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Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- -- The draft header indicates that this document obsoletes RFC3047, but the abstract doesn't seem to mention this, which it should. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust Copyright Line does not match the current year -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (August 22, 2008) is 5726 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Possible downref: Non-RFC (?) normative reference: ref. 'ITU.G7221' ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) -- Obsolete informational reference (is this intentional?): RFC 3047 (Obsoleted by RFC 5577) -- Obsolete informational reference (is this intentional?): RFC 4288 (Obsoleted by RFC 6838) Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 11 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 AVT P. Luthi 3 Internet-Draft Tandberg 4 Obsoletes: 3047 (If approved) R. Even 5 (if approved) REL 6 Intended status: Standards Track August 22, 2008 7 Expires: February 23, 2009 9 RTP Payload Format for ITU-T Recommendation G.722.1 10 draft-ietf-avt-rfc3047-bis-08.txt 12 Status of this Memo 14 By submitting this Internet-Draft, each author represents that any 15 applicable patent or other IPR claims of which he or she is aware 16 have been or will be disclosed, and any of which he or she becomes 17 aware will be disclosed, in accordance with Section 6 of BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 This Internet-Draft will expire on February 23, 2009. 37 Copyright Notice 39 Copyright (C) The IETF Trust (2008). 41 Abstract 43 International Telecommunication Union (ITU-T) Recommendation G.722.1 44 is a wide-band audio codec. This document describes the payload 45 format for including G.722.1 generated bit streams within an RTP 46 packet. The document also describes the syntax and semantics of the 47 SDP parameters needed to support G.722.1 audio codec. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 52 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 53 3. RTP usage for G.722.1 . . . . . . . . . . . . . . . . . . . . 5 54 3.1. RTP G.722.1 Header Fields . . . . . . . . . . . . . . . . 5 55 3.2. RTP payload format for G.722.1 . . . . . . . . . . . . . . 5 56 3.3. Multiple G.722.1 frames in a RTP packet . . . . . . . . . 7 57 3.4. Computing the number of G.722.1 frames . . . . . . . . . . 7 58 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 59 4.1. Media Type Registration . . . . . . . . . . . . . . . . . 8 60 4.1.1. Registration of media type audio/G7221 . . . . . . . . 8 61 5. SDP Parameters . . . . . . . . . . . . . . . . . . . . . . . . 10 62 5.1. Usage with the SDP Offer Answer Model . . . . . . . . . . 10 63 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 64 7. Changes from RFC 3047 . . . . . . . . . . . . . . . . . . . . 12 65 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 66 9. RFC editor note . . . . . . . . . . . . . . . . . . . . . . . 14 67 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 68 10.1. Normative References . . . . . . . . . . . . . . . . . . . 15 69 10.2. Informative References . . . . . . . . . . . . . . . . . . 15 70 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 71 Intellectual Property and Copyright Statements . . . . . . . . . . 17 73 1. Introduction 75 ITU-T G.722.1 [ITU.G7221] is a low complexity coder, it compresses 50 76 Hz - 14 kHz audio signals into one of the following bit rates, 24 77 kbit/s, 32 kbit/s or 48 kbit/s. 79 The coder may be used for speech, music and other types of audio. 81 Some of the applications for which this coder is suitable are: 83 o Real-time communications such as videoconferencing and telephony. 85 o Streaming audio 87 o Archival and messaging 89 ITU-T G.722.1 [ITU.G7221] uses 20 ms frames and a sampling rate clock 90 of 16 kHz or 32kHz. The encoding and decoding algorithm can change 91 the bit rate at any 20ms frame boundary, but no bit rate change 92 notification is provided in-band with the bit stream. 94 For any given bit rate the number of bits in a frame is a constant. 95 Within this fixed frame, G.722.1 uses variable length coding (e.g. 96 Huffman coding) to represent most of the encoded parameters. All 97 variable length codes are transmitted in order from the left most 98 (most significant - MSB) bit to the right most (least significant - 99 LSB) bit, see [ITU.G7221] for more details. 101 The ITU-T standardized bit rates for G.722.1 are 24 kbit/s or 102 32kbit/s at 16 Khz sample rate, and 24 kbit/s, 32 kbit/s or 48 kbit/s 103 at 32 Khz sample rate. However, the coding algorithm itself has the 104 capability to run at any user specified bit rate (not just 24, 32 and 105 48 kbit/s) while maintaining an audio bandwidth of 50 Hz to 14 kHz. 106 This rate change is accomplished by a linear scaling of the codec 107 operation, resulting in frames with size in bits equal to 1/50 of the 108 corresponding bit rate. 110 2. Terminology 112 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 113 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 114 document are to be interpreted as described in RFC2119 [RFC2119] and 115 indicate requirement levels for compliant RTP implementations. 117 3. RTP usage for G.722.1 119 3.1. RTP G.722.1 Header Fields 121 The RTP header is defined in the RTP specification [RFC3550]. This 122 section defines how fields in the RTP header are used. 124 Payload Type (PT): The assignment of an RTP payload type for this 125 packet format is outside the scope of this document; it is 126 specified by the RTP profile under which this payload format is 127 used, or signaled dynamically out-of-band (e.g., using SDP). 129 Marker (M) bit: The M bit is set to zero. 131 Extension (X) bit: Defined by the RTP profile used. 133 Timestamp: A 32-bit word that corresponds to the sampling instant 134 for the first frame in the RTP packet. The sampling frequency can 135 be 16 Khz or 32 Khz. The RTP timestamp clock frequency of 32 Khz 136 SHOULD be used unless only an RTP stream sampled at 16 Khz is 137 going to be sent. 139 3.2. RTP payload format for G.722.1 141 The RTP payload for G.722.1 has the format shown in Figure 1. No 142 additional header fields specific to this payload format are 143 required. 145 0 1 2 3 146 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 1 147 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 148 | RTP Header | 149 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 150 | | 151 + one or more frames of G.722.1 | 152 | .... | 153 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 155 Figure 1: RTP payload for G.722.1 157 Because bit rate is not signaled in-band, a separate out-of-band 158 method is REQUIRED to indicate the bit rate (see section 5 for an 159 example of signaling bit rate information using SDP). For the 160 payload format specified here, the bit rate MUST remain constant for 161 a particular payload type value. An application MAY switch bit rates 162 and clock rates from packet to packet by defining different payload 163 type value and switching between them. 165 The use of Huffman coding means that it is not possible to identify 166 the various encoded parameters/fields contained within the bit stream 167 without first completely decoding the entire frame. For the purposes 168 of packetizing the bit stream in RTP, it is only necessary to 169 consider the sequence of bits as output by the G.722.1 encoder, and 170 present the same sequence to the decoder. The payload format 171 described here maintains this sequence. 173 When operating at 24 kbit/s, 480 bits (60 octets) are produced per 174 frame. When operating at 32 kbit/s, 640 bits (80 octets) are 175 produced per frame. When operating at 48 kbit/s, 960 bits (120 176 octets) are produced per frame. Thus, all three bit rates allow for 177 octet alignment without the need for padding bits. 179 Figure 2 illustrates how the G.722.1 bit stream MUST be mapped into 180 an octet aligned RTP payload. 182 first bit last bit 183 transmitted transmitted 184 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 185 | | 186 + sequence of bits (480, 640 or 960) generated by the | 187 | G.722.1 encoder for transmission | 188 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 190 | | | | | 191 | | | ... | | 192 | | | | | 194 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+ 195 |MSB... LSB|MSB... LSB| |MSB... LSB| 196 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+ 197 RTP RTP RTP 198 octet 1 octet 2 octet 199 60, 80, 120 201 Figure 2: The G.722.1 encoder bit stream is split into 202 a sequence of octets (60, 80 or 120 depending on 203 the bit rate), and each octet is in turn 204 mapped into an RTP octet. 206 When operating at non-standard rates the payload format MUST follow 207 the guidelines illustrated in Figure 2. It is RECOMMENDED that 208 values in the range 16000 to 48000 be used. Non standard rates MUST 209 have a value that is a multiple of 400 (this maintains octet 210 alignment and does not then require (undefined) padding bits for each 211 frame if not octet aligned). For example, a bit rate of 16.4 kbit/s 212 will result in a frame of size 328 bits or 41 octets which are mapped 213 into RTP per Figure 2. 215 3.3. Multiple G.722.1 frames in a RTP packet 217 A sender may include more than one consecutive G.722.1 frame in a 218 single RTP packet. 220 Senders have the following additional restrictions: 222 o Sender SHOULD NOT include more G.722.1 frames in a single RTP 223 packet than will fit in the MTU of the RTP transport protocol. 225 o All frames contained in a single RTP packet MUST be of the same 226 length and sampled at the same clock rate. They MUST have the 227 same bit rate (octets per frame). 229 o Frames MUST NOT be split between RTP packets. 231 It is RECOMMENDED that the number of frames contained within an RTP 232 packet be consistent with the application. For example, in a 233 telephony application where delay is important, then the fewer frames 234 per packet the lower the delay, whereas for a delay insensitive 235 streaming or messaging application, many frames per packet would be 236 acceptable. 238 3.4. Computing the number of G.722.1 frames 240 Information describing the number of frames contained in an RTP 241 packet is not transmitted as part of the RTP payload. The only way 242 to determine the number of G.722.1 frames is to count the total 243 number of octets within the RTP packet, and divide the octet count by 244 the number of expected octets per frame. This expected octet per 245 frame count is derived from the bit rate, and is therefore a function 246 of the payload type. 248 4. IANA Considerations 250 This document updates the G7221 media type described in RFC3047. 252 4.1. Media Type Registration 254 This section describes the media types and names associated with this 255 payload format. The section registers the media types, as per 256 RFC4288 [RFC4288] 258 4.1.1. Registration of media type audio/G7221 260 Media type name: audio 262 Media subtype name: G7221 264 Required parameters: 266 bitrate: the data rate for the audio bit stream. This parameter 267 is mandatory because the bit rate is not signaled within the 268 G.722.1 bit stream. At the standard G.722.1 bit rates, the value 269 MUST be either 24000 or 32000 at 16 Khz sample rate, and 24000, 270 32000 or 48000 at 32 Khz sample rate. If using the non-standard 271 bit rates, then it is RECOMMENDED that values in the range 16000 272 to 48000 be used. Non standard rates MUST have a value that is a 273 multiple of 400 (this maintains octet alignment and does not then 274 require (undefined) padding bits for each frame if not octet 275 aligned). 277 Optional parameters: 279 rate: RTP timestamp clock rate, which is equal to the sampling 280 rate. If the parameter is not specified a clock rate of 16 Khz is 281 assumed. 283 ptime: see RFC 4566. SHOULD be a multiple of 20 msec. 285 maxptime: see RFC 4566. SHOULD be a multiple of 20 msec. 287 Encoding considerations: 289 This media type is framed and binary, see section 4.8 in 290 [RFC4288]. 292 Security considerations: See Section 6 294 Interoperability considerations: 296 Terminals SHOULD offer a media type at 16 Khz sample rate in order 297 to interoperate with terminals that do not support the new 32 Khz 298 sample rate. 300 Published specification: RFC yyy [see RFCeditor notes]. 302 Applications which use this media type: 304 Audio and Video streaming and conferencing applications. 306 Additional information: none 308 Person and email address to contact for further information : 310 Roni Even: ron.even.tlv@gmail.com 312 Intended usage: COMMON 314 Restrictions on usage: 316 This media type depends on RTP framing, and hence is only defined 317 for transfer via RTP [RFC3550]. Transport within other framing 318 protocols is not defined at this time. 320 Author: Roni Even 322 Change controller: 324 IETF Audio/Video Transport working group delegated from the IESG. 326 5. SDP Parameters 328 The media types audio/G7221 are mapped to fields in the Session 329 Description Protocol (SDP) [RFC4566] as follows: 331 o The media name in the "m=" line of SDP MUST be audio. 333 o The encoding name in the "a=rtpmap" line of SDP MUST be G7221 (the 334 media subtype). 336 o The parameters "rate" goes in "a=rtpmap" as clock rate parameter 338 o Only one bitrate SHALL be defined (using the "bitrate=" parameter 339 in the a=fmtp line) for each payload type. 341 5.1. Usage with the SDP Offer Answer Model 343 When offering G.722.1 over RTP using SDP in an Offer/Answer model 344 [RFC3264] the following considerations are necessary. 346 The combination of the clock rate in the rtpmap and the bitrate 347 parameter defines the configuration of each payload type. Each 348 configuration intended to be used, MUST be declared. 350 There are two sampling clock rates defined for G.722.1 in this 351 document. RFC3047 [RFC3047] supported only the 16 Khz clock rate. 352 Therefore a system that wants to use G.722.1 SHOULD offer a payload 353 type with clock rate of 16000 for backward interoperability. 355 An example of an offer that includes a 16000 and 32000 clock rate is: 357 m=audio 49000 RTP/AVP 121 122 358 a=rtpmap:121 G7221/16000 359 a=fmtp:121 bitrate=24000 360 a=rtpmap:122 G7221/32000 361 a=fmtp:122 bitrate=48000 363 6. Security Considerations 365 RTP packets using the payload format defined in this specification 366 are subject to the security considerations discussed in the RTP 367 specification [RFC3550], and any appropriate RTP profile. This 368 implies that confidentiality of the media streams is achieved by 369 encryption. 371 A potential denial-of-service threat exists for data encoding using 372 compression techniques that have non-uniform receiver-end 373 computational load. The attacker can inject pathological datagrams 374 into the stream which are complex to decode and cause the receiver to 375 be overloaded. However, this encoding does not exhibit any 376 significant non-uniformity. 378 7. Changes from RFC 3047 380 The new draft obsoletes RFC3047 adding the support for the 381 Superwideband (14 Khz) audio support defined in annex C of the new 382 revision of ITU-T G.722.1. 384 Other changes 386 Update the text to be in line with the current rules for RFC and with 387 media type registration conforming to RFC 4288. 389 8. Acknowledgements 391 The authors would like to thank Tom Taylor for his contribution to 392 this work. 394 9. RFC editor note 396 Please replace RFC yyy giving the number assigned to this RFC. 398 10. References 400 10.1. Normative References 402 [ITU.G7221] 403 International Telecommunications Union, "Low-complexity 404 coding at 24 and 32 kbit/s for hands-free operation in 405 systems with low frame loss", ITU-T Recommendation 406 G.722.1, 2005. 408 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 409 Requirement Levels", BCP 14, RFC 2119, March 1997. 411 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 412 with Session Description Protocol (SDP)", RFC 3264, 413 June 2002. 415 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 416 Jacobson, "RTP: A Transport Protocol for Real-Time 417 Applications", STD 64, RFC 3550, July 2003. 419 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 420 Description Protocol", RFC 4566, July 2006. 422 10.2. Informative References 424 [RFC3047] Luthi, P., "RTP Payload Format for ITU-T Recommendation 425 G.722.1", RFC 3047, January 2001. 427 [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and 428 Registration Procedures", BCP 13, RFC 4288, December 2005. 430 Authors' Addresses 432 Patrick Luthi 433 Tandberg 434 Philip Pedersens vei 22 435 1366 Lysaker 436 Norway 438 Email: patrick.luthi@tandberg.no 440 Roni Even 441 REL 442 14 David Hamelech 443 Tel Aviv 64953 444 Israel 446 Email: ron.even.tlv@gmail.com 448 Full Copyright Statement 450 Copyright (C) The IETF Trust (2008). 452 This document is subject to the rights, licenses and restrictions 453 contained in BCP 78, and except as set forth therein, the authors 454 retain all their rights. 456 This document and the information contained herein are provided on an 457 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 458 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 459 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 460 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 461 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 462 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 464 Intellectual Property 466 The IETF takes no position regarding the validity or scope of any 467 Intellectual Property Rights or other rights that might be claimed to 468 pertain to the implementation or use of the technology described in 469 this document or the extent to which any license under such rights 470 might or might not be available; nor does it represent that it has 471 made any independent effort to identify any such rights. 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