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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 FEC Framework A. Begen 3 Internet-Draft Cisco 4 Intended status: Standards Track January 8, 2010 5 Expires: July 12, 2010 7 RTP Payload Format for 1-D Interleaved Parity FEC 8 draft-ietf-fecframe-interleaved-fec-scheme-08 10 Abstract 12 This document defines a new RTP payload format for the Forward Error 13 Correction (FEC) that is generated by the 1-D interleaved parity code 14 from a source media encapsulated in RTP. The 1-D interleaved parity 15 code is a systematic code, where a number of repair symbols are 16 generated from a set of source symbols and sent in a repair flow 17 separate from the source flow that carries the source symbols. The 18 1-D interleaved parity code offers a good protection against bursty 19 packet losses at a cost of reasonable complexity. The new payload 20 format defined in this document is used (with some exceptions) as a 21 part of the DVB Application-layer FEC specification. 23 Status of this Memo 25 This Internet-Draft is submitted to IETF in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF), its areas, and its working groups. Note that 30 other groups may also distribute working documents as Internet- 31 Drafts. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 The list of current Internet-Drafts can be accessed at 39 http://www.ietf.org/ietf/1id-abstracts.txt. 41 The list of Internet-Draft Shadow Directories can be accessed at 42 http://www.ietf.org/shadow.html. 44 This Internet-Draft will expire on July 12, 2010. 46 Copyright Notice 48 Copyright (c) 2010 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 1.1. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . 6 65 1.2. Overhead Computation . . . . . . . . . . . . . . . . . . . 8 66 1.3. Relation to Existing Specifications . . . . . . . . . . . 8 67 1.3.1. RFC 2733 and RFC 3009 . . . . . . . . . . . . . . . . 8 68 1.3.2. SMPTE 2022-1 . . . . . . . . . . . . . . . . . . . . . 8 69 1.3.3. ETSI TS 102 034 . . . . . . . . . . . . . . . . . . . 9 70 1.4. Scope of the Payload Format . . . . . . . . . . . . . . . 10 71 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 10 72 3. Definitions, Notations and Abbreviations . . . . . . . . . . . 10 73 3.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 10 74 3.2. Notations . . . . . . . . . . . . . . . . . . . . . . . . 11 75 4. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 11 76 4.1. Source Packets . . . . . . . . . . . . . . . . . . . . . . 11 77 4.2. Repair Packets . . . . . . . . . . . . . . . . . . . . . . 11 78 5. Payload Format Parameters . . . . . . . . . . . . . . . . . . 15 79 5.1. Media Type Registration . . . . . . . . . . . . . . . . . 15 80 5.1.1. Registration of audio/1d-interleaved-parityfec . . . . 15 81 5.1.2. Registration of video/1d-interleaved-parityfec . . . . 16 82 5.1.3. Registration of text/1d-interleaved-parityfec . . . . 18 83 5.1.4. Registration of 84 application/1d-interleaved-parityfec . . . . . . . . . 19 85 5.2. Mapping to SDP Parameters . . . . . . . . . . . . . . . . 20 86 5.2.1. Offer-Answer Model Considerations . . . . . . . . . . 21 87 5.2.2. Declarative Considerations . . . . . . . . . . . . . . 21 88 6. Protection and Recovery Procedures . . . . . . . . . . . . . . 22 89 6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 22 90 6.2. Repair Packet Construction . . . . . . . . . . . . . . . . 22 91 6.3. Source Packet Reconstruction . . . . . . . . . . . . . . . 24 92 6.3.1. Associating the Source and Repair Packets . . . . . . 24 93 6.3.2. Recovering the RTP Header and Payload . . . . . . . . 25 94 7. Session Description Protocol (SDP) Signaling . . . . . . . . . 27 95 8. Congestion Control Considerations . . . . . . . . . . . . . . 27 96 9. Security Considerations . . . . . . . . . . . . . . . . . . . 28 97 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 98 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 29 99 12. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 29 100 12.1. draft-ietf-fecframe-interleaved-fec-scheme-08 . . . . . . 29 101 12.2. draft-ietf-fecframe-interleaved-fec-scheme-07 . . . . . . 29 102 12.3. draft-ietf-fecframe-interleaved-fec-scheme-06 . . . . . . 29 103 12.4. draft-ietf-fecframe-interleaved-fec-scheme-05 . . . . . . 29 104 12.5. draft-ietf-fecframe-interleaved-fec-scheme-04 . . . . . . 30 105 12.6. draft-ietf-fecframe-interleaved-fec-scheme-03 . . . . . . 30 106 12.7. draft-ietf-fecframe-interleaved-fec-scheme-02 . . . . . . 30 107 12.8. draft-ietf-fecframe-interleaved-fec-scheme-01 . . . . . . 30 108 12.9. draft-ietf-fecframe-interleaved-fec-scheme-00 . . . . . . 30 109 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31 110 13.1. Normative References . . . . . . . . . . . . . . . . . . . 31 111 13.2. Informative References . . . . . . . . . . . . . . . . . . 31 112 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 32 114 1. Introduction 116 This document extends the Forward Error Correction (FEC) header 117 defined in [RFC2733] and uses this new FEC header for the FEC that is 118 generated by the 1-D interleaved parity code from a source media 119 encapsulated in RTP [RFC3550]. The resulting new RTP payload format 120 is registered by this document. 122 The type of the source media protected by the 1-D interleaved parity 123 code can be audio, video, text or application. The FEC data are 124 generated according to the media type parameters that are 125 communicated through out-of-band means. The associations/ 126 relationships between the source and repair flows are also 127 communicated through out-of-band means. 129 The 1-D interleaved parity FEC uses the exclusive OR (XOR) operation 130 to generate the repair symbols. In a nutshell, the following steps 131 take place: 133 1. The sender determines a set of source packets to be protected 134 together based on the media type parameters. 136 2. The sender applies the XOR operation on the source symbols to 137 generate the required number of repair symbols. 139 3. The sender packetizes the repair symbols and sends the repair 140 packet(s) along with the source packets to the receiver(s) (in 141 different flows). The repair packets MAY be sent proactively or 142 on-demand. 144 Note that the source and repair packets belong to different source 145 and repair flows, and the sender needs to provide a way for the 146 receivers to demultiplex them, even in the case they are sent in the 147 same transport flow (i.e., same source/destination address/port with 148 UDP). This is required to offer backward compatibility (See 149 Section 4). At the receiver side, if all of the source packets are 150 successfully received, there is no need for FEC recovery and the 151 repair packets are discarded. However, if there are missing source 152 packets, the repair packets can be used to recover the missing 153 information. Block diagrams for the systematic parity FEC encoder 154 and decoder are sketched in Figure 1 and Figure 2, respectively. 156 +------------+ 157 +--+ +--+ +--+ +--+ --> | Systematic | --> +--+ +--+ +--+ +--+ 158 +--+ +--+ +--+ +--+ | Parity FEC | +--+ +--+ +--+ +--+ 159 | Encoder | 160 | (Sender) | --> +==+ +==+ 161 +------------+ +==+ +==+ 163 Source Packet: +--+ Repair Packet: +==+ 164 +--+ +==+ 166 Figure 1: Block diagram for systematic parity FEC encoder 168 +------------+ 169 +--+ X X +--+ --> | Systematic | --> +--+ +--+ +--+ +--+ 170 +--+ +--+ | Parity FEC | +--+ +--+ +--+ +--+ 171 | Decoder | 172 +==+ +==+ --> | (Receiver) | 173 +==+ +==+ +------------+ 175 Source Packet: +--+ Repair Packet: +==+ Lost Packet: X 176 +--+ +==+ 178 Figure 2: Block diagram for systematic parity FEC decoder 180 Suppose that we have a group of D x L source packets that have 181 sequence numbers starting from 1 running to D x L. If we apply the 182 XOR operation to the group of the source packets whose sequence 183 numbers are L apart from each other as sketched in Figure 3, we 184 generate L repair packets. This process is referred to as 1-D 185 interleaved FEC protection, and the resulting L repair packets are 186 referred to as interleaved (or column) FEC packets. 188 +-------------+ +-------------+ +-------------+ +-------+ 189 | S_1 | | S_2 | | S3 | ... | S_L | 190 | S_L+1 | | S_L+2 | | S_L+3 | ... | S_2xL | 191 | . | | . | | | | | 192 | . | | . | | | | | 193 | . | | . | | | | | 194 | S_(D-1)xL+1 | | S_(D-1)xL+2 | | S_(D-1)xL+3 | ... | S_DxL | 195 +-------------+ +-------------+ +-------------+ +-------+ 196 + + + + 197 ------------- ------------- ------------- ------- 198 | XOR | | XOR | | XOR | ... | XOR | 199 ------------- ------------- ------------- ------- 200 = = = = 201 +===+ +===+ +===+ +===+ 202 |C_1| |C_2| |C_3| ... |C_L| 203 +===+ +===+ +===+ +===+ 205 Figure 3: Generating interleaved (column) FEC packets 207 In Figure 3, S_n and C_m denote the source packet with a sequence 208 number n and the interleaved (column) FEC packet with a sequence 209 number m, respectively. 211 1.1. Use Cases 213 We generate one interleaved FEC packet out of D non-consecutive 214 source packets. This repair packet can provide a full recovery of 215 the missing information if there is only one packet missing among the 216 corresponding source packets. This implies that 1-D interleaved FEC 217 protection performs well under bursty loss conditions provided that L 218 is chosen large enough, i.e., L-packet duration should not be shorter 219 than the duration of the burst that is intended to be repaired. 221 For example, consider the scenario depicted in Figure 4 where the 222 sender generates interleaved FEC packets and a bursty loss hits the 223 source packets. Since the number of columns is larger than the 224 number of packets lost due to the bursty loss, the repair operation 225 succeeds. 227 +---+ 228 | 1 | X X X 229 +---+ 231 +---+ +---+ +---+ +---+ 232 | 5 | | 6 | | 7 | | 8 | 233 +---+ +---+ +---+ +---+ 235 +---+ +---+ +---+ +---+ 236 | 9 | | 10| | 11| | 12| 237 +---+ +---+ +---+ +---+ 239 +===+ +===+ +===+ +===+ 240 |C_1| |C_2| |C_3| |C_4| 241 +===+ +===+ +===+ +===+ 243 Figure 4: Example scenario where 1-D interleaved FEC protection 244 succeeds error recovery 246 The sender may generate interleaved FEC packets to combat with the 247 bursty packet losses. However, two or more random packet losses may 248 hit the source and repair packets in the same column. In that case, 249 the repair operation fails. This is illustrated in Figure 5. Note 250 that it is possible that two or more bursty losses may occur in the 251 same source block, in which case interleaved FEC packets may still 252 fail to recover the lost data. 254 +---+ +---+ +---+ 255 | 1 | X | 3 | | 4 | 256 +---+ +---+ +---+ 258 +---+ +---+ +---+ 259 | 5 | X | 7 | | 8 | 260 +---+ +---+ +---+ 262 +---+ +---+ +---+ +---+ 263 | 9 | | 10| | 11| | 12| 264 +---+ +---+ +---+ +---+ 266 +===+ +===+ +===+ +===+ 267 |C_1| |C_2| |C_3| |C_4| 268 +===+ +===+ +===+ +===+ 270 Figure 5: Example scenario where 1-D interleaved FEC protection fails 271 error recovery 273 1.2. Overhead Computation 275 The overhead is defined as the ratio of the number of bytes belonging 276 to the repair packets to the number of bytes belonging to the 277 protected source packets. 279 Assuming that each repair packet carries an equal number of bytes 280 carried by a source packet, we can compute the overhead as follows: 282 Overhead = 1/D 284 where D is the number of rows in the source block. 286 1.3. Relation to Existing Specifications 288 This section discusses the relation of the current specification to 289 other existing specifications. 291 1.3.1. RFC 2733 and RFC 3009 293 The current specification extends the FEC header defined in [RFC2733] 294 and registers a new RTP payload format. This new payload format is 295 not backward compatible with the payload format that was registered 296 by [RFC3009]. 298 1.3.2. SMPTE 2022-1 300 In 2007, the Society of Motion Picture and Television Engineers 301 (SMPTE) - Technology Committee N26 on File Management and Networking 302 Technology - decided to revise the Pro-MPEG Code of Practice (CoP) #3 303 Release 2 specification, which (was initially produced by the Pro- 304 MPEG Forum in 2004) discussed the several aspects of the transmission 305 of MPEG-2 transport streams over IP networks. The new SMPTE 306 specification is referred to as [SMPTE2022-1]. 308 The Pro-MPEG CoP #3 r2 document was originally based on [RFC2733]. 309 SMPTE revised the document by extending the FEC header (by setting 310 the E bit) proposed in [RFC2733]. This extended header offers some 311 improvements. 313 For example, instead of utilizing the bitmap field used in [RFC2733], 314 [SMPTE2022-1] introduces separate fields to convey the number of rows 315 (D) and columns (L) of the source block as well as the type of the 316 repair packet (i.e., whether the repair packet is an interleaved FEC 317 packet computed over a column or a non-interleaved FEC packet 318 computed over a row). These fields plus the base sequence number 319 allow the receiver side to establish the associations between the 320 source and repair packets. Note that although the bitmap field is 321 not utilized, the FEC header of [SMPTE2022-1] inherently carries over 322 the bitmap field from [RFC2733]. 324 On the other hand, some parts of [SMPTE2022-1] are not in compliant 325 with RTP [RFC3550]. For example, [SMPTE2022-1] sets the SSRC field 326 to zero and does not use the timestamp field in the RTP headers of 327 the repair packets (Receivers ignore the timestamps of the repair 328 packets). Furthermore, [SMPTE2022-1] also sets the CC field in the 329 RTP header to zero and does not allow any Contributing Source (CSRC) 330 entry in the RTP header. 332 The current document adopts the extended FEC header of [SMPTE2022-1] 333 and registers a new RTP payload format. At the same time, this 334 document fixes the parts of [SMPTE2022-1] that are not compliant with 335 RTP [RFC3550], except the one discussed below. 337 The baseline header format first proposed in [RFC2733] does not have 338 fields to protect the P and X bits and the CC fields of the source 339 packets associated with a repair packet. Rather, the P bit, X bit 340 and CC field in the RTP header of the repair packet are used to 341 protect those bits and fields. This, however, may sometimes result 342 in failures when doing the RTP header validity checks as specified in 343 [RFC3550]. While this behavior has been fixed in [RFC5109] that 344 obsoleted [RFC2733], the RTP payload format defined in this document 345 still allows for this behavior for legacy purposes. Implementations 346 following this specification must be aware of this potential issue 347 when RTP header validity checks are applied. 349 1.3.3. ETSI TS 102 034 351 In 2009, the Digital Video Broadcasting (DVB) consortium published a 352 technical specification [ETSI-TS-102-034] through European 353 Telecommunications Standards Institute (ETSI). This specification 354 covers several areas related to the transmission of MPEG-2 transport 355 stream-based services over IP networks. 357 The Annex E of [ETSI-TS-102-034] defines an optional protocol for 358 Application-layer FEC (AL-FEC) protection of streaming media for 359 DVB-IP services carried over RTP [RFC3550] transport. AL-FEC 360 protocol uses two layers for protection: a base layer that is 361 produced by a packet-based interleaved parity code, and an 362 enhancement layer that is produced by a Raptor code 363 [I-D.ietf-fecframe-dvb-al-fec]. While the use of the enhancement 364 layer is optional, the use of the base layer is mandatory wherever 365 AL-FEC is used. The DVB AL-FEC protocol is also described in 366 [I-D.ietf-fecframe-dvb-al-fec]. 368 The interleaved parity code that is used in the base layer is a 369 subset of [SMPTE2022-1]. In particular, AL-FEC base layer uses only 370 the 1-D interleaved FEC protection from [SMPTE2022-1]. The new RTP 371 payload format that is defined and registered in this document (with 372 some exceptions listed in [I-D.ietf-fecframe-dvb-al-fec]) is used as 373 the AL-FEC base layer. 375 1.4. Scope of the Payload Format 377 The payload format specified in this document must only be used in 378 legacy applications where the limitations explained in Section 1.3.2 379 are known not to impact any system components or other RTP elements. 380 Whenever possible a payload format that is fully compliant with 381 [RFC3550], such as [RFC5109] or other newer payload formats, must be 382 used. 384 2. Requirements Notation 386 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 387 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 388 document are to be interpreted as described in [RFC2119]. 390 3. Definitions, Notations and Abbreviations 392 The definitions and notations commonly used in this document are 393 summarized in this section. 395 3.1. Definitions 397 This document uses the following definitions: 399 Source Flow: The packet flow(s) carrying the source data and to 400 which FEC protection is to be applied. 402 Repair Flow: The packet flow(s) carrying the repair data. 404 Symbol: A unit of data. Its size, in bytes, is referred to as the 405 symbol size. 407 Source Symbol: The smallest unit of data used during the encoding 408 process. 410 Repair Symbol: Repair symbols are generated from the source symbols. 412 Source Packet: Data packets that contain only source symbols. 414 Repair Packet: Data packets that contain only repair symbols. 416 Source Block: A block of source symbols that are considered together 417 in the encoding process. 419 3.2. Notations 421 o L: Number of columns of the source block. 423 o D: Number of rows of the source block. 425 4. Packet Formats 427 This section defines the formats of the source and repair packets. 429 4.1. Source Packets 431 The source packets need to contain information that identifies the 432 source block and the position within the source block occupied by the 433 packet. Since the source packets that are carried within an RTP 434 stream already contain unique sequence numbers in their RTP headers 435 [RFC3550], we can identify the source packets in a straightforward 436 manner and there is no need to append additional field(s). The 437 primary advantage of not modifying the source packets in any way is 438 that it provides backward compatibility for the receivers that do not 439 support FEC at all. In multicast scenarios, this backward 440 compatibility becomes quite useful as it allows the non-FEC-capable 441 and FEC-capable receivers to receive and interpret the same source 442 packets sent in the same multicast session. 444 4.2. Repair Packets 446 The repair packets MUST contain information that identifies the 447 source block they pertain to and the relationship between the 448 contained repair symbols and the original source block. For this 449 purpose, we use the RTP header of the repair packets as well as 450 another header within the RTP payload, which we refer to as the FEC 451 header, as shown in Figure 6. 453 +------------------------------+ 454 | IP Header | 455 +------------------------------+ 456 | Transport Header | 457 +------------------------------+ 458 | RTP Header | __ 459 +------------------------------+ | 460 | FEC Header | \ 461 +------------------------------+ > RTP Payload 462 | Repair Symbols | / 463 +------------------------------+ __| 465 Figure 6: Format of repair packets 467 The RTP header is formatted according to [RFC3550] with some further 468 clarifications listed below: 470 o Version: The version field is set to 2. 472 o Padding (P) Bit: This bit is equal to the XOR sum of the 473 corresponding P bits from the RTP headers of the source packets 474 protected by this repair packet. However, padding octets are 475 never present in a repair packet, independent of the value of the 476 P bit. 478 o Extension (X) Bit: This bit is equal to the XOR sum of the 479 corresponding X bits from the RTP headers of the source packets 480 protected by this repair packet. However, an RTP header extension 481 is never present in a repair packet, independent of the value of 482 the X bit. 484 o CSRC Count (CC): This field is equal to the XOR sum of the 485 corresponding CC values from the RTP headers of the source packets 486 protected by this repair packet. However, a CSRC list is never 487 present in a repair packet, independent of the value of the CC 488 field. 490 o Marker (M) Bit: This bit is equal to the XOR sum of the 491 corresponding M bits from the RTP headers of the source packets 492 protected by this repair packet. 494 o Payload Type: The (dynamic) payload type for the repair packets 495 is determined through out-of-band means. Note that this document 496 registers a new payload format for the repair packets (Refer to 497 Section 5 for details). According to [RFC3550], an RTP receiver 498 that cannot recognize a payload type must discard it. This action 499 provides backward compatibility. The FEC mechanisms can then be 500 used in a multicast group with mixed FEC-capable and non-FEC- 501 capable receivers. If a non-FEC-capable receiver receives a 502 repair packet, it will not recognize the payload type, and hence, 503 discards the repair packet. 505 o Sequence Number (SN): The sequence number has the standard 506 definition. It MUST be one higher than the sequence number in the 507 previously transmitted repair packet. The initial value of the 508 sequence number SHOULD be random (unpredictable) [RFC3550]. 510 o Timestamp (TS): The timestamp SHALL be set to a time 511 corresponding to the repair packet's transmission time. Note that 512 the timestamp value has no use in the actual FEC protection 513 process and is usually useful for jitter calculations. 515 o Synchronization Source (SSRC): The SSRC value SHALL be randomly 516 assigned as suggested by [RFC3550]. This allows the sender to 517 multiplex the source and repair flows on the same port, or 518 multiplex multiple repair flows on a single port. The repair 519 flows SHOULD use the RTCP CNAME field to associate themselves with 520 the source flow. 522 In some networks, the RTP Source, which produces the source 523 packets and the FEC Source, which generates the repair packets 524 from the source packets may not be the same host. In such 525 scenarios, using the same CNAME for the source and repair flows 526 means that the RTP Source and the FEC Source MUST share the same 527 CNAME (for this specific source-repair flow association). A 528 common CNAME may be produced based on an algorithm that is known 529 both to the RTP and FEC Source. This usage is compliant with 530 [RFC3550]. 532 Note that due to the randomness of the SSRC assignments, there is 533 a possibility of SSRC collision. In such cases, the collisions 534 MUST be resolved as described in [RFC3550]. 536 Note that the P bit, X bit, CC field and M bit of the source packets 537 are protected by the corresponding bits/fields in the RTP header of 538 the repair packet. On the other hand, the payload of a repair packet 539 protects the concatenation of (if present) the CSRC list, RTP 540 extension, payload and padding of the source RTP packets associated 541 with this repair packet. 543 The FEC header is 16 octets. The format of the FEC header is shown 544 in Figure 7. 546 0 1 2 3 547 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 1 548 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 549 | SN base low | Length recovery | 550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 551 |E| PT recovery | Mask | 552 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 553 | TS recovery | 554 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 555 |N|D|Type |Index| Offset | NA | SN base ext | 556 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 558 Figure 7: Format of the FEC header 560 The FEC header consists of the following fields: 562 o The SN base low field is used to indicate the lowest sequence 563 number, taking wrap around into account, of those source packets 564 protected by this repair packet. 566 o The Length recovery field is used to determine the length of any 567 recovered packets. 569 o The E bit is the extension flag introduced in [RFC2733] and used 570 to extend the [RFC2733] FEC header. 572 o The PT recovery field is used to determine the payload type of the 573 recovered packets. 575 o The Mask field is not used. 577 o The TS recovery field is used to determine the timestamp of the 578 recovered packets. 580 o The N bit is the extension flag that is reserved for future uses. 582 o The D bit is not used. 584 o The Type field indicates the type of the error-correcting code 585 used. This document defines only one error-correcting code. 587 o The Index field is not used. 589 o The Offset and NA fields are used to indicate the number of 590 columns (L) and rows (D) of the source block, respectively. 592 o The SN base ext field is not used. 594 The details on setting the fields in the FEC header are provided in 595 Section 6.2. 597 It should be noted that a mask-based approach (similar to the one 598 specified in [RFC2733]) may not be very efficient to indicate which 599 source packets in the current source block are associated with a 600 given repair packet. In particular, for the applications that would 601 like to use large source block sizes, the size of the mask that is 602 required to describe the source-repair packet associations may be 603 prohibitively large. Instead, a systematized approach is inherently 604 more efficient. 606 5. Payload Format Parameters 608 This section provides the media subtype registration for the 1-D 609 interleaved parity FEC. The parameters that are required to 610 configure the FEC encoding and decoding operations are also defined 611 in this section. 613 5.1. Media Type Registration 615 This registration is done using the template defined in [RFC4288] and 616 following the guidance provided in [RFC3555]. 618 Note to the RFC Editor: In the following sections, please replace 619 "XXXX" with the number of this document prior to publication as an 620 RFC. 622 5.1.1. Registration of audio/1d-interleaved-parityfec 624 Type name: audio 626 Subtype name: 1d-interleaved-parityfec 628 Required parameters: 630 o rate: The RTP timestamp (clock) rate in Hz. The (integer) rate 631 SHALL be larger than 1000 to provide sufficient resolution to RTCP 632 operations. However, it is RECOMMENDED to select the rate that 633 matches the rate of the protected source RTP stream. 635 o L: Number of columns of the source block. L is a positive 636 integer that is less than or equal to 255. 638 o D: Number of rows of the source block. D is a positive integer 639 that is less than or equal to 255. 641 o repair-window: The time that spans the source packets and the 642 corresponding repair packets. An FEC encoder processes a block of 643 source packets and generates a number of repair packets, which are 644 then transmitted within a certain duration. At the receiver, the 645 FEC decoder tries to decode all the packets received within the 646 repair window to recover the missing packets. Assuming that there 647 is no issue of delay variation, the FEC decoder SHOULD NOT wait 648 longer than the repair window since additional waiting would not 649 help the recovery process. The size of the repair window is 650 specified in microseconds. 652 Optional parameters: None. 654 Encoding considerations: This media type is framed (See Section 4.8 655 in the template document [RFC4288]) and contains binary data. 657 Security considerations: See Section 9 of [RFCXXXX]. 659 Interoperability considerations: None. 661 Published specification: [RFCXXXX]. 663 Applications that use this media type: Multimedia applications that 664 want to improve resiliency against packet loss by sending redundant 665 data in addition to the source media. 667 Additional information: None. 669 Person & email address to contact for further information: Ali Begen 670 and IETF Audio/Video Transport Working Group. 672 Intended usage: COMMON. 674 Restriction on usage: This media type depends on RTP framing, and 675 hence, is only defined for transport via RTP [RFC3550]. 677 Author: Ali Begen . 679 Change controller: IETF Audio/Video Transport Working Group 680 delegated from the IESG. 682 5.1.2. Registration of video/1d-interleaved-parityfec 684 Type name: video 686 Subtype name: 1d-interleaved-parityfec 688 Required parameters: 690 o rate: The RTP timestamp (clock) rate in Hz. The (integer) rate 691 SHALL be larger than 1000 to provide sufficient resolution to RTCP 692 operations. However, it is RECOMMENDED to select the rate that 693 matches the rate of the protected source RTP stream. 695 o L: Number of columns of the source block. L is a positive 696 integer that is less than or equal to 255. 698 o D: Number of rows of the source block. D is a positive integer 699 that is less than or equal to 255. 701 o repair-window: The time that spans the source packets and the 702 corresponding repair packets. An FEC encoder processes a block of 703 source packets and generates a number of repair packets, which are 704 then transmitted within a certain duration. At the receiver, the 705 FEC decoder tries to decode all the packets received within the 706 repair window to recover the missing packets. Assuming that there 707 is no issue of delay variation, the FEC decoder SHOULD NOT wait 708 longer than the repair window since additional waiting would not 709 help the recovery process. The size of the repair window is 710 specified in microseconds. 712 Optional parameters: None. 714 Encoding considerations: This media type is framed (See Section 4.8 715 in the template document [RFC4288]) and contains binary data. 717 Security considerations: See Section 9 of [RFCXXXX]. 719 Interoperability considerations: None. 721 Published specification: [RFCXXXX]. 723 Applications that use this media type: Multimedia applications that 724 want to improve resiliency against packet loss by sending redundant 725 data in addition to the source media. 727 Additional information: None. 729 Person & email address to contact for further information: Ali Begen 730 and IETF Audio/Video Transport Working Group. 732 Intended usage: COMMON. 734 Restriction on usage: This media type depends on RTP framing, and 735 hence, is only defined for transport via RTP [RFC3550]. 737 Author: Ali Begen . 739 Change controller: IETF Audio/Video Transport Working Group 740 delegated from the IESG. 742 5.1.3. Registration of text/1d-interleaved-parityfec 744 Type name: text 746 Subtype name: 1d-interleaved-parityfec 748 Required parameters: 750 o rate: The RTP timestamp (clock) rate in Hz. The (integer) rate 751 SHALL be larger than 1000 to provide sufficient resolution to RTCP 752 operations. However, it is RECOMMENDED to select the rate that 753 matches the rate of the protected source RTP stream. 755 o L: Number of columns of the source block. L is a positive 756 integer that is less than or equal to 255. 758 o D: Number of rows of the source block. D is a positive integer 759 that is less than or equal to 255. 761 o repair-window: The time that spans the source packets and the 762 corresponding repair packets. An FEC encoder processes a block of 763 source packets and generates a number of repair packets, which are 764 then transmitted within a certain duration. At the receiver, the 765 FEC decoder tries to decode all the packets received within the 766 repair window to recover the missing packets. Assuming that there 767 is no issue of delay variation, the FEC decoder SHOULD NOT wait 768 longer than the repair window since additional waiting would not 769 help the recovery process. The size of the repair window is 770 specified in microseconds. 772 Optional parameters: None. 774 Encoding considerations: This media type is framed (See Section 4.8 775 in the template document [RFC4288]) and contains binary data. 777 Security considerations: See Section 9 of [RFCXXXX]. 779 Interoperability considerations: None. 781 Published specification: [RFCXXXX]. 783 Applications that use this media type: Multimedia applications that 784 want to improve resiliency against packet loss by sending redundant 785 data in addition to the source media. 787 Additional information: None. 789 Person & email address to contact for further information: Ali Begen 790 and IETF Audio/Video Transport Working Group. 792 Intended usage: COMMON. 794 Restriction on usage: This media type depends on RTP framing, and 795 hence, is only defined for transport via RTP [RFC3550]. 797 Author: Ali Begen . 799 Change controller: IETF Audio/Video Transport Working Group 800 delegated from the IESG. 802 5.1.4. Registration of application/1d-interleaved-parityfec 804 Type name: application 806 Subtype name: 1d-interleaved-parityfec 808 Required parameters: 810 o rate: The RTP timestamp (clock) rate in Hz. The (integer) rate 811 SHALL be larger than 1000 to provide sufficient resolution to RTCP 812 operations. However, it is RECOMMENDED to select the rate that 813 matches the rate of the protected source RTP stream. 815 o L: Number of columns of the source block. L is a positive 816 integer that is less than or equal to 255. 818 o D: Number of rows of the source block. D is a positive integer 819 that is less than or equal to 255. 821 o repair-window: The time that spans the source packets and the 822 corresponding repair packets. An FEC encoder processes a block of 823 source packets and generates a number of repair packets, which are 824 then transmitted within a certain duration. At the receiver, the 825 FEC decoder tries to decode all the packets received within the 826 repair window to recover the missing packets. Assuming that there 827 is no issue of delay variation, the FEC decoder SHOULD NOT wait 828 longer than the repair window since additional waiting would not 829 help the recovery process. The size of the repair window is 830 specified in microseconds. 832 Optional parameters: None. 834 Encoding considerations: This media type is framed (See Section 4.8 835 in the template document [RFC4288]) and contains binary data. 837 Security considerations: See Section 9 of [RFCXXXX]. 839 Interoperability considerations: None. 841 Published specification: [RFCXXXX]. 843 Applications that use this media type: Multimedia applications that 844 want to improve resiliency against packet loss by sending redundant 845 data in addition to the source media. 847 Additional information: None. 849 Person & email address to contact for further information: Ali Begen 850 and IETF Audio/Video Transport Working Group. 852 Intended usage: COMMON. 854 Restriction on usage: This media type depends on RTP framing, and 855 hence, is only defined for transport via RTP [RFC3550]. 857 Author: Ali Begen . 859 Change controller: IETF Audio/Video Transport Working Group 860 delegated from the IESG. 862 5.2. Mapping to SDP Parameters 864 Applications that are using RTP transport commonly use Session 865 Description Protocol (SDP) [RFC4566] to describe their RTP sessions. 866 The information that is used to specify the media types in an RTP 867 session has specific mappings to the fields in an SDP description. 868 In this section, we provide these mappings for the media subtype 869 registered by this document ("1d-interleaved-parityfec"). Note that 870 if an application does not use SDP to describe the RTP sessions, an 871 appropriate mapping must be defined and used to specify the media 872 types and their parameters for the control/description protocol 873 employed by the application. 875 The mapping of the media type specification for "1d-interleaved- 876 parityfec" and its parameters in SDP is as follows: 878 o The media type (e.g., "application") goes into the "m=" line as 879 the media name. 881 o The media subtype ("1d-interleaved-parityfec") goes into the 882 "a=rtpmap" line as the encoding name. The RTP clock rate 883 parameter ("rate") also goes into the "a=rtpmap" line as the clock 884 rate. 886 o The remaining required payload-format-specific parameters go into 887 the "a=fmtp" line by copying them directly from the media type 888 string as a semicolon-separated list of parameter=value pairs. 890 SDP examples are provided in Section 7. 892 5.2.1. Offer-Answer Model Considerations 894 When offering 1-D interleaved parity FEC over RTP using SDP in an 895 Offer/Answer model [RFC3264], the following considerations apply: 897 o Each combination of the L and D parameters produces a different 898 FEC data and is not compatible with any other combination. A 899 sender application may desire to offer multiple offers with 900 different sets of L and D values as long as the parameter values 901 are valid. The receiver SHOULD normally choose the offer that has 902 a sufficient amount of interleaving. If multiple such offers 903 exist, the receiver may choose the offer that has the lowest 904 overhead or the one that requires the smallest amount of 905 buffering. The selection depends on the application requirements. 907 o The value for the repair-window parameter depends on the L and D 908 values and cannot be chosen arbitrarily. More specifically, L and 909 D values determine the lower limit for the repair-window size. 910 The upper limit of the repair-window size does not depend on the L 911 and D values. 913 o Although combinations with the same L and D values but with 914 different repair-window sizes produce the same FEC data, such 915 combinations are still considered different offers. The size of 916 the repair-window is related to the maximum delay between the 917 transmission of a source packet and the associated repair packet. 918 This directly impacts the buffering requirement on the receiver 919 side and the receiver must consider this when choosing an offer. 921 o There are no optional format parameters defined for this payload. 922 Any unknown option in the offer MUST be ignored and deleted from 923 the answer. If FEC is not desired by the receiver, it can be 924 deleted from the answer. 926 5.2.2. Declarative Considerations 928 In declarative usage, like SDP in the Real-time Streaming Protocol 929 (RTSP) [RFC2326] or the Session Announcement Protocol (SAP) 930 [RFC2974], the following considerations apply: 932 o The payload format configuration parameters are all declarative 933 and a participant MUST use the configuration that is provided for 934 the session. 936 o More than one configuration may be provided (if desired) by 937 declaring multiple RTP payload types. In that case, the receivers 938 should choose the repair flow that is best for them. 940 6. Protection and Recovery Procedures 942 This section provides a complete specification of the 1-D interleaved 943 parity code and its RTP payload format. 945 6.1. Overview 947 The following sections specify the steps involved in generating the 948 repair packets and reconstructing the missing source packets from the 949 repair packets. 951 6.2. Repair Packet Construction 953 The RTP header of a repair packet is formed based on the guidelines 954 given in Section 4.2. 956 The FEC header includes 16 octets. It is constructed by applying the 957 XOR operation on the bit strings that are generated from the 958 individual source packets protected by this particular repair packet. 959 The set of the source packets that are associated with a given repair 960 packet can be computed by the formula given in Section 6.3.1. 962 The bit string is formed for each source packet by concatenating the 963 following fields together in the order specified: 965 o Padding bit (1 bit) (This is the most significant bit of the bit 966 string) 968 o Extension bit (1 bit) 970 o CC field (4 bits) 972 o Marker bit (1 bit) 974 o PT field (7 bits) 976 o Timestamp (32 bits) 977 o Unsigned network-ordered 16-bit representation of the source 978 packet length in bytes minus 12 (for the fixed RTP header), i.e., 979 the sum of the lengths of all the following if present: the CSRC 980 list, header extension, RTP payload and RTP padding (16 bits) 982 o If CC is nonzero, the CSRC list (variable length) 984 o If X is 1, the header extension (variable length) 986 o Payload (variable length) 988 o Padding, if present (variable length) 990 Note that if the lengths of the source packets are not equal, each 991 shorter packet MUST be padded to the length of the longest packet by 992 adding octet 0's at the end. Due to this possible padding and 993 mandatory FEC header, a repair packet has a larger size than the 994 source packets it protects. This may cause problems if the resulting 995 repair packet size exceeds the Maximum Transmission Unit (MTU) size 996 of the path over which the repair flow is sent. 998 By applying the parity operation on the bit strings produced from the 999 source packets, we generate the FEC bit string. Some parts of the 1000 RTP header and the FEC header of the repair packet are generated from 1001 the FEC bit string as follows: 1003 o The first (most significant) bit in the FEC bit string is written 1004 into the Padding bit in the RTP header of the repair packet. 1006 o The next bit in the FEC bit string is written into the Extension 1007 bit in the RTP header of the repair packet. 1009 o The next 4 bits of the FEC bit string are written into the CC 1010 field in the RTP header of the repair packet. 1012 o The next bit of the FEC bit string is written into the Marker bit 1013 in the RTP header of the repair packet. 1015 o The next 7 bits of the FEC bit string are written into the PT 1016 recovery field in the FEC header. 1018 o The next 32 bits of the FEC bit string are written into the TS 1019 recovery field in the FEC header. 1021 o The next 16 bits are written into the Length recovery field in the 1022 FEC header. This allows the FEC procedure to be applied even when 1023 the lengths of the protected source packets are not identical. 1025 o The remaining bits are set to be the payload of the repair packet. 1027 The remaining parts of the FEC header are set as follows: 1029 o The SN base low field MUST be set to the lowest sequence number, 1030 taking wrap around into account, of those source packets protected 1031 by this repair packet. 1033 o The E bit MUST be set to 1 to extend the [RFC2733] FEC header. 1035 o The Mask field SHALL be set to 0 and ignored by the receiver. 1037 o The N bit SHALL be set to 0 and ignored by the receiver. 1039 o The D bit SHALL be set to 0 and ignored by the receiver. 1041 o The Type field MUST be set to 0. 1043 o The Index field SHALL be set to 0 and ignored by the receiver. 1045 o The Offset field MUST be set to the number of columns of the 1046 source block (L). 1048 o The NA field MUST be set to the number of rows of the source block 1049 (D). 1051 o The SN base ext field SHALL be set to 0 and ignored by the 1052 receiver. 1054 6.3. Source Packet Reconstruction 1056 This section describes the recovery procedures that are required to 1057 reconstruct the missing source packets. The recovery process has two 1058 steps. In the first step, the FEC decoder determines which source 1059 and repair packets should be used in order to recover a missing 1060 packet. In the second step, the decoder recovers the missing packet, 1061 which consists of an RTP header and RTP payload. 1063 In the following, we describe the RECOMMENDED algorithms for the 1064 first and second steps. Based on the implementation, different 1065 algorithms MAY be adopted. However, the end result MUST be identical 1066 to the one produced by the algorithms described below. 1068 6.3.1. Associating the Source and Repair Packets 1070 The first step is to associate the source and repair packets. The SN 1071 base low field in the FEC header shows the lowest sequence number of 1072 the source packets that form the particular column. In addition, the 1073 information of how many source packets are available in each column 1074 and row is available from the media type parameters specified in the 1075 SDP description. This set of information uniquely identifies all of 1076 the source packets associated with a given repair packet. 1078 Mathematically, for any received repair packet, p*, we can determine 1079 the sequence numbers of the source packets that are protected by this 1080 repair packet as follows: 1082 p*_snb + i * L (modulo 65536) 1084 where p*_snb denotes the value in the SN base low field of p*'s FEC 1085 header, L is the number of columns of the source block and 1087 0 <= i < D 1089 where D is the number of rows of the source block. 1091 We denote the set of the source packets associated with repair packet 1092 p* by set T(p*). Note that in a source block whose size is L columns 1093 by D rows, set T includes D source packets. Recall that 1-D 1094 interleaved FEC protection can fully recover the missing information 1095 if there is only one source packet missing in set T. If the repair 1096 packet that protects the source packets in set T is missing, or the 1097 repair packet is available but two or more source packets are 1098 missing, then missing source packets in set T cannot be recovered by 1099 1-D interleaved FEC protection. 1101 6.3.2. Recovering the RTP Header and Payload 1103 For a given set T, the procedure for the recovery of the RTP header 1104 of the missing packet, whose sequence number is denoted by SEQNUM, is 1105 as follows: 1107 1. For each of the source packets that are successfully received in 1108 set T, compute the bit string as described in Section 6.2. 1110 2. For the repair packet associated with set T, compute the bit 1111 string in the same fashion except use the PT recovery field 1112 instead of the PT field and TS recovery field instead of the 1113 Timestamp field, and set the CSRC list, header extension and 1114 padding to null regardless of the values of the CC field, X bit 1115 and P bit. 1117 3. If any of the bit strings generated from the source packets are 1118 shorter than the bit string generated from the repair packet, 1119 pad them to be the same length as the bit string generated from 1120 the repair packet. For padding, the padding of octet 0 MUST be 1121 added at the end of the bit string. 1123 4. Calculate the recovered bit string as the XOR of the bit strings 1124 generated from all source packets in set T and the FEC bit 1125 string generated from the repair packet associated with set T. 1127 5. Create a new packet with the standard 12-byte RTP header and no 1128 payload. 1130 6. Set the version of the new packet to 2. 1132 7. Set the Padding bit in the new packet to the first bit in the 1133 recovered bit string. 1135 8. Set the Extension bit in the new packet to the next bit in the 1136 recovered bit string. 1138 9. Set the CC field to the next 4 bits in the recovered bit string. 1140 10. Set the Marker bit in the new packet to the next bit in the 1141 recovered bit string. 1143 11. Set the Payload type in the new packet to the next 7 bits in the 1144 recovered bit string. 1146 12. Set the SN field in the new packet to SEQNUM. 1148 13. Set the TS field in the new packet to the next 32 bits in the 1149 recovered bit string. 1151 14. Take the next 16 bits of the recovered bit string and set the 1152 new variable Y to whatever unsigned integer this represents 1153 (assuming network order). Convert Y to host order and then take 1154 Y bytes from the recovered bit string and append them to the new 1155 packet. Y represents the length of the new packet in bytes 1156 minus 12 (for the fixed RTP header), i.e., the sum of the 1157 lengths of all the following if present: the CSRC list, header 1158 extension, RTP payload and RTP padding. 1160 15. Set the SSRC of the new packet to the SSRC of the source RTP 1161 stream. 1163 This procedure completely recovers both the header and payload of an 1164 RTP packet. 1166 7. Session Description Protocol (SDP) Signaling 1168 This section provides an SDP [RFC4566] example. The following 1169 example uses the FEC grouping semantics [I-D.ietf-mmusic-rfc4756bis]. 1171 In this example, we have one source video stream (mid:S1) and one FEC 1172 repair stream (mid:R1). We form one FEC group with the "a=group:FEC 1173 S1 R1" line. The source and repair streams are sent to the same port 1174 on different multicast groups. The repair window is set to 200 ms. 1176 v=0 1177 o=ali 1122334455 1122334466 IN IP4 fec.example.com 1178 s=Interleaved Parity FEC Example 1179 t=0 0 1180 a=group:FEC S1 R1 1181 m=video 30000 RTP/AVP 100 1182 c=IN IP4 233.252.0.1/127 1183 a=rtpmap:100 MP2T/90000 1184 a=mid:S1 1185 m=application 30000 RTP/AVP 110 1186 c=IN IP4 233.252.0.2/127 1187 a=rtpmap:110 1d-interleaved-parityfec/90000 1188 a=fmtp:110 L:5; D:10; repair-window:200000 1189 a=mid:R1 1191 8. Congestion Control Considerations 1193 FEC is an effective approach to provide applications resiliency 1194 against packet losses. However, in networks where the congestion is 1195 a major contributor to the packet loss, the potential impacts of 1196 using FEC SHOULD be considered carefully before injecting the repair 1197 flows into the network. In particular, in bandwidth-limited 1198 networks, FEC repair flows may consume most or all of the available 1199 bandwidth and may consequently congest the network. In such cases, 1200 the applications MUST NOT arbitrarily increase the amount of FEC 1201 protection since doing so may lead to a congestion collapse. If 1202 desired, stronger FEC protection MAY be applied only after the source 1203 rate has been reduced. 1205 In a network-friendly implementation, an application SHOULD NOT send/ 1206 receive FEC repair flows if it knows that sending/receiving those FEC 1207 repair flows would not help at all in recovering the missing packets. 1208 Such a practice helps reduce the amount of wasted bandwidth. It is 1209 RECOMMENDED that the amount of FEC protection is adjusted dynamically 1210 based on the packet loss rate observed by the applications. 1212 In multicast scenarios, it may be difficult to optimize the FEC 1213 protection per receiver. If there is a large variation among the 1214 levels of FEC protection needed by different receivers, it is 1215 RECOMMENDED that the sender offers multiple repair flows with 1216 different levels of FEC protection and the receivers join the 1217 corresponding multicast sessions to receive the repair flow(s) that 1218 is best for them. 1220 9. Security Considerations 1222 RTP packets using the payload format defined in this specification 1223 are subject to the security considerations discussed in the RTP 1224 specification [RFC3550] and in any applicable RTP profile. 1226 The main security considerations for the RTP packet carrying the RTP 1227 payload format defined within this memo are confidentiality, 1228 integrity and source authenticity. Confidentiality is achieved by 1229 encrypting the RTP payload. Altering the FEC packets can have a big 1230 impact on the reconstruction operation. An attack by changing some 1231 bits in the FEC packets can have a significant effect on the 1232 calculation and the recovery of the source packets. For example, 1233 changing the length recovery field can result in the recovery of a 1234 packet that is too long. Depending on the application, it may be 1235 helpful to perform a sanity check on the received source and FEC 1236 packets before performing the recovery operation and to determine the 1237 validity of the recovered packets before using them. 1239 Integrity of the RTP packets is achieved through a suitable 1240 cryptographic integrity protection mechanism. Such a cryptographic 1241 system may also allow the authentication of the source of the 1242 payload. A suitable security mechanism for this RTP payload format 1243 should provide source authentication capable of determining if an RTP 1244 packet is from a member of the RTP session. 1246 Note that the appropriate mechanism to provide security to RTP and 1247 payloads following this memo may vary. It is dependent on the 1248 application, transport and signaling protocol employed. Therefore, a 1249 single mechanism is not sufficient, although if suitable, using the 1250 Secure Real-time Transport Protocol (SRTP) [RFC3711] is RECOMMENDED. 1251 Other mechanisms that may be used are IPsec [RFC4301] and Transport 1252 Layer Security (TLS) [RFC5246]; other alternatives may exist. 1254 If FEC protection is applied on already encrypted source packets, 1255 there is no need for additional encryption. However, if the source 1256 packets are encrypted after FEC protection is applied, the FEC 1257 packets should be cryptographically as secure as the source packets. 1258 Failure to provide an equal level of confidentiality, integrity and 1259 authentication to the FEC packets can compromise the source packets' 1260 confidentiality, integrity or authentication since the FEC packets 1261 are generated by applying XOR operation across the source packets. 1263 10. IANA Considerations 1265 New media subtypes are subject to IANA registration. For the 1266 registration of the payload format and its parameters introduced in 1267 this document, refer to Section 5. 1269 11. Acknowledgments 1271 A major part of this document is borrowed from [RFC2733], [RFC5109] 1272 and [SMPTE2022-1]. Thus, the author would like to thank the authors 1273 and editors of these earlier specifications. The author also thanks 1274 Colin Perkins for his constructive suggestions for this document. 1276 12. Change Log 1278 12.1. draft-ietf-fecframe-interleaved-fec-scheme-08 1280 The following are the major changes compared to version 07: 1282 o Comments from the gen-art, media-type and IESG reviews have been 1283 addressed. 1285 12.2. draft-ietf-fecframe-interleaved-fec-scheme-07 1287 The following are the major changes compared to version 06: 1289 o The definition of "rate" in the media type registration has been 1290 clarified. 1292 12.3. draft-ietf-fecframe-interleaved-fec-scheme-06 1294 The following are the major changes compared to version 05: 1296 o Comments from IETF LC have been addressed. 1298 12.4. draft-ietf-fecframe-interleaved-fec-scheme-05 1300 The following are the major changes compared to version 04: 1302 o Comments from Vincent Roca have been addressed. 1304 12.5. draft-ietf-fecframe-interleaved-fec-scheme-04 1306 The following are the major changes compared to version 03: 1308 o Further comments from AVT WG have been addressed. 1310 12.6. draft-ietf-fecframe-interleaved-fec-scheme-03 1312 The following are the major changes compared to version 02: 1314 o Comments from WGLC have been addressed. 1316 12.7. draft-ietf-fecframe-interleaved-fec-scheme-02 1318 The following are the major changes compared to version 01: 1320 o Some details were added regarding the use of CNAME field. 1322 o Offer-Answer and Declarative Considerations sections have been 1323 completed. 1325 o Security Considerations section has been completed. 1327 12.8. draft-ietf-fecframe-interleaved-fec-scheme-01 1329 The following are the major changes compared to version 00: 1331 o The timestamp field definition has changed. 1333 12.9. draft-ietf-fecframe-interleaved-fec-scheme-00 1335 This is the initial version, which is based on an earlier individual 1336 submission. The following are the major changes compared to that 1337 document: 1339 o Per the discussion in the WG, references to the FEC Framework have 1340 been removed and the document has been turned into a pure RTP 1341 payload format specification. 1343 o A new section is added for congestion control considerations. 1345 o Editorial changes to clarify a few points. 1347 13. References 1348 13.1. Normative References 1350 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1351 Requirement Levels", BCP 14, RFC 2119, March 1997. 1353 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 1354 Jacobson, "RTP: A Transport Protocol for Real-Time 1355 Applications", STD 64, RFC 3550, July 2003. 1357 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1358 Description Protocol", RFC 4566, July 2006. 1360 [I-D.ietf-mmusic-rfc4756bis] 1361 Begen, A., "Forward Error Correction Grouping Semantics in 1362 Session Description Protocol", 1363 draft-ietf-mmusic-rfc4756bis-05 (work in progress), 1364 October 2009. 1366 [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and 1367 Registration Procedures", BCP 13, RFC 4288, December 2005. 1369 [RFC3555] Casner, S. and P. Hoschka, "MIME Type Registration of RTP 1370 Payload Formats", RFC 3555, July 2003. 1372 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1373 with Session Description Protocol (SDP)", RFC 3264, 1374 June 2002. 1376 13.2. Informative References 1378 [I-D.ietf-fecframe-dvb-al-fec] 1379 Begen, A. and T. Stockhammer, "Guidelines for Implementing 1380 DVB-IPTV Application-Layer Hybrid FEC Protection", 1381 draft-ietf-fecframe-dvb-al-fec-04 (work in progress), 1382 December 2009. 1384 [RFC2733] Rosenberg, J. and H. Schulzrinne, "An RTP Payload Format 1385 for Generic Forward Error Correction", RFC 2733, 1386 December 1999. 1388 [RFC3009] Rosenberg, J. and H. Schulzrinne, "Registration of 1389 parityfec MIME types", RFC 3009, November 2000. 1391 [RFC5109] Li, A., "RTP Payload Format for Generic Forward Error 1392 Correction", RFC 5109, December 2007. 1394 [ETSI-TS-102-034] 1395 ETSI TS 102 034 V1.4.1, "Transport of MPEG 2 TS Based DVB 1396 Services over IP Based Networks", August 2009. 1398 [RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time 1399 Streaming Protocol (RTSP)", RFC 2326, April 1998. 1401 [RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session 1402 Announcement Protocol", RFC 2974, October 2000. 1404 [SMPTE2022-1] 1405 SMPTE 2022-1-2007, "Forward Error Correction for Real-Time 1406 Video/Audio Transport over IP Networks", 2007. 1408 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 1409 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 1410 RFC 3711, March 2004. 1412 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1413 Internet Protocol", RFC 4301, December 2005. 1415 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 1416 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 1418 Author's Address 1420 Ali Begen 1421 Cisco 1422 170 West Tasman Drive 1423 San Jose, CA 95134 1424 USA 1426 Email: abegen@cisco.com