Audio/Video Transport WG                                M.M. Hannuksela
Internet Draft                                               Y.-K. Wang
Intended status: Standards track                                  Nokia
Expires: December 2008                                     June 4, 2008





                    Session Multiplexing for SVC Video
                    draft-hannuksela-avt-rtp-svc-00.txt




Status of this Memo

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   This Internet-Draft will expire on December 4, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2008).








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Abstract

   This memo describes a method for decoding order recovery of the
   Network Abstraction Layer (NAL) units carried in multiple session-
   multiplexed RTP sessions for Scalable Video Coding (SVC), which is
   defined in Annex G of the ITU-T Recommendation H.264 video codec that
   is technically identical to Amendment 3 of ISO/IEC International
   Standard 14496-10.  The method applies when non-interleaved
   transmission of NAL units using the Single NAL Unit packetization
   mode or the Non-Interleaved packetization mode defined in RFC 3984 is
   in use.



Table of Contents


   Status of this Memo...............................................1
   Copyright Notice..................................................1
   Abstract..........................................................2
   Table of Contents.................................................2
   1. Introduction...................................................3
   2. Conventions....................................................3
   3. The SVC Codec..................................................3
   4. Scope..........................................................3
   5. Definitions and Abbreviations..................................4
      5.1. Definitions...............................................4
         5.1.1. Definitions Per SVC Specification....................4
         5.1.2. Definitions Local to This Memo.......................4
      5.2. Abbreviations.............................................4
   6. RTP Payload Format.............................................4
      6.1. Design Principles.........................................4
      6.2. RTP Header Usage..........................................4
      6.3. Common Structure of the RTP Payload Format................4
      6.4. NAL Unit Header Usage.....................................4
      6.5. Packetization Modes.......................................5
         6.5.1. Packetization Modes for Session Multiplexing.........5
      6.6. Decoding Order Number (DON)...............................8
         6.6.1. Access Unit DON (AU-DON) for Session Multiplexing....8
         6.6.2. Cross-Session DON (CS-DON) for Session Multiplexing..8
      6.7. Aggregation Packets.......................................8
      6.8. Fragmentation Units (FUs).................................8
      6.9. Payload Content Scalability Information (PACSI) NAL Unit..8
   7. Packetization Rules............................................9
      7.1. Packetization Rules for Session Multiplexing..............9
         7.1.1. NI-A Session-Multiplexing Packetization Rules........9
         7.1.2. I-C Session-Multiplexing Packetization Rules........10


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         7.1.3. Packetization rules for non-VCL NAL units...........10
         7.1.4. Packetization rules for Prefix NAL units............10
   8. De-Packetization Process......................................10
      8.1. De-Packetization Process for Session Multiplexing........10
         8.1.1. Decoding Order Recovery for the NI-A Mode...........10
            8.1.1.1. Informative Algorithm for NI-A Decoding Order
            Recovery within an Access Unit..........................13
         8.1.2. Decoding Order Recovery for the I-C Mode............13
   9. Payload Format Parameters.....................................13
      9.1. Media Type Registration..................................13
      9.2. SDP Parameters...........................................15
      9.3. Examples.................................................15
      9.4. Parameter Set Considerations.............................15
   10. Security Considerations......................................15
   11. Congestion Control...........................................15
   12. IANA Consideration...........................................15
   13. Informative Appendix: Application Examples...................15
   14. References...................................................15
      14.1. Normative References....................................15
      14.2. Informative References..................................16
   15. Authors' Addresses...........................................16
   Intellectual Property Statement..................................16
   Disclaimer of Validity...........................................17
   Copyright Statement..............................................17
   Acknowledgement..................................................17



1. Introduction

   Section 1 of draft-ietf-avt-rtp-svc-10 applies.

   In addition, this memo specifies an alternative method for decoder
   order recovery of NAL units carried in multiple session-multiplexed
   RTP sessions.

2. Conventions

   Section 2 of draft-ietf-avt-rtp-svc-10 applies.

3. The SVC Codec

   Section 3 of draft-ietf-avt-rtp-svc-10 applies.

4. Scope

   Section 4 of draft-ietf-avt-rtp-svc-10 applies.


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5. Definitions and Abbreviations

5.1. Definitions

5.1.1. Definitions Per SVC Specification

   Section 5.1.1 of draft-ietf-avt-rtp-svc-10 applies.

5.1.2. Definitions Local to This Memo

   Section 5.1.2 of draft-ietf-avt-rtp-svc-10 applies with the following
   addition.

      access unit decoding order number (AU-DON): A variable that is
      derived for each access unit when the single NAL unit
      packetization mode or the non-interleaved packetization mode is
      in use. AU-DON indicates the decoding order of an access unit.

5.2. Abbreviations

   Section 5.2 of draft-ietf-avt-rtp-svc-10 applies with the following
   addition.

      AU-DON:     Access Unit Decoding Order Number

6. RTP Payload Format

6.1. Design Principles

   Section 6.1 of draft-ietf-avt-rtp-svc-10 applies.

6.2. RTP Header Usage

   Section 6.2 of draft-ietf-avt-rtp-svc-10 applies.

6.3. Common Structure of the RTP Payload Format

   Section 6.3 of draft-ietf-avt-rtp-svc-10 applies.

6.4. NAL Unit Header Usage

   Section 6.4 of draft-ietf-avt-rtp-svc-10 applies.







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6.5. Packetization Modes

   Section 5.4 of RFC 3984 applies when session multiplexing is not in
   use.  The packetization modes specified in Section 5.4 of RFC 3984
   are also referred to as session-specific packetization modes.

   When session multiplexing is in use, the following applies in
   addition.

6.5.1. Packetization Modes for Session Multiplexing

   This memo specifies two cases of session-multiplexing packetization
   modes when session multiplexing is in use:

   o  Non-interleaved AU-DON (NI-A) mode

   o  Interleaved CS-DON (I-C) mode

   The NI-A mode is targeted for systems that require relatively low
   end-to-end latency, e.g. conversational systems.  In the NI-A mode,
   NAL units in each RTP session are transmitted in NAL unit decoding
   order.  The I-C mode is targeted for systems that do not require very
   low end-to-end latency.  The I-C mode allows transmission of NAL
   units out of NAL unit decoding order in each RTP session.

   The session-multiplexing packetization mode in use MAY be signaled by
   the value of the OPTIONAL session-multiplexing-packetization-mode
   media type parameter or by external means.  When the value of
   session-multiplexing-packetization-mode is equal to 0, the NI-A mode
   MUST be used.  When the value of session-multiplexing-packetization-
   mode is equal to 1, the I-C mode MUST be used.  [Ed.Note(YkW): There
   MAY be at most one global session-multiplexing-packetization-mode
   present in the SDP common for all the multiplexed RTP sessions.  It
   is also possible to have session-multiplexing-packetization-mode
   session-specific in the SDP, but then all the multiplexed sessions
   MUST have the same value of this parameter.  When session-
   multiplexing-packetization-mode is not present, the NI-A mode is
   implied.]

   The used session-multiplexing packetization mode governs which
   session-specific packetization modes are allowed in the multiplexed
   RTP sessions, which in turn govern which NAL unit types are allowed
   as RTP payloads.

   Table 3.1 summarizes the allowed session-specific packetization modes
   for the NI-A session-multiplexing packetizatio modes.  Table 3.2



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   summarizes the allowed session-specific packetization modes for the
   I-C session-multiplexing packetization mode.

    Table 3.1  Summary of allowed session-specific packetization modes
   for the NI-A session-multiplexing packetization modes (yes = allowed,
                             no = disallowed)

      Session-Specific Mode    Base Session    Enhancement Session
      ----------------------------------------------------------
      Single NAL Unit Mode         yes             no
      Non-Interleaved Mode         yes            yes
      Interleaved Mode              no             no

    Table 3.2  Summary of allowed session-specific packetization modes
    for the I-C session-multiplexing packetization mode (yes = allowed,
                             no = disallowed)

      Session-Specific Mode    Base Session    Enhancement Session
      ----------------------------------------------------------
      Single NAL Unit Mode          no             no
      Non-Interleaved Mode          no             no
      Interleaved Mode             yes            yes

   Table 3.3 summarizes the allowed NAL unit types for each allowed
   session-specific packetization mode of the NI-A session-multiplexing
   packetization mode.  Table 3.4 summarizes the allowed NAL unit types
   for the only allowed session-specific packetization mode (i.e. the
   interleaved mode) of the I-C session-multiplexing packetization mode.





















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      Table 3.3  Summary of allowed NAL unit types for each session-
       specific packetization mode of the NI-A session-multiplexing
     packetization mode (yes = allowed, no = disallowed, ig = ignore)

      Type   Packet    Single NAL    Non-Interleaved
                       Unit Mode           Mode
      ------------------------------------------------
      0      undefined     ig               ig
      1-23   NAL unit     yes              yes
      24     STAP-A        no              yes
      25     STAP-B        no               no
      26     MTAP16        no               no
      27     MTAP24        no               no
      28     FU-A          no              yes
      29     FU-B          no               no
      30     PACSI        yes              yes
      31     undefined     ig               ig

   Table 3.4  Summary of allowed NAL unit types for the session-specific
   packetization mode of the I-C session-multiplexing packetization mode
               (yes = allowed, no = disallowed, ig = ignore)

      Type   Packet    Interleaved
                         Mode
      ------------------------------
      0      undefined     ig
      1-23   NAL unit      no
      24     STAP-A        no
      25     STAP-B       yes
      26     MTAP16       yes
      27     MTAP24       yes
      28     FU-A         yes
      29     FU-B         yes
      30     PACSI         no (see the informative note below)
      31     undefined     no

         Informative note: PACSI NAL units are allowed to be included
         in an aggregation packet but disallowed as single NAL unit
         packets.

   The NAL unit type values indicated as undefined in Tables 3.3 and 3.4
   are reserved for future extensions.  NAL units of those types SHOULD
   NOT be sent by a sender and MUST be ignored by a receiver.  Note that
   NAL unit type 30 and 31 are indicated as undefined in RFC 3984,
   therefore RFC 3984 receivers MUST ignore NAL units of this type, if
   present.



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6.6. Decoding Order Number (DON)

   Section 5.5 of [RFC3984] applies when session multiplexing is not in
   use.

   When session multiplexing is in use, the following applies in
   addition.

6.6.1. Access Unit DON (AU-DON) for Session Multiplexing

   When the NI-A session-multiplexing packetization mode is in use, the
   packetization of each session MUST be as specified in Section 7.1.,
   and the following applies for the derivation of the AU-DON value for
   each non-PACSI NAL unit.

   The AU-DON value for all NAL units having the same NALU time is
   identical and MUST be conveyed in at least one PACSI NAL unit.

6.6.2. Cross-Session DON (CS-DON) for Session Multiplexing

   When the I-C session-multiplexing packetization mode is in use, the
   DON values derived according to RFC 3984 of all the NAL units in each
   of the multiplexed RTP sessions MUST indicate CS-DON values.

6.7. Aggregation Packets

   Section 6.7 of draft-ietf-avt-rtp-svc-10 applies.

6.8. Fragmentation Units (FUs)

   Section 6.8 of draft-ietf-avt-rtp-svc-10 applies.

6.9. Payload Content Scalability Information (PACSI) NAL Unit

   Section 6.9 of draft-ietf-avt-rtp-svc-10 applies with the following
   modifications.

   The name of the DONC field is changed to AU-DON.

   The semantics of DONC are removed.

   The occurrences of "DONC" are replaced with "AU-DON".

   The semantics of AU-DON are specified as follows.





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   o  When present, the field AU-DON indicates the access unit decoding
      order number for all the NAL units in the aggregation packet (when
      the PACSI NAL unit is included in an aggregation packet) or the
      AU-DON of the next non-PACSI NAL unit in transmission order (when
      the PACSI NAL unit is included in a single NAL unit packet).

7. Packetization Rules

   Section 7 of draft-ietf-avt-rtp-svc-10 applies.

7.1. Packetization Rules for Session Multiplexing

   When session multiplexing is used, decoding order recovery for NAL
   units carried in all the multiplexed RTP sessions is needed.  The
   following packetization rules ensure that decoding order of NAL units
   carried in the multiplexed sessions can be correctly recovered for
   each of the session-multiplexing packetization modes according to the
   de-packetization process specified in Section 8.1. .

7.1.1. NI-A Session-Multiplexing Packetization Rules

   When the NI-A session-multiplexing packetization mode is in use, the
   following applies.

   o  For each single NAL unit packet containing a non-PACSI NAL unit,
      if present, the previous packet MUST have the same RTP timestamp
      as the single NAL unit packet, and the following applies.

         If the NALU time of the non-PACSI NAL unit is not equal to the
          NALU time of the previous non-PACSI NAL unit in decoding
          order, the previous packet MUST contain a PACSI NAL unit
          containing the AU-DON field;

         Otherwise (the NALU time of the non-PACSI NAL unit is equal to
          the NALU time of the previous non-PACSI NAL unit in decoding
          order), the previous packet MAY contain a PACSI NAL unit
          containing the AU-DON field.

   o  For each STAP-A packet, if present, if the RTP timestamp is
      different from the RTP timestamp of the previous STAP-A packet,
      the first NAL unit in the STAP-A packet MUST be a PACSI NAL unit
      containing the AU-DON field.

   o  For each FU-A packet, if present, the previous packet MUST have
      the same RTP timestamp as the FU-A packet, and the following
      applies.



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         If the FU-A packet is the start of the fragmented NAL unit, the
          following applies;

              If the NALU time of the fragmented NAL unit is not equal
               to the NALU time of the previous non-PACSI NAL unit in
               decoding order, the previous packet MUST contain a PACSI
               NAL unit containing the AU-DON field;

              Otherwise (the NALU time of the fragmented NAL unit is
               equal to the NALU time of the previous non-PACSI NAL unit
               in decoding order), the previous packet MAY contain a
               PACSI NAL unit containing the AU-DON field.

   o  For each single NAL unit packet containing a PACSI NAL unit, if
      present, the PACSI NAL unit MUST contain the AU-DON field.

7.1.2. I-C Session-Multiplexing Packetization Rules

   Section 7.1.2 of draft-ietf-avt-rtp-svc-10 applies.

7.1.3. Packetization rules for non-VCL NAL units

   Section 7.1.3 of draft-ietf-avt-rtp-svc-10 applies.

7.1.4. Packetization rules for Prefix NAL units

   Section 7.1.4 of draft-ietf-avt-rtp-svc-10 applies.

8. De-Packetization Process

   Section 8 of draft-ietf-avt-rtp-svc-10 applies.

8.1. De-Packetization Process for Session Multiplexing

   Section 8.1 of draft-ietf-avt-rtp-svc-10 applies.

8.1.1. Decoding Order Recovery for the NI-A Mode

   The following process SHALL be applied when the NI-A session-
   multiplexing packetization mode is in use.

   The RTP packets output from the RTP-level reception processing for
   each session are placed into the de-session-multiplexing buffer.

   It is RECOMMENDED to set the size of the de-session-multiplexing
   buffer, in terms of number of bytes, equal to or greater than the



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   value of the sprop-desemul-buf-req media type parameter of the
   highest RTP session the receiver receives.

   The AU-DON value is inferred and stored for each NAL unit.

   The receiver operation is described below with the help of the
   following functions and constants:

   o  Function AbsDON is specified in Section 8.1 of RFC 3984.

   o  Function don_diff is specified in Section 5.5 of RFC 3984.

   o  Constant N is the value of the OPTIONAL sprop-session-
      multiplexing-depth media type parameter of the highest RTP session
      incremented by 1.

   Initial buffering lasts until one of the following conditions is
   fulfilled:

   o  There are N or more VCL NAL units in the de-session-multiplexing
      buffer.

   o  If sprop-semul-max-don-diff of the highest SVC RTP session is
      present, don_diff(m,n) is greater than the value of sprop-semul-
      max-don-diff of the highest RTP session, in which n corresponds to
      the NAL unit having the greatest value of AbsDON among the
      received NAL units and m corresponds to the NAL unit having the
      smallest value of AbsDON among the received NAL units.

   o  Initial buffering has lasted for the duration equal to or greater
      than the value of the OPTIONAL sprop-desemul-init-buf-time media
      type parameter of the highest SVC RTP session.

   The NAL units to be removed from the de-session-multiplexing buffer
   are determined as follows:

   o  If the de-session-multiplexing buffer contains at least N VCL NAL
      units, NAL units are removed from the de-session-multiplexing
      buffer and passed to the decoder in the order specified below
      until the buffer contains N-1 or fewer VCL NAL units.









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   o  If sprop-semul-max-don-diff of the highest SVC RTP session is
      present, all NAL units m for which don_diff(m,n) is greater than
      sprop-max-don-diff of the highest RTP session are removed from the
      de-session-multiplexing buffer and passed to the decoder in the
      order specified below.  Herein, n corresponds to the NAL unit
      having the greatest value of AbsDON among the NAL units in the de-
      session-multiplexing buffer.

   The order in which NAL units are passed to the decoder is specified
   as follows:

   o  Let PDON be a variable that is initialized to 0 at the beginning
      of the RTP sessions.

   o  For each NAL unit associated with a value of AU-DON, an AU-DON
      distance is calculated as follows.  If the value of AU-DON of the
      NAL unit is greater than the value of PDON, the AU-DON distance is
      equal to AU-DON - PDON.  Otherwise, the AU-DON distance is equal
      to 65535 - PDON + AU-DON + 1.

   o  NAL units are delivered to the decoder in ascending order of AU-
      DON distance.  If several NAL units share the same value of AU-DON
      distance, the following applies.

         An initial NAL unit order for an access unit is formed
          starting from the base session and proceeding to the highest
          session in the session dependency order specified according to
          [I-D.ietf-mmusic-decoding-dependency].  Within a session, NAL
          units sharing the same value of AU-DON are ordered into the
          initial NAL unit order for the access unit in their
          transmission order.

         A NAL unit decoding order for the access unit is derived from
          the initial NAL unit order for the access unit by reordering
          SEI NAL units conveyed in a non-base session and not included
          PACSI NAL units as specified for the NAL unit decoding order
          in [SVC].

         NAL units are passed to the decoder in the NAL unit decoding
          order for the access unit.

   o  When a desired number of NAL units have been passed to the
      decoder, the value of PDON is set to the value of AU-DON for the
      last NAL unit passed to the decoder.





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8.1.1.1. Informative Algorithm for NI-A Decoding Order Recovery within
   an Access Unit

   Section 8.1.1.1 of draft-ietf-avt-rtp-svc-10 applies.

8.1.2. Decoding Order Recovery for the I-C Mode

   Section 8.1.2 of draft-ietf-avt-rtp-svc-10 applies.

9. Payload Format Parameters

   Section 9 of draft-ietf-avt-rtp-svc-10 applies.

9.1. Media Type Registration

   Section 9.1 of draft-ietf-avt-rtp-svc-10 applies with the following
   modifications.

      session-multiplexing-packetization-mode:
         This parameter MUST be present when the current RTP depends
         one or more other RTP sessions.

         This parameter signals the properties of a NAL unit stream
         carried in more than one RTP session using session
         multiplexing or the capabilities of a receiver implementation.
         When the value of session-multiplexing-packetization-mode is
         equal to 0, the NI-A mode MUST be used.  When the value of
         session-multiplexing-packetization-mode is equal to 1, the I-C
         mode MUST be used.  The value of session-multiplexing-
         packetization-mode MUST be an integer in the range of 0 to 1,
         inclusive.

      sprop-session-multiplexing-depth:
         This parameter MUST be present when the current RTP depends
         one or more other RTP sessions.

         This parameter signals the properties of a NAL unit stream
         carried in the current RTP session and the RTP sessions the
         current RTP session depends on.  It is guaranteed that
         receivers can reconstruct NAL unit decoding order as specified
         in section 8.1.  of this memo when the de-session-multiplexing
         buffer size is at least the value of sprop-session-
         multiplexing-depth + 1 in terms of VCL NAL units.

         The value of sprop-session-multiplexing-depth MUST be an
         integer in the range of 0 to 32767, inclusive.



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      sprop-desemul-buf-req:
         This parameter MUST be present when the current RTP depends
         one or more other RTP sessions.

         sprop-desemul-buf-req signals the required size of the de-
         session-multiplexing buffer for the NAL unit stream carried in
         the current RTP session and the RTP sessions the current RTP
         session depends on.  It is guaranteed that receivers can
         recover the decoding order of the received NAL units from the
         current RTP session and the RTP sessions the current RTP
         session depends on as specified in section 8.1. , when the de-
         session-multiplexing buffer size is at least the value of
         sprop-desemul-buf-req in terms of bytes.

         The value of sprop-desemul-buf-req MUST be an integer in the
         range of 0 to 4294967295, inclusive.

      desemul-buf-cap:
         This parameter signals the capabilities of a receiver
         implementation and indicates the amount of de-session-
         multiplexing buffer space in units of bytes that the receiver
         has available for recovering the NAL unit decoding order as
         specified in section 8.1. .  A receiver is able to handle any
         NAL unit stream for which the value of the sprop-desemul-buf-
         req parameter is smaller than or equal to this parameter.

         If the parameter is not present, then a value of 0 MUST be
         used for desemul-buf-cap.  The value of desemul-buf-cap MUST
         be an integer in the range of 0 to 4294967295, inclusive.

      sprop-desemul-init-buf-time:
         This parameter MAY be used to signal the properties of a NAL
         unit stream carried in the current RTP session and the RTP
         sessions the current RTP session depends on.

         The parameter signals the initial buffering time that a
         receiver MUST wait before starting to recover the NAL unit
         decoding order as specified in section 8.1.  of this memo.

         The parameter is coded as a non-negative base10 integer
         representation in clock ticks of a 90-kHz clock.  If the
         parameter is not present, then no initial buffering time value
         is defined.  Otherwise the value of sprop-desemul-init-buf-
         time MUST be an integer in the range of 0 to 4294967295,
         inclusive.




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      sprop-semul-max-don-diff:
         This parameter MAY be used to signal the properties of a NAL
         unit stream carried in the current RTP session and the RTP
         sessions the current RTP session depends on.  It MUST NOT be
         used to signal transmitter or receiver or codec capabilities.
         sprop-semul-max-don-diff is an integer in the range of 0 to
         32767, inclusive.  If sprop-semul-max-don-diff is not present,
         the value of the parameter is unspecified.  sprop-semul-max-
         don-diff is calculated same as sprop-max-don-diff as specified
         in RFC 3984, with decoding order number being replaced by AU-
         DON or CS-DON when the NI-A mode or the I-C mode is in use,
         respectively.

9.2. SDP Parameters

   Section 9.2 of draft-ietf-avt-rtp-svc-10 applies.

9.3. Examples

   Section 9.3 of draft-ietf-avt-rtp-svc-10 applies.

9.4. Parameter Set Considerations

   Section 9.4 of draft-ietf-avt-rtp-svc-10 applies.

10. Security Considerations

   Section 10 of draft-ietf-avt-rtp-svc-10 applies.

11. Congestion Control

   Section 11 of draft-ietf-avt-rtp-svc-10 applies.

12. IANA Consideration

   Section 12 of draft-ietf-avt-rtp-svc-10 applies.

13. Informative Appendix: Application Examples

   Section 13 of draft-ietf-avt-rtp-svc-10 applies.

14. References

14.1. Normative References

   Section 14.1 of draft-ietf-avt-rtp-svc-10 applies with the following
   addition.


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   [I-D.ietf-avt-rtp-svc]  Wenger, S., Wang, Y.-K."RTP payload format
             for SVC video", draft-ietf-avt-rtp-svc-10 (work in
             progress), May 2008.

14.2. Informative References

   Section 14.2 of draft-ietf-avt-rtp-svc-10 applies.

15. Authors' Addresses

   Miska M. Hannuksela
   Nokia Research Center
   P.O. Box 1000
   33721 Tampere
   Finland

   Phone: +358-7180-73151
   EMail: miska.hannuksela@nokia.com

   Ye-Kui Wang
   Nokia Research Center
   P.O. Box 1000
   33721 Tampere
   Finland

   Phone: +358-50-466-7004
   EMail: ye-kui.wang@nokia.com


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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.  Further, the author Thomas Schierl of Fraunhofer
   HHI is sponsored by the European Commission under the contract number
   FP7-ICT-214063, project SEA.  The authors want to thank Jonathan
   Lennox for his valuable comments on and input to the draft.















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