idnits 2.17.1 draft-ietf-siprec-protocol-04.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 : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == The document seems to lack the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords. (The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: The SRC can temporarily discontinue streaming and collection of recorded media from the SRC to the SRS for reason such as masking the recording. In this case, the SRC sends a new SDP offer and sets the media stream to inactive (a=inactive) for each recorded stream to be paused, as per the procedures in [RFC3264]. To resume streaming and collection of recorded media, the SRC sends a new SDP offer and sets the media streams with a=sendonly attribute. Note that when a CS stream is muted/unmuted, this information is conveyed in the metadata by the SRC. The SRC SHOULD not modify the media stream with a=inactive for mute since this operation is reserved for pausing the RS media. == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: When the SRS explicitly requests for a full metadata snapshot, the SRS MUST send an UPDATE request without an SDP offer. A metadata snapshot request contains a content with the content disposition type "recording-session". Note that the SRS MAY generate an INVITE request without an SDP offer but this MUST not include a metadata snapshot request. The format of the content is "application/ rs-metadata-request", and the body format is chosen to be a simple text-based format. The following shows an example: -- The document date (May 08, 2012) is 4365 days in the past. Is this intentional? 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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SIPREC L. Portman 3 Internet-Draft NICE Systems 4 Intended status: Standards Track H. Lum, Ed. 5 Expires: November 9, 2012 Genesys 6 C. Eckel 7 Cisco 8 A. Johnston 9 Avaya 10 A. Hutton 11 Siemens Enterprise 12 Communications 13 May 08, 2012 15 Session Recording Protocol 16 draft-ietf-siprec-protocol-04 18 Abstract 20 This document specifies the use of the Session Initiation Protocol 21 (SIP), the Session Description Protocol (SDP), and the Real Time 22 Protocol (RTP) for delivering real-time media and metadata from a 23 Communication Session (CS) to a recording device. The Session 24 Recording Protocol specifies the use of SIP, SDP, and RTP to 25 establish a Recording Session (RS) between the Session Recording 26 Client (SRC), which is on the path of the CS, and a Session Recording 27 Server (SRS) at the recording device. 29 Status of this Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at http://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on November 9, 2012. 46 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 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 66 4. Overview of operations . . . . . . . . . . . . . . . . . . . . 5 67 4.1. Delivering recorded media . . . . . . . . . . . . . . . . 5 68 4.2. Delivering recording metadata . . . . . . . . . . . . . . 7 69 5. Initiating a Recording Session . . . . . . . . . . . . . . . . 8 70 5.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 8 71 5.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 9 72 6. SDP Handling . . . . . . . . . . . . . . . . . . . . . . . . . 9 73 6.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 9 74 6.1.1. Handling media stream updates . . . . . . . . . . . . 11 75 6.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 11 76 7. RTP Handling . . . . . . . . . . . . . . . . . . . . . . . . . 12 77 7.1. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 12 78 7.1.1. SRC acting as an RTP Translator . . . . . . . . . . . 13 79 7.1.1.1. Forwarding Translator . . . . . . . . . . . . . . 13 80 7.1.1.2. Transcoding Translator . . . . . . . . . . . . . . 14 81 7.1.2. SRC acting as an RTP Mixer . . . . . . . . . . . . . . 15 82 7.1.3. SRC acting as an RTP Endpoint . . . . . . . . . . . . 15 83 7.2. RTCP . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 84 7.3. RTP Profile . . . . . . . . . . . . . . . . . . . . . . . 16 85 7.4. SSRC . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 86 7.5. CSRC . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 87 7.6. SDES . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 88 7.6.1. CNAME . . . . . . . . . . . . . . . . . . . . . . . . 17 89 7.7. Keepalive . . . . . . . . . . . . . . . . . . . . . . . . 18 90 7.8. RTCP Feedback Messages . . . . . . . . . . . . . . . . . . 18 91 7.8.1. Full Intra Request . . . . . . . . . . . . . . . . . . 18 92 7.8.1.1. SIP INFO for FIR . . . . . . . . . . . . . . . . . 18 93 7.8.2. Picture Loss Indicator . . . . . . . . . . . . . . . . 18 94 7.8.3. Temporary Maximum Media Stream Bit Rate Request . . . 19 95 7.8.3.1. Renegotiation of SDP bandwidth attribute . . . . . 19 97 7.9. Symmetric RTP/RTCP for Sending and Receiving . . . . . . . 19 98 8. Metadata . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 99 8.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 20 100 8.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 21 101 8.2.1. Formal Syntax . . . . . . . . . . . . . . . . . . . . 23 102 9. Persistent Recording . . . . . . . . . . . . . . . . . . . . . 23 103 10. Extensions for Recording-aware User Agents . . . . . . . . . . 23 104 10.1. Procedures at the record-aware user agent . . . . . . . . 24 105 10.1.1. Recording preference . . . . . . . . . . . . . . . . . 24 106 10.2. Procedures at the SRC . . . . . . . . . . . . . . . . . . 25 107 10.2.1. Recording indication . . . . . . . . . . . . . . . . . 25 108 10.2.2. Recording preference . . . . . . . . . . . . . . . . . 27 109 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 110 11.1. Registration of Option Tags . . . . . . . . . . . . . . . 27 111 11.1.1. siprec Option Tag . . . . . . . . . . . . . . . . . . 27 112 11.1.2. record-aware Option Tag . . . . . . . . . . . . . . . 27 113 11.2. Registration of media feature tags . . . . . . . . . . . . 27 114 11.2.1. src feature tag . . . . . . . . . . . . . . . . . . . 28 115 11.2.2. srs feature tag . . . . . . . . . . . . . . . . . . . 28 116 11.3. New Content-Disposition Parameter Registrations . . . . . 29 117 11.4. Media Type Registration . . . . . . . . . . . . . . . . . 29 118 11.4.1. Registration of MIME Type application/rs-metadata . . 29 119 11.4.2. Registration of MIME Type 120 application/rs-metadata-request . . . . . . . . . . . 29 121 11.5. SDP Attributes . . . . . . . . . . . . . . . . . . . . . . 29 122 11.5.1. 'record' SDP Attribute . . . . . . . . . . . . . . . . 29 123 11.5.2. 'recordpref' SDP Attribute . . . . . . . . . . . . . . 30 124 12. Security Considerations . . . . . . . . . . . . . . . . . . . 30 125 12.1. RTP handling . . . . . . . . . . . . . . . . . . . . . . . 30 126 12.2. Authentication and Authorization . . . . . . . . . . . . . 31 127 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 31 128 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31 129 14.1. Normative References . . . . . . . . . . . . . . . . . . . 31 130 14.2. Informative References . . . . . . . . . . . . . . . . . . 32 131 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 33 133 1. Introduction 135 This document specifies the mechanism to record a Communication 136 Session (CS) by delivering real-time media and metadata from the CS 137 to a recording device. In accordance to the architecture 138 [I-D.ietf-siprec-architecture], the Session Recording Protocol 139 specifies the use of SIP, SDP, and RTP to establish a Recording 140 Session (RS) between the Session Recording Client (SRC), which is on 141 the path of the CS, and a Session Recording Server (SRS) at the 142 recording device. 144 SIP is also used to deliver metadata to the recording device, as 145 specified in [I-D.ietf-siprec-metadata]. Metadata is information 146 that describes recorded media and the CS to which they relate. 148 The Session Recording Protocol intends to satisfy the SIP-based Media 149 Recording requirements listed in [RFC6341]. 151 2. Definitions 153 This document refers to the core definitions provided in the 154 architecture document [I-D.ietf-siprec-architecture]. 156 The RTP Handling section uses the definitions provided in "RTP: A 157 Transport Protocol for Real-Time Application" [RFC3550]. 159 3. Scope 161 The scope of the Session Recording Protocol includes the 162 establishment of the recording sessions and the reporting of the 163 metadata. The scope also includes extensions supported by User 164 Agents participating in the CS such as indication of recording. The 165 user agents need not be recording-aware in order to participate in a 166 CS being recorded. 168 The following items, which are not an exhaustive list, do not 169 represent the protocol itself and are considered out of the scope of 170 the Session Recording Protocol: 172 o Delivering recorded media in real-time as the CS media 174 o Specifications of criteria to select a specific CS to be recorded 175 or triggers to record a certain CS in the future 177 o Recording policies that determine whether the CS should be 178 recorded and whether parts of the CS are to be recorded 180 o Retention policies that determine how long a recording is stored 182 o Searching and accessing the recorded media and metadata 184 o Policies governing how CS users are made aware of recording 186 o Delivering additional recording session metadata through non-SIP 187 mechanism 189 4. Overview of operations 191 This section is informative and provides a description of recording 192 operations. 194 As mentioned in the architecture document 195 [I-D.ietf-siprec-architecture], there are a number of types of call 196 flows based on the location of the Session Recording Client. The 197 following sample call flows provide a quick overview of the 198 operations between the SRC and the SRS. 200 4.1. Delivering recorded media 202 When a SIP Back-to-back User Agent (B2BUA) with SRC functionality 203 routes a call from UA(A) to UA(B), the SRC has access to the media 204 path between the user agents. When the SRC is aware that it should 205 be recording the conversation, the SRC can cause the B2BUA to bridge 206 the media between UA(A) and UA(B). The SRC then establishes the 207 Recording Session with the SRS and sends replicated media towards the 208 SRS. 210 An endpoint may also have SRC functionality, where the endpoint 211 itself establishes the Recording Session to the SRS. Since the 212 endpoint has access to the media in the Communication Session, the 213 endpoint can send replicated media towards the SRS. 215 The following is a sample call flow that shows the SRC establishing a 216 recording session towards the SRS. The call flow is essentially 217 identical when the SRC is a B2BUA or as the endpoint itself. Note 218 that the SRC can choose when to establish the Recording Session 219 independent of the Communication Session, even though the following 220 call flow suggests that the SRC is establishing the Recording Session 221 (message #5) after the Communication Session is established. 223 UA A SRC UA B SRS 224 |(1)CS INVITE | | | 225 |------------->| | | 226 | |(2)CS INVITE | | 227 | |---------------------->| | 228 | | (3) 200 OK | | 229 | |<----------------------| | 230 | (4) 200 OK | | | 231 |<-------------| | | 232 | |(5)RS INVITE with SDP | | 233 | |--------------------------------------------->| 234 | | | (6) 200 OK with SDP | 235 | |<---------------------------------------------| 236 |(7)CS RTP | | | 237 |=============>|======================>| | 238 |<=============|<======================| | 239 | |(8)RS RTP | | 240 | |=============================================>| 241 | |=============================================>| 242 |(9)CS BYE | | | 243 |------------->| | | 244 | |(10)CS BYE | | 245 | |---------------------->| | 246 | |(11)RS BYE | | 247 | |--------------------------------------------->| 248 | | | | 250 Figure 1: Basic Recording Call flow 252 The above call flow can also apply to the case of a centralized 253 conference with a mixer. For clarity, ACKs to INVITEs and 200 OKs to 254 BYEs are not shown. The conference focus can provide the SRC 255 functionality since the conference focus has access to all the media 256 from each conference participant. When a recording is requested, the 257 SRC delivers the metadata and the media streams to the SRS. Since 258 the conference focus has access to a mixer, the SRC may choose to mix 259 the media streams from all participants as a single mixed media 260 stream towards the SRS. 262 An SRC can use a single recording session to record multiple 263 communication sessions. Every time the SRC wants to record a new 264 call, the SRC updates the recording session with a new SDP offer to 265 add new recorded streams to the recording session, and 266 correspondingly also update the metadata for the new call. 268 4.2. Delivering recording metadata 270 The SRC is responsible for the delivery of metadata to the SRS. The 271 SRC may provide an initial metadata snapshot about recorded media 272 streams in the initial INVITE content in the recording session. 273 Subsequent metadata updates can be represented as a stream of events 274 in UPDATE or reINVITE requests sent by the SRC. These metadata 275 updates are normally incremental updates to the initial metadata 276 snapshot to optimize on the size of updates, however, the SRC may 277 also decide to send a new metadata snapshot anytime. 279 Metadata is transported in the body of INVITE or UPDATE messages. 280 Certain metadata, such as the attributes of the recorded media stream 281 are located in the SDP of the recording session. 283 The SRS has the ability to send a request to the SRC to request for a 284 new metadata snapshot update from the SRC. This can happen when the 285 SRS fails to understand the current stream of incremental updates for 286 whatever reason, for example, when SRS loses the current state due to 287 internal failure. The SRS may optionally attach a reason along with 288 the snapshot request. This request allows both SRC and SRS to 289 restart the states with a new metadata snapshot so that further 290 metadata incremental updates will be based on the latest metadata 291 snapshot. Similar to the metadata content, the metadata snapshot 292 request is transported as content in UPDATE or INVITE sent by the SRS 293 in the recording session. 295 SRC SRS 296 | | 297 |(1) INVITE (metadata snapshot) | 298 |---------------------------------------------------->| 299 | (2)200 OK | 300 |<----------------------------------------------------| 301 |(3) ACK | 302 |---------------------------------------------------->| 303 |(4) RTP | 304 |====================================================>| 305 |====================================================>| 306 |(5) UPDATE (metadata update 1) | 307 |---------------------------------------------------->| 308 | (6) 200 OK | 309 |<----------------------------------------------------| 310 |(7) UPDATE (metadata update 2) | 311 |---------------------------------------------------->| 312 | (8) 200 OK | 313 |<----------------------------------------------------| 314 | (9) UPDATE (metadata snapshot request) | 315 |<----------------------------------------------------| 316 | (10) 200 OK | 317 |---------------------------------------------------->| 318 | (11) INVITE (metadata snapshot 2 + SDP offer) | 319 |---------------------------------------------------->| 320 | (12) 200 OK (SDP answer) | 321 |<----------------------------------------------------| 322 | (13) UPDATE (metadata update 1 based on snapshot 2) | 323 |---------------------------------------------------->| 324 | (14) 200 OK | 325 |<----------------------------------------------------| 327 Figure 3: Delivering metadata via SIP UPDATE 329 5. Initiating a Recording Session 331 5.1. Procedures at the SRC 333 The SRC can initiate a recording session by sending a SIP INVITE 334 request to the SRS. The SRC and the SRS are identified in the From 335 and To headers, respectively. 337 The SRC MUST include the '+sip.src' feature tag in the Contact URI, 338 defined in this specification as an extension to [RFC3840], for all 339 recording sessions. An SRS uses the presence of the '+sip.src' 340 feature tag in dialog creating and modifying requests and responses 341 to confirm that the dialog being created is for the purpose of a 342 Recording Session. In addition, when an SRC sends a REGISTER request 343 to a registrar, the SRC MUST include the '+sip.src' feature tag to 344 indicate the that it is a SRC. 346 Since SIP Caller Preferences extensions are optional to implement for 347 routing proxies, there is no guarantee that a recording session will 348 be routed to an SRC or SRS. A new options tag is introduced: 349 "siprec". As per [RFC3261], only an SRC or an SRS can accept this 350 option tag in a recording session. An SRC MUST include the "siprec" 351 option tag in the Require header when initiating a Recording Session 352 so that UA's which do not support the session recording protocol 353 extensions will simply reject the INVITE request with a 420 Bad 354 Extension. 356 5.2. Procedures at the SRS 358 The SRS can initiate a recording session by sending a SIP INVITE 359 request to the SRC. The SRS and the SRC are identified in the From 360 and To headers, respectively. 362 The SRS MUST include the '+sip.srs' feature tag in the Contact URI, 363 as per [RFC3840], for all recording sessions. An SRC uses the 364 presence of this feature tag in dialog creating and modifying 365 requests and responses to confirm that the dialog being created is 366 for the purpose of a Recording Session (REQ-30). In addition, when 367 an SRS sends a REGISTER request to a registrar, the SRS MUST include 368 the '+sip.srs' feature tag to indicate that it is a SRS. 370 An SRS MUST include the "siprec" option tag in the Require header as 371 per [RFC3261] when initiating a Recording Session so that UA's which 372 do not support the session recording protocol extensions will simply 373 reject the INVITE request with a 420 Bad Extension. 375 6. SDP Handling 377 The SRC and SRS follows the SDP offer/answer model in [RFC3264]. The 378 rest of this section describes conventions used in a recording 379 session. 381 6.1. Procedures at the SRC 383 Since the SRC does not expect to receive media from the SRS, the SRC 384 typically sets each media stream of the SDP offer to only send media, 385 by qualifying them with the a=sendonly attribute, according to the 386 procedures in [RFC3264]. 388 The SRC sends recorded streams of participants to the SRS, and the 389 SRC MUST provide a label attribute (a=label), as per [RFC4574], on 390 each media stream in order to identify the recorded stream with the 391 rest of the metadata. The a=label attribute identifies each recorded 392 media stream, and the label name is mapped to the Media Stream 393 Reference in the metadata as per [I-D.ietf-siprec-metadata]. The 394 scope of the label name only applies to the same SIP message as the 395 SDP, meaning that the label name can be reused by another media 396 stream within the same recording session. Note that a recorded 397 stream is distinct from a CS stream; the metadata provides a list of 398 participants that contributes to each recorded stream. 400 The following is an example of SDP with both audio and video recorded 401 streams. Note that the following example contain unfolded lines 402 longer than 72 characters. These are captured between 403 tags. 405 v=0 406 o=SRS 2890844526 2890844526 IN IP4 198.51.100.1 407 s=- 408 c=IN IP4 198.51.100.1 409 t=0 0 410 m=audio 12240 RTP/AVP 0 4 8 411 a=sendonly 412 a=label:1 413 m=video 22456 RTP/AVP 98 414 a=rtpmap:98 H264/90000 415 416 a=fmtp:98 profile-level-id=42A01E; 417 sprop-parameter-sets=Z0IACpZTBYmI,aMljiA== 418 419 a=sendonly 420 a=label:2 421 m=audio 12242 RTP/AVP 0 4 8 422 a=sendonly 423 a=label:3 424 m=audio 22458 RTP/AVP 98 425 a=rtpmap:98 H264/90000 426 427 a=fmtp:98 profile-level-id=42A01E; 428 sprop-parameter-sets=Z0IACpZTBYmI,aMljiA== 429 430 a=sendonly 431 a=label:4 433 Figure 4: Sample SDP with audio and video streams 435 6.1.1. Handling media stream updates 437 Over the lifetime of a recording session, the SRC can add and remove 438 recorded streams from the recording session for various reasons. For 439 example, when a CS stream is added or removed from the CS, or when a 440 CS is created or terminated if a recording session handles multiple 441 CSes. To remove a recorded stream from the recording session, the 442 SRC sends a new SDP offer where the port of the media stream to be 443 removed is set to zero, according to the procedures in [RFC3264]. To 444 add a recorded stream to the recording session, the SRC sends a new 445 SDP offer by adding a new media stream description or by reusing an 446 old media stream which had been previously disabled, according to the 447 procedures in [RFC3264]. 449 The SRC can temporarily discontinue streaming and collection of 450 recorded media from the SRC to the SRS for reason such as masking the 451 recording. In this case, the SRC sends a new SDP offer and sets the 452 media stream to inactive (a=inactive) for each recorded stream to be 453 paused, as per the procedures in [RFC3264]. To resume streaming and 454 collection of recorded media, the SRC sends a new SDP offer and sets 455 the media streams with a=sendonly attribute. Note that when a CS 456 stream is muted/unmuted, this information is conveyed in the metadata 457 by the SRC. The SRC SHOULD not modify the media stream with 458 a=inactive for mute since this operation is reserved for pausing the 459 RS media. 461 6.2. Procedures at the SRS 463 The SRS only receives RTP streams from the SRC, the SDP answer 464 normally sets each media stream to receive media, by setting them 465 with the a=recvonly attribute, according to the procedures of 466 [RFC3264]. When the SRS is not ready to receive a recorded stream, 467 the SRS sets the media stream as inactive in the SDP offer or answer 468 by setting it with a=inactive attribute, according to the procedures 469 of [RFC3264]. When the SRS is ready to receive recorded streams, the 470 SRS sends a new SDP offer and sets the media streams with a=recvonly 471 attribute. 473 Over the lifetime of a recording session, the SRS can remove recorded 474 streams from the recording session for various reasons. To remove a 475 recorded stream from the recording session, the SRS sends a new SDP 476 offer where the port of the media stream to be removed is set to 477 zero, according to the procedures in [RFC3264]. 479 The following sequence diagram shows an example where the SRS is 480 initially not ready to receive recorded streams, and later updates 481 the recording session when the SRS is ready to record. 483 SRC SRS 484 | | 485 |(1) INVITE (SDP offer) | 486 |---------------------------------------------------->| 487 | [not ready to record] 488 | (2)200 OK with SDP inactive | 489 |<----------------------------------------------------| 490 |(3) ACK | 491 |---------------------------------------------------->| 492 | ... | 493 | [ready to record] 494 | (4) re-INVITE with SDP recvonly | 495 |<----------------------------------------------------| 496 |(5)200 OK with SDP sendonly | 497 |---------------------------------------------------->| 498 | (6) ACK | 499 |<----------------------------------------------------| 500 |(7) RTP | 501 |====================================================>| 502 | ... | 503 |(8) BYE | 504 |---------------------------------------------------->| 505 | (9) OK | 506 |<----------------------------------------------------| 508 Figure 5: SRS responding to offer with a=inactive 510 7. RTP Handling 512 This section provides recommendations and guidelines for RTP and RTCP 513 in the context of SIPREC. In order to communicate most effectively, 514 the Session Recording Client (SRC) and the Session Recording Server 515 (SRS) SHOULD utilize the mechanisms provided by RTP in a well defined 516 and predicable manner. It is the goal of this document to make the 517 reader aware of these mechanisms and provide recommendations and 518 guidelines. 520 7.1. Roles 522 An SRC has the task of gathering media from the various UAs in a 523 Communication Session (CS) and forwarding the information to the SRS 524 within the context of a Recording Session (RS). There are numerous 525 ways in which an SRC may do this is, including appearing as one of 526 the UAs within a CS, or as a B2BUA between UAs within a CS. 528 SRS 529 ^ 530 | 531 RS 532 | 533 v 534 UA <-- CS --> SRC 536 Figure 1: UA as SRC 538 SRS 539 ^ 540 | 541 RS 542 | 543 v 544 UA1 <-- CS --> SRC <-- CS --> UA2 546 Figure 2: B2BUA as SRC 548 The following subsections define a set of roles an SRC may choose to 549 play based on its position with respect to a UA within a CS, and an 550 SRS within an RS. 552 7.1.1. SRC acting as an RTP Translator 554 The SRC may act as a translator, as defined in [RFC3550]. A defining 555 characteristic of a translator is that it forwards RTP packets with 556 their SSRC identifier intact. There are two types of translators, 557 one that simply forwards, and another that performs transcoding 558 (e.g., from one codec to another) in addition to forwarding. 560 7.1.1.1. Forwarding Translator 562 When acting as a forwarding translator, RTP received as separate 563 streams from different sources (e.g., from different UAs with 564 different SSRCs) cannot be mixed by the SRC and MUST be sent 565 separately to the SRS. All RTCP reports MUST be passed by the SRC 566 between the UAs and the SRS, such that the UAs and SRS are able to 567 detect any SSRC collisions. 569 RTCP Sender Reports generated by a UA sending a stream MUST be 570 forwarded to the SRS. RTCP Receiver Reports generated by the SRS 571 MUST be forwarded to the relevant UA. 573 UAs may receive multiple sets of RTCP Receiver Reports, one or more 574 from other UAs participating in the CS, and one from the SRS 575 participating in the RS. A SIPREC aware UA SHOULD be prepared to 576 process the RTCP Receiver Reports from the SRS, whereas a SIPREC 577 unaware UA may discard such RTCP packets as not of relevance. 579 If SRTP is used on both the CS and the RS, decryption and/or re- 580 encryption may occur. For example, if different keys are used, it 581 will occur. If the same keys are used, it need not occur. 583 If packet loss occurs, either from the UA to the SRC or from the SRC 584 to the SRS, the SRS SHOULD detect and attempt to recover from the 585 loss. The SRC does not play a role in this other than forwarding the 586 associated RTP and RTCP packets. 588 7.1.1.2. Transcoding Translator 590 When acting as a transcoding translator, an SRC MAY perform 591 transcoding (e.g., from one codec to another), and this may result in 592 a different rate of packets between what the SRC receives and what 593 the sends. As when acting as a forwarding translator, RTP received 594 as separate streams from different sources (e.g., from different UAs 595 with different SSRCs) cannot be mixed by the SRC and MUST be sent 596 separately to the SRS. All RTCP reports MUST passed by the SRC 597 between the UAs and the SRS, such the UAs and SRS they are able to 598 detect any SSRC collisions. 600 RTCP Sender Reports generated by a UA sending a stream MUST be 601 forwarded to the SRS. RTCP Receiver Reports generated by the SRS 602 MUST be forwarded to the relevant UA. The SRC may need to manipulate 603 the RTCP Receiver Reports to take account of any transcoding that has 604 taken place. 606 UAs may receive multiple sets of RTCP Receiver Reports, one or more 607 from other UAs participating in the CS, and one from the SRS 608 participating in the RS. A SIPREC aware UA SHOULD be prepared to 609 process the RTCP Receiver Reports from the SRS, whereas a SIPREC 610 unaware UA may discard such RTCP packets as not of relevance. 612 If SRTP is used on both the CS and the RS, decryption and/or re- 613 encryption may occur. For example, if different keys are used, it 614 will occur. If the same keys are used, it need not occur. 616 If packet loss occurs, either from the UA to the SRC or from the SRC 617 to the SRS, the SRS SHOULD detect and attempt to recover from the 618 loss. The SRC does not play a role in this other than forwarding the 619 associated RTP and RTCP packets. 621 7.1.2. SRC acting as an RTP Mixer 623 In the case of the SRC acting as a RTP mixer, as defined in 624 [RFC3550], the SRC combines RTP streams from different UA and sends 625 them towards the SRS using its own SSRC. The SSRCs from the 626 contributing UA SHOULD be conveyed as CSRCs identifiers within this 627 stream. The SRC may make timing adjustments among the received 628 streams and generate its own timing on the stream sent to the SRS. 629 Optionally an SRC acting as a mixer can perform transcoding, and can 630 even cope with different codings received from different UAs. RTCP 631 Sender Reports and Receiver Reports are not forwarded by an SRC 632 acting as mixer, but there are requirements for forwarding RTCP 633 Source Description (SDES) packets. The SRC generates its own RTCP 634 Sender and Receiver reports toward the associated UAs and SRS. The 635 use of SRTP between the SRC and the SRS for the RS is independent of 636 the use of SRTP between the UAs and SRC for the CS. 638 If packet loss occurs from the UA to the SRC, the SRC SHOULD detect 639 and attempt to recover from the loss. If packet loss occurs from the 640 SRC to the SRS, the SRS SHOULD detect and attempt to recover from the 641 loss. 643 7.1.3. SRC acting as an RTP Endpoint 645 The case of the SRC acting as an RTP endpoint, as defined in 646 [RFC3550], is similar to the mixer case, except that the RTP session 647 between the SRC and the SRS is considered completely independent from 648 the RTP session that is part of the CS. The SRC can, but need not, 649 mix RTP streams from different participants prior to sending to the 650 SRS. RTCP between the SRC and the SRS is completely independent of 651 RTCP on the CS. The use of SRTP between the SRC and the SRS is 652 independent of the use of SRTP on the CS. 654 If packet loss occurs from the UA to the SRC, the SRC SHOULD detect 655 and attempt to recover from the loss. If packet loss occurs from the 656 SRC to the SRS, the SRS SHOULD detect and attempt to recover from the 657 loss. 659 7.2. RTCP 661 The RTP data transport is augmented by a control protocol (RTCP) to 662 allow monitoring of the data delivery. RTCP, as defined in 663 [RFC3550], is based on the periodic transmission of control packets 664 to all participants in the RTP session, using the same distribution 665 mechanism as the data packets. Support for RTCP is REQUIRED, per 666 [RFC3550], and it provides, among other things, the following 667 important functionality in relation to SIPREC: 669 1) Feedback on the quality of the data distribution 671 This feedback from the receivers may be used to diagnose faults in 672 the distribution. As such, RTCP is a well defined and efficient 673 mechanism for the SRS to inform the SRC of issues that arise with 674 respect to its reception of media that is to be recorded. 676 2) Carries a persistent transport-level identifier for an RTP source 677 called the canonical name or CNAME 679 The SSRC identifier may change if a conflict is discovered or a 680 program is restarted; in which case receivers can use the CNAME to 681 keep track of each participant. Receivers may also use the CNAME to 682 associate multiple data streams from a given participant in a set of 683 related RTP sessions, for example to synchronize audio and video. 684 Synchronization of media streams is also facilitated by the NTP and 685 RTP timestamps included in RTCP packets by data senders. 687 7.3. RTP Profile 689 The RECOMMENDED RTP profiles for both the SRC and SRS are "Extended 690 Secure RTP Profile for Real-time Transport Control Protocol (RTCP)- 691 Based Feedback (RTP/SAVPF)", [RFC5124] when using encrypted RTP 692 streams, and "Extended RTP Profile for Real-time Transport Control 693 Protocol (RTCP)-Based Feedback (RTP/AVPF)", [RFC4585] when using non 694 encrypted media streams. However, as this is not a requirement, some 695 implementations may use "The Secure Real-time Transport Protocol 696 (SRTP)", [RFC3711] and "RTP Profile for Audio and Video Conferences 697 with Minimal Control", AVP [RFC3551]. Therefore, it is RECOMMENDED 698 that the SRC and SRS not rely entirely on SAVPF or AVPF for core 699 functionality that may be at least partially achievable using SAVP 700 and AVP. 702 AVPF and SAVPF provide an improved RTCP timer model that allows more 703 flexible transmission of RTCP packets as response to events, rather 704 than strictly according to bandwidth. AVPF based codec control 705 messages provide efficient mechanisms for an SRC and SRS to handle 706 events such as scene changes, error recovery, and dynamic bandwidth 707 adjustments. These messages are discussed in more detail later in 708 this document. 710 SAVP and SAVPF provide media encryption, integrity protection, replay 711 protection, and a limited form of source authentication. They do not 712 contain or require a specific keying mechanism. 714 7.4. SSRC 716 The synchronization source (SSRC), as defined in [RFC3550], is 717 carried in the RTP header and in various fields of RTCP packets. It 718 is a random 32-bit number that is required to be globally unique 719 within an RTP session. It is crucial that the number be chosen with 720 care in order that participants on the same network or starting at 721 the same time are not likely to choose the same number. Guidelines 722 regarding SSRC value selection and conflict resolution are provided 723 in [RFC3550]. 725 The SSRC may also be used to separate different sources of media 726 within a single RTP session. For this reason as well as for conflict 727 resolution, it is important that the SRC and SRS handle changes in 728 SSRC values and properly identify the reason of the change. The 729 CNAME values carried in RTCP facilitate this identification. 731 7.5. CSRC 733 The contributing source (CSRC), as defined in [RFC3550], identifies 734 the source of a stream of RTP packets that has contributed to the 735 combined stream produced by an RTP mixer. The mixer inserts a list 736 of the SSRC identifiers of the sources that contributed to the 737 generation of a particular packet into the RTP header of that packet. 738 This list is called the CSRC list. It is RECOMMENDED that a SRC, 739 when acting a mixer, sets the CSRC list accordingly, and that the SRS 740 interprets the CSRC list appropriately when received. 742 7.6. SDES 744 The Source Description (SDES), as defined in [RFC3550], contains an 745 SSRC/CSRC identifier followed by a list of zero or more items, which 746 carry information about the SSRC/CSRC. End systems send one SDES 747 packet containing their own source identifier (the same as the SSRC 748 in the fixed RTP header). A mixer sends one SDES packet containing a 749 chunk for each contributing source from which it is receiving SDES 750 information, or multiple complete SDES packets if there are more than 751 31 such sources. 753 7.6.1. CNAME 755 The Canonical End-Point Identifier (CNAME), as defined in [RFC3550], 756 provides the binding from the SSRC identifier to an identifier for 757 the source (sender or receiver) that remains constant. It is 758 important the an SRC and SRS generate CNAMEs appropriately and use 759 them for this purpose. Guidelines for generating CNAME values are 760 provided in "Guidelines for Choosing RTP Control Protocol (RTCP) 761 Canonical Names (CNAMEs)" [RFC6222]. 763 7.7. Keepalive 765 It is anticipated that media streams in SIPREC may exist in inactive 766 states for extended periods of times for an of a number of valid 767 reasons. In order for the bindings and any pinholes in NATs/ 768 firewalls to remain active during such intervals, it is RECOMMENDED 769 to follow the keep-alive procedure recommended in "Application 770 Mechanism for Keeping Alive the NAT Mappings Associated to RTP/RTP 771 Control Protocol (RTCP) Flows" [RFC6263] for all RTP media streams. 773 7.8. RTCP Feedback Messages 775 "Codec Control Messages in the RTP Audio-Visual Profile with Feedback 776 (AVPF)" [RFC5104] specifies extensions to the messages defined in 777 AVPF [RFC4585]. Support for and proper usage of these messages is 778 important to SRC and SRS implementations. Note that these messages 779 are applicable only when using the AVFP or SAVPF RTP profiles. 781 7.8.1. Full Intra Request 783 A Full Intra Request (FIR) Command, when received by the designate 784 media sender, requires that the media sender sends a Decoder Refresh 785 Point at the earliest opportunity. Using a decoder refresh point 786 implies refraining from using any picture sent prior to that point as 787 a reference for the encoding process of any subsequent picture sent 788 in the stream. 790 Decoder refresh points, especially Intra or IDR pictures for H.264 791 video codecs, are in general several times larger in size than 792 predicted pictures. Thus, in scenarios in which the available bit 793 rate is small, the use of a decoder refresh point implies a delay 794 that is significantly longer than the typical picture duration. 796 7.8.1.1. SIP INFO for FIR 798 "XML Schema for Media Control" [RFC5168] defines an Extensible Markup 799 Language (XML) Schema for video fast update. Implementations are 800 discouraged from using the method described except for backward 801 compatibility purposes. Implementations SHOULD use FIR messages 802 instead. 804 7.8.2. Picture Loss Indicator 806 Picture Loss Indication (PLI), as defined in [RFC4585], informs the 807 encoder of the loss of an undefined amount of coded video data 808 belonging to one or more pictures. Using the FIR command to recover 809 from errors is explicitly disallowed, and instead the PLI message 810 SHOULD be used. FIR SHOULD be used only in situations where not 811 sending a decoder refresh point would render the video usable for the 812 users. Examples where sending FIR is appropriate include a 813 multipoint conference when a new user joins the conference and no 814 regular decoder refresh point interval is established, and a video 815 switching MCU that changes streams. 817 7.8.3. Temporary Maximum Media Stream Bit Rate Request 819 A receiver, translator, or mixer uses the Temporary Maximum Media 820 Stream Bit Rate Request (TMMBR) to request a sender to limit the 821 maximum bit rate for a media stream to the provided value. 822 Appropriate use of TMMBR facilitates rapid adaptation to changes in 823 available bandwidth. 825 7.8.3.1. Renegotiation of SDP bandwidth attribute 827 If it is likely that the new value indicated by TMMBR will be valid 828 for the remainder of the session, the TMMBR sender is expected to 829 perform a renegotiation of the session upper limit using the session 830 signaling protocol. Therefore for SIPREC, implementations are 831 RECOMMENDED to use TMMBR for temporary changes, and renegotiation of 832 bandwidth via SDP offer/answer of more permanent changes. 834 7.9. Symmetric RTP/RTCP for Sending and Receiving 836 Within an SDP offer/answer exchange, RTP entities choose the RTP and 837 RTCP transport addresses (i.e., IP addresses and port numbers) on 838 which to receive packets. When sending packets, the RTP entities may 839 use the same source port or a different source port as those signaled 840 for receiving packets. When the transport address used to send and 841 receive RTP is the same, it is termed "symmetric RTP" [RFC4961]. 842 Likewise, when the transport address used to send and receive RTCP is 843 the same, it is termed "symmetric RTCP" [RFC4961]. 845 When sending RTP, it is REQUIRED to use symmetric RTP. When sending 846 RTCP, it is REQUIRED to use symmetric RTCP. Although an SRS will not 847 normally send RTP, it will send RTCP as well as receive RTP and RTCP. 848 Likewise, although an SRC will not normally receive RTP from the SRS, 849 it will receive RTCP as well as send RTP and RTCP. 851 Note: Symmetric RTP and symmetric RTCP are different from RTP/RTCP 852 multiplexing [RFC5761]. 854 8. Metadata 855 8.1. Procedures at the SRC 857 The SRC is responsible to deliver metadata to the SRS in a recording 858 session. Metadata can be provided by the SRC in the initial INVITE 859 request when establishing the recording session, and subsequent 860 metadata updates can be provided by the SRC in reINVITE and UPDATE 861 requests and responses in the recording session. 863 Certain metadata attributes are contained in the SDP, and others are 864 contained in a new content type "application/rs-metadata". The 865 format of the metadata is described as part of the mechanism in 866 [I-D.ietf-siprec-metadata]. A new "disposition-type" of Content- 867 Disposition is defined for the purpose of carrying metadata and the 868 value is "recording-session". The "recording-session" value 869 indicates that the "application/rs-metadata" content contains 870 metadata to be handled by the SRS, and the disposition can be carried 871 in either INVITE or UPDATE requests or responses sent by the SRC. 873 Metadata sent by the SRC can be categorized as either a full metadata 874 snapshot or partial update. A full metadata snapshot describes all 875 the recorded streams and all metadata associated with the recording 876 session. When the SRC sends a full metadata snapshot, the SRC MUST 877 send an INVITE or an UPDATE request with an SDP offer and the 878 "recording-session" disposition. A partial update represents an 879 incremental update since the last metadata update sent by the SRC. A 880 partial update sent by the SRC can be an INVITE request or response 881 with an SDP offer, or an INVITE/UPDATE request or response containing 882 a "recording-session" disposition, or an INVITE request containing 883 both an SDP offer and the "recording-session" disposition. 885 The following is an example of a full metadata snapshot sent by the 886 SRC in the initial INVITE request: 888 INVITE sip:recorder@example.com SIP/2.0 889 Via: SIP/2.0/TCP src.example.com;branch=z9hG4bKdf6b622b648d9 890 From: ;tag=35e195d2-947d-4585-946f-098392474 891 To: 892 Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a 893 CSeq: 101 INVITE 894 Max-Forwards: 70 895 Require: siprec 896 Accept: application/sdp, application/rs-metadata, 897 application/rs-metadata-request 898 Contact: ;+sip.src 899 Content-Type: multipart/mixed;boundary=foobar 900 Content-Length: [length] 902 --foobar 903 Content-Type: application/sdp 905 v=0 906 o=SRS 2890844526 2890844526 IN IP4 198.51.100.1 907 s=- 908 c=IN IP4 198.51.100.1 909 t=0 0 910 m=audio 12240 RTP/AVP 0 4 8 911 a=sendonly 912 a=label:1 914 --foobar 915 Content-Type: application/rs-metadata 916 Content-Disposition: recording-session 918 [metadata content] 920 Figure 6: Sample INVITE request for the recording session 922 8.2. Procedures at the SRS 924 The SRS receives metadata updates from the SRC in INVITE and UPDATE 925 requests. Since the SRC can send partial updates based on the 926 previous update, the SRS needs to keep track of the sequence of 927 updates from the SRC. 929 In the case of an internal failure at the SRS, the SRS may fail to 930 recognize a partial update from the SRC. The SRS may be able to 931 recover from the internal failure by requesting for a full metadata 932 snapshot from the SRC. Certain errors, such syntax errors or 933 semantic errors in the metadata information, are likely caused by an 934 error on the SRC side, and it is likely the same error will occur 935 again even when a full metadata snapshot is requested. In order to 936 avoid repeating the same error, the SRS can simply terminate the 937 recording session when a syntax error or semantic error is detected 938 in the metadata. 940 When the SRS explicitly requests for a full metadata snapshot, the 941 SRS MUST send an UPDATE request without an SDP offer. A metadata 942 snapshot request contains a content with the content disposition type 943 "recording-session". Note that the SRS MAY generate an INVITE 944 request without an SDP offer but this MUST not include a metadata 945 snapshot request. The format of the content is "application/ 946 rs-metadata-request", and the body format is chosen to be a simple 947 text-based format. The following shows an example: 949 UPDATE sip:2000@src.exmaple.com SIP/2.0 950 Via: SIP/2.0/UDP srs.example.com;branch=z9hG4bKdf6b622b648d9 951 To: ;tag=35e195d2-947d-4585-946f-098392474 952 From: ;tag=1234567890 953 Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a 954 CSeq: 1 UPDATE 955 Max-Forwards: 70 956 Require: siprec 957 Contact: ;+sip.srs 958 Accept: appliation/sdp, application/rs-metadata 959 Content-Disposition: recording-session 960 Content-Type: application/rs-metadata-request 961 Content-Length: [length] 963 SRS internal error 965 Figure 7: Metadata Request 967 The SRS MAY include the reason why a metadata snapshot request is 968 being made to the SRC in the reason line. This reason line is free 969 form text, mainly designed for logging purposes on the SRC side. The 970 processing of the content by the SRC is entirely optional since the 971 content is for logging only, and the snapshot request itself is 972 indicated by the use of the application/rs-metadata-request content 973 type. 975 When the SRC receives the request for a metadata snapshot, the SRC 976 MUST provide a full metadata snapshot in a separate INVITE or UPDATE 977 transaction, along with an SDP offer. All subsequent metadata 978 updates sent by the SRC MUST be based on the new metadata snapshot. 980 8.2.1. Formal Syntax 982 The formal syntax for the application/rs-metadata-request MIME is 983 described below using the augmented Backus-Naur Form (BNF) as 984 described in [RFC2234]. 986 snapshot-request = srs-reason-line CRLF 988 srs-reason-line = [TEXT-UTF8-TRIM] 990 9. Persistent Recording 992 Persistent recording is a specific use case outlined in REQ-005 or 993 Use Case 4 in [RFC6341], where a recording session can be established 994 in the absence of a communication session. The SRC continuously 995 records media in a recording session to the SRS even in the absence 996 of a CS for all user agents that are part of persistent recording. 997 By allocating recorded streams and continuously sending recorded 998 media to the SRS, the SRC does not have to prepare new recorded 999 streams with new SDP offer when a new communication session is 1000 created and also does not impact the timing of the CS. The SRC only 1001 needs to update the metadata when new communication sessions are 1002 created. 1004 When there is no communication sessions running on the devices with 1005 persistent recording, there is no recorded media to stream from the 1006 SRC to the SRS. In certain environments where Network Address 1007 Translator (NAT) is used, typically a minimum of flow activity is 1008 required to maintain the NAT binding for each port opened. Agents 1009 that support Interactive Connectivity Establishment (ICE) solves this 1010 problem. For non-ICE agents, in order not to lose the NAT bindings 1011 for the RTP/RTCP ports opened for the recorded streams, the SRC and 1012 SRS SHOULD follow the recommendations provided in [RFC6263] to 1013 maintain the NAT bindings. 1015 10. Extensions for Recording-aware User Agents 1017 The following sections describe the SIP and SDP extensions for 1018 recording-aware user agents. A recording-aware user agent is a 1019 participant in the CS that supports the SIP and SDP extensions for 1020 receiving recording indication and for requesting recording 1021 preferences for the call. 1023 10.1. Procedures at the record-aware user agent 1025 A recording-aware UA SHOULD indicate that it can accept reporting of 1026 recording indication provided by the SRC. A new option tag "record- 1027 aware" is introduced to indicate such awareness. The recording-aware 1028 UA SHOULD include the "record-aware" option tag in the Supported 1029 header when initiating or establishing a CS. A recording-aware UA 1030 that has indicated recording awareness MUST provide at recording 1031 indication to the end user through an appropriate user interface an 1032 indication whether recording is on or off for a given medium based on 1033 the most recently received a=record SDP attribute for that medium. 1035 Some user agents that are automatons (eg. IVR, media server, PSTN 1036 gateway) may not have a user interface to render recording 1037 indication. When such user agent indicates recording awareness, the 1038 UA SHOULD render recording indication through other means, such as 1039 passing an inband tone on the PSTN gateway, putting the recording 1040 indication in a log file, or raising an application event in a 1041 VoiceXML dialog. These user agents MAY also choose not to indicate 1042 recording awareness, thereby relying on whatever mechanism an SRC 1043 chooses to indicate recording, such as playing a tone inband. 1045 10.1.1. Recording preference 1047 A recording-aware UA involved in a CS MAY request the CS to be 1048 recorded or not recorded. This indication of recording preference 1049 can be sent at session establishment time or during the session. 1051 A new SDP attribute "recordpref" is introduced. The SDP attribute 1052 appears at the media level or session level and can appear in an SDP 1053 offer or answer. The recording indication applies to the specified 1054 media stream only. The following is the ABNF of the recordpref 1055 attribute: 1057 recordpref-attr = "a=recordpref:" pref 1059 pref = "on" / "off" / "pause" / "nopreference" 1061 on Request for recording if it has not already been started. If the 1062 recording is currently paused, request to resume recording. 1064 off Request for no recording. If recording has already been 1065 started, then this preference indicates a request to stop 1066 recording. 1068 pause Request to pause recording if recording is currently in 1069 progress. 1071 nopreference To indicate that the UA has no preference on recording. 1072 While the absence of this attribute indirectly implies the lack of 1073 preference, using this value allows the UA to explicitly state no 1074 preference to being recorded. 1076 10.2. Procedures at the SRC 1078 When a UA has indicated that it is recording-aware through the 1079 "record-aware" option tag, the SRC MUST provide recording indications 1080 in a new SDP attribute described in the following section. In the 1081 absence of the "record-aware" option tag, meaning that the UA is not 1082 recording-aware, an SRC MUST provide recording indications, where SRC 1083 is required to do so based on policies, through other means such as 1084 playing a tone inband. 1086 10.2.1. Recording indication 1088 While there are existing mechanisms for providing an indication that 1089 a CS is being recorded, these mechanisms are usually delivered on the 1090 CS media streams such as playing an in-band tone or an announcement 1091 to the participants. A new SDP attribute is introduced to allow a 1092 recording-aware UA to render recording indication at the user 1093 interface. 1095 The 'record' SDP attribute appears at the media level or session 1096 level in either SDP offer or answer. The recording indication 1097 applies to the specified media stream only, for example, only the 1098 audio portion of the call is recorded in an audio/video call. The 1099 following is the ABNF of the 'record' attribute: 1101 attribute /= record-attr 1103 ; attribute defined in RFC 4566 1105 record-attr = "record:" indication 1107 indication = "on" / "off" / "paused" 1109 on Recording is in progress. 1111 off No recording is in progress. 1113 paused Recording is in progress by media is paused. 1115 The recording attribute is a declaration by the SRC in the CS to 1116 indicate whether recording is taking place. For example, if a UA (A) 1117 is initiating a call to UA (B) and UA (A) is also an SRC that is 1118 performing the recording, then UA (A) provides the recording 1119 indication in the SDP offer with a=record:on. When UA (B) receives 1120 the SDP offer, UA (B) will see that recording is happening on the 1121 other endpoint of this session. If UA (B) does not wish to perform 1122 recording itself, UA (B) provides the recording indication as 1123 a=record:off in the SDP answer. 1125 Whenever the recording indication needs to change, such as 1126 termination of recording, then the UA MUST initiate a reINVITE or 1127 UPDATE to update the SDP attribute to a=record:off. The following 1128 call flow shows an example of the offer/answer with the recording 1129 indication attribute. 1131 UA A UA B 1132 (SRC) | 1133 | | 1134 | [SRC recording starts] | 1135 |(1) INVITE (SDP offer + a=record:on) | 1136 |---------------------------------------------------->| 1137 | 200 OK (SDP answer) | 1138 |<----------------------------------------------------| 1139 |(3) ACK | 1140 |---------------------------------------------------->| 1141 |(4) RTP | 1142 |<===================================================>| 1143 | [SRC stops recording] | 1144 |(5) re-INVITE (SDP + a=record:off) | 1145 |---------------------------------------------------->| 1146 | (6) 200 OK (SDP + a=record:off)| 1147 |<----------------------------------------------------| 1148 | (6) ACK | 1149 |---------------------------------------------------->| 1151 Figure 8: Recording indication example 1153 If a call is traversed through one or more SIP B2BUA, and it happens 1154 that there are more than one SRC in the call path, the recording 1155 indication attribute does not provide any hint as to which SRC is 1156 performing the recording, meaning the endpoint only knows that the 1157 call is being recorded. This attribute is also not used as an 1158 indication to negotiate which SRC in the call path will perform 1159 recording and is not used as a request to start/stop recording if 1160 there are multiple SRCs in the call path. 1162 10.2.2. Recording preference 1164 When the SRC receives the a=recordpref SDP in an SDP offer or answer, 1165 the SRC chooses to honor such request to record the request based on 1166 local policy on the SRC. When the SRC honors the request, the SRC 1167 MUST also update the recording indication to reflect the current 1168 state of the recording (on/off/paused). 1170 11. IANA Considerations 1172 11.1. Registration of Option Tags 1174 This specification registers two option tags. The required 1175 information for this registration, as specified in [RFC3261], is as 1176 follows. 1178 11.1.1. siprec Option Tag 1180 Name: siprec 1182 Description: This option tag is for identifying the SIP session 1183 for the purpose of recording session only. This is typically not 1184 used in a Supported header. When present in a Require header in a 1185 request, it indicates that the UAS MUST be either a SRC or SRS 1186 capable of handling the contexts of a recording session. 1188 11.1.2. record-aware Option Tag 1190 Name: record-aware 1192 Description: This option tag is to indicate the ability for the 1193 user agent to receive recording indicators in media level or 1194 session level SDP. When present in a Supported header, it 1195 indicates that the UA can receive recording indicators in media 1196 level or session level SDP. 1198 11.2. Registration of media feature tags 1200 This document registers two new media feature tags in the SIP tree 1201 per the process defined in [RFC2506] and [RFC3840] 1203 11.2.1. src feature tag 1205 Media feature tag name: sip.src 1207 ASN.1 Identifier: 25 1209 Summary of the media feature indicated by this tag: This feature 1210 tag indicates that the user agent is a Session Recording Client 1211 for the purpose for Recording Session. 1213 Values appropriate for use with this feature tag: boolean 1215 The feature tag is intended primarily for use in the following 1216 applications, protocols, services, or negotiation mechanisms: This 1217 feature tag is only useful for a Recording Session. 1219 Examples of typical use: Routing the request to a Session 1220 Recording Server. 1222 Security Considerations: Security considerations for this media 1223 feature tag are discussed in Section 11.1 of RFC 3840. 1225 11.2.2. srs feature tag 1227 Media feature tag name: sip.srs 1229 ASN.1 Identifier: 26 1231 Summary of the media feature indicated by this tag: This feature 1232 tag indicates that the user agent is a Session Recording Server 1233 for the purpose for Recording Session. 1235 Values appropriate for use with this feature tag: boolean 1237 The feature tag is intended primarily for use in the following 1238 applications, protocols, services, or negotiation mechanisms: This 1239 feature tag is only useful for a Recording Session. 1241 Examples of typical use: Routing the request to a Session 1242 Recording Client. 1244 Security Considerations: Security considerations for this media 1245 feature tag are discussed in Section 11.1 of RFC 3840. 1247 11.3. New Content-Disposition Parameter Registrations 1249 This document registers a new "disposition-type" value in Content- 1250 Disposition header: recording-session. 1252 recording-session the body describes the metadata information about 1253 the recording session 1255 11.4. Media Type Registration 1257 11.4.1. Registration of MIME Type application/rs-metadata 1259 This document registers the application/rs-metadata MIME media type 1260 in order to describe the recording session metadata. This media type 1261 is defined by the following information: 1263 Media type name: application 1265 Media subtype name: rs-metadata 1267 Required parameters: none 1269 Options parameters: none 1271 11.4.2. Registration of MIME Type application/rs-metadata-request 1273 This document registers the application/rs-metadata-request MIME 1274 media type in order to describe a recording session metadata snapshot 1275 request. This media type is defined by the following information: 1277 Media type name: application 1279 Media subtype name: rs-metadata-request 1281 Required parameters: none 1283 Options parameters: none 1285 11.5. SDP Attributes 1287 This document registers the following new SDP attributes. 1289 11.5.1. 'record' SDP Attribute 1291 Contact names: Leon Portman leon.portman@nice.com, Henry Lum 1292 henry.lum@genesyslab.com 1294 Attribute name: record 1295 Long form attribute name: Recording Indication 1297 Type of attribute: session or media level 1299 Subject to charset: no 1301 This attribute provides the recording indication for the session or 1302 media stream. 1304 Allowed attribute values: on, off, paused 1306 11.5.2. 'recordpref' SDP Attribute 1308 Contact names: Leon Portman leon.portman@nice.com, Henry Lum 1309 henry.lum@genesyslab.com 1311 Attribute name: recordpref 1313 Long form attribute name: Recording Preference 1315 Type of attribute: session or media level 1317 Subject to charset: no 1319 This attribute provides the recording indication for the session or 1320 media stream. 1322 Allowed attribute values: on, off, pause, nopreference 1324 12. Security Considerations 1326 The recording session is fundamentally a standard SIP dialog 1327 [RFC3261], therefore, the recording session can reuse any of the 1328 existing SIP security mechanism available for securing the recorded 1329 media as well as metadata. Other security considerations are 1330 outlined in the use cases and requirements document [RFC6341]. 1332 12.1. RTP handling 1334 In many scenarios it will be critical that the media transported 1335 between the SRC and SRS to be protected. Media encryption is an 1336 important element in the overall SIPREC solution, therefore, it is 1337 RECOMMENDED that SRC and SRS support RTP/SAVP [RFC3711] and RTP/SAVPF 1338 [RFC5124]. RTP/SAVP and RTP/SAVPF provide media encryption, 1339 integrity protection, replay protection, and a limited form of source 1340 authentication. They do not contain or require a specific keying 1341 mechanism. 1343 12.2. Authentication and Authorization 1345 The recording session reuses the SIP mechanism to challenge requests 1346 that is based on HTTP authentication. The mechanism relies on 401 1347 and 407 SIP responses as well as other SIP header fields for carrying 1348 challenges and credentials. 1350 The SRS may have its own set of recording policies to authorize 1351 recording requests from the SRC. The use of recording policies is 1352 outside the scope of the Session Recording Protocol. 1354 13. Acknowledgements 1356 We want to thank John Elwell, Paul Kyzivat, Partharsarathi R, Ram 1357 Mohan R, Charles Eckel, Hadriel Kaplan, Adam Roach, Miguel Garcia for 1358 their valuable comments and inputs to this document. 1360 We also want to thank Andrew Hutton, Ram Mohan, Muthu Perumal, John 1361 Elwell, Dan Wing, Hadriel Kaplan, Paul Kyzivat, and Magnus Westerlund 1362 for their valuable contributions to the RTP Handling portion. 1364 14. References 1366 14.1. Normative References 1368 [I-D.ietf-siprec-metadata] 1369 R, R., Ravindran, P., and P. Kyzivat, "Session Initiation 1370 Protocol (SIP) Recording Metadata", 1371 draft-ietf-siprec-metadata-06 (work in progress), 1372 March 2012. 1374 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1375 Requirement Levels", BCP 14, RFC 2119, March 1997. 1377 [RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 1378 Specifications: ABNF", RFC 2234, November 1997. 1380 [RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag 1381 Registration Procedure", BCP 31, RFC 2506, March 1999. 1383 [RFC2804] IAB and IESG, "IETF Policy on Wiretapping", RFC 2804, 1384 May 2000. 1386 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 1387 A., Peterson, J., Sparks, R., Handley, M., and E. 1388 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 1389 June 2002. 1391 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1392 with Session Description Protocol (SDP)", RFC 3264, 1393 June 2002. 1395 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 1396 "Indicating User Agent Capabilities in the Session 1397 Initiation Protocol (SIP)", RFC 3840, August 2004. 1399 [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller 1400 Preferences for the Session Initiation Protocol (SIP)", 1401 RFC 3841, August 2004. 1403 [RFC4574] Levin, O. and G. Camarillo, "The Session Description 1404 Protocol (SDP) Label Attribute", RFC 4574, August 2006. 1406 [RFC6341] Rehor, K., Portman, L., Hutton, A., and R. Jain, "Use 1407 Cases and Requirements for SIP-Based Media Recording 1408 (SIPREC)", RFC 6341, August 2011. 1410 14.2. Informative References 1412 [I-D.ietf-siprec-architecture] 1413 Hutton, A., Portman, L., Jain, R., and K. Rehor, "An 1414 Architecture for Media Recording using the Session 1415 Initiation Protocol", draft-ietf-siprec-architecture-04 1416 (work in progress), March 2012. 1418 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 1419 Jacobson, "RTP: A Transport Protocol for Real-Time 1420 Applications", STD 64, RFC 3550, July 2003. 1422 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 1423 Video Conferences with Minimal Control", STD 65, RFC 3551, 1424 July 2003. 1426 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 1427 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 1428 RFC 3711, March 2004. 1430 [RFC4508] Levin, O. and A. Johnston, "Conveying Feature Tags with 1431 the Session Initiation Protocol (SIP) REFER Method", 1432 RFC 4508, May 2006. 1434 [RFC4579] Johnston, A. and O. Levin, "Session Initiation Protocol 1435 (SIP) Call Control - Conferencing for User Agents", 1436 BCP 119, RFC 4579, August 2006. 1438 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 1439 "Extended RTP Profile for Real-time Transport Control 1440 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, 1441 July 2006. 1443 [RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)", 1444 BCP 131, RFC 4961, July 2007. 1446 [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, 1447 "Codec Control Messages in the RTP Audio-Visual Profile 1448 with Feedback (AVPF)", RFC 5104, February 2008. 1450 [RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for 1451 Real-time Transport Control Protocol (RTCP)-Based Feedback 1452 (RTP/SAVPF)", RFC 5124, February 2008. 1454 [RFC5168] Levin, O., Even, R., and P. Hagendorf, "XML Schema for 1455 Media Control", RFC 5168, March 2008. 1457 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 1458 Control Packets on a Single Port", RFC 5761, April 2010. 1460 [RFC6222] Begen, A., Perkins, C., and D. Wing, "Guidelines for 1461 Choosing RTP Control Protocol (RTCP) Canonical Names 1462 (CNAMEs)", RFC 6222, April 2011. 1464 [RFC6263] Marjou, X. and A. Sollaud, "Application Mechanism for 1465 Keeping Alive the NAT Mappings Associated with RTP / RTP 1466 Control Protocol (RTCP) Flows", RFC 6263, June 2011. 1468 Authors' Addresses 1470 Leon Portman 1471 NICE Systems 1472 8 Hapnina 1473 Ra'anana 43017 1474 Israel 1476 Email: leon.portman@nice.com 1477 Henry Lum (editor) 1478 Genesys 1479 1380 Rodick Road, Suite 200 1480 Markham, Ontario L3R4G5 1481 Canada 1483 Email: henry.lum@genesyslab.com 1485 Charles Eckel 1486 Cisco 1487 170 West Tasman Drive 1488 San Jose, CA 95134 1489 United States 1491 Email: eckelcu@cisco.com 1493 Alan Johnston 1494 Avaya 1495 St. Louis, MO 63124 1497 Email: alan.b.johnston@gmail.com 1499 Andrew Hutton 1500 Siemens Enterprise Communications 1501 Brickhill Street 1502 Milton Keynes MK15 0DJ 1503 United Kingdom 1505 Email: andrew.hutton@siemens-enterprise.com