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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 Systems 4 Intended status: Standards Track April 18, 2009 5 Expires: October 20, 2009 7 RTP Payload Format for 1-D Interleaved Parity FEC 8 draft-ietf-fecframe-interleaved-fec-scheme-03 10 Status of this Memo 12 This Internet-Draft is submitted to IETF in full conformance with the 13 provisions of BCP 78 and BCP 79. 15 Internet-Drafts are working documents of the Internet Engineering 16 Task Force (IETF), its areas, and its working groups. Note that 17 other groups may also distribute working documents as Internet- 18 Drafts. 20 Internet-Drafts are draft documents valid for a maximum of six months 21 and may be updated, replaced, or obsoleted by other documents at any 22 time. It is inappropriate to use Internet-Drafts as reference 23 material or to cite them other than as "work in progress." 25 The list of current Internet-Drafts can be accessed at 26 http://www.ietf.org/ietf/1id-abstracts.txt. 28 The list of Internet-Draft Shadow Directories can be accessed at 29 http://www.ietf.org/shadow.html. 31 This Internet-Draft will expire on October 20, 2009. 33 Copyright Notice 35 Copyright (c) 2009 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents in effect on the date of 40 publication of this document (http://trustee.ietf.org/license-info). 41 Please review these documents carefully, as they describe your rights 42 and restrictions with respect to this document. 44 Abstract 46 This document defines a new RTP payload format for the Forward Error 47 Correction (FEC) that is generated by the 1-D interleaved parity code 48 from a source media encapsulated in RTP. The 1-D interleaved parity 49 code is a systematic code, where a number of repair symbols are 50 generated from a set of source symbols and sent in a repair flow 51 separate from the source flow that carries the source symbols. The 52 1-D interleaved parity code offers a good protection against bursty 53 packet losses at a cost of decent complexity. The new payload format 54 defined in this document is used (with some exceptions) as a part of 55 the DVB Application-layer FEC specification. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 60 1.1. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . 6 61 1.2. Overhead Computation . . . . . . . . . . . . . . . . . . . 8 62 1.3. Relation to Existing Specifications . . . . . . . . . . . 8 63 1.3.1. RFC 2733 and RFC 3009 . . . . . . . . . . . . . . . . 8 64 1.3.2. SMPTE 2022-1 . . . . . . . . . . . . . . . . . . . . . 8 65 1.3.3. ETSI TS 102 034 . . . . . . . . . . . . . . . . . . . 9 66 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 10 67 3. Definitions, Notations and Abbreviations . . . . . . . . . . . 10 68 3.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 10 69 3.2. Notations . . . . . . . . . . . . . . . . . . . . . . . . 10 70 3.3. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 11 71 4. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 11 72 4.1. Source Packets . . . . . . . . . . . . . . . . . . . . . . 11 73 4.2. Repair Packets . . . . . . . . . . . . . . . . . . . . . . 11 74 5. Payload Format Parameters . . . . . . . . . . . . . . . . . . 15 75 5.1. Media Type Registration . . . . . . . . . . . . . . . . . 15 76 5.1.1. Registration of audio/1d-interleaved-parityfec . . . . 15 77 5.1.2. Registration of video/1d-interleaved-parityfec . . . . 16 78 5.1.3. Registration of text/1d-interleaved-parityfec . . . . 18 79 5.1.4. Registration of 80 application/1d-interleaved-parityfec . . . . . . . . . 19 81 5.2. Mapping to SDP Parameters . . . . . . . . . . . . . . . . 20 82 5.2.1. Offer-Answer Model Considerations . . . . . . . . . . 21 83 5.2.2. Declarative Considerations . . . . . . . . . . . . . . 21 84 6. Protection and Recovery Procedures . . . . . . . . . . . . . . 22 85 6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 22 86 6.2. Repair Packet Construction . . . . . . . . . . . . . . . . 22 87 6.3. Source Packet Reconstruction . . . . . . . . . . . . . . . 24 88 6.3.1. Associating the Source and Repair Packets . . . . . . 24 89 6.3.2. Recovering the RTP Header and Payload . . . . . . . . 25 90 7. Session Description Protocol (SDP) Signaling . . . . . . . . . 26 91 8. Congestion Control Considerations . . . . . . . . . . . . . . 27 92 9. Security Considerations . . . . . . . . . . . . . . . . . . . 28 93 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 94 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28 95 12. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 28 96 12.1. draft-ietf-fecframe-interleaved-fec-scheme-03 . . . . . . 28 97 12.2. draft-ietf-fecframe-interleaved-fec-scheme-02 . . . . . . 29 98 12.3. draft-ietf-fecframe-interleaved-fec-scheme-01 . . . . . . 29 99 12.4. draft-ietf-fecframe-interleaved-fec-scheme-00 . . . . . . 29 100 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29 101 13.1. Normative References . . . . . . . . . . . . . . . . . . . 29 102 13.2. Informative References . . . . . . . . . . . . . . . . . . 30 103 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 31 105 1. Introduction 107 This document extends the Forward Error Correction (FEC) header 108 defined in [RFC2733] and uses this new FEC header for the FEC that is 109 generated by the 1-D interleaved parity code from a source media 110 encapsulated in RTP [RFC3550]. The resulting new RTP payload format 111 is registered by this document. 113 The type of the source media protected by the 1-D interleaved parity 114 code can be audio, video, text or application. The FEC data are 115 generated according to the media type parameters that are 116 communicated through out-of-band means. The associations/ 117 relationships between the source and repair flows are also 118 communicated through out-of-band means. 120 The 1-D interleaved parity FEC uses the exclusive OR (XOR) operation 121 to generate the repair symbols. In a nutshell, the following steps 122 take place: 124 1. The sender determines a set of source packets to be protected 125 together based on the media type parameters. 127 2. The sender applies the XOR operation on the source symbols to 128 generate the required number of repair symbols. 130 3. The sender packetizes the repair symbols and sends the repair 131 packet(s) along with the source packets to the receiver(s) (in 132 different flows). The repair packets MAY be sent proactively or 133 on-demand. 135 Note that the sender MUST transmit the source and repair packets in 136 different source and repair flows, respectively to offer backward 137 compatibility (See Section 4). At the receiver side, if all of the 138 source packets are successfully received, there is no need for FEC 139 recovery and the repair packets are discarded. However, if there are 140 missing source packets, the repair packets can be used to recover the 141 missing information. Block diagrams for the systematic parity FEC 142 encoder and decoder are sketched in Figure 1 and Figure 2, 143 respectively. 145 +------------+ 146 +--+ +--+ +--+ +--+ --> | Systematic | --> +--+ +--+ +--+ +--+ 147 +--+ +--+ +--+ +--+ | Parity FEC | +--+ +--+ +--+ +--+ 148 | Encoder | 149 | (Sender) | --> +==+ +==+ 150 +------------+ +==+ +==+ 152 Source Packet: +--+ Repair Packet: +==+ 153 +--+ +==+ 155 Figure 1: Block diagram for systematic parity FEC encoder 157 +------------+ 158 +--+ X X +--+ --> | Systematic | --> +--+ +--+ +--+ +--+ 159 +--+ +--+ | Parity FEC | +--+ +--+ +--+ +--+ 160 | Decoder | 161 +==+ +==+ --> | (Receiver) | 162 +==+ +==+ +------------+ 164 Source Packet: +--+ Repair Packet: +==+ Lost Packet: X 165 +--+ +==+ 167 Figure 2: Block diagram for systematic parity FEC decoder 169 Suppose that we have a group of D x L source packets that have 170 sequence numbers starting from 1 running to D x L. If we apply the 171 XOR operation to the group of the source packets whose sequence 172 numbers are L apart from each other as sketched in Figure 3, we 173 generate L repair packets. This process is referred to as 1-D 174 interleaved FEC protection, and the resulting L repair packets are 175 referred to as interleaved (or column) FEC packets. 177 +-------------+ +-------------+ +-------------+ +-------+ 178 | S_1 | | S_2 | | S3 | ... | S_L | 179 | S_L+1 | | S_L+2 | | S_L+3 | ... | S_2xL | 180 | . | | . | | | | | 181 | . | | . | | | | | 182 | . | | . | | | | | 183 | S_(D-1)xL+1 | | S_(D-1)xL+2 | | S_(D-1)xL+3 | ... | S_DxL | 184 +-------------+ +-------------+ +-------------+ +-------+ 185 + + + + 186 ------------- ------------- ------------- ------- 187 | XOR | | XOR | | XOR | ... | XOR | 188 ------------- ------------- ------------- ------- 189 = = = = 190 +===+ +===+ +===+ +===+ 191 |C_1| |C_2| |C_3| ... |C_L| 192 +===+ +===+ +===+ +===+ 194 Figure 3: Generating interleaved (column) FEC packets 196 In Figure 3, S_n and C_m denote the source packet with a sequence 197 number n and the interleaved (column) FEC packet with a sequence 198 number m, respectively. 200 1.1. Use Cases 202 We generate one interleaved FEC packet out of D non-consecutive 203 source packets. This repair packet can provide a full recovery of 204 the missing information if there is only one packet missing among the 205 corresponding source packets. This implies that 1-D interleaved FEC 206 protection performs well under bursty loss conditions provided that L 207 is chosen large enough, i.e., L-packet duration SHOULD NOT be shorter 208 than the duration of the burst that is intended to be repaired. 210 For example, consider the scenario depicted in Figure 4 where the 211 sender generates interleaved FEC packets and a bursty loss hits the 212 source packets. Since the number of columns is larger than the 213 number of packets lost due to the bursty loss, the repair operation 214 succeeds. 216 +---+ 217 | 1 | X X X 218 +---+ 220 +---+ +---+ +---+ +---+ 221 | 5 | | 6 | | 7 | | 8 | 222 +---+ +---+ +---+ +---+ 224 +---+ +---+ +---+ +---+ 225 | 9 | | 10| | 11| | 12| 226 +---+ +---+ +---+ +---+ 228 +===+ +===+ +===+ +===+ 229 |C_1| |C_2| |C_3| |C_4| 230 +===+ +===+ +===+ +===+ 232 Figure 4: Example scenario where 1-D interleaved FEC protection 233 succeeds error recovery 235 The sender may generate interleaved FEC packets to combat with the 236 bursty packet losses. However, two or more random packet losses may 237 hit the source and repair packets in the same column. In that case, 238 the repair operation fails. This is illustrated in Figure 5. Note 239 that it is possible that two or more bursty losses may occur in the 240 same source block, in which case interleaved FEC packets may still 241 fail to recover the lost data. 243 +---+ +---+ +---+ 244 | 1 | X | 3 | | 4 | 245 +---+ +---+ +---+ 247 +---+ +---+ +---+ 248 | 5 | X | 7 | | 8 | 249 +---+ +---+ +---+ 251 +---+ +---+ +---+ +---+ 252 | 9 | | 10| | 11| | 12| 253 +---+ +---+ +---+ +---+ 255 +===+ +===+ +===+ +===+ 256 |C_1| |C_2| |C_3| |C_4| 257 +===+ +===+ +===+ +===+ 259 Figure 5: Example scenario where 1-D interleaved FEC protection fails 260 error recovery 262 1.2. Overhead Computation 264 The overhead is defined as the ratio of the number of bytes belonging 265 to the repair packets to the number of bytes belonging to the 266 protected source packets. 268 Assuming that each repair packet carries an equal number of bytes 269 carried by a source packet, we can compute the overhead as follows: 271 Overhead = 1/D 273 where D is the number of rows in the source block. 275 1.3. Relation to Existing Specifications 277 This section discusses the relation of the current specification to 278 other existing specifications. 280 1.3.1. RFC 2733 and RFC 3009 282 The current specification extends the FEC header defined in [RFC2733] 283 and registers a new RTP payload format. This new payload format is 284 not backward compatible with the payload format that was registered 285 by [RFC3009]. 287 1.3.2. SMPTE 2022-1 289 In 2007, the Society of Motion Picture and Television Engineers 290 (SMPTE) - Technology Committee N26 on File Management and Networking 291 Technology - decided to revise the Pro-MPEG Code of Practice (CoP) #3 292 Release 2 specification, which (was initially produced by the Pro- 293 MPEG Forum in 2004) discussed the several aspects of the transmission 294 of MPEG-2 transport streams over IP networks. The new SMPTE 295 specification is referred to as [SMPTE2022-1]. 297 The Pro-MPEG CoP #3 r2 document was originally based on [RFC2733]. 298 SMPTE revised the document by extending the FEC header (by setting 299 the E bit) proposed in [RFC2733]. This extended header offers some 300 improvements. 302 For example, instead of utilizing the bitmap field used in [RFC2733], 303 [SMPTE2022-1] introduces separate fields to convey the number of rows 304 (D) and columns (L) of the source block as well as the type of the 305 repair packet (i.e., whether the repair packet is an interleaved FEC 306 packet computed over a column or a non-interleaved FEC packet 307 computed over a row). These fields plus the base sequence number 308 allow the receiver side to establish the associations between the 309 source and repair packets. Note that although the bitmap field is 310 not utilized, the FEC header of [SMPTE2022-1] inherently carries over 311 the bitmap field from [RFC2733]. 313 On the other hand, some parts of [SMPTE2022-1] are not in compliant 314 with RTP [RFC3550]. For example, [SMPTE2022-1] sets the SSRC field 315 to zero and does not use the timestamp field in the RTP headers of 316 the repair packets (Receivers ignore the timestamps of the repair 317 packets). Furthermore, [SMPTE2022-1] also sets the CC field in the 318 RTP header to zero and does not allow any Contributing Source (CSRC) 319 entry in the RTP header. 321 The current document adopts the extended FEC header of [SMPTE2022-1] 322 and registers a new RTP payload format. At the same time, this 323 document fixes the parts of [SMPTE2022-1] that are not compliant with 324 RTP [RFC3550], except the one discussed below. 326 The baseline header format first proposed in [RFC2733] does not have 327 fields to protect the P and X bits and the CC fields of the source 328 packets associated with a repair packet. Rather, the P bit, X bit 329 and CC field in the RTP header of the repair packet are used to 330 protect those bits and fields. This, however, may sometimes result 331 in failures when doing the RTP header validity checks as specified in 332 [RFC3550]. While this behavior has been fixed in [RFC5109] that 333 obsoleted [RFC2733], the RTP payload format defined in this document 334 still allows for this behavior for legacy purposes. Implementations 335 following this specification MUST be aware of this potential issue 336 when RTP header validity checks are applied. 338 1.3.3. ETSI TS 102 034 340 In 2007, the Digital Video Broadcasting (DVB) consortium published a 341 technical specification [ETSI-TS-102-034] through European 342 Telecommunications Standards Institute (ETSI). This specification 343 covers several areas related to the transmission of MPEG-2 transport 344 stream-based services over IP networks. 346 The Annex E of [ETSI-TS-102-034] defines an optional protocol for 347 Application-layer FEC (AL-FEC) protection of streaming media for 348 DVB-IP services carried over RTP [RFC3550] transport. AL-FEC 349 protocol uses two layers for protection: a base layer that is 350 produced by a packet-based interleaved parity code, and an 351 enhancement layer that is produced by a Raptor code. While the use 352 of the enhancement layer is optional, the use of the base layer is 353 mandatory wherever AL-FEC is used. The DVB AL-FEC protocol is also 354 described in [I-D.ietf-fecframe-dvb-al-fec]. 356 The interleaved parity code that is used in the base layer is a 357 subset of [SMPTE2022-1]. In particular, AL-FEC base layer uses only 358 the 1-D interleaved FEC protection from [SMPTE2022-1]. The new RTP 359 payload format that is defined and registered in this document (with 360 some exceptions listed in [I-D.ietf-fecframe-dvb-al-fec]) is used as 361 the AL-FEC base layer. 363 2. Requirements Notation 365 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 366 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 367 document are to be interpreted as described in [RFC2119]. 369 3. Definitions, Notations and Abbreviations 371 The definitions, notations and abbreviations commonly used in this 372 document are summarized in this section. 374 3.1. Definitions 376 This document uses the following definitions: 378 Source Flow: The packet flow(s) carrying the source data and to 379 which FEC protection is to be applied. 381 Repair Flow: The packet flow(s) carrying the repair data. 383 Symbol: A unit of data. Its size, in bytes, is referred to as the 384 symbol size. 386 Source Symbol: The smallest unit of data used during the encoding 387 process. 389 Repair Symbol: Repair symbols are generated from the source symbols. 391 Source Packet: Data packets that contain only source symbols. 393 Repair Packet: Data packets that contain only repair symbols. 395 Source Block: A block of source symbols that are considered together 396 in the encoding process. 398 3.2. Notations 400 o L: Number of columns of the source block. 402 o D: Number of rows of the source block. 404 3.3. Abbreviations 406 o XOR: Bitwise exclusive OR operation. 407 0 XOR 0 = 0 408 0 XOR 1 = 1 409 1 XOR 0 = 1 410 1 XOR 1 = 0 412 4. Packet Formats 414 This section defines the formats of the source and repair packets. 416 4.1. Source Packets 418 The source packets MUST contain the information that identifies the 419 source block and the position within the source block occupied by the 420 packet. Since the source packets that are carried within an RTP 421 stream already contain unique sequence numbers in their RTP headers 422 [RFC3550], we can identify the source packets in a straightforward 423 manner and there is no need to append additional field(s). The 424 primary advantage of not modifying the source packets in any way is 425 that it provides backward compatibility for the receivers that do not 426 support FEC at all. In multicast scenarios, this backward 427 compatibility becomes quite useful as it allows the non-FEC-capable 428 and FEC-capable receivers to receive and interpret the same source 429 packets sent in the same multicast session. 431 4.2. Repair Packets 433 The repair packets MUST contain information that identifies the 434 source block they pertain to and the relationship between the 435 contained repair symbols and the original source block. For this 436 purpose, we use the RTP header of the repair packets as well as 437 another header within the RTP payload, which we refer to as the FEC 438 header, as shown in Figure 6. 440 +------------------------------+ 441 | IP Header | 442 +------------------------------+ 443 | Transport Header | 444 +------------------------------+ 445 | RTP Header | __ 446 +------------------------------+ | 447 | FEC Header | \ 448 +------------------------------+ > RTP Payload 449 | Repair Symbols | / 450 +------------------------------+ __| 452 Figure 6: Format of repair packets 454 The RTP header is formatted according to [RFC3550] with some further 455 clarifications listed below: 457 o Version: The version field is set to 2. 459 o Padding (P) Bit: This bit is obtained by applying protection to 460 the corresponding P bits from the RTP headers of the source 461 packets protected by this repair packet. However, padding octets 462 are never present in a repair packet, independent of the value of 463 the P bit. 465 o Extension (X) Bit: This bit is obtained by applying protection to 466 the corresponding X bits from the RTP headers of the source 467 packets protected by this repair packet. However, an RTP header 468 extension is never present in a repair packet, independent of the 469 value of the X bit. 471 o CSRC Count (CC): This field is obtained by applying protection to 472 the corresponding CC values from the RTP headers of the source 473 packets protected by this repair packet. However, a CSRC list is 474 never present in a repair packet, independent of the value of the 475 CC field. 477 o Marker (M) Bit: This bit is obtained by applying protection to 478 the corresponding M bits from the RTP headers of the source 479 packets protected by this repair packet. 481 o Payload Type: The (dynamic) payload type for the repair packets 482 is determined through out-of-band means. Note that this document 483 registers a new payload format for the repair packets (Refer to 484 Section 5 for details). According to [RFC3550], an RTP receiver 485 that cannot recognize a payload type must discard it. This 486 provides backward compatibility. The FEC mechanisms can then be 487 used in a multicast group with mixed FEC-capable and non-FEC- 488 capable receivers. If a non-FEC-capable receiver receives a 489 repair packet, it will not recognize the payload type, and hence, 490 discards the repair packet. 492 o Sequence Number (SN): The sequence number has the standard 493 definition. It MUST be one higher than the sequence number in the 494 previously transmitted repair packet. The initial value of the 495 sequence number SHOULD be random (unpredictable) [RFC3550]. 497 o Timestamp (TS): The timestamp SHALL be set to a time 498 corresponding to the repair packet's transmission time. Note that 499 the timestamp value has no use in the actual FEC protection 500 process and is usually useful for jitter calculations. 502 o Synchronization Source (SSRC): The SSRC value SHALL be randomly 503 assigned as suggested by [RFC3550]. This allows the sender to 504 multiplex the source and repair flows on the same port, or 505 multiplex multiple repair flows on a single port. The repair 506 flows SHOULD use the RTCP CNAME field to associate themselves with 507 the source flow. 509 In some networks, the RTP Source, which produces the source 510 packets and the FEC Source, which generates the repair packets 511 from the source packets may not be the same host. In such 512 scenarios, using the same CNAME for the source and repair flows 513 means that the RTP Source and the FEC Source MUST share the same 514 CNAME (for this specific source-repair flow association). A 515 common CNAME may be produced based on an algorithm that is known 516 both to the RTP and FEC Source. This usage is compliant with 517 [RFC3550]. 519 Note that due to the randomness of the SSRC assignments, there is 520 a possibility of SSRC collision. In such cases, the collisions 521 MUST be resolved as described in [RFC3550]. 523 Note that the P bit, X bit, CC field and M bit of the source packets 524 are protected by the corresponding bits/fields in the RTP header of 525 the repair packet. On the other hand, the payload of a repair packet 526 protects the concatenation of (if present) the CSRC list, RTP 527 extension, payload and padding of the source RTP packets associated 528 with this repair packet. 530 The FEC header is 16 octets. The format of the FEC header is shown 531 in Figure 7. 533 0 1 2 3 534 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 1 535 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 536 | SN base low | Length recovery | 537 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 538 |E| PT recovery | Mask | 539 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 540 | TS recovery | 541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 542 |N|D|Type |Index| Offset | NA | SN base ext | 543 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 545 Figure 7: Format of the FEC header 547 The FEC header consists of the following fields: 549 o The SN base low field is used to indicate the lowest sequence 550 number, taking wrap around into account, of those source packets 551 protected by this repair packet. 553 o The Length recovery field is used to determine the length of any 554 recovered packets. 556 o The E bit is the extension flag introduced in [RFC2733] and used 557 to extend the [RFC2733] FEC header. 559 o The PT recovery field is used to determine the payload type of the 560 recovered packets. 562 o The Mask field is not used. 564 o The TS recovery field is used to determine the timestamp of the 565 recovered packets. 567 o The N bit is the extension flag that is reserved for future uses. 569 o The D bit is not used. 571 o The Type field indicates the type of the error-correcting code 572 used. This document defines only one error-correcting code. 574 o The Index field is not used. 576 o The Offset and NA fields are used to indicate the number of 577 columns (L) and rows (D) of the source block, respectively. 579 o The SN base ext field is not used. 581 The details on setting the fields in the FEC header are provided in 582 Section 6.2. 584 It should be noted that a mask-based approach (similar to the one 585 specified in [RFC2733]) may not be very efficient to indicate which 586 source packets in the current source block are associated with a 587 given repair packet. In particular, for the applications that would 588 like to use large source block sizes, the size of the mask that is 589 required to describe the source-repair packet associations may be 590 prohibitively large. Instead, a systematic approach is inherently 591 more efficient. 593 5. Payload Format Parameters 595 This section provides the media subtype registration for the 1-D 596 interleaved parity FEC. The parameters that are required to 597 configure the FEC encoding and decoding operations are also defined 598 in this section. 600 5.1. Media Type Registration 602 This registration is done using the template defined in [RFC4288] and 603 following the guidance provided in [RFC3555]. 605 5.1.1. Registration of audio/1d-interleaved-parityfec 607 Type name: audio 609 Subtype name: 1d-interleaved-parityfec 611 Required parameters: 613 o rate: The RTP timestamp (clock) rate. The rate SHALL be larger 614 than 1000 Hz to provide sufficient resolution to RTCP operations. 615 However, it is RECOMMENDED to select the rate that matches the 616 rate of the protected source RTP stream. 618 o L: Number of columns of the source block. L is a positive 619 integer that is less than or equal to 255. 621 o D: Number of rows of the source block. D is a positive integer 622 that is less than or equal to 255. 624 o repair-window: The time that spans the source packets and the 625 corresponding repair packets. An FEC encoder processes a block of 626 source packets and generates a number of repair packets, which are 627 then transmitted within a certain duration. At the receiver, the 628 FEC decoder tries to decode all the packets received within the 629 repair window to recover the missing packets. Assuming that there 630 is no issue of delay variation, the FEC decoder SHOULD NOT wait 631 longer than the repair window since additional waiting would not 632 help the recovery process. The size of the repair window is 633 specified in microseconds. 635 Optional parameters: None. 637 Encoding considerations: This media type is framed (See Section 4.8 638 in the template document [RFC4288]) and contains binary data. 640 Security considerations: See Section 9 of this document. 642 Interoperability considerations: None. 644 Published specification: This document. 646 Applications that use this media type: Multimedia applications that 647 want to improve resiliency against packet loss by sending redundant 648 data in addition to the source media. 650 Additional information: None. 652 Person & email address to contact for further information: Ali Begen 653 and IETF Audio/Video Transport Working Group. 655 Intended usage: COMMON. 657 Restriction on usage: None. 659 Author: Ali Begen . 661 Change controller: IETF Audio/Video Transport Working Group 662 delegated from the IESG. 664 5.1.2. Registration of video/1d-interleaved-parityfec 666 Type name: video 668 Subtype name: 1d-interleaved-parityfec 670 Required parameters: 672 o rate: The RTP timestamp (clock) rate. The rate SHALL be larger 673 than 1000 Hz to provide sufficient resolution to RTCP operations. 674 However, it is RECOMMENDED to select the rate that matches the 675 rate of the protected source RTP stream. 677 o L: Number of columns of the source block. L is a positive 678 integer that is less than or equal to 255. 680 o D: Number of rows of the source block. D is a positive integer 681 that is less than or equal to 255. 683 o repair-window: The time that spans the source packets and the 684 corresponding repair packets. An FEC encoder processes a block of 685 source packets and generates a number of repair packets, which are 686 then transmitted within a certain duration. At the receiver, the 687 FEC decoder tries to decode all the packets received within the 688 repair window to recover the missing packets. Assuming that there 689 is no issue of delay variation, the FEC decoder SHOULD NOT wait 690 longer than the repair window since additional waiting would not 691 help the recovery process. The size of the repair window is 692 specified in microseconds. 694 Optional parameters: None. 696 Encoding considerations: This media type is framed (See Section 4.8 697 in the template document [RFC4288]) and contains binary data. 699 Security considerations: See Section 9 of this document. 701 Interoperability considerations: None. 703 Published specification: This document. 705 Applications that use this media type: Multimedia applications that 706 want to improve resiliency against packet loss by sending redundant 707 data in addition to the source media. 709 Additional information: None. 711 Person & email address to contact for further information: Ali Begen 712 and IETF Audio/Video Transport Working Group. 714 Intended usage: COMMON. 716 Restriction on usage: None. 718 Author: Ali Begen . 720 Change controller: IETF Audio/Video Transport Working Group 721 delegated from the IESG. 723 5.1.3. Registration of text/1d-interleaved-parityfec 725 Type name: text 727 Subtype name: 1d-interleaved-parityfec 729 Required parameters: 731 o rate: The RTP timestamp (clock) rate. The rate SHALL be larger 732 than 1000 Hz to provide sufficient resolution to RTCP operations. 733 However, it is RECOMMENDED to select the rate that matches the 734 rate of the protected source RTP stream. 736 o L: Number of columns of the source block. L is a positive 737 integer that is less than or equal to 255. 739 o D: Number of rows of the source block. D is a positive integer 740 that is less than or equal to 255. 742 o repair-window: The time that spans the source packets and the 743 corresponding repair packets. An FEC encoder processes a block of 744 source packets and generates a number of repair packets, which are 745 then transmitted within a certain duration. At the receiver, the 746 FEC decoder tries to decode all the packets received within the 747 repair window to recover the missing packets. Assuming that there 748 is no issue of delay variation, the FEC decoder SHOULD NOT wait 749 longer than the repair window since additional waiting would not 750 help the recovery process. The size of the repair window is 751 specified in microseconds. 753 Optional parameters: None. 755 Encoding considerations: This media type is framed (See Section 4.8 756 in the template document [RFC4288]) and contains binary data. 758 Security considerations: See Section 9 of this document. 760 Interoperability considerations: None. 762 Published specification: This document. 764 Applications that use this media type: Multimedia applications that 765 want to improve resiliency against packet loss by sending redundant 766 data in addition to the source media. 768 Additional information: None. 770 Person & email address to contact for further information: Ali Begen 771 and IETF Audio/Video Transport Working Group. 773 Intended usage: COMMON. 775 Restriction on usage: None. 777 Author: Ali Begen . 779 Change controller: IETF Audio/Video Transport Working Group 780 delegated from the IESG. 782 5.1.4. Registration of application/1d-interleaved-parityfec 784 Type name: application 786 Subtype name: 1d-interleaved-parityfec 788 Required parameters: 790 o rate: The RTP timestamp (clock) rate. The rate SHALL be larger 791 than 1000 Hz to provide sufficient resolution to RTCP operations. 792 However, it is RECOMMENDED to select the rate that matches the 793 rate of the protected source RTP stream. 795 o L: Number of columns of the source block. L is a positive 796 integer that is less than or equal to 255. 798 o D: Number of rows of the source block. D is a positive integer 799 that is less than or equal to 255. 801 o repair-window: The time that spans the source packets and the 802 corresponding repair packets. An FEC encoder processes a block of 803 source packets and generates a number of repair packets, which are 804 then transmitted within a certain duration. At the receiver, the 805 FEC decoder tries to decode all the packets received within the 806 repair window to recover the missing packets. Assuming that there 807 is no issue of delay variation, the FEC decoder SHOULD NOT wait 808 longer than the repair window since additional waiting would not 809 help the recovery process. The size of the repair window is 810 specified in microseconds. 812 Optional parameters: None. 814 Encoding considerations: This media type is framed (See Section 4.8 815 in the template document [RFC4288]) and contains binary data. 817 Security considerations: See Section 9 of this document. 819 Interoperability considerations: None. 821 Published specification: This document. 823 Applications that use this media type: Multimedia applications that 824 want to improve resiliency against packet loss by sending redundant 825 data in addition to the source media. 827 Additional information: None. 829 Person & email address to contact for further information: Ali Begen 830 and IETF Audio/Video Transport Working Group. 832 Intended usage: COMMON. 834 Restriction on usage: None. 836 Author: Ali Begen . 838 Change controller: IETF Audio/Video Transport Working Group 839 delegated from the IESG. 841 5.2. Mapping to SDP Parameters 843 Applications that are using RTP transport commonly use Session 844 Description Protocol (SDP) [RFC4566] to describe their RTP sessions. 845 The information that is used to specify the media types in an RTP 846 session has specific mappings to the fields in an SDP description. 847 In this section, we provide these mappings for the media subtype 848 registered by this document ("1d-interleaved-parityfec"). Note that 849 if an application does not use SDP to describe the RTP sessions, an 850 appropriate mapping must be defined and used to specify the media 851 types and their parameters for the control/description protocol 852 employed by the application. 854 The mapping of the media type specification for "1d-interleaved- 855 parityfec" and its parameters in SDP is as follows: 857 o The media type (e.g., "application") goes into the "m=" line as 858 the media name. 860 o The media subtype ("1d-interleaved-parityfec") goes into the 861 "a=rtpmap" line as the encoding name. The RTP clock rate 862 parameter ("rate") also goes into the "a=rtpmap" line as the clock 863 rate. 865 o The remaining required payload-format-specific parameters go into 866 the "a=fmtp" line by copying them directly from the media type 867 string as a semicolon-separated list of parameter=value pairs. 869 SDP examples are provided in Section 7. 871 5.2.1. Offer-Answer Model Considerations 873 When offering 1-D interleaved parity FEC over RTP using SDP in an 874 Offer/Answer model [RFC3264], the following considerations apply: 876 o Each combination of the L and D parameters produces a different 877 FEC data and is not compatible with any other combination. A 878 sender application may desire to offer multiple offers with 879 different sets of L and D values as long as the parameter values 880 are valid. The receiver SHOULD normally choose the offer that has 881 a sufficient amount of interleaving. If multiple such offers 882 exist, the receiver may choose the offer that has the lowest 883 overhead or the one that requires the smallest amount of 884 buffering. The selection depends on the application requirements. 886 o The value for the repair-window parameter depends on the L and D 887 values and cannot be chosen arbitrarily. More specifically, L and 888 D values determine the lower limit for the repair-window size. 889 The upper limit of the repair-window size does not depend on the L 890 and D values. 892 o Although combinations with the same L and D values but with 893 different repair-window sizes produce the same FEC data, such 894 combinations are still considered different offers. The size of 895 the repair-window is related to how fast the sender will send the 896 repair packets. This directly impacts the buffering requirement 897 on the receiver side and the receiver must consider this when 898 choosing an offer. 900 o There are no optional format parameters defined for this payload. 901 Any unknown option in the offer MUST be ignored and deleted from 902 the answer. 904 5.2.2. Declarative Considerations 906 In declarative usage, like SDP in the Real-time Streaming Protocol 907 (RTSP) [RFC2326] or the Session Announcement Protocol (SAP) 908 [RFC2974], the following considerations apply: 910 o The payload format configuration parameters are all declarative 911 and a participant MUST use the configuration that is provided for 912 the session. 914 o More than one configuration may be provided (if desired) by 915 declaring multiple RTP payload types. In that case, the receivers 916 should choose the repair flow that is best for them. 918 6. Protection and Recovery Procedures 920 This section provides a complete specification of the 1-D interleaved 921 parity code. 923 6.1. Overview 925 The following sections specify the steps involved in generating the 926 repair packets and reconstructing the missing source packets from the 927 repair packets. 929 6.2. Repair Packet Construction 931 The RTP header of a repair packet is formed based on the guidelines 932 given in Section 4.2. 934 The FEC header includes 16 octets. It is constructed by applying the 935 XOR operation on the bit strings that are generated from the 936 individual source packets protected by this particular repair packet. 937 The set of the source packets that are associated with a given repair 938 packet can be computed by the formula given in Section 6.3.1. 940 The bit string is formed for each source packet by concatenating the 941 following fields together in the order specified: 943 o Padding bit (1 bit) (This is the most significant bit of the bit 944 string) 946 o Extension bit (1 bit) 948 o CC field (4 bits) 950 o Marker bit (1 bit) 952 o PT field (7 bits) 954 o Timestamp (32 bits) 956 o Unsigned network-ordered 16-bit representation of the source 957 packet length in bytes minus 12 (for the fixed RTP header), i.e., 958 the sum of the lengths of all the following if present: the CSRC 959 list, header extension, RTP payload and RTP padding (16 bits) 961 o If CC is nonzero, the CSRC list (variable length) 963 o If X is 1, the header extension (variable length) 965 o Payload (variable length) 967 o Padding, if present (variable length) 969 Note that if the payload lengths of the source packets are not equal, 970 each shorter packet MUST be padded to the length of the longest 971 packet by adding octet 0's at the end. Due to this possible padding 972 and mandatory FEC header, a repair packet usually has a larger size 973 than the source packets it protects. This may cause problems if the 974 resulting repair packet size exceeds the Maximum Transmission Unit 975 (MTU) size of the path over which the repair flow is sent. 977 By applying the parity operation on the bit strings produced from the 978 source packets, we generate the FEC bit string. Some parts of the 979 RTP header and the FEC header of the repair packet are generated from 980 the FEC bit string as follows: 982 o The first (most significant) bit in the FEC bit string is written 983 into the Padding bit in the RTP header of the repair packet. 985 o The next bit in the FEC bit string is written into the Extension 986 bit in the RTP header of the repair packet. 988 o The next 4 bits of the FEC bit string are written into the CC 989 field in the RTP header of the repair packet. 991 o The next bit of the FEC bit string is written into the Marker bit 992 in the RTP header of the repair packet. 994 o The next 7 bits of the FEC bit string are written into the PT 995 recovery field in the FEC header. 997 o The next 32 bits of the FEC bit string are written into the TS 998 recovery field in the FEC header. 1000 o The next 16 bits are written into the Length recovery field in the 1001 FEC header. This allows the FEC procedure to be applied even when 1002 the lengths of the protected source packets are not identical. 1004 o The remaining bits are set to be the payload of the repair packet. 1006 The remaining parts of the FEC header are set as follows: 1008 o The SN base low field MUST be set to the lowest sequence number, 1009 taking wrap around into account, of those source packets protected 1010 by this repair packet. 1012 o The E bit MUST be set to 1 to extend the [RFC2733] FEC header. 1014 o The Mask field SHALL be set to 0 and ignored by the receiver. 1016 o The N bit SHALL be set to 0 and ignored by the receiver. 1018 o The D bit SHALL be set to 0 and ignored by the receiver. 1020 o The Type field MUST be set to 0. 1022 o The Index field SHALL be set to 0 and ignored by the receiver. 1024 o The Offset field MUST be set to the number of columns of the 1025 source block (L). 1027 o The NA field MUST be set to the number of rows of the source block 1028 (D). 1030 o The SN base ext field SHALL be set to 0 and ignored by the 1031 receiver. 1033 6.3. Source Packet Reconstruction 1035 This section describes the recovery procedures that are required to 1036 reconstruct the missing packets. The recovery process has two steps. 1037 In the first step, the FEC decoder determines which source and repair 1038 packets should be used in order to recover a missing packet. In the 1039 second step, the decoder recovers the missing packet, which consists 1040 of an RTP header and RTP payload. 1042 In the following, we describe the RECOMMENDED algorithms for the 1043 first and second steps. Based on the implementation, different 1044 algorithms MAY be adopted. However, the end result MUST be identical 1045 to the one produced by the algorithms described below. 1047 6.3.1. Associating the Source and Repair Packets 1049 The first step is to associate the source and repair packets. The SN 1050 base low field in the FEC header shows the lowest sequence number of 1051 the source packets that form the particular column. In addition, the 1052 information of how many source packets are available in each column 1053 and row is available from the media type parameters specified in the 1054 SDP description. This set of information uniquely identifies all of 1055 the source packets associated with a given repair packet. 1057 Mathematically, for any received repair packet, p*, we can determine 1058 the sequence numbers of the source packets that are protected by this 1059 repair packet as follows: 1061 p*_snb + i * L 1063 where p*_snb denotes the value in the SN base low field of p*'s FEC 1064 header, L is the number of columns of the source block and 1066 0 <= i < D 1068 where D is the number of rows of the source block. 1070 We denote the set of the source packets associated with repair packet 1071 p* by set T(p*). Note that in a source block whose size is L columns 1072 by D rows, set T includes D source packets. Recall that 1-D 1073 interleaved FEC protection can fully recover the missing information 1074 if there is only one source packet is missing in set T. If the repair 1075 packet that protects the source packets in set T is missing, or the 1076 repair packet is available but two or more source packets are 1077 missing, then missing source packets in set T cannot be recovered by 1078 1-D interleaved FEC protection. 1080 6.3.2. Recovering the RTP Header and Payload 1082 For a given set T, the procedure for the recovery of the RTP header 1083 of the missing packet, whose sequence number is denoted by SEQNUM, is 1084 as follows: 1086 1. For each of the source packets that are successfully received in 1087 set T, compute the bit string as described in Section 6.2. 1089 2. For the repair packet associated with set T, compute the bit 1090 string in the same fashion except use the PT recovery field 1091 instead of the PT field and TS recovery field instead of the 1092 Timestamp field, and set the CSRC list, header extension and 1093 padding to null regardless of the values of the CC field, X bit 1094 and P bit. 1096 3. If any of the bit strings generated from the source packets are 1097 shorter than the bit string generated from the repair packet, 1098 pad them to be the same length as the bit string generated from 1099 the repair packet. For padding, the padding of octet 0 MUST be 1100 added at the end of the bit string. 1102 4. Calculate the recovered bit string as the XOR of the bit strings 1103 generated from all source packets in set T and the FEC bit 1104 string generated from the repair packet associated with set T. 1106 5. Create a new packet with the standard 12-byte RTP header and no 1107 payload. 1109 6. Set the version of the new packet to 2. 1111 7. Set the Padding bit in the new packet to the first bit in the 1112 recovered bit string. 1114 8. Set the Extension bit in the new packet to the next bit in the 1115 recovered bit string. 1117 9. Set the CC field to the next 4 bits in the recovered bit string. 1119 10. Set the Marker bit in the new packet to the next bit in the 1120 recovered bit string. 1122 11. Set the Payload type in the new packet to the next 7 bits in the 1123 recovered bit string. 1125 12. Set the SN field in the new packet to SEQNUM. 1127 13. Set the TS field in the new packet to the next 32 bits in the 1128 recovered bit string. 1130 14. Take the next 16 bits of the recovered bit string and set Y to 1131 whatever unsigned integer this represents (assuming network- 1132 order). Take Y bytes from the recovered bit string and append 1133 them to the new packet. Y represents the length of the new 1134 packet in bytes minus 12 (for the fixed RTP header), i.e., the 1135 sum of the lengths of all the following if present: the CSRC 1136 list, header extension, RTP payload and RTP padding. 1138 15. Set the SSRC of the new packet to the SSRC of the source RTP 1139 stream. 1141 This procedure completely recovers both the header and payload of an 1142 RTP packet. 1144 7. Session Description Protocol (SDP) Signaling 1146 This section provides an SDP [RFC4566] example. The following 1147 example uses the FEC grouping semantics [RFC4756]. 1149 In this example, we have one source video stream (mid:S1) and one FEC 1150 repair stream (mid:R1). We form one FEC group with the "a=group:FEC 1151 S1 R1" line. The source and repair streams are sent to the same port 1152 on different multicast groups. The repair window is set to 200 ms. 1154 v=0 1155 o=ali 1122334455 1122334466 IN IP4 fec.example.com 1156 s=Interleaved Parity FEC Example 1157 t=0 0 1158 a=group:FEC S1 R1 1159 m=video 30000 RTP/AVP 100 1160 c=IN IP4 224.1.1.1/127 1161 a=rtpmap:100 MP2T/90000 1162 a=mid:S1 1163 m=application 30000 RTP/AVP 110 1164 c=IN IP4 224.1.2.1/127 1165 a=rtpmap:110 1d-interleaved-parityfec/90000 1166 a=fmtp:110 L:5; D:10; repair-window: 200000 1167 a=mid:R1 1169 8. Congestion Control Considerations 1171 FEC is an effective approach to provide applications resiliency 1172 against packet losses. However, in networks where the congestion is 1173 a major contributor to the packet loss, the potential impacts of 1174 using FEC SHOULD be considered carefully before injecting the repair 1175 flows into the network. In particular, in bandwidth-limited 1176 networks, FEC repair flows may consume most or all of the available 1177 bandwidth and may consequently congest the network. In such cases, 1178 the applications MUST NOT arbitrarily increase the amount of FEC 1179 protection since doing so may lead to a congestion collapse. If 1180 desired, stronger FEC protection MAY be applied only after the source 1181 rate has been reduced. 1183 In a network-friendly implementation, an application SHOULD NOT send/ 1184 receive FEC repair flows if it knows that sending/receiving those FEC 1185 repair flows would not help at all in recovering the missing packets. 1186 Such a practice helps reduce the amount of wasted bandwidth. It is 1187 RECOMMENDED that the amount of FEC protection is adjusted dynamically 1188 based on the packet loss rate observed by the applications. 1190 In multicast scenarios, it may be difficult to optimize the FEC 1191 protection per receiver. If there is a large variation among the 1192 levels of FEC protection needed by different receivers, it is 1193 RECOMMENDED that the sender offers multiple repair flows with 1194 different levels of FEC protection and the receivers join the 1195 corresponding multicast sessions to receive the repair flow(s) that 1196 is best for them. 1198 9. Security Considerations 1200 RTP packets using the payload format defined in this specification 1201 are subject to the security considerations discussed in the RTP 1202 specification [RFC3550] and in any applicable RTP profile. The main 1203 security considerations for the RTP packet carrying the RTP payload 1204 format defined within this memo are confidentiality, integrity and 1205 source authenticity. Confidentiality is achieved by encrypting the 1206 RTP payload. Integrity of the RTP packets is achieved through a 1207 suitable cryptographic integrity protection mechanism. Such a 1208 cryptographic system may also allow the authentication of the source 1209 of the payload. A suitable security mechanism for this RTP payload 1210 format should provide confidentiality, integrity protection, and at 1211 least source authentication capable of determining if an RTP packet 1212 is from a member of the RTP session. 1214 Note that the appropriate mechanism to provide security to RTP and 1215 payloads following this memo may vary. It is dependent on the 1216 application, transport and signaling protocol employed. Therefore, a 1217 single mechanism is not sufficient, although if suitable, using the 1218 Secure Real-time Transport Protocol (SRTP) [RFC3711] is recommended. 1219 Other mechanisms that may be used are IPsec [RFC4301] and Transport 1220 Layer Security (TLS) [RFC5246] (RTP over TCP); other alternatives may 1221 exist. 1223 10. IANA Considerations 1225 New media subtypes are subject to IANA registration. For the 1226 registration of the payload format and its parameters introduced in 1227 this document, refer to Section 5. 1229 11. Acknowledgments 1231 A major part of this document is borrowed from [RFC2733] and 1232 [SMPTE2022-1]. Thus, the author would like to thank the authors and 1233 editors of these earlier specifications. The author also thanks 1234 Colin Perkins for his constructive suggestions for this document. 1236 12. Change Log 1238 12.1. draft-ietf-fecframe-interleaved-fec-scheme-03 1240 The following are the major changes compared to version 02: 1242 o Comments from WGLC have been addressed. 1244 12.2. draft-ietf-fecframe-interleaved-fec-scheme-02 1246 The following are the major changes compared to version 01: 1248 o Some details were added regarding the use of CNAME field. 1250 o Offer-Answer and Declarative Considerations sections have been 1251 completed. 1253 o Security Considerations section has been completed. 1255 12.3. draft-ietf-fecframe-interleaved-fec-scheme-01 1257 The following are the major changes compared to version 00: 1259 o The timestamp field definition has changed. 1261 12.4. draft-ietf-fecframe-interleaved-fec-scheme-00 1263 This is the initial version, which is based on an earlier individual 1264 submission. The following are the major changes compared to that 1265 document: 1267 o Per the discussion in the WG, references to the FEC Framework have 1268 been removed and the document has been turned into a pure RTP 1269 payload format specification. 1271 o A new section is added for congestion control considerations. 1273 o Editorial changes to clarify a few points. 1275 13. References 1277 13.1. Normative References 1279 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1280 Requirement Levels", BCP 14, RFC 2119, March 1997. 1282 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 1283 Jacobson, "RTP: A Transport Protocol for Real-Time 1284 Applications", STD 64, RFC 3550, July 2003. 1286 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1287 Description Protocol", RFC 4566, July 2006. 1289 [RFC4756] Li, A., "Forward Error Correction Grouping Semantics in 1290 Session Description Protocol", RFC 4756, November 2006. 1292 [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and 1293 Registration Procedures", BCP 13, RFC 4288, December 2005. 1295 [RFC3555] Casner, S. and P. Hoschka, "MIME Type Registration of RTP 1296 Payload Formats", RFC 3555, July 2003. 1298 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1299 with Session Description Protocol (SDP)", RFC 3264, 1300 June 2002. 1302 13.2. Informative References 1304 [I-D.ietf-fecframe-dvb-al-fec] 1305 Begen, A. and T. Stockhammer, "DVB Application-Layer 1306 Hybrid FEC Protection", draft-ietf-fecframe-dvb-al-fec-01 1307 (work in progress), January 2009. 1309 [RFC2733] Rosenberg, J. and H. Schulzrinne, "An RTP Payload Format 1310 for Generic Forward Error Correction", RFC 2733, 1311 December 1999. 1313 [RFC3009] Rosenberg, J. and H. Schulzrinne, "Registration of 1314 parityfec MIME types", RFC 3009, November 2000. 1316 [RFC5109] Li, A., "RTP Payload Format for Generic Forward Error 1317 Correction", RFC 5109, December 2007. 1319 [ETSI-TS-102-034] 1320 ETSI TS 102 034 V1.3.1, "Transport of MPEG 2 TS Based DVB 1321 Services over IP Based Networks", October 2007. 1323 [RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time 1324 Streaming Protocol (RTSP)", RFC 2326, April 1998. 1326 [RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session 1327 Announcement Protocol", RFC 2974, October 2000. 1329 [SMPTE2022-1] 1330 SMPTE 2022-1-2007, "Forward Error Correction for Real-Time 1331 Video/Audio Transport over IP Networks", 2007. 1333 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 1334 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 1335 RFC 3711, March 2004. 1337 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1338 Internet Protocol", RFC 4301, December 2005. 1340 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 1341 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 1343 Author's Address 1345 Ali Begen 1346 Cisco Systems 1347 170 West Tasman Drive 1348 San Jose, CA 95134 1349 USA 1351 Email: abegen@cisco.com