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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-22) exists of draft-ietf-siprec-metadata-08 == Outdated reference: A later version (-12) exists of draft-ietf-siprec-architecture-06 -- Obsolete informational reference (is this intentional?): RFC 6222 (Obsoleted by RFC 7022) Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). 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: April 25, 2013 Genesys 6 C. Eckel 7 Cisco 8 A. Johnston 9 Avaya 10 A. Hutton 11 Siemens Enterprise 12 Communications 13 October 22, 2012 15 Session Recording Protocol 16 draft-ietf-siprec-protocol-08 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 April 25, 2013. 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4 66 4. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 67 5. Overview of operations . . . . . . . . . . . . . . . . . . . . 5 68 5.1. Delivering recorded media . . . . . . . . . . . . . . . . 5 69 5.2. Delivering recording metadata . . . . . . . . . . . . . . 7 70 5.3. Receiving recording indications and providing 71 recording preferences . . . . . . . . . . . . . . . . . . 8 72 6. SIP Handling . . . . . . . . . . . . . . . . . . . . . . . . . 9 73 6.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 9 74 6.1.1. Initiating a Recording Session . . . . . . . . . . . . 10 75 6.1.2. SIP extensions for recording indication and 76 preference . . . . . . . . . . . . . . . . . . . . . . 10 77 6.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 11 78 6.3. Procedures for Recording-aware User Agents . . . . . . . . 11 79 7. SDP Handling . . . . . . . . . . . . . . . . . . . . . . . . . 12 80 7.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 12 81 7.1.1. SDP handling in RS . . . . . . . . . . . . . . . . . . 12 82 7.1.1.1. Handling media stream updates . . . . . . . . . . 13 83 7.1.2. Recording indication in CS . . . . . . . . . . . . . . 14 84 7.1.3. Recording preference in CS . . . . . . . . . . . . . . 15 85 7.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 15 86 7.3. Procedures for Recording-aware User Agents . . . . . . . . 17 87 7.3.1. Recording indication . . . . . . . . . . . . . . . . . 17 88 7.3.2. Recording preference . . . . . . . . . . . . . . . . . 18 89 8. RTP Handling . . . . . . . . . . . . . . . . . . . . . . . . . 19 90 8.1. RTP Mechanisms . . . . . . . . . . . . . . . . . . . . . . 19 91 8.1.1. RTCP . . . . . . . . . . . . . . . . . . . . . . . . . 19 92 8.1.2. RTP Profile . . . . . . . . . . . . . . . . . . . . . 19 93 8.1.3. SSRC . . . . . . . . . . . . . . . . . . . . . . . . . 20 94 8.1.4. CSRC . . . . . . . . . . . . . . . . . . . . . . . . . 20 95 8.1.5. SDES . . . . . . . . . . . . . . . . . . . . . . . . . 21 96 8.1.5.1. CNAME . . . . . . . . . . . . . . . . . . . . . . 21 97 8.1.6. Keepalive . . . . . . . . . . . . . . . . . . . . . . 21 98 8.1.7. RTCP Feedback Messages . . . . . . . . . . . . . . . . 21 99 8.1.7.1. Full Intra Request . . . . . . . . . . . . . . . . 22 100 8.1.7.2. Picture Loss Indicator . . . . . . . . . . . . . . 22 101 8.1.7.3. Temporary Maximum Media Stream Bit Rate Request . 22 102 8.1.8. Symmetric RTP/RTCP for Sending and Receiving . . . . . 23 103 8.2. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 23 104 8.2.1. SRC acting as an RTP Translator . . . . . . . . . . . 24 105 8.2.1.1. Forwarding Translator . . . . . . . . . . . . . . 25 106 8.2.1.2. Transcoding Translator . . . . . . . . . . . . . . 25 107 8.2.2. SRC acting as an RTP Mixer . . . . . . . . . . . . . . 26 108 8.2.3. SRC acting as an RTP Endpoint . . . . . . . . . . . . 26 109 8.3. RTP Session Usage by SRC . . . . . . . . . . . . . . . . . 27 110 8.3.1. SRC Using Multiple m-lines . . . . . . . . . . . . . . 27 111 8.3.2. SRC Using SSRC Multiplexing . . . . . . . . . . . . . 28 112 8.3.3. SRC Using Mixing . . . . . . . . . . . . . . . . . . . 29 113 9. Metadata . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 114 9.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 30 115 9.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 32 116 9.2.1. Formal Syntax . . . . . . . . . . . . . . . . . . . . 34 117 10. Persistent Recording . . . . . . . . . . . . . . . . . . . . . 34 118 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34 119 11.1. Registration of Option Tags . . . . . . . . . . . . . . . 34 120 11.1.1. siprec Option Tag . . . . . . . . . . . . . . . . . . 35 121 11.1.2. record-aware Option Tag . . . . . . . . . . . . . . . 35 122 11.2. Registration of media feature tags . . . . . . . . . . . . 35 123 11.2.1. src feature tag . . . . . . . . . . . . . . . . . . . 35 124 11.2.2. srs feature tag . . . . . . . . . . . . . . . . . . . 36 125 11.3. New Content-Disposition Parameter Registrations . . . . . 36 126 11.4. Media Type Registration . . . . . . . . . . . . . . . . . 36 127 11.4.1. Registration of MIME Type application/rs-metadata . . 36 128 11.4.2. Registration of MIME Type 129 application/rs-metadata-request . . . . . . . . . . . 37 130 11.5. SDP Attributes . . . . . . . . . . . . . . . . . . . . . . 37 131 11.5.1. 'record' SDP Attribute . . . . . . . . . . . . . . . . 37 132 11.5.2. 'recordpref' SDP Attribute . . . . . . . . . . . . . . 37 133 12. Security Considerations . . . . . . . . . . . . . . . . . . . 38 134 12.1. Authentication and Authorization . . . . . . . . . . . . . 38 135 12.2. RTP handling . . . . . . . . . . . . . . . . . . . . . . . 39 136 12.3. Metadata . . . . . . . . . . . . . . . . . . . . . . . . . 39 137 12.4. Storage and playback . . . . . . . . . . . . . . . . . . . 40 138 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 40 139 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40 140 14.1. Normative References . . . . . . . . . . . . . . . . . . . 40 141 14.2. Informative References . . . . . . . . . . . . . . . . . . 41 142 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 42 144 1. Introduction 146 This document specifies the mechanism to record a Communication 147 Session (CS) by delivering real-time media and metadata from the CS 148 to a recording device. In accordance to the architecture 149 [I-D.ietf-siprec-architecture], the Session Recording Protocol 150 specifies the use of SIP, SDP, and RTP to establish a Recording 151 Session (RS) between the Session Recording Client (SRC), which is on 152 the path of the CS, and a Session Recording Server (SRS) at the 153 recording device. 155 SIP is also used to deliver metadata to the recording device, as 156 specified in [I-D.ietf-siprec-metadata]. Metadata is information 157 that describes recorded media and the CS to which they relate. 159 The Session Recording Protocol intends to satisfy the SIP-based Media 160 Recording requirements listed in [RFC6341]. 162 In addition to the Session Recording Protocol, this document 163 specifies extensions for user agents that are participants in a CS to 164 receive recording indications and to provide preferences for 165 recording. 167 2. Terminology 169 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 170 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 171 document are to be interpreted as described in [RFC2119]. 173 3. Definitions 175 This document refers to the core definitions provided in the 176 architecture document [I-D.ietf-siprec-architecture]. 178 The RTP Handling section uses the definitions provided in "RTP: A 179 Transport Protocol for Real-Time Application" [RFC3550]. 181 4. Scope 183 The scope of the Session Recording Protocol includes the 184 establishment of the recording sessions and the reporting of the 185 metadata. The scope also includes extensions supported by User 186 Agents participating in the CS such as indication of recording. The 187 user agents need not be recording-aware in order to participate in a 188 CS being recorded. 190 The following items, which are not an exhaustive list, do not 191 represent the protocol itself and are considered out of the scope of 192 the Session Recording Protocol: 194 o Delivering recorded media in real-time as the CS media 196 o Specifications of criteria to select a specific CS to be recorded 197 or triggers to record a certain CS in the future 199 o Recording policies that determine whether the CS should be 200 recorded and whether parts of the CS are to be recorded 202 o Retention policies that determine how long a recording is stored 204 o Searching and accessing the recorded media and metadata 206 o Policies governing how CS users are made aware of recording 208 o Delivering additional recording session metadata through non-SIP 209 mechanism 211 5. Overview of operations 213 This section is informative and provides a description of recording 214 operations. 216 Section 6 describes SIP the handling in a recording session between a 217 SRC and a SRS, and the procedures for recording-aware user agents 218 participating in a CS. Section 7 describes the SDP in a recording 219 session, and the procedures for recording indications and recording 220 preferences. Section 8 describes the RTP handling in a recording 221 session. Section 9 describes the mechanism to deliver recording 222 metadata from the SRC to the SRS. 224 As mentioned in the architecture document 225 [I-D.ietf-siprec-architecture], there are a number of types of call 226 flows based on the location of the Session Recording Client. The 227 following sample call flows provide a quick overview of the 228 operations between the SRC and the SRS. 230 5.1. Delivering recorded media 232 When a SIP Back-to-back User Agent (B2BUA) with SRC functionality 233 routes a call from UA(A) to UA(B), the SRC has access to the media 234 path between the user agents. When the SRC is aware that it should 235 be recording the conversation, the SRC can cause the B2BUA to bridge 236 the media between UA(A) and UA(B). The SRC then establishes the 237 Recording Session with the SRS and sends replicated media towards the 238 SRS. 240 An endpoint may also have SRC functionality, where the endpoint 241 itself establishes the Recording Session to the SRS. Since the 242 endpoint has access to the media in the Communication Session, the 243 endpoint can send replicated media towards the SRS. 245 The following is a sample call flow that shows the SRC establishing a 246 recording session towards the SRS. The call flow is essentially 247 identical when the SRC is a B2BUA or as the endpoint itself. Note 248 that the SRC can choose when to establish the Recording Session 249 independent of the Communication Session, even though the following 250 call flow suggests that the SRC is establishing the Recording Session 251 (message #5) after the Communication Session is established. 253 UA A SRC UA B SRS 254 |(1)CS INVITE | | | 255 |------------->| | | 256 | |(2)CS INVITE | | 257 | |---------------------->| | 258 | | (3) 200 OK | | 259 | |<----------------------| | 260 | (4) 200 OK | | | 261 |<-------------| | | 262 | |(5)RS INVITE with SDP | | 263 | |--------------------------------------------->| 264 | | | (6) 200 OK with SDP | 265 | |<---------------------------------------------| 266 |(7)CS RTP | | | 267 |=============>|======================>| | 268 |<=============|<======================| | 269 | |(8)RS RTP | | 270 | |=============================================>| 271 | |=============================================>| 272 |(9)CS BYE | | | 273 |------------->| | | 274 | |(10)CS BYE | | 275 | |---------------------->| | 276 | |(11)RS BYE | | 277 | |--------------------------------------------->| 278 | | | | 280 Figure 1: Basic recording call flow 282 The above call flow can also apply to the case of a centralized 283 conference with a mixer. For clarity, ACKs to INVITEs and 200 OKs to 284 BYEs are not shown. The conference focus can provide the SRC 285 functionality since the conference focus has access to all the media 286 from each conference participant. When a recording is requested, the 287 SRC delivers the metadata and the media streams to the SRS. Since 288 the conference focus has access to a mixer, the SRC may choose to mix 289 the media streams from all participants as a single mixed media 290 stream towards the SRS. 292 An SRC can use a single recording session to record multiple 293 communication sessions. Every time the SRC wants to record a new 294 call, the SRC updates the recording session with a new SDP offer to 295 add new recorded streams to the recording session, and 296 correspondingly also update the metadata for the new call. 298 An SRS can also establish a recording session to an SRC, although it 299 is beyond the scope of this document to define how an SRS would 300 specify which calls to record. 302 5.2. Delivering recording metadata 304 The SRC is responsible for the delivery of metadata to the SRS. The 305 SRC may provide an initial metadata snapshot about recorded media 306 streams in the initial INVITE content in the recording session. 307 Subsequent metadata updates can be represented as a stream of events 308 in UPDATE or reINVITE requests sent by the SRC. These metadata 309 updates are normally incremental updates to the initial metadata 310 snapshot to optimize on the size of updates, however, the SRC may 311 also decide to send a new metadata snapshot anytime. 313 Metadata is transported in the body of INVITE or UPDATE messages. 314 Certain metadata, such as the attributes of the recorded media stream 315 are located in the SDP of the recording session. 317 The SRS has the ability to send a request to the SRC to request for a 318 new metadata snapshot update from the SRC. This can happen when the 319 SRS fails to understand the current stream of incremental updates for 320 whatever reason, for example, when SRS loses the current state due to 321 internal failure. The SRS may optionally attach a reason along with 322 the snapshot request. This request allows both SRC and SRS to 323 synchronize the states with a new metadata snapshot so that further 324 metadata incremental updates will be based on the latest metadata 325 snapshot. Similar to the metadata content, the metadata snapshot 326 request is transported as content in UPDATE or INVITE sent by the SRS 327 in the recording session. 329 SRC SRS 330 | | 331 |(1) INVITE (metadata snapshot) | 332 |---------------------------------------------------->| 333 | (2)200 OK | 334 |<----------------------------------------------------| 335 |(3) ACK | 336 |---------------------------------------------------->| 337 |(4) RTP | 338 |====================================================>| 339 |====================================================>| 340 |(5) UPDATE (metadata update 1) | 341 |---------------------------------------------------->| 342 | (6) 200 OK | 343 |<----------------------------------------------------| 344 |(7) UPDATE (metadata update 2) | 345 |---------------------------------------------------->| 346 | (8) 200 OK | 347 |<----------------------------------------------------| 348 | (9) UPDATE (metadata snapshot request) | 349 |<----------------------------------------------------| 350 | (10) 200 OK | 351 |---------------------------------------------------->| 352 | (11) INVITE (metadata snapshot 2 + SDP offer) | 353 |---------------------------------------------------->| 354 | (12) 200 OK (SDP answer) | 355 |<----------------------------------------------------| 356 | (13) UPDATE (metadata update 1 based on snapshot 2) | 357 |---------------------------------------------------->| 358 | (14) 200 OK | 359 |<----------------------------------------------------| 361 Figure 2: Delivering metadata via SIP UPDATE 363 5.3. Receiving recording indications and providing recording 364 preferences 366 The SRC is responsible to provide recording indications to the 367 participants in the CS. A recording-aware UA supports receiving 368 recording indications via the SDP attribute a=record, and it can 369 specify a recording preference in the CS by including the SDP 370 attribute a=recordpref. The recording attribute is a declaration by 371 the SRC in the CS to indicate whether recording is taking place. The 372 recording preference attribute is a declaration by the recording- 373 aware UA in the CS to indicate the recording preference. 375 To illustrate how the attributes are used, if a UA (A) is initiating 376 a call to UA (B) and UA (A) is also an SRC that is performing the 377 recording, then UA (A) provides the recording indication in the SDP 378 offer with a=record:on. Since UA (A) is the SRC, UA (A) receives the 379 recording indication from the SRC directly. When UA (B) receives the 380 SDP offer, UA (B) will see that recording is happening on the other 381 endpoint of this session. Since UA (B) is not an SRC and does not 382 provide any recording preference, the SDP answer does not contain 383 a=record nor a=recordpref. 385 UA A UA B 386 (SRC) | 387 | | 388 | [SRC recording starts] | 389 |(1) INVITE (SDP offer + a=record:on) | 390 |---------------------------------------------------->| 391 | (2) 200 OK (SDP answer) | 392 |<----------------------------------------------------| 393 |(3) ACK | 394 |---------------------------------------------------->| 395 |(4) RTP | 396 |<===================================================>| 397 | | 398 | [UA B wants to set preference to no recording] | 399 | (5) INVITE (SDP offer + a=recordpref:off) | 400 |<----------------------------------------------------| 401 | [SRC honors the preference and stops recording] | 402 |(6) 200 OK (SDP answer + a=record:off) | 403 |---------------------------------------------------->| 404 | (7) ACK | 405 |<----------------------------------------------------| 407 Figure 3: Recording indication and recording preference 409 After the call is established and recording is in progress, UA (B) 410 later decides to change the recording preference to no recording and 411 sends a reINVITE with the a=recordpref attribute. It is up to the 412 SRC to honor the preference, and in this case SRC decides to stop the 413 recording and updates the recording indication in the SDP answer. 415 6. SIP Handling 417 6.1. Procedures at the SRC 418 6.1.1. Initiating a Recording Session 420 A recording session is a SIP session with specific extensions 421 applied, and these extensions are listed in the procedures for SRC 422 and SRS below. When an SRC or an SRS receives a SIP session that is 423 not a recording session, it is up to the SRC or the SRS to determine 424 what to do with the SIP session. 426 The SRC can initiate a recording session by sending a SIP INVITE 427 request to the SRS. The SRC and the SRS are identified in the From 428 and To headers, respectively. 430 The SRC MUST include the '+sip.src' feature tag in the Contact URI, 431 defined in this specification as an extension to [RFC3840], for all 432 recording sessions. An SRS uses the presence of the '+sip.src' 433 feature tag in dialog creating and modifying requests and responses 434 to confirm that the dialog being created is for the purpose of a 435 Recording Session. In addition, when an SRC sends a REGISTER request 436 to a registrar, the SRC MUST include the '+sip.src' feature tag to 437 indicate the that it is a SRC. 439 Since SIP Caller Preferences extensions are optional to implement for 440 routing proxies, there is no guarantee that a recording session will 441 be routed to an SRC or SRS. A new options tag is introduced: 442 "siprec". As per [RFC3261], only an SRC or an SRS can accept this 443 option tag in a recording session. An SRC MUST include the "siprec" 444 option tag in the Require header when initiating a Recording Session 445 so that UA's which do not support the session recording protocol 446 extensions will simply reject the INVITE request with a 420 Bad 447 Extension. 449 When an SRC receives a new INVITE, the SRC MUST only consider the SIP 450 session as a recording session when both the '+sip.srs' feature tag 451 and 'siprec' option tag are included in the INVITE request. 453 6.1.2. SIP extensions for recording indication and preference 455 For the communication session, the SRC MUST provide recording 456 indication to all participants in the CS. A participant UA in a CS 457 can indicate that it is recording-aware by providing the "record- 458 aware" option tag, and the SRC MUST provide recording indications in 459 the new SDP a=record attribute described in the SDP Handling section. 460 In the absence of the "record-aware" option tag, meaning that the 461 participant UA is not recording-aware, an SRC MUST provide recording 462 indications through other means such as playing a tone inband, if the 463 SRC is required to do so (e.g. based on policies). 465 An SRC in the CS may also indicate itself as a session recording 466 client by including the '+sip.src' feature tag. A recording-aware 467 participant can learn that a SRC is in the CS, and can set the 468 recording preference for the CS with the new SDP a=recordpref 469 attribute described in the SDP Handling section below. 471 6.2. Procedures at the SRS 473 When an SRS receives a new INVITE, the SRS MUST only consider the SIP 474 session as a recording session when both the '+sip.src' feature tag 475 and 'siprec' option tag are included in the INVITE request. 477 The SRS can initiate a recording session by sending a SIP INVITE 478 request to the SRC. The SRS and the SRC are identified in the From 479 and To headers, respectively. 481 The SRS MUST include the '+sip.srs' feature tag in the Contact URI, 482 as per [RFC3840], for all recording sessions. An SRC uses the 483 presence of this feature tag in dialog creating and modifying 484 requests and responses to confirm that the dialog being created is 485 for the purpose of a Recording Session (REQ-30). In addition, when 486 an SRS sends a REGISTER request to a registrar, the SRS MUST include 487 the '+sip.srs' feature tag to indicate that it is a SRS. 489 An SRS MUST include the "siprec" option tag in the Require header as 490 per [RFC3261] when initiating a Recording Session so that UA's which 491 do not support the session recording protocol extensions will simply 492 reject the INVITE request with a 420 Bad Extension. 494 6.3. Procedures for Recording-aware User Agents 496 A recording-aware user agent is a participant in the CS that supports 497 the SIP and SDP extensions for receiving recording indication and for 498 requesting recording preferences for the call. A recording-aware UA 499 MUST indicate that it can accept reporting of recording indication 500 provided by the SRC with a new option tag "record-aware" when 501 initiating or establishing a CS, meaning including the "record-aware" 502 tag in the Supported header in the initial INVITE request or 503 response. 505 A recording-aware UA MUST be prepared to provide recording indication 506 to the end user through an appropriate user interface an indication 507 whether recording is on, off, or paused for each medium. Some user 508 agents that are automatons (e.g. IVR, media server, PSTN gateway) 509 may not have a user interface to render recording indication. When 510 such user agent indicates recording awareness, the UA SHOULD render 511 recording indication through other means, such as passing an inband 512 tone on the PSTN gateway, putting the recording indication in a log 513 file, or raising an application event in a VoiceXML dialog. These 514 user agents MAY also choose not to indicate recording awareness, 515 thereby relying on whatever mechanism an SRC chooses to indicate 516 recording, such as playing a tone inband. 518 7. SDP Handling 520 7.1. Procedures at the SRC 522 The SRC and SRS follows the SDP offer/answer model in [RFC3264]. The 523 procedures for SRC and SRS describe the conventions used in a 524 recording session. 526 7.1.1. SDP handling in RS 528 Since the SRC does not expect to receive media from the SRS, the SRC 529 typically sets each media stream of the SDP offer to only send media, 530 by qualifying them with the a=sendonly attribute, according to the 531 procedures in [RFC3264]. 533 The SRC sends recorded streams of participants to the SRS, and the 534 SRC MUST provide a label attribute (a=label), as per [RFC4574], on 535 each media stream in order to identify the recorded stream with the 536 rest of the metadata. The a=label attribute identifies each recorded 537 media stream, and the label name is mapped to the Media Stream 538 Reference in the metadata as per [I-D.ietf-siprec-metadata]. The 539 scope of the a=label attribute only applies to the SDP and Metadata 540 conveyed in the bodies of the SIP request or response that the label 541 appeared in. Note that a recorded stream is distinct from a CS 542 stream; the metadata provides a list of participants that contributes 543 to each recorded stream. 545 The following is an example SDP offer from SRC with both audio and 546 video recorded streams. Note that the following example contains 547 unfolded lines longer than 72 characters. These are captured between 548 tags. 550 v=0 551 o=SRC 2890844526 2890844526 IN IP4 198.51.100.1 552 s=- 553 c=IN IP4 198.51.100.1 554 t=0 0 555 m=audio 12240 RTP/AVP 0 4 8 556 a=sendonly 557 a=label:1 558 m=video 22456 RTP/AVP 98 559 a=rtpmap:98 H264/90000 560 561 a=fmtp:98 profile-level-id=42A01E; 562 sprop-parameter-sets=Z0IACpZTBYmI,aMljiA== 563 564 a=sendonly 565 a=label:2 566 m=audio 12242 RTP/AVP 0 4 8 567 a=sendonly 568 a=label:3 569 m=video 22458 RTP/AVP 98 570 a=rtpmap:98 H264/90000 571 572 a=fmtp:98 profile-level-id=42A01E; 573 sprop-parameter-sets=Z0IACpZTBYmI,aMljiA== 574 575 a=sendonly 576 a=label:4 578 Figure 4: Sample SDP offer from SRC with audio and video streams 580 7.1.1.1. Handling media stream updates 582 Over the lifetime of a recording session, the SRC can add and remove 583 recorded streams from the recording session for various reasons. For 584 example, when a CS stream is added or removed from the CS, or when a 585 CS is created or terminated if a recording session handles multiple 586 CSes. To remove a recorded stream from the recording session, the 587 SRC sends a new SDP offer where the port of the media stream to be 588 removed is set to zero, according to the procedures in [RFC3264]. To 589 add a recorded stream to the recording session, the SRC sends a new 590 SDP offer by adding a new media stream description or by reusing an 591 old media stream which had been previously disabled, according to the 592 procedures in [RFC3264]. 594 The SRC can temporarily discontinue streaming and collection of 595 recorded media from the SRC to the SRS for reason such as masking the 596 recording. In this case, the SRC sends a new SDP offer and sets the 597 media stream to inactive (a=inactive) for each recorded stream to be 598 paused, as per the procedures in [RFC3264]. To resume streaming and 599 collection of recorded media, the SRC sends a new SDP offer and sets 600 the media streams with a=sendonly attribute. Note that when a CS 601 stream is muted/unmuted, this information is conveyed in the metadata 602 by the SRC. The SRC SHOULD NOT modify the media stream with 603 a=inactive for mute since this operation is reserved for pausing the 604 RS media. 606 7.1.2. Recording indication in CS 608 While there are existing mechanisms for providing an indication that 609 a CS is being recorded, these mechanisms are usually delivered on the 610 CS media streams such as playing an in-band tone or an announcement 611 to the participants. A new 'record' SDP attribute is introduced to 612 allow the SRC to indicate recording state to a recording-aware UA in 613 CS. 615 The 'record' SDP attribute appears at the media level or session 616 level in either SDP offer or answer. When the attribute is applied 617 at the session level, the indication applies to all media streams in 618 the SDP. When the attribute is applied at the media level, the 619 indication applies to the media stream only, and that overrides the 620 indication if also set at the session level. Whenever the recording 621 indication needs to change, such as termination of recording, then 622 the SRC MUST initiate a reINVITE or UPDATE to update the SDP a=record 623 attribute. 625 The following is the ABNF of the 'record' attribute: 627 attribute /= record-attr 629 ; attribute defined in RFC 4566 631 record-attr = "record:" indication 633 indication = "on" / "off" / "paused" 635 on Recording is in progress. 637 off No recording is in progress. 639 paused Recording is in progress but media is paused. 641 7.1.3. Recording preference in CS 643 When the SRC receives the a=recordpref SDP in an SDP offer or answer, 644 the SRC chooses to honor the preference to record based on local 645 policy at the SRC. Whether or not the SRC honors the recording 646 preference, the SRC MUST update the a=record attribute to indicate 647 the current state of the recording (on/off/paused). 649 7.2. Procedures at the SRS 651 Typically the SRS only receives RTP streams from the SRC; therefore, 652 the SDP offer/answer from the SRS normally sets each media stream to 653 receive media, by setting them with the a=recvonly attribute, 654 according to the procedures of [RFC3264]. When the SRS is not ready 655 to receive a recorded stream, the SRS sets the media stream as 656 inactive in the SDP offer or answer by setting it with a=inactive 657 attribute, according to the procedures of [RFC3264]. When the SRS is 658 ready to receive recorded streams, the SRS sends a new SDP offer and 659 sets the media streams with a=recvonly attribute. 661 The following is an example of SDP answer from SRS for the SDP offer 662 from the above sample. Note that the following example contain 663 unfolded lines longer than 72 characters. These are captured between 664 tags. 666 v=0 667 o=SRS 0 0 IN IP4 198.51.100.20 668 s=- 669 c=IN IP4 198.51.100.20 670 t=0 0 671 m=audio 10000 RTP/AVP 0 672 a=recvonly 673 a=label:1 674 m=video 10002 RTP/AVP 98 675 a=rtpmap:98 H264/90000 676 677 a=fmtp:98 profile-level-id=42A01E; 678 sprop-parameter-sets=Z0IACpZTBYmI,aMljiA== 679 680 a=recvonly 681 a=label:2 682 m=audio 10004 RTP/AVP 0 683 a=recvonly 684 a=label:3 685 m=video 10006 RTP/AVP 98 686 a=rtpmap:98 H264/90000 687 688 a=fmtp:98 profile-level-id=42A01E; 689 sprop-parameter-sets=Z0IACpZTBYmI,aMljiA== 690 691 a=recvonly 692 a=label:4 694 Figure 5: Sample SDP answer from SRS with audio and video streams 696 Over the lifetime of a recording session, the SRS can remove recorded 697 streams from the recording session for various reasons. To remove a 698 recorded stream from the recording session, the SRS sends a new SDP 699 offer where the port of the media stream to be removed is set to 700 zero, according to the procedures in [RFC3264]. 702 The SRS SHOULD NOT add recorded streams in the recording session when 703 SRS sends a new SDP offer. Similarly, when the SRS starts a 704 recording session, the SRS SHOULD initiate the INVITE without an SDP 705 offer to let the SRC generate the SDP offer with recorded streams. 707 The following sequence diagram shows an example where the SRS is 708 initially not ready to receive recorded streams, and later updates 709 the recording session when the SRS is ready to record. 711 SRC SRS 712 | | 713 |(1) INVITE (SDP offer) | 714 |---------------------------------------------------->| 715 | [not ready to record] 716 | (2)200 OK with SDP inactive | 717 |<----------------------------------------------------| 718 |(3) ACK | 719 |---------------------------------------------------->| 720 | ... | 721 | [ready to record] 722 | (4) re-INVITE with SDP recvonly | 723 |<----------------------------------------------------| 724 |(5)200 OK with SDP sendonly | 725 |---------------------------------------------------->| 726 | (6) ACK | 727 |<----------------------------------------------------| 728 |(7) RTP | 729 |====================================================>| 730 | ... | 731 |(8) BYE | 732 |---------------------------------------------------->| 733 | (9) OK | 734 |<----------------------------------------------------| 736 Figure 6: SRS responding to offer with a=inactive 738 7.3. Procedures for Recording-aware User Agents 740 7.3.1. Recording indication 742 When a recording-aware UA receives an SDP offer or answer that 743 includes the a=record attribute, the UA MUST provide the recording 744 indication to the end user whether the recording is on, off, or 745 paused for each medium based on the most recently received a=record 746 SDP attribute for that medium. 748 If a call is traversed through one or more SIP B2BUA, and it happens 749 that there are more than one SRC in the call path, the recording 750 indication attribute does not provide any hint as to which SRC is 751 performing the recording, meaning the endpoint only knows that the 752 call is being recorded. This attribute is also not used as an 753 indication to negotiate which SRC in the call path will perform 754 recording and is not used as a request to start/stop recording if 755 there are multiple SRCs in the call path. 757 7.3.2. Recording preference 759 A participant in a CS MAY set the recording preference in the CS to 760 be recorded or not recorded at session establishment or during the 761 session. A new 'recordpref' SDP attribute is introduced, and the 762 participant in CS may set this recording preference atrribute in any 763 SDP offer/answer at session establishment time or during the session. 764 The SRC is not required to honor the recording preference from a 765 participant based on local policies at the SRC, and the participant 766 can learn the recording indication through the a=record SDP attribute 767 as described in the above section. 769 The SDP a=recordpref attribute can appear at the media level or 770 session level and can appear in an SDP offer or answer. When the 771 attribute is applied at the session level, the recording preference 772 applies to all media stream in the SDP. When the attribute is 773 applied at the media level, the recording preference applies to the 774 media stream only, and that overrides the recording preference if 775 also set at the session level. The user agent can change the 776 recording preference by changing the a=recordpref attribute in 777 subsequent SDP offer or answer. The absence of the a=recordpref 778 attribute in the SDP indicates that the UA has no recording 779 preference. 781 The following is the ABNF of the recordpref attribute: 783 attribute /= recordpref-attr 785 ; attribute defined in RFC 4566 787 recordpref-attr = "a=recordpref:" pref 789 pref = "on" / "off" / "pause" / "nopreference" 791 on Sets the preference to record if it has not already been started. 792 If the recording is currently paused, the preference is to resume 793 recording. 795 off Sets the preference for no recording. If recording has already 796 been started, then the preference is to stop the recording. 798 pause If the recording is currently in progress, sets the preference 799 to pause the recording. 801 nopreference To indicate that the UA has no preference on recording. 803 8. RTP Handling 805 This section provides recommendations and guidelines for RTP and RTCP 806 in the context of SIPREC. In order to communicate most effectively, 807 the Session Recording Client (SRC), the Session Recording Server 808 (SRS), and any Recording aware User Agents (UAs) SHOULD utilize the 809 mechanisms provided by RTP in a well-defined and predicable manner. 810 It is the goal of this document to make the reader aware of these 811 mechanisms and provide recommendations and guidelines. 813 8.1. RTP Mechanisms 815 This section briefly describes important RTP/RTCP constructs and 816 mechanisms that are particularly useful within the content of SIPREC. 818 8.1.1. RTCP 820 The RTP data transport is augmented by a control protocol (RTCP) to 821 allow monitoring of the data delivery. RTCP, as defined in 822 [RFC3550], is based on the periodic transmission of control packets 823 to all participants in the RTP session, using the same distribution 824 mechanism as the data packets. Support for RTCP is REQUIRED, per 825 [RFC3550], and it provides, among other things, the following 826 important functionality in relation to SIPREC: 828 1) Feedback on the quality of the data distribution 830 This feedback from the receivers may be used to diagnose faults in 831 the distribution. As such, RTCP is a well-defined and efficient 832 mechanism for the SRS to inform the SRC, and for the SRC to inform 833 Recording aware UAs, of issues that arise with respect to the 834 reception of media that is to be recorded. 836 2) Carries a persistent transport-level identifier for an RTP source 837 called the canonical name or CNAME 839 The SSRC identifier may change if a conflict is discovered or a 840 program is restarted; in which case receivers can use the CNAME to 841 keep track of each participant. Receivers may also use the CNAME to 842 associate multiple data streams from a given participant in a set of 843 related RTP sessions, for example to synchronize audio and video. 844 Synchronization of media streams is also facilitated by the NTP and 845 RTP timestamps included in RTCP packets by data senders. 847 8.1.2. RTP Profile 849 The RECOMMENDED RTP profiles for the SRC, SRS, and Recording aware 850 UAs are "Extended Secure RTP Profile for Real-time Transport Control 851 Protocol (RTCP)-Based Feedback (RTP/SAVPF)", [RFC5124] when using 852 encrypted RTP streams, and "Extended RTP Profile for Real-time 853 Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF)", 854 [RFC4585] when using non encrypted media streams. However, as this 855 is not a requirement, some implementations may use "The Secure Real- 856 time Transport Protocol (SRTP)", [RFC3711] and "RTP Profile for Audio 857 and Video Conferences with Minimal Control", AVP [RFC3551]. 858 Therefore, it is RECOMMENDED that the SRC, SRS, and Recording aware 859 UAs not rely entirely on SAVPF or AVPF for core functionality that 860 may be at least partially achievable using SAVP and AVP. 862 AVPF and SAVPF provide an improved RTCP timer model that allows more 863 flexible transmission of RTCP packets in response to events, rather 864 than strictly according to bandwidth. AVPF based codec control 865 messages provide efficient mechanisms for an SRC, SRS, and Recording 866 aware UAs to handle events such as scene changes, error recovery, and 867 dynamic bandwidth adjustments. These messages are discussed in more 868 detail later in this document. 870 SAVP and SAVPF provide media encryption, integrity protection, replay 871 protection, and a limited form of source authentication. They do not 872 contain or require a specific keying mechanism. 874 8.1.3. SSRC 876 The synchronization source (SSRC), as defined in [RFC3550] is carried 877 in the RTP header and in various fields of RTCP packets. It is a 878 random 32-bit number that is required to be globally unique within an 879 RTP session. It is crucial that the number be chosen with care in 880 order that participants on the same network or starting at the same 881 time are not likely to choose the same number. Guidelines regarding 882 SSRC value selection and conflict resolution are provided in 883 [RFC3550]. 885 The SSRC may also be used to separate different sources of media 886 within a single RTP session. For this reason as well as for conflict 887 resolution, it is important that the SRC, SRS, and Recording aware 888 UAs handle changes in SSRC values and properly identify the reason of 889 the change. The CNAME values carried in RTCP facilitate this 890 identification. 892 8.1.4. CSRC 894 The contributing source (CSRC), as defined in [RFC3550], identifies 895 the source of a stream of RTP packets that has contributed to the 896 combined stream produced by an RTP mixer. The mixer inserts a list 897 of the SSRC identifiers of the sources that contributed to the 898 generation of a particular packet into the RTP header of that packet. 900 This list is called the CSRC list. It is RECOMMENDED that a SRC or 901 Recording aware UA, when acting a mixer, sets the CSRC list 902 accordingly, and that the SRC and SRS interpret the CSRC list 903 appropriately when received. 905 8.1.5. SDES 907 The Source Description (SDES), as defined in [RFC3550], contains an 908 SSRC/CSRC identifier followed by a list of zero or more items, which 909 carry information about the SSRC/CSRC. End systems send one SDES 910 packet containing their own source identifier (the same as the SSRC 911 in the fixed RTP header). A mixer sends one SDES packet containing a 912 chunk for each contributing source from which it is receiving SDES 913 information, or multiple complete SDES packets if there are more than 914 31 such sources. 916 8.1.5.1. CNAME 918 The Canonical End-Point Identifier (CNAME), as defined in [RFC3550], 919 provides the binding from the SSRC identifier to an identifier for 920 the source (sender or receiver) that remains constant. It is 921 important the SRC and Recording aware UAs generate CNAMEs 922 appropriately and that the SRC and SRS interpret and use them for 923 this purpose. Guidelines for generating CNAME values are provided in 924 "Guidelines for Choosing RTP Control Protocol (RTCP) Canonical Names 925 (CNAMEs)" [RFC6222]. 927 8.1.6. Keepalive 929 It is anticipated that media streams in SIPREC may exist in an 930 inactive state for extended periods of times for any of a number of 931 valid reasons. In order for the bindings and any pinholes in NATs/ 932 firewalls to remain active during such intervals, it is RECOMMENDED 933 that the SRC, SRS, and Recording aware UAs follow the keep-alive 934 procedure recommended in "Application Mechanism for Keeping Alive the 935 NAT Mappings Associated to RTP/RTP Control Protocol (RTCP) Flows" 936 [RFC6263] for all RTP media streams. 938 8.1.7. RTCP Feedback Messages 940 "Codec Control Messages in the RTP Audio-Visual Profile with Feedback 941 (AVPF)" [RFC5104] specifies extensions to the messages defined in 942 AVPF [RFC4585]. Support for and proper usage of these messages is 943 important to SRC, SRS, and Recording aware UA implementations. Note 944 that these messages are applicable only when using the AVFP or SAVPF 945 RTP profiles 947 8.1.7.1. Full Intra Request 949 A Full Intra Request (FIR) Command, when received by the designated 950 media sender, requires that the media sender sends a Decoder Refresh 951 Point at the earliest opportunity. Using a decoder refresh point 952 implies refraining from using any picture sent prior to that point as 953 a reference for the encoding process of any subsequent picture sent 954 in the stream. 956 Decoder refresh points, especially Intra or IDR pictures for H.264 957 video codecs, are in general several times larger in size than 958 predicted pictures. Thus, in scenarios in which the available bit 959 rate is small, the use of a decoder refresh point implies a delay 960 that is significantly longer than the typical picture duration. 962 8.1.7.1.1. SIP INFO for FIR 964 "XML Schema for Media Control" [RFC5168] defines an Extensible Markup 965 Language (XML) Schema for video fast update. Implementations are 966 discouraged from using the method described except for backward 967 compatibility purposes. Implementations SHOULD use FIR messages 968 instead. 970 8.1.7.2. Picture Loss Indicator 972 Picture Loss Indication (PLI), as defined in [RFC4585], informs the 973 encoder of the loss of an undefined amount of coded video data 974 belonging to one or more pictures. Using the FIR command to recover 975 from errors is explicitly disallowed, and instead the PLI message 976 SHOULD be used. FIR SHOULD be used only in situations where not 977 sending a decoder refresh point would render the video unusable for 978 the users. Examples where sending FIR is appropriate include a 979 multipoint conference when a new user joins the conference and no 980 regular decoder refresh point interval is established, and a video 981 switching MCU that changes streams. 983 8.1.7.3. Temporary Maximum Media Stream Bit Rate Request 985 A receiver, translator, or mixer uses the Temporary Maximum Media 986 Stream Bit Rate Request (TMMBR) to request a sender to limit the 987 maximum bit rate for a media stream to the provided value. 988 Appropriate use of TMMBR facilitates rapid adaptation to changes in 989 available bandwidth. 991 8.1.7.3.1. Renegotiation of SDP bandwidth attribute 993 If it is likely that the new value indicated by TMMBR will be valid 994 for the remainder of the session, the TMMBR sender is expected to 995 perform a renegotiation of the session upper limit using the session 996 signaling protocol. Therefore for SIPREC, implementations are 997 RECOMMENDED to use TMMBR for temporary changes, and renegotiation of 998 bandwidth via SDP offer/answer for more permanent changes. 1000 8.1.8. Symmetric RTP/RTCP for Sending and Receiving 1002 Within an SDP offer/answer exchange, RTP entities choose the RTP and 1003 RTCP transport addresses (i.e., IP addresses and port numbers) on 1004 which to receive packets. When sending packets, the RTP entities may 1005 use the same source port or a different source port as those signaled 1006 for receiving packets. When the transport address used to send and 1007 receive RTP is the same, it is termed "symmetric RTP" [RFC4961]. 1008 Likewise, when the transport address used to send and receive RTCP is 1009 the same, it is termed "symmetric RTCP" [RFC4961]. 1011 When sending RTP, it is REQUIRED to use symmetric RTP. When sending 1012 RTCP, it is REQUIRED to use symmetric RTCP. Although an SRS will not 1013 normally send RTP, it will send RTCP as well as receive RTP and RTCP. 1014 Likewise, although an SRC will not normally receive RTP from the SRS, 1015 it will receive RTCP as well as send RTP and RTCP. 1017 Note: Symmetric RTP and symmetric RTCP are different from RTP/RTCP 1018 multiplexing [RFC5761]. 1020 8.2. Roles 1022 An SRC has the task of gathering media from the various UAs in one or 1023 more Communication Sessions (CSs) and forwarding the information to 1024 the SRS within the context of a corresponding Recording Session (RS). 1025 There are numerous ways in which an SRC may do this is, including but 1026 not limited to, appearing as a UA within a CS, or as a B2BUA between 1027 UAs within a CS. 1029 (Recording Session) +---------+ 1030 +------------SIP------->| | 1031 | +------RTP/RTCP----->| SRS | 1032 | | +-- Metadata -->| | 1033 | | | +---------+ 1034 v v | 1035 +---------+ 1036 | SRC | 1037 |---------| (Communication Session) +---------+ 1038 | |<----------SIP---------->| | 1039 | UA-A | | UA-B | 1040 | |<-------RTP/RTCP-------->| | 1041 +---------+ +---------+ 1043 Figure 7: UA as SRC 1045 (Recording Session) +---------+ 1046 +------------SIP------->| | 1047 | +------RTP/RTCP----->| SRS | 1048 | | +-- Metadata -->| | 1049 | | | +---------+ 1050 v v | 1051 +---------+ 1052 | SRC | 1053 +---------+ |---------| +---------+ 1054 | |<----SIP----->| |<----SIP----->| | 1055 | UA-A | | B2BUA | | UA-B | 1056 | |<--RTP/RTCP-->| |<--RTP/RTCP-->| | 1057 +---------+ +---------+ +---------+ 1058 |_______________________________________________| 1059 (Communication Session) 1061 Figure 8: B2BUA as SRC 1063 The following subsections define a set of roles an SRC may choose to 1064 play based on its position with respect to a UA within a CS, and an 1065 SRS within an RS. A CS and a corresponding RS are independent 1066 sessions; therefore, an SRC may play a different role within a CS 1067 than it does within the corresponding RS. 1069 8.2.1. SRC acting as an RTP Translator 1071 The SRC may act as a translator, as defined in [RFC3550]. A defining 1072 characteristic of a translator is that it forwards RTP packets with 1073 their SSRC identifier intact. There are two types of translators, 1074 one that simply forwards, and another that performs transcoding 1075 (e.g., from one codec to another) in addition to forwarding. 1077 8.2.1.1. Forwarding Translator 1079 When acting as a forwarding translator, RTP received as separate 1080 streams from different sources (e.g., from different UAs with 1081 different SSRCs) cannot be mixed by the SRC and MUST be sent 1082 separately to the SRS. All RTCP reports MUST be passed by the SRC 1083 between the UAs and the SRS, such that the UAs and SRS are able to 1084 detect any SSRC collisions. 1086 RTCP Sender Reports generated by a UA sending a stream MUST be 1087 forwarded to the SRS. RTCP Receiver Reports generated by the SRS 1088 MUST be forwarded to the relevant UA. 1090 UAs may receive multiple sets of RTCP Receiver Reports, one or more 1091 from other UAs participating in the CS, and one from the SRS 1092 participating in the RS. A Recording aware UA SHOULD be prepared to 1093 process the RTCP Receiver Reports from the SRS, whereas a recording 1094 unaware UA may discard such RTCP packets as not of relevance. 1096 If SRTP is used on both the CS and the RS, decryption and/or re- 1097 encryption may occur. For example, if different keys are used, it 1098 will occur. If the same keys are used, it need not occur. 1099 Section 12 provides additional information on SRTP and keying 1100 mechanisms. 1102 If packet loss occurs, either from the UA to the SRC or from the SRC 1103 to the SRS, the SRS SHOULD detect and attempt to recover from the 1104 loss. The SRC does not play a role in this other than forwarding the 1105 associated RTP and RTCP packets. 1107 8.2.1.2. Transcoding Translator 1109 When acting as a transcoding translator, an SRC MAY perform 1110 transcoding (e.g., from one codec to another), and this may result in 1111 a different rate of packets between what the SRC receives and what 1112 the SRC sends. As when acting as a forwarding translator, RTP 1113 received as separate streams from different sources (e.g., from 1114 different UAs with different SSRCs) cannot be mixed by the SRC and 1115 MUST be sent separately to the SRS. All RTCP reports MUST be passed 1116 by the SRC between the UAs and the SRS, such that the UAs and SRS are 1117 able to detect any SSRC collisions. 1119 RTCP Sender Reports generated by a UA sending a stream MUST be 1120 forwarded to the SRS. RTCP Receiver Reports generated by the SRS 1121 MUST be forwarded to the relevant UA. The SRC may need to manipulate 1122 the RTCP Receiver Reports to take account of any transcoding that has 1123 taken place. 1125 UAs may receive multiple sets of RTCP Receiver Reports, one or more 1126 from other UAs participating in the CS, and one from the SRS 1127 participating in the RS. A Recording aware UA SHOULD be prepared to 1128 process the RTCP Receiver Reports from the SRS, whereas a recording 1129 unaware UA may discard such RTCP packets as not of relevance. 1131 If SRTP is used on both the CS and the RS, decryption and/or re- 1132 encryption may occur. For example, if different keys are used, it 1133 will occur. If the same keys are used, it need not occur. 1134 Section 12 provides additional information on SRTP and keying 1135 mechanisms. 1137 If packet loss occurs, either from the UA to the SRC or from the SRC 1138 to the SRS, the SRS SHOULD detect and attempt to recover from the 1139 loss. The SRC does not play a role in this other than forwarding the 1140 associated RTP and RTCP packets. 1142 8.2.2. SRC acting as an RTP Mixer 1144 In the case of the SRC acting as a RTP mixer, as defined in 1145 [RFC3550], the SRC combines RTP streams from different UA and sends 1146 them towards the SRS using its own SSRC. The SSRCs from the 1147 contributing UA SHOULD be conveyed as CSRCs identifiers within this 1148 stream. The SRC may make timing adjustments among the received 1149 streams and generate its own timing on the stream sent to the SRS. 1150 Optionally an SRC acting as a mixer can perform transcoding, and can 1151 even cope with different codings received from different UAs. RTCP 1152 Sender Reports and Receiver Reports are not forwarded by an SRC 1153 acting as mixer, but there are requirements for forwarding RTCP 1154 Source Description (SDES) packets. The SRC generates its own RTCP 1155 Sender and Receiver reports toward the associated UAs and SRS. 1157 The use of SRTP between the SRC and the SRS for the RS is independent 1158 of the use of SRTP between the UAs and SRC for the CS. Section 12 1159 provides additional information on SRTP and keying mechanisms. 1161 If packet loss occurs from the UA to the SRC, the SRC SHOULD detect 1162 and attempt to recover from the loss. If packet loss occurs from the 1163 SRC to the SRS, the SRS SHOULD detect and attempt to recover from the 1164 loss. 1166 8.2.3. SRC acting as an RTP Endpoint 1168 The case of the SRC acting as an RTP endpoint, as defined in 1169 [RFC3550], is similar to the mixer case, except that the RTP session 1170 between the SRC and the SRS is considered completely independent from 1171 the RTP session that is part of the CS. The SRC can, but need not, 1172 mix RTP streams from different participants prior to sending to the 1173 SRS. RTCP between the SRC and the SRS is completely independent of 1174 RTCP on the CS. 1176 The use of SRTP between the SRC and the SRS for the RS is independent 1177 of the use of SRTP between the UAs and SRC for the CS. Section 12 1178 provides additional information on SRTP and keying mechanisms. 1180 If packet loss occurs from the UA to the SRC, the SRC SHOULD detect 1181 and attempt to recover from the loss. If packet loss occurs from the 1182 SRC to the SRS, the SRS SHOULD detect and attempt to recover from the 1183 loss. 1185 8.3. RTP Session Usage by SRC 1187 There are multiple ways that an SRC may choose to deliver recorded 1188 media to an SRS. In some cases, it may use a single RTP session for 1189 all media within the RS, whereas in others it may use multiple RTP 1190 sessions. The following subsections provide examples of basic RTP 1191 session usage by the SRC, including a discussion of how the RTP 1192 constructs and mechanisms covered previously are used. An SRC may 1193 choose to use one or more of the RTP session usages within a single 1194 RS. The set of RTP session usages described is not meant to be 1195 exhaustive. 1197 8.3.1. SRC Using Multiple m-lines 1199 When using multiple m-lines, an SRC includes each m-line in an SDP 1200 offer to the SRS. The SDP answer from the SRS MUST include all 1201 m-lines, with any rejected m-lines indicated with a zero port, per 1202 [RFC3264]. Having received the answer, the SRC starts sending media 1203 to the SRS as indicated in the answer. Alternatively, if the SRC 1204 deems the level of support indicated in the answer to be 1205 unacceptable, it may initiate another SDP offer/answer exchange in 1206 which an alternative RTP session usage is negotiated. 1208 In order to preserve the mapping of media to participant within the 1209 CSs in the RS, the SRC SHOULD map each unique CNAME within the CSs to 1210 a unique CNAME within the RS. Additionally, the SRC SHOULD map each 1211 unique combination of CNAME/SSRC within the CSs to a unique CNAME/ 1212 SSRC within the RS. In doing to, the SRC may act as an RTP 1213 translator or as an RTP endpoint. 1215 The following figure illustrates a case in which each UA represents a 1216 participant contributing two RTP sessions (e.g. one for audio and one 1217 for video), each with a single SSRC. The SRC acts as an RTP 1218 translator and delivers the media to the SRS using four RTP sessions, 1219 each with a single SSRC. The CNAME and SSRC values used by the UAs 1220 within their media streams are preserved in the media streams from 1221 the SRC to the SRS. 1223 +---------+ 1224 +------------SSRC Aa--->| | 1225 | + --------SSRC Av--->| | 1226 | | +------SSRC Ba--->| SRS | 1227 | | | +---SSRC Bv--->| | 1228 | | | | +---------+ 1229 | | | | 1230 | | | | 1231 +---------+ +----------+ +---------+ 1232 | |---SSRC Aa-->| SRC |<--SSRC Ba---| | 1233 | UA-A | |(CNAME-A, | | UA-B | 1234 |(CNAME-A)|---SSRC Av-->| CNAME-B) |<--SSRC Bv---|(CNAME-B)| 1235 +---------+ +----------+ +---------+ 1237 Figure 9: SRC Using Multiple m-lines 1239 8.3.2. SRC Using SSRC Multiplexing 1241 When using SSRC multiplexing, an SRC multiplexes RTP packets of the 1242 same media type from multiple RTP sessions into a single RTP session 1243 with multiple SSRC values. The SRC includes one m-line for each RTP 1244 session in an SDP offer to the SRS. The SDP answer from the SRS MUST 1245 include all m-lines, with any rejected m-lines indicated with the 1246 zero port, per [RFC3264]. Having received the answer, the SRC starts 1247 sending media to the SRS as indicated in the answer. 1249 In order to preserve the mapping of media to participant within the 1250 CSs in the RS, the SRC SHOULD map each unique combination of CNAME/ 1251 SSRC within the CSs to a unique SSRC within the RS. The CNAMEs used 1252 in the CSs are not preserved within the RS. The SRS relies on the 1253 SIPREC metadata to determine the participants included within each 1254 multiplexed stream. The SRC MUST avoid SSRC collisions, rewriting 1255 SSRCs if necessary. In doing to, the SRC acts as an RTP endpoint. 1257 In the event the SRS does not support SSRC multiplexing, the SRC 1258 becomes aware of this when it receives RTCP receiver reports from the 1259 SRS indicating the absence of any packets for one or more of the 1260 multiplexed SSRC values. If the SRC deems the level of support 1261 indicated in the RTCP receiver report to be unacceptable, it may 1262 initiate another SDP offer/answer exchange in which an alternative 1263 RTP session usage is negotiated. 1265 The following figure illustrates a case in which each UA represents a 1266 participant contributing two RTP sessions (e.g. one for audio and 1267 another for video), each with a single SSRC. The SRC delivers the 1268 media to the SRS using two RTP sessions, multiplexing one stream with 1269 the same media type from each participant into a single RTP session 1270 containing two SSRCs. The SRC uses its own CNAME and SSRC values, 1271 but it preserves the mapping of unique CNAME/SSRC used by the UAs 1272 within their media streams in the media streams from the SRC to the 1273 SRS. 1275 +---------+ 1276 | | 1277 +-----SSRC SAa,SBa--->| | 1278 | +-SSRC SAv,SBv--->| SRS | 1279 | | | | 1280 | | +---------+ 1281 | | 1282 | | 1283 +---------+ +----------+ +---------+ 1284 | |---SSRC Aa-->| SRC |<--SSRC Ba---| | 1285 | UA-A | |(CNAME-S) | | UA-B | 1286 |(CNAME-A)|---SSRC Av-->| |<--SSRC Bv---|(CNAME-B)| 1287 +---------+ +----------+ +---------+ 1289 Figure 10: SRC Using SSRC Multiplexing 1291 8.3.3. SRC Using Mixing 1293 When using mixing, the SRC combines RTP streams from different 1294 participants and sends them towards the SRS using its own SSRC. The 1295 SSRCs from the contributing participants SHOULD be conveyed as CSRCs 1296 identifiers. The SRC includes one m-line for each RTP session in an 1297 SDP offer to the SRS. The SDP answer from the SRS MUST include all 1298 m-lines, with any rejected m-lines indicated with the zero port, per 1299 [RFC3264]. Having received the answer, the SRC starts sending media 1300 to the SRS as indicated in the answer. 1302 In order to preserve the mapping of media to participant within the 1303 CSs in the RS, the SRC SHOULD map each unique CNAME within the CSs to 1304 a unique CNAME within the RS. Additionally, the SRC SHOULD map each 1305 unique combination of CNAME/SSRC within the CSs to a unique CNAME/ 1306 SSRC within the RS. The SRC MUST avoid SSRC collisions, rewriting 1307 SSRCs if necessary when used as CSRCs in the RS. In doing to, the 1308 SRC acts as an RTP mixer. 1310 In the event the SRS does not support this usage of CSRC values, it 1311 relies entirely on the SIPREC metadata to determine the participants 1312 included within each mixed stream. 1314 The following figure illustrates a case in which each UA represents a 1315 participant contributing two RTP sessions (e.g. one for audio and one 1316 for video), each with a single SSRC. The SRC acts as an RTP mixer 1317 and delivers the media to the SRS using two RTP sessions, mixing 1318 media from each participant into a single RTP session containing a 1319 single SSRC and two CSRCs. 1321 SSRC Sa +---------+ 1322 +-------CSRC Aa,Ba--->| | 1323 | | | 1324 | SSRC Sa | SRS | 1325 | +---CSRC Av,Bv--->| | 1326 | | +---------+ 1327 | | 1328 +----------+ 1329 +---------+ | SRC | +---------+ 1330 | |---SSRC Aa-->|(CNAME-S, |<--SSRC Ba---| | 1331 | UA-A | | CNAME-A, | | UA-B | 1332 |(CNAME-A)|---SSRC Aa-->| CNAME-B) |<--SSRC Bv---|(CNAME-B)| 1333 +---------+ +----------+ +---------+ 1335 Figure 11: SRC Using Mixing 1337 9. Metadata 1339 9.1. Procedures at the SRC 1341 The SRC MUST deliver metadata to the SRS in a recording session; the 1342 timing of which SRC sends the metadata depends on when the metadata 1343 becomes available. Metadata SHOULD be provided by the SRC in the 1344 initial INVITE request when establishing the recording session, and 1345 subsequent metadata updates can be provided by the SRC in reINVITE 1346 and UPDATE requests ([RFC3311]) and responses in the recording 1347 session. There are cases that metadata is not available in the 1348 initial INVITE request sent by the SRC, for example, when a recording 1349 session is established in the absence of a communication session, and 1350 the SRC would update the recording session with metadata whenever 1351 metadata becomes available. 1353 Certain metadata attributes are contained in the SDP, and others are 1354 contained in a new content type "application/rs-metadata". The 1355 format of the metadata is described as part of the mechanism in 1356 [I-D.ietf-siprec-metadata]. A new "disposition-type" of Content- 1357 Disposition is defined for the purpose of carrying metadata and the 1358 value is "recording-session". The "recording-session" value 1359 indicates that the "application/rs-metadata" content contains 1360 metadata to be handled by the SRS, and the disposition can be carried 1361 in either INVITE or UPDATE requests or responses sent by the SRC. 1363 Metadata sent by the SRC can be categorized as either a full metadata 1364 snapshot or partial update. A full metadata snapshot describes all 1365 the recorded streams and all metadata associated with the recording 1366 session. When the SRC sends a full metadata snapshot, the SRC MUST 1367 send an INVITE or an UPDATE request ([RFC3311]) with an SDP offer and 1368 the "recording-session" disposition. A partial update represents an 1369 incremental update since the last metadata update sent by the SRC. A 1370 partial update sent by the SRC can be an INVITE request or response 1371 with an SDP offer, or an INVITE/UPDATE request or response containing 1372 a "recording-session" disposition, or an INVITE request containing 1373 both an SDP offer and the "recording-session" disposition. 1375 The following is an example of a full metadata snapshot sent by the 1376 SRC in the initial INVITE request: 1378 INVITE sip:recorder@example.com SIP/2.0 1379 Via: SIP/2.0/TCP src.example.com;branch=z9hG4bKdf6b622b648d9 1380 From: ;tag=35e195d2-947d-4585-946f-098392474 1381 To: 1382 Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a 1383 CSeq: 101 INVITE 1384 Max-Forwards: 70 1385 Require: siprec 1386 Accept: application/sdp, application/rs-metadata, 1387 application/rs-metadata-request 1388 Contact: ;+sip.src 1389 Content-Type: multipart/mixed;boundary=foobar 1390 Content-Length: [length] 1392 --foobar 1393 Content-Type: application/sdp 1395 v=0 1396 o=SRS 2890844526 2890844526 IN IP4 198.51.100.1 1397 s=- 1398 c=IN IP4 198.51.100.1 1399 t=0 0 1400 m=audio 12240 RTP/AVP 0 4 8 1401 a=sendonly 1402 a=label:1 1404 --foobar 1405 Content-Type: application/rs-metadata 1406 Content-Disposition: recording-session 1408 [metadata content] 1410 Figure 12: Sample INVITE request for the recording session 1412 9.2. Procedures at the SRS 1414 The SRS receives metadata updates from the SRC in INVITE and UPDATE 1415 requests. Since the SRC can send partial updates based on the 1416 previous update, the SRS needs to keep track of the sequence of 1417 updates from the SRC. 1419 In the case of an internal failure at the SRS, the SRS may fail to 1420 recognize a partial update from the SRC. The SRS may be able to 1421 recover from the internal failure by requesting for a full metadata 1422 snapshot from the SRC. Certain errors, such as syntax errors or 1423 semantic errors in the metadata information, are likely caused by an 1424 error on the SRC side, and it is likely the same error will occur 1425 again even when a full metadata snapshot is requested. In order to 1426 avoid repeating the same error, the SRS can simply terminate the 1427 recording session when a syntax error or semantic error is detected 1428 in the metadata. 1430 When the SRS explicitly requests for a full metadata snapshot, the 1431 SRS MUST send an UPDATE request without an SDP offer. A metadata 1432 snapshot request contains a content with the content disposition type 1433 "recording-session". Note that the SRS MAY generate an INVITE 1434 request without an SDP offer but this MUST NOT include a metadata 1435 snapshot request. The format of the content is "application/ 1436 rs-metadata-request", and the body format is chosen to be a simple 1437 text-based format. The following shows an example: 1439 UPDATE sip:2000@src.exmaple.com SIP/2.0 1440 Via: SIP/2.0/UDP srs.example.com;branch=z9hG4bKdf6b622b648d9 1441 To: ;tag=35e195d2-947d-4585-946f-098392474 1442 From: ;tag=1234567890 1443 Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a 1444 CSeq: 1 UPDATE 1445 Max-Forwards: 70 1446 Require: siprec 1447 Contact: ;+sip.srs 1448 Accept: application/sdp, application/rs-metadata 1449 Content-Disposition: recording-session 1450 Content-Type: application/rs-metadata-request 1451 Content-Length: [length] 1453 SRS internal error 1455 Figure 13: Metadata Request 1457 The SRS MAY include the reason why a metadata snapshot request is 1458 being made to the SRC in the reason line. This reason line is free 1459 form text, mainly designed for logging purposes on the SRC side. The 1460 processing of the content by the SRC is entirely optional since the 1461 content is for logging only, and the snapshot request itself is 1462 indicated by the use of the application/rs-metadata-request content 1463 type. 1465 When the SRC receives the request for a metadata snapshot, the SRC 1466 MUST provide a full metadata snapshot in a separate INVITE or UPDATE 1467 transaction, along with an SDP offer. All subsequent metadata 1468 updates sent by the SRC MUST be based on the new metadata snapshot. 1470 9.2.1. Formal Syntax 1472 The formal syntax for the application/rs-metadata-request MIME is 1473 described below using the augmented Backus-Naur Form (BNF) as 1474 described in [RFC5234]. 1476 snapshot-request = srs-reason-line CRLF 1478 srs-reason-line = [TEXT-UTF8-TRIM] 1480 10. Persistent Recording 1482 Persistent recording is a specific use case outlined in REQ-005 or 1483 Use Case 4 in [RFC6341], where a recording session can be established 1484 in the absence of a communication session. The SRC continuously 1485 records media in a recording session to the SRS even in the absence 1486 of a CS for all user agents that are part of persistent recording. 1487 By allocating recorded streams and continuously sending recorded 1488 media to the SRS, the SRC does not have to prepare new recorded 1489 streams with new SDP offer when a new communication session is 1490 created and also does not impact the timing of the CS. The SRC only 1491 needs to update the metadata when new communication sessions are 1492 created. 1494 When there is no communication sessions running on the devices with 1495 persistent recording, there is no recorded media to stream from the 1496 SRC to the SRS. In certain environments where Network Address 1497 Translator (NAT) is used, typically a minimum of flow activity is 1498 required to maintain the NAT binding for each port opened. Agents 1499 that support Interactive Connectivity Establishment (ICE) solves this 1500 problem. For non-ICE agents, in order not to lose the NAT bindings 1501 for the RTP/RTCP ports opened for the recorded streams, the SRC and 1502 SRS SHOULD follow the recommendations provided in [RFC6263] to 1503 maintain the NAT bindings. 1505 11. IANA Considerations 1507 11.1. Registration of Option Tags 1509 This specification registers two option tags. The required 1510 information for this registration, as specified in [RFC3261], is as 1511 follows. 1513 11.1.1. siprec Option Tag 1515 Name: siprec 1517 Description: This option tag is for identifying the SIP session 1518 for the purpose of recording session only. This is typically not 1519 used in a Supported header. When present in a Require header in a 1520 request, it indicates that the UAS MUST be either a SRC or SRS 1521 capable of handling the contexts of a recording session. 1523 11.1.2. record-aware Option Tag 1525 Name: record-aware 1527 Description: This option tag is to indicate the ability for the 1528 user agent to receive recording indicators in media level or 1529 session level SDP. When present in a Supported header, it 1530 indicates that the UA can receive recording indicators in media 1531 level or session level SDP. 1533 11.2. Registration of media feature tags 1535 This document registers two new media feature tags in the SIP tree 1536 per the process defined in [RFC2506] and [RFC3840] 1538 11.2.1. src feature tag 1540 Media feature tag name: sip.src 1542 ASN.1 Identifier: 25 1544 Summary of the media feature indicated by this tag: This feature 1545 tag indicates that the user agent is a Session Recording Client 1546 for the purpose for Recording Session. 1548 Values appropriate for use with this feature tag: boolean 1550 The feature tag is intended primarily for use in the following 1551 applications, protocols, services, or negotiation mechanisms: This 1552 feature tag is only useful for a Recording Session. 1554 Examples of typical use: Routing the request to a Session 1555 Recording Server. 1557 Security Considerations: Security considerations for this media 1558 feature tag are discussed in Section 11.1 of RFC 3840. 1560 11.2.2. srs feature tag 1562 Media feature tag name: sip.srs 1564 ASN.1 Identifier: 26 1566 Summary of the media feature indicated by this tag: This feature 1567 tag indicates that the user agent is a Session Recording Server 1568 for the purpose for Recording Session. 1570 Values appropriate for use with this feature tag: boolean 1572 The feature tag is intended primarily for use in the following 1573 applications, protocols, services, or negotiation mechanisms: This 1574 feature tag is only useful for a Recording Session. 1576 Examples of typical use: Routing the request to a Session 1577 Recording Client. 1579 Security Considerations: Security considerations for this media 1580 feature tag are discussed in Section 11.1 of RFC 3840. 1582 11.3. New Content-Disposition Parameter Registrations 1584 This document registers a new "disposition-type" value in Content- 1585 Disposition header: recording-session. 1587 recording-session the body describes the metadata information about 1588 the recording session 1590 11.4. Media Type Registration 1592 11.4.1. Registration of MIME Type application/rs-metadata 1594 This document registers the application/rs-metadata MIME media type 1595 in order to describe the recording session metadata. This media type 1596 is defined by the following information: 1598 Media type name: application 1600 Media subtype name: rs-metadata 1602 Required parameters: none 1604 Options parameters: none 1606 11.4.2. Registration of MIME Type application/rs-metadata-request 1608 This document registers the application/rs-metadata-request MIME 1609 media type in order to describe a recording session metadata snapshot 1610 request. This media type is defined by the following information: 1612 Media type name: application 1614 Media subtype name: rs-metadata-request 1616 Required parameters: none 1618 Options parameters: none 1620 11.5. SDP Attributes 1622 This document registers the following new SDP attributes. 1624 11.5.1. 'record' SDP Attribute 1626 Contact names: Leon Portman leon.portman@nice.com, Henry Lum 1627 henry.lum@genesyslab.com 1629 Attribute name: record 1631 Long form attribute name: Recording Indication 1633 Type of attribute: session or media level 1635 Subject to charset: no 1637 This attribute provides the recording indication for the session or 1638 media stream. 1640 Allowed attribute values: on, off, paused 1642 11.5.2. 'recordpref' SDP Attribute 1644 Contact names: Leon Portman leon.portman@nice.com, Henry Lum 1645 henry.lum@genesyslab.com 1647 Attribute name: recordpref 1649 Long form attribute name: Recording Preference 1651 Type of attribute: session or media level 1653 Subject to charset: no 1654 This attribute provides the recording preference for the session or 1655 media stream. 1657 Allowed attribute values: on, off, pause, nopreference 1659 12. Security Considerations 1661 The recording session is fundamentally a standard SIP dialog 1662 [RFC3261], therefore, the recording session can reuse any of the 1663 existing SIP security mechanism available for securing the session 1664 signaling, the recorded media as well as the metadata. The use cases 1665 and requirements document [RFC6341] outlines the general security 1666 considerations, and the following describe specific security 1667 recommendations. 1669 The SRC and SRS MUST support SIP with TLS and MAY support SIPS with 1670 TLS as per [RFC5630]. The Recording Session SHOULD be at least as 1671 secure as the Communication Session, meaning using at least the same 1672 strength of cipher suite as the CS if the CS is secured. For 1673 example, if the CS uses SIPS for signalling and RTP/SAVP for media, 1674 then the RS does not downgrade the level of security in the RS to SIP 1675 or plain RTP since doing so will mean an automatic security downgrade 1676 for the CS. In deployments where the SRC and the SRS are in the same 1677 administrative domain and the same physical switch that prevents 1678 outside user access, some SRC may choose lower the level of security 1679 when establishing the recording session. While physically securing 1680 the SRC and SRS may prevent an outside attacker from accessing 1681 important call recordings, this still does not prevent an inside 1682 attacker from accessing the internal network to gain access to the 1683 call recordings. 1685 12.1. Authentication and Authorization 1687 The recording session reuses the SIP mechanism to challenge requests 1688 that are based on HTTP authentication. The mechanism relies on 401 1689 and 407 SIP responses as well as other SIP header fields for carrying 1690 challenges and credentials. 1692 At the transport level, the recording session uses TLS authentication 1693 to validate the authenticity of the SRC and SRS. The SRC and SRS 1694 MUST implement TLS mutual authentication for establishing the 1695 recording session, and whether the SRC/SRS chooses to use 1696 authentication is a deployment decision. In deployments where the 1697 SRC and the SRS are in the same administrative domain, the deployment 1698 may choose not to authenticate each other or only to have SRC 1699 authenticate the SRS as there is an inherent trust relation between 1700 the SRC and the SRS when they are hosted in the same administrative 1701 domain. In deployments where the SRS can be hosted on a different 1702 administrative domain, then it is important to perform mutual 1703 authentication to ensure the authenticity of both the SRC and the SRS 1704 before transmitting any recorded media. The risk of not 1705 authenticating the SRS is that the recording may be sent to a 1706 compromised SRS and that sensitive call recording will be obtained by 1707 an attacker. On the other hand, the risk of not authenticating the 1708 SRC is that an SRS will accept calls from an unknown SRC and allow 1709 potential forgery of call recordings. 1711 The SRS may have its own set of recording policies to authorize 1712 recording requests from the SRC. The use of recording policies is 1713 outside the scope of the Session Recording Protocol. 1715 12.2. RTP handling 1717 In many scenarios it will be critical that the media transported 1718 between the SRC and SRS to be protected. Media encryption is an 1719 important element in the overall SIPREC solution; therefore SRC and 1720 SRS MUST support RTP/SAVP [RFC3711] and RTP/SAVPF [RFC5124]. RTP/ 1721 SAVP and RTP/SAVPF provide media encryption, integrity protection, 1722 replay protection, and a limited form of source authentication. They 1723 do not contain or require a specific keying mechanism. 1725 When RTP/SAVP or RTP/SAVPF is used, RS can choose to use the same or 1726 different security keys than the ones used in the CS. Some SRCs are 1727 designed to simply replicate RTP packets from the CS media stream to 1728 the SRS, and the SRC will be reusing the same keys as the CS. In 1729 this case, the SRC MUST secure the SDP with SDP Security Descriptions 1730 (SDES) [RFC4568] in the RS with at least the same level of security 1731 as the CS. The risk of lowering the level of security in the RS for 1732 this case is that it will effectively become a downgrade attack on 1733 the CS since the same key is used for both CS and RS. 1735 For SRCs that perform transcoding or mixing of media before sending 1736 to the SRS, the SRC MUST negotiate a different security key than the 1737 one being used in the CS, to ensure that the security in the CS is 1738 not compromised by the SRC when reusing the same security key. 1740 12.3. Metadata 1742 Metadata contains sensitive information such as the address of record 1743 of the participants and other extension data placed by the SRC. It 1744 is essential to protect the content of the metadata in the RS. Since 1745 metadata is a content type transmitted in SIP signalling, metadata 1746 SHOULD be protected at the transport level by SIPS/TLS. 1748 12.4. Storage and playback 1750 While storage and playback of the call recording is beyond the scope 1751 of this document, it is worthwhile to mention here that it is also 1752 important for the recording storage and playback to provide a level 1753 of security that is comparable to the communication session. It 1754 would defeat the purpose of securing both the communication session 1755 and the recording session mentioned in the previous sections if the 1756 recording can be easily played back with a simple unsecured HTTP 1757 interface without any form of authentication or authorization. 1759 13. Acknowledgements 1761 We want to thank John Elwell, Paul Kyzivat, Partharsarathi R, Ram 1762 Mohan R, Hadriel Kaplan, Adam Roach, Miguel Garcia, Thomas Stach, 1763 Muthu Perumal, Dan Wing, and Magnus Westerlund for their valuable 1764 comments and inputs to this document. 1766 14. References 1768 14.1. Normative References 1770 [I-D.ietf-siprec-metadata] 1771 R, R., Ravindran, P., and P. Kyzivat, "Session Initiation 1772 Protocol (SIP) Recording Metadata", 1773 draft-ietf-siprec-metadata-08 (work in progress), 1774 October 2012. 1776 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1777 Requirement Levels", BCP 14, RFC 2119, March 1997. 1779 [RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag 1780 Registration Procedure", BCP 31, RFC 2506, March 1999. 1782 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 1783 A., Peterson, J., Sparks, R., Handley, M., and E. 1784 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 1785 June 2002. 1787 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1788 with Session Description Protocol (SDP)", RFC 3264, 1789 June 2002. 1791 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 1792 "Indicating User Agent Capabilities in the Session 1793 Initiation Protocol (SIP)", RFC 3840, August 2004. 1795 [RFC4574] Levin, O. and G. Camarillo, "The Session Description 1796 Protocol (SDP) Label Attribute", RFC 4574, August 2006. 1798 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 1799 Specifications: ABNF", STD 68, RFC 5234, January 2008. 1801 14.2. Informative References 1803 [I-D.ietf-siprec-architecture] 1804 Hutton, A., Portman, L., Jain, R., and K. Rehor, "An 1805 Architecture for Media Recording using the Session 1806 Initiation Protocol", draft-ietf-siprec-architecture-06 1807 (work in progress), September 2012. 1809 [RFC3311] Rosenberg, J., "The Session Initiation Protocol (SIP) 1810 UPDATE Method", RFC 3311, October 2002. 1812 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 1813 Jacobson, "RTP: A Transport Protocol for Real-Time 1814 Applications", STD 64, RFC 3550, July 2003. 1816 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 1817 Video Conferences with Minimal Control", STD 65, RFC 3551, 1818 July 2003. 1820 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 1821 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 1822 RFC 3711, March 2004. 1824 [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session 1825 Description Protocol (SDP) Security Descriptions for Media 1826 Streams", RFC 4568, July 2006. 1828 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 1829 "Extended RTP Profile for Real-time Transport Control 1830 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, 1831 July 2006. 1833 [RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)", 1834 BCP 131, RFC 4961, July 2007. 1836 [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, 1837 "Codec Control Messages in the RTP Audio-Visual Profile 1838 with Feedback (AVPF)", RFC 5104, February 2008. 1840 [RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for 1841 Real-time Transport Control Protocol (RTCP)-Based Feedback 1842 (RTP/SAVPF)", RFC 5124, February 2008. 1844 [RFC5168] Levin, O., Even, R., and P. Hagendorf, "XML Schema for 1845 Media Control", RFC 5168, March 2008. 1847 [RFC5630] Audet, F., "The Use of the SIPS URI Scheme in the Session 1848 Initiation Protocol (SIP)", RFC 5630, October 2009. 1850 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 1851 Control Packets on a Single Port", RFC 5761, April 2010. 1853 [RFC6222] Begen, A., Perkins, C., and D. Wing, "Guidelines for 1854 Choosing RTP Control Protocol (RTCP) Canonical Names 1855 (CNAMEs)", RFC 6222, April 2011. 1857 [RFC6263] Marjou, X. and A. Sollaud, "Application Mechanism for 1858 Keeping Alive the NAT Mappings Associated with RTP / RTP 1859 Control Protocol (RTCP) Flows", RFC 6263, June 2011. 1861 [RFC6341] Rehor, K., Portman, L., Hutton, A., and R. Jain, "Use 1862 Cases and Requirements for SIP-Based Media Recording 1863 (SIPREC)", RFC 6341, August 2011. 1865 Authors' Addresses 1867 Leon Portman 1868 NICE Systems 1869 8 Hapnina 1870 Ra'anana 43017 1871 Israel 1873 Email: leon.portman@nice.com 1875 Henry Lum (editor) 1876 Genesys 1877 1380 Rodick Road, Suite 201 1878 Markham, Ontario L3R4G5 1879 Canada 1881 Email: henry.lum@genesyslab.com 1882 Charles Eckel 1883 Cisco 1884 170 West Tasman Drive 1885 San Jose, CA 95134 1886 United States 1888 Email: eckelcu@cisco.com 1890 Alan Johnston 1891 Avaya 1892 St. Louis, MO 63124 1894 Email: alan.b.johnston@gmail.com 1896 Andrew Hutton 1897 Siemens Enterprise Communications 1898 Brickhill Street 1899 Milton Keynes MK15 0DJ 1900 United Kingdom 1902 Email: andrew.hutton@siemens-enterprise.com