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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) -- 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 (==), 10 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 AVT R. Even 3 Internet-Draft Polycom 4 Intended status: Standards Track P. Luthi 5 Expires: November 23, 2008 Tandberg 6 May 22, 2008 8 RTP Payload Format for ITU-T Recommendation G.722.1 9 draft-ietf-avt-rfc3047-bis-06.txt 11 Status of this Memo 13 By submitting this Internet-Draft, each author represents that any 14 applicable patent or other IPR claims of which he or she is aware 15 have been or will be disclosed, and any of which he or she becomes 16 aware will be disclosed, in accordance with Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on November 23, 2008. 36 Copyright Notice 38 Copyright (C) The IETF Trust (2008). 40 Abstract 42 International Telecommunication Union (ITU-T) Recommendation G.722.1 43 is a wide-band audio codec. This document describes the payload 44 format for including G.722.1 generated bit streams within an RTP 45 packet. The document also describes the syntax and semantics of the 46 SDP parameters needed to support G.722.1 audio codec. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 51 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 52 3. RTP usage for G.722.1 . . . . . . . . . . . . . . . . . . . . 5 53 3.1. RTP G.722.1 Header Fields . . . . . . . . . . . . . . . . 5 54 3.2. RTP payload format for G.722.1 . . . . . . . . . . . . . . 5 55 3.3. Multiple G.722.1 frames in a RTP packet . . . . . . . . . 7 56 3.4. Computing the number of G.722.1 frames . . . . . . . . . . 7 57 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 58 4.1. Media Type Registration . . . . . . . . . . . . . . . . . 8 59 4.1.1. Registration of media type audio/G7221 . . . . . . . . 8 60 5. SDP Parameters . . . . . . . . . . . . . . . . . . . . . . . . 10 61 5.1. Usage with the SDP Offer Answer Model . . . . . . . . . . 10 62 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 63 7. Changes from RFC 3047 . . . . . . . . . . . . . . . . . . . . 12 64 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 65 9. RFC editor note . . . . . . . . . . . . . . . . . . . . . . . 14 66 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 67 10.1. Normative References . . . . . . . . . . . . . . . . . . . 15 68 10.2. Informative References . . . . . . . . . . . . . . . . . . 15 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 70 Intellectual Property and Copyright Statements . . . . . . . . . . 17 72 1. Introduction 74 ITU-T G.722.1 [ITU.G7221] is a low complexity coder, it compresses 50 75 Hz - 14 kHz audio signals into one of the following bit rates, 24 76 kbit/s, 32 kbit/s or 48 kbit/s. 78 The coder may be used for speech, music and other types of audio. 80 Some of the applications for which this coder is suitable are: 82 o Real-time communications such as videoconferencing and telephony. 84 o Streaming audio 86 o Archival and messaging 88 ITU-T G.722.1 [ITU.G7221] uses 20 ms frames and a sampling rate clock 89 of 16 kHz or 32kHz. The encoding and decoding algorithm can change 90 the bit rate at any 20ms frame boundary, but no bit rate change 91 notification is provided in-band with the bit stream. 93 For any given bit rate the number of bits in a frame is a constant. 94 Within this fixed frame, G.722.1 uses variable length coding (e.g. 95 Huffman coding) to represent most of the encoded parameters. All 96 variable length codes are transmitted in order from the left most 97 (most significant - MSB) bit to the right most (least significant - 98 LSB) bit, see [ITU.G7221] for more details. 100 The ITU-T standardized bit rates for G.722.1 are 24 kbit/s or 101 32kbit/s at 16 Khz sample rate, and 24 kbit/s, 32 kbit/s or 48 kbit/s 102 at 32 Khz sample rate. However, the coding algorithm itself has the 103 capability to run at any user specified bit rate (not just 24, 32 and 104 48 kbit/s) while maintaining an audio bandwidth of 50 Hz to 14 kHz. 105 This rate change is accomplished by a linear scaling of the codec 106 operation, resulting in frames with size in bits equal to 1/50 of the 107 corresponding bit rate. 109 2. Terminology 111 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 112 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 113 document are to be interpreted as described in RFC2119 [RFC2119] and 114 indicate requirement levels for compliant RTP implementations. 116 3. RTP usage for G.722.1 118 3.1. RTP G.722.1 Header Fields 120 The RTP header is defined in the RTP specification [RFC3550]. This 121 section defines how fields in the RTP header are used. 123 Payload Type (PT): The assignment of an RTP payload type for this 124 packet format is outside the scope of this document; it is 125 specified by the RTP profile under which this payload format is 126 used, or signaled dynamically out-of-band (e.g., using SDP). 128 Marker (M) bit: The M bit is set to zero. 130 Extension (X) bit: Defined by the RTP profile used. 132 Timestamp: A 32-bit word that corresponds to the sampling instant 133 for the first frame in the RTP packet. 135 3.2. RTP payload format for G.722.1 137 The RTP payload for G.722.1 has the format shown in Figure 1. No 138 additional header fields specific to this payload format are 139 required. 141 0 1 2 3 142 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 1 143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 144 | RTP Header | 145 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 146 | | 147 + one or more frames of G.722.1 | 148 | .... | 149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 151 Figure 1: RTP payload for G.722.1 153 Because bit rate is not signaled in-band, a separate out-of-band 154 method is REQUIRED to indicate the bit rate (see section 5 for an 155 example of signaling bit rate information using SDP). For the 156 payload format specified here, the bit rate MUST remain constant for 157 a particular payload type value. An application MAY switch bit rates 158 from packet to packet by defining two payload type values and 159 switching between them. 161 The use of Huffman coding means that it is not possible to identify 162 the various encoded parameters/fields contained within the bit stream 163 without first completely decoding the entire frame. For the purposes 164 of packetizing the bit stream in RTP, it is only necessary to 165 consider the sequence of bits as output by the G.722.1 encoder, and 166 present the same sequence to the decoder. The payload format 167 described here maintains this sequence. 169 When operating at 24 kbit/s, 480 bits (60 octets) are produced per 170 frame. When operating at 32 kbit/s, 640 bits (80 octets) are 171 produced per frame. When operating at 48 kbit/s, 960 bits (120 172 octets) are produced per frame. Thus, all three bit rates allow for 173 octet alignment without the need for padding bits. 175 Figure 2 illustrates how the G.722.1 bit stream MUST be mapped into 176 an octet aligned RTP payload. 178 first bit last bit 179 transmitted transmitted 180 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 181 | | 182 + sequence of bits (480, 640 or 960) generated by the | 183 | G.722.1 encoder for transmission | 184 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 186 | | | | | 187 | | | ... | | 188 | | | | | 190 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+ 191 |MSB... LSB|MSB... LSB| |MSB... LSB| 192 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+ 193 RTP RTP RTP 194 octet 1 octet 2 octet 195 60, 80, 120 197 Figure 2: The G.722.1 encoder bit stream is split into 198 a sequence of octets (60, 80 or 120 depending on 199 the bit rate), and each octet is in turn 200 mapped into an RTP octet. 202 When operating at non-standard rates the payload format MUST follow 203 the guidelines illustrated in Figure 2. It is RECOMMENDED that 204 values in the range 16000 to 48000 be used. Non standard rates MUST 205 have a value that is a multiple of 400 (this maintains octet 206 alignment and does not then require (undefined) padding bits for each 207 frame if not octet aligned). For example, a bit rate of 16.4 kbit/s 208 will result in a frame of size 328 bits or 41 octets which are mapped 209 into RTP per Figure 2. 211 3.3. Multiple G.722.1 frames in a RTP packet 213 A sender may include more than one consecutive G.722.1 frame in a 214 single RTP packet. 216 Senders have the following additional restrictions: 218 o Sender SHOULD NOT include more G.722.1 frames in a single RTP 219 packet than will fit in the MTU of the RTP transport protocol. 221 o All frames contained in a single RTP packet MUST be of the same 222 length and sampled at the same clock rate. They MUST have the 223 same bit rate (octets per frame). 225 o Frames MUST NOT be split between RTP packets. 227 It is RECOMMENDED that the number of frames contained within an RTP 228 packet be consistent with the application. For example, in a 229 telephony application where delay is important, then the fewer frames 230 per packet the lower the delay, whereas for a delay insensitive 231 streaming or messaging application, many frames per packet would be 232 acceptable. 234 3.4. Computing the number of G.722.1 frames 236 Information describing the number of frames contained in an RTP 237 packet is not transmitted as part of the RTP payload. The only way 238 to determine the number of G.722.1 frames is to count the total 239 number of octets within the RTP packet, and divide the octet count by 240 the number of expected octets per frame. This expected octet per 241 frame count is derived from the bit rate, and is therefore a function 242 of the payload type. 244 4. IANA Considerations 246 This document updates the G7221 media type described in RFC3047. 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/G7221 256 Media type name: audio 258 Media subtype name: G7221 260 Required parameters: 262 bitrate: the data rate for the audio bit stream. This parameter 263 is mandatory because the bit rate is not signaled within the 264 G.722.1 bit stream. At the standard G.722.1 bit rates, the value 265 MUST be either 24000 or 32000 at 16 Khz sample rate, and 24000, 266 32000 or 48000 at 32 Khz sample rate. If using the non-standard 267 bit rates, then it is RECOMMENDED that values in the range 16000 268 to 48000 be used. Non standard rates MUST have a value that is a 269 multiple of 400 (this maintains octet alignment and does not then 270 require (undefined) padding bits for each frame if not octet 271 aligned). 273 Optional parameters: 275 ptime: see RFC 4566. SHOULD be a multiple of 20 msec. 277 maxptime: see RFC 4566. SHOULD be a multiple of 20 msec. 279 Encoding considerations: 281 This media type is framed and binary, see section 4.8 in 282 [RFC4288]. 284 Security considerations: See Section 6 286 Interoperability considerations: 288 Terminals SHOULD offer a media type at 16 Khz sample rate in order 289 to interoperate with terminals that do not support the new 32 Khz 290 sample rate. 292 Published specification: RFC yyy [see RFCeditor notes]. 294 Applications which use this media type: 296 Audio and Video streaming and conferencing applications. 298 Additional information: none 300 Person and email address to contact for further information : 302 Roni Even: roni.even@polycom.co.il 304 Intended usage: COMMON 306 Restrictions on usage: 308 This media type depends on RTP framing, and hence is only defined 309 for transfer via RTP [RFC3550]. Transport within other framing 310 protocols is not defined at this time. 312 Author: Roni Even 314 Change controller: 316 IETF Audio/Video Transport working group delegated from the IESG. 318 5. SDP Parameters 320 The media types audio/G7221 are mapped to fields in the Session 321 Description Protocol (SDP) [RFC4566] as follows: 323 o The media name in the "m=" line of SDP MUST be audio. 325 o The encoding name in the "a=rtpmap" line of SDP MUST be G7221 (the 326 media subtype). 328 o The clock rate in the "a=rtpmap" line MUST be 16000 or 32000. 330 o Only one bitrate SHALL be defined (using the "bitrate=" parameter 331 in the a=fmtp line) for each payload type. 333 5.1. Usage with the SDP Offer Answer Model 335 When offering G.722.1 over RTP using SDP in an Offer/Answer model 336 [RFC3264] the following considerations are necessary. 338 The combination of the clock rate in the rtpmap and the bitrate 339 parameter defines the configuration of each payload type. Each 340 configuration intended to be used, MUST be declared. 342 There are two sampling clock rates defined for G.722.1 in this 343 document. RFC3047 [RFC3047] supported only the 16 Khz clock rate. 344 Therefore a system that wants to use G.722.1 SHOULD offer a payload 345 type with clock rate of 16000 for backward interoperability. 347 An example of an offer that includes a 16000 and 32000 clock rate is: 349 m=audio 49000 RTP/AVP 121 122 350 a=rtpmap:121 G7221/16000 351 a=fmtp:121 bitrate=24000 352 a=rtpmap:122 G7221/32000 353 a=fmtp:122 bitrate=48000 355 6. Security Considerations 357 RTP packets using the payload format defined in this specification 358 are subject to the security considerations discussed in the RTP 359 specification [RFC3550], and any appropriate RTP profile. This 360 implies that confidentiality of the media streams is achieved by 361 encryption. 363 A potential denial-of-service threat exists for data encoding using 364 compression techniques that have non-uniform receiver-end 365 computational load. The attacker can inject pathological datagrams 366 into the stream which are complex to decode and cause the receiver to 367 be overloaded. However, this encoding does not exhibit any 368 significant non-uniformity. 370 7. Changes from RFC 3047 372 The new draft updates RFC3047 adding the support for the Wideband 373 audio support defined in the new revision of ITU-T G.722.1. 375 Other changes 377 Update the text to be in line with the current rules for RFC and with 378 media type registration conforming to RFC 4288. 380 8. Acknowledgements 382 The authors would like to thank Tom Taylor for his contribution to 383 this work. 385 9. RFC editor note 387 Please replace RFC yyy giving the number assigned to this RFC. 389 10. References 391 10.1. Normative References 393 [ITU.G7221] 394 International Telecommunications Union, "Low-complexity 395 coding at 24 and 32 kbit/s for hands-free operation in 396 systems with low frame loss", ITU-T Recommendation 397 G.722.1, 2005. 399 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 400 Requirement Levels", BCP 14, RFC 2119, March 1997. 402 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 403 with Session Description Protocol (SDP)", RFC 3264, 404 June 2002. 406 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 407 Jacobson, "RTP: A Transport Protocol for Real-Time 408 Applications", STD 64, RFC 3550, July 2003. 410 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 411 Description Protocol", RFC 4566, July 2006. 413 10.2. Informative References 415 [RFC3047] Luthi, P., "RTP Payload Format for ITU-T Recommendation 416 G.722.1", RFC 3047, January 2001. 418 [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and 419 Registration Procedures", BCP 13, RFC 4288, December 2005. 421 Authors' Addresses 423 Roni Even 424 Polycom 425 94 Derech Em Hamoshavot 426 Petach Tikva 49130 427 Israel 429 Email: roni.even@polycom.co.il 431 Patrick Luthi 432 Tandberg 433 Philip Pedersens vei 22 434 Lysaker 1366 435 Norway 437 Email: patrick.luthi@tandberg.no 439 Full Copyright Statement 441 Copyright (C) The IETF Trust (2008). 443 This document is subject to the rights, licenses and restrictions 444 contained in BCP 78, and except as set forth therein, the authors 445 retain all their rights. 447 This document and the information contained herein are provided on an 448 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 449 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 450 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 451 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 452 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 453 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 455 Intellectual Property 457 The IETF takes no position regarding the validity or scope of any 458 Intellectual Property Rights or other rights that might be claimed to 459 pertain to the implementation or use of the technology described in 460 this document or the extent to which any license under such rights 461 might or might not be available; nor does it represent that it has 462 made any independent effort to identify any such rights. 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