Audio/Video Transport WG Ari Lakaniemi Internet Draft Nokia Intended status: Standards track Expires: May 2008 November 12, 2007 RTP payload format for the ITU-T Embedded Variable Bit-Rate speech/audio codec draft-lakaniemi-avt-rtp-evbr-00.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 May 12, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document specifies the Real-Time Transport Protocol (RTP) payload format for the Embedded Variable Bit-Rate (EV-VBR) speech/audio codec. A media type registration for this RTP payload format is also included. Lakaniemi Expires May 12, 2008 [Page 1] Internet-Draft RTP payload for EV-VBR November 2007 Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Table of Contents 1. Introduction...................................................3 2. Background.....................................................3 2.1. EV-VBR codec..............................................3 2.2. Benefits of layered design................................4 2.3. Transmitting layered data.................................5 2.4. Scaling scenarios & rate control..........................5 3. EV-VBR RTP payload format......................................6 3.1. Payload Structure.........................................6 3.1.1. Payload Header.......................................6 3.1.2. EV-VBR transport blocks..............................7 3.2. Handling the Encoded data.................................9 3.3. CRC verification.........................................11 3.4. EV-VBR session...........................................12 3.5. RTP Header usage.........................................12 4. Codec bit-rate control........................................12 5. Payload Format Parameters.....................................14 5.1. Media Type Registration..................................15 5.2. Mapping to SDP Parameters................................16 5.3. Offer/answer considerations..............................17 5.4. Declarative usage of SDP.................................17 5.5. SDP examples.............................................18 6. Security Considerations.......................................19 7. Congestion control............................................20 8. IANA Considerations...........................................21 APPENDIX A: Payload examples.....................................22 A.1. Simple payload examples..................................22 A.1.1. All the layers in the same payload..................22 A.1.2. Layers in separate RTP streams......................23 A.2. Advanced examples........................................24 A.2.1. Different update rate for subset of layers..........24 A.2.2. Redundant frames with limited set of layers.........25 9. References....................................................26 9.1. Normative References.....................................26 9.2. Informative References...................................27 Author's Addresses...............................................27 Intellectual Property Statement..................................27 Disclaimer of Validity...........................................28 Lakaniemi Expires May 12, 2008 [Page 2] Internet-Draft RTP payload for EV-VBR November 2007 1. Introduction The International Telecommunication Union (ITU-T) recommendation G.xxx [ev-vbr] specifies the Embedded Variable Bit Rate (EV-VBR) speech/audio codec. This document specifies the Real-time Transport Protocol (RTP) [RFC3550] payload format for this codec. 2. Background 2.1. EV-VBR codec EV-VBR is an embedded variable rate speech codec having a layered design. This implies that the bitstream of the EV-VBR core codec consists of a core layer, denoted as L1, and four enhancement layers, denoted as L2-L5. The bit-rates of the EV-VBR core codec range from 8 kbit/s (core layer only) to 32 kbit/s (with all layers up to L5). Furthermore, the EV-VBR codec supports also discontinuous transmission (DTX) and comfort noise generation (CNG) by sending Silence Descriptor (SID) frames during periods of non-active input signal. The sampling frequency of the core codec is 16 kHz and the codec operates on 20 ms frames. Note that the EV-VBR codec is also capable of narrowband operation with audio input and/or output at 8 kHz sampling frequency. While transmitting/receiving the core layer L1 is enough for successful decoding of audio content, each of the enhancement layers Ln provides an improvement to reconstructed audio quality. Thus, the core layer ensures the basic communication while the enhancement layers can be used to improve the perceptual quality. Furthermore, enhancement layers are dependent on all the lower layers in a sense that successful decoding of layer n requires also all the layers m with mn MUST also be discarded. Lakaniemi Expires May 12, 2008 [Page 11] Internet-Draft RTP payload for EV-VBR November 2007 3.4. EV-VBR session An EV-VBR session consists of one or several RTP sessions carrying encoded EV-VBR data according the payload format specified in section 3.2. 3.5. RTP Header usage This section specifies the usage of some fields of the RTP header (specified in section 5 of [RFC3550]) with the EV-VBR RTP payload format. In case the EV-VBR session consists multiple RTP sessions, the RTP sessions are further separated by using different payload type (PT) values for each of the RTP streams. In case of all layers carried within a single RTP session there is need for only one PT. Note that the assignment of the PT number(s) for this payload format are outside the scope of this document. It is expected that the RTP profile under which this payload is used will either assign PT number(s) for this encoding or specify the PT number(s) to be dynamically assigned. Each of the RTP sessions involved in the EV-VBR session SHALL use the same SSRC value. The RTP timestamp corresponds to the sampling instant of the first encoded sample of the earliest frame in the payload. The timestamp clock frequency is 32 kHz. All RTP streams involved in the session SHALL use the same timestamp space. The marker bit (M) of each of the RTP streams of the session SHALL be set to value 1 if the payload carries an EDU belonging to the first speech frame after an inactive period, i.e. an EDU from the first speech frame of a talkspurt. For all other packets the marker bit is set to value 0. 4. Codec bit-rate control The media parameters defined in section 5.1 can be used to negotiate/declare the employed layer configuration by defining the lowest and highest layer numbers for each employed RTP session. The highest layer defined for the session specifies the initial maximum bandwidth, which cannot be changed without a session re-negotiation or codec bit-rate control signaling during the session. The codec bit-rate control during a session can be performed by instructing the transmitter in the far-end to change the layer Lakaniemi Expires May 12, 2008 [Page 12] Internet-Draft RTP payload for EV-VBR November 2007 configuration it is encoding/sending. In case of an EV-VBR session consisting of single RTP session this will change the size of the inbound payloads, whereas in case of an EV-VBR session employing multiple RTP sessions either the number of streams will change and/or the configuration of the streams carrying the highest layers will change. The codec bit-rate control request to the far-end transmitter is sent by using an application-defined RTCP packet, as specified below. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |V=2|P| subtype | PT=APP=204 | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SSRC/CSRC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | name (ASCII) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | padding | SWB |Stereo | ML | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The V, P, PT, length and SSRC/CSRC fields are used as specified in section 6.7 of [RFC3550]. The rest of the fields are used as defined below. subtype SHALL be set to zero by the sender and ignored by the receiver. name SHALL be set to value "EV-VBR configuration". padding SHALL be set to zero by the sender and ignored by the receiver. SWB Indicates the super-wideband configuration the sender of this packet would like to receive. Value 0 indicates that the sender of this packet would not like to receive the super-wideband option. Other values are T.B.D. Stereo Lakaniemi Expires May 12, 2008 [Page 13] Internet-Draft RTP payload for EV-VBR November 2007 Indicates the stereo configuration the sender of this packet would like to receive. Value 0 indicates that the sender of this packet would not like to receive the stereo option. Other values are T.B.D. ML Indicates the number of the highest layer of the core codec the sender of this packet wishes to receive. The valid values of ML are in the range from 1 to 5. Other values are reserved for future use. The receiver MUST ignore invalid values. A transmitter that has received a codec bit-rate control request SHOULD start using the requested mode configuration as soon as possible. The transmitter MAY transmit fewer layers than requested. The codec bit-rate control request is valid until the next request is received. Thus, a transmitter that has received a codec bit-rate control request message SHOULD follow the most recent request until a new request is received. This APP packet can be included in a compound RTCP packet or it can be send using the non-compound RTCP approach (FFS). Author's note: One alternative method would be to use in-band signaling, e.g. by adding one byte to the payload header including the similar information as defined for the application- dependent part of the APP packet specified above. However, although effective, this would be a non-desirable (i.e. "non- RTP") way to do it. Author's note: Further alternatives include exploitation of existing codec bit-rate control mechanisms. One possibility would be to use the TIMBR message defined as part of the Codec Control Messages (CCM) [ccm] for codec bit-rate control. Another possibility could be to specify a new dedicated feedback message within Audio/Video Profile with Feedback (AVPF) [RFC4585] framework. However, in both this scenarios the codec bit-rate control would be available only when using the AVPF profile. 5. Payload Format Parameters This section defines the parameters that may be used to configure optional features in the EV-VBR RTP transmission. The parameters are defined here as part of the media subtype registration for the EV-VBR codec. Mapping of the parameters into Lakaniemi Expires May 12, 2008 [Page 14] Internet-Draft RTP payload for EV-VBR November 2007 the Session Description Protocol (SDP) [RFC4566] is also provided for those applications that use SDP. In control protocols that do not use MIME or SDP, the media type parameters must be mapped to the appropriate format used with that control protocol. 5.1. Media Type Registration This registration is done using the template defined in RFC 4288 [RFC4288] and following RFC 4855 [RFC4855]. Type name: audio Subtype name: EV-VBR Required parameters: none Optional parameters: layers: The numbers of the layers (in range from 1 to 5, denoting layers from L1 to L5, respectively) transmitted in this session, expressed as comma- separated list of layer numbers. If the parameter is present, at least layer L1 MUST be included in the list of layers (at least?) in one of the RTP sessions included in the EV-VBR session. If the parameter is not present, all layers up to layer L5 MAY be used in the session. ptime: the recommended length of time (in milliseconds) represented by the media in a packet. See Section 6 of [RFC4566]. maxptime: the maximum length of time (in milliseconds) that can be encapsulated in a packet. See Section 6 of [RFC4566] Author's note: Some further study needed to see if separate parameters for sending and receiving capabilities/preferences are needed -- especially for upcoming stereo and SWB options. Author's note: The support for upcoming SWB and stereo options needs to be taken into account. Basically we can either 1) extend the parameter "layers" to cover also this aspect, or 2) define separate parameter(s) for these new options when more details on the stereo/SWB support are available. Encoding considerations: Lakaniemi Expires May 12, 2008 [Page 15] Internet-Draft RTP payload for EV-VBR November 2007 This media type is framed and contains binary data; see Section 4.8 of [RFC4288]. Security considerations: See Section 6 of RFC xxxx Interoperability considerations: none Published specification: RFC xxxx Applications which use this media type: For example Voice over IP, audio and video conferencing, audio streaming and voice messaging. Additional information: none Person & email address to contact for further information: Ari Lakaniemi, ari.lakaniemi@nokia.com Intended usage: COMMON Restrictions on usage: This media type depends on RTP framing, and hence is only defined for transfer via RTP [RFC3550] Author: Ari Lakaniemi, ari.lakaniemi@nokia.com Change controller: IETF Audio/Video Transport working group delegated from the IESG 5.2. Mapping to SDP Parameters The information carried in the media type specification has a specific mapping to fields of the SDP [RFC4566], which is commonly used to describe RTP sessions. When SDP is used to specify sessions employing the EV-VBR codec, the mapping is as follows: o The media type ("audio") goes in SDP "m=" as the media name. Lakaniemi Expires May 12, 2008 [Page 16] Internet-Draft RTP payload for EV-VBR November 2007 o The media subtype ("EV-VBR") goes in SDP "a=rtpmap" as the encoding name. The RTP clock rate in "a=rtpmap" MUST be 32000 for EV-VBR. Author's note: The current choice for the RTP clock rate is a 'placeholder'. The clock rate needs to be set according to SWB sampling rate, which is still T.B.D. Since the core codec employs 16000 Hz sampling rate, an integer multiple of 16000 Hz seems a preferable choice. o The parameters "ptime" and "maxptime" go in the SDP "a=ptime" and "a=maxptime" attributes, respectively. o Any remaining parameters go in the SDP "a=fmtp" attribute by copying them directly from the media type string as a semicolon separated list of parameter=value pairs. 5.3. Offer/answer considerations The following considerations apply when using the SDP offer/answer [RFC3264] mechanism to negotiate the EV-VBR transport. The parameter "layers" MAY be used to indicate the layer configuration for the each RTP session belonging to current EV-VBR session an end-point making the offer is ready to transmit and wishes to receive. o In case the EV-VBR session consists of a single RTP session, it is RECOMMENDED not to impose any layer restrictions for the session but to use the rate control functionality to set possible restrictions on usage of the higher/st layers. If the offer includes a layer configuration parameter, the answer MAY use different configuration, but the highest layer in the answer MUST NOT be higher than the highest layer of the offered configuration. Author's note: Support for answer modifying the layer configuration is FFS. In case the EV-VBR session consists of multiple RTP sessions, the answer MUST use the layer configurations provided in the offer for the sessions it accepts. 5.4. Declarative usage of SDP In declarative usage, such as SDP in RTSP [RFC2326] or SAP [RFC2974], the parameter "layers" SHALL be interpreted to provide a set of layers that the sender may use in the session. Lakaniemi Expires May 12, 2008 [Page 17] Internet-Draft RTP payload for EV-VBR November 2007 5.5. SDP examples Some example SDP session descriptions utilizing EV-VBR encodings are provided below. The first example illustrates the simple case where the EV-VBR session employing a single RTP session and the AVPF profile is offered, and the answer accepts the offer without any changes. Offer: m=audio 49120 RTP/AVPF 97 a=rtpmap:97 EV-VBR/32000/1 Answer: m=audio 49120 RTP/AVPF 97 a=rtpmap:97 EV-VBR/32000/1 The second example shows a bit more complex case where the EV-VBR session using a single RTP session and the AVPF profile is offered with restriction to send/receive only with layers L1 and L2. The answer indicates that the other end-point is happy to receive (and send) layers up to L5. Offer: m=audio 49120 RTP/AVPF 97 a=rtpmap:97 EV-VBR/32000/1 a=fmtp:97 layers=1,2 Answer: m=audio 49120 RTP/AVPF 97 a=rtpmap:97 EV-VBR/32000/1 a=fmtp:97 layers=1,2,3,4,5 The third example shows an EV-VBR session using multiple RTP sessions with the AVPF profile. The answerer wishes to use only layers up to L3. Offer: Lakaniemi Expires May 12, 2008 [Page 18] Internet-Draft RTP payload for EV-VBR November 2007 m=audio 49120 RTP/AVPF 97 a=rtpmap:97 EV-VBR/32000/1 a=fmtp:97 layers=1,2 a=mid=1 m=audio 49122 RTP/AVPF 98 a=rtpmap:98 EV-VBR/32000/1 a=fmtp:98 layers=3 a=mid=2 a=depend:lay 1 m=audio 49124 RTP/AVPF 99 a=rtpmap:99 EV-VBR/32000/1 a=fmtp:99 layers=4,5 a=mid=3 a=depend:lay 1 2 Answer: m=audio 49120 RTP/AVPF 97 a=rtpmap:97 EV-VBR/32000/1 a=fmtp:97 layers=1,2 a=mid=1 m=audio 49120 RTP/AVPF 98 a=rtpmap:98 EV-VBR/32000/1 a=fmtp:98 layers=3 a=mid=2 a=depend:lay 1 Note that the dependency signaling according to [smd-sdp] is used in the third example above to indicate the relationship between the layers distributed into separate RTP sessions. 6. Security Considerations RTP packets using the payload format defined in this specification are subject to the security considerations discussed in the RTP specification [RFC3550], and in any appropriate RTP profile (for example [RFC3551] or [RFC4585]). This implies that confidentiality of the media streams is achieved by encryption; for example, through the application of SRTP [RFC3711]. Because the data compression used with this payload format is applied end-to-end, any encryption needs to be performed after compression. A potential denial-of-service threat exists for data encodings using compression techniques that have non-uniform receiver-end Lakaniemi Expires May 12, 2008 [Page 19] Internet-Draft RTP payload for EV-VBR November 2007 computational load. The attacker can inject pathological datagrams into the stream that will increase the processing load of the decoder and may cause the receiver to be overloaded. For example inserting additional EDUs representing the higher enhancement layers on top of the ones actually transmitted may increase the decoder load. However, the EV-VBR codec is not particularly vulnerable to such an attack, since the majority of the computational load in an EV-VBR session is associated to the encoder. Another form of possible attach might be forging of codec bit-rate control messages, which may result in encoder operating employing higher number of enhancement layers than originally intended and thereby requiring larger amount of computation resources. Therefore, the usage of data origin authentication and data integrity protection of at least the RTP packet is RECOMMENDED; for example, with SRTP [RFC3711]. Note that the appropriate mechanism to ensure confidentiality and integrity of RTP packets and their payloads is very dependent on the application and on the transport and signaling protocols employed. Thus, although SRTP is given as an example above, other possible choices exist. Note that end-to-end security with either authentication, integrity or confidentiality protection will prevent a network element not within the security context from performing media-aware operations other than discarding complete packets. To allow any (media-aware) intermediate network element to perform its operations, it is required to be a trusted entity which is included in the security context establishment. 7. Congestion control As scalable codec EV-VBR implicitly provides means for congestion control by providing a possibility for 'thinning' the bitstream. The RTP payload format according to this specification provides several different means for reducing the EV-VBR session bandwidth. The most appropriate mechanism (in terms of impact to the user experience) depends on the employed payload structure and also on the employed session configuration (single RTP session or multiple RTP sessions). The following means (in no particular order) can be used to assist congestion control procedures -- either by the sender or by the intermediate node. o The transport blocks carrying the EDUs representing the highest layers within the payload may be dropped. o The payloads carrying the EDUs representing the highest layers in an EV-VBR session are dropped. Lakaniemi Expires May 12, 2008 [Page 20] Internet-Draft RTP payload for EV-VBR November 2007 o Transport blocks or payloads carrying EDUs belonging to redundant frames included in the payload are dropped. 8. IANA Considerations IANA is kindly requested to register a media type for the EV-VBR codec for RTP transport, as specified in section 5.1 of this document. Lakaniemi Expires May 12, 2008 [Page 21] Internet-Draft RTP payload for EV-VBR November 2007 APPENDIX A: Payload examples The EV-VBR payload structure enables flexible transport either by carrying all layers in the same payload or separating the layers into separate payloads. The following subsections illustrate different possibilities for transport by simple examples. Note that examples do not show the full payload structure to keep the illustration simple. A.1. Simple payload examples A.1.1. All the layers in the same payload The illustration below shows layers L1-L3 from two encoded frames encapsulated into separate payloads using single transport block. +-------+--------+-----+------+------+------+ | RTP1 | L-ID=3 |NF=1 |F1-L1 |F1-L2 |F1-L3 | +-------+--------+-----+------+------+------+ +-------+--------+-----+------+------+------+ | RTP2 | L-ID=3 |NF=1 |F2-L1 |F2-L2 |F3-L3 | +-------+--------+-----+------+------+------+ In case the same layers from two input frames are encapsulated into one payload using single transport block, the structure is as shown below. +-------+--------+-----+------+------+------+------+------+------+ | RTP1 | L-ID=3 |NF=2 |F1-L1 |F2-L1 |F1-L2 |F2-L2 |F3-L3 |F2-L3 | +-------+--------+-----+------+------+------+------+------+------+ The third example illustrates the case where the layers L1-L3 from two input frames are encapsulated into one payload using two separate transport blocks, the first one carrying L1 and the other one containing L2 and L3. Lakaniemi Expires May 12, 2008 [Page 22] Internet-Draft RTP payload for EV-VBR November 2007 +-------+--------+-----+------+------+ | RTP1 | L-ID=1 |NF=2 |F1-L1 |F2-L1 | +-------+--------+-----+------+------+------+------+ | L-ID=7 |NF=2 |F1-L2 |F2-L2 |F3-L3 |F2-L3 | +--------+-----+------+------+------+------+ A.1.2. Layers in separate RTP streams In this case the data for each layer is transmitted in its own payload. In the first example each transport block including a single EDU is carried in its own RTP payload. +-------+--------+-----+-----+ +-------+--------+-----+-----+ | RTP1a | L-ID=1 |NF=1 |F1-L1| | RTP1b | L-ID=6 |NF=1 |F1-L2| +-------+--------+-----+-----+ +-------+--------+-----+-----+ +-------+--------+-----+-----+ +-------+--------+-----+-----+ | RTP1c |L-ID=10 |NF=1 |F1-L3| | RTP2a | L-ID=1 |NF=1 |F2-L1| +-------+--------+-----+-----+ +-------+--------+-----+-----+ +-------+--------+-----+-----+ +-------+--------+-----+-----+ | RTP2b | L-ID=6 |NF=1 |F2-L2| | RTP2c |L-ID=10 |NF=1 |F2-L3| +-------+--------+-----+-----+ +-------+--------+-----+-----+ If the payloads carry data from two consecutive input frames, the same encoded data as in the previous example is arranged as follows. Lakaniemi Expires May 12, 2008 [Page 23] Internet-Draft RTP payload for EV-VBR November 2007 +-------+--------+-----+-----+-----+ | RTP1a | L-ID=1 |NF=2 |F1-L1|F2-L1| +-------+--------+-----+-----+-----+ +-------+--------+-----+-----+-----+ | RTP1b | L-ID=6 |NF=2 |F1-L2|F2-L2| +-------+--------+-----+-----+-----+ +-------+--------+-----+-----+-----+ | RTP1c |L-ID=10 |NF=2 |F1-L3|F2-L3| +-------+--------+-----+-----+-----+ A.2. Advanced examples A.2.1. Different update rate for subset of layers An example employing different update rates (i.e. different number of frames per packet) for selected subsets of layers. In these examples all core codec layers L1-L5 are shown. Lakaniemi Expires May 12, 2008 [Page 24] Internet-Draft RTP payload for EV-VBR November 2007 +-------+--------+-----+-----+-----+-----+-----+ | RTP1 | L-ID=1 |NF=4 |F1-L1|F2-L1|F3-L1|F4-L1| +-------+--------+-----+-----+-----+-----+-----+ +-------+--------+-----+-----+-----+-----+-----+ | RTP2a | L-ID=7 |NF=2 |F1-L2|F2-L2|F1-L3|F2-L3| +-------+--------+-----+-----+-----+-----+-----+ +-------+--------+-----+-----+-----+ | RTP3a |L-ID=14 |NF=1 |F1-L4|F1-L5| +-------+--------+-----+-----+-----+ +-------+--------+-----+-----+-----+ | RTP3b |L-ID=14 |NF=1 |F2-L4|F2-L5| +-------+--------+-----+-----+-----+ +-------+--------+-----+-----+-----+-----+-----+ | RTP2b | L-ID=7 |NF=2 |F3-L2|F4-L2|F3-L3|F4-L3| +-------+--------+-----+-----+-----+-----+-----+ +-------+--------+-----+-----+-----+ | RTP3c |L-ID=14 |NF=1 |F3-L4|F3-L5| +-------+--------+-----+-----+-----+ +-------+--------+-----+-----+-----+ | RTP3d |L-ID=14 |NF=1 |F4-L4|F4-L5| +-------+--------+-----+-----+-----+ A.2.2. Redundant frames with limited set of layers An example transmitting layers L1-L3 as primary data and L1 (of the previous frame) as redundant data is shown below. Each payload carries one primary (i.e. new) frame and one redundant frame. +-------+--------+-----+-----+--------+-----+-----+-----+-----+ | RTP1 | L-ID=1 |NF=1 |F0-L1| L-ID=3 |NF=1 |F1-L1|F1-L2|F1-L3| +-------+--------+-----+-----+--------+-----+-----+-----+-----+ +-------+--------+-----+-----+--------+-----+-----+-----+-----+ | RTP2 | L-ID=1 |NF=1 |F1-L1| L-ID=3 |NF=1 |F2-L1|F2-L2|F2-L3| +-------+--------+-----+-----+--------+-----+-----+-----+-----+ +-------+--------+-----+-----+--------+-----+-----+-----+-----+ | RTP3 | L-ID=1 |NF=1 |F2-L1| L-ID=3 |NF=1 |F3-L1|F3-L2|F3-L3| +-------+--------+-----+-----+--------+-----+-----+-----+-----+ Lakaniemi Expires May 12, 2008 [Page 25] Internet-Draft RTP payload for EV-VBR November 2007 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R. and Jacobson, V., "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [ev-vbr] ITU-T Recommendation G.xxx [amr-wb] 3GPP TS 26.171, "Adaptive Multi-Rate Wideband (AMR-WB) speech codec; General description (Release 7)", v7.0.0, September 2006. [RFC4867] Sjoberg, J., Westerlund, M., Lakaniemi, A., Xie, Q., "RTP Payload Format and File Storage Format fort he Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio Codecs", RFC 4867, April 2007. [ccm] Wenger, S., Chandra, U., Westerlund, M., Burman, B., "Codec Control Messages in the RTP Audio-Visual Profile with Feedback (AVPF)", draft-ietf-avt-avpf-ccm-10 (work in progress), October 2007. [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., Rey, J., "Extended RTP Profile for Real-Time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, July 2006. [RFC4566] Handley, M., Jacobson, V. and Perkins, C., "SDP: Session Description Protocol", RFC 4566, July 2006. [RFC4288] Freed, N., Klensin, J., "Media Type Specifications and Registration Procedures", BCP 13, RFC 4288, December 2005. [RFC4855] Casner, S., "Media Type Registration of RTP Payload Formats", RFC 4855, February 2007. [RFC3264] Rosenberg, J., Schulzrinne, H., "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002. Lakaniemi Expires May 12, 2008 [Page 26] Internet-Draft RTP payload for EV-VBR November 2007 [smd-sdp] Schierl, T., Wenger, S., "Signaling media decoding dependency in Session Description Protocol (SDP)", draft- schierl-mmusic-layered-codec-04 (work in progress), June 2007. [RFC3551] Schulzrinne, H., Casner, S., "RTP Profile for Audio and Video Conferences with Minimal Control", STD 65, RFC 3551, July 2003. [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., Norrman, K., "The Secure Real-Time Transport Protocol (SRTP)", RFC 3711, March 2004. 9.2. Informative References [topo] Westerlund, M., Wenger, S., "RTP Topologies", draft-ietf- avt-topologies-07 (work in progress), October 2007. [RFC2326] Schulzrinne, H., Rao, A., Lanphier, R., "Real Time Streaming Protocol (RTSP)", RFC 2326, April 1998. [RFC2974] Handley, M., Perkins, C., Whelan, E., "Session Announcement Protocol", RFC 2974, October 2000. Author's Addresses Ari Lakaniemi Nokia Research Center P.O.Box 407 FIN-00045 Nokia Group, FINLAND Phone: +358-71-8008000 Email: ari.lakaniemi@nokia.com Intellectual Property Statement 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. Lakaniemi Expires May 12, 2008 [Page 27] Internet-Draft RTP payload for EV-VBR November 2007 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. 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. 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. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Lakaniemi Expires May 12, 2008 [Page 28]