Network Working Group S. Wenger Internet-Draft Y.-K. Wang Intended status: Standards Track Nokia Expires: January 09, 2008 T. Schierl Fraunhofer HHI July 09, 2007 RTP Payload Format for SVC Video draft-ietf-avt-rtp-svc-02.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 09, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Internet-Draft RTP Payload Format for SVC Video July 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. The RTP payload format allows for packetization of one or more Network Abstraction Layer (NAL) units, produced by the video encoder, in each RTP payload. The payload format has wide applicability, such as low bit-rate conversational, Internet video streaming, or high bit-rate entertainment quality video. Wenger, Wang, Schierl Expires January 09, 2008 [page 2] Internet-Draft RTP Payload Format for SVC Video July 2007 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........................................................11 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............................13 5.2. Abbreviations.............................................14 6. RTP Payload Format...........................................14 6.1. Design Principles.........................................14 6.2. RTP Header Usage..........................................15 6.3. Common Structure of the RTP Payload Format................15 6.4. NAL Unit Header Usage.....................................15 6.5. Packetization Modes.......................................16 6.6. Decoding Order Number (DON)...............................17 6.7. Aggregation Packets.......................................17 6.8. Fragmentation Units (FUs).................................18 6.9. Payload Content Scalability Information (PACSI) NAL Unit..18 7. Packetization Rules..........................................22 8. De-Packetization Process (Informative).......................23 9. Payload Format Parameters....................................23 9.1. MIME Registration.........................................24 9.2. SDP Parameters............................................26 9.2.1. Mapping of MIME Parameters to SDP.........................26 9.2.2. Usage with the SDP Offer/Answer Model.....................26 9.2.3. Usage with Session multiplexing...........................26 9.2.4. Usage in Declarative Session Descriptions.................27 9.3. Examples..................................................27 9.4. Parameter Set Considerations..............................27 10. Security Considerations......................................27 11. Congestion Control...........................................27 12. IANA Consideration...........................................28 Wenger, Wang, Schierl Expires January 09, 2008 [page 3] Internet-Draft RTP Payload Format for SVC Video July 2007 13. Informative Appendix: Application Examples...................28 13.1. Introduction..............................................28 13.2. Layered Multicast.........................................29 13.3. Streaming of an SVC scalable stream.......................30 13.4. Multicast to MANE, SVC scalable stream to endpoint........30 13.5. Scenarios currently not considered for complexity reasons.32 13.6. Scenarios currently not considered for being unaligned with IP philosophy.....................................................33 13.7. SSRC Multiplexing.........................................34 14. References...................................................35 14.1. Normative References......................................35 14.2. Informative References....................................36 15. Author's Addresses...........................................36 16. Copyright Statement..........................................37 17. Disclaimer of Validity.......................................37 18. Intellectual Property Statement..............................37 19. Acknowledgement..............................................38 20. RFC Editor Considerations....................................38 21. Open Issues..................................................38 22. Changes Log..................................................38 Wenger, Wang, Schierl Expires January 09, 2008 [page 4] Internet-Draft RTP Payload Format for SVC Video July 2007 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 coding standard, known as Scalable Video Coding (SVC). Formally, SVC takes the form of Amendment 3 to ISO/IEC 14496 Part 10 [MPEG4-10], and ITU-T Rec. H.264 [H.264]. The current specification of SVC is available in [SVC]. In this memo, SVC is used as an acronym for the mentioned scalable extension of H.264/AVC as defined in the new Annex G of ISO/IEC 14496 Part 10 and ITU-T Rec. H.264. 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 format [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 that bit the value of 1 (On). Clearing a bit is the same as assigning that bit the value of 0 (Off). Wenger, Wang, Schierl Expires January 09, 2008 [page 5] Internet-Draft RTP Payload Format for SVC Video July 2007 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 profiles of H.264 as defined in Annex A of [H.264], and one or more enhancement layers, denoted as Layers. A Layer may be the base Layer or enhance the temporal resolution (i.e. the frame rate), the spatial resolution, or the quality of the video content, relative to the quality represented without the Layer. Note, that the definition of Layer in this memo encompasses temporal, spatial and fidelity enhancements. Each RTP session can carry NAL units belonging to one or more Layers. The NAL unit headers include information associating a given NAL unit to a Layer. Therefore, extracting individual Layers from an RTP session 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 sessions, regardless of whether they carry a single Layer or multiple Layers as discussed above, can meaningfully be used to transport the whole scalable bitstream, or Operation Points thereof. An Operation Point consists of only those Layers necessary to reconstruct a given quality (in temporal, spatial and fidelity dimensions). 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. Within one access unit, a coded picture representing an Operation Point consists of all the coded slices required for decoding up to a particular Layer at the time instance corresponding to the access unit. The Network Abstraction Layer (NAL) encapsulates each slice generated by the VCL into one or more Network Abstraction Layer Units (NAL units). Please consult RFC Wenger, Wang, Schierl Expires January 09, 2008 [page 6] Internet-Draft RTP Payload Format for SVC Video July 2007 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 profiles conforming to Annex A of [H.264] already support 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 scalability information within the NAL unit header, or prefix NAL units, as discussed in section 3.3 of this memo and in [SVC]. 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 Layers, is denoted as spatial scalability or Signal-to-Noise Ratio (SNR) scalability, the latter is also know as Coarse-Grained Scalability (CGS). This is what is commonly understood as scalability in the IETF community. In addition, SVC also offers the concept another type of SNR scalability, the Medium- Grained Scalability (MGS). MGS involves selectively omitting the reconstruction of NAL units belonging to the MGS layer. The selection of the NAL units to omit can be based on fixed length fields in the NAL unit header. 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. In SVC, pictures from different layers, defined as layer representations in [SVC] (Note: A layer representation in [SVC] is identified by a single value of dependency_id and a single value of Wenger, Wang, Schierl Expires January 09, 2008 [page 7] Internet-Draft RTP Payload Format for SVC Video July 2007 quality_id), may use the same sequence or picture parameter set, but may also use different sequence or picture parameter sets. If different sequence parameter sets are used, then, at any time instant during the decoding process, there may be one active sequence parameter set (for the layer representation with the highest dependency_id) and one or more active layer sequence parameter set(s) (for lower layer representations). Any specific active sequence parameter set and active layer 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 (type 20) consists of a header of four octets and the payload byte string. It encapsulates VCL data as defined in Annex G of [SVC]. A special type of an SVC NAL unit is the prefix NAL unit (type 14) that includes descriptive information of the following NAL unit. SVC extends the NAL unit header defined for NAL units conforming to profiles defined in Annex A of [H.264] by three additional octets. 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 other fields as discussed below. This RTP payload specification is designed to be unaware of the octet 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 defined for NAL units conforming to Wenger, Wang, Schierl Expires January 09, 2008 [page 8] Internet-Draft RTP Payload Format for SVC Video July 2007 profiles defined in Annex A of [H.264] and [RFC3984], while the semantics have changed slightly, in a backward compatible way): +---------------+ |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 future 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 reference pictures, or that the NAL unit contains parameter sets. 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 14, 15 and 20 have been reserved for future extensions. SVC is using these three NAL unit types. NAL unit type 14 is used for the prefix NAL unit, NAL unit type 15 is used for SVC sequence parameter sets and NAL unit type 20 is used for coded slice in scalable extension (see section 7.4.1 in [SVC]). NAL unit types 14 and 20 indicate the presence of three additional octets in the NAL unit header, 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| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |R|I| PRID |N| DID | QID | TID |U|D|O| RR| Wenger, Wang, Schierl Expires January 09, 2008 [page 9] Internet-Draft RTP Payload Format for SVC Video July 2007 +---------------+---------------+---------------+ R: 1 bit reserved_one_bit. Reserved bit for future extension. R MUST be equal to one. I: 1 bit idr_flag. This component specifies whether the layer picture is an instantaneous decoding refresh (IDR) layer picture (when equal to 1) or not (when equal to 0). PRID: 6 bits priority_id. This flag specifies a priority identifier for the NAL unit. A lower value of PRID indicates a higher priority. N: 1 bit no_inter_layer_pred_flag. This flag specifies, when present in a coded slice NAL unit, whether inter-layer prediction may be used for decoding the coded slice (when equal to 1) or not (when equal to 0). DID: 3 bits dependency_id. This component denotes the inter-layer coding dependency hierarchy. At any access unit, a layer picture with a less dependency_id may be used for inter-layer prediction for coding of a layer picture with a greater dependency_id, while a layer picture with a greater dependency_id shall not be used for inter- layer prediction for coding of a layer picture with a less dependency_id. QID: 4 bits quality_id. This component designates the quality level hierarchy of a MGS layer picture. At any access unit and with identical dependency_id value, a layer picture with quality_id equal to ql uses a layer picture with quality_id equal to ql-1 for inter-layer prediction. TID: 3 bits temporal_id. This component indicates the temporal layer (or frame rate) hierarchy. Informally put, a layer consisted of pictures with a less temporal_id has a lower frame rate. A given temporal layer Wenger, Wang, Schierl Expires January 09, 2008 [page 10] Internet-Draft RTP Payload Format for SVC Video July 2007 typically depends on the lower temporal layers (i.e. the temporal layers with less temporal_id) but never depends on any higher temporal layer. U: 1 bit use_ref_base_pic_flag. A value of 1 indicates that only reference base pictures are used during the inter prediction process. A value of 0 indicates that the reference base pictures are not used during the inter prediction process. D: 1 bit discardable_flag. A value of 1 indicates that the current NAL unit is not used for decoding NAL units of the current access unit and all subsequent access units that have a greater value of dependency_id than the current NAL unit. Such NAL units can be discarded without risking the integrity of higher layers with greater dependency_id. discardable_flag equal to 0 indicates that the decoding of the NAL unit is required to maintain the integrity of higher layers with greater dependency_id. O: 1 bit output_flag: Affects the decoded picture output process as defined in Annex C of [SVC]. RR: 2 bits reserved_three_2bits. Reserved bits for future extension. RR MUST be equal to three. 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, I, PRID, DID, QID, TID, U, and D 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 Wenger, Wang, Schierl Expires January 09, 2008 [page 11] Internet-Draft RTP Payload Format for SVC Video July 2007 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 This document uses the definitions of [SVC]. The following terms, defined in [SVC], are summed up for convenience: scalable bitstream: A bitstream with the property that one or more bitstream subsets that are not identical to the scalable bitstream form another bitstream that conforms to the SVC specification. prefix NAL unit: A NAL unit with nal_unit_type equal to 14 that immediately precedes a NAL unit with nal_unit_type equal to 1, 5, or 12. The NAL unit that succeeds the prefix NAL unit is also referred to as the associated NAL unit. The prefix NAL unit contains data associated with the associated NAL unit, which are considered to be part of the associated NAL unit. 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. Wenger, Wang, Schierl Expires January 09, 2008 [page 12] Internet-Draft RTP Payload Format for SVC Video July 2007 IDR access unit: An access unit in which the layer picture with the maximum present value of dependency_id is an IDR picture. IDR picture: A coded picture in which all slices with the maximum present value of dependency_id within the access unit are I or EI slices that causes the decoding process to mark all reference pictures as "unused for reference" immediately after decoding the IDR picture. After the decoding of an IDR picture all following coded pictures in decoding order can be decoded without inter prediction from any picture decoded prior to the IDR picture. The first picture of each coded video sequence is an IDR picture. 5.1.2. Definitions local to this memo Layer: A Layer may be the base Layer or an enhancement Layer that enhances the temporal resolution (i.e. the frame rate), the spatial resolution, or the quality of the video content, relative to the quality represented without the Layer. base Layer: The base Layer is typically representing the minimal spatial resolution, the minimal fidelity, and the minimal frame rate of an SVC bitstream. In other words, the base Layer consists of all the VCL NAL units with dependency_id, quality_id and temporal_level equal to 0 and the associated non-VCL NAL units. The bitstream containing the base Layer and the temporal enhancement Layers with dependency_id and quality_id both equal to 0, which is referred as the full base Layer, must only contain NAL units conforming to profiles defined in Annex A of [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 prefix NAL unit, which has a four bytes NAL unit header containing all the syntax elements described in section 3.3. Note that this definition is different from the definition of "base layer" in Annex G of [SVC]. enhancement Layer: An SVC enhancement Layer is identified by temporal_level, dependency_id, and quality_level as defined in Annex G of [SVC] and summarized in section 3.3. Wenger, Wang, Schierl Expires January 09, 2008 [page 13] Internet-Draft RTP Payload Format for SVC Video July 2007 Operation Point: An Operation Point of a SVC bitstream represents a certain level of temporal, spatial and quality scalability. An Operation Point contains only those NAL units required for restoring a valid bitstream (conforming to profiles defined in Annex A or Annex G of [SVC]) to represent a certain quality. The Operation Point is described by the maximum present value of dependency_id, and, within that maximum present value of dependency_id, by the maximum quality_id and temporal_id. 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. 5.2. Abbreviations In addition to the abbreviations defined in [RFC3984], the following ones are defined. CGS: Coarse-Grain Scalability MGS: Medium-Grain Scalability 6. RTP Payload Format 6.1. Design Principles The following design principles have been observed: o Backward compatibility with [RFC3984] wherever possible. o As the SVC full base Layer is H.264/AVC compatible, we assume the full base Layer or any subset (when transmitted in its own session) to be Wenger, Wang, Schierl Expires January 09, 2008 [page 14] Internet-Draft RTP Payload Format for SVC Video July 2007 encapsulated using [RFC3984]. Requiring this has the desirable side effect that it can be used by [RFC3984] 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. 6.2. RTP Header Usage Please see section 5.1 of [RFC3984]. The following applies in addition. 6.3. Common Structure of the RTP Payload Format Please see section 5.2 of [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, I, PRID, DID, QID, TID, U, and D according to this specification. The semantics of F specified in section 5.3 of [RFC3984] also applies herein. For NRI, for the bitstream containing NAL units conforming with profiles defined in Annex A of [H.264] and transported using [RFC3984], the semantics specified in section 5.3 of [RFC3984] are applicable, i.e., NRI also indicates the relative importance of NAL Wenger, Wang, Schierl Expires January 09, 2008 [page 15] Internet-Draft RTP Payload Format for SVC Video July 2007 units. In SVC context, only the semantics specified in Annex G of [SVC] are applicable, i.e., NRI does not indicate the relative importance of NAL units. For I, in addition to the semantics specified in Annex G of [SVC], according to this memo, MANEs MAY use this information to protect NAL units with I equal to 1 better than NAL units with I equal to 0. MANEs MAY also utilize information of NAL units with I equal to 1 to decide when to forward more packets for an RTP session. For PRID, the semantics specified in Annex G of [SVC] applies. Note, that 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 DID, QID, TID, in addition to the semantics specified in Annex G of [SVC], according to this memo, values of DID, QID, or TID indicate the relative importance in their respective dimension. A lower value of DID, QID, or TID indicates a higher importance if the other two components are identical. MANEs MAY use this information to protect more important NAL units better than less important NAL units. For U, in addition to the semantics specified in Annex G of [SVC], according to this memo, MANEs MAY use this information to protect NAL units with U equal to 1 better than NAL units with U equal to 0. For D, in addition to the semantics specified in Annex G of [SVC], according to this memo, MANEs MAY use this information to determine whether a given NAL unit is required for successfully decoding a certain Operation Point of the SVC bitstream, hence to decide whether to forward the NAL unit. 6.5. Packetization Modes Please see section 5.4 of [RFC3984]. The single NAL unit packetization mode SHALL NOT be used. Wenger, Wang, Schierl Expires January 09, 2008 [page 16] Internet-Draft RTP Payload Format for SVC Video July 2007 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 [RFC3984]. The following applies in addition. When different layers of a SVC bitstream are transported in more than one RTP session, 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 sessions. When more than one RTP session is used to convey an Operation Point of a SVC bitstream, 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. [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. Aggregation Packets Wenger, Wang, Schierl Expires January 09, 2008 [page 17] Internet-Draft RTP Payload Format for SVC Video July 2007 Please see section 5.7 of [RFC3984]. 6.8. Fragmentation Units (FUs) Please see section 5.8 of [RFC3984]. 6.9. 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, a 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. Note that the NAL unit type for the PACSI NAL unit is selected among those values that are unspecified in [SVC] and [RFC3984]. 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 (MTAP), the decoding order number (DON) for the PACSI NAL unit MUST be set to indicate either 1) the PACSI NAL unit is the first NAL unit in decoding order among the NAL units in the aggregation packet or 2) the PACSI NAL unit has an identical DON to the first NAL unit in decoding order among the remaining NAL units in the aggregation packet. The structure of a PACSI NAL unit is as follows. The first four octets are exactly the same as the four-byte SVC NAL unit header as discussed in section 3.3. They are 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 Wenger, Wang, Schierl Expires January 09, 2008 [page 18] Internet-Draft RTP Payload Format for SVC Video July 2007 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 |R|I| PRID |N| DID | QID | TID |U|D|O| RR| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |A|T|P|C|S|E|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. o The Type field MUST be set to 30. o The R bit MUST be set to 1. o The I bit MUST be set to 1 if the I bit of at least one of the remaining NAL units in the payload is equal to 1. Otherwise, the I bit MUST be set to 0. Wenger, Wang, Schierl Expires January 09, 2008 [page 19] Internet-Draft RTP Payload Format for SVC Video July 2007 o The PRID field MUST be set to the lowest value of the PRID values of all the remaining NAL units in the payload. o The N bit MUST be set to 1 if the N bit of all the remaining NAL units in the payload is equal to 1. Otherwise, the N bit MUST be set to 0. o The DID field MUST be set to the lowest value of the DID values of all the remaining NAL units in the payload. o The QID field MUST be set to the lowest value of the QID values of all the remaining NAL units with the lowest value of DID in the payload. o The TID field MUST be set to the lowest value of the TID values of all the remaining NAL units with the lowest value of DID in the payload. o The U bit MUST be set to 1 if the U bit of at least one of 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 of all the remaining NAL unit in the payload is equal to 0. Otherwise, the D bit MUST be set to 1. o The O bit MUST be set to 1 if the O bit of at least one of the remaining NAL units in the payload is equal to 1. Otherwise, the O bit MUST be set to 0. o The RR field MUST be set to be equal to 3. o The A bit MUST be set to 1 if all the layer pictures containing the target NAL units are anchor pictures. Otherwise, the A bit 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 layer picture that, if Wenger, Wang, Schierl Expires January 09, 2008 [page 20] Internet-Draft RTP Payload Format for SVC Video July 2007 decoding of the layer starts from the layer picture, all the following layer pictures of the layer, in output order, can be correctly decoded. Informative note: An anchor picture is a random access point to the layer the anchor picture belongs to. However, some layer pictures succeeding an anchor picture in decoding order but preceding the anchor picture in output order may refer to earlier layer pictures hence may not be correctly decoded, if random access is performed at the anchor picture. o The T bit MUST be set to 1 if all the layer pictures containing the target NAL units (as defined above) are temporal scalable layer switching points. Otherwise, the T bit MUST be set to 0. For a temporal scalable layer switching point, all the layer pictures with the same value of temporal_id at and after the switching point in decoding order do not refer to any layer picture with the same value of temporal_id preceding the switching point in decoding order. o The P bit MUST be set to 1 if all the layer pictures containing the target NAL units (as defined above) are redundant pictures. Otherwise, the P bit MUST be set to 0. o The C bit MUST be set to 1 if the layer picture that has the greatest value of dependency_id among all the layer pictures containing the target NAL units (as defined above) is an intra picture, i.e., the layer picture does not refer to any earlier layer picture in decoding order in the same layer. Otherwise, the C bit MUST be set to 0. o The S bit MUST be set to 1, if the first VCL NAL unit of the layer picture containing the first target NAL unit (as defined above) in decoding order is present in the payload. Otherwise, the S bit MUST be set to 0. o The E bit MUST be set to 1, if the last VCL NAL unit of the layer picture containing the first target NAL unit (as defined above) in decoding order is present in the payload. Otherwise, the E field MUST be set to 0. Wenger, Wang, Schierl Expires January 09, 2008 [page 21] Internet-Draft RTP Payload Format for SVC Video July 2007 o The RES field MUST be set to 0. o The TL0PICIDX field specifies either an identifier for the layer picture containing the first target NAL unit (as defined above) when TL of the layer picture is equal to 0, or the identifier of the most recent layer picture of TID equal to 0 in decoding order, when TID of the layer picture containing the first target NAL unit is greater than 0. If the bitstream contains no earlier access unit than the access unit containing the target NAL units in decoding order with TID 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 TID equal to 0. If TID is equal to 0, the field TL0PICIDX MUST be equal to ( prevTL0FrameIdx + 1 ) % 256. Otherwise (TID is greater than 0), TL0PICIDX MUST be equal to prevTL0FrameIdx. SEI NAL units included in the PACSI NAL unit, if any, MUST contain a subset of the SEI messages associated with 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 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 NAL unit and included in one of the NAL units contained in the same packet at the same time. 7. Packetization Rules Please see section 6 of [RFC3984]. The following rules apply in addition. The single NAL unit mode SHALL NOT be used. (See also section 6.5 for the motivation). Wenger, Wang, Schierl Expires January 09, 2008 [page 22] Internet-Draft RTP Payload Format for SVC Video July 2007 When a prefix NAL unit is encapsulated for transmission, it SHOULD be aggregated to the same transmission packet as the associated NAL unit following the prefix NAL unit in decoding order. Informative note: When either the prefix NAL unit or the associated NAL unit containing an H.264/AVC coded slice is lost, the remaining one would be hardly useful 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 [RFC3984]. The following rules apply in addition. To re-assemble a conforming NAL unit stream that has been conveyed in more than one RTP session, DON SHOULD be utilized to re-sequence NAL unit stemming from the different RTP sessions. 9. Payload Format Parameters [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." Wenger, Wang, Schierl Expires January 09, 2008 [page 23] Internet-Draft RTP Payload Format for SVC Video July 2007 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: 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. Wenger, Wang, Schierl Expires January 09, 2008 [page 24] Internet-Draft RTP Payload Format for SVC Video July 2007 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 Annex G of [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 DID, QID, and TID of the SVC NAL unit header, for one or more Layer(s) conveyed in one RTP session. A layer identification is a three character value base64 coded. If more than one Layer is transmitted within one RTP session, the layer identification value of each Layer MUST be itemized in order of decreasing importance, 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 Wenger, Wang, Schierl Expires January 09, 2008 [page 25] Internet-Draft RTP Payload Format for SVC Video July 2007 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. * 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 multiplexing Wenger, Wang, Schierl Expires January 09, 2008 [page 26] Internet-Draft RTP Payload Format for SVC Video July 2007 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 [RFC3984]. 10. Security Considerations Please see section 11 of [RFC3984]. 11. Congestion Control Within any given RTP session carrying payload according to this specification, the provisions of section 12 of [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) within the highest Layer identified by the DID field, utilize the TID and/or QID fields in the NAL unit header to drop NAL units with lower importance for the decoding process or human perception. b) drop all NAL units belonging to the highest enhancement Layer as identified by the highest DID value. c) dropping NAL units according to their importance for the decoding process, as indicated by the fields in the NAL unit header of the NAL units or in the prefix NAL units. d) dropping NAL units or entire packets not according to the aforementioned rules (media-unaware stream thinning). This Wenger, Wang, Schierl Expires January 09, 2008 [page 27] Internet-Draft RTP Payload Format for SVC Video July 2007 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. 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 Wenger, Wang, Schierl Expires January 09, 2008 [page 28] Internet-Draft RTP Payload Format for SVC Video July 2007 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. 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]. Wenger, Wang, Schierl Expires January 09, 2008 [page 29] Internet-Draft RTP Payload Format for SVC Video July 2007 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. 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. Wenger, Wang, Schierl Expires January 09, 2008 [page 30] Internet-Draft RTP Payload Format for SVC Video July 2007 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. 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 Wenger, Wang, Schierl Expires January 09, 2008 [page 31] Internet-Draft RTP Payload Format for SVC Video July 2007 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. 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 -- Wenger, Wang, Schierl Expires January 09, 2008 [page 32] Internet-Draft RTP Payload Format for SVC Video July 2007 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. 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 Wenger, Wang, Schierl Expires January 09, 2008 [page 33] Internet-Draft RTP Payload Format for SVC Video July 2007 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. 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 Wenger, Wang, Schierl Expires January 09, 2008 [page 34] Internet-Draft RTP Payload Format for SVC Video July 2007 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, its transport addresses needs to be manipulated. This, in turn, is incompatible with the mandatory authentication of RTCP RRs. As a result, there would be a 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 14496-10:2005. [H.264] ITU-T Recommendation H.264, "Advanced video coding for generic audiovisual services", Version 4, July 2005. [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-04 (work in progress), June 2007. [SVC] Joint Video Team, ''Joint Draft 11 of SVC Amendment'', available from http://ftp3.itu.ch/av-arch/jvt-site /2007_06_Geneva/JVT-X201.zip, Geneva, Switzerland, June 2007. [RFC3984] Wenger, S., Hannuksela, M, Stockhammer, T, Westerlund, M, Singer, D, ''RTP Payload Format for H.264 Video'', RFC 3984, February 2005. Wenger, Wang, Schierl Expires January 09, 2008 [page 35] Internet-Draft RTP Payload Format for SVC Video July 2007 [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 [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: +1-650-862-7368 Nokia Email: stewe@stewe.org 955 Page Mill Road Palo Alto, CA 94304 USA 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 Wenger, Wang, Schierl Expires January 09, 2008 [page 36] Internet-Draft RTP Payload Format for SVC Video July 2007 Einsteinufer 37 D-10587 Berlin Germany 16. Copyright Statement Full Copyright Statement Copyright (C) The IETF Trust (2007). 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 Wenger, Wang, Schierl Expires January 09, 2008 [page 37] Internet-Draft RTP Payload Format for SVC Video July 2007 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. 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 Wenger, Wang, Schierl Expires January 09, 2008 [page 38] Internet-Draft RTP Payload Format for SVC Video July 2007 - 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 >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 Wenger, Wang, Schierl Expires January 09, 2008 [page 39] Internet-Draft RTP Payload Format for SVC Video July 2007 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. 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 Wenger, Wang, Schierl Expires January 09, 2008 [page 40] Internet-Draft RTP Payload Format for SVC Video July 2007 - 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 >From draft-ietf-avt-rtp-svc-01 to draft-ietf-avt-rtp-svc-02 25-June-2007: TS Clarified definitions Layer, Operation Points, Removed FGS Aligned with JVT-W201 spec Use of DON in de-packetization Congestion control 25-June-2007: YkW Edit throughout the spec, aligned with JVT-X201 SVC spec 09-July-2007: TS Further modifications and alignments with JVT-X201. Wenger, Wang, Schierl Expires January 09, 2008 [page 41]