idnits 2.17.1 draft-singh-avtcore-mprtp-05.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- -- The document has examples using IPv4 documentation addresses according to RFC6890, but does not use any IPv6 documentation addresses. Maybe there should be IPv6 examples, too? Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (July 10, 2012) is 4307 days in the past. Is this intentional? Checking references for intended status: Experimental ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 5245 (ref. '3') (Obsoleted by RFC 8445, RFC 8839) == Outdated reference: A later version (-04) exists of draft-singh-mmusic-mprtp-sdp-extension-00 ** Obsolete normative reference: RFC 5285 (ref. '8') (Obsoleted by RFC 8285) -- Obsolete informational reference (is this intentional?): RFC 4960 (ref. '11') (Obsoleted by RFC 9260) -- Obsolete informational reference (is this intentional?): RFC 5117 (ref. '14') (Obsoleted by RFC 7667) == Outdated reference: A later version (-40) exists of draft-ietf-mmusic-rfc2326bis-29 -- Obsolete informational reference (is this intentional?): RFC 4566 (ref. '19') (Obsoleted by RFC 8866) Summary: 2 errors (**), 0 flaws (~~), 3 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 AVT Core Working Group V. Singh 3 Internet-Draft T. Karkkainen 4 Intended status: Experimental J. Ott 5 Expires: January 11, 2013 S. Ahsan 6 Aalto University 7 L. Eggert 8 NetApp 9 July 10, 2012 11 Multipath RTP (MPRTP) 12 draft-singh-avtcore-mprtp-05 14 Abstract 16 The Real-time Transport Protocol (RTP) is used to deliver real-time 17 content and, along with the RTP Control Protocol (RTCP), forms the 18 control channel between the sender and receiver. However, RTP and 19 RTCP assume a single delivery path between the sender and receiver 20 and make decisions based on the measured characteristics of this 21 single path. Increasingly, endpoints are becoming multi-homed, which 22 means that they are connected via multiple Internet paths. Network 23 utilization can be improved when endpoints use multiple parallel 24 paths for communication. The resulting increase in reliability and 25 throughput can also enhance the user experience. This document 26 extends the Real-time Transport Protocol (RTP) so that a single 27 session can take advantage of the availability of multiple paths 28 between two endpoints. 30 Status of this Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on January 11, 2013. 47 Copyright Notice 48 Copyright (c) 2012 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 Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 65 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 66 1.3. Use-cases . . . . . . . . . . . . . . . . . . . . . . . . 5 67 2. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 68 2.1. Functional goals . . . . . . . . . . . . . . . . . . . . . 5 69 2.2. Compatibility goals . . . . . . . . . . . . . . . . . . . 6 70 3. RTP Topologies . . . . . . . . . . . . . . . . . . . . . . . . 6 71 4. MPRTP Architecture . . . . . . . . . . . . . . . . . . . . . . 6 72 5. Example Media Flow Diagrams . . . . . . . . . . . . . . . . . 8 73 5.1. Streaming use-case . . . . . . . . . . . . . . . . . . . . 8 74 5.2. Conversational use-case . . . . . . . . . . . . . . . . . 9 75 6. MPRTP Functional Blocks . . . . . . . . . . . . . . . . . . . 10 76 7. Available Mechanisms within the Functional Blocks . . . . . . 11 77 7.1. Session Setup . . . . . . . . . . . . . . . . . . . . . . 11 78 7.1.1. Connectivity Checks . . . . . . . . . . . . . . . . . 11 79 7.1.2. Adding New or Updating Interfaces . . . . . . . . . . 11 80 7.1.3. In-band vs. Out-of-band Signaling . . . . . . . . . . 11 81 7.2. Expanding RTP . . . . . . . . . . . . . . . . . . . . . . 13 82 7.3. Expanding RTCP . . . . . . . . . . . . . . . . . . . . . . 13 83 7.4. Failure Handling and Teardown . . . . . . . . . . . . . . 13 84 8. MPRTP Protocol . . . . . . . . . . . . . . . . . . . . . . . . 14 85 8.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 14 86 8.1.1. Gather or Discovering Candidates . . . . . . . . . . . 15 87 8.1.2. NAT Traversal . . . . . . . . . . . . . . . . . . . . 15 88 8.1.3. Choosing between In-band (in RTCP) and Out-of-band 89 (in SDP) Interface Advertisement . . . . . . . . . . . 15 90 8.1.4. In-band Interface Advertisement . . . . . . . . . . . 16 91 8.1.5. Subflow ID Assignment . . . . . . . . . . . . . . . . 16 92 8.1.6. Active and Passive Subflows . . . . . . . . . . . . . 16 93 8.2. RTP Transmission . . . . . . . . . . . . . . . . . . . . . 17 94 8.3. Playout Considerations at the Receiver . . . . . . . . . . 17 95 8.4. Subflow-specific RTCP Statistics and RTCP Aggregation . . 17 96 8.5. RTCP Transmission . . . . . . . . . . . . . . . . . . . . 18 97 9. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 18 98 9.1. RTP Header Extension for MPRTP . . . . . . . . . . . . . . 18 99 9.1.1. MPRTP RTP Extension for a Subflow . . . . . . . . . . 20 100 9.2. RTCP Extension for MPRTP (MPRTCP) . . . . . . . . . . . . 20 101 9.2.1. MPRTCP Extension for Subflow Reporting . . . . . . . . 22 102 9.2.1.1. MPRTCP for Subflow-specific SR, RR and XR . . . . 23 103 9.3. MPRTCP Extension for Interface advertisement . . . . . . . 25 104 10. RTCP Timing reconsiderations for MPRTCP . . . . . . . . . . . 26 105 11. SDP Considerations . . . . . . . . . . . . . . . . . . . . . . 26 106 11.1. Signaling MPRTP Header Extension in SDP . . . . . . . . . 27 107 11.2. Signaling MPRTP capability in SDP . . . . . . . . . . . . 27 108 11.3. MPRTP with ICE . . . . . . . . . . . . . . . . . . . . . . 28 109 11.4. Increased Throughput . . . . . . . . . . . . . . . . . . . 28 110 11.5. Offer/Answer . . . . . . . . . . . . . . . . . . . . . . . 28 111 11.5.1. In-band Signaling Example . . . . . . . . . . . . . . 29 112 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 113 12.1. MPRTP Header Extension . . . . . . . . . . . . . . . . . . 30 114 12.2. MPRTCP Packet Type . . . . . . . . . . . . . . . . . . . . 30 115 12.3. SDP Attributes . . . . . . . . . . . . . . . . . . . . . . 31 116 12.3.1. "mprtp" attribute . . . . . . . . . . . . . . . . . . 31 117 13. Security Considerations . . . . . . . . . . . . . . . . . . . 32 118 14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 32 119 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 32 120 15.1. Normative References . . . . . . . . . . . . . . . . . . . 32 121 15.2. Informative References . . . . . . . . . . . . . . . . . . 33 122 Appendix A. Interoperating with Legacy Applications . . . . . . . 34 123 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 34 124 B.1. Changes in draft-singh-avtcore-mprtp-05 . . . . . . . . . 34 125 B.2. Changes in draft-singh-avtcore-mprtp-04 . . . . . . . . . 34 126 B.3. Changes in draft-singh-avtcore-mprtp-03 . . . . . . . . . 35 127 B.4. Changes in draft-singh-avtcore-mprtp-02 . . . . . . . . . 35 128 B.5. Changes in draft-singh-avtcore-mprtp-01 . . . . . . . . . 35 129 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35 131 1. Introduction 133 Multi-homed endpoints are becoming common in today's Internet, e.g., 134 devices that support multiple wireless access technologies such as 3G 135 and Wireless LAN. This means that there is often more than one 136 network path available between two endpoints. Transport protocols, 137 such as RTP, have not been designed to take advantage of the 138 availability of multiple concurrent paths and therefore cannot 139 benefit from the increased capacity and reliability that can be 140 achieved by pooling their respective capacities. 142 Multipath RTP (MPRTP) is an OPTIONAL extension to RTP [1] that allows 143 splitting a single RTP stream into multiple subflows that are 144 transmitted over different paths. In effect, this pools the resource 145 capacity of multiple paths. Multipath RTCP (MPRTCP) is an extension 146 to RTCP, it is used along with MPRTP to report per-path sender and 147 receiver characteristics. 149 Other IETF transport protocols that are capable of using multiple 150 paths include SCTP [11], MPTCP [12] and SHIM6 [13]. However, these 151 protocols are not suitable for real-time communications. 153 1.1. Requirements Language 155 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 156 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 157 document are to be interpreted as described in [2]. 159 1.2. Terminology 161 o Endpoint: host either initiating or terminating an RTP flow. 163 o Interface: logical or physical component that is capable of 164 acquiring a unique IP address. 166 o Path: sequence of links between a sender and a receiver. 167 Typically, defined by a set of source and destination addresses. 169 o Subflow: flow of RTP packets along a specific path, i.e., a subset 170 of the packets belonging to an RTP stream. The combination of all 171 RTP subflows forms the complete RTP stream. Typically, a subflow 172 would map to a unique path, i.e., each combination of IP addresses 173 and port pairs (5-tuple, including protocol) is a unique subflow. 175 1.3. Use-cases 177 The primary use-case for MPRTP is transporting high bit-rate 178 streaming multimedia content between endpoints, where at least one is 179 multi-homed. Such endpoints could be residential IPTV devices that 180 connect to the Internet through two different Internet service 181 providers (ISPs), or mobile devices that connect to the Internet 182 through 3G and WLAN interfaces. By allowing RTP to use multiple 183 paths for transmission, the following gains can be achieved: 185 o Higher quality: Pooling the resource capacity of multiple Internet 186 paths allows higher bit-rate and higher quality codecs to be used. 187 From the application perspective, the available bandwidth between 188 the two endpoints increases. 190 o Load balancing: Transmitting an RTP stream over multiple paths 191 reduces the bandwidth usage on a single path, which in turn 192 reduces the impact of the media stream on other traffic on that 193 path. 195 o Fault tolerance: When multiple paths are used in conjunction with 196 redundancy mechanisms (FEC, re-transmissions, etc.), outages on 197 one path have less impact on the overall perceived quality of the 198 stream. 200 A secondary use-case for MPRTP is transporting Voice over IP (VoIP) 201 calls to a device with multiple interfaces. Again, such an endpoint 202 could be a mobile device with multiple wireless interfaces. In this 203 case, little is to be gained from resource pooling, i.e., higher 204 capacity or load balancing, because a single path should be easily 205 capable of handling the required load. However, using multiple 206 concurrent subflows can improve fault tolerance, because traffic can 207 shift between the subflows when path outages occur. This results in 208 very fast transport-layer handovers that do not require support from 209 signaling. 211 2. Goals 213 This section outlines the basic goals that multipath RTP aims to 214 meet. These are broadly classified as Functional goals and 215 Compatibility goals. 217 2.1. Functional goals 219 Allow unicast RTP session to be split into multiple subflows in order 220 to be carried over multiple paths. This may prove beneficial in case 221 of video streaming. 223 o Increased Throughput: Cumulative capacity of the two paths may 224 meet the requirements of the multimedia session. Therefore, MPRTP 225 MUST support concurrent use of the multiple paths. 227 o Improved Reliability: MPRTP SHOULD be able to send redundant 228 packets or re-transmit packets along any available path to 229 increase reliability. 231 The protocol SHOULD be able to open new subflows for an existing 232 session when new paths appear and MUST be able to close subflows when 233 paths disappear. 235 2.2. Compatibility goals 237 MPRTP MUST be backwards compatible; an MPRTP stream needs to fall 238 back to be compatible with legacy RTP stacks if MPRTP support is not 239 successfully negotiated. 241 o Application Compatibility: MPRTP service model MUST be backwards 242 compatible with existing RTP applications, i.e., an MPRTP stack 243 MUST be able to work with legacy RTP applications and not require 244 changes to them. Therefore, the basic RTP APIs MUST remain 245 unchanged, but an MPRTP stack MAY provide extended APIs so that 246 the application can configure any additional features provided by 247 the MPRTP stack. 249 o Network Compatibility: individual RTP subflows MUST themselves be 250 well-formed RTP flows, so that they are able to traverse NATs and 251 firewalls. This MUST be the case even when interfaces appear 252 after session initiation. Interactive Connectivity Establishment 253 (ICE) [3] MAY be used for discovering new interfaces or performing 254 connectivity checks. 256 3. RTP Topologies 258 RFC 5117 [14] describes a number of scenarios using mixers and 259 translators in single-party (point-to-point), and multi-party (point- 260 to-multipoint) scenarios. RFC 3550 [1] (Section 2.3 and 7.x) discuss 261 in detail the impact of mixers and translators on RTP and RTCP 262 packets. MPRTP assumes that if a mixer or translator exists in the 263 network, then either all of the multiple paths or none of the 264 multiple paths go via this component. 266 4. MPRTP Architecture 268 In a typical scenario, an RTP session uses a single path. In an 269 MPRTP scenario, an RTP session uses multiple subflows that each use a 270 different path. Figure 1 shows the difference. 272 +--------------+ Signaling +--------------+ 273 | |------------------------------------>| | 274 | Client |<------------------------------------| Server | 275 | | Single RTP flow | | 276 +--------------+ +--------------+ 278 +--------------+ Signaling +--------------+ 279 | |------------------------------------>| | 280 | Client |<------------------------------------| Server | 281 | |<------------------------------------| | 282 +--------------+ MPRTP subflows +--------------+ 284 Figure 1: Comparison between traditional RTP streaming and MPRTP 286 +-----------------------+ +-------------------------------+ 287 | Application | | Application | 288 +-----------------------+ +-------------------------------+ 289 | | | MPRTP | 290 + RTP + +- - - - - - - -+- - - - - - - -+ 291 | | | RTP subflow | RTP subflow | 292 +-----------------------+ +---------------+---------------+ 293 | UDP | | UDP | UDP | 294 +-----------------------+ +---------------+---------------+ 295 | IP | | IP | IP | 296 +-----------------------+ +---------------+---------------+ 298 Figure 2: MPRTP Architecture 300 Figure 2 illustrates the differences between the standard RTP stack 301 and the MPRTP stack. MPRTP receives a normal RTP session from the 302 application and splits it into multiple RTP subflows. Each subflow 303 is then sent along a different path to the receiver. To the network, 304 each subflow appears as an independent, well-formed RTP flow. At the 305 receiver, the subflows are combined to recreate the original RTP 306 session. The MPRTP layer performs the following functions: 308 o Path Management: The layer is aware of alternate paths to the 309 other host, which may, for example, be the peer's multiple 310 interfaces. This enables the endpoint to transmit differently 311 marked packets along separate paths. MPRTP also selects 312 interfaces to send and receive data. Furthermore, it manages the 313 port and IP address pair bindings for each subflow. 315 o Packet Scheduling: the layer splits a single RTP flow into 316 multiple subflows and sends them across multiple interfaces 317 (paths). The splitting MAY BE done using different path 318 characteristics. 320 o Subflow recombination: the layer creates the original stream by 321 recombining the independent subflows. Therefore, the multipath 322 subflows appear as a single RTP stream to applications. 324 5. Example Media Flow Diagrams 326 There may be many complex technical scenarios for MPRTP, however, 327 this memo only considers the following two scenarios: 1) a 328 unidirectional media flow that represents the streaming use-case, and 329 2) a bidirectional media flow that represents a conversational use- 330 case. 332 5.1. Streaming use-case 334 In the unidirectional scenario, the receiver (client) initiates a 335 multimedia session with the sender (server). The receiver or the 336 sender may have multiple interfaces and both endpoints are MPRTP- 337 capable. Figure 3 shows this scenario. In this case, host A has 338 multiple interfaces. Host B performs connectivity checks on host A's 339 multiple interfaces. If the interfaces are reachable, then host B 340 streams multimedia data along multiple paths to host A. Moreover, 341 host B also sends RTCP Sender Reports (SR) for each subflow and host 342 A responds with a normal RTCP Receiver Report (RR) for the overall 343 session as well as the receiver statistics for each subflow. Host B 344 distributes the packets across the subflows based on the individually 345 measured path characteristics. 347 Alternatively, to reduce media startup time, host B may start 348 streaming multimedia data to host A's initiating interface and then 349 perform connectivity checks for the other interfaces. This method of 350 updating a single path session to a multipath session is called 351 "multipath session upgrade". 353 Host A Host B 354 ----------------------- ---------- 355 Interface A1 Interface A2 Interface B1 356 ----------------------- ---------- 357 | | 358 |------------------------------------->| Session setup with 359 |<-------------------------------------| multiple interfaces 360 | | | 361 | | | 362 | (RTP data B1->A1, B1->A2) | 363 |<=====================================| 364 | |<========================| 365 | | | 366 Note: there may be more scenarios. 368 Figure 3: Unidirectional media flow 370 5.2. Conversational use-case 372 In the bidirectional scenario, multimedia data flows in both 373 directions. The two hosts exchange their lists of interfaces with 374 each other and perform connectivity checks. Communication begins 375 after each host finds suitable address, port pairs. Interfaces that 376 receive data send back RTCP receiver statistics for that path (based 377 on the 5-tuple). The hosts balance their multimedia stream across 378 multiple paths based on the per path reception statistics and its own 379 volume of traffic. Figure 4 describes an example of a bidirectional 380 flow. 382 Host A Host B 383 --------------------------- --------------------------- 384 Interface A1 Interface A2 Interface B1 Interface B2 385 --------------------------- --------------------------- 386 | | | | 387 | | | |Session setup 388 |----------------------------------->| |with multiple 389 |<-----------------------------------| |interfaces 390 | | | | 391 | | | | 392 | (RTP data B1<->A1, B2<->A2) | | 393 |<===================================| | 394 | |<===================================| 395 |===================================>| | 396 | |===================================>| 397 | | | | 398 Note: the address pairs may have other permutations, 399 and they may be symmetric or asymmetric combinations. 401 Figure 4: Bidirectional flow 403 6. MPRTP Functional Blocks 405 This section describes some of the functional blocks needed for 406 MPRTP. We then investigate each block and consider available 407 mechanisms in the next section. 409 1. Session Setup: Interfaces may appear or disappear at anytime 410 during the session. To preserve backward compatibility with 411 legacy applications, a multipath session MUST look like a bundle 412 of individual RTP sessions. A multipath session may be upgraded 413 from a typical single path session, as and when new interfaces 414 appear or disappear. However, it is also possible to setup a 415 multipath session from the beginning, if the interfaces are 416 available at the start of the multimedia session. 418 2. Expanding RTP: For a multipath session, each subflow MUST look 419 like an independent RTP flow, so that individual RTCP messages 420 can be generated per subflow. Furthermore, MPRTP splits the 421 single multimedia stream into multiple subflows based on path 422 characteristics (e.g. RTT, loss-rate, receiver rate, bandwidth- 423 delay product etc.) and dynamically adjusts the load on each 424 link. 426 3. Adding Interfaces: Interfaces on the host need to be regularly 427 discovered and advertised. This can be done at session setup 428 and/or during the session. Discovering interfaces is outside the 429 scope of this document. 431 4. Expanding RTCP: MPRTP MUST provide per path RTCP reports for 432 monitoring the quality of the path, for load balancing, or for 433 congestion control, etc. To maintain backward compatibility with 434 legacy applications, the receiver MUST also send aggregate RTCP 435 reports along with the per-path reports. 437 5. Maintenance and Failure Handling: In a multi-homed endpoint 438 interfaces may appear and disappear. If this occurs at the 439 sender, it has to re-adjust the load on the available links. On 440 the other hand, if this occurs at the receiver, then the 441 multimedia data transmitted by the sender to those interfaces is 442 lost. This data may be re-transmitted along a different path 443 i.e., to a different interface on the receiver. Furthermore, the 444 endpoint has to either explicitly signal the disappearance of an 445 interface, or the other endpoint has to detect it (by lack of 446 media packets, RTCP feedback, or keep-alive packets). 448 6. Teardown: The MPRTP layer releases the occupied ports on the 449 interfaces. 451 7. Available Mechanisms within the Functional Blocks 453 This section discusses some of the possible alternatives for each 454 functional block mentioned in the previous section. 456 7.1. Session Setup 458 MPRTP session can be set up in many possible ways e.g., during 459 handshake, or upgraded mid-session. The capability exchange may be 460 done using out-of-band signaling (e.g., Session Description Protocol 461 (SDP) [15] in Session Initiation Protocol (SIP) [16], Real-Time 462 Streaming Protocol (RTSP) [17]) or in-band signaling (e.g., RTP/RTCP 463 header extension, Session Traversal Utilities for NAT (STUN) 464 messages). 466 7.1.1. Connectivity Checks 468 The endpoint SHOULD be capable of performing connectivity checks 469 (e.g., using ICE [3]). If the IP addresses of the endpoints are 470 reachable (e.g., globally addressable, same network etc) then 471 connectivity checks are not needed. 473 7.1.2. Adding New or Updating Interfaces 475 Interfaces can appear and disappear during a session, the endpoint 476 MUST be capable of advertising the changes in its set of usable 477 interfaces. Additionally, the application or OS may define a policy 478 on when and/or what interfaces are usable. However, MPRTP requires a 479 method to advertise or notify the other endpoint about the updated 480 set of usable interfaces. 482 7.1.3. In-band vs. Out-of-band Signaling 484 MTRTP nodes will generally use a signaling protocol to establish 485 their MPRTP session. With the existence of such a signaling 486 relationship, two alternatives become available to exchange 487 information about the available interfaces on each side for extending 488 RTP sessions to MPRTP and for modifying MPRTP sessions: in-band and 489 out-of-band signaling. 491 In-band signaling refers to using mechanisms of RTP/RTCP itself to 492 communicate interface addresses, e.g., a dedicated RTCP extensions 493 along the lines of the one defined to communicate information about 494 the feedback target for RTP over SSM [4]. In-band signaling does not 495 rely on the availability of a separate signaling connection and the 496 information flows along the same path as the media streams, thus 497 minimizing dependencies. Moreover, if the media channel is secured 498 (e.g., by means of SRTP), the signaling is implicitly protected as 499 well if SRTCP encryption and authentication are chosen. In-band 500 signaling is also expected to take a direct path to the peer, 501 avoiding any signaling overlay-induced indirections and associated 502 processing overheads in signaling elements -- avoiding such may be 503 especially worthwhile if frequent updates may occur as in the case of 504 mobile users. Finally, RTCP is usually sent sufficiently frequently 505 (in point-to-point settings) to provide enough opportunities for 506 transmission and (in case of loss) retransmission of the 507 corresponding RTCP packets. 509 Examples for in-band signaling include RTCP extensions as noted above 510 or suitable extensions to STUN. 512 Out-of-band signaling refers to using a separate signaling connection 513 (via SIP, RTSP, or HTTP) to exchange interface information, e.g., 514 expressed in SDP. Clear benefits are that signaling occurs at setup 515 time anyway and that experience and SDP syntax (and procedures) are 516 available that can be re-used or easily adapted to provide the 517 necessary capabilities. In contrast to RTCP, SDP offers a reliable 518 communication channel so that no separate retransmissions logic is 519 necessary. In SDP, especially when combined with ICE, connectivity 520 check mechanisms including sophisticated rules are readily available. 521 While SDP is not inherently protected, suitable security may need to 522 be applied anyway to the basic session setup. 524 Examples for out-of-band signaling are dedicated extensions to SDP; 525 those may be combined with ICE. 527 Both types of mechanisms have their pros and cons for middleboxes. 528 With in-band signaling, control packets take the same path as the 529 media packets and they can be directly inspected by middleboxes so 530 that the elements operating on the signaling channel do not need to 531 understand new SDP. With out-of-band signaling, only the middleboxes 532 processing the signaling need to be modified and those on the data 533 forwarding path can remain untouched. 535 Overall, it may appear sensible to provide a combination of both 536 mechanisms: out-of-band signaling for session setup and initial 537 interface negotiation and in-band signaling to deal with frequent 538 changes in interface state (and for the potential case, albeit rather 539 theoretical case of MPRTP communication without a signaling channel). 541 In its present version, this document explores both options to 542 provide a broad understanding of how the corresponding mechanisms 543 would look like. 545 [[Comment.1: Some have suggested STUN may be suitable for doing in- 546 band interface advertisement. This is still under consideration, but 547 depends on implementation challenges as many legacy systems don't 548 implement STUN and many RTP systems ignore STUN messages. --Editor]] 550 7.2. Expanding RTP 552 RTCP [1] is generated per media session. However, with MPRTP, the 553 media sender spreads the RTP load across several interfaces. The 554 media sender SHOULD make the path selection, load balancing and fault 555 tolerance decisions based on the characteristics of each path. 556 Therefore, apart from normal RTP sequence numbers defined in [1], the 557 MPRTP sender MUST add subflow-specific sequence numbers to help 558 calculate fractional losses, jitter, RTT, playout time, etc., for 559 each path, and a subflow identifier to associate the characteristics 560 with a path. The RTP header extension for MPRTP is shown in 561 Section 9.1. 563 7.3. Expanding RTCP 565 To provide accurate per path information an MPRTP endpoint MUST send 566 (SR/RR) report for each unique subflow along with the overall session 567 RTCP report. Therefore, the additional subflow reporting affects the 568 RTCP bandwidth and the RTCP reporting interval. RTCP report 569 scheduling for each subflow may cause a problem for RTCP 570 recombination and reconstruction in cases when 1) RTCP for a subflow 571 is lost, and 2) RTCP for a subflow arrives later than the other 572 subflows. (There may be other cases as well.) 574 The sender distributes the media across different paths using the per 575 path RTCP reports. However, this document doesn't cover algorithms 576 for congestion control or load balancing. 578 7.4. Failure Handling and Teardown 580 An MPRTP endpoint MUST keep alive subflows that have been negotiated 581 but no media is sent on them. Moreover, using the information in the 582 subflow reports, a sender can monitor an active subflow for failure 583 (errors, unreachability, congestion) and decide not to use (make the 584 active subflow passive), or teardown the subflow. 586 If an interface disappears, the endpoint MUST send an updated 587 interface advertisement without the interface and release the the 588 associated subflows. 590 8. MPRTP Protocol 592 Host A Host B 593 ----------------------- ----------------------- 594 Interface A1 Interface A2 Interface B1 Interface B2 595 ----------------------- ----------------------- 596 | | | | 597 | | (1) | | 598 |--------------------------------------->| | 599 |<---------------------------------------| | 600 | | (2) | | 601 |<=======================================| | 602 |<=======================================| (3) | 603 | | (4) | | 604 |<- - - - - - - - - - - - - - - - - - - -| | 605 |<- - - - - - - - - - - - - - - - - - - -| | 606 |<- - - - - - - - - - - - - - - - - - - -| | 607 | | (5) | | 608 |- - - - - - - - - - - - - - - - - - - ->| | 609 |<=======================================| (6) | 610 |<=======================================| | 611 | |<========================================| 612 |<=======================================| | 613 | |<========================================| 615 Key: 616 | Interface 617 ---> Signaling Protocol 618 <=== RTP Packets 619 - -> RTCP Packet 621 Figure 5: MPRTP New Interface 623 8.1. Overview 625 The bullet points explain the different steps shown in Figure 5 for 626 upgrading a single path multimedia session to multipath session. 628 (1) The first two interactions between the hosts represents the 629 establishment of a normal RTP session. This may performed e.g. 630 using SIP or RTSP. 632 (2) When the RTP session has been established, host B streams 633 media using its interface B1 to host A at interface A1. 635 (3) Host B supports sending media using MPRTP and becomes aware of 636 an additional interface B2. 638 (4) Host B advertises the multiple interface addresses. 640 (5) Host A supports receiving media using MPRTP and becomes aware 641 of an additional interface A2. 643 Side note, even if an MPRTP-capable host has only one interface, 644 it MUST respond to the advertisement with its single interface. 646 (6) Each host receives information about the additional interfaces 647 and the appropriate endpoints starts to stream the multimedia 648 content using the additional paths. 650 If needed, each endpoint will need to independently perform 651 connectivity checks (not shown in figure) and ascertain 652 reachability before using the paths. 654 8.1.1. Gather or Discovering Candidates 656 The endpoint periodically polls the operating system or is notified 657 when an additional interface appears. If the endpoint wants to use 658 the additional interface for MPRTP it MUST advertise it to the other 659 peers. The endpoint may also use ICE [3] to gather additional 660 candidates. 662 8.1.2. NAT Traversal 664 After gathering their interface candidates, the endpoints decide 665 internally if they wish to perform connectivity checks. 667 [[Comment.2: Legacy applications do not require ICE for session 668 establishment, therefore, MPRTP should not require it as well. 669 --Editor]] 671 If the endpoint chooses to perform connectivity checks then it MUST 672 first advertise the gathered candidates as ICE candidates in SDP 673 during session setup and let ICE perform the connectivity checks. As 674 soon as a sufficient number of connectivity checks succeed, the 675 endpoint can use the successful candidates to advertise its MPRTP 676 interface candidates. 678 8.1.3. Choosing between In-band (in RTCP) and Out-of-band (in SDP) 679 Interface Advertisement 681 If there is no media flowing at the moment and the application wants 682 to use the interfaces from the start of the session, it should 683 advertise them in SDP (See [5]). Alternatively, the endpoint can 684 setup the session as a single path media session and upgrade the 685 session to multipath by advertising the session in-band (See 686 Section 8.1.4). Moreover, if an interface appears and disappears, 687 the endpoint SHOULD prefer to advertise it in-band because the 688 endpoint would not have to wait for a response from the other 689 endpoint before starting to use the interface. However, if there is 690 a conflict between an in-band and out-of-band advertisement, i.e., 691 the endpoint receives an in-band advertisement while it has a pending 692 out-of-band advertisement, or vice versa then the session is setup 693 using out-of-band mechanisms. 695 8.1.4. In-band Interface Advertisement 697 To advertise the multiple interfaces in RTCP, an MPRTP-capable 698 endpoint MUST add the MPRTP Interface Advertisement defined in 699 Figure 13 with the RTCP Sender Report (SR). Each unique address is 700 encapsulated in an Interface Advertisement block and contains the IP 701 address, RTP and RTCP port addresses. The Interface Advertisement 702 blocks are ordered based on a decreasing priority level. On 703 receiving the MPRTP Interface Advertisement, an MPRTP-capable 704 receiver MUST respond with the set of interfaces (subset or all 705 available) it wants to use. 707 If the sender and receiver have only one interface, then the 708 endpoints MUST indicate the negotiated single path IP, RTP port and 709 RTCP port addresses. 711 8.1.5. Subflow ID Assignment 713 After interface advertisements have been exchanged, the endpoint MUST 714 associate a Subflow ID to each unique subflow. Each combination of 715 sender and receiver IP addresses and port pairs (5-tuple) is a unique 716 subflow. If the connectivity checks have been performed then the 717 endpoint MUST only use the subflows for which the connectivity checks 718 have succeeded. 720 8.1.6. Active and Passive Subflows 722 To send and receive data an endpoint MAY use any number of subflows 723 from the set of available subflows. The subflows that carry media 724 data are called active subflows, while those subflows that don't send 725 any media packets (fallback paths) are called passive subflows. 727 An endpoint MUST multiplex the subflow specific RTP and RTCP packets 728 on the same port to keep the NAT bindings alive. This is inline with 729 the recommendation made in RFC6263[18]. Moreover, if an endpoint 730 uses ICE, multiplexing RTP and RTCP reduces the number of components 731 from 2 to 1 per media stream. If no MPRTP or MPRTCP packets are 732 received on a particular subflow at a receiver, the receiver SHOULD 733 remove the subflow from active and passive lists and not send any 734 MPRTCP reports for that subflow. It may keep the bindings in a dead- 735 pool, so that if the 5-tuple or subflow reappears, it can quickly 736 reallocate it based on past history. 738 8.2. RTP Transmission 740 If both endpoints are MPRTP-capable and if they want to use their 741 multiple interfaces for sending the media stream then they MUST use 742 the MPRTP header extensions. They MAY use normal RTP with legacy 743 endpoints (see Appendix A). 745 An MPRTP endpoint sends RTP packets with an MPRTP extension that maps 746 the media packet to a specific subflow (see Figure 8). The MPRTP 747 layer SHOULD associate an RTP packet with a subflow based on a 748 scheduling strategy. The scheduling strategy may either choose to 749 augment the paths to create higher throughput or use the alternate 750 paths for enhancing resilience or error-repair. Due to the changes 751 in path characteristics, the endpoint should be able change its 752 scheduling strategy during an ongoing session. The MPRTP sender MUST 753 also populate the subflow specific fields described in the MPRTP 754 extension header (see Section 9.1.1). 756 8.3. Playout Considerations at the Receiver 758 A media receiver, irrespective of MPRTP support or not, should be 759 able to playback the media stream because the received RTP packets 760 are compliant to [1], i.e., a non-MPRTP receiver will ignore the 761 MPRTP header and still be able to playback the RTP packets. However, 762 the variation of jitter and loss per path may affect proper playout. 763 The receiver can compensate for the jitter by modifying the playout 764 delay (i.e., by calculating skew across all paths) of the received 765 RTP packets. 767 8.4. Subflow-specific RTCP Statistics and RTCP Aggregation 769 Aggregate RTCP provides the overall media statistics and follows the 770 normal RTCP defined in RFC3550 [1]. However, subflow specific RTCP 771 provides the per path media statistics because the aggregate RTCP 772 report may not provide sufficient per path information to an MPRTP 773 scheduler. Specifically, the scheduler should be aware of each 774 path's RTT and loss-rate, which an aggregate RTCP cannot provide. 775 The sender/receiver MUST use non-compound RTCP reports defined in 776 RFC5506 [6] to transmit the aggregate and subflow-specific RTCP 777 reports. Also, each subflow and the aggregate RTCP report MUST 778 follow the timing rules defined in [7]. 780 The RTCP reporting interval is locally implemented and the scheduling 781 of the RTCP reports may depend on the the behavior of each path. For 782 instance, the RTCP interval may be different for a passive path than 783 an active path to keep port bindings alive. Additionally, an 784 endpoint may decide to share the RTCP reporting bit rate equally 785 across all its paths or schedule based on the receiver rate on each 786 path. 788 8.5. RTCP Transmission 790 The sender sends an RTCP SR on each active path. For each SR the 791 receiver gets, it echoes one back to the same IP address-port pair 792 that sent the SR. The receiver tries to choose the symmetric path 793 and if the routing is symmetric then the per-path RTT calculations 794 will work out correctly. However, even if the paths are not 795 symmetric, the sender would at maximum, under-estimate the RTT of the 796 path by a factor of half of the actual path RTT. 798 9. Packet Formats 800 In this section we define the protocol structures described in the 801 previous sections. 803 9.1. RTP Header Extension for MPRTP 805 The MPRTP header extension is used to distribute a single RTP stream 806 over multiple subflows. 808 The header conforms to the one-byte RTP header extension defined in 809 [8]. The header extension contains a 16-bit length field that counts 810 the number of 32-bit words in the extension, excluding the four-octet 811 extension header (therefore zero is a valid length, see Section 5.3.1 812 of [1] for details). 814 The RTP header for each subflow is defined below: 816 0 1 2 3 817 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 1 818 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 819 |V=2|P|1| CC |M| PT | sequence number | 820 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 821 | timestamp | 822 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 823 | synchronization source (SSRC) identifier | 824 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 825 | 0xBE | 0xDE | length=N-1 | 826 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 827 | ID | LEN | MPID |LENGTH | MPRTP header data | 828 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 829 | .... | 830 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 831 | RTP payload | 832 | .... | 833 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 835 Figure 6: Generic MPRTP header extension 837 MPID: 839 The MPID field corresponds to the type of MPRTP packet. 840 Namely: 842 +---------------+--------------------------------------------------+ 843 | MPID ID | Use | 844 | Value | | 845 +---------------+--------------------------------------------------+ 846 | 0x0 | Subflow RTP Header. For this case the Length is | 847 | | set to 4 | 848 +---------------+--------------------------------------------------+ 850 Figure 7: RTP header extension values for MPRTP (H-Ext ID) 852 length 854 The 4-bit length field is the length of extension data in bytes 855 not including the H-Ext ID and length fields. The value zero 856 indicates there is no data following. 858 MPRTP header data 860 Carries the MPID specific data as described in the following 861 sub-sections. 863 9.1.1. MPRTP RTP Extension for a Subflow 865 The RTP header for each subflow is defined below: 867 0 1 2 3 868 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 1 869 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 870 |V=2|P|1| CC |M| PT | sequence number | 871 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 872 | timestamp | 873 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 874 | synchronization source (SSRC) identifier | 875 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 876 | 0xBE | 0xDE | length=2 | 877 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 878 | ID | LEN=4 | 0x0 | LEN=4 | Subflow ID | 879 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 880 | Subflow-specific Seq Number | Pad (0) | Pad (0) | 881 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 882 | RTP payload | 883 | .... | 884 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 886 Figure 8: MPRTP header for subflow 888 MP ID = 0x0 890 Indicates that the MPRTP header extension carries subflow 891 specific information. 893 length = 4 895 Subflow ID: Identifier of the subflow. Every RTP packet belonging 896 to the same subflow carries the same unique subflow identifier. 898 Flow-Specific Sequence Number (FSSN): Sequence of the packet in 899 the subflow. Each subflow has its own strictly monotonically 900 increasing sequence number space. 902 9.2. RTCP Extension for MPRTP (MPRTCP) 904 The MPRTP RTCP header extension is used to 1) provide RTCP feedback 905 per subflow to determine the characteristics of each path, and 2) 906 advertise each interface. 908 0 1 2 3 909 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 1 910 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 911 |V=2|P|reserved | PT=MPRTCP=211 | length | 912 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 913 | SSRC of packet sender | 914 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 915 | SSRC_1 (SSRC of first source) | 916 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 917 | MPRTCP_Type | block length | | 918 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ MPRTCP Reports | 919 | ... | 920 | ... | 921 | ... | 922 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 924 Figure 9: Generic RTCP Extension for MPRTP (MPRTCP) [appended to 925 normal SR/RR] 927 MPRTCP: 8 bits 929 Contains the constant 211 to identify this as an Multipath RTCP 930 packet. 932 length: 16 bits 934 As described for the RTCP packet (see Section 6.4.1 of the RTP 935 specification [1]), the length of this is in 32-bit words minus 936 one, including the header and any padding. 938 MPRTCP_Type: 8-bits 940 The MPRTCP_Type field corresponds to the type of MPRTP RTCP 941 packet. Namely: 943 +---------------+--------------------------------------------------+ 944 | MPRTCP_Type | Use | 945 | Value | | 946 +---------------+--------------------------------------------------+ 947 | 0 | Subflow Specific Report | 948 | 1 | Interface Advertisement (IPv4 Address) | 949 | 2 | Interface Advertisement (IPv4 Address) | 950 | 3 | Interface Advertisement (DNS Address) | 951 +---------------+--------------------------------------------------+ 953 Figure 10: RTP header extension values for MPRTP (MPRTCP_Type) 955 block length: 8-bits 957 The 8-bit length field is the length of the encapsulated MPRTCP 958 reports in 32-bit word length not including the MPRTCP_Type and 959 length fields. The value zero indicates there is no data 960 following. 962 MPRTCP Reports: variable size 964 Defined later in 9.2.1 and 9.3. 966 9.2.1. MPRTCP Extension for Subflow Reporting 968 When sending a report for a specific subflow the sender or receiver 969 MUST add only the reports associated with that 5-tuple. Each subflow 970 is reported independently using the following MPRTCP Feedback header. 972 0 1 2 3 973 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 1 974 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 975 |V=2|P|reserved | PT=MPRTCP=211 | length | 976 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 977 | SSRC of packet sender | 978 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 979 | SSRC_1 (SSRC of first source) | 980 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 981 | MPRTCP_Type=0 | block length | Subflow ID #1 | 982 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 983 | Subflow-specific reports | 984 | .... | 985 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 986 | MPRTCP_Type=0 | block length | Subflow ID #2 | 987 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 988 | Subflow-specific reports | 989 | .... | 990 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 992 Figure 11: MPRTCP Subflow Reporting Header 994 MPRTCP_Type: 0 996 The value indicates that the encapsulated block is a subflow 997 report. 999 block length: 8-bits 1001 The 8-bit length field is the length of the encapsulated subflow- 1002 specific reports in 32-bit word length not including the 1003 MPRTCP_Type and length fields. 1005 Subflow ID: 16 bits 1007 Subflow identifier is the value associated with the subflow the 1008 endpoint is reporting about. If it is a sender it MUST use the 1009 Subflow ID associated with the 5-tuple. If it is a receiver it 1010 MUST use the Subflow ID received in the Subflow-specific Sender 1011 Report. 1013 Subflow-specific reports: variable 1015 Subflow-specific report contains all the reports associated with 1016 the Subflow ID. For a sender, it MUST include the Subflow- 1017 specific Sender Report (SSR). For a receiver, it MUST include 1018 Subflow-specific Receiver Report (SRR). Additionally, if the 1019 receiver supports subflow-specific extension reports then it MUST 1020 append them to the SRR. 1022 9.2.1.1. MPRTCP for Subflow-specific SR, RR and XR 1024 [[Comment.3: inside the context of subflow specific reports can we 1025 reuse the payload type code for Sender Report (PT=200), Receiver 1026 Report (PT=201), Extension Report (PT=207).Transport and Payload 1027 specific RTCP messages are session specific and SHOULD be used as 1028 before. --Editor]] 1030 Example: 1032 0 1 2 3 1033 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 1034 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1035 |V=2|P|reserved | PT=MPRTCP=211 | length | 1036 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1037 | SSRC of packet sender | 1038 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 1039 | SSRC_1 (SSRC of first source) | 1040 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1041 | MPRTCP_Type=0 | block length | Subflow ID #1 | 1042 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 1043 |V=2|P| RC | PT=SR=200 | length | 1044 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1045 | SSRC of sender | 1046 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 1047 | NTP timestamp, most significant word | 1048 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1049 | NTP timestamp, least significant word | 1050 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1051 | RTP timestamp | 1052 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1053 | subflow's packet count | 1054 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1055 | subflow's octet count | 1056 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1057 | MPRTCP_Type=0 | block length | Subflow ID #2 | 1058 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 1059 |V=2|P| RC | PT=RR=201 | length | 1060 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1061 | SSRC of packet sender | 1062 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 1063 | fraction lost | cumulative number of packets lost | 1064 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1065 | extended highest sequence number received | 1066 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1067 | inter-arrival jitter | 1068 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1069 | last SR (LSR) | 1070 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1071 | delay since last SR (DLSR) | 1072 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 1073 | Subflow specific extension reports | 1074 | .... | 1075 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1077 Figure 12: Example of reusing RTCP SR and RR inside an MPRTCP header 1078 (Bi-directional use-case, in case of uni-directional flow the subflow 1079 will only send an SR or RR). 1081 9.3. MPRTCP Extension for Interface advertisement 1083 This sub-section defines the RTCP header extension for in-band 1084 interface advertisement by the receiver. The interface advertisement 1085 block describes a method to represent IPv4, IPv6 and generic DNS-type 1086 addresses in a block format. It is based on the sub-reporting block 1087 in [4]. The interface advertisement SHOULD immediately follow the 1088 Receiver Report. If the Receiver Report is not present, then it MUST 1089 be appended to the Sender Report. 1091 The endpoint MUST advertise the interfaces it wants to use whenever 1092 an interface appears or disappears and also when it receives an 1093 Interface Advertisement. 1095 0 1 2 3 1096 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 1097 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1098 |V=2|P|reserved | PT=MPRTCP=211 | length | 1099 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1100 | SSRC of packet sender | 1101 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 1102 | SSRC_1 (SSRC of first source) | 1103 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1104 | MPRTCP_Type | block length | RTP Port | 1105 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1106 | Interface Address #1 | 1107 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1108 | MPRTCP_Type | block length | RTP Port | 1109 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1110 | Interface Address #2 | 1111 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1112 | MPRTCP_Type | block length | RTP Port | 1113 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1114 | Interface Address #.. | 1115 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1116 | MPRTCP_Type | block length | RTP Port | 1117 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1118 | Interface Address #m | 1119 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 1121 Figure 13: MPRTP Interface Advertisement. (appended to SR/RR) 1123 MPRTCP_Type: 8 bits 1125 The MPRTCP_Type corresponds to the type of interface address. 1126 Namely: 1128 1: IPv4 address 1130 2: IPv6 address 1132 3: DNS name 1134 block length: 8 bits 1136 The length of the Interface Advertisement block in bytes. 1138 For an IPv4 address, this should be 9 (i.e., 5 octets for 1139 the header and 4 octets for IPv4 address). 1141 For an IPv6 address, this should be 21. 1143 For a DNS name, the length field indicates the number of 1144 octets making up the string plus the 5 byte header. 1146 RTP Port: 2 octets 1148 The port number to which the sender sends RTP data. A port 1149 number of 0 is invalid and MUST NOT be used. 1151 Interface Address: 4 octets (IPv4), 16 octets (IPv6), or n octets 1152 (DNS name) 1154 The address to which receivers send feedback reports. For IPv4 1155 and IPv6, fixed-length address fields are used. A DNS name is 1156 an arbitrary-length string. The string MAY contain 1157 Internationalizing Domain Names in Applications (IDNA) domain 1158 names and MUST be UTF-8 [9] encoded. 1160 10. RTCP Timing reconsiderations for MPRTCP 1162 MPRTP endpoints MUST conform to the timing rule imposed in [7], i.e., 1163 the total RTCP rate between the participants MUST NOT exceed 5% of 1164 the media rate. For each endpoint, a subflow MUST send the aggregate 1165 and subflow-specific report. The endpoint SHOULD schedule the RTCP 1166 reports for the active subflows based on the share of the transmitted 1167 or received bit rate to the average media bit rate, this method 1168 ensures fair sharing of the RTCP bandwidth. Alternatively, the 1169 endpoint MAY schedule the reports in round-robin. 1171 11. SDP Considerations 1172 11.1. Signaling MPRTP Header Extension in SDP 1174 To indicate the use of the MPRTP header extensions (see Section 9) in 1175 SDP, the sender MUST use the following URI in extmap: 1176 urn:ietf:params:rtp-hdrext:mprtp. This is a media level parameter. 1177 Legacy RTP (non-MPRTP) clients will ignore this header extension, but 1178 can continue to parse and decode the packet (see Appendix A). 1180 Example: 1182 v=0 1183 o=alice 2890844526 2890844527 IN IP4 192.0.2.1 1184 s= 1185 c=IN IP4 192.0.2.1 1186 t=0 0 1187 m=video 49170 RTP/AVP 98 1188 a=rtpmap:98 H264/90000 1189 a=fmtp:98 profile-level-id=42A01E; 1190 a=extmap:1 urn:ietf:params:rtp-hdrext:mprtp 1192 11.2. Signaling MPRTP capability in SDP 1194 A participant of a media session MUST use SDP to indicate that it 1195 supports MPRTP. Not providing this information will make the other 1196 endpoint ignore the RTCP extensions. 1198 mprtp-attrib = "a=" "mprtp" [ 1199 SP mprtp-optional-parameter] 1200 CRLF ; flag to enable MPRTP 1202 The endpoint MUST use 'a=mprtp', if it is able to send and receive 1203 MPRTP packets. Generally, senders and receivers MUST indicate this 1204 capability if they support MPRTP and would like to use it in the 1205 specific media session being signaled. To exchange the additional 1206 interfaces, the endpoint SHOULD use the in-band signaling (See 1207 Section 9.3). Alternatively, advertise in SDP (See [5]). 1209 MPRTP endpoint multiplexes RTP and RTCP on a single port, sender MUST 1210 indicate support by adding "a=rtcp-mux" in SDP [10]. If an endpoint 1211 receives an SDP without "a=rtcp-mux" but contains "a=mprtp", then the 1212 endpoint MUST infer support for multiplexing. 1214 [[Comment.4: If a=mprtp is indicated, does the endpoint need to 1215 indicate a=rtcp-mux? because MPRTP mandates RTP RTCP multiplexing. 1216 --Editor]] 1218 11.3. MPRTP with ICE 1220 If the endpoints intend to use ICE [3] for discovering interfaces and 1221 running connectivity checks then the endpoint MUST advertise its ICE 1222 candidates in the initial OFFER, as defined in ICE [3]. Thereafter 1223 the endpoints run connectivity checks. 1225 When an endpoint uses ICE's regular nomination [3] procedure, it 1226 chooses the best ICE candidate as the default path. In the case of 1227 an MPRTP endpoint, if more than one ICE candidate succeeded the 1228 connectivity checks then an MPRTP endpoint MAY advertise (some of) 1229 these in-band in RTCP as MPRTP interfaces. 1231 When an endpoint uses ICE's aggressive nomination [3] procedure, the 1232 selected candidate may change as more ICE checks complete. Instead 1233 of sending updated offers as additional ICE candidates appear 1234 (transience), the endpoint it MAY use in-band signaling to advertise 1235 its interfaces, as defined in Section 9.3. 1237 If the default interface disappears and the paths used for MPRTP are 1238 different from the one in the c= and m= lines then the an alternate 1239 interface for which the ICE checks were successful should be promoted 1240 to the c= and m= lines in the updated offer. 1242 When a new interface appears then the application/endpoint should 1243 internally decide if it wishes to use it and sends an updated offer 1244 with ICE candidates of the all its interfaces including the new 1245 interface. The receiving endpoint responds to the offer with all its 1246 ICE candidates in the answer and starts connectivity checks between 1247 all its candidates and the offerer's ICE candidates. Similarly, the 1248 initiating endpoint starts connectivity checks between the its 1249 interfaces (incl. the new interface) and all the received ICE 1250 candidates in the answer. If the connectivity checks succeed, the 1251 initiating endpoint MAY use in-band signaling (See Section 9.3) to 1252 advertise its new set of interfaces. 1254 11.4. Increased Throughput 1256 The MPRTP layer MAY choose to augment paths to increase throughput. 1257 If the desired media rate exceeds the current media rate, the 1258 endpoints MUST renegotiate the application specific ("b=AS:xxx") [19] 1259 bandwidth. 1261 11.5. Offer/Answer 1263 When SDP [19] is used to negotiate MPRTP sessions following the 1264 offer/answer model [15], the "a=mprtp" attribute (see Section 11.2) 1265 indicates the desire to use multiple interfaces to send or receive 1266 media data. The initial SDP offer MUST include this attribute at the 1267 media level. If the answerer wishes to also use MPRTP, it MUST 1268 include a media-level "a=mprtp" attribute in the answer. If the 1269 answer does not contain an "a=mprtp" attribute, the offerer MUST NOT 1270 stream media over multiple paths and the offerer MUST NOT advertise 1271 additional MPRTP interfaces in-band or out-of-band. 1273 When SDP is used in a declarative manner, the presence of an 1274 "a=mprtp" attribute signals that the sender can send or receive media 1275 data over multiple interfaces. The receiver SHOULD be capable to 1276 stream media to the multiple interfaces and be prepared to receive 1277 media from multiple interfaces. 1279 The following sections shows examples of SDP offer and answer for in- 1280 band and out-of-band signaling. 1282 11.5.1. In-band Signaling Example 1284 The following offer/answer shows that both the endpoints are MPRTP 1285 capable and SHOULD use in-band signaling for interfaces 1286 advertisements. 1288 Offer: 1289 v=0 1290 o=alice 2890844526 2890844527 IN IP4 192.0.2.1 1291 s= 1292 c=IN IP4 192.0.2.1 1293 t=0 0 1294 m=video 49170 RTP/AVP 98 1295 a=rtpmap:98 H264/90000 1296 a=fmtp:98 profile-level-id=42A01E; 1297 a=rtcp-mux 1298 a=mprtp 1300 Answer: 1301 v=0 1302 o=bob 2890844528 2890844529 IN IP4 192.0.2.2 1303 s= 1304 c=IN IP4 192.0.2.2 1305 t=0 0 1306 m=video 4000 RTP/AVP 98 1307 a=rtpmap:98 H264/90000 1308 a=fmtp:98 profile-level-id=42A01E; 1309 a=rtcp-mux 1310 a=mprtp 1312 The endpoint MAY now use in-band RTCP signaling to advertise its 1313 multiple interfaces. Alternatively, it MAY make another offer with 1314 the interfaces in SDP (out-of-band signaling) [5]. 1316 12. IANA Considerations 1318 The following contact information shall be used for all registrations 1319 in this document: 1321 Contact: Varun Singh 1322 mailto:varun.singh@iki.fi 1323 tel:+358-9-470-24785 1325 Note to the RFC-Editor: When publishing this document as an RFC, 1326 please replace "RFC XXXX" with the actual RFC number of this document 1327 and delete this sentence. 1329 12.1. MPRTP Header Extension 1331 This document defines a new extension URI to the RTP Compact Header 1332 Extensions sub-registry of the Real-Time Transport Protocol (RTP) 1333 Parameters registry, according to the following data: 1335 Extension URI: urn:ietf:params:rtp-hdrext:mprtp 1336 Description: Multipath RTP 1337 Reference: RFC XXXX 1339 12.2. MPRTCP Packet Type 1341 A new RTCP packet format has been registered with the RTCP Control 1342 Packet type (PT) Registry: 1344 Name: MPRTCP 1345 Long name: Multipath RTCP 1346 Value: 211 1347 Reference: RFC XXXX. 1349 This document defines a substructure for MPRTCP packets. A new sub- 1350 registry has been set up for the sub-report block type (MPRTCP_Type) 1351 values for the MPRTCP packet, with the following registrations 1352 created initially: 1354 Name: Subflow Specific Report 1355 Long name: Multipath RTP Subflow Specific Report 1356 Value: 0 1357 Reference: RFC XXXX. 1359 Name: IPv4 Address 1360 Long name: IPv4 Interface Address 1361 Value: 1 1362 Reference: RFC XXXX. 1364 Name: IPv6 Address 1365 Long name: IPv6 Interface Address 1366 Value: 2 1367 Reference: RFC XXXX. 1369 Name: DNS Name 1370 Long name: DNS Name indicating Interface Address 1371 Value: 3 1372 Reference: RFC XXXX. 1374 Further values may be registered on a first come, first served basis. 1375 For each new registration, it is mandatory that a permanent, stable, 1376 and publicly accessible document exists that specifies the semantics 1377 of the registered parameter as well as the syntax and semantics of 1378 the associated sub-report block. The general registration procedures 1379 of [19] apply. 1381 12.3. SDP Attributes 1383 This document defines a new SDP attribute, "mprtp", within the 1384 existing IANA registry of SDP Parameters. 1386 12.3.1. "mprtp" attribute 1388 o Attribute Name: MPRTP 1390 o Long Form: Multipath RTP 1392 o Type of Attribute: media-level 1394 o Charset Considerations: The attribute is not subject to the 1395 charset attribute. 1397 o Purpose: This attribute is used to indicate support for Multipath 1398 RTP. It can also provide one of many possible interfaces for 1399 communication. These interface addresses may have been validated 1400 using ICE procedures. 1402 o Appropriate Values: See Section 11.2 of RFC XXXX. 1404 13. Security Considerations 1406 TBD 1408 All drafts are required to have a security considerations section. 1409 See RFC 3552 [20] for a guide. 1411 14. Acknowledgements 1413 Varun Singh, Saba Ahsan, and Teemu Karkkainen are supported by 1414 Trilogy (http://www.trilogy-project.org), a research project (ICT- 1415 216372) partially funded by the European Community under its Seventh 1416 Framework Program. The views expressed here are those of the 1417 author(s) only. The European Commission is not liable for any use 1418 that may be made of the information in this document. 1420 Thanks to Miguel A. Garcia, Ralf Globisch, Christer Holmberg, and 1421 Roni Even for providing valuable feedback on earlier versions of this 1422 draft 1424 15. References 1426 15.1. Normative References 1428 [1] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, 1429 "RTP: A Transport Protocol for Real-Time Applications", STD 64, 1430 RFC 3550, July 2003. 1432 [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement 1433 Levels", BCP 14, RFC 2119, March 1997. 1435 [3] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A 1436 Protocol for Network Address Translator (NAT) Traversal for 1437 Offer/Answer Protocols", RFC 5245, April 2010. 1439 [4] Ott, J., Chesterfield, J., and E. Schooler, "RTP Control 1440 Protocol (RTCP) Extensions for Single-Source Multicast Sessions 1441 with Unicast Feedback", RFC 5760, February 2010. 1443 [5] Singh, V., Ott, J., Karkkainen, T., Globisch, R., and T. 1444 Schierl, "Multipath RTP (MPRTP) attribute in Session 1445 Description Protocol", 1446 draft-singh-mmusic-mprtp-sdp-extension-00 (work in progress), 1447 July 2012. 1449 [6] Johansson, I. and M. Westerlund, "Support for Reduced-Size 1450 Real-Time Transport Control Protocol (RTCP): Opportunities and 1451 Consequences", RFC 5506, April 2009. 1453 [7] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 1454 "Extended RTP Profile for Real-time Transport Control Protocol 1455 (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, July 2006. 1457 [8] Singer, D. and H. Desineni, "A General Mechanism for RTP Header 1458 Extensions", RFC 5285, July 2008. 1460 [9] Yergeau, F., "UTF-8, a transformation format of ISO 10646", 1461 STD 63, RFC 3629, November 2003. 1463 [10] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 1464 Control Packets on a Single Port", RFC 5761, April 2010. 1466 15.2. Informative References 1468 [11] Stewart, R., "Stream Control Transmission Protocol", RFC 4960, 1469 September 2007. 1471 [12] Ford, A., Raiciu, C., Handley, M., Barre, S., and J. Iyengar, 1472 "Architectural Guidelines for Multipath TCP Development", 1473 RFC 6182, March 2011. 1475 [13] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming Shim 1476 Protocol for IPv6", RFC 5533, June 2009. 1478 [14] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 5117, 1479 January 2008. 1481 [15] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with 1482 Session Description Protocol (SDP)", RFC 3264, June 2002. 1484 [16] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., 1485 Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: 1486 Session Initiation Protocol", RFC 3261, June 2002. 1488 [17] Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M., and M. 1489 Stiemerling, "Real Time Streaming Protocol 2.0 (RTSP)", 1490 draft-ietf-mmusic-rfc2326bis-29 (work in progress), March 2012. 1492 [18] Marjou, X. and A. Sollaud, "Application Mechanism for Keeping 1493 Alive the NAT Mappings Associated with RTP / RTP Control 1494 Protocol (RTCP) Flows", RFC 6263, June 2011. 1496 [19] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1497 Description Protocol", RFC 4566, July 2006. 1499 [20] Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on 1500 Security Considerations", BCP 72, RFC 3552, July 2003. 1502 Appendix A. Interoperating with Legacy Applications 1504 An MPRTP sender can use its multiple interfaces to send media to a 1505 legacy RTP client. The legacy receiver will ignore the subflow RTP 1506 header and the receiver's de-jitter buffer will try to compensate for 1507 the mismatch in per-path delay. However, the receiver can only send 1508 the overall or aggregate RTCP report which may be insufficient for an 1509 MPRTP sender to adequately schedule packets or detect if a path 1510 disappeared. 1512 An MPRTP receiver can only use one of its interface when 1513 communicating with a legacy sender. 1515 Appendix B. Change Log 1517 Note to the RFC-Editor: please remove this section prior to 1518 publication as an RFC. 1520 B.1. Changes in draft-singh-avtcore-mprtp-05 1522 o SDP extensions moved to draft-singh-mmusic-mprtp-sdp-attribute-00. 1523 Kept only the basic 'a=mprtp' attribute in this document. 1525 o Cleaned up ICE procedures for advertising only using in-band 1526 signaling. 1528 B.2. Changes in draft-singh-avtcore-mprtp-04 1530 o Fixed missing 0xBEDE header in MPRTP header format. 1532 o Removed connectivity checks and keep-alives from in-band 1533 signaling. 1535 o MPRTP and MPRTCP are multiplexed on a single port. 1537 o MPRTCP packet headers optimized. 1539 o Made ICE optional 1540 o Updated Sections: 7.1.2, 8.1.x, 11.2, 11.4, 11.6. 1542 o Added how to use MPRTP in RTSP (Section 12). 1544 o Updated IANA Considerations section. 1546 B.3. Changes in draft-singh-avtcore-mprtp-03 1548 o Added this change log. 1550 o Updated section 6, 7 and 8 based on comments from MMUSIC. 1552 o Updated section 11 (SDP) based on comments of MMUSIC. 1554 o Updated SDP examples with ICE and non-ICE in out-of-band signaling 1555 scenario. 1557 o Added Appendix A on interop with legacy. 1559 o Updated IANA Considerations section. 1561 B.4. Changes in draft-singh-avtcore-mprtp-02 1563 o MPRTCP protocol extensions use only one PT=210, instead of 210 and 1564 211. 1566 o RTP header uses 1-byte extension instead of 2-byte. 1568 o Added section on RTCP Interval Calculations. 1570 o Added "mprtp-interface" attribute in SDP considerations. 1572 B.5. Changes in draft-singh-avtcore-mprtp-01 1574 o Added MPRTP and MPRTCP protocol extensions and examples. 1576 o WG changed from -avt to -avtcore. 1578 Authors' Addresses 1580 Varun Singh 1581 Aalto University 1582 School of Science and Technology 1583 Otakaari 5 A 1584 Espoo, FIN 02150 1585 Finland 1587 Email: varun@comnet.tkk.fi 1588 URI: http://www.netlab.tkk.fi/~varun/ 1590 Teemu Karkkainen 1591 Aalto University 1592 School of Science and Technology 1593 Otakaari 5 A 1594 Espoo, FIN 02150 1595 Finland 1597 Email: teemuk@comnet.tkk.fi 1599 Joerg Ott 1600 Aalto University 1601 School of Science and Technology 1602 Otakaari 5 A 1603 Espoo, FIN 02150 1604 Finland 1606 Email: jo@comnet.tkk.fi 1608 Saba Ahsan 1609 Aalto University 1610 School of Science and Technology 1611 Otakaari 5 A 1612 Espoo, FIN 02150 1613 Finland 1615 Email: sahsan@cc.hut.fi 1616 Lars Eggert 1617 NetApp 1618 Sonnenallee 1 1619 Kirchheim 85551 1620 Germany 1622 Phone: +49 151 12055791 1623 Email: lars@netapp.com 1624 URI: http://eggert.org/