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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) -- Obsolete informational reference (is this intentional?): RFC 4288 (Obsoleted by RFC 6838) Summary: 2 errors (**), 0 flaws (~~), 2 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 AVT G. Herlein 3 Internet-Draft 4 Intended status: Standards Track J. Valin 5 Expires: October 15, 2009 CSIRO 6 A. Heggestad 7 Creytiv.com 8 A. Moizard 9 Antisip 10 April 13, 2009 12 RTP Payload Format for the Speex Codec 13 draft-ietf-avt-rtp-speex-06 15 Status of this Memo 17 This Internet-Draft is submitted to IETF in full conformance with the 18 provisions of BCP 78 and BCP 79. This document may not be modified, 19 and derivative works of it may not be created, except to format it 20 for publication as an RFC or to translate it into languages other 21 than English. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF), its areas, and its working groups. Note that 25 other groups may also distribute working documents as Internet- 26 Drafts. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 The list of current Internet-Drafts can be accessed at 34 http://www.ietf.org/ietf/1id-abstracts.txt. 36 The list of Internet-Draft Shadow Directories can be accessed at 37 http://www.ietf.org/shadow.html. 39 This Internet-Draft will expire on October 15, 2009. 41 Copyright Notice 43 Copyright (c) 2009 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents in effect on the date of 48 publication of this document (http://trustee.ietf.org/license-info). 49 Please review these documents carefully, as they describe your rights 50 and restrictions with respect to this document. 52 Abstract 54 Speex is an open-source voice codec suitable for use in Voice over IP 55 (VoIP) type applications. This document describes the payload format 56 for Speex generated bit streams within an RTP packet. Also included 57 here are the necessary details for the use of Speex with the Session 58 Description Protocol (SDP). 60 Editors Note 62 All references to RFC XXXX are to be replaced by references to the 63 RFC number of this memo, when published. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 68 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 69 3. RTP usage for Speex . . . . . . . . . . . . . . . . . . . . . 7 70 3.1. RTP Speex Header Fields . . . . . . . . . . . . . . . . . 7 71 3.2. RTP payload format for Speex . . . . . . . . . . . . . . . 7 72 3.3. Speex payload . . . . . . . . . . . . . . . . . . . . . . 7 73 3.4. Example Speex packet . . . . . . . . . . . . . . . . . . . 8 74 3.5. Multiple Speex frames in a RTP packet . . . . . . . . . . 8 75 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 76 4.1. Media Type Registration . . . . . . . . . . . . . . . . . 10 77 4.1.1. Registration of media type audio/speex . . . . . . . . 10 78 5. SDP usage of Speex . . . . . . . . . . . . . . . . . . . . . . 13 79 5.1. Example supporting all modes, prefer mode 4 . . . . . . . 16 80 5.2. Example supporting only mode 3 and 5 . . . . . . . . . . . 16 81 5.3. Example with Variable Bit Rate and Comfort Noise . . . . . 16 82 5.4. Example with Voice Activity Detection . . . . . . . . . . 16 83 5.5. Example with Multiple sampling rates . . . . . . . . . . . 16 84 5.6. Example with ptime and Multiple Speex frames . . . . . . . 17 85 5.7. Example with Complete Offer/Answer exchange . . . . . . . 17 86 6. Implementation Guidelines . . . . . . . . . . . . . . . . . . 18 87 7. Security Considerations . . . . . . . . . . . . . . . . . . . 19 88 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20 89 9. Copying conditions . . . . . . . . . . . . . . . . . . . . . . 21 90 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 91 10.1. Normative References . . . . . . . . . . . . . . . . . . . 22 92 10.2. Informative References . . . . . . . . . . . . . . . . . . 22 93 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23 95 1. Introduction 97 Speex is based on the CELP [CELP] encoding technique with support for 98 either narrowband (nominal 8kHz), wideband (nominal 16kHz) or ultra- 99 wideband (nominal 32kHz). The main characteristics can be summarized 100 as follows: 102 o Free software/open-source 104 o Integration of wideband and narrowband in the same bit-stream 106 o Wide range of bit-rates available 108 o Dynamic bit-rate switching and variable bit-rate (VBR) 110 o Voice Activity Detection (VAD, integrated with VBR) 112 o Variable complexity 114 The Speex codec supports a wide range of bit-rates from 2.15 kbit/s 115 to 44 kbit/s. In some cases however, it may not be possible for an 116 implementation to include support for all rates (e.g. because of 117 bandwidth, RAM or CPU constraints). In those cases, to be compliant 118 with this specification, implementations MUST support at least 119 narrowband (8 kHz) encoding and decoding at 8 kbit/s bit-rate 120 (narrowband mode 3). Support for narrowband at 15 kbit/s (narrowband 121 mode 5) is RECOMMENDED and support for wideband at 27.8 kbit/s 122 (wideband mode 8) is also RECOMMENDED. The sampling rate MUST be 8, 123 16 or 32 kHz. This specification defines only single channel audio 124 (mono). 126 2. Terminology 128 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 129 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 130 document are to be interpreted as described in RFC2119 [RFC2119] and 131 indicate requirement levels for compliant RTP implementations. 133 3. RTP usage for Speex 135 3.1. RTP Speex Header Fields 137 The RTP header is defined in the RTP specification [RFC3550]. This 138 section defines how fields in the RTP header are used. 140 Payload Type (PT): The assignment of an RTP payload type for this 141 packet format is outside the scope of this document; it is 142 specified by the RTP profile under which this payload format is 143 used, or signaled dynamically out-of-band (e.g., using SDP). 145 Marker (M) bit: The M bit is set to one on the first packet sent 146 after a silence period, during which packets have not been 147 transmitted contiguously. 149 Extension (X) bit: Defined by the RTP profile used. 151 Timestamp: A 32-bit word that corresponds to the sampling instant 152 for the first frame in the RTP packet. 154 3.2. RTP payload format for Speex 156 The RTP payload for Speex has the format shown in Figure 1. No 157 additional header fields specific to this payload format are 158 required. For RTP based transportation of Speex encoded audio the 159 standard RTP header [RFC3550] is followed by one or more payload data 160 blocks. An optional padding terminator may also be used. 162 0 1 2 3 163 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 1 164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 165 | RTP Header | 166 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 167 | one or more frames of Speex .... | 168 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 169 | one or more frames of Speex .... | padding | 170 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 172 Figure 1: RTP payload for Speex 174 3.3. Speex payload 176 For the purposes of packetizing the bit stream in RTP, it is only 177 necessary to consider the sequence of bits as output by the Speex 178 encoder [speex_manual], and present the same sequence to the decoder. 179 The payload format described here maintains this sequence. 181 A typical Speex frame, encoded at the maximum bitrate, is approx. 110 182 octets and the total number of Speex frames SHOULD be kept less than 183 the path MTU to prevent fragmentation. Speex frames MUST NOT be 184 fragmented across multiple RTP packets, 186 An RTP packet MAY contain Speex frames of the same bit rate or of 187 varying bit rates, since the bit-rate for a frame is conveyed in band 188 with the signal. 190 The encoding and decoding algorithm can change the bit rate at any 20 191 msec frame boundary, with the bit rate change notification provided 192 in-band with the bit stream. Each frame contains both sampling rate 193 (narrowband, wideband or ultra-wideband) and "mode" (bit-rate) 194 information in the bit stream. No out-of-band notification is 195 required for the decoder to process changes in the bit rate sent by 196 the encoder. 198 The sampling rate MUST be either 8000 Hz, 16000 Hz, or 32000 Hz. 200 The RTP payload MUST be padded to provide an integer number of octets 201 as the payload length. These padding bits are LSB aligned in network 202 octet order and consist of a 0 followed by all ones (until the end of 203 the octet). This padding is only required for the last frame in the 204 packet, and only to ensure the packet contents ends on an octet 205 boundary. 207 3.4. Example Speex packet 209 In the example below we have a single Speex frame with 5 bits of 210 padding to ensure the packet size falls on an octet boundary. 212 0 1 2 3 213 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 1 214 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 215 | RTP Header | 216 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 217 | ..speex data.. | 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 219 | ..speex data.. |0 1 1 1 1| 220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 222 3.5. Multiple Speex frames in a RTP packet 224 Below is an example of two Speex frames contained within one RTP 225 packet. The Speex frame length in this example fall on an octet 226 boundary so there is no padding. 228 The Speex decoder [speex_manual] can detect the bitrate from the 229 payload and is responsible for detecting the 20 msec boundaries 230 between each frame. 232 0 1 2 3 233 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 1 234 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 235 | RTP Header | 236 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 237 | ..speex frame 1.. | 238 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 239 | ..speex frame 1.. | ..speex frame 2.. | 240 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 241 | ..speex frame 2.. | 242 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 244 4. IANA Considerations 246 This document defines the Speex media type. 248 4.1. Media Type Registration 250 This section describes the media types and names associated with this 251 payload format. The section registers the media types, as per 252 RFC4288 [RFC4288] 254 4.1.1. Registration of media type audio/speex 256 Media type name: audio 258 Media subtype name: speex 260 Required parameters: 262 rate: RTP timestamp clock rate, which is equal to the sampling 263 rate in Hz. The sampling rate MUST be either 8000, 16000, or 264 32000. 266 Optional parameters: 268 ptime: SHOULD be a multiple of 20 msec [RFC4566] 270 maxptime: SHOULD be a multiple of 20 msec [RFC4566] 272 vbr: variable bit rate - either 'on' 'off' or 'vad' (defaults to 273 off). If on, variable bit rate is enabled. If off, disabled. If 274 set to 'vad' then constant bit rate is used but silence will be 275 encoded with special short frames to indicate a lack of voice for 276 that period. This parameter is a preference to the encoder. 278 cng: comfort noise generation - either 'on' or 'off' (defaults to 279 off). If off then silence frames will be silent; if 'on' then 280 those frames will be filled with comfort noise. This parameter is 281 a preference to the encoder. 283 mode: Comma-separated list of supported Speex decoding modes, in 284 order of preference. The first is the most preferred and the 285 remaining is in decreasing order of preference. The valid modes 286 are different for narrowband and wideband, and are defined as 287 follows: 289 * {1,2,3,4,5,6,7,8,any} for narrowband 291 * {0,1,2,3,4,5,6,7,8,9,10,any} for wideband and ultra-wideband 293 The 'mode' parameters may contain multiple values. In this case, 294 the remote party SHOULD configure its encoder using the first 295 supported mode provided. When 'any' is used, the offerer 296 indicates that it supports all decoding modes. If the 'mode' 297 parameter is not provided, the mode value is considered to be 298 equivalent to 'mode=3,any' in narrowband and 'mode=8,any' in 299 wideband and ultra-wideband. Note that each Speex frame does 300 contains the mode (or bit-rate) that should be used to decode it. 301 Thus application MUST be able to decode any Speex frame unless the 302 SDP clearly specify that some modes are not supported. (e.g., by 303 not including 'mode=any') Indicating support for a given set of 304 decoding modes, also implies that the implementation support the 305 same encoding modes. 307 Encoding considerations: 309 This media type is framed and binary, see section 4.8 in 310 [RFC4288]. 312 Security considerations: See Section 6 314 Interoperability considerations: 316 None. 318 Published specification: 320 RFC XXXX [RFC Editor: please replace by the RFC number of this 321 memo, when published] 323 Applications which use this media type: 325 Audio streaming and conferencing applications. 327 Additional information: none 329 Person and email address to contact for further information : 331 Alfred E. Heggestad: aeh@db.org 333 Intended usage: COMMON 335 Restrictions on usage: 337 This media type depends on RTP framing, and hence is only defined 338 for transfer via RTP [RFC3550]. Transport within other framing 339 protocols is not defined at this time. 341 Author: Alfred E. Heggestad 343 Change controller: 345 IETF Audio/Video Transport working group delegated from the IESG. 347 5. SDP usage of Speex 349 The information carried in the media type specification has a 350 specific mapping to fields in the Session Description Protocol (SDP) 351 [RFC4566], which is commonly used to describe RTP sessions. When SDP 352 is used to specify sessions employing the Speex codec, the mapping is 353 as follows: 355 o The media type ("audio") goes in SDP "m=" as the media name. 357 o The media subtype ("speex") goes in SDP "a=rtpmap" as the encoding 358 name. The required parameter "rate" also goes in "a=rtpmap" as 359 the clock rate. 361 o The parameters "ptime" and "maxptime" go in the SDP "a=ptime" and 362 "a=maxptime" attributes, respectively. 364 o Any remaining parameters go in the SDP "a=fmtp" attribute by 365 copying them directly from the media type string as a semicolon 366 separated list of parameter=value pairs. 368 The tables below include the equivalence between modes and bitrates 369 for narrowband, wideband and ultra-wideband. Also, the corresponding 370 "Speex quality" setting (see SPEEX_SET_QUALITY in The Speex Codec 371 Manual [speex_manual]) is included as an indication. 373 +------+---------------+-------------+ 374 | mode | Speex quality | bitrate | 375 +------+---------------+-------------+ 376 | 1 | 0 | 2.15 kbit/s | 377 | | | | 378 | 2 | 2 | 5.95 kbit/s | 379 | | | | 380 | 3 | 3 or 4 | 8.00 kbit/s | 381 | | | | 382 | 4 | 5 or 6 | 11.0 kbit/s | 383 | | | | 384 | 5 | 7 or 8 | 15.0 kbit/s | 385 | | | | 386 | 6 | 9 | 18.2 kbit/s | 387 | | | | 388 | 7 | 10 | 24.6 kbit/s | 389 | | | | 390 | 8 | 1 | 3.95 kbit/s | 391 +------+---------------+-------------+ 393 Mode vs Bitrate table for narrowband 395 Table 1 397 +------+---------------+------------------+------------------------+ 398 | mode | Speex quality | wideband bitrate | ultra wideband bitrate | 399 +------+---------------+------------------+------------------------+ 400 | 0 | 0 | 3.95 kbit/s | 5.75 kbit/s | 401 | | | | | 402 | 1 | 1 | 5.75 kbit/s | 7.55 kbit/s | 403 | | | | | 404 | 2 | 2 | 7.75 kbit/s | 9.55 kbit/s | 405 | | | | | 406 | 3 | 3 | 9.80 kbit/s | 11.6 kbit/s | 407 | | | | | 408 | 4 | 4 | 12.8 kbit/s | 14.6 kbit/s | 409 | | | | | 410 | 5 | 5 | 16.8 kbit/s | 18.6 kbit/s | 411 | | | | | 412 | 6 | 6 | 20.6 kbit/s | 22.4 kbit/s | 413 | | | | | 414 | 7 | 7 | 23.8 kbit/s | 25.6 kbit/s | 415 | | | | | 416 | 8 | 8 | 27.8 kbit/s | 29.6 kbit/s | 417 | | | | | 418 | 9 | 9 | 34.2 kbit/s | 36.0 kbit/s | 419 | | | | | 420 | 10 | 10 | 42.2 kbit/s | 44.0 kbit/s | 421 +------+---------------+------------------+------------------------+ 423 Mode vs Bitrate table for wideband and ultra-wideband 425 Table 2 427 The Speex parameters indicate the decoding capabilities of the agent, 428 and what the agent prefers to receive. 430 The Speex parameters in an SDP Offer/Answer exchange are completely 431 orthogonal, and there is no relationship between the SDP Offer and 432 the Answer. 434 Several Speex specific parameters can be given in a single a=fmtp 435 line provided that they are separated by a semi-colon: 437 a=fmtp:97 mode=1,any;vbr=on 439 Some example SDP session descriptions utilizing Speex encodings 440 follow. 442 5.1. Example supporting all modes, prefer mode 4 444 The offerer indicates that it wishes to receive a Speex stream at 445 8000Hz, and wishes to receive Speex 'mode 4'. It is important to 446 understand that any other mode might still be sent by remote party: 447 the device might have bandwidth limitation or might only be able to 448 send 'mode=3'. Thus, application that support all decoding modes 449 SHOULD include 'mode=any' as shown in the example below: 451 m=audio 8088 RTP/AVP 97 452 a=rtpmap:97 speex/8000 453 a=fmtp:97 mode=4,any 455 5.2. Example supporting only mode 3 and 5 457 The offerer indicates the mode he wishes to receive (Speex 'mode 3'). 458 This offer indicates mode 3 and mode 5 are supported and that no 459 other modes are supported. The remote party MUST NOT configure its 460 encoder using another Speex mode. 462 m=audio 8088 RTP/AVP 97 463 a=rtmap:97 speex/8000 464 a=fmtp:97 mode=3,5 466 5.3. Example with Variable Bit Rate and Comfort Noise 468 The offerer indicates that it wishes to receive variable bit rate 469 frames with comfort noise: 471 m=audio 8088 RTP/AVP 97 472 a=rtmap:97 speex/8000 473 a=fmtp:97 vbr=on;cng=on 475 5.4. Example with Voice Activity Detection 477 The offerer indicates that it wishes to use silence suppression. In 478 this case vbr=vad parameter will be used: 480 m=audio 8088 RTP/AVP 97 481 a=rtmap:97 speex/8000 482 a=fmtp:97 vbr=vad 484 5.5. Example with Multiple sampling rates 486 The offerer indicates that it wishes to receive Speex audio at 16000 487 Hz with mode 10 (42.2 kbit/s), alternatively Speex audio at 8000 Hz 488 with mode 7 (24.6 kbit/s). The offerer supports decoding all modes. 490 m=audio 8088 RTP/AVP 97 98 491 a=rtmap:97 speex/16000 492 a=fmtp:97 mode=10,any 493 a=rtmap:98 speex/8000 494 a=fmtp:98 mode=7,any 496 5.6. Example with ptime and Multiple Speex frames 498 The "ptime" attribute is used to denote the packetization interval 499 (ie, how many milliseconds of audio is encoded in a single RTP 500 packet). Since Speex uses 20 msec frames, ptime values of multiples 501 of 20 denote multiple Speex frames per packet. Values of ptime which 502 are not multiples of 20 MUST be rounded up to the first multiple of 503 20 above the ptime value. 505 In the example below the ptime value is set to 40, indicating that 506 there are 2 frames in each packet. 508 m=audio 8088 RTP/AVP 97 509 a=rtpmap:97 speex/8000 510 a=ptime:40 512 Note that the ptime parameter applies to all payloads listed in the 513 media line and is not used as part of an a=fmtp directive. 515 Care must be taken when setting the value of ptime so that the RTP 516 packet size does not exceed the path MTU. 518 5.7. Example with Complete Offer/Answer exchange 520 The offerer indicates that it wishes to receive Speex audio at 16000 521 Hz, alternatively Speex audio at 8000 Hz. The offerer does support 522 ALL modes because no mode is specified. 524 m=audio 8088 RTP/AVP 97 98 525 a=rtmap:97 speex/16000 526 a=rtmap:98 speex/8000 528 The answerer indicates that it wishes to receive Speex audio at 8000 529 Hz, which is the only sampling rate it supports. The answerer does 530 support ALL modes because no mode is specified. 532 m=audio 8088 RTP/AVP 99 533 a=rtmap:99 speex/8000 535 6. Implementation Guidelines 537 Implementations that supports Speex are responsible for correctly 538 decoding incoming Speex frames. 540 Each Speex frame does contains all needed informations to decode 541 itself. In particular, the 'mode' and 'ptime' values proposed in the 542 SDP contents MUST NOT be used for decoding: those values are not 543 needed to properly decode a RTP Speex stream. 545 7. Security Considerations 547 RTP packets using the payload format defined in this specification 548 are subject to the security considerations discussed in the RTP 549 specification [RFC3550], and any appropriate RTP profile. This 550 implies that confidentiality of the media streams is achieved by 551 encryption. Because the data compression used with this payload 552 format is applied end-to-end, encryption may be performed after 553 compression so there is no conflict between the two operations. 555 A potential denial-of-service threat exists for data encodings using 556 compression techniques that have non-uniform receiver-end 557 computational load. The attacker can inject pathological datagrams 558 into the stream which are complex to decode and cause the receiver to 559 be overloaded. However, this encoding does not exhibit any 560 significant non-uniformity. 562 As with any IP-based protocol, in some circumstances a receiver may 563 be overloaded simply by the receipt of too many packets, either 564 desired or undesired. Network-layer authentication may be used to 565 discard packets from undesired sources, but the processing cost of 566 the authentication itself may be too high. 568 8. Acknowledgements 570 The authors would like to thank Equivalence Pty Ltd of Australia for 571 their assistance in attempting to standardize the use of Speex in 572 H.323 applications, and for implementing Speex in their open source 573 OpenH323 stack. The authors would also like to thank Brian C. Wiles 574 of StreamComm for his assistance in developing 575 the proposed standard for Speex use in H.323 applications. 577 The authors would also like to thank the following members of the 578 Speex and AVT communities for their input: Ross Finlayson, Federico 579 Montesino Pouzols, Henning Schulzrinne, Magnus Westerlund, Colin 580 Perkins, Ivo Emanuel Goncalves. 582 Thanks to former authors of this document; Simon Morlat, Roger 583 Hardiman, Phil Kerr. 585 9. Copying conditions 587 The authors agree to grant third parties the irrevocable right to 588 copy, use and distribute the work, with or without modification, in 589 any medium, without royalty, provided that, unless separate 590 permission is granted, redistributed modified works do not contain 591 misleading author, version, name of work, or endorsement information. 593 10. References 595 10.1. Normative References 597 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 598 Requirement Levels", BCP 14, RFC 2119, March 1997. 600 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 601 Jacobson, "RTP: A Transport Protocol for Real-Time 602 Applications", STD 64, RFC 3550, July 2003. 604 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 605 Description Protocol", RFC 4566, July 2006. 607 10.2. Informative References 609 [CELP] "CELP, U.S. Federal Standard 1016.", National Technical 610 Information Service (NTIS) website http://www.ntis.gov/. 612 [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and 613 Registration Procedures", BCP 13, RFC 4288, December 2005. 615 [speex_manual] 616 Valin, J., "The Speex Codec Manual", Speex 617 website http://www.speex.org/docs/. 619 Authors' Addresses 621 Greg Herlein 622 2034 Filbert Street 623 San Francisco, California 94123 624 United States 626 Email: gherlein@herlein.com 628 Jean-Marc Valin 629 CSIRO 630 PO Box 76 631 Epping, NSW 1710 632 Australia 634 Email: jean-marc.valin@usherbrooke.ca 636 Alfred E. Heggestad 637 Creytiv.com 638 Biskop J. Nilssonsgt. 20a 639 Oslo 0659 640 Norway 642 Email: aeh@db.org 644 Aymeric Moizard 645 Antisip 646 4 Quai Perrache 647 Lyon 69002 648 France 650 Email: jack@atosc.org