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Versions: (draft-wenger-avt-rtp-svc) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 RFC 6190

Network Working Group                                         S. Wenger
Internet-Draft                                               Y.-K. Wang
Intended status: Standards Track                                  Nokia
Expires: September 4, 2007                                   T. Schierl
                                                         Fraunhofer HHI
                                                          March 5, 2007


                   RTP Payload Format for SVC Video
                     draft-ietf-avt-rtp-svc-01.txt


Status of this Memo

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   This Internet-Draft will expire on September 4, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2007).



Internet-Draft        RTP Payload Format for SVC Video       March 2007

Abstract

   This memo describes an RTP Payload format for the scalable extension
   of the ITU-T Recommendation H.264 video codec which is technically
   identical to ISO/IEC International Standard 14496-10 video codec.
   The RTP payload format allows for packetization of one or more
   Network Abstraction Layer Units (NAL units), produced by the video
   encoder, in each RTP payload.  The payload format has wide
   applicability, as it supports applications from simple low bit-rate
   conversational, through Internet video streaming with interleaved
   transmission, to high bit-rate video-on-demand.





































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Table of Content

   RTP Payload Format for SVC Video...................................1
   1.   Introduction..................................................5
   1.1.    SVC -- the scalable extension of H.264/AVC.................5
   2.   Conventions...................................................5
   3.   The SVC Codec.................................................6
   3.1.    Overview...................................................6
   3.2.    Parameter Set Concept......................................7
   3.3.    Network Abstraction Layer Unit Header......................8
   4.   Scope........................................................12
   5.   Definitions and Abbreviations................................12
   5.1.    Definitions...............................................12
   5.1.1.  Definitions per SVC specification.........................12
   5.1.2.  Definitions local to this memo............................14
   5.2.    Abbreviations.............................................15
   6.   RTP Payload Format...........................................15
   6.1.    Design Principles.........................................15
   6.2.    RTP Header Usage..........................................16
   6.3.    Common Structure of the RTP Payload Format................16
   6.4.    NAL Unit Header Usage.....................................16
   6.5.    Packetization Modes.......................................17
   6.6.    Decoding Order Number (DON)...............................18
   6.7.    Single NAL Unit Packet....................................18
   6.8.    Aggregation Packets.......................................19
   6.9.    Fragmentation Units (FUs).................................19
   6.10.   Payload Content Scalability Information (PACSI) NAL Unit..19
   7.   Packetization Rules..........................................24
   8.   De-Packetization Process (Informative).......................24
   9.   Payload Format Parameters....................................24
   9.1.    MIME Registration.........................................25
   9.2.    SDP Parameters............................................27
   9.2.1.  Mapping of MIME Parameters to SDP.........................27
   9.2.2.  Usage with the SDP Offer/Answer Model.....................28
   9.2.3.  Usage with Session and SSRC multiplexing..................28
   9.2.4.  Usage in Declarative Session Descriptions.................28
   9.3.    Examples..................................................28
   9.4.    Parameter Set Considerations..............................28
   10.  Security Considerations......................................28
   11.  Congestion Control...........................................28

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   12.  IANA Consideration...........................................30
   13.  Informative Appendix: Application Examples...................30
   13.1.   Introduction..............................................30
   13.2.   Layered Multicast.........................................31
   13.3.   Streaming of an SVC scalable stream.......................31
   13.4.   Multicast to MANE, SVC scalable stream to endpoint........32
   13.5.   Scenarios currently not considered for complexity reasons.34
   13.6.   Scenarios currently not considered for being unaligned with
   IP philosophy.....................................................34
   13.7.   SSRC Multiplexing.........................................36
   14.  References...................................................37
   14.1.   Normative References......................................37
   14.2.   Informative References....................................37
   15.  Author's Addresses...........................................38
   16.  Copyright Statement..........................................38
   17.  Disclaimer of Validity.......................................39
   18.  Intellectual Property Statement..............................39
   19.  Acknowledgement..............................................40
   20.  RFC Editor Considerations....................................40
   21.  Open Issues..................................................40
   22.  Changes Log..................................................40
























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1. Introduction

1.1. SVC -- the scalable extension of H.264/AVC

   This memo specifies an RTP [RFC3550] payload format for a
   forthcoming new mode of the H.264/AVC video codec, known as Scalable
   Video Coding (SVC). Formally, SVC will take the form of an Amendment
   to ISO/IEC 14496 Part 10 [MPEG4-10], and likely as one or more new
   Annexes of ITU-T Rec. H.264 [H.264].  It is planned to keep the
   technical alignment between the two mentioned specifications, as
   well as backward compatibility with previous versions of H.264/AVC.

   The current working draft of SVC is available for public review
   [SVC]. In this memo, SVC is used as an acronym for the mentioned
   scalable extension of H.264/AVC. In that, SVC is a superset of
   H.264/AVC.

   SVC covers the whole application ranges of H.264/AVC.  This range is
   considerable, starting with low bit-rate Internet streaming
   applications to HDTV broadcast and Digital Cinema with nearly
   lossless coding and requiring dozens or hundreds of MBit/s.

   This memo tries to follow a backward compatible enhancement
   philosophy similar to what the video coding standardization
   committees implement, by keeping as close an alignment to the
   H.264/AVC payload RFC [RFC3984] as possible.  It documents the
   enhancements relevant from an RTP transport viewpoint, defines
   signaling support for SVC, and deprecates the single NAL unit
   packetization mode of RFC 3984.

2. Conventions

   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 BCP 14, RFC 2119
   [RFC2119].

   This specification uses the notion of setting and clearing a bit
   when bit fields are handled.  Setting a bit is the same as assigning

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   that bit the value of 1 (On).  Clearing a bit is the same as
   assigning that bit the value of 0 (Off).

3. The SVC Codec

3.1. Overview

   SVC provides scalable video bitstreams.  In SVC, a scalable video
   bitstream contains a base layer conforming to the existing profiles
   of H.264 as defined in [H.264], and one or more enhancement layers.
   An enhancement layer may enhance the temporal resolution (i.e. the
   frame rate), the spatial resolution, or the quality of the video
   content represented by the lower layer or part thereof.

   Each RTP packet stream can carry NAL units belonging to one or more
   layers.  The NAL unit headers include information of the association
   of a given NAL unit to a layer.  Therefore, extracting individual
   layers from an RTP packet stream containing more than one layer is a
   lightweight operation, involving only fixed length bit fields in the
   header as documented in this memo and in [SVC].

   Multiple RTP packet streams, regardless whether they carry a single
   or multiple layers as discussed above, can be used to transport the
   whole scalable bitstream, or operation points thereof.  When
   multiple RTP packet streams are in use, they are session
   multiplexed, i.e. form their own RTP session and therefore have
   their own SSRC, PT, and Sequence numbering space, among all other
   properties of a session as spelled out in section xxx of [RFC3550].

   The concept of video coding layer (VCL) and network abstraction
   layer (NAL) is inherited from H.264. The VCL contains the signal
   processing functionality of the codec; mechanisms such as transform,
   quantization, motion-compensated prediction, loop filtering and
   inter-layer prediction.  A coded picture in H.264 consists of one or
   more slices.  In SVC, a particular layer consists of all the coded
   slices required for decoding up to that layer.  Within one access
   unit, a coded picture representing a particular layer consists of
   all the coded slices required for decoding up to the particular
   layer at the time instance corresponding to the access unit.  The
   Network Abstraction Layer (NAL) encapsulates each slice generated by

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   the VCL into one or more Network Abstraction Layer Units (NAL
   units). Please consult RFC 3984 for a more in-depth discussion of
   the NAL unit concept.  SVC specifies the decoding order of the NAL
   units.

   ``Layer'' in the terms ``Video Coding Layer'' and ``Network
   Abstraction Layer'' refers to a conceptual distinction, and is
   closely related to syntax layers (block, macroblock, slice, ...
   layers). ``Layer'' here describes a syntax level of the bitstream in
   contrast to a part of the layered bitstream, which may be discarded.
   It should not be confused with base and enhancement layers.

   The concept of temporal scalability is not newly introduced by SVC,
   as H.264 already supports it.  In [H.264], sub-sequences have been
   introduced in order to allow optional use of temporal layers.  SVC
   extends this approach by advertising the temporal layer information
   within the NAL unit header, or suffix NAL units, as discussed in
   section 3.3 of this memo and in [SVC].  By our definition, the base
   layer may be scalable in the temporal dimension.

   The concept of scaling the visual content quality in the granularity
   of complete enhancement layers, i.e. through omitting the transport
   and decoding of entire enhancement layers, is denoted as coarse-
   grained scalability (CGS).  This is what is commonly understood as
   scalability in the IETF community.  According to SVC, a CGS layer
   may be a spatial or quality (SNR) enhancement layer.

   In some cases, the bit rate of a given enhancement layer may be
   reduced by truncating bits from individual NAL units.  Truncation
   leads to a graceful degradation of the video quality of the
   reproduced enhancement layer.  This concept is known as Fine
   Granularity Scalability (FGS).  In SVC, FGS is provided by a concept
   known as progressive refinement slices.


3.2. Parameter Set Concept

   The parameter set concept is inherited from [H.264]. Please refer to
   section 1.2 of RFC 3984 for more details.


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   In SVC, pictures from different layers may use the same sequence or
   picture parameter set, but may also use different sequence or
   picture parameter sets.  If different sequence or picture parameter
   sets are used, then, at any time instant during the decoding
   process, there may be more than one active sequence or picture
   parameter set. Any specific active sequence parameter set remains
   unchanged throughout a coded video sequence in the layer in which
   the active sequence parameter set is referred to.  The active
   picture parameter set remains unchanged within a coded picture.

3.3. Network Abstraction Layer Unit Header

   An SVC NAL unit, i.e., a NAL units of type 20 and 21, consists of a
   header of four or five bytes and the payload byte string.  An SVC
   NAL unit typically encapsulates VCL data as defined in Annex G of
   [SVC] but may also contain VCL data compliant to older profiles of
   [H.264]. A special type of an SVC NAL unit is the suffix NAL unit
   that includes descriptive information of a preceding NAL unit.

   SVC extends the NAL unit header defined in [H.264] by three or four
   additional bytes.  The header indicates the type of the NAL unit,
   the (potential) presence of bit errors or syntax violations in the
   NAL unit payload, information regarding the relative importance of
   the NAL unit for the decoding process, the layer decoding dependency
   information, and FGS fragmentation information. This RTP payload
   specification is designed to be unaware of the bit string in the NAL
   unit payload.

   The NAL unit header co-serves as the payload header of this RTP
   payload format.  The payload of a NAL unit follows immediately.

   The syntax and semantics of the NAL unit header are formally
   specified in [SVC], but the essential properties of the NAL unit
   header are summarized below.

   The first byte of the NAL unit header has the following format (the
   bit fields are the same as in [H.264] and [RFC3984], while the
   semantics have changed slightly, in a backward compatible way):



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         +---------------+
         |0|1|2|3|4|5|6|7|
         +-+-+-+-+-+-+-+-+
         |F|NRI|  Type   |
         +---------------+

   F: 1 bit
   forbidden_zero_bit.  H.264 declares a value of 1 as a syntax
   violation.

   NRI: 2 bits
   nal_ref_idc.  A value of 00 indicates that the content of the NAL
   unit is not used to reconstruct reference pictures for inter picture
   prediction.  Such NAL units can be discarded without risking the
   integrity of the reference pictures in the same layer.  Values
   greater than 00 indicate that the decoding of the NAL unit is
   required to maintain the integrity of the reference pictures.

   Type: 5 bits
   nal_unit_type.  This component specifies the NAL unit payload type
   as defined in table 7-1 of [SVC], and later within this memo.  For a
   reference of all currently defined NAL unit types and their
   semantics, please refer to section 7.4.1 in [SVC].

   Previously, NAL unit types 20 and 21 (among others) have been
   reserved for future extensions.  SVC is using these two NAL unit
   types.  They indicate the presence of three or four additional bytes
   in the NAL unit header. The first three additional bytes are as
   shown below.

            +---------------+---------------+---------------+
            |0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7|
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |RR |   PRID    | TL  | DID | QL|B|U|D|G|L| O |E|
            +---------------+---------------+---------------+

   RR: 2 bits
   reserved_zero_two_bits.  Reserved bits for future extension.  RR
   MUST be zero.


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   PRID: 6 bits
   priority_id.  This component specifies a priority identifier for the
   NAL unit.  A lower value of PRID indicates a higher priority.

   TL: 3 bits
   temporal_id. This component indicates the temporal layer (or frame
   rate) hierarchy.  Informally put, a layer consisted of pictures of a
   smaller temporal_id value has a smaller frame rate.  A given
   temporal layer typically depends on the lower temporal layers (i.e.
   the temporal layers with smaller temporal_id values) but never
   depends on any higher temporal layer.

   DID: 3 bits
   dependency_id. This component denotes the inter-layer coding
   dependency hierarchy. At any temporal location, a picture of a
   smaller dependency_id value may be used for inter-layer prediction
   for coding of a picture of a larger dependency_id value, while a
   picture of a larger dependency_id value is disallowed to be used for
   inter-layer prediction for coding of a picture of a smaller
   dependency_id value.

   QL: 2 bits
   quality_id. This component designates the quality level hierarchy of
   a progressive refinement (PR) or quality (SNR) enhancement layer
   slice. At any temporal location and with identical dependency_id
   value, a picture with quality_id equal to ql uses a picture with
   quality_id equal to ql-1 for inter-layer prediction.

   B: 1 bit
   layer_base_flag. A value of 1 indicates that no inter-layer
   prediction (of coding mode, motion, sample value, and/or residual
   prediction) is used for the current slice. A value of 0 indicates
   that inter-layer prediction may be used for the current slice.

   U: 1 bit
   use_base_prediction_flag. A value of 1 indicates that only the base
   representations of the reference pictures are used during the inter
   prediction process of the current slice. A value of 0 indicates that
   the base representations of the reference pictures are not used
   during the inter prediction process of the current slice.

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   D: 1 bit
   discardable_flag.  A value of 1 indicates that the content of the
   NAL unit with dependency_id equal to currDependencyId is not used in
   the decoding process of NAL units with dependency_id larger than
   currDependencyId.  Such NAL units can be discarded without risking
   the integrity of higher scalable layers with larger values of
   dependency_id.  discardable_flag equal to 0 indicates that the
   decoding of the NAL unit is required to maintain the integrity of
   higher scalable layers with larger values of dependency_id.

   G: 1 bit
   fragmented_flag. A value of 1 indicates that the current NAL unit is
   a FGS (progressive refinement) slice. A value of 0 indicates that
   the current NAL unit is not a FGS slice. If quality_id is equal to
   0, fragmented_flag shall be equal to 0.

   L: 1 bit
   last_fragment_flag. When fragmented_flag is equal to 0, the
   semantics of this component is unspecified. When fragmented_flag is
   equal to 1, this component, together with fragment_order, specifies
   whether the current NAL unit is a fragmented FGS slice, and if yes,
   whether the current NAL unit is the last fragment of the fragmented
   slice, as follows. When fragment_order is equal to 0 and
   last_fragment_flag is equal to 1, the current NAL unit is an un-
   fragmented FGS slice. When fragment_order is greater than 0 and
   last_fragment_flag is equal to 1, the current NAL unit is the last
   fragment of a fragmented FGS slice. When last_fragment_flag is equal
   to 0, the current NAL unit is a fragment but not the last fragment
   of a fragmented FGS slice.

   O: 2 bits
   fragment_order. When fragmented_flag is equal to 0, the semantics of
   this component is unspecified. When fragmented_flag is equal to 1,
   this component, together with last_fragment_flag, specifies whether
   the current NAL unit is a fragmented FGS slice, and if yes, the
   fragment order, as follows. When fragment_order is equal to 0 and
   last_fragment_flag is equal to 1, the current NAL unit is an un-
   fragmented FGS slice. When fragment_order is greater than 0 and
   last_fragment_flag is equal to 1, the current NAL unit is the last

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   fragment of a fragmented FGS slice, and fragment_order indicates the
   fragment order. When last_fragment_flag is equal to 0, the current
   NAL unit is a fragment but not the last fragment of a fragmented FGS
   slice, and fragment_order indicates the fragment order.

   E: 1 bit
   extension_flag. A value of 1 indicates the existence of the last
   byte, tl0_frame_idx, in the NAL unit header. A value of 0 indicates
   that tl0_frame_idx is not present in the NAL unit header.  Please
   refer to [SVC] for information in detail about tl0_frame_idx.

   This memo introduces the same additional NAL unit types as RFC 3984,
   which are presented in section 6.3.  The NAL unit types defined in
   this memo are marked as unspecified in [SVC].  Moreover, this
   specification extends the semantics of F, NRI, PRID, D, TL, DID and
   QL as described in section 6.4.

4. Scope

   This payload specification can only be used to carry the "naked" NAL
   unit stream over RTP, and not the byte stream format according to
   Annex B of [SVC].  Likely, the applications of this specification
   will be in the IP based multimedia communications fields including
   conversational multimedia, video telephony or video conferencing,
   Internet streaming and TV over IP.

   This specification allows, in a given RTP session, to encapsulate
   NAL units belonging to
     o the base layer only, detailed specification in [RFC3984], or
     o one or more enhancement layers, or
     o the base layer and one or more enhancement layers


5. Definitions and Abbreviations

5.1. Definitions

5.1.1.    Definitions per SVC specification



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   This document uses the definitions of [SVC].  The following terms,
   defined in [SVC], are summed up for convenience:

   scalable bitstream:  A bitstream that uses the scalable extensions
   defined in Annex G of [SVC], i.e. a bitstream with a base layer and
   at least one enhancement layer.

   suffix NAL unit:  A NAL unit that immediately follows another NAL
   unit in decoding order and contains descriptive information of the
   preceding NAL unit, which is referred to as the associated NAL unit.
   A suffix NAL unit shall have nal_ref_idc equal to 20 or 21, shall
   have dependency_id and quality_level both equal to 0, and shall not
   contain a coded slice.  A suffix NAL unit belongs to the same coded
   picture as the associated NAL unit.  A suffix NAL unit may be used
   for indicating temporal levels within the base layer.

   base layer:  The base layer is typically representing the minimal
   spatial resolution and the minimal fidelity of an SVC bitstream.
   The base layer must be fully complying with [H.264].  The base layer
   is independently decodable without the requirement of using any
   other layer of the SVC bitstream.  In SVC context each slice NAL
   unit in the base layer is associated with a suffix NAL unit, which
   has a four or five bytes NAL unit header containing all the syntax
   elements described in section 3.3.  The base layer may be temporally
   scalable.

   enhancement layer:  An SVC enhancement layer is identified by
   priority_id, temporal_level, dependency_id, and quality_level as
   defined in [SVC] and summarized in section 3.3.

   access unit:  A set of NAL units pertaining to a certain temporal
   location. An access unit includes the coded slices of all the
   scalable layers at that temporal location and possibly other
   associated data, e.g. SEI messages and parameter sets.

   coded video sequence:  A sequence of access units that consists, in
   decoding order, of an instantaneous decoding refresh (IDR) access
   unit followed by zero or more non-IDR access units including all
   subsequent access units up to but not including any subsequent IDR
   access unit.

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   IDR access unit:  An access unit in which all the primary coded
   pictures are IDR pictures.  Such an access unit allows for random
   access to any operation point.

   IDR picture:  A coded picture with the property that the decoding of
   this coded picture and all the following coded pictures in decoding
   order, with the same value of dependency_id, can be performed
   without inter prediction from any picture prior to the coded picture
   in decoding order with the same value of dependency_id.  Thus an IDR
   picture allows for random access to the scalable layer, which it
   belongs to.  An IDR picture causes a "reset" in the decoding process
   of the scalable layer containing the IDR picture.

   progressive refinement (PR) slice:  A progressive refinement slice
   is contained in an SVC NAL unit that may be truncated since the end
   of the slice header for bit-rate and quality reduction.  PR slices
   provide Fine Granularity Scalability (FGS).

5.1.2.    Definitions local to this memo

   operation point:  An operation point of a SVC bitstream represents a
   certain level of temporal, spatial and quality scalability.  An
   operation point contains all NAL units required for restoring a
   valid bitstream (conforming to [SVC]) up to a certain SVC layer.
   The operation point is further described by priority_id,
   temporal_level, dependency_id, and quality_level values of that
   layer.

   RTP packet stream: A sequence of RTP packets with increasing
   sequence numbers, identical PT and SSRC, carried in one RTP session.
   Within the scope of this memo, one RTP packet stream is utilized to
   transport an integer number of SVC layers.

   Session multiplexing:  The scalable SVC bitstream is distributed
   onto different RTP sessions, whereby each RTP session carries a
   single RTP packet stream.  Each RTP session requires a separate
   signaling and has a separate Timestamp, Sequence Number, and SSRC
   space. Dependency between sessions MUST be signaled according to
   [I-D.schierl-mmusic-layered-codec] and this memo.

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5.2. Abbreviations

   In addition to the abbreviations defined in [RFC3984], the following
   ones are defined.

   CGS:       Coarse Granularity Scalability
   FGS:       Fine Granularity Scalability

6. RTP Payload Format

6.1. Design Principles

   The following design principles have been observed:

   o Backward compatibility with RFC 3984 wherever possible.

   o As the SVC base layer is H.264/AVC compatible, we assume the base
     layer (when transmitted in its own session) to be
     encapsulated using RFC 3984.  Requiring this has the desirable
     side effect that it can be used by RFC 3984 legacy devices.

   o MANEs are signaling aware and rely on signaling information.
     MANEs have state.

   o MANEs can terminate RTP sessions, and create different RTP
   sessions
     with perhaps modified content.  This form of a MANE acts as an RTP
     mixer.

   o MANEs can also act as RTP translators.  The perhaps most likely
     use case is media-aware stream thinning.  By using the payload
     header information identifying layers within an RTP session,
     MANEs are able to remove packets from the RTP session while
     otherwise keeping the session intact.  This implies rewriting
     the RTP headers of the outgoing packet stream and rewriting of
     RTCP Receiver Reports.




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   o Packet integrity needs to be preserved end-to-end (whereby
     end-to-end can mean endpoint to endpoint but also endpoint to
     MANE, if (and only if) the MANE acts as a Mixer).

   o In case of layered multicast transmission as motivated in section
     13.2, each RTP packet stream in a given session may contain NAL
     units belong to one or more SVC layer(s) of the same scalable
     bitstream. The layers contained within a RTP session may be
     identified by using payload header structures as defined in this
     memo.

6.2. RTP Header Usage

   Please see section 5.1 of RFC 3984 [RFC3984].  The following applies
   in addition.

   When layers of an SVC scalable bitstream are transported in more
   than one RTP session, e.g. in layered multicast for which the use
   case is given in 13.2, session multiplexing MUST be used only as RTP
   multiplexing technique.

6.3. Common Structure of the RTP Payload Format

   Please see section 5.2 of RFC 3984 [RFC3984].

6.4. NAL Unit Header Usage

   The structure and semantics of the NAL unit header were introduced
   in section 3.3.  This section specifies the semantics of F, NRI,
   PRID, D, TL, DID, QL, B, U, G, L, and O according to this
   specification.

   The semantics of F specified in section 5.3 of [RFC3984] also
   applies herein.

   For NRI, for the bitstream that is compliant with [H.264] and
   transported using RFC 3984, the semantics specified in section 5.3
   of [RFC3984] are applicable, i.e., NRI also indicates the relative
   importance of NAL units. In SVC context, only the semantics


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   specified in [SVC] are applicable, i.e., NRI does not indicate the
   relative importance of NAL units.

   For PRID, the semantics specified in [SVC] applies.  In addition,
   MANEs implementing unequal error protection may use this information
   to protect NAL units with smaller PRID values better than those with
   larger PRID values, for example by including only the more important
   NAL units in a FEC protection mechanism.  The importance for the
   decoding process decreases as the PRID value increases.

   For D, in addition to the semantics specified in [SVC], according to
   this memo, MANEs may use this information to protect NAL units with
   D equal to 0 better than NAL units with D equal to 1. Furthermore,
   based on this information, a MANE or a receiver may determine
   whether a given NAL unit is required for successfully decoding a
   certain operation point of the SVC bitstream.

   For TL, DID and QL, in addition to the semantics specified in [SVC],
   according to this memo, values of TL, DID or QL indicate the
   relative priority in their respective dimension.  A lower value of
   TL, DID or QL indicates a higher priority if the other two
   components are identical correspondingly.  MANEs may use this
   information to protect more important NAL units better than less
   important NAL units.

      Informative note: PRID, D, TL, DID, and QL, in combination,
      provide complete information of the relative priority of a NAL
      unit compared to any other NAL unit. [Edt. note: examples may be
      provided in Informative Appendix 13 in future versions.]


   For U, in addition to the semantics specified in [SVC], according to
   this memo, MANEs may use this information to protect NAL units with
   U equal to 1 (which are referred to as key picture NAL units) better
   than NAL units with U equal to 0.

6.5. Packetization Modes

   Please see section 5.4 of RFC 3984 [RFC3984].  The single NAL unit
   packetization mode SHALL NOT be used.

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     Informative note: The non-interleaved mode allows an application
     to encapsulate a single NAL unit in a single RTP packet.
     Historically, the single NAL unit mode has been included into
     [RFC3984] only for compatibility with ITU-T Rec. H.241 Annex A
     [H.241].  There is no point in carrying this historic ballast
     towards a new application space such as the one provided with SVC.
     More technically speaking, the implementation complexity increase
     for providing the additional mechanisms of the non-interleaved
     mode (namely STAPs) is so minor, and the benefits are so great,
     that we require STAP implementation.

6.6. Decoding Order Number (DON)

   Please see section 5.5 of RFC 3984 [RFC3984]. The following applies
   in addition.

   When different layers of a SVC bitstream are transported in more
   than one RTP packet stream, the interleaved packetization mode MUST
   be used, and the DON values of all the NAL units MUST indicate the
   correct NAL unit decoding order over all the RTP packet streams.

   If Session multiplexing is used, each session MUST signal an
   identical value for the MIME parameters sprop-interleaving-depth,
   sprop-max-don-diff, sprop-deint-buf-req, and sprop-init-buf-time.
   Further, these values must be valid for the reception capabilities
   over all sessions.  A receiver MUST signal the same MIME parameter
   deint-buf-cap for all sessions used for Session multiplexing.
   [Ed.Note(YkW): I think we need more thinking on the value of the
   parameters. For example, requiring the parameters be the same for
   all the RTP streams and clients might be overkill for receivers of
   only lower layers.]
   Edt. Note (StW): In RFC3984, the aforementioned codepoints are
   optional.  It appears that for SVC, when used in conjunction with
   session mux, they are mandatory.  I don't know how to express this
   in the MIME registration; we'll cross that bridge once we are
   getting to it.

6.7. Single NAL Unit Packet


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   Please see section 5.6 of RFC 3984 [RFC3984].

6.8. Aggregation Packets

   Please see section 5.7 of RFC 3984 [RFC3984].

6.9. Fragmentation Units (FUs)

   Please see section 5.8 of RFC 3984 [RFC3984].

6.10.     Payload Content Scalability Information (PACSI) NAL Unit

   A new NAL unit type is specified in this memo, and referred to as
   payload content scalability information (PACSI) NAL unit.  The PACSI
   NAL unit, if present, MUST be the first NAL unit in an aggregation
   packet, and it MUST NOT be present in other types of packets.  The
   PACSI NAL unit indicates scalability and other characteristics that
   are common for all the remaining NAL units in the payload, thus
   making it easier for MANEs to decide whether to
   forward/process/discard the aggregation packet.  Furthermore, PACSI
   NAL unit MAY contain zero or more SEI NAL units.  Senders MAY create
   PACSI NAL units and receivers MAY ignore them, or use them as hints
   to enable efficient aggregation packet processing.

      Informative note: The NAL unit type for the PACSI NAL unit is
      selected among those values that are unspecified in the SVC
      specification and in RFC 3984 -- and therefore are ignored by
      H.264/AVC or SVC decoders and RFC 3984 receivers.  Hence an SVC
      stream, even when including PACSI NAL units, can be processed
      with RFC 3984 receivers and H.264/AVC or SVC decoders.

   When the first aggregation unit of an aggregation packet contains a
   PACSI NAL unit, there MUST be at least one additional aggregation
   unit present in the same packet.  The RTP header fields are set
   according to the remaining NAL units in the aggregation packet.

   When a PACSI NAL unit is included in a multi-time aggregation
   packet, the decoding order number for the PACSI NAL unit MUST be set
   to indicate that the PACSI NAL unit is the first NAL unit in
   decoding order among the NAL units in the aggregation packet or the

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   PACSI NAL unit has an identical decoding order number to the first
   NAL unit in decoding order among the remaining NAL units in the
   aggregation packet.

   The structure of PACSI NAL unit is as follows. The first four octets
   are exactly the same as the four-byte SVC NAL unit header (where E
   is equal to 0) specified in 3.3, followed by one additional octet
   and zero or more SEI NAL units, each preceded by a 16-bit unsigned
   size information (in network byte order) that indicates the size of
   the following NAL unit in bytes (excluding these two octets, but
   including the NAL unit type octet of the NAL unit). Following is an
   example of a PACSI NAL unit containing two SEI NAL units.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |F|NRI|  Type   |RR |   PRID    | TL  | DID | QL|B|U|D|G|L| O |E|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |R|T|D|I|S|N|RES|   TL0PICIDX   |        NAL unit size 1        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                          SEI NAL unit 1                       |
      |                                                               |
      |                         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         :        NAL unit size 2        |     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |
      |                                                               |
      |            SEI NAL unit 2                                     |
      |                                           +-+-+-+-+-+-+-+-+-+-+
      |                                           :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The values of the fields in PACSI NAL unit MUST be set as follows.

   o The F bit MUST be set to 1 if the F bit in at least one remaining
     NAL unit in the payload is equal to 1.  Otherwise, the F bit MUST
     be set to 0.

   o The NRI field MUST be set to the highest value of NRI field among
     all the remaining NAL units in the payload.


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   o The Type field MUST be set to 30.

   o The RR field MUST be set to 0.

   o The PRID field MUST be set to the lowest value of the PRID values
     associated with all the remaining NAL units in the payload.

   o The TL field MUST be set to the lowest value of the TL values
     associated with all the remaining NAL units in the payload.

   o The DID field MUST be set to the lowest value of the DID values
     associated with all the remaining NAL units in the payload.

   o The QL field MUST be set to the lowest value of the QL values
     associated with all the remaining NAL units in the payload.

   o The B bit MUST be set to 1 if
     the B bit associated with all the remaining NAL units in
     the payload is equal to 1.  Otherwise, the B bit MUST be set
     to 0.

   o The U bit MUST be set
     to 1 if the U bit associated with all the
     remaining NAL units in the payload is equal to 1.  Otherwise, the
   U bit
     MUST be set to 0.

   o The D bit MUST be set to 0 if the D value associated with at least
     one remaining NAL unit in the payload is equal to 0.  Otherwise,
     the D bit MUST be set to 1.

   o The G bit MUST be set to 1 if
     the G bit associated with at least one of the remaining NAL units
   in
     the payload is equal to 1.  Otherwise, the G bit MUST be set
     to 0.

   o The L bit MUST be set to 1 if
     for any NAL unit having fragmented_flag equal to 1 in the payload,

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   the corresponding NAL unit having the bit L equal to 1 is also in
   the payload.  Otherwise, the bit L MUST
     be set to 0.

   o The O field MUST be set to the
     lowest value of the O values associated with all the remaining NAL
     units in the payload.

   o The E field or extension_flag field (1 bit) MUST be set to 0.

   o The R field MUST be set to 1 if all the coded pictures containing
   the target NAL units are anchor pictures. Otherwise, the bit R MUST
   be set to 0.  The target NAL units are such NAL units contained in
   the aggregation packet, but not included in the PACSI NAL unit, that
   are within the access unit to which the first NAL unit following the
   PACSI NAL unit in the aggregation packet belongs.  An anchor picture
   is such a picture that, if decoding of the layer starts from the
   picture, all the following pictures of the layer, in output order,
   can be correctly decoded.

      Informative note: Anchor pictures are random access points to the
      layers the anchor pictures belong to.  However, some pictures
      succeeding an anchor picture in decoding order but preceding the
      anchor picture in output order may refer to earlier pictures
      hence may not be correctly decoded, if random access is performed
      at the anchor picture.

   o The T field MUST be set to 1 if all the coded pictures containing
   the target NAL units (as defined above) are temporal scalable layer
   switching points.  Otherwise, the bit T MUST be set to 0.  For a
   temporal scalable layer switching point, all the coded pictures with
   the same value of temporal_level at and after the switching point in
   decoding order do not refer to any coded picture with the same value
   of temporal_level preceding the switching point in decoding order.

   o The D field MUST be set to 1 if all the coded pictures containing
   the target NAL units (as defined above) are redundant pictures.
   Otherwise, the D field MUST be set to 0.



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   o The I field MUST be set to 1 if the picture that has the greatest
   value of dependency_id among all the coded pictures containing the
   target NAL units (as defined above) is an intra coded picture, i.e.,
   the coded picture does not refer to any earlier coded picture in
   decoding order in the same layer.

   o The S field MUST be set to 1, if the first NAL unit of the coded
   picture containing the first target NAL unit (as defined above) in
   decoding order is present in the payload. Otherwise, the S field
   MUST be set to 0.

   o The N field MUST be set to 1, if the last NAL unit of the coded
   picture containing the first target NAL unit (as defined above) in
   decoding order is present in the payload. Otherwise, the N field
   MUST be set to 0.

   o The RES field MUST be set to 0.

   o The TL0PICIDX field specifies either an identifier for the coded
   picture containing the first target NAL unit (as defined above) when
   TL of the coded picture is equal to 0, or the identifier of the most
   recent coded picture of TL equal to 0 in decoding order, when TL of
   the coded picture containing the first target NAL unit is greater
   than 0. If the bitstream contained no earlier access unit than the
   access unit containing the target NAL units in decoding order with
   TL being equal to 0, TL0PICIDX MAY have any value. Otherwise, let
   prevTL0FrameIdx be equal to the field TL0PICIDX of the most recent
   access unit relative to the access unit containing the target NAL
   units in decoding order with TL equal to 0. If TL is equal to 0, the
   field TL0PICIDX MUST be equal to ( prevTL0FrameIdx + 1 ) % 256.
   Otherwise (TL is greater than 0), TL0PICIDX MUST be equal to
   prevTL0FrameIdx.

   The SEI NAL units included in the PACSI NAL unit, if any, MUST
   contain a subset of the SEI messages of the access unit of the first
   NAL unit following the PACSI NAL unit within the aggregation packet.

      Informative note: Senders may repeat such SEI NAL units in the
      PACSI NAL unit the presence of which in more than one packet is


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      essential for packet loss robustness.  Receivers may use the
      repeated SEI messages in place of missing SEI messages.

   An SEI message SHOULD NOT be included in a PACSI if it is already
   included in one of the NAL unit contained in the same packet.

7. Packetization Rules

   Please see section 6 of RFC 3984 [RFC3984].  The following rules
   apply in addition.

   The single NAL unit mode SHALL NOT be used.  (See also section 6.5
   for the motivation).

   Except for the SEI messages that may be repeated in the PACSI NAL
   unit, the non-VCL NAL units (e.g. access unit delimiter, parameter
   sets, and SEI NAL units) of one access unit SHOULD be placed in the
   same RTP packet.

   When a suffix NAL unit is encapsulated for transmission, it SHOULD
   be aggregated to the same transmission packet as the NAL unit
   preceding the suffix NAL unit in decoding order.

      Informative note: When either the suffix NAL unit or the
      associated NAL unit containing an H.264/AVC coded slice is lost,
      the remaining one would be of no use in SVC context.

   When layers of a SVC bitstream are transported in more than one RTP
   session, the interleaved packetization mode MUST be used.

8. De-Packetization Process (Informative)

   Please see section 7 of RFC 3984 [RFC3984].  The following rules
   apply in addition.

   [Edt. Do we need here more information about cross layer DON?  TS:
   Yes, in the next version.]

9. Payload Format Parameters


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   [Edt. note: this section 9 and its subsections will be updated
   according to the changes listed below, a little later in the
   process.  For now, we just list the adjustments necessary, so not to
   bury any new information in the RFC 3984 text.]

   Section 8 of [RFC3984] applies with the following modification.

   The sentence

   "The parameters are specified here as part of the MIME subtype
   registration for the ITU-T H.264 | ISO/IEC 14496-10 codec."

   is replaced with

   "The parameters are specified here as part of the MIME subtype
   registration for the SVC codec."

9.1. MIME Registration

          Editor's note: this needs to be updated by copy-pasting the
          RFC 3984 MIME registration into this document, so to make it
          self-contained.  Will be done later in the process.

   The MIME subtype for the SVC codec is allocated from the IETF tree.

   The receiver MUST ignore any unspecified parameter.

   Media Type name:     video

   Media subtype name:  H.264-SVC

   Required parameters: none

   OPTIONAL parameters:

   The optional MIME parameters specified in [RFC3984] apply, with the
   following constraints (to be edited in at the appropriate time):

   sprop-interleaving-depth:


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   In case of using Session multiplexing, the same sprop-interleaving-
   depth value MUST be signaled for all sessions and MUST be valid over
   all sessions of the multiplex.

   sprop-max-don-diff:
   In case of using Session multiplexing, the same sprop-max-don-diff
   value MUST be signaled for all sessions and MUST be valid over all
   sessions of the multiplex.

   sprop-deint-buf-req:
   In case of using Session multiplexing, the same sprop-deint-buf-req
   value MUST be signaled for all sessions and MUST be valid over all
   sessions of the multiplex.

   sprop-init-buf-time:
   In case of using Session multiplexing, the same sprop-init-buf-time
   value MUST be signaled for all sessions and MUST be valid over all
   sessions of the multiplex.

   deint-buf-cap:
   In case of using Session multiplexing, the same deint-buf-cap value
   MUST be signaled by the receiver for all sessions and MUST be valid
   over all sessions of the multiplex.

   In addition the following optional MIME parameters apply:

   sprop-scalability-info:
   This parameter MAY be used to convey the NAL unit containing the
   scalability information SEI message as specified in [SVC].  The
   parameter MUST NOT be used to indicate codec capability in any
   capability exchange procedure.  The value of the parameter is the
   base64 representation of the NAL unit containing the scalability
   information SEI message.

   sprop-layer-ids:
   This parameter MAY be used to signal the layer identification
   value(s), expressed by the value of the the second and the third
   byte of the SVC NAL unit header, for one or more SVC layer(s)
   conveyed in one RTP session.  A layer identification is a three
   character value base64 coded.  If more than one layer is transmitted

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   within one RTP session, the layer identification value of each layer
   MUST be itemized with decreasing importance for decoding and MUST be
   comma-separated.

      Encoding considerations:
                           This type is only defined for transfer
                           via RTP (RFC 3550).

      Security considerations:
                           See section 9 of RFC XXXX.

      Public specification:
                           Please refer to section 15 of RFC XXXX.

      Additional information:
                           None

      File extensions:     none
      Macintosh file type code: none
      Object identifier or OID: none
      Person & email address to contact for further information:
      Intended usage:      COMMON
      Author:
      Change controller:
                           IETF Audio/Video Transport working group
                           delegated from the IESG.

9.2. SDP Parameters

9.2.1.    Mapping of MIME Parameters to SDP

   The MIME media type video/SVC string is mapped to fields in the
   Session Description Protocol (SDP) as follows:

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

   *  The encoding name in the "a=rtpmap" line of SDP MUST be SVC (the
      MIME subtype).

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

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   *  The OPTIONAL parameters "profile-level-id", "max-mbps", "max-fs",
      "max-cpb", "max-dpb", "max-br", "redundant-pic-cap", "sprop-
      parameter-sets", "parameter-add", "packetization-mode", "sprop-
      interleaving-depth", "deint-buf-cap", "sprop-deint-buf-req",
      "sprop-init-buf-time", "sprop-max-don-diff", "max-rcmd-nalu-
      size", "sprop-layer-ids", and "sprop-scalability-info", when
      present, MUST be included in the "a=fmtp" line of SDP. These
      parameters are expressed as a MIME media type string, in the form
      of a semicolon separated list of parameter=value pairs.

9.2.2.    Usage with the SDP Offer/Answer Model

   TBD.

9.2.3.    Usage with Session and SSRC multiplexing

   If Session multiplexing is used, the rules on signaling media
   decoding dependency in SDP as defined in
   [I-D.schierl-mmusic-layered-codec] apply.

9.2.4.    Usage in Declarative Session Descriptions

   TBD.

9.3. Examples

   TBD.

9.4. Parameter Set Considerations

   Please see section 10 of RFC 3984 [RFC3984].

10.  Security Considerations

   Please see section 11 of RFC 3984 [RFC3984].

11.  Congestion Control



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   Within any given RTP session carrying payload according to this
   specification, the provisions of section 12 of RFC 3984 [RFC3984]
   apply.  Reducing the session bandwidth is possible by one or more of
   the following means, listed in an order that, in most cases, will
   assure the least negative impact to the user experience:

   a) removing some or all bits of a given FGS NAL unit as long as the
      remaining bits still form a conforming SVC NAL unit.  Note: doing
      so does not reduce the number of NAL units, but the bit rate of
      the highest enhancement layer.  This can be translated into a
      reduced packet count when aggregating those smaller NAL units
      into packets small enough to fit the MTU size.
   b) stop sending NAL units belonging to the highest enhancement
      layer(s), when more than one layer is transported in the session.
   c) dropping NAL units of the base layer according to their
      importance for the decoding process, as indicated in the NAL
      unit's NRI field (this may lead to a non-compliant bitstream, and
      annoying artifacts)
   d) dropping NAL units or entire packets not according to the
      aforementioned rules (media-unaware stream thinning).  This
      results in the reception of a non-compliant bitstream and, most
      likely, in very annoying artifacts

          Informative note: The discussion above is centered on NAL
          units and not on packets, primarily because that is the level
          where senders can meaningfully manipulate the scalable
          bitstream.  The mapping of NAL units to RTP packets is fairly
          flexible when using aggregation packets.  Depending on the
          nature of the congestion control algorithm, the "dimension"
          of congestion measurement (packet count or bitrate) and
          reaction to it (reducing packet count or bitrate or both) can
          be adjusted accordingly.

   When multiple sessions are SSRC multiplexed onto the same transport
   address, a receiver can still calculate and communicate in RTCP-RRs
   the per-session congestion.  However, when it is known that these
   SSRC-multiplexed sessions originate from the same sender's transport
   address (a condition henceforth referred to as "on the same path



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   All aforementioned means are available to the RTP sender, regardless
   whether that sender is located in the sending endpoint or in a mixer
   based MANE.

   When a translator-based MANE is employed, then the MANE MAY
   manipulate the session only on the MANE's outgoing path, so that the
   sensed end-to-end congestion falls within the permissible envelope.
   As all translators, in this case the MANE needs to rewrite RTCP RRs
   to reflect the manipulations it has performed on the session.

12.  IANA Consideration

   [Edt. Note: A new MIME type should be registered from IANA.]

13.  Informative Appendix: Application Examples

13.1.     Introduction

   Scalable video coding is a concept that has been around at least
   since MPEG-2 [MPEG2], which goes back as early as 1993.
   Nevertheless, it has never gained wide acceptance; perhaps partly
   because applications didn't materialize in the form envisioned
   during standardization.

   MPEG and JVT, respectively, performed a requirement analysis before
   the SVC project was launched.  Dozens of scenarios have been
   studied.  While some of the scenarios appear not to follow the most
   basic design principles of the Internet -- and are therefore not
   appropriate for IETF standardization -- others are clearly in the
   scope of IETF work.  Of these, this draft chooses the following
   subset for immediate consideration.  Note that we do not reference
   the MPEG and JVT documents directly; partly, because at least the
   MPEG documents have a limited lifespan and are not publicly
   available, and partly because the language used in these documents
   is inappropriately video centric and imprecise, when it comes to
   protocol matters.

   With these remarks, we now introduce three main application
   scenarios that we consider as relevant, and that are implementable
   with this specification.

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13.2.     Layered Multicast

   This well-understood form of the use of layered coding
   [McCanne/Vetterli] implies that all layers are individually conveyed
   in their own RTP packet streams, each carried in its own RTP session
   using the IP (multicast) address and port number as the single
   demultiplexing point.  Receivers "tune" into the layers by
   subscribing to the IP multicast, normally by using IGMP [IGMP].

   Layered Multicast has the great advantage of simplicity and easy
   implementation.  However, it has also the great disadvantage of
   utilizing many different transport addresses.  While we consider
   this not to be a major problem for a professionally maintained
   content server, receiving client endpoints need to open many ports
   to IP multicast addresses in their firewalls.  This is a practical
   problem from a firewall/NAT viewpoint.  Furthermore, even today IP
   multicast is not as widely deployed as many wish.

   We consider layered multicast an important application scenario for
   three reasons.  First, it is well understood and the implementation
   constraints are well known.  There may well be large scale IP
   networks outside the immediate Internet context that may wish to
   employ layered multicast in the future.  One possible example could
   be a combination of content creation and core-network distribution
   for the various mobile TV services, e.g. those being developed by
   3GPP (MBMS) [MBMS] and DVB (DVB-H) [DVB-H].

13.3.     Streaming of an SVC scalable stream

   In this scenario, a streaming server has a repository of stored SVC
   coded layers for a given content.  At the time of streaming, and
   according to the capabilities, connectivity, and congestion
   situation of the client(s), the streaming server generates and
   serves a scalable stream.  Both unicast and multicast serving is
   possible.  At the same time, the streaming server may use the same
   repository of stored layers to compose different streams (with a
   different set of layers) intended for other audiences.



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   As every endpoint receives only a single SVC RTP session, the number
   of firewall pinholes can be optimized to one.

   The main difference between this scenario and straightforward
   simulcasting lies in the architecture and the requirements of the
   streaming server, and is therefore out of the scope of IETF
   standardization.  However, compelling arguments can be made why such
   a streaming server design makes sense.  One possible argument is
   related to storage space and channel bandwidth.  Another is
   bandwidth adaptivity without transcoding -- a considerable advantage
   in a congestion controlled network.  When the streaming server
   learns about congestion, it can reduce sending bitrate by choosing
   fewer layers or utilizing FGS, when composing the layered stream;
   see section 10.  SVC is designed to gracefully support both
   bandwidth rampdown and bandwidth rampup with a considerable dynamic
   range.  This payload format is designed to allow for bandwidth
   flexibility in the mentioned sense, both for CGS and FGS layers.
   While, in theory, a transcoding step could achieve a similar dynamic
   range, the computational demands are impractically high and video
   quality is typically lowered -- therefore, few (if any) streaming
   servers implement full transcoding.

13.4.     Multicast to MANE, SVC scalable stream to endpoint

   This scenario is a bit more complex, and designed to optimize the
   network traffic in a core network, while still requiring only a
   single pinhole in the endpoint's firewall.  One of its key
   applications is the mobile TV market.

   Consider a large private IP network, e.g. the core network of 3GPP.
   Streaming servers within this core network can be assumed to be
   professionally maintained.  We assume that these servers can have
   many ports open to the network and that layered multicast is a real
   option.  Therefore, we assume that the streaming server multicasts
   SVC scalable layers, instead of simulcasting different
   representations of the same content at different bit rates.

   Also consider many endpoints of different classes.  Some of these
   endpoints may not have the processing power or the display size to
   meaningfully decode all layers; other may have these capabilities.

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   Users of some endpoints may not wish to pay for high quality and are
   happy with a base service, which may be cheaper or even free.  Other
   users are willing to pay for high quality.  Finally, some connected
   users may have a bandwidth problem in that they can't receive the
   bandwidth they would want to receive -- be it through congestion,
   connectivity, change of service quality, or for whatever other
   reasons.  However, all these users have in common that they don't
   want to be exposed too much, and therefore the number of firewall
   pinholes need to be small.

   This situation can be handled best by introducing middleboxes close
   to the edge of the core network, which receive the layered multicast
   streams and compose the single SVC scalable bit stream according to
   the needs of the endpoint connected.  These middleboxes are called
   MANEs throughout this specification.  In practice, we envision the
   MANE to be part of (or at least physically and topologically close
   to) the base station of a mobile network, where all the signaling
   and media traffic necessarily are multiplexed on the same physical
   link.  This is why we do not worry too much about decomposition
   aspects of the MANE as such.

   MANEs necessarily need to be fairly complex devices.  They certainly
   need to understand the signaling, so, for example, to associate the
   PT octet in the RTP header with the SVC payload type.

   A MANE may terminate the multicasted layered RTP sessions incoming
   from the core network side, and create new RTP sessions (perhaps
   even multicast sessions) to the endpoints connected to them.  In RTP
   terminology, these types of MANEs are RTP mixers.  This implies, per
   RFC 3550, a very loose relationship between the incoming and
   outgoing RTP sessions.  In particular, there is no direct
   relationship between the incoming and outgoing RTP sequence numbers,
   RTP timestamps, payload types used, etc.

   Mixer-based MANEs are conceptually easy to implement and can offer
   powerful features, primarily because they necessarily can "see" the
   payload (including the RTP payload headers), utilize the wealth of
   layering information available therein, and manipulate it.



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   While a mixer-based MANE operation in its most trivial form
   (combining multiple RTP packet streams into a single one) can be
   implemented comparatively simply -- reordering the incoming packets
   according to the DON and sending them in the appropriate order --
   more complex forms can also be envisioned.  For example, a mixer-
   type MANE can be optimizing the outgoing RTP stream to the MTU size
   of the outgoing path by utilizing the aggregation and fragmentation
   mechanisms of this memo.

   A MANE can also act as a translator.  In this case, we envision its
   functionality to stream thinning, so to adhere to congestion control
   principles as discussed in section 11.  While the implementation of
   the forward (media) channel of such a MANE appears to be
   comparatively simple, the need to rewrite RTCP RRs makes even such a
   MANE a complex device.

   While the implementation complexity of either case of a MANE, as
   discussed above, is fairly high, the computational demands are
   comparatively low.  In particular, SVC and/or this specification
   contain means to easily generate the correct inter-layer decoding
   order of NAL units.  It is also simple to identify the fine
   granularity scalable bits in a given NAL unit.  No serious bit-
   oriented processing is required and no significant state information
   (beyond that of the signaling and perhaps the SVC sequence parameter
   sets) need to be kept.

13.5.     Scenarios currently not considered for complexity reasons

   -- vacat --

13.6.     Scenarios currently not considered for being unaligned with
          IP philosophy

   Remarks have been made that the current draft does not take into
   consideration at least one application scenario which some JVT folks
   consider important.  In particular, their idea is to make the RTP
   payload format (or the media stream itself) self-contained enough
   that a stateless, non signaling aware device can "thin" an RTP
   session to meet the bandwidth demands of the endpoint.  They call
   this device a "Router" or "Gateway", and sometimes a MANE.

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   Obviously, it's not a Router or Gateway in the IETF sense.  To
   distinguish it from a MANE as defined in RFC 3984 and in this
   specification, let's call it a MDfH (Magic Device from Heaven).

   To simplify discussions, let's assume point-to-point traffic only.
   The endpoint has a signaling relationship with the streaming server,
   but it is known that the MDfH is somewhere in the media path (e.g.
   because the physical network topology ensures this).  It has been
   requested, at least implicitly through MPEG's and JVT's requirements
   document, that the MDfH should be capable to intercept the SVC
   scalable bit stream, modify it by dropping packets or parts thereof,
   and forwarding the resulting packet stream to the receiving
   endpoint.  It has been requested that this payload specification
   contains protocol elements facilitating such an operation, and the
   argument has been made that the NRI field of RFC 3984 serves exactly
   the same purpose.

   The authors of this I-D do not consider the scenario above to be
   aligned with the most basic design philosophies the IETF follows,
   and therefore have not addressed the comments made (except through
   this section).  In particular, we see the following problems with
   the MDfH approach):

   - As the very minimum, the MDfH would need to know which RTP
     streams are carrying SVC.  We don't see how this could be
     accomplished but by using a static payload type.  None of the
     IETF defined RTP profiles envision static payload types for SVC,
     and even the de-facto profiles developed by some application
     standard organizations (3GPP for example) do not use this
     outdated concept.  Therefore, the MDfH necessarily needs to be at
     least "listening" to the signaling.
   - If the RTP packet payload were encrypted, it would be impossible
     to interpret the payload header and/or the first bytes of the
     media stream.  We understand that there are crypto schemes under
     discussion that encrypt only the last n bytes of an RTP payload,
     but we are more than unsure that this is fully in line with the
     IETF's security vision.




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   Even if the above two problems would have been overcome through
   standardization outside of the IETF, we still foresee serious design
   flaws:

   - An MDfH can't simply dump RTP packets it doesn't want to forward.
     It either needs to act as a full RTP Translator (implying that it
     rewrites RTCP RRs and such), or it needs to patch the RTP
     sequence numbers to fulfill the RTP specification.  Not doing
     either would, for the receiver, look like the gaps in the
     sequence numbers occurred due to unintentional erasures, which
     has interesting effects on congestion control (if implemented),
     will break pretty much every meta-payload ever developed, and so
     on.  (Many more points could be made here).
   - An MDfH also can't "prune" FGS packets.  Again, doing so would
     not be compatible with meta payloads, and would mess up RTCP RRs
     and congestion control (if the congestion control is based on
     octet count and not on packet count; there are discussions
     related to the former at least in the context of TFRC).

   In summary, based on our current knowledge we are not willing to
   specify protocol mechanisms that support an operation point that has
   so little in common with classic RTP use.

13.7.     SSRC Multiplexing

   The authors have complentated the idea of introducing SSRC
   multiplexing, i.e. allowing to send multiple RTP packet streams
   containing layers in the same RTP session, differentiated by SSRC
   values.  Our intention was to minimize the number of firewall
   pinholes in an endpoint to one, by using MANEs to aggregate multiple
   outgoing sessions stemming from a server into a single session (with
   SSRC multiplexed packet streams).  We were hoping that would be
   feasible even with encrypted packets in an SRTP context.

   While an implementation along these lines indeed appears to be
   feasible for the forward media path, the RTCP RR rewrite cannot be
   implemented in the way necessary for this scheme to work.  This
   relates to the need to authenticate the RTCP RRs as per SRTP
   [RFC3711].  While the RTCP RR itself does not need to be rewritten
   by the scheme we envisioned, it's transport addresses needs to be

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   manipulated.  This, in turn, is incompatible with the mandatory
   authetification of RTCP RRs.  As a result, there would be an
   requirement that a MANE needs to be in the RTCP security context of
   the sessions, which was not envisioned in our use case.

   As the envisioned use case cannot be implemented, we refrained to
   add the considerable document complexity to support SSRC
   multiplexing herein.

14.  References

14.1.     Normative References

[RFC3550]   Schulzrinne, H., Casner, S., Frederick, R., and V.
            Jacobson, "RTP: A Transport Protocol for Real-Time
            Applications", STD 64, RFC 3550, July 2003.
[MPEG4-10]  ISO/IEC International Standard 14496-10:2003.
[H.264]     ITU-T Recommendation H.264, "Advanced video coding for
            generic audiovisual services", May 2003.
[I-D.schierl-mmusic-layered-codec]
            Schierl, T., and Wenger, S, "Signaling media decoding
            dependency in Session Description Protocol (SDP)",
            draft-schierl-mmusic-layered-codec-03 (work in progress),
            March 2007.
[SVC]       Joint Video Team, "Joint Scalable Video Model 8: Joint
            Draft 8 with proposed changes", available from
            http://ftp3.itu.ch/av-arch/jvt-site/jvt-site/
            2006_10_Hangzhou/JVT-U202.zip , October 2006.
[RFC3984]   Wenger, S., Hannuksela, M, Stockhammer, T, Westerlund, M,
            Singer, D, "RTP Payload Format for H.264 Video", RFC 3984,
            February 2005.
[RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.

14.2.     Informative References

[DVB-H]     DVB - Digital Video Broadcasting (DVB); DVB-H
            Implementation Guidelines, ETSI TR 102 377, 2005
[H.241]     ITU-T Rec. H.241, "Extended video procedures and control
            signals for H.300-series terminals", May 2006

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[IGMP]      Cain, B., Deering S., Kovenlas, I., Fenner, B. and
            Thyagarajan, A., "Internet Group Management Protocol,
            Version 3", RFC 3376, October 2002.
[McCanne/Vetterli]
            V. Jacobson, S. McCanne and M. Vetterli. Receiver-
            driven layered multicast. In Proc. of ACM SIGCOMM'96, pages
            117--130, Stanford, CA, August 1996.
[MBMS]      3GPP - Technical Specification Group Services and System
            Aspects; Multimedia Broadcast/Multicast Service (MBMS);
            Protocols and codecs (Release 6), December 2005.
[MPEG2]     ISO/IEC International Standard 13818-2:1993.
[RFC3711]   Baugher, M., McGrew, D, Naslund, M, Carrara, E,
            Norrman, K, "The secure real-time transport protocol
            (SRTP)", RFC 3711, March 2004.

15.  Author's Addresses

   Stephan Wenger                 Phone: +358-50-486-0637
   Nokia Research Center          Email: stewe@stewe.org
   P.O. Box 100
   FIN-33721 Tampere
   Finland

   Ye-Kui Wang                    Phone: +358-50-486-7004
   Nokia Research Center          Email: ye-kui.wang@nokia.com
   P.O. Box 100
   FIN-33721 Tampere
   Finland

   Thomas Schierl                 Phone: +49-30-31002-227
   Fraunhofer HHI                 Email: schierl@hhi.fhg.de
   Einsteinufer 37
   D-10587 Berlin
   Germany

16.  Copyright Statement

   Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

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   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

17.  Disclaimer of Validity

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

18.  Intellectual Property Statement

   Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.

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19.  Acknowledgement

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).
   Further, the author Thomas Schierl of Fraunhofer HHI is sponsored
   by the European Commission under the contract number
   FP6-IST-0028097, project ASTRALS.

20.  RFC Editor Considerations

   none

21.  Open Issues

   1. Packetization rules need work.
   2. Alignment with the SVC specification (ongoing)


22.  Changes Log

Version 00

- 29.08.2005, YkW: Initial version
- 29.09.2005, Miska: Reviewed and commented throughout the document
- 05.10.2006, StW: Editorial changes through the document, and
formatted the document in RFC payload format style

>From -00 to -01

- 04.02.2006, StW: Added details to scope
- 04.02.2006, StW: Added short subsection 6.1 "Design Principles"
- 04.02.2006, StW: Added section 15, "Application Examples"
- 06.02 - 03.03.2006, YkW: Various modifications throughout the
document
- 13.02.2006 - 03.03.2006 , ThS: Added definitions and additional
information to section 3.3, 5.1, 7 and 8, parameters in section 9.1 and
added section 14 for NAL unit re-ordering for layered multicast.
Further modifications throughout the document


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>From -01 to -02

- 06.03.2006, StW: Editorial improvements
- 26.05.2006, YkW: Updated NAL unit header syntax and semantics
according to the latest draft SVC spec
- 20.06.2006, Miska/YkW: Added section 6.10 "Payload Content
Scalability Information (PACSI) NAL Unit"
- 20.06.2006, YkW: Updated the NAL unit reordering process for layered
multicast (removed the old section 14 "Informative Appendix: NAL Unit
Re-ordering for Layered Multicast" and added the new section 13 "NAL
Unit Reordering for Layered Multicast")

>From -02 to -03

- 05.09.2006, YkW: Updated the NAL unit header syntax, definitions,
etc., according to the foreseen July JVT output.  Updated possible MANE
adaptation operations according to SPID, TL, DID and QL.  Clarified the
removal of single NAL unit packetiztaion mode.  Added the support of
SSRC multiplexing in layered multicast.
- 08.09.2006, StW: Editorial changes throughout the document
- 08.09.2006, YkW: Added the packetization rule for suffix NAL unit.
- 19.09.2006, YkW: Moved/updated SSRC multiplexing support to section
6.2 ``RTP header usage''. Moved/updated the cross layer DON constraint
to Section 6.6 ``Decoding order number''. Moved/updated the
packetization rule when a SVC bistream is transported over more than
one RTP session to Section 7 ``Packetization rules''. Removed Section
13 "Support of layered multicast".
- 16.10, TS: Added detailed four-byte NAL unit header description.
Change "AVC" to "H.264" conforming to 3984. Modifications throughout
the document. Extended description of 3rd byte of PACSI NAL unit.
Corrected terms RTP session and RTP packet stream in case of SSRC
multiplexing. Added terms in definition section on RTP multiplexing.
Constraints on optional MIME parameters of 3984 for cross-layer DON
(DON section and MIME parameters). Copied parts of SI paper regarding
mixer, translator and SSRC mux with SRTP to section application
examples. Added section on SDP usage with Session and SSRC
multiplexing. Added points in Design principles on translator/mixer and
RTP multiplexing. Added additional founding information in Ack-
section. Corrected reference for SVC and added reference for generic
signaling.

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17.10, StW: Fixed many editorials, clarified MANE, mixer, translator
and RTP packet stream throughout doc (hopefully consistently)
18.10., removed comments, clarified B-Bit, changed definition of base-
layer (do not need to be of the lowest temporal resolution),

>From -03 to draft-ietf-avt-rtp-svc-00

   - 23.11.06, StW: Editorials throughout the memo
   - 23.11.06, StW: removed all occurrences of the security
     discussions, as they are incorrect.  When using SRTP, the RTCP is
     authenticated, implying that a translator cannot rewrite RTCP
     RRs, implying that RRs would be incorrect as soon as the session
     is modified (i.e. packets are being removed), implying that SSRC-
     mux does not work in multicast.
   - 23.11.06, StW: rewrote congestion control
   - 23.11.06, StW: removed application scenario related to SRTP, as
     this does not work (see above
   - 23.11.06, StW: added informative reference to H.241
   - 27/29.11.06, YkW: editorial changes throughout the document
   - 27/29.11.06, YkW: alignment with the SVC specification
   - 19.12.06, TS:
     TS: [SVC] is now the complete Joint Draft of H.264
     TS: Removed SSRC Multiplexing
     TS: Changed use cases for MANE as a translator
     TS: Editorials throughout the document, alignment with SVC spec.
   - 20-28.12.06, StW/TS/YkW: editorial changes throughout the
     document

>From draft-ietf-avt-rtp-svc-00 to draft-ietf-avt-rtp-svc-01
   - 23.02.07, YkW/Miska Hannuksela: Added enhancements to PACSI NAL
     unit
   - 01.03.07, Jonathan Lennox/YkW: Added recommendatory packetization
     rules for SEI messages and non-VCL NAL units
   - 05.03.07, Thomas Wiegand/YkW: Added the fields of picture start,
     picture end, and Tl0PicIdx to PACSI NAL unit
   - 05.03.07, TS: Draft conforms to new I-D style






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