  The only reasonable need
      for a slice to be fragmented across packet boundaries is when the
      encoder that generated the H.263+ data stream could not be
      influenced by an awareness of the packetization process (such as
      when sending H.263+ data through a network other than the one to
      which the encoder is attached, as in network gateway
      implementations).  Optimally, each packet will contain only one
      slice.








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   o  The independent segment decoding (ISD) described in Annex R of
      [H263] prevents any data dependency across slice or GOB boundaries
      in the reference picture.  It can be utilized to improve
      resiliency further in high loss conditions.

   o  If ISD is used in conjunction with the slice structure, the
      rectangular slice submode shall be enabled, and the dimensions and
      quantity of the slices present in a frame shall remain the same
      between each two intra-coded frames (I-frames), as required in
      H.263+.  The individual ISD segments may also be entirely intra
      coded from time to time to realize quick error recovery without
      adding the latency time associated with sending complete INTRA-
      pictures.

   o  When the slice structure is not applied, the insertion of a
      (preferably byte-aligned) GOB header can be used to provide resync
      boundaries in the bitstream, as the presence of a GOB header
      eliminates the dependency of motion vector prediction across GOB
      boundaries.  These resync boundaries provide natural locations for
      packet payload boundaries.

   o  H.263+ allows picture headers to be sent in an abbreviated form in
      order to prevent repetition of overhead information that does not
      change from picture to picture.  For resiliency, sending a
      complete picture header for every frame is often advisable.  This
      means (especially in cases with high packet loss probability in
      which picture header contents are not expected to be highly
      predictable) that the sender may find it advisable always to set
      the subfield UFEP in PLUSPTYPE to '001' in the H.263+ video
      bitstream.  (See [H263] for the definition of the UFEP and
      PLUSPTYPE fields).

   o  In a multi-layer scenario, each layer may be transmitted to a
      different network address.  The configuration of each layer, such
      as the enhancement layer number (ELNUM), reference layer number
      (RLNUM), and scalability type should be determined at the start of
      the session and should not change during the course of the
      session.

   o  All start codes can be byte aligned, and picture, slice, and EOSBS
      start codes are always byte aligned.  The boundaries of these
      syntactical elements provide ideal locations for placing packet
      boundaries.

   o  We assume that a maximum Picture Header size of 504 bits is
      sufficient.  The syntax of H.263+ does not explicitly prohibit
      larger picture header sizes, but the use of such extremely large
      picture headers is not expected.



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RFC 4629                H.263 RTP Payload Format            January 2007


5.  H.263+ Payload Header

   For H.263+ video streams, each RTP packet shall carry only one H.263+
   video packet.  The H.263+ payload header shall always be present for
   each H.263+ video packet.  The payload header is of variable length.
   A 16-bit field of the general payload header, defined in 5.1, may be
   followed by an 8 bit field for Video Redundancy Coding (VRC)
   information, and/or by a variable-length extra picture header as
   indicated by PLEN.  These optional fields appear in the order given
   above, when present.

   If an extra picture header is included in the payload header, the
   length of the picture header in number of bytes is specified by PLEN.
   The minimum length of the payload header is 16 bits, PLEN equal to 0
   and no VRC information being present.

   The remainder of this section defines the various components of the
   RTP payload header.  Section 6 defines the various packet types that
   are used to carry different types of H.263+ coded data, and Section 7
   summarizes how to distinguish between the various packet types.

5.1.  General H.263+ Payload Header

   The H.263+ payload header is structured as follows:

         0                   1
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |   RR    |P|V|   PLEN    |PEBIT|
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   RR: 5 bits

      Reserved bits.  It SHALL be zero and MUST be ignored by receivers.

   P: 1 bit

      Indicates the picture start or a picture segment (GOB/Slice) start
      or a video sequence end (EOS or EOSBS).  Two bytes of zero bits
      then have to be prefixed to the payload of such a packet to
      compose a complete picture/GOB/slice/EOS/EOSBS start code.  This
      bit allows the omission of the two first bytes of the start codes,
      thus improving the compression ratio.








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   V: 1 bit

      Indicates the presence of an 8-bit field containing information
      for Video Redundancy Coding (VRC), which follows immediately after
      the initial 16 bits of the payload header, if present.  For syntax
      and semantics of that 8-bit VRC field, see Section 5.2.

   PLEN: 6 bits

      Length, in bytes, of the extra picture header.  If no extra
      picture header is attached, PLEN is 0.  If PLEN>0, the extra
      picture header is attached immediately following the rest of the
      payload header.  Note that the length reflects the omission of the
      first two bytes of the picture start code (PSC).  See Section 6.1.

   PEBIT: 3 bits

      Indicates the number of bits that shall be ignored in the last
      byte of the picture header.  If PLEN is not zero, the ignored bits
      shall be the least significant bits of the byte.  If PLEN is zero,
      then PEBIT shall also be zero.

5.2.  Video Redundancy Coding Header Extension

   Video Redundancy Coding (VRC) is an optional mechanism intended to
   improve error resilience over packet networks.  Implementing VRC in
   H.263+ will require the Reference Picture Selection option described
   in Annex N of [H263].  By having multiple "threads" of independently
   inter-frame predicted pictures, damage to an individual frame will
   cause distortions only within its own thread, leaving the other
   threads unaffected.  From time to time, all threads converge to a
   so-called sync frame (an INTRA picture or a non-INTRA picture that is
   redundantly represented within multiple threads); from this sync
   frame, the independent threads are started again.  For more
   information on codec support for VRC, see [Vredun].

   P-picture temporal scalability is another use of the reference
   picture selection mode and can be considered a special case of VRC in
   which only one copy of each sync frame may be sent.  It offers a
   thread-based method of temporal scalability without the increased
   delay caused by the use of B pictures.  In this use, sync frames sent
   in the first thread of pictures are also used for the prediction of a
   second thread of pictures that fall temporally between the sync
   frames to increase the resulting frame rate.  In this use, the
   pictures in the second thread can be discarded in order to obtain a
   reduction of bit rate or decoding complexity without harming the
   ability to decode later pictures.  A third or more threads, can also
   be added, but each thread is predicted only from the sync frames



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   (which are sent at least in thread 0) or from frames within the same
   thread.

   While a VRC data stream is (like all H.263+ data) totally self-
   contained, it may be useful for the transport hierarchy
   implementation to have knowledge about the current damage status of
   each thread.  On the Internet, this status can easily be determined
   by observing the marker bit, the sequence number of the RTP header,
   the thread-id, and a circling "packet per thread" number.  The latter
   two numbers are coded in the VRC header extension.

   The format of the VRC header extension is as follows:

         0 1 2 3 4 5 6 7
        +-+-+-+-+-+-+-+-+
        | TID | Trun  |S|
        +-+-+-+-+-+-+-+-+

   TID: 3 bits

   Thread ID.  Up to 7 threads are allowed.  Each frame of H.263+ VRC
   data will use as reference information only sync frames or frames
   within the same thread.  By convention, thread 0 is expected to be
   the "canonical" thread, which is the thread from which the sync frame
   should ideally be used.  In the case of corruption or loss of the
   thread 0 representation, a representation of the sync frame with a
   higher thread number can be used by the decoder.  Lower thread
   numbers are expected to contain representations of the sync frames
   equal to or better than higher thread numbers in the absence of data
   corruption or loss.  See [Vredun] for a detailed discussion of VRC.

   Trun: 4 bits

   Monotonically increasing (modulo 16) 4-bit number counting the packet
   number within each thread.

   S: 1 bit

   A bit that indicates that the packet content is for a sync frame.  An
   encoder using VRC may send several representations of the same "sync"
   picture, in order to ensure that, regardless of which thread of
   pictures is corrupted by errors or packet losses, the reception of at
   least one representation of a particular picture is ensured (within
   at least one thread).  The sync picture can then be used for the
   prediction of any thread.  If packet losses have not occurred, then
   the sync frame contents of thread 0 can be used, and those of other
   threads can be discarded (and similarly for other threads).  Thread 0
   is considered the "canonical" thread, the use of which is preferable



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   to all others.  The contents of packets having lower thread numbers
   shall be considered as having a higher processing and delivery
   priority than those with higher thread numbers.  Thus, packets having
   lower thread numbers for a given sync frame shall be delivered first
   to the decoder under loss-free and low-time-jitter conditions, which
   will result in the discarding of the sync contents of the higher-
   numbered threads as specified in Annex N of [H263].

6.  Packetization Schemes

6.1.  Picture Segment Packets and Sequence Ending Packets (P=1)

   A picture segment packet is defined as a packet that starts at the
   location of a Picture, GOB, or slice start code in the H.263+ data
   stream.  This corresponds to the definition of the start of a video
   picture segment as defined in H.263+.  For such packets, P=1 always.

   An extra picture header can sometimes be attached in the payload
   header of such packets.  Whenever an extra picture header is attached
   as signified by PLEN>0, only the last six bits of its picture start
   code, '100000', are included in the payload header.  A complete
   H.263+ picture header with byte-aligned picture start code can be
   conveniently assembled on the receiving end by prepending the sixteen
   leading '0' bits.

   When PLEN>0, the end bit position corresponding to the last byte of
   the picture header data is indicated by PEBIT.  The actual bitstream
   data shall begin on an 8-bit byte boundary following the payload
   header.

   A sequence ending packet is defined as a packet that starts at the
   location of an EOS or EOSBS code in the H.263+ data stream.  This
   delineates the end of a sequence of H.263+ video data (more H.263+
   video data may still follow later, however, as specified in ITU-T
   Recommendation H.263).  For such packets, P=1 and PLEN=0 always.

   The optional header extension for VRC may or may not be present as
   indicated by the V bit flag.

6.1.1.  Packets that begin with a Picture Start Code

   Any packet that contains the whole or the start of a coded picture
   shall start at the location of the picture start code (PSC) and
   should normally be encapsulated with no extra copy of the picture
   header.  In other words, normally PLEN=0 in such a case.  However, if
   the coded picture contains an incomplete picture header (UFEP =
   "000"), then a representation of the complete (UFEP = "001") picture
   header may be attached during packetization in order to provide



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   greater error resilience.  Thus, for packets that start at the
   location of a picture start code, PLEN shall be zero unless both of
   the following conditions apply:

   1) The picture header in the H.263+ bitstream payload is incomplete
      (PLUSPTYPE present and UFEP="000").

   2) The additional picture header that is attached is not incomplete
      (UFEP="001").

   A packet that begins at the location of a Picture, GOB, slice, EOS,
   or EOSBS start code shall omit the first two (all zero) bytes from
   the H.263+ bitstream and signify their presence by setting P=1 in the
   payload header.

   Here is an example of encapsulating the first packet in a frame
   (without an attached redundant complete picture header):

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   RR    |1|V|0|0|0|0|0|0|0|0|0| bitstream data without the    :
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     : first two 0 bytes of the PSC
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

6.1.2.  Packets that begin with GBSC or SSC

   For a packet that begins at the location of a GOB or slice start code
   (GBSC), PLEN may be zero or nonzero, depending on whether a redundant
   picture header is attached to the packet.  In environments with very
   low packet loss rates, or when picture header contents are very
   seldom likely to change (except as can be detected from the GOB Frame
   ID (GFID) syntax of H.263+), a redundant copy of the picture header
   is not required.  However, in less ideal circumstances a redundant
   picture header should be attached for enhanced error resilience, and
   its presence is indicated by PLEN>0.














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   Assuming a PLEN of 9 and P=1, below is an example of a packet that
   begins with a byte-aligned GBSC or a Slice Start Code (SSC):

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   RR    |1|V|0 0 1 0 0 1|PEBIT|1 0 0 0 0 0| picture header    :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       : starting with TR, PTYPE ...                                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | ...                                           | bitstream     :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       : data starting with GBSC/SSC without its first two 0 bytes
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Notice that only the last six bits of the picture start code,
   '100000', are included in the payload header.  A complete H.263+
   picture header with byte aligned picture start code can be
   conveniently assembled, if needed, on the receiving end by prepending
   the sixteen leading '0' bits.

6.1.3.  Packets that begin with an EOS or EOSBS Code

   For a packet that begins with an EOS or EOSBS code, PLEN shall be
   zero, and no Picture, GOB, or Slice start codes shall be included
   within the same packet.  As with other packets beginning with start
   codes, the two all-zero bytes that begin the EOS or EOSBS code at the
   beginning of the packet shall be omitted, and their presence shall be
   indicated by setting the P bit to 1 in the payload header.

   System designers should be aware that some decoders may interpret the
   loss of a packet containing only EOS or EOSBS information as the loss
   of essential video data and may thus respond by not displaying some
   subsequent video information.  Since EOS and EOSBS codes do not
   actually affect the decoding of video pictures, they are somewhat
   unnecessary to send at all.  Because of the danger of
   misinterpretation of the loss of such a packet (which can be detected
   by the sequence number), encoders are generally to be discouraged
   from sending EOS and EOSBS.

   Below is an example of a packet containing an EOS code:

         0                   1                   2
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |   RR    |1|V|0|0|0|0|0|0|0|0|0|1|1|1|1|1|1|0|0|
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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6.2.  Encapsulating Follow-on Packet (P=0)

   A Follow-on Packet contains a number of bytes of coded H.263+ data
   that do not start at a synchronization point.  That is, a Follow-on
   Packet does not start with a Picture, GOB, Slice, EOS, or EOSBS
   header, and it may or may not start at a macroblock boundary.  Since
   Follow-on Packets do not start at synchronization points, the data at
   the beginning of a Follow-on Packet is not independently decodable.
   For such packets, P=0 always.  If the preceding packet of a Follow-on
   Packet got lost, the receiver may discard that Follow-on Packet, as
   well as all other following Follow-on Packets.  Better behavior, of
   course, would be for the receiver to scan the interior of the packet
   payload content to determine whether any start codes are found in the
   interior of the packet that can be used as resync points.  The use of
   an attached copy of a picture header for a Follow-on Packet is useful
   only if the interior of the packet or some subsequent Follow-on
   Packet contains a resync code, such as a GOB or slice start code.
   PLEN>0 is allowed, since it may allow resync in the interior of the
   packet.  The decoder may also be resynchronized at the next segment
   or picture packet.

   Here is an example of a Follow-on Packet (with PLEN=0):

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
     |   RR    |0|V|0|0|0|0|0|0|0|0|0| bitstream data
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

7.  Use of this Payload Specification

   There is no syntactical difference between a picture segment packet
   and a Follow-on Packet, other than the indication P=1 for picture
   segment or sequence ending packets and P=0 for Follow-on Packets.
   See the following for a summary of the entire packet types and ways
   to distinguish between them.

   It is possible to distinguish between the different packet types by
   checking the P bit and the first 6 bits of the payload along with the
   header information.  The following table shows the packet type for
   permutations of this information (see also the picture/GOB/Slice
   header descriptions in H.263+ for details):









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   -------------+--------------+----------------------+----------------
   First 6 bits | P-Bit | PLEN |  Packet              |  Remarks
   of Payload   |(payload hdr.)|                      |
   -------------+--------------+----------------------+----------------
   100000       |   1   |  0   |  Picture             | Typical Picture
   100000       |   1   | > 0  |  Picture             | Note UFEP
   1xxxxx       |   1   |  0   |  GOB/Slice/EOS/EOSBS | See possible GNs
   1xxxxx       |   1   | > 0  |  GOB/Slice           | See possible GNs
   Xxxxxx       |   0   |  0   |  Follow-on           |
   Xxxxxx       |   0   | > 0  |  Follow-on           | Interior Resync
   -------------+--------------+----------------------+----------------

   The details regarding the possible values of the five bit Group
   Number (GN) field that follows the initial "1" bit when the P-bit is
   "1" for a GOB, Slice, EOS, or EOSBS packet are found in Section 5.2.3
   of H.263 [H263].

   As defined in this specification, every start of a coded frame (as
   indicated by the presence of a PSC) has to be encapsulated as a
   picture segment packet.  If the whole coded picture fits into one
   packet of reasonable size (which is dependent on the connection
   characteristics), this is the only type of packet that may need to be
   used.  Due to the high compression ratio achieved by H.263+, it is
   often possible to use this mechanism, especially for small spatial
   picture formats such as Quarter Common Intermediate Format (QCIF) and
   typical Internet packet sizes around 1500 bytes.

   If the complete coded frame does not fit into a single packet, two
   different ways for the packetization may be chosen.  In case of very
   low or zero packet loss probability, one or more Follow-on Packets
   may be used for coding the rest of the picture.  Doing so leads to
   minimal coding and packetization overhead, as well as to an optimal
   use of the maximal packet size, but does not provide any added error
   resilience.

   The alternative is to break the picture into reasonably small
   partitions, called Segments (by using the Slice or GOB mechanism),
   that do offer synchronization points.  By doing so and using the
   Picture Segment payload with PLEN>0, decoding of the transmitted
   packets is possible even in cases in which the Picture packet
   containing the picture header was lost (provided any necessary
   reference picture is available).  Picture Segment packets can also be
   used in conjunction with Follow-on Packets for large segment sizes.








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8.  Media Type Definition

   This section specifies optional parameters that MAY be used to select
   optional features of the H.263 codec.  The parameters are specified
   here as part of the Media Type registration for the ITU-T H.263
   codec.  A mapping of the parameters into the Session Description
   Protocol (SDP) [RFC4566] is also provided for applications that use
   SDP.  Multiple parameters SHOULD be expressed as a media type string,
   in the form of a semicolon-separated list of parameter=value pairs.

8.1.  Media Type Registrations

   This section describes the media types and names associated with this
   payload format.  The section updates the previous registered version
   in RFC 3555 [RFC3555].

8.1.1.  Registration of Media Type video/H263-1998

   Type name: video

   Subtype name: H263-1998

   Required parameters: None

   Optional parameters:

      SQCIF: Specifies the MPI (Minimum Picture Interval) for SQCIF
      resolution.  Permissible values are integer values from 1 to 32,
      which correspond to a maximum frame rate of 30/(1.001 * the
      specified value) frames per second.

      QCIF: Specifies the MPI (Minimum Picture Interval) for QCIF
      resolution.  Permissible values are integer values from 1 to 32,
      which correspond to a maximum frame rate of 30/(1.001 * the
      specified value) frames per second.

      CIF: Specifies the MPI (Minimum Picture Interval) for CIF
      resolution.  Permissible values are integer values from 1 to 32,
      which correspond to a maximum frame rate of 30/(1.001 * the
      specified value) frames per second.

      CIF4: Specifies the MPI (Minimum Picture Interval) for 4CIF
      resolution.  Permissible values are integer values from 1 to 32,
      which correspond to a maximum frame rate of 30/(1.001 * the
      specified value) frames per second.






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      CIF16: Specifies the MPI (Minimum Picture Interval) for 16CIF
      resolution.  Permissible values are integer values from 1 to 32,
      which correspond to a maximum frame rate of 30/(1.001 * the
      specified value) frames per second.

      CUSTOM: Specifies the MPI (Minimum Picture Interval) for a
      custom-defined resolution.  The custom parameter receives three
      comma-separated values, Xmax, Ymax, and MPI.  The Xmax and Ymax
      parameters describe the number of pixels in the X and Y axis and
      must be evenly divisible by 4.  The permissible values for MPI are
      integer values from 1 to 32, which correspond to a maximum frame
      rate of 30/(1.001 *the specified value).

      A system that declares support of a specific MPI for one of the
      resolutions SHALL also implicitly support a lower resolution with
      the same MPI.

      A list of optional annexes specifies which annexes of H.263 are
      supported.  The optional annexes are defined as part of H263-1998,
      H263-2000.  H.263 annex X [H263] defines profiles that group
      annexes for specific applications.  A system that supports a
      specific annex SHALL specify its support using the optional
      parameters.  If no annex is specified, then the stream is Baseline
      H.263.

      The allowed optional parameters for the annexes are "F", "I", "J",
      "T", "K", "N", and "P".

      "F", "I", "J", and "T" if supported, SHALL have the value "1".  If
      not supported, they should not be listed or SHALL have the value
      "0".

      "K" can receive one of four values 1 - 4:

      1: Slices In Order, Non-Rectangular

      2: Slices In Order, Rectangular

      3: Slices Not Ordered, Non-Rectangular

      4: Slices Not Ordered, Rectangular

      "N": Reference Picture Selection mode -  Four numeric choices
      (1 - 4) are available, representing the following modes:

      1: NEITHER:  No back-channel data is returned from the decoder to
         the encoder.




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      2: ACK:  The decoder returns only acknowledgment messages.

      3: NACK:  The decoder returns only non-acknowledgment messages.

      4: ACK+NACK:  The decoder returns both acknowledgment and non-
         acknowledgment messages.

      No special provision is made herein for carrying back channel
      information.  The Extended RTP Profile for RTCP-based Feedback
      [RFC4585] MAY be used as a back channel mechanism.

      "P": Reference Picture Resampling, in which the following submodes
      are represented as a number from 1 to 4:

      1: dynamicPictureResizingByFour

      2: dynamicPictureResizingBySixteenthPel

      3: dynamicWarpingHalfPel

      4: dynamicWarpingSixteenthPel

      Example: P=1,3

      PAR: Arbitrary Pixel Aspect Ratio.  Defines the width:height ratio
      by two colon-separated integers between 0 and 255.  Default ratio
      is 12:11, if not otherwise specified.

      CPCF: Arbitrary (Custom) Picture Clock Frequency: CPCF is a
      comma-separated list of eight parameters specifying a custom
      picture clock frequency and the MPI (minimum picture interval) for
      the supported picture sizes when using that picture clock
      frequency.  The first two parameters are cd, which is an integer
      from 1 to 127, and cf, which is either 1000 or 1001.  The custom
      picture clock frequency is given by the formula 1800000/(cd*cf)
      provided in the RTP Timestamp semantics in Section 3.1 above (as
      specified in H.263 section 5.1.7).  Following the values of cd and
      cf, the remaining six parameters are SQCIFMPI, QCIFMPI, CIFMPI,
      CIF4MPI, CIF16MPI, and CUSTOMMPI, which each specify an integer
      MPI (minimum picture interval) for the standard picture sizes
      SQCIF, QCIF, CIF, 4CIF, 16CIF, and CUSTOM, respectively, as
      described above.  The MPI value indicates a maximum frame rate of
      1800000/(cd*cf*MPI) frames per second for MPI parameters having a
      value in the range from 1 to 2048, inclusive.  An MPI value of 0
      specifies that the associated picture size is not supported for
      the custom picture clock frequency.  If the CUSTOMMPI parameter is
      not equal to 0, the CUSTOM parameter SHALL also be present (so




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      that the Xmax and Ymax dimensions of the custom picture size are
      defined).

      BPP: BitsPerPictureMaxKb.  Maximum number of bits in units of 1024
      bits allowed to represent a single picture.  If this parameter is
      not present, then the default value, based on the maximum
      supported resolution, is used.  BPP is integer value between 0 and
      65536.

      HRD: Hypothetical Reference Decoder.  See annex B of H.263
      specification [H263].  This parameter, if supported, SHALL have
      the value "1".  If not supported, it should not be listed or SHALL
      have the value "0".

   Encoding considerations:

      This media type is framed and binary; see Section 4.8 in [RFC4288]

   Security considerations: See Section 11 of RFC 4629

   Interoperability considerations:

      These are receiver options; current implementations will not send
      any optional parameters in their SDP.  They will ignore the
      optional parameters and will encode the H.263 stream without any
      of the annexes.  Most decoders support at least QCIF and CIF fixed
      resolutions, and they are expected to be available almost in every
      H.263-based video application.

   Published specification: RFC 4629

   Applications that use this media type:

      Audio and video streaming and conferencing tools.

      Additional information: None

      Person and email address to contact for further information:

   Roni Even: roni.even@polycom.co.il

      Intended usage: COMMON

      Restrictions on usage:

      This media type depends on RTP framing and thus is only defined
      for transfer via RTP [RFC3550].  Transport within other framing
      protocols is not defined at this time.



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   Author: Roni Even

   Change controller:

      IETF Audio/Video Transport working group, delegated from the IESG.

8.1.2.  Registration of Media Type video/H263-2000

   Type name: video

   Subtype name: H263-2000

   Required parameters: None

   Optional parameters:

      The optional parameters of the H263-1998 type MAY be used with
      this media subtype.  Specific optional parameters that may be used
      with the H263-2000 type are as follows:

      PROFILE:  H.263 profile number, in the range 0 through 10,
      specifying the supported H.263 annexes/subparts based on H.263
      annex X [H263].  The annexes supported in each profile are listed
      in table X.1 of H.263 annex X.  If no profile or H.263 annex is
      specified, then the stream is Baseline H.263 (profile 0 of H.263
      annex X).

      LEVEL:  Level of bitstream operation, in the range 0 through 100,
      specifying the level of computational complexity of the decoding
      process.  The level are described in table X.2 of H.263 annex X.

      According to H.263 annex X, support of any level other than level
      45 implies support of all lower levels.  Support of level 45
      implies support of level 10.

      A system that specifies support of a PROFILE MUST specify the
      supported LEVEL.

      INTERLACE:  Interlaced or 60 fields indicates the support for
      interlace display mode, as specified in H.263 annex W.6.3.11.
      This parameter, if supported SHALL have the value "1".  If not
      supported, it should not be listed or SHALL have the value "0".

   Encoding considerations:

      This media type is framed and binary; see Section 4.8 in [RFC4288]

   Security considerations: See Section 11 of RFC 4629



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   Interoperability considerations:

      The optional parameters PROFILE and LEVEL SHALL NOT be used with
      any of the other optional parameters.

   Published specification: RFC 4629

   Applications that use this media type:

      Audio and video streaming and conferencing tools.

   Additional information: None

   Person and email address to contact for further information :

      Roni Even: roni.even@polycom.co.il

   Intended usage: COMMON

   Restrictions on usage:

      This media type depends on RTP framing and thus is only defined
      for transfer via RTP [RFC3550].  Transport within other framing
      protocols is not defined at this time.

   Author: Roni Even

   Change controller:

      IETF Audio/Video Transport working group delegated from the IESG.

8.2.  SDP Usage

   The media types video/H263-1998 and video/H263-2000 are mapped to
   fields in the Session Description Protocol (SDP) as follows:

   o The media name in the "m=" line of SDP MUST be video.

   o The encoding name in the "a=rtpmap" line of SDP MUST be H263-1998
     or H263-2000 (the media subtype).

   o The clock rate in the "a=rtpmap" line MUST be 90000.

   o The optional parameters, if any, MUST be included in the "a=fmtp"
     line of SDP.  These parameters are expressed as a media type
     string, in the form of a semicolon-separated list of
     parameter=value pairs.  The optional parameters PROFILE and LEVEL
     SHALL NOT be used with any of the other optional parameters.



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8.2.1.  Usage with the SDP Offer Answer Model

   For offering H.263 over RTP using SDP in an Offer/Answer model
   [RFC3264], the following considerations are necessary.

   Codec options (F,I,J,K,N,P,T): These options MUST NOT appear unless
   the sender of these SDP parameters is able to decode those options.
   These options designate receiver capabilities even when sent in a
   "sendonly" offer.

   Profile: The offer of a SDP profile parameter signals that the
   offerer can decode a stream that uses the specified profile.  Each
   profile uses different H.263 annexes, so there is no implied
   relationship between them.  An answerer SHALL NOT change the profile
   parameter and MUST reject the payload type containing an unsupported
   profile.  A decoder that supports a profile SHALL also support H.263
   baseline profile (profile 0).  An offerer is RECOMMENDED to offer all
   the different profiles it is interested to use as individual payload
   types.  In addition an offerer, sending an offer using the PROFILE
   optional parameter, is RECOMMENDED to offer profile 0, as this will
   enable communication, and in addition allows an answerer to add those
   profiles it does support in an answer.

   LEVEL: The LEVEL parameter in an offer indicates the maximum
   computational complexity supported by the offerer in performing
   decoding for the given PROFILE.  An answerer MAY change the value
   (both up and down) of the LEVEL parameter in its answer to indicate
   the highest value it supports.

   INTERLACE: The parameter MAY be included in either offer or answer to
   indicate that the offerer or answerer respectively supports reception
   of interlaced content.  The inclusion in either offer or answer is
   independent of each other.

   Picture sizes and MPI: Supported picture sizes and their
   corresponding minimum picture interval (MPI) information for H.263
   can be combined.  All picture sizes can be advertised to the other
   party, or only a subset.  The terminal announces only those picture
   sizes (with their MPIs) which it is willing to receive.  For example,
   MPI=2 means that the maximum (decodable) picture rate per second is
   15/1.001 (approximately 14.985).

   If the receiver does not specify the picture size/MPI optional
   parameter, then it SHOULD be ready to receive QCIF resolution with
   MPI=1.

   Parameters offered first are the most preferred picture mode to be
   received.



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   Here is an example of the usage of these parameters:

      CIF=4;QCIF=3;SQCIF=2;CUSTOM=360,240,2

   This means that the encoder SHOULD send CIF picture size, which it
   can decode at MPI=4.  If that is not possible, then QCIF with MPI
   value 3 should be sent; if neither are possible, then SQCIF with MPI
   value=2.  The receiver is capable of (but least preferred) decoding
   custom picture sizes (max 360x240) with MPI=2.  Note that most
   decoders support at least QCIF and CIF fixed resolutions, and that
   they are expected to be available almost in every H.263-based video
   application.

   Below is an example of H.263 SDP in an offer:

      a=fmtp:xx CIF=4;QCIF=2;F=1;K=1

   This means that the sender of this message can decode an H.263 bit
   stream with the following options and parameters: preferred
   resolution is CIF (at up to 30/4.004 frames per second), but if that
   is not possible then QCIF size is also supported (at up to 30/2.002
   frames per second).  Advanced Prediction mode (AP) and
   slicesInOrder-NonRect options MAY be used.

   Below is an example of H.263 SDP in an offer that includes the CPCF
   parameter.

      a=fmtp:xx CPCF=36,1000,0,1,1,0,0,2;CUSTOM=640,480,2;CIF=1;QCIF=1

   This means that the sender of this message can decode an H.263 bit
   stream with a preferred custom picture size of 640x480 at a maximum
   frame rate of 25 frames per second using a custom picture clock
   frequency of 50 Hz.  If that is not possible, then the 640x480
   picture size is also supported at up to 30/2.002 frames per second
   using the ordinary picture clock frequency of 30/1.001 Hz.  If
   neither of those is possible, then the CIF and QCIF picture sizes are
   also supported at up to 50 frames per second using the custom picture
   clock frequency of 50 Hz or up to 30/1.001 frames per second using
   the ordinary picture clock frequency of 30/1.001 Hz, and CIF is
   preferred over QCIF.

   The following limitation applies for usage of these media types when
   performing offer/answer for sessions using multicast transport.  An
   answerer SHALL NOT change any of the parameters in an answer, instead
   if the indicated values are not supported the payload type MUST be
   rejected.





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9.  Backward Compatibility to RFC 2429

   The current document is a revision of RFC 2429 and obsoletes it.
   This section will address the backward compatibility issues.

9.1.  New Optional Parameters for SDP

   The document adds new optional parameters to the H263-1998 and H263-
   2000 payload type, defined in RFC 3555 [RFC3555].  Since these are
   optional parameters we expect that old implementations will ignore
   these parameters, and that new implementations that will receive the
   H263-1998 and H263-2000 payload types with no parameters will behave
   as if the other side can accept H.263 at QCIF resolution at a frame
   rate not exceeding 15/1.001 (approximately 14.985) frames per second.

10.  IANA Considerations

   This document updates the H.263 (1998) and H.263 (2000) media types,
   described in RFC 3555 [RFC3555].  The updated media type
   registrations are in Section 8.1.

11.  Security Considerations

   RTP packets using the payload format defined in this specification
   are subject to the security considerations discussed in the RTP
   specification [RFC3550] and any appropriate RTP profile (for example,
   [RFC3551]).  This implies that confidentiality of the media streams
   is achieved by encryption.  Because 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.

   A potential denial-of-service threat exists for data encoding using
   compression techniques that have non-uniform receiver-end
   computational load.  The attacker can inject pathological datagrams
   into the stream that are complex to decode and cause the receiver to
   be overloaded.  The usage of authentication of at least the RTP
   packet is RECOMMENDED.

   As with any IP-based protocol, in some circumstances a receiver may
   be overloaded simply by the receipt of too many packets, either
   desired or undesired.  Network-layer authentication may be used to
   discard packets from undesired sources, but the processing cost of
   the authentication itself may be too high.  In a multicast
   environment, pruning of specific sources may be implemented in future
   versions of IGMP [RFC2032] and in multicast routing protocols to
   allow a receiver to select which sources are allowed to reach it.




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   A security review of this payload format found no additional
   considerations beyond those in the RTP specification.

12.  Acknowledgements

   This is to acknowledge the work done by Chad Zhu, Linda Cline, Gim
   Deisher, Tom Gardos, Christian Maciocco, and Donald Newell from Intel
   Corp., who co-authored RFC 2429.

   We would also like to acknowledge the work of Petri Koskelainen from
   Nokia and Nermeen Ismail from Cisco, who helped with composing the
   text for the new media types.

13.  Changes from Previous Versions of the Documents

13.1.  Changes from RFC 2429

   The changes from the RFC 2429 are:

   1.  The H.263 1998 and 2000 media type are now in the payload
       specification.

   2.  Added optional parameters to the H.263 1998 and 2000 media types.

   3.  Mandate the usage of RFC 2429 for all H.263.  RFC 2190 payload
       format should be used only to interact with legacy systems.

13.2.  Changes from RFC 3555

   This document adds new optional parameters to the H263-1998 and
   H263-2000 payload types.

14.  References

14.1.  Normative References

   [H263]     International Telecommunications Union - Telecommunication
              Standardization Sector, "Video coding for low bit rate
              communication", ITU-T Recommendation H.263, January 2005.

   [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.





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   [RFC3551]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
              Video Conferences with Minimal Control", STD 65, RFC 3551,
              July 2003.

   [RFC3555]  Casner, S. and P. Hoschka, "MIME Type Registration of RTP
              Payload Formats", RFC 3555, July 2003.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

14.2.  Informative References

   [RFC2032]  Turletti, T., "RTP Payload Format for H.261 Video
              Streams", RFC 2032, October 1996.

   [RFC2190]  Zhu, C., "RTP Payload Format for H.263 Video Streams", RFC
              2190, September 1997.

   [RFC2429]  Bormann, C., Cline, L., Deisher, G., Gardos, T., Maciocco,
              C., Newell, D., Ott, J., Sullivan, G., Wenger, S., and C.
              Zhu, "RTP Payload Format for the 1998 Version of ITU-T
              Rec. H.263 Video (H.263+)", RFC 2429, October 1998.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264, June
              2002.

   [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
              Registration Procedures", BCP 13, RFC 4288, December 2005.

   [RFC4585]  Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
              "Extended RTP Profile for Real-time Transport Control
              Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, July
              2006.

   [RFC4628]  Even, R., "RTP Payload Format for H.263 Moving RFC 2190 to
              Historic Status", RFC 4628, January 2007.

   [Vredun]   Wenger, S., "Video Redundancy Coding in H.263+", Proc.
              Audio-Visual Services over Packet Networks, Aberdeen, U.K.
              9/1997, September 1997.










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Authors' Addresses

   Joerg Ott
   Helsinki University of Technology
   Networking Laboratory
   PO Box 3000
   02015 TKK, Finland

   EMail: jo@netlab.tkk.fi


   Carsten Bormann
   Universitaet Bremen TZI
   Postfach 330440
   D-28334 Bremen, GERMANY

   Phone: +49.421.218-7024
   Fax: +49.421.218-7000
   EMail: cabo@tzi.org


   Gary Sullivan
   Microsoft Corp.
   One Microsoft Way
   Redmond, WA 98052
   USA

   EMail: garysull@microsoft.com


   Stephan Wenger
   Nokia Research Center
   P.O. Box 100
   33721 Tampere
   Finland

   EMail: stewe@stewe.org


   Roni Even (editor)
   Polycom
   94 Derech Em Hamoshavot
   Petach Tikva  49130
   Israel

   EMail: roni.even@polycom.co.il





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