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AVTNetwork Working Group G. HerleinInternet-Draft Intended status:Request for Comments: 5574 Independent Category: Standards Track J. ValinExpires: November 8, 2009Xiph.Org Foundation A. Heggestad Creytiv.com A. Moizard AntisipMay 7,June 2009 RTP Payload Format for the Speex Codecdraft-ietf-avt-rtp-speex-07Status ofthisThis Memo ThisInternet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents ofdocument specifies an Internet standards track protocol for the InternetEngineering Task Force (IETF), its areas,community, andits working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents validrequests discussion and suggestions fora maximumimprovements. Please refer to the current edition ofsix monthsthe "Internet Official Protocol Standards" (STD 1) for the standardization state andmay 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 liststatus ofcurrent Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The listthis protocol. Distribution ofInternet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on November 8, 2009.this memo is unlimited. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document.Herlein, et al. Expires November 8, 2009 [Page 1] Internet-Draft Speex May 2009Abstract Speex is an open-source voice codec suitable for use inVoiceVoIP (Voice overIP (VoIP)IP) type applications. This document describes the payload format forSpeex generatedSpeex-generated bit streams within an RTP packet. Also included here are the necessary details for the use of Speex with the Session Description Protocol (SDP). Herlein, et al.Expires November 8, 2009Standards Track [Page2] Internet-Draft1] RFC 5574 SpeexMayJune 2009Editors Note All references to RFC XXXX are to be replaced by references to the RFC number of this memo, when published.Table of Contents 1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 4....................................................3 2. Terminology. . . . . . . . . . . . . . . . . . . . . . . . . 5.....................................................3 3. RTPusageUsage for Speex. . . . . . . . . . . . . . . . . . . . . 6.............................................3 3.1. RTP Speex Header Fields. . . . . . . . . . . . . . . . . 6....................................3 3.2. RTPpayload formatPayload Format for Speex. . . . . . . . . . . . . . . 6...............................4 3.3. Speexpayload . . . . . . . . . . . . . . . . . . . . . . 6Payload ..............................................4 3.4. Example Speexpacket . . . . . . . . . . . . . . . . . . . 7Packet .......................................5 3.5. Multiple SpeexframesFrames inaan RTPpacket . . . . . . . . . . 8Packet .....................5 4. IANA Considerations. . . . . . . . . . . . . . . . . . . . . 9.............................................6 4.1. Media Type Registration. . . . . . . . . . . . . . . . . 9....................................6 4.1.1. Registration ofmedia type audio/speex . . . . . . . . 9Media Type Audio/Speex ..............6 5. SDPusageUsage of Speex. . . . . . . . . . . . . . . . . . . . . . 12..............................................8 5.1. Examplesupporting all modes, prefer modeSupporting All Modes, Prefer Mode 4. . . . . . . 15...............10 5.2. Examplesupporting only modeSupporting Only Modes 3 and 5. . . . . . . . . . . 15.....................10 5.3. Example with VariableBit RateBit-Rate and Comfort Noise. . . . . 15..........10 5.4. Example with Voice Activity Detection. . . . . . . . . . 15.....................11 5.5. Example with Multiplesampling rates . . . . . . . . . . . 15Sampling Rates ......................11 5.6. Example withptimePtime and Multiple Speexframes . . . . . . . 16Frames ..............11 5.7. Example with Complete Offer/Answerexchange . . . . . . . 16Exchange ...............12 6. Implementation Guidelines. . . . . . . . . . . . . . . . . . 18......................................12 7. Security Considerations. . . . . . . . . . . . . . . . . . . 19........................................12 8.Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20Acknowledgments ................................................13 9. References. . . . . . . . . . . . . . . . . . . . . . . . . . 21.....................................................13 9.1. Normative References. . . . . . . . . . . . . . . . . . . 21......................................13 9.2. Informative References. . . . . . . . . . . . . . . . . . 21 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22....................................13 Herlein, et al.Expires November 8, 2009Standards Track [Page3] Internet-Draft2] RFC 5574 SpeexMayJune 2009 1. Introduction Speex is based on theCELPCode Excited Linear Prediction [CELP] encoding technique with support for either narrowband (nominal8kHz),8 kHz), wideband (nominal16kHz)16 kHz), orultra- widebandultra-wideband (nominal32kHz).32 kHz). The main characteristics can be summarized as follows: o Free software/open-source o Integration of wideband and narrowband in the same bit-stream o Wide range of bit-rates available o Dynamic bit-rate switching and variable bit-rate (VBR) o Voice Activity Detection (VAD, integrated with VBR) o Variable complexity The Speex codec supports a wide range of bit-rates from 2.15 kbit/s to 44 kbit/s. In some cases however, it may not be possible for an implementation to include support for all rates(e.g.(e.g., because ofbandwidth,bandwidth or RAM or CPU constraints). In those cases, to be compliant with this specification, implementations MUST support at least narrowband (8 kHz) encoding and decoding at 8 kbit/s bit-rate (narrowband mode 3). Support for narrowband at 15 kbit/s (narrowband mode 5) is RECOMMENDED and support for wideband at 27.8 kbit/s (wideband mode 8) is also RECOMMENDED. The sampling rate MUST be 8, 16 or 32 kHz. This specification defines only single channel audio (mono).Herlein, et al. Expires November 8, 2009 [Page 4] Internet-Draft Speex May 20092. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119 [RFC2119] and indicate requirement levels for compliant RTP implementations.Herlein, et al. Expires November 8, 2009 [Page 5] Internet-Draft Speex May 20093. RTPusageUsage for Speex 3.1. RTP Speex Header Fields The RTP header is defined in the RTP specification [RFC3550]. This section defines how fields in the RTP header are used. Herlein, et al. Standards Track [Page 3] RFC 5574 Speex June 2009 Payload Type (PT): The assignment of an RTP payload type for this packet format is outside the scope of this document; it is specified by the RTP profile under which this payload format is used, or signaled dynamically out-of-band (e.g., using SDP). Marker (M) bit: The M bit is set to one on the first packet sent after a silence period, during which packets have not been transmitted contiguously. Extension (X) bit: Defined by the RTP profile used. Timestamp: A 32-bit word that corresponds to the sampling instant for the first frame in the RTP packet. 3.2. RTPpayload formatPayload Format for Speex The RTP payload for Speex has the format shown in Figure 1. No additional header fields specific to this payload format are required. ForRTP basedRTP-based transportation ofSpeex encoded audioSpeex-encoded audio, the standard RTP header [RFC3550] is followed by one or more payload data blocks. An optional padding terminator may also be used. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RTP Header | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | one or more frames of Speex .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | one or more frames of Speex .... | padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: RTPpayloadPayload for Speex 3.3. SpeexpayloadPayload For the purposes of packetizing the bit stream in RTP, it is only necessary to consider the sequence of bits as output by the Speex encoder[speex_manual],[SPEEX], and present the same sequence to the decoder. The payload format described here maintains this sequence.Herlein, et al. Expires November 8, 2009 [Page 6] Internet-Draft Speex May 2009A typical Speex frame, encoded at the maximumbitrate,bit-rate, isapprox.approximately 110 octets and the total number of Speex frames SHOULD be kept less than the path MTU to prevent fragmentation. Speex frames MUST NOT be fragmented across multiple RTPpackets,packets. The Speex frames must be placed starting with the oldest frame and then continueconsecutiveconsecutively in time. Herlein, et al. Standards Track [Page 4] RFC 5574 Speex June 2009 An RTP packet MAY contain Speex frames of the samebit ratebit-rate or of varyingbit rates,bit-rates, since the bit-rate for a frame is conveyedin bandin-band with the signal. The encoding and decoding algorithm can change thebit ratebit-rate at any 20 msec frame boundary, with thebit ratebit-rate change notification provided in-band with the bit stream. Each frame contains both sampling rate (narrowband,widebandwideband, or ultra-wideband) and "mode" (bit-rate) information in the bit stream. No out-of-band notification is required for the decoder to process changes in thebit ratebit-rate sent by the encoder. The sampling rate MUST be either 8000 Hz, 16000 Hz, or 32000 Hz. The RTP payload MUST be padded to provide an integer number of octets as the payload length. These padding bits areLSB alignedLSB-aligned (Least Significant Bit) in network octet order and consist of a 0 followed by all ones (until the end of the octet). This padding is only required for the last frame in the packet, and only to ensure the packet contentsendsend on an octet boundary. 3.4. Example SpeexpacketPacket In the examplebelowbelow, we have a single Speex frame with 5 bits of padding to ensure the packet size falls on an octet boundary. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RTP Header | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | ..speex data.. | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ..speex data.. |0 1 1 1 1| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Herlein, et al. Expires November 8, 2009 [Page 7] Internet-Draft Speex May 20093.5. Multiple SpeexframesFrames inaan RTPpacketPacket Below is an example of two Speex frames contained within one RTP packet. The Speex frame length in this examplefallfalls on an octet boundary so there is no padding. The Speex decoder[speex_manual][SPEEX] can detect thebitratebit-rate from the payload and is responsible for detecting the 20 msec boundaries between each frame. Herlein, et al. Standards Track [Page 5] RFC 5574 Speex June 2009 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RTP Header | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | ..speex frame 1.. | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ..speex frame 1.. | ..speex frame 2.. | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ..speex frame 2.. | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Herlein, et al. Expires November 8, 2009 [Page 8] Internet-Draft Speex May 20094. IANA Considerations This document defines the Speex media type. 4.1. Media Type Registration This section describes the media types and names associated with this payload format. The section registers the media types, as perRFC4288 [RFC4288]RFC 4288 [RFC4288]. 4.1.1. Registration ofmedia type audio/speexMedia Type Audio/Speex Media type name: audio Media subtype name: speex Required parameters: rate: RTP timestamp clock rate, which is equal to the sampling rate in Hz. The sampling rate MUST be either 8000, 16000, or 32000. Optional parameters: ptime: SHOULD be a multiple of 20 msec [RFC4566] maxptime: SHOULD be a multiple of 20 msec [RFC4566] vbr: variablebit ratebit-rate - either'on' 'off''on', 'off', or 'vad' (defaults tooff).'off'). Ifon,'on', variablebit ratebit-rate is enabled. Ifoff,'off', disabled. If set to'vad''vad', then constantbit ratebit-rate isusedused, but silence will be encoded with special short frames to indicate a lack of voice for that period. This parameter is a preference to the encoder. Herlein, et al. Standards Track [Page 6] RFC 5574 Speex June 2009 cng: comfort noise generation - either 'on' or 'off' (defaults tooff).'off'). Ifoff'off', then silence frames will be silent; if'on''on', then those frames will be filled with comfort noise. This parameter is a preference to the encoder. mode: Comma-separated list of supported Speex decoding modes, in order of preference. The first is the most preferred and the remaining is in decreasing order of preference. The valid modes are different for narrowband and wideband, and are defined as follows:Herlein, et al. Expires November 8, 2009 [Page 9] Internet-Draft Speex May 2009* {1,2,3,4,5,6,7,8,any} for narrowband * {0,1,2,3,4,5,6,7,8,9,10,any} for wideband and ultra-wideband The 'mode' parameters may contain multiple values. In this case, the remote party SHOULD configure its encoder using the first supported mode provided. When 'any' is used, the offerer indicates that it supports all decoding modes. The 'mode' parameter value MUST always be quoted. If the 'mode' parameter is not provided, the mode value is considered to be equivalent to 'mode="3,any"' in narrowband and 'mode="8,any"' in wideband and ultra-wideband. Note that each Speex frame doescontainscontain the mode (or bit-rate) that should be used to decode it.ThusThus, an application MUST be able to decode any Speex frame unless the SDP clearlyspecifyspecifies that some modes are notsupported.supported (e.g., by not including'mode="any"')'mode="any"'). Indicating support for a given set of decodingmodes,modes also implies that the implementation support the same encoding modes. Encoding considerations: This media type is framed and binary, seesectionSection 4.8 in [RFC4288]. Security considerations: See Section66. Interoperability considerations: None. Published specification: RFCXXXX [RFC Editor: please replace by the5574. Herlein, et al. Standards Track [Page 7] RFCnumber of this memo, when published]5574 Speex June 2009 Applicationswhichthat use this media type: Audio streaming and conferencing applications. Additional information:nonenone. Person andinformation :information: Alfred E. Heggestad: aeh@db.org Intended usage: COMMON Restrictions on usage:Herlein, et al. Expires November 8, 2009 [Page 10] Internet-Draft Speex May 2009This media type depends on RTP framing, and hence is only defined for transfer via RTP [RFC3550]. Transport within other framing protocols is not defined at this time. Author: Alfred E. Heggestad Change controller: IETF Audio/Video Transport working group delegated from the IESG.Herlein, et al. Expires November 8, 2009 [Page 11] Internet-Draft Speex May 20095. SDPusageUsage of Speex The information carried in the media type specification has a specific mapping to fields in the Session Description Protocol (SDP) [RFC4566], which is commonly used to describe RTP sessions. When SDP is used to specify sessions employing the Speex codec, the mapping is as follows: o The media type ("audio") goes in SDP "m=" as the media name. o The media subtype ("speex") goes in SDP "a=rtpmap" as the encoding name. The required parameter "rate" also goes in "a=rtpmap" as the clock rate. 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 asemicolonsemicolon- separated list of parameter=value pairs. Herlein, et al. Standards Track [Page 8] RFC 5574 Speex June 2009 The tables below include the equivalence between modes andbitratesbit-rates for narrowband,widebandwideband, and ultra-wideband. Also, the corresponding "Speex quality" setting (see SPEEX_SET_QUALITY inThethe Speex Codec Manual[speex_manual])[SPEEX]) is included as an indication.Herlein, et al. Expires November 8, 2009 [Page 12] Internet-Draft Speex May 2009+------+---------------+-------------+ | mode | Speex quality |bitratebit-rate | +------+---------------+-------------+ | 1 | 0 | 2.15 kbit/s | || | | |2 | 2 | 5.95 kbit/s | || | | |3 | 3 or 4 | 8.00 kbit/s | || | | |4 | 5 or 6 | 11.0 kbit/s | || | | |5 | 7 or 8 | 15.0 kbit/s | || | | |6 | 9 | 18.2 kbit/s | || | | |7 | 10 | 24.6 kbit/s | || | | |8 | 1 | 3.95 kbit/s | +------+---------------+-------------+ Table 1: Modevs Bitrate tablevs. Bit-Rate fornarrowband Table 1 Herlein, et al. Expires November 8, 2009 [Page 13] Internet-Draft Speex May 2009 +------+---------------+------------------+------------------------+Narrowband +------+---------------+-------------------+------------------------+ | mode | Speex quality | widebandbitratebit-rate | ultra widebandbitrate|+------+---------------+------------------+------------------------+| | | | bit-rate | +------+---------------+-------------------+------------------------+ | 0 | 0 | 3.95 kbit/s | 5.75 kbit/s | || | | | |1 | 1 | 5.75 kbit/s | 7.55 kbit/s | || | | | |2 | 2 | 7.75 kbit/s | 9.55 kbit/s | || | | | |3 | 3 | 9.80 kbit/s | 11.6 kbit/s | || | | | |4 | 4 | 12.8 kbit/s | 14.6 kbit/s | || | | | |5 | 5 | 16.8 kbit/s | 18.6 kbit/s | || | | | |6 | 6 | 20.6 kbit/s | 22.4 kbit/s | || | | | |7 | 7 | 23.8 kbit/s | 25.6 kbit/s | || | | | |8 | 8 | 27.8 kbit/s | 29.6 kbit/s | || | | | |9 | 9 | 34.2 kbit/s | 36.0 kbit/s | || | | | |10 | 10 | 42.2 kbit/s | 44.0 kbit/s |+------+---------------+------------------+------------------------++------+---------------+-------------------+------------------------+ Table 2: Modevs Bitrate tablevs. Bit-Rate forwidebandWideband andultra-wideband Table 2Ultra-Wideband The Speex parameters indicate the decoding capabilities of the agent, and what the agent prefers to receive. The Speex parameters in an SDP Offer/Answer exchange are completely orthogonal, and there is no relationship between the SDP Offer and the Answer. Herlein, et al. Standards Track [Page 9] RFC 5574 Speex June 2009 Several Speex specific parameters can be given in a single a=fmtp line provided that they are separated by asemi-colon:semicolon: a=fmtp:97 mode="1,any";vbr=on Some example SDP session descriptions utilizing Speex encodings follow.Herlein, et al. Expires November 8, 2009 [Page 14] Internet-Draft Speex May 20095.1. Examplesupporting all modes, prefer modeSupporting All Modes, Prefer Mode 4 The offerer indicates that it wishes to receive a Speex stream at8000Hz,8000 Hz, and wishes to receive Speex 'mode 4'. It is important to understand that any other mode might still be sent by remote party: the device might have bandwidth limitation or might only be able to send 'mode="3"'. Thus,applicationapplications that support all decoding modes SHOULD include 'mode="any"' as shown in the example below: m=audio 8088 RTP/AVP 97 a=rtpmap:97 speex/8000 a=fmtp:97 mode="4,any" 5.2. Examplesupporting only modeSupporting Only Modes 3 and 5 The offerer indicates the mode he wishes to receive (Speex 'mode 3'). This offer indicates mode 3 and mode 5 are supported and that no other modes are supported. The remote party MUST NOT configure its encoder using another Speex mode. m=audio 8088 RTP/AVP 97 a=rtmap:97 speex/8000 a=fmtp:97 mode="3,5" 5.3. Example with VariableBit RateBit-Rate and Comfort Noise The offerer indicates that it wishes to receive variablebit ratebit-rate frames with comfort noise: m=audio 8088 RTP/AVP 97 a=rtmap:97 speex/8000 a=fmtp:97 vbr=on;cng=on Herlein, et al. Standards Track [Page 10] RFC 5574 Speex June 2009 5.4. Example with Voice Activity Detection The offerer indicates that it wishes to use silence suppression. In thiscasecase, the vbr=vad parameter will be used: m=audio 8088 RTP/AVP 97 a=rtmap:97 speex/8000 a=fmtp:97 vbr=vad 5.5. Example with Multiplesampling ratesSampling Rates The offerer indicates that it wishes to receive Speex audio at 16000 Hz with mode 10 (42.2kbit/s), alternativelykbit/s) or, alternatively, Speex audio at 8000 Hz with mode 7 (24.6 kbit/s). The offerer supports decoding all modes.Herlein, et al. Expires November 8, 2009 [Page 15] Internet-Draft Speex May 2009m=audio 8088 RTP/AVP 97 98 a=rtmap:97 speex/16000 a=fmtp:97 mode="10,any" a=rtmap:98 speex/8000 a=fmtp:98 mode="7,any" 5.6. Example withptimePtime and Multiple SpeexframesFrames The "ptime" SDP attribute is used to denote the packetization interval(ie,(i.e., how many milliseconds of audio is encoded in a single RTP packet). Since Speex uses 20 msec frames, ptime values of multiples of 20 denote multiple Speex frames per packet. It is recommended to use ptime valueswhichthat are a multiple of 20. If ptime contains a valuewhichthat is not multiple of 20, the internal interpretation of it should be rounded up to the nearest multiple of 20 before the number of Speex frames is calculated. Forexampleexample, if the "ptime" attribute is set to 30, the internal interpretation should be rounded up to 40 and then used to calculate2two Speex frames per packet. In the examplebelowbelow, the ptime value is set to 40, indicating that there are2two frames in each packet. m=audio 8088 RTP/AVP 97 a=rtpmap:97 speex/8000 a=ptime:40 Note that the ptime parameter applies to all payloads listed in the media line and is not used as part of an a=fmtp directive. Herlein, et al. Standards Track [Page 11] RFC 5574 Speex June 2009 Care must be taken when setting the value of ptime so that the RTP packet size does not exceed the path MTU. 5.7. Example with Complete Offer/AnswerexchangeExchange The offerer indicates that it wishes to receive Speex audio at 16000Hz, alternativelyHz or, alternatively, Speex audio at 8000 Hz. The offerer does support ALL modes because no mode is specified. m=audio 8088 RTP/AVP 97 98 a=rtmap:97 speex/16000 a=rtmap:98 speex/8000 The answerer indicates that it wishes to receive Speex audio at 8000 Hz, which is the only sampling rate it supports. The answerer does support ALL modes because no mode is specified.Herlein, et al. Expires November 8, 2009 [Page 16] Internet-Draft Speex May 2009m=audio 8088 RTP/AVP 99 a=rtmap:99 speex/8000Herlein, et al. Expires November 8, 2009 [Page 17] Internet-Draft Speex May 20096. Implementation Guidelines Implementations thatsupportssupport Speex are responsible for correctly decoding incoming Speex frames. Each Speex frame doescontainscontain all neededinformationsinformation to decode itself. In particular, the 'mode' and 'ptime' values proposed in the SDP contents MUST NOT be used for decoding: those values are not needed to properly decode a RTP Speex stream.Herlein, et al. Expires November 8, 2009 [Page 18] Internet-Draft Speex May 20097. Security Considerations RTP packets using the payload format defined in this specification are subject to the security considerations discussed in the RTP specification [RFC3550], and any appropriate RTP profile. This implies that confidentiality of the media streams is achieved by encryption. Because the data compression used with this payload format is applied end-to-end, encryption may be performed after compression so there is no conflict between the two operations. A potential denial-of-service threat exists for data encodings using compression techniques that have non-uniform receiver-end computational load. The attacker can inject pathological datagrams into the streamwhichthat are complex to decode and cause the receiver to be overloaded. However, this encoding does not exhibit any significant non-uniformity. Herlein, et al. Standards Track [Page 12] RFC 5574 Speex June 2009 As with any IP-based protocol, in somecircumstancescircumstances, a receiver may be overloaded simply by the receipt of too many packets, either desired or undesired. Network-layer authentication may be used to discard packets from undesired sources, but the processing cost of the authentication itself may be too high.Herlein, et al. Expires November 8, 2009 [Page 19] Internet-Draft Speex May 20098.AcknowledgementsAcknowledgments The authors would like to thank Equivalence Pty Ltd of Australia for their assistance in attempting to standardize the use of Speex in H.323 applications, and for implementing Speex in theiropen sourceopen-source OpenH323 stack. The authors would also like to thank Brian C. Wiles <brian@streamcomm.com> of StreamComm for his assistance in developing the proposed standard for Speex use in H.323 applications. The authors would also like to thank the following members of the Speex and AVT communities for their input: Ross Finlayson, Federico Montesino Pouzols, Henning Schulzrinne, Magnus Westerlund, Colin Perkins, and Ivo Emanuel Goncalves. Thanks to former authors of this document; Simon Morlat, Roger Hardiman, and Phil Kerr.Herlein, et al. Expires November 8, 2009 [Page 20] Internet-Draft Speex May 20099. 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 V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. 9.2. Informative References [CELP]"CELP, U.S. Federal Standard 1016.", National Technical Information Service (NTIS) website http://www.ntis.gov/.Schroeder, M. and B. Atal, "Code-excited linear prediction(CELP): High-quality speech at very low bit rates", Proc. International Conference on Acoustics, Speech, and Signal Processing (ICASSP), Vol 10, pp. 937- 940, 1985, <http://www.ntis.gov/>. [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and Registration Procedures", BCP 13, RFC 4288, December 2005.[speex_manual] Valin, J., "The Speex Codec Manual", Speex website http://www.speex.org/docs/.Herlein, et al.Expires November 8, 2009Standards Track [Page21] Internet-Draft13] RFC 5574 SpeexMayJune 2009 [SPEEX] Valin, J., "The Speex Codec Manual", <http://www.speex.org/docs/>. Authors' Addresses Greg Herlein Independent 2034 Filbert Street San Francisco, California 94123 United StatesEmail:EMail: gherlein@herlein.com Jean-Marc Valin Xiph.Org FoundationEmail:EMail: jean-marc.valin@usherbrooke.ca Alfred E. Heggestad Creytiv.com Biskop J. Nilssonsgt. 20a Oslo 0659 NorwayEmail:EMail: aeh@db.org Aymeric Moizard Antisip 5 Place Benoit Crepu Lyon, 69005 France EMail: jack@atosc.org Herlein, et al.Expires November 8, 2009Standards Track [Page22]14] ----