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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-22) exists of draft-ietf-siprec-metadata-17 ** Downref: Normative reference to an Informational RFC: RFC 7245 -- Obsolete informational reference (is this intentional?): RFC 7525 (Obsoleted by RFC 9325) Summary: 1 error (**), 0 flaws (~~), 2 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: January 3, 2016 Genesys 6 C. Eckel 7 Cisco 8 A. Johnston 9 Avaya 10 A. Hutton 11 Unify 12 July 2, 2015 14 Session Recording Protocol 15 draft-ietf-siprec-protocol-17 17 Abstract 19 This document specifies the use of the Session Initiation Protocol 20 (SIP), the Session Description Protocol (SDP), and the Real Time 21 Protocol (RTP) for delivering real-time media and metadata from a 22 Communication Session (CS) to a recording device. The Session 23 Recording Protocol specifies the use of SIP, SDP, and RTP to 24 establish a Recording Session (RS) between the Session Recording 25 Client (SRC), which is on the path of the CS, and a Session Recording 26 Server (SRS) at the recording device. This document considers only 27 active recording, where the SRC purposefully streams media to an SRS 28 and all participating user agents are notified of the recording. 29 Passive recording, where a recording device detects media directly 30 from the network (e.g., using port-mirroring techniques), is outside 31 the scope of this document. In addition, lawful intercept is outside 32 the scope of this document. 34 Status of This Memo 36 This Internet-Draft is submitted in full conformance with the 37 provisions of BCP 78 and BCP 79. 39 Internet-Drafts are working documents of the Internet Engineering 40 Task Force (IETF). Note that other groups may also distribute 41 working documents as Internet-Drafts. The list of current Internet- 42 Drafts is at http://datatracker.ietf.org/drafts/current/. 44 Internet-Drafts are draft documents valid for a maximum of six months 45 and may be updated, replaced, or obsoleted by other documents at any 46 time. It is inappropriate to use Internet-Drafts as reference 47 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on January 3, 2016. 50 Copyright Notice 52 Copyright (c) 2015 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (http://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 68 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 69 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4 70 4. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 71 5. Overview of operations . . . . . . . . . . . . . . . . . . . 5 72 5.1. Delivering recorded media . . . . . . . . . . . . . . . . 5 73 5.2. Delivering recording metadata . . . . . . . . . . . . . . 8 74 5.3. Receiving recording indications and providing recording 75 preferences . . . . . . . . . . . . . . . . . . . . . . . 9 76 6. SIP Handling . . . . . . . . . . . . . . . . . . . . . . . . 11 77 6.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 11 78 6.1.1. Initiating a Recording Session . . . . . . . . . . . 11 79 6.1.2. SIP extensions for recording indication and 80 preference . . . . . . . . . . . . . . . . . . . . . 11 81 6.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 12 82 6.3. Procedures for Recording-aware User Agents . . . . . . . 12 83 7. SDP Handling . . . . . . . . . . . . . . . . . . . . . . . . 13 84 7.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 13 85 7.1.1. SDP handling in RS . . . . . . . . . . . . . . . . . 13 86 7.1.1.1. Handling media stream updates . . . . . . . . . . 14 87 7.1.2. Recording indication in CS . . . . . . . . . . . . . 15 88 7.1.3. Recording preference in CS . . . . . . . . . . . . . 16 89 7.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 16 90 7.3. Procedures for Recording-aware User Agents . . . . . . . 18 91 7.3.1. Recording indication . . . . . . . . . . . . . . . . 18 92 7.3.2. Recording preference . . . . . . . . . . . . . . . . 19 93 8. RTP Handling . . . . . . . . . . . . . . . . . . . . . . . . 20 94 8.1. RTP Mechanisms . . . . . . . . . . . . . . . . . . . . . 20 95 8.1.1. RTCP . . . . . . . . . . . . . . . . . . . . . . . . 20 96 8.1.2. RTP Profile . . . . . . . . . . . . . . . . . . . . . 21 97 8.1.3. SSRC . . . . . . . . . . . . . . . . . . . . . . . . 21 98 8.1.4. CSRC . . . . . . . . . . . . . . . . . . . . . . . . 22 99 8.1.5. SDES . . . . . . . . . . . . . . . . . . . . . . . . 22 100 8.1.5.1. CNAME . . . . . . . . . . . . . . . . . . . . . . 22 101 8.1.6. Keepalive . . . . . . . . . . . . . . . . . . . . . . 22 102 8.1.7. RTCP Feedback Messages . . . . . . . . . . . . . . . 23 103 8.1.7.1. Full Intra Request . . . . . . . . . . . . . . . 23 104 8.1.7.2. Picture Loss Indicator . . . . . . . . . . . . . 23 105 8.1.7.3. Temporary Maximum Media Stream Bit Rate Request . 24 106 8.1.8. Symmetric RTP/RTCP for Sending and Receiving . . . . 24 107 8.2. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 25 108 8.2.1. SRC acting as an RTP Translator . . . . . . . . . . . 26 109 8.2.1.1. Forwarding Translator . . . . . . . . . . . . . . 26 110 8.2.1.2. Transcoding Translator . . . . . . . . . . . . . 26 111 8.2.2. SRC acting as an RTP Mixer . . . . . . . . . . . . . 27 112 8.2.3. SRC acting as an RTP Endpoint . . . . . . . . . . . . 28 113 8.3. RTP Session Usage by SRC . . . . . . . . . . . . . . . . 28 114 8.3.1. SRC Using Multiple m-lines . . . . . . . . . . . . . 28 115 8.3.2. SRC Using Mixing . . . . . . . . . . . . . . . . . . 29 116 8.4. RTP Session Usage by SRS . . . . . . . . . . . . . . . . 30 117 9. Metadata . . . . . . . . . . . . . . . . . . . . . . . . . . 31 118 9.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 31 119 9.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 33 120 9.2.1. Formal Syntax . . . . . . . . . . . . . . . . . . . . 35 121 10. Persistent Recording . . . . . . . . . . . . . . . . . . . . 35 122 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35 123 11.1. Registration of Option Tags . . . . . . . . . . . . . . 35 124 11.1.1. siprec Option Tag . . . . . . . . . . . . . . . . . 36 125 11.1.2. record-aware Option Tag . . . . . . . . . . . . . . 36 126 11.2. Registration of media feature tags . . . . . . . . . . . 36 127 11.2.1. src feature tag . . . . . . . . . . . . . . . . . . 36 128 11.2.2. srs feature tag . . . . . . . . . . . . . . . . . . 37 129 11.3. New Content-Disposition Parameter Registrations . . . . 37 130 11.4. Media Type Registration . . . . . . . . . . . . . . . . 37 131 11.4.1. Registration of MIME Type application/rs-metadata- 132 request . . . . . . . . . . . . . . . . . . . . . . 37 133 11.5. SDP Attributes . . . . . . . . . . . . . . . . . . . . . 38 134 11.5.1. 'record' SDP Attribute . . . . . . . . . . . . . . . 38 135 11.5.2. 'recordpref' SDP Attribute . . . . . . . . . . . . . 38 136 12. Security Considerations . . . . . . . . . . . . . . . . . . . 38 137 12.1. Authentication and Authorization . . . . . . . . . . . . 39 138 12.2. RTP handling . . . . . . . . . . . . . . . . . . . . . . 40 139 12.3. Metadata . . . . . . . . . . . . . . . . . . . . . . . . 40 140 12.4. Storage and playback . . . . . . . . . . . . . . . . . . 41 141 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 41 142 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 41 143 14.1. Normative References . . . . . . . . . . . . . . . . . . 41 144 14.2. Informative References . . . . . . . . . . . . . . . . . 42 145 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43 147 1. Introduction 149 This document specifies the mechanism to record a Communication 150 Session (CS) by delivering real-time media and metadata from the CS 151 to a recording device. In accordance with the architecture 152 [RFC7245], the Session Recording Protocol specifies the use of SIP, 153 SDP, and RTP to establish a Recording Session (RS) between the 154 Session Recording Client (SRC), which is on the path of the CS, and a 155 Session Recording Server (SRS) at the recording device. SIP is also 156 used to deliver metadata to the recording device, as specified in 157 [I-D.ietf-siprec-metadata]. Metadata is information that describes 158 recorded media and the CS to which they relate. The Session 159 Recording Protocol intends to satisfy the SIP-based Media Recording 160 requirements listed in [RFC6341]. In addition to the Session 161 Recording Protocol, this document specifies extensions for user 162 agents that are participants in a CS to receive recording indications 163 and to provide preferences for recording. 165 This document considers only active recording, where the SRC 166 purposefully streams media to an SRS and all participating user 167 agents are notified of the recording. Passive recording, where a 168 recording device detects media directly from the network (e.g., using 169 port-mirroring techniques), is outside the scope of this document. 170 In addition, lawful intercept is outside the scope of this document, 171 in accordance with [RFC2804]. 173 2. Terminology 175 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 176 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 177 document are to be interpreted as described in [RFC2119]. 179 3. Definitions 181 This document refers to the core definitions provided in the 182 architecture document [RFC7245]. 184 The RTP Handling section uses the definitions provided in "RTP: A 185 Transport Protocol for Real-Time Application" [RFC3550]. 187 4. Scope 189 The scope of the Session Recording Protocol includes the 190 establishment of the recording sessions and the reporting of the 191 metadata. The scope also includes extensions supported by User 192 Agents participating in the CS such as indication of recording. The 193 user agents need not be recording-aware in order to participate in a 194 CS being recorded. 196 The following items, which are not an exhaustive list, do not 197 represent the protocol itself and are considered out of the scope of 198 the Session Recording Protocol: 200 o Delivering recorded media in real-time as the CS media 202 o Specifications of criteria to select a specific CS to be recorded 203 or triggers to record a certain CS in the future 205 o Recording policies that determine whether the CS should be 206 recorded and whether parts of the CS are to be recorded 208 o Retention policies that determine how long a recording is stored 210 o Searching and accessing the recorded media and metadata 212 o Policies governing how CS users are made aware of recording 214 o Delivering additional recording session metadata through a non-SIP 215 mechanism 217 5. Overview of operations 219 This section is informative and provides a description of recording 220 operations. 222 Section 6 describes the SIP communication in a recording session 223 between an SRC and an SRS, and the procedures for recording-aware 224 user agents participating in a CS. Section 7 describes the SDP in a 225 recording session, and the procedures for recording indications and 226 recording preferences. Section 8 describes the RTP handling in a 227 recording session. Section 9 describes the mechanism to deliver 228 recording metadata from the SRC to the SRS. 230 As mentioned in the architecture document [RFC7245], there are a 231 number of types of call flows based on the location of the Session 232 Recording Client. The following sample call flows provide a quick 233 overview of the operations between the SRC and the SRS. 235 5.1. Delivering recorded media 237 When a SIP Back-to-Back User Agent (B2BUA) with SRC functionality 238 routes a call from UA(A) to UA(B), the SRC has access to the media 239 path between the user agents. When the SRC is aware that it should 240 be recording the conversation, the SRC can cause the B2BUA to relay 241 the media between UA(A) and UA(B). The SRC then establishes the 242 Recording Session with the SRS and sends replicated media towards the 243 SRS. 245 An endpoint may also have SRC functionality, where the endpoint 246 itself establishes the Recording Session to the SRS. Since the 247 endpoint has access to the media in the Communication Session, the 248 endpoint can send replicated media towards the SRS. 250 The following example call flows shows an SRC establishing a 251 recording session towards an SRS. The first call flow illustrates 252 UA(A) acting as the SRC. The second illustrates a B2BUA acting as 253 the SRC. Note that the SRC can choose when to establish the 254 Recording Session independent of the Communication Session, even 255 though the following call flows suggest that the SRC is establishing 256 the Recording Session (message #5) after the Communication Session is 257 established. 259 UA A/SRC UA B SRS 260 |(1)CS INVITE | | 261 |---------------------->| | 262 | (2) 200 OK | | 263 |<----------------------| | 264 | | | 265 |(3)RS INVITE with SDP | | 266 |--------------------------------------------->| 267 | | (4) 200 OK with SDP | 268 |<---------------------------------------------| 269 |(5)CS RTP | | 270 |======================>| | 271 |<======================| | 272 |(6)RS RTP | | 273 |=============================================>| 274 |=============================================>| 275 | | | 276 |(7)CS BYE | | 277 |---------------------->| | 278 |(8)RS BYE | | 279 |--------------------------------------------->| 280 | | | 282 Figure 1: Basic recording call flow with UA as SRC 284 UA A SRC UA B SRS 285 |(1)CS INVITE | | | 286 |------------->| | | 287 | |(2)CS INVITE | | 288 | |---------------------->| | 289 | | (3) 200 OK | | 290 | |<----------------------| | 291 | (4) 200 OK | | | 292 |<-------------| | | 293 | |(5)RS INVITE with SDP | | 294 | |--------------------------------------------->| 295 | | | (6) 200 OK with SDP | 296 | |<---------------------------------------------| 297 |(7)CS RTP | | | 298 |=============>|======================>| | 299 |<=============|<======================| | 300 | |(8)RS RTP | | 301 | |=============================================>| 302 | |=============================================>| 303 |(9)CS BYE | | | 304 |------------->| | | 305 | |(10)CS BYE | | 306 | |---------------------->| | 307 | |(11)RS BYE | | 308 | |--------------------------------------------->| 309 | | | | 311 Figure 2: Basic recording call flow with B2BUA as SRC 313 The above call flow can also apply to the case of a centralized 314 conference with a mixer. For clarity, ACKs to INVITEs and 200 OKs to 315 BYEs are not shown. The conference focus can provide the SRC 316 functionality since the conference focus has access to all the media 317 from each conference participant. When a recording is requested, the 318 SRC delivers the metadata and the media streams to the SRS. Since 319 the conference focus has access to a mixer, the SRC may choose to mix 320 the media streams from all participants as a single mixed media 321 stream towards the SRS. 323 An SRC can use a single recording session to record multiple 324 communication sessions. Every time the SRC wants to record a new 325 call, the SRC updates the recording session with a new SDP offer to 326 add new recorded streams to the recording session, and 327 correspondingly also update the metadata for the new call. 329 An SRS can also establish a recording session to an SRC, although it 330 is beyond the scope of this document to define how an SRS would 331 specify which calls to record. 333 5.2. Delivering recording metadata 335 The SRC is responsible for the delivery of metadata to the SRS. The 336 SRC may provide an initial metadata snapshot about recorded media 337 streams in the initial INVITE content in the recording session. 338 Subsequent metadata updates can be represented as a stream of events 339 in UPDATE [RFC3311] or reINVITE requests sent by the SRC. These 340 metadata updates are normally incremental updates to the initial 341 metadata snapshot to optimize on the size of updates. However, the 342 SRC may also decide to send a new metadata snapshot any time. 344 Metadata is transported in the body of INVITE or UPDATE messages. 345 Certain metadata, such as the attributes of the recorded media 346 stream, are located in the SDP of the recording session. 348 The SRS has the ability to send a request to the SRC to request for a 349 new metadata snapshot update from the SRC. This can happen when the 350 SRS fails to understand the current stream of incremental updates for 351 whatever reason, for example, when the SRS loses the current state 352 due to internal failure. The SRS may optionally attach a reason 353 along with the snapshot request. This request allows both SRC and 354 SRS to synchronize the states with a new metadata snapshot so that 355 further metadata incremental updates will be based on the latest 356 metadata snapshot. Similar to the metadata content, the metadata 357 snapshot request is transported as content in UPDATE or INVITE sent 358 by the SRS in the recording session. 360 SRC SRS 361 | | 362 |(1) INVITE (metadata snapshot 1) | 363 |---------------------------------------------------->| 364 | (2)200 OK | 365 |<----------------------------------------------------| 366 |(3) ACK | 367 |---------------------------------------------------->| 368 |(4) RTP | 369 |====================================================>| 370 |====================================================>| 371 |(5) UPDATE (metadata update 1) | 372 |---------------------------------------------------->| 373 | (6) 200 OK | 374 |<----------------------------------------------------| 375 |(7) UPDATE (metadata update 2) | 376 |---------------------------------------------------->| 377 | (8) 200 OK | 378 |<----------------------------------------------------| 379 | (9) UPDATE (metadata snapshot request) | 380 |<----------------------------------------------------| 381 | (10) 200 OK | 382 |---------------------------------------------------->| 383 | (11) INVITE (metadata snapshot 2 + SDP offer) | 384 |---------------------------------------------------->| 385 | (12) 200 OK (SDP answer) | 386 |<----------------------------------------------------| 387 | (13) UPDATE (metadata update 1 based on snapshot 2) | 388 |---------------------------------------------------->| 389 | (14) 200 OK | 390 |<----------------------------------------------------| 392 Figure 3: Delivering metadata via SIP UPDATE 394 5.3. Receiving recording indications and providing recording 395 preferences 397 The SRC is responsible to provide recording indications to the 398 participants in the CS. A recording-aware UA supports receiving 399 recording indications via the SDP attribute a=record, and it can 400 specify a recording preference in the CS by including the SDP 401 attribute a=recordpref. The recording attribute is a declaration by 402 the SRC in the CS to indicate whether recording is taking place. The 403 recording preference attribute is a declaration by the recording- 404 aware UA in the CS to indicate its recording preference. A UA that 405 does not want to be recorded may still be notified recording is 406 occurring for a number of reasons (e.g., it was not capable of 407 indicating its preference, its preference was ignored, etc.) If this 408 occurs, the UA's only mechanism to avoid being recorded is to 409 terminate its participation in the session. 411 To illustrate how the attributes are used, if a UA (A) is initiating 412 a call to UA (B) and UA (A) is also an SRC that is performing the 413 recording, then UA (A) provides the recording indication in the SDP 414 offer with a=record:on. Since UA (A) is the SRC, UA (A) receives the 415 recording indication from the SRC directly. When UA (B) receives the 416 SDP offer, UA (B) will see that recording is happening on the other 417 endpoint of this session. Since UA (B) is not an SRC and does not 418 provide any recording preference, the SDP answer does not contain 419 a=record nor a=recordpref. 421 UA A UA B 422 (SRC) | 423 | | 424 | [SRC recording starts] | 425 |(1) INVITE (SDP offer + a=record:on) | 426 |---------------------------------------------------->| 427 | (2) 200 OK (SDP answer) | 428 |<----------------------------------------------------| 429 |(3) ACK | 430 |---------------------------------------------------->| 431 |(4) RTP | 432 |<===================================================>| 433 | | 434 | [UA B wants to set preference to no recording] | 435 | (5) INVITE (SDP offer + a=recordpref:off) | 436 |<----------------------------------------------------| 437 | [SRC honors the preference and stops recording] | 438 |(6) 200 OK (SDP answer + a=record:off) | 439 |---------------------------------------------------->| 440 | (7) ACK | 441 |<----------------------------------------------------| 443 Figure 4: Recording indication and recording preference 445 After the call is established and recording is in progress, UA (B) 446 later decides to change the recording preference to no recording and 447 sends a reINVITE with the a=recordpref attribute. It is up to the 448 SRC to honor the preference, and in this case SRC decides to stop the 449 recording and updates the recording indication in the SDP answer. 451 Note that UA (B) could have explicitly indicated a recording 452 preference in (2), the 200 OK for the original INVITE. Indicating a 453 preference of no recording in an initial INVITE or an initial 454 response to an INVITE may reduce the chance of a user being recorded 455 in the first place. 457 6. SIP Handling 459 6.1. Procedures at the SRC 461 6.1.1. Initiating a Recording Session 463 A recording session is a SIP session with specific extensions 464 applied, and these extensions are listed in the procedures for SRC 465 and SRS below. When an SRC or an SRS receives a SIP session that is 466 not a recording session, it is up to the SRC or the SRS to determine 467 what to do with the SIP session. 469 The SRC can initiate a recording session by sending a SIP INVITE 470 request to the SRS. The SRC and the SRS are identified in the From 471 and To headers, respectively. 473 The SRC MUST include the '+sip.src' feature tag in the Contact URI, 474 defined in this specification as an extension to [RFC3840], for all 475 recording sessions. An SRS uses the presence of the '+sip.src' 476 feature tag in dialog creating and modifying requests and responses 477 to confirm that the dialog being created is for the purpose of a 478 Recording Session. In addition, when an SRC sends a REGISTER request 479 to a registrar, the SRC MAY include the '+sip.src' feature tag to 480 indicate the that it is an SRC. 482 Since SIP Caller Preferences extensions are optional to implement for 483 routing proxies, there is no guarantee that a recording session will 484 be routed to an SRC or SRS. A new options tag is introduced: 485 "siprec". As per [RFC3261], only an SRC or an SRS can accept this 486 option tag in a recording session. An SRC MUST include the "siprec" 487 option tag in the Require header when initiating a Recording Session 488 so that UA's which do not support the session recording protocol 489 extensions will simply reject the INVITE request with a 420 Bad 490 Extension. 492 When an SRC receives a new INVITE, the SRC MUST only consider the SIP 493 session as a recording session when both the '+sip.srs' feature tag 494 and 'siprec' option tag are included in the INVITE request. 496 6.1.2. SIP extensions for recording indication and preference 498 For the communication session, the SRC MUST provide recording 499 indications to all participants in the CS. A participant UA in a CS 500 can indicate that it is recording-aware by providing the "record- 501 aware" option tag, and the SRC MUST provide recording indications in 502 the new SDP a=record attribute described in the SDP Handling section. 503 In the absence of the "record-aware" option tag, meaning that the 504 participant UA is not recording-aware, an SRC MUST provide recording 505 indications through other means, such as playing a tone in-band, 506 having a signed participant contract in place, etc. 508 An SRC in the CS may also indicate itself as a session recording 509 client by including the '+sip.src' feature tag. A recording-aware 510 participant can learn that an SRC is in the CS, and can set the 511 recording preference for the CS with the new SDP a=recordpref 512 attribute described in the SDP Handling section below. 514 6.2. Procedures at the SRS 516 When an SRS receives a new INVITE, the SRS MUST only consider the SIP 517 session as a recording session when both the '+sip.src' feature tag 518 and 'siprec' option tag are included in the INVITE request. 520 The SRS can initiate a recording session by sending a SIP INVITE 521 request to the SRC. The SRS and the SRC are identified in the From 522 and To headers, respectively. 524 The SRS MUST include the '+sip.srs' feature tag in the Contact URI, 525 as per [RFC3840], for all recording sessions. An SRC uses the 526 presence of this feature tag in dialog creating and modifying 527 requests and responses to confirm that the dialog being created is 528 for the purpose of a Recording Session (REQ-30). In addition, when 529 an SRS sends a REGISTER request to a registrar, the SRS SHOULD 530 include the '+sip.srs' feature tag to indicate that it is an SRS. 532 An SRS MUST include the "siprec" option tag in the Require header as 533 per [RFC3261] when initiating a Recording Session so that UA's which 534 do not support the session recording protocol extensions will simply 535 reject the INVITE request with a 420 Bad Extension. 537 6.3. Procedures for Recording-aware User Agents 539 A recording-aware user agent is a participant in the CS that supports 540 the SIP and SDP extensions for receiving recording indications and 541 for requesting recording preferences for the call. A recording-aware 542 UA MUST indicate that it can accept reporting of recording indication 543 provided by the SRC with a new option tag "record-aware" when 544 initiating or establishing a CS, meaning including the "record-aware" 545 tag in the Supported header in the initial INVITE request or 546 response. 548 A recording-aware UA MUST provide a recording indication to the end 549 user through an appropriate user interface, indicating whether 550 recording is on, off, or paused for each medium. Appropriate user 551 interfaces may include real-time notification or previously 552 established agreements that use of the device is subject to 553 recording. Some user agents that are automatons (e.g., IVR, media 554 server, PSTN gateway) may not have a user interface to render 555 recording indication. When such a user agent indicates recording 556 awareness, the UA SHOULD render recording indication through other 557 means, such as passing an in-band tone on the PSTN gateway, putting 558 the recording indication in a log file, or raising an application 559 event in a VoiceXML dialog. These user agents MAY also choose not to 560 indicate recording awareness, thereby relying on whatever mechanism 561 an SRC chooses to indicate recording, such as playing a tone in-band. 563 7. SDP Handling 565 7.1. Procedures at the SRC 567 The SRC and SRS follows the SDP offer/answer model in [RFC3264]. The 568 procedures for SRC and SRS describe the conventions used in a 569 recording session. 571 7.1.1. SDP handling in RS 573 Since the SRC does not expect to receive media from the SRS, the SRC 574 typically sets each media stream of the SDP offer to only send media, 575 by qualifying them with the a=sendonly attribute, according to the 576 procedures in [RFC3264]. 578 The SRC sends recorded streams of participants to the SRS, and the 579 SRC MUST provide a label attribute (a=label), as per [RFC4574], on 580 each media stream in order to identify the recorded stream with the 581 rest of the metadata. The a=label attribute identifies each recorded 582 media stream, and the label name is mapped to the Media Stream 583 Reference in the metadata as per [I-D.ietf-siprec-metadata]. The 584 scope of the a=label attribute only applies to the SDP and Metadata 585 conveyed in the bodies of the SIP request or response that the label 586 appeared in. Note that a recorded stream is distinct from a CS 587 stream; the metadata provides a list of participants that contribute 588 to each recorded stream. 590 The following is an example SDP offer from an SRC with both audio and 591 video recorded streams. Note that the following example contains 592 unfolded lines longer than 72 characters. These are captured between 593 tags. 595 v=0 596 o=SRC 2890844526 2890844526 IN IP4 198.51.100.1 597 s=- 598 c=IN IP4 198.51.100.1 599 t=0 0 600 m=audio 12240 RTP/AVP 0 4 8 601 a=sendonly 602 a=label:1 603 m=video 22456 RTP/AVP 98 604 a=rtpmap:98 H264/90000 605 606 a=fmtp:98 profile-level-id=42A01E; 607 sprop-parameter-sets=Z0IACpZTBYmI,aMljiA== 608 609 a=sendonly 610 a=label:2 611 m=audio 12242 RTP/AVP 0 4 8 612 a=sendonly 613 a=label:3 614 m=video 22458 RTP/AVP 98 615 a=rtpmap:98 H264/90000 616 617 a=fmtp:98 profile-level-id=42A01E; 618 sprop-parameter-sets=Z0IACpZTBYmI,aMljiA== 619 620 a=sendonly 621 a=label:4 623 Figure 5: Sample SDP offer from SRC with audio and video streams 625 7.1.1.1. Handling media stream updates 627 Over the lifetime of a recording session, the SRC can add and remove 628 recorded streams from the recording session for various reasons. For 629 example, when a CS stream is added or removed from the CS, or when a 630 CS is created or terminated if a recording session handles multiple 631 CSes. To remove a recorded stream from the recording session, the 632 SRC sends a new SDP offer where the port of the media stream to be 633 removed is set to zero, according to the procedures in [RFC3264]. To 634 add a recorded stream to the recording session, the SRC sends a new 635 SDP offer by adding a new media stream description or by reusing an 636 old media stream which had been previously disabled, according to the 637 procedures in [RFC3264]. 639 The SRC can temporarily discontinue streaming and collection of 640 recorded media from the SRC to the SRS for reasons such as masking 641 the recording. In this case, the SRC sends a new SDP offer and sets 642 the media stream to inactive (a=inactive) for each recorded stream to 643 be paused, as per the procedures in [RFC3264]. To resume streaming 644 and collection of recorded media, the SRC sends a new SDP offer and 645 sets the media stream to sendonly (a=sendonly). Note that a CS 646 itself may change the media stream direction by updating the SDP, for 647 example, by setting a=inactive for SDP hold. Media stream direction 648 changes in CS are conveyed in the metadata by the SRC. When a CS 649 media stream is changed to/from inactive, the effect on the 650 corresponding RS media stream is governed by SRC policy. The SRC MAY 651 have a local policy to pause an RS media stream when the 652 corresponding CS media stream is inactive, or it MAY leave the RS 653 media stream as sendonly. 655 7.1.2. Recording indication in CS 657 While there are existing mechanisms for providing an indication that 658 a CS is being recorded, these mechanisms are usually delivered on the 659 CS media streams such as playing an in-band tone or an announcement 660 to the participants. A new 'record' SDP attribute is introduced to 661 allow the SRC to indicate recording state to a recording-aware UA in 662 a CS. 664 The 'record' SDP attribute appears at the media-level or session- 665 level in either SDP offer or answer. When the attribute is applied 666 at the session-level, the indication applies to all media streams in 667 the SDP. When the attribute is applied at the media-level, the 668 indication applies to the media stream only, and that overrides the 669 indication if also set at the session-level. Whenever the recording 670 indication needs to change, such as termination of recording, then 671 the SRC MUST initiate a reINVITE or UPDATE to update the SDP a=record 672 attribute. 674 The following is the ABNF of the 'record' attribute: 676 attribute =/ record-attr 677 ; attribute defined in RFC 4566 679 record-attr = "record:" indication 680 indication = "on" / "off" / "paused" 682 on: Recording is in progress. 684 off: No recording is in progress. 686 paused: Recording is in progress but media is paused. 688 7.1.3. Recording preference in CS 690 When the SRC receives the a=recordpref SDP in an SDP offer or answer, 691 the SRC chooses to honor the preference to record based on local 692 policy at the SRC. If the SRC makes a change in recording state, the 693 SRC MUST report the new recording state in the a=record attribute in 694 the SDP answer or in a subsequent SDP offer. 696 7.2. Procedures at the SRS 698 Typically the SRS only receives RTP streams from the SRC; therefore, 699 the SDP offer/answer from the SRS normally sets each media stream to 700 receive media, by setting them with the a=recvonly attribute, 701 according to the procedures of [RFC3264]. When the SRS is not ready 702 to receive a recorded stream, the SRS sets the media stream as 703 inactive in the SDP offer or answer by setting it with an a=inactive 704 attribute, according to the procedures of [RFC3264]. When the SRS is 705 ready to receive recorded streams, the SRS sends a new SDP offer and 706 sets the media streams with an a=recvonly attribute. 708 The following is an example of an SDP answer from the SRS for the SDP 709 offer from the above sample. Note that the following example contain 710 unfolded lines longer than 72 characters. These are captured between 711 tags. 713 v=0 714 o=SRS 0 0 IN IP4 198.51.100.20 715 s=- 716 c=IN IP4 198.51.100.20 717 t=0 0 718 m=audio 10000 RTP/AVP 0 719 a=recvonly 720 a=label:1 721 m=video 10002 RTP/AVP 98 722 a=rtpmap:98 H264/90000 723 724 a=fmtp:98 profile-level-id=42A01E; 725 sprop-parameter-sets=Z0IACpZTBYmI,aMljiA== 726 727 a=recvonly 728 a=label:2 729 m=audio 10004 RTP/AVP 0 730 a=recvonly 731 a=label:3 732 m=video 10006 RTP/AVP 98 733 a=rtpmap:98 H264/90000 734 735 a=fmtp:98 profile-level-id=42A01E; 736 sprop-parameter-sets=Z0IACpZTBYmI,aMljiA== 737 738 a=recvonly 739 a=label:4 741 Figure 6: Sample SDP answer from SRS with audio and video streams 743 Over the lifetime of a recording session, the SRS can remove recorded 744 streams from the recording session for various reasons. To remove a 745 recorded stream from the recording session, the SRS sends a new SDP 746 offer where the port of the media stream to be removed is set to 747 zero, according to the procedures in [RFC3264]. 749 The SRS MUST NOT add recorded streams in the recording session when 750 the SRS sends a new SDP offer. Similarly, when the SRS starts a 751 recording session, the SRS MUST initiate the INVITE without an SDP 752 offer to let the SRC generate the SDP offer with the streams to be 753 recorded. 755 The following sequence diagram shows an example where the SRS is 756 initially not ready to receive recorded streams, and later updates 757 the recording session when the SRS is ready to record. 759 SRC SRS 760 | | 761 |(1) INVITE (SDP offer) | 762 |---------------------------------------------------->| 763 | [not ready to record] 764 | (2)200 OK with SDP inactive | 765 |<----------------------------------------------------| 766 |(3) ACK | 767 |---------------------------------------------------->| 768 | ... | 769 | [ready to record] 770 | (4) re-INVITE with SDP recvonly | 771 |<----------------------------------------------------| 772 |(5)200 OK with SDP sendonly | 773 |---------------------------------------------------->| 774 | (6) ACK | 775 |<----------------------------------------------------| 776 |(7) RTP | 777 |====================================================>| 778 | ... | 779 |(8) BYE | 780 |---------------------------------------------------->| 781 | (9) OK | 782 |<----------------------------------------------------| 784 Figure 7: SRS responding to offer with a=inactive 786 7.3. Procedures for Recording-aware User Agents 788 7.3.1. Recording indication 790 When a recording-aware UA receives an SDP offer or answer that 791 includes the a=record attribute, the UA provides an indication to the 792 end user whether the recording is on, off, or paused for each medium 793 based on the most recently received a=record SDP attribute for that 794 medium. 796 When a CS is traversed through multiple UAs such as a B2BUA or a 797 conference focus, each UA involved in the CS that is aware that the 798 CS is being recorded MUST provide the recording indication through 799 the a=record attribute to all other parties in the CS. 801 It is possible that more than one SRC is in the call path of the same 802 CS, but the recording indication attribute does not provide any hint 803 as to which SRC or how many SRCs are recording. An endpoint knows 804 only that the call is being recorded. Furthermore, this attribute is 805 not used as a request for a specific SRC to start/stop recording. 807 7.3.2. Recording preference 809 A participant in a CS MAY set the recording preference in the CS to 810 be recorded or not recorded at session establishment or during the 811 session. A new 'recordpref' SDP attribute is introduced, and the 812 participant in CS may set this recording preference attribute in any 813 SDP offer/answer at session establishment time or during the session. 814 The SRC is not required to honor the recording preference from a 815 participant based on local policies at the SRC, and the participant 816 can learn the recording indication through the a=record SDP attribute 817 as described in the above section. 819 The SDP a=recordpref attribute can appear at the media-level or 820 session-level and can appear in an SDP offer or answer. When the 821 attribute is applied at the session-level, the recording preference 822 applies to all media stream in the SDP. When the attribute is 823 applied at the media-level, the recording preference applies to the 824 media stream only, and that overrides the recording preference if 825 also set at the session-level. The user agent can change the 826 recording preference by changing the a=recordpref attribute in 827 subsequent SDP offer or answer. The absence of the a=recordpref 828 attribute in the SDP indicates that the UA has no recording 829 preference. 831 The following is the ABNF of the recordpref attribute: 833 attribute =/ recordpref-attr 834 ; attribute defined in RFC 4566 836 recordpref-attr = "a=recordpref:" pref 837 pref = "on" / "off" / "pause" / "nopreference" 839 on: Sets the preference to record if it has not already been 840 started. If the recording is currently paused, the preference is 841 to resume recording. 843 off: Sets the preference for no recording. If recording has already 844 been started, then the preference is to stop the recording. 846 pause: If the recording is currently in progress, sets the 847 preference to pause the recording. 849 nopreference: To indicate that the UA has no preference on 850 recording. 852 8. RTP Handling 854 This section provides recommendations and guidelines for RTP and RTCP 855 in the context of SIPREC. In order to communicate most effectively, 856 the Session Recording Client (SRC), the Session Recording Server 857 (SRS), and any Recording-aware User Agents (UAs) should utilize the 858 mechanisms provided by RTP in a well-defined and predicable manner. 859 It is the goal of this document to make the reader aware of these 860 mechanisms and provide recommendations and guidelines. 862 8.1. RTP Mechanisms 864 This section briefly describes important RTP/RTCP constructs and 865 mechanisms that are particularly useful within the context of SIPREC. 867 8.1.1. RTCP 869 The RTP data transport is augmented by a control protocol (RTCP) to 870 allow monitoring of the data delivery. RTCP, as defined in 871 [RFC3550], is based on the periodic transmission of control packets 872 to all participants in the RTP session, using the same distribution 873 mechanism as the data packets. Support for RTCP is REQUIRED, per 874 [RFC3550], and it provides, among other things, the following 875 important functionality in relation to SIPREC: 877 1) Feedback on the quality of the data distribution 879 This feedback from the receivers may be used to diagnose faults in 880 the distribution. As such, RTCP is a well-defined and efficient 881 mechanism for the SRS to inform the SRC, and for the SRC to inform 882 Recording-aware UAs, of issues that arise with respect to the 883 reception of media that is to be recorded. 885 2) Carries a persistent transport-level identifier for an RTP source 886 called the canonical name or CNAME 888 The SSRC identifier may change if a conflict is discovered or a 889 program is restarted, in which case receivers can use the CNAME to 890 keep track of each participant. Receivers may also use the CNAME to 891 associate multiple data streams from a given participant in a set of 892 related RTP sessions, for example to synchronize audio and video. 893 Synchronization of media streams is also facilitated by the NTP and 894 RTP timestamps included in RTCP packets by data senders. 896 8.1.2. RTP Profile 898 The RECOMMENDED RTP profiles for the SRC, SRS, and Recording-aware 899 UAs are "Extended Secure RTP Profile for Real-time Transport Control 900 Protocol (RTCP)-Based Feedback (RTP/SAVPF)" [RFC5124], when using 901 encrypted RTP streams, and "Extended RTP Profile for Real-time 902 Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF)" 903 [RFC4585], when using non-encrypted media streams. However, as these 904 are not requirements, some implementations may use "The Secure Real- 905 time Transport Protocol (SRTP)" [RFC3711], and "RTP Profile for Audio 906 and Video Conferences with Minimal Control" [RFC3551]. Therefore, it 907 is RECOMMENDED that the SRC, SRS, and Recording-aware UAs not rely 908 entirely on RTP/SAVPF or RTP/AVPF for core functionality that may be 909 at least partially achievable using RTP/SAVP and RTP/AVP. 911 AVPF and SAVPF provide an improved RTCP timer model that allows more 912 flexible transmission of RTCP packets in response to events, rather 913 than strictly according to bandwidth. AVPF-based codec control 914 messages provide efficient mechanisms for an SRC, SRS, and Recording- 915 aware UAs to handle events such as scene changes, error recovery, and 916 dynamic bandwidth adjustments. These messages are discussed in more 917 detail later in this document. 919 SAVP and SAVPF provide media encryption, integrity protection, replay 920 protection, and a limited form of source authentication. They do not 921 contain or require a specific keying mechanism. 923 8.1.3. SSRC 925 The synchronization source (SSRC), as defined in [RFC3550], is 926 carried in the RTP header and in various fields of RTCP packets. It 927 is a random 32-bit number that is required to be globally unique 928 within an RTP session. It is crucial that the number be chosen with 929 care in order that participants on the same network or starting at 930 the same time are not likely to choose the same number. Guidelines 931 regarding SSRC value selection and conflict resolution are provided 932 in [RFC3550]. 934 The SSRC may also be used to separate different sources of media 935 within a single RTP session. For this reason as well as for conflict 936 resolution, it is important that the SRC, SRS, and Recording-aware 937 UAs handle changes in SSRC values and properly identify the reason of 938 the change. The CNAME values carried in RTCP facilitate this 939 identification. 941 8.1.4. CSRC 943 The contributing source (CSRC), as defined in [RFC3550], identifies 944 the source of a stream of RTP packets that has contributed to the 945 combined stream produced by an RTP mixer. The mixer inserts a list 946 of the SSRC identifiers of the sources that contributed to the 947 generation of a particular packet into the RTP header of that packet. 948 This list is called the CSRC list. It is RECOMMENDED that an SRC or 949 Recording-aware UA, when acting as a mixer, set the CSRC list 950 accordingly, and that the SRC and SRS interpret the CSRC list per 951 [RFC3550] when received. 953 8.1.5. SDES 955 The Source Description (SDES), as defined in [RFC3550], contains an 956 SSRC/CSRC identifier followed by a list of zero or more items, which 957 carry information about the SSRC/CSRC. End systems send one SDES 958 packet containing their own source identifier (the same as the SSRC 959 in the fixed RTP header). A mixer sends one SDES packet containing a 960 chunk for each contributing source from which it is receiving SDES 961 information, or multiple complete SDES packets if there are more than 962 31 such sources. 964 The ability to identify individual contributing sources is important 965 in the context of SIPREC. Metadata [I-D.ietf-siprec-metadata] 966 provides a mechanism to achieve this at the signaling level. SDES 967 provides a mechanism at the RTP level. 969 8.1.5.1. CNAME 971 The Canonical End-Point Identifier (CNAME), as defined in [RFC3550], 972 provides the binding from the SSRC identifier to an identifier for 973 the source (sender or receiver) that remains constant. It is 974 important the SRC and Recording-aware UAs generate CNAMEs 975 appropriately and that the SRC and SRS interpret and use them for 976 this purpose. Guidelines for generating CNAME values are provided in 977 "Guidelines for Choosing RTP Control Protocol (RTCP) Canonical Names 978 (CNAMEs)" [RFC7022]. 980 8.1.6. Keepalive 982 It is anticipated that media streams in SIPREC may exist in an 983 inactive state for extended periods of times for any of a number of 984 valid reasons. In order for the bindings and any pinholes in NATs/ 985 firewalls to remain active during such intervals, it is RECOMMENDED 986 that the SRC, SRS, and Recording-aware UAs follow the keep-alive 987 procedure recommended in "Application Mechanism for Keeping Alive the 988 NAT Mappings Associated to RTP/RTP Control Protocol (RTCP) Flows" 989 [RFC6263] for all RTP media streams. 991 8.1.7. RTCP Feedback Messages 993 "Codec Control Messages in the RTP Audio-Visual Profile with Feedback 994 (AVPF)" [RFC5104] specifies extensions to the messages defined in 995 AVPF [RFC4585]. Support for and proper usage of these messages is 996 important to SRC, SRS, and Recording-aware UA implementations. Note 997 that these messages are applicable only when using the AVPF or SAVPF 998 RTP profiles 1000 8.1.7.1. Full Intra Request 1002 A Full Intra Request (FIR) Command, when received by the designated 1003 media sender, requires that the media sender sends a Decoder Refresh 1004 Point at the earliest opportunity. Using a decoder refresh point 1005 implies refraining from using any picture sent prior to that point as 1006 a reference for the encoding process of any subsequent picture sent 1007 in the stream. 1009 Decoder refresh points, especially Intra or IDR pictures for H.264 1010 video codecs, are in general several times larger in size than 1011 predicted pictures. Thus, in scenarios in which the available bit 1012 rate is small, the use of a decoder refresh point implies a delay 1013 that is significantly longer than the typical picture duration. 1015 8.1.7.1.1. SIP INFO for FIR 1017 "XML Schema for Media Control" [RFC5168] defines an Extensible Markup 1018 Language (XML) Schema for video fast update. Implementations are 1019 discouraged from using the method described except for backward 1020 compatibility purposes. Implementations SHOULD use FIR messages 1021 instead. 1023 To make sure a common mechanism exists between the SRC and SRS, the 1024 SRS MUST support both mechanisms (FIR and SIP INFO), using FIR when 1025 negotiated successfully with the SRC, and using SIP INFO otherwise. 1027 8.1.7.2. Picture Loss Indicator 1029 Picture Loss Indication (PLI), as defined in [RFC4585], informs the 1030 encoder of the loss of an undefined amount of coded video data 1031 belonging to one or more pictures. [RFC4585] recommends using PLI 1032 instead of FIR to recover from errors. FIR is appropriate only in 1033 situations where not sending a decoder refresh point would render the 1034 video unusable for the users. Examples where sending FIR is 1035 appropriate include a multipoint conference when a new user joins the 1036 conference and no regular decoder refresh point interval is 1037 established, and a video switching MCU that changes streams. 1039 Appropriate use of PLI and FIR is important to ensure with minimum 1040 overhead that the recorded video is usable (e.g., the necessary 1041 reference frames exist for a player to render the recorded video). 1043 8.1.7.3. Temporary Maximum Media Stream Bit Rate Request 1045 A receiver, translator, or mixer uses the Temporary Maximum Media 1046 Stream Bit Rate Request (TMMBR) to request a sender to limit the 1047 maximum bit rate for a media stream to the provided value. 1048 Appropriate use of TMMBR facilitates rapid adaptation to changes in 1049 available bandwidth. 1051 8.1.7.3.1. Renegotiation of SDP bandwidth attribute 1053 If it is likely that the new value indicated by TMMBR will be valid 1054 for the remainder of the session, the TMMBR sender is expected to 1055 perform a renegotiation of the session upper limit using the session 1056 signaling protocol. Therefore for SIPREC, implementations are 1057 RECOMMENDED to use TMMBR for temporary changes, and renegotiation of 1058 bandwidth via SDP offer/answer for more permanent changes. 1060 8.1.8. Symmetric RTP/RTCP for Sending and Receiving 1062 Within an SDP offer/answer exchange, RTP entities choose the RTP and 1063 RTCP transport addresses (i.e., IP addresses and port numbers) on 1064 which to receive packets. When sending packets, the RTP entities may 1065 use the same source port or a different source port as those signaled 1066 for receiving packets. When the transport address used to send and 1067 receive RTP is the same, it is termed "symmetric RTP" [RFC4961]. 1068 Likewise, when the transport address used to send and receive RTCP is 1069 the same, it is termed "symmetric RTCP" [RFC4961]. 1071 When sending RTP, it is REQUIRED to use symmetric RTP. When sending 1072 RTCP, it is REQUIRED to use symmetric RTCP. Although an SRS will not 1073 normally send RTP, it will send RTCP as well as receive RTP and RTCP. 1074 Likewise, although an SRC will not normally receive RTP from the SRS, 1075 it will receive RTCP as well as send RTP and RTCP. 1077 Note: Symmetric RTP and symmetric RTCP are different from RTP/RTCP 1078 multiplexing [RFC5761]. 1080 8.2. Roles 1082 An SRC has the task of gathering media from the various UAs in one or 1083 more Communication Sessions (CSs) and forwarding the information to 1084 the SRS within the context of a corresponding Recording Session (RS). 1085 There are numerous ways in which an SRC may do this, including but 1086 not limited to appearing as a UA within a CS, or as a B2BUA between 1087 UAs within a CS. 1089 (Recording Session) +---------+ 1090 +------------SIP------->| | 1091 | +------RTP/RTCP----->| SRS | 1092 | | +-- Metadata -->| | 1093 | | | +---------+ 1094 v v | 1095 +---------+ 1096 | SRC | 1097 |---------| (Communication Session) +---------+ 1098 | |<----------SIP---------->| | 1099 | UA-A | | UA-B | 1100 | |<-------RTP/RTCP-------->| | 1101 +---------+ +---------+ 1103 Figure 8: UA as SRC 1105 (Recording Session) +---------+ 1106 +------------SIP------->| | 1107 | +------RTP/RTCP----->| SRS | 1108 | | +-- Metadata -->| | 1109 | | | +---------+ 1110 v v | 1111 +---------+ 1112 | SRC | 1113 +---------+ |---------| +---------+ 1114 | |<----SIP----->| |<----SIP----->| | 1115 | UA-A | | B2BUA | | UA-B | 1116 | |<--RTP/RTCP-->| |<--RTP/RTCP-->| | 1117 +---------+ +---------+ +---------+ 1118 |_______________________________________________| 1119 (Communication Session) 1121 Figure 9: B2BUA as SRC 1123 The following subsections define a set of roles an SRC may choose to 1124 play based on its position with respect to a UA within a CS, and an 1125 SRS within an RS. A CS and a corresponding RS are independent 1126 sessions; therefore, an SRC may play a different role within a CS 1127 than it does within the corresponding RS. 1129 8.2.1. SRC acting as an RTP Translator 1131 The SRC may act as a translator, as defined in [RFC3550]. A defining 1132 characteristic of a translator is that it forwards RTP packets with 1133 their SSRC identifier intact. There are two types of translators, 1134 one that simply forwards, and another that performs transcoding 1135 (e.g., from one codec to another) in addition to forwarding. 1137 8.2.1.1. Forwarding Translator 1139 When acting as a forwarding translator, RTP received as separate 1140 streams from different sources (e.g., from different UAs with 1141 different SSRCs) cannot be mixed by the SRC and MUST be sent 1142 separately to the SRS. All RTCP reports MUST be passed by the SRC 1143 between the UAs and the SRS, such that the UAs and SRS are able to 1144 detect any SSRC collisions. 1146 RTCP Sender Reports generated by a UA sending a stream MUST be 1147 forwarded to the SRS. RTCP Receiver Reports generated by the SRS 1148 MUST be forwarded to the relevant UA. 1150 UAs may receive multiple sets of RTCP Receiver Reports, one or more 1151 from other UAs participating in the CS, and one from the SRS 1152 participating in the RS. A UA SHOULD process the RTCP Receiver 1153 Reports from the SRS if it is recording-aware. 1155 If SRTP is used on both the CS and the RS, decryption and/or re- 1156 encryption may occur. For example, if different keys are used, it 1157 will occur. If the same keys are used, it need not occur. 1158 Section 12 provides additional information on SRTP and keying 1159 mechanisms. 1161 If packet loss occurs, either from the UA to the SRC or from the SRC 1162 to the SRS, the SRS SHOULD detect and attempt to recover from the 1163 loss. The SRC does not play a role in this other than forwarding the 1164 associated RTP and RTCP packets. 1166 8.2.1.2. Transcoding Translator 1168 When acting as a transcoding translator, an SRC MAY perform 1169 transcoding (e.g., from one codec to another), and this may result in 1170 a different rate of packets between what the SRC receives on the CS 1171 and what the SRC sends on the RS. As when acting as a forwarding 1172 translator, RTP received as separate streams from different sources 1173 (e.g., from different UAs with different SSRCs) cannot be mixed by 1174 the SRC and MUST be sent separately to the SRS. All RTCP reports 1175 MUST be passed by the SRC between the UAs and the SRS, such that the 1176 UAs and SRS are able to detect any SSRC collisions. 1178 RTCP Sender Reports generated by a UA sending a stream MUST be 1179 forwarded to the SRS. RTCP Receiver Reports generated by the SRS 1180 MUST be forwarded to the relevant UA. The SRC may need to manipulate 1181 the RTCP Receiver Reports to take account of any transcoding that has 1182 taken place. 1184 UAs may receive multiple sets of RTCP Receiver Reports, one or more 1185 from other UAs participating in the CS, and one from the SRS 1186 participating in the RS. A Recording-aware UA SHOULD be prepared to 1187 process the RTCP Receiver Reports from the SRS, whereas a recording 1188 unaware UA may discard such RTCP packets as not of relevance. 1190 If SRTP is used on both the CS and the RS, decryption and/or re- 1191 encryption may occur. For example, if different keys are used, it 1192 will occur. If the same keys are used, it need not occur. 1193 Section 12 provides additional information on SRTP and keying 1194 mechanisms. 1196 If packet loss occurs, either from the UA to the SRC or from the SRC 1197 to the SRS, the SRS SHOULD detect and attempt to recover from the 1198 loss. The SRC does not play a role in this other than forwarding the 1199 associated RTP and RTCP packets. 1201 8.2.2. SRC acting as an RTP Mixer 1203 In the case of the SRC acting as a RTP mixer, as defined in 1204 [RFC3550], the SRC combines RTP streams from different UAs and sends 1205 them towards the SRS using its own SSRC. The SSRCs from the 1206 contributing UA SHOULD be conveyed as CSRCs identifiers within this 1207 stream. The SRC may make timing adjustments among the received 1208 streams and generate its own timing on the stream sent to the SRS. 1209 Optionally an SRC acting as a mixer can perform transcoding, and can 1210 even cope with different codings received from different UAs. RTCP 1211 Sender Reports and Receiver Reports are not forwarded by an SRC 1212 acting as mixer, but there are requirements for forwarding RTCP 1213 Source Description (SDES) packets. The SRC generates its own RTCP 1214 Sender and Receiver reports toward the associated UAs and SRS. 1216 The use of SRTP between the SRC and the SRS for the RS is independent 1217 of the use of SRTP between the UAs and SRC for the CS. Section 12 1218 provides additional information on SRTP and keying mechanisms. 1220 If packet loss occurs from the UA to the SRC, the SRC SHOULD detect 1221 and attempt to recover from the loss. If packet loss occurs from the 1222 SRC to the SRS, the SRS SHOULD detect and attempt to recover from the 1223 loss. 1225 8.2.3. SRC acting as an RTP Endpoint 1227 The case of the SRC acting as an RTP endpoint, as defined in 1228 [RFC3550], is similar to the mixer case, except that the RTP session 1229 between the SRC and the SRS is considered completely independent from 1230 the RTP session that is part of the CS. The SRC can, but need not, 1231 mix RTP streams from different participants prior to sending to the 1232 SRS. RTCP between the SRC and the SRS is completely independent of 1233 RTCP on the CS. 1235 The use of SRTP between the SRC and the SRS for the RS is independent 1236 of the use of SRTP between the UAs and SRC for the CS. Section 12 1237 provides additional information on SRTP and keying mechanisms. 1239 If packet loss occurs from the UA to the SRC, the SRC SHOULD detect 1240 and attempt to recover from the loss. If packet loss occurs from the 1241 SRC to the SRS, the SRS SHOULD detect and attempt to recover from the 1242 loss. 1244 8.3. RTP Session Usage by SRC 1246 There are multiple ways that an SRC may choose to deliver recorded 1247 media to an SRS. In some cases, it may use a single RTP session for 1248 all media within the RS, whereas in others it may use multiple RTP 1249 sessions. The following subsections provide examples of basic RTP 1250 session usage by the SRC, including a discussion of how the RTP 1251 constructs and mechanisms covered previously are used. An SRC may 1252 choose to use one or more of the RTP session usages within a single 1253 RS. For the purpose of base interoperability between SRC and SRS, an 1254 SRC MUST support separate m-lines in SDP, one per CS media direction. 1255 The set of RTP session usages described is not meant to be 1256 exhaustive. 1258 8.3.1. SRC Using Multiple m-lines 1260 When using multiple m-lines, an SRC includes each m-line in an SDP 1261 offer to the SRS. The SDP answer from the SRS MUST include all 1262 m-lines, with any rejected m-lines indicated with a zero port, per 1263 [RFC3264]. Having received the answer, the SRC starts sending media 1264 to the SRS as indicated in the answer. Alternatively, if the SRC 1265 deems the level of support indicated in the answer to be 1266 unacceptable, it may initiate another SDP offer/answer exchange in 1267 which an alternative RTP session usage is negotiated. 1269 In order to preserve the mapping of media to participant within the 1270 CSs in the RS, the SRC SHOULD map each unique CNAME within the CSs to 1271 a unique CNAME within the RS. Additionally, the SRC SHOULD map each 1272 unique combination of CNAME/SSRC within the CSs to a unique CNAME/ 1273 SSRC within the RS. In doing so, the SRC may act as an RTP 1274 translator or as an RTP endpoint. 1276 The following figure illustrates a case in which each UA represents a 1277 participant contributing two RTP sessions (e.g., one for audio and 1278 one for video), each with a single SSRC. The SRC acts as an RTP 1279 translator and delivers the media to the SRS using four RTP sessions, 1280 each with a single SSRC. The CNAME and SSRC values used by the UAs 1281 within their media streams are preserved in the media streams from 1282 the SRC to the SRS. 1284 +---------+ 1285 +------------SSRC Aa--->| | 1286 | + --------SSRC Av--->| | 1287 | | +------SSRC Ba--->| SRS | 1288 | | | +---SSRC Bv--->| | 1289 | | | | +---------+ 1290 | | | | 1291 | | | | 1292 +---------+ +----------+ +---------+ 1293 | |---SSRC Aa-->| SRC |<--SSRC Ba---| | 1294 | UA-A | |(CNAME-A, | | UA-B | 1295 |(CNAME-A)|---SSRC Av-->| CNAME-B) |<--SSRC Bv---|(CNAME-B)| 1296 +---------+ +----------+ +---------+ 1298 Figure 10: SRC Using Multiple m-lines 1300 8.3.2. SRC Using Mixing 1302 When using mixing, the SRC combines RTP streams from different 1303 participants and sends them towards the SRS using its own SSRC. The 1304 SSRCs from the contributing participants SHOULD be conveyed as CSRCs 1305 identifiers. The SRC includes one m-line for each RTP session in an 1306 SDP offer to the SRS. The SDP answer from the SRS MUST include all 1307 m-lines, with any rejected m-lines indicated with the zero port, per 1308 [RFC3264]. Having received the answer, the SRC starts sending media 1309 to the SRS as indicated in the answer. 1311 In order to preserve the mapping of media to participant within the 1312 CSs in the RS, the SRC SHOULD map each unique CNAME within the CSs to 1313 a unique CNAME within the RS. Additionally, the SRC SHOULD map each 1314 unique combination of CNAME/SSRC within the CSs to a unique CNAME/ 1315 SSRC within the RS. The SRC MUST avoid SSRC collisions, rewriting 1316 SSRCs if necessary when used as CSRCs in the RS. In doing so, the 1317 SRC acts as an RTP mixer. 1319 In the event the SRS does not support this usage of CSRC values, it 1320 relies entirely on the SIPREC metadata to determine the participants 1321 included within each mixed stream. 1323 The following figure illustrates a case in which each UA represents a 1324 participant contributing two RTP sessions (e.g., one for audio and 1325 one for video), each with a single SSRC. The SRC acts as an RTP 1326 mixer and delivers the media to the SRS using two RTP sessions, 1327 mixing media from each participant into a single RTP session 1328 containing a single SSRC and two CSRCs. 1330 SSRC Sa +---------+ 1331 +-------CSRC Aa,Ba--->| | 1332 | | | 1333 | SSRC Sv | SRS | 1334 | +---CSRC Av,Bv--->| | 1335 | | +---------+ 1336 | | 1337 +----------+ 1338 +---------+ | SRC | +---------+ 1339 | |---SSRC Aa-->|(CNAME-S, |<--SSRC Ba---| | 1340 | UA-A | | CNAME-A, | | UA-B | 1341 |(CNAME-A)|---SSRC Av-->| CNAME-B) |<--SSRC Bv---|(CNAME-B)| 1342 +---------+ +----------+ +---------+ 1344 Figure 11: SRC Using Mixing 1346 8.4. RTP Session Usage by SRS 1348 An SRS that supports recording an audio CS MUST support SRC usage of 1349 separate audio m-lines in SDP, one per CS media direction. An SRS 1350 that supports recording a video CS MUST support SRC usage of separate 1351 video m-lines in SDP, one per CS media direction. Therefore, for an 1352 SRS supporting a typical audio call, the SRS has to support receiving 1353 at least two audio m-lines. For an SRS supporting a typical audio 1354 and video call, the SRS has to support receiving at least four total 1355 m-lines in the SDP, two audio m-lines and two video m-lines. 1357 These requirements allow an SRS to be implemented that supports video 1358 only, without requiring support for audio recording. They also allow 1359 an SRS to be implemented that supports recording only one direction 1360 of one stream in a CS; for example, an SRS designed to record 1361 security monitoring cameras that only send (not receive) video 1362 without any audio. These requirements were not written to prevent 1363 other modes being implemented and used, such as using a single m-line 1364 and mixing the separate audio streams together. Rather, the 1365 requirements were written to provide a common base mode to implement 1366 for the sake of interoperability. It is important to note that an 1367 SRS implementation supporting the common base may not record all 1368 media streams in a CS if a participant supports more than one m-line 1369 in a video call, such as one for camera and one for presentation. 1370 SRS implementations may support other modes as well, but have to at 1371 least support the ones above such that they interoperate in the 1372 common base mode for basic interoperability. 1374 9. Metadata 1376 Some metadata attributes are contained in SDP, and others are 1377 contained in a new content type "application/rs-metadata". The 1378 format of the metadata is described as part of the mechanism in 1379 [I-D.ietf-siprec-metadata]. A new "disposition-type" of Content- 1380 Disposition is defined for the purpose of carrying metadata. The 1381 value is "recording-session", which indicates the "application/rs- 1382 metadata" content contains metadata to be handled by the SRS. 1384 9.1. Procedures at the SRC 1386 The SRC MUST send metadata to the SRS in an RS. The SRC SHOULD send 1387 metadata as soon as it becomes available and whenever it changes. 1388 Cases in which an SRC may be justified in waiting temporarily before 1389 sending metadata include: 1391 o waiting for a previous metadata exchange to complete (i.e., the 1392 SRC cannot send another SDP offer until the previous offer/answer 1393 completes, and may prefer not to send an UPDATE during this time 1394 either). 1396 o constraining the signaling rate on the RS. 1398 o sending metadata when key events occur rather than for every event 1399 that has any impact on metadata. 1401 The SRC may also be configured to suppress certain metadata out of 1402 concern for privacy or perceived lack of need for it to be included 1403 in the recording. 1405 Metadata sent by the SRC is categorized as either a full metadata 1406 snapshot or a partial update. A full metadata snapshot describes all 1407 metadata associated with the RS. The SRC MAY send a full metadata 1408 snapshot at any time. The SRC MAY send a partial update only if a 1409 full metadata snapshot has been sent previously. 1411 The SRC MAY send metadata (either a full metadata snapshot or a 1412 partial update) in an INVITE request, an UPDATE request [RFC3311], or 1413 a 200 response to an offerless INVITE from the SRS. If the metadata 1414 contains a reference to any SDP labels, the request containing the 1415 metadata MUST also contain an SDP offer that defines those labels. 1417 When a SIP message contains both an SDP offer and metadata, the 1418 request body MUST have content type "multipart/mixed", with one 1419 subordinate body part containing the SDP offer and another containing 1420 the metadata. When a SIP message contains only an SDP offer or 1421 metadata, the "multipart/mixed" container is optional. 1423 The SRC SHOULD include a full metadata snapshot in the initial INVITE 1424 request establishing the RS. If metadata is not yet available (e.g., 1425 an RS established in absence of a CS), the SRC SHOULD send a full 1426 metadata snapshot as soon as metadata becomes available. 1428 If the SRC receives a snapshot request from the SRS, it MUST 1429 immediately send a full metadata snapshot. 1431 The following is an example of a full metadata snapshot sent by the 1432 SRC in the initial INVITE request: 1434 INVITE sip:recorder@example.com SIP/2.0 1435 Via: SIP/2.0/TCP src.example.com;branch=z9hG4bKdf6b622b648d9 1436 From: ;tag=35e195d2-947d-4585-946f-09839247 1437 To: 1438 Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a 1439 CSeq: 101 INVITE 1440 Max-Forwards: 70 1441 Require: siprec 1442 Accept: application/sdp, application/rs-metadata-request 1443 Contact: ;+sip.src 1444 Content-Type: multipart/mixed;boundary=foobar 1445 Content-Length: [length] 1447 --foobar 1448 Content-Type: application/sdp 1450 v=0 1451 o=SRS 2890844526 2890844526 IN IP4 198.51.100.1 1452 s=- 1453 c=IN IP4 198.51.100.1 1454 t=0 0 1455 m=audio 12240 RTP/AVP 0 4 8 1456 a=sendonly 1457 a=label:1 1459 --foobar 1460 Content-Type: application/rs-metadata 1461 Content-Disposition: recording-session 1463 [metadata content] 1465 Figure 12: Sample INVITE request for the recording session 1467 9.2. Procedures at the SRS 1469 The SRS receives metadata updates from the SRC in INVITE and UPDATE 1470 requests. Since the SRC can send partial updates based on the 1471 previous update, the SRS needs to keep track of the sequence of 1472 updates from the SRC. 1474 In the case of an internal failure at the SRS, the SRS may fail to 1475 recognize a partial update from the SRC. The SRS may be able to 1476 recover from the internal failure by requesting a full metadata 1477 snapshot from the SRC. Certain errors, such as syntax errors or 1478 semantic errors in the metadata information, are likely caused by an 1479 error on the SRC side, and it is likely the same error will occur 1480 again even when a full metadata snapshot is requested. In order to 1481 avoid repeating the same error, the SRS can simply terminate the 1482 recording session when a syntax error or semantic error is detected 1483 in the metadata. 1485 The SRS MAY explicitly request a full metadata snapshot by sending an 1486 UPDATE request. This request MUST contain a body with content 1487 disposition type "recording-session", and MUST NOT contain an SDP 1488 body. The SRS MUST NOT request a full metadata snapshot in an UPDATE 1489 response or in any other SIP transaction. The format of the content 1490 is "application/rs-metadata-request", and the body format is a simple 1491 text-based format. The following shows an example: 1493 UPDATE sip:2000@src.exmaple.com SIP/2.0 1494 Via: SIP/2.0/UDP srs.example.com;branch=z9hG4bKdf6b622b648d9 1495 To: ;tag=35e195d2-947d-4585-946f-098392474 1496 From: ;tag=1234567890 1497 Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a 1498 CSeq: 1 UPDATE 1499 Max-Forwards: 70 1500 Require: siprec 1501 Contact: ;+sip.srs 1502 Accept: application/sdp, application/rs-metadata 1503 Content-Disposition: recording-session 1504 Content-Type: application/rs-metadata-request 1505 Content-Length: [length] 1507 SRS internal error 1509 Figure 13: Metadata Request 1511 Note that UPDATE was chosen for the SRS to request metadata snapshot 1512 because it can be sent regardless of the state of the dialog. This 1513 was seen as better than requiring support for both UPDATE and re- 1514 INVITE for this operation. 1516 When the SRC receives a request for a metadata snapshot, it MUST 1517 immediately provide a full metadata snapshot in a separate INVITE or 1518 UPDATE transaction. Any subsequent partial updates will not be 1519 dependent on any metadata sent prior to this full metadata snapshot. 1521 The metadata received by the SRS can contain ID elements used to 1522 cross reference one element to another. An element containing the 1523 definition of an ID, and an element containing a reference to that ID 1524 will often be received from the same SRC. It is also valid for those 1525 elements to be received from different SRCs, for example, when each 1526 endpoint in the same CS act as an SRC to record the call and a common 1527 ID refers to the same CS. The SRS MUST NOT consider this an error. 1529 9.2.1. Formal Syntax 1531 The formal syntax for the application/rs-metadata-request MIME is 1532 described below using the Augmented Backus-Naur Form (ABNF) as 1533 described in [RFC5234]. 1535 snapshot-request = srs-reason-line CRLF 1536 srs-reason-line = [TEXT-UTF8-TRIM] 1537 ; TEXT-UTF8-TRIM defined in RFC 3261 1539 10. Persistent Recording 1541 Persistent recording is a specific use case outlined in REQ-005 or 1542 Use Case 4 in [RFC6341], where a recording session can be established 1543 in the absence of a communication session. The SRC continuously 1544 records media in a recording session to the SRS even in the absence 1545 of a CS for all user agents that are part of persistent recording. 1546 By allocating recorded streams and continuously sending recorded 1547 media to the SRS, the SRC does not have to prepare new recorded 1548 streams with a new SDP offer when a new communication session is 1549 created and also does not impact the timing of the CS. The SRC only 1550 needs to update the metadata when new communication sessions are 1551 created. 1553 When there is no communication session running on the devices with 1554 persistent recording, there is no recorded media to stream from the 1555 SRC to the SRS. In certain environments where Network Address 1556 Translator (NAT) is used, typically a minimum of flow activity is 1557 required to maintain the NAT binding for each port opened. Agents 1558 that support Interactive Connectivity Establishment (ICE) solve this 1559 problem. For non-ICE agents, in order not to lose the NAT bindings 1560 for the RTP/RTCP ports opened for the recorded streams, the SRC and 1561 SRS SHOULD follow the recommendations provided in [RFC6263] to 1562 maintain the NAT bindings. 1564 11. IANA Considerations 1566 11.1. Registration of Option Tags 1568 This specification registers two option tags. The required 1569 information for this registration, as specified in [RFC3261], is as 1570 follows. 1572 11.1.1. siprec Option Tag 1574 Name: siprec 1576 Description: This option tag is for identifying that the SIP 1577 session is for the purpose of a recording session. This is 1578 typically not used in a Supported header. When present in a 1579 Require header in a request, it indicates that the UA is either an 1580 SRC or SRS capable of handling a recording session. 1582 11.1.2. record-aware Option Tag 1584 Name: record-aware 1586 Description: This option tag is to indicate the ability for the 1587 user agent to receive recording indicators in media-level or 1588 session-level SDP. When present in a Supported header, it 1589 indicates that the UA can receive recording indicators in media- 1590 level or session-level SDP. 1592 11.2. Registration of media feature tags 1594 This document registers two new media feature tags in the SIP tree 1595 per the process defined in [RFC2506] and [RFC3840] 1597 11.2.1. src feature tag 1599 Media feature tag name: sip.src 1601 ASN.1 Identifier: TBD at registration 1603 Summary of the media feature indicated by this tag: This feature 1604 tag indicates that the user agent is a Session Recording Client 1605 for the purpose of a Recording Session. 1607 Values appropriate for use with this feature tag: boolean 1609 The feature tag is intended primarily for use in the following 1610 applications, protocols, services, or negotiation mechanisms: This 1611 feature tag is only useful for a Recording Session. 1613 Examples of typical use: Routing the request to a Session 1614 Recording Server. 1616 Security Considerations: Security considerations for this media 1617 feature tag are discussed in Section 11.1 of RFC 3840. 1619 11.2.2. srs feature tag 1621 Media feature tag name: sip.srs 1623 ASN.1 Identifier: TBD at registration 1625 Summary of the media feature indicated by this tag: This feature 1626 tag indicates that the user agent is a Session Recording Server 1627 for the purpose of a Recording Session. 1629 Values appropriate for use with this feature tag: boolean 1631 The feature tag is intended primarily for use in the following 1632 applications, protocols, services, or negotiation mechanisms: This 1633 feature tag is only useful for a Recording Session. 1635 Examples of typical use: Routing the request to a Session 1636 Recording Client. 1638 Security Considerations: Security considerations for this media 1639 feature tag are discussed in Section 11.1 of RFC 3840. 1641 11.3. New Content-Disposition Parameter Registrations 1643 This document registers a new "disposition-type" value in Content- 1644 Disposition header: recording-session. 1646 recording-session: The body describes either: 1648 * metadata about the recording session 1650 * reason for metadata snapshot request 1652 as determined by the MIME value indicated in the Content-Type. 1654 11.4. Media Type Registration 1656 11.4.1. Registration of MIME Type application/rs-metadata-request 1658 This document registers the application/rs-metadata-request MIME 1659 media type in order to describe a recording session metadata snapshot 1660 request. This media type is defined by the following information: 1662 Media type name: application 1664 Media subtype name: rs-metadata-request 1666 Required parameters: none 1667 Options parameters: none 1669 11.5. SDP Attributes 1671 This document registers the following new SDP attributes. 1673 11.5.1. 'record' SDP Attribute 1675 Contact names: Leon Portman leon.portman@gmail.com, Henry Lum 1676 henry.lum@genesyslab.com 1678 Attribute name: record 1680 Long form attribute name: Recording Indication 1682 Type of attribute: session or media-level 1684 Subject to charset: no 1686 This attribute provides the recording indication for the session or 1687 media stream. 1689 Allowed attribute values: on, off, paused 1691 11.5.2. 'recordpref' SDP Attribute 1693 Contact names: Leon Portman leon.portman@nice.com, Henry Lum 1694 henry.lum@genesyslab.com 1696 Attribute name: recordpref 1698 Long form attribute name: Recording Preference 1700 Type of attribute: session or media-level 1702 Subject to charset: no 1704 This attribute provides the recording preference for the session or 1705 media stream. 1707 Allowed attribute values: on, off, pause, nopreference 1709 12. Security Considerations 1711 The recording session is fundamentally a standard SIP dialog 1712 [RFC3261]; therefore, the recording session can reuse any of the 1713 existing SIP security mechanisms available for securing the session 1714 signaling, the recorded media, and the metadata. The use cases and 1715 requirements document [RFC6341] outlines the general security 1716 considerations, and this document describes specific security 1717 recommendations. 1719 The SRC and SRS MUST support SIP with TLS version 1.2, SHOULD follow 1720 the best practices when using TLS as per [RFC7525], and MAY use SIPS 1721 with TLS as per [RFC5630]. The Recording Session SHOULD be at least 1722 as secure as the Communication Session, meaning using at least the 1723 same strength of cipher suite as the CS if the CS is secured. For 1724 example, if the CS uses SIPS for signaling and RTP/SAVP for media, 1725 then the RS SHOULD NOT downgrade the level of security in the RS to 1726 SIP or plain RTP since doing so will mean an effective security 1727 downgrade for the CS. In deployments where the SRC and the SRS are 1728 in the same administrative domain and the same physical switch that 1729 prevents outside user access, some SRCs may choose to lower the level 1730 of security when establishing a recording session. While physically 1731 securing the SRC and SRS may prevent an outside attacker from 1732 accessing important call recordings, this still does not prevent an 1733 inside attacker from accessing the internal network to gain access to 1734 the call recordings. 1736 12.1. Authentication and Authorization 1738 At the transport level, the recording session uses TLS authentication 1739 to validate the authenticity of the SRC and SRS. The SRC and SRS 1740 MUST implement TLS mutual authentication for establishing the 1741 recording session. Whether the SRC/SRS chooses to use TLS mutual 1742 authentication is a deployment decision. In deployments where a UA 1743 acts as its own SRC, this requires the UA have its own certificate as 1744 needed for TLS mutual authentication. In deployments where the SRC 1745 and the SRS are in the same administrative domain and have some other 1746 means of assuring authenticity, the SRC and SRS may choose not to 1747 authenticate each other, or to have the SRC authenticate the SRS 1748 only. In deployments where the SRS can be hosted on a different 1749 administrative domain, it is important to perform mutual 1750 authentication to ensure the authenticity of both the SRC and the SRS 1751 before transmitting any recorded media. The risk of not 1752 authenticating the SRS is that the recording may be sent to an entity 1753 other than the intended SRS, allowing a sensitive call recording to 1754 be received by an attacker. On the other hand, the risk of not 1755 authenticating the SRC is that an SRS will accept calls from an 1756 unknown SRC and allow potential forgery of call recordings. 1758 There may be scenarios in which the signaling between the SRC and SRS 1759 is not direct, e.g., a SIP proxy exists between the SRC and the SRS. 1760 In such scenarios, each hop is subject to the TLS mutual 1761 authentication constraint and transitive trust at each hop is 1762 utilized. Additionally, an SRC or SRS may use other existing SIP 1763 mechanisms available, including but not limited to, Digest 1764 Authentication [RFC3261], Asserted Identity [RFC3325], and Connected 1765 Identity [RFC4916]. 1767 The SRS may have its own set of recording policies to authorize 1768 recording requests from the SRC. The use of recording policies is 1769 outside the scope of the Session Recording Protocol. 1771 12.2. RTP handling 1773 In many scenarios it will be critical for the media transported 1774 between the SRC and the SRS to be protected. Media encryption is an 1775 important element in the overall SIPREC solution; therefore the SRC 1776 and the SRS MUST support RTP/SAVP [RFC3711] and RTP/SAVPF [RFC5124]. 1777 RTP/SAVP and RTP/SAVPF provide media encryption, integrity 1778 protection, replay protection, and a limited form of source 1779 authentication. They do not contain or require a specific keying 1780 mechanism. At a minimum, the SRC and SRS MUST support the SDP 1781 Security Descriptions (SDES) key negotiation mechanism [RFC4568]. 1782 For cases in which DTLS-SRTP is used to encrypt a CS media stream, an 1783 SRC may use SRTP Encrypted Key Transport (EKT) 1784 [I-D.ietf-avtcore-srtp-ekt] in order to use SRTP-SDES in the RS 1785 without needing to re-encrypt the media. 1787 When RTP/SAVP or RTP/SAVPF is used, an SRC can choose to use the same 1788 or different keys in the RS than the ones used in the CS. Some SRCs 1789 are designed to simply replicate RTP packets from a CS media stream 1790 to the SRS, in which case the SRC will use the same key in the RS as 1791 used in the CS. In this case, the SRC MUST secure the SDP containing 1792 the keying material in the RS with at least the same level of 1793 security as in the CS. The risk of lowering the level of security in 1794 the RS is that it will effectively become a downgrade attack on the 1795 CS since the same key is used for both CS and RS. 1797 SRCs that decrypt an encrypted CS media stream and re-encrypt it when 1798 sending it to the SRS MUST use a different key than what is used for 1799 the CS media stream, to ensure that it is not possible for someone 1800 who has the key for the CS media stream to access recorded data they 1801 are not authorized to access. In order to maintain a comparable 1802 level of security, the key used in the RS SHOULD of equivalent or 1803 greater strength than that used in the CS. 1805 12.3. Metadata 1807 Metadata contains sensitive information such as the address of record 1808 of the participants and other extension data placed by the SRC. It 1809 is essential to protect the content of the metadata in the RS. Since 1810 metadata is a content type transmitted in SIP signaling, metadata 1811 SHOULD be protected at the transport level by SIPS/TLS. 1813 12.4. Storage and playback 1815 While storage and playback of the call recording is beyond the scope 1816 of this document, it is worthwhile to mention here that it is also 1817 important for the recording storage and playback to provide a level 1818 of security that is comparable to the communication session. It 1819 would defeat the purpose of securing both the communication session 1820 and the recording session mentioned in the previous sections if the 1821 recording can be easily played back with a simple, unsecured HTTP 1822 interface without any form of authentication or authorization. 1824 13. Acknowledgements 1826 We want to thank John Elwell, Paul Kyzivat, Partharsarathi R, Ram 1827 Mohan R, Hadriel Kaplan, Adam Roach, Miguel Garcia, Thomas Stach, 1828 Muthu Perumal, Dan Wing, and Magnus Westerlund for their valuable 1829 comments and inputs to this document. 1831 14. References 1833 14.1. Normative References 1835 [I-D.ietf-siprec-metadata] 1836 R, R., Ravindran, P., and P. Kyzivat, "Session Initiation 1837 Protocol (SIP) Recording Metadata", draft-ietf-siprec- 1838 metadata-17 (work in progress), February 2015. 1840 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1841 Requirement Levels", BCP 14, RFC 2119, March 1997. 1843 [RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag 1844 Registration Procedure", BCP 31, RFC 2506, March 1999. 1846 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 1847 A., Peterson, J., Sparks, R., Handley, M., and E. 1848 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 1849 June 2002. 1851 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1852 with Session Description Protocol (SDP)", RFC 3264, June 1853 2002. 1855 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 1856 Jacobson, "RTP: A Transport Protocol for Real-Time 1857 Applications", STD 64, RFC 3550, July 2003. 1859 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 1860 "Indicating User Agent Capabilities in the Session 1861 Initiation Protocol (SIP)", RFC 3840, August 2004. 1863 [RFC4574] Levin, O. and G. Camarillo, "The Session Description 1864 Protocol (SDP) Label Attribute", RFC 4574, August 2006. 1866 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 1867 Specifications: ABNF", STD 68, RFC 5234, January 2008. 1869 [RFC7245] Hutton, A., Portman, L., Jain, R., and K. Rehor, "An 1870 Architecture for Media Recording Using the Session 1871 Initiation Protocol", RFC 7245, May 2014. 1873 14.2. Informative References 1875 [I-D.ietf-avtcore-srtp-ekt] 1876 Mattsson, J., McGrew, D., and D. Wing, "Encrypted Key 1877 Transport for Secure RTP", draft-ietf-avtcore-srtp-ekt-03 1878 (work in progress), October 2014. 1880 [RFC2804] IAB and IESG, "IETF Policy on Wiretapping", RFC 2804, May 1881 2000. 1883 [RFC3311] Rosenberg, J., "The Session Initiation Protocol (SIP) 1884 UPDATE Method", RFC 3311, October 2002. 1886 [RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private 1887 Extensions to the Session Initiation Protocol (SIP) for 1888 Asserted Identity within Trusted Networks", RFC 3325, 1889 November 2002. 1891 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 1892 Video Conferences with Minimal Control", STD 65, RFC 3551, 1893 July 2003. 1895 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 1896 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 1897 RFC 3711, March 2004. 1899 [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session 1900 Description Protocol (SDP) Security Descriptions for Media 1901 Streams", RFC 4568, July 2006. 1903 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 1904 "Extended RTP Profile for Real-time Transport Control 1905 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, July 1906 2006. 1908 [RFC4916] Elwell, J., "Connected Identity in the Session Initiation 1909 Protocol (SIP)", RFC 4916, June 2007. 1911 [RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)", 1912 BCP 131, RFC 4961, July 2007. 1914 [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, 1915 "Codec Control Messages in the RTP Audio-Visual Profile 1916 with Feedback (AVPF)", RFC 5104, February 2008. 1918 [RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for 1919 Real-time Transport Control Protocol (RTCP)-Based Feedback 1920 (RTP/SAVPF)", RFC 5124, February 2008. 1922 [RFC5168] Levin, O., Even, R., and P. Hagendorf, "XML Schema for 1923 Media Control", RFC 5168, March 2008. 1925 [RFC5630] Audet, F., "The Use of the SIPS URI Scheme in the Session 1926 Initiation Protocol (SIP)", RFC 5630, October 2009. 1928 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 1929 Control Packets on a Single Port", RFC 5761, April 2010. 1931 [RFC6263] Marjou, X. and A. Sollaud, "Application Mechanism for 1932 Keeping Alive the NAT Mappings Associated with RTP / RTP 1933 Control Protocol (RTCP) Flows", RFC 6263, June 2011. 1935 [RFC6341] Rehor, K., Portman, L., Hutton, A., and R. Jain, "Use 1936 Cases and Requirements for SIP-Based Media Recording 1937 (SIPREC)", RFC 6341, August 2011. 1939 [RFC7022] Begen, A., Perkins, C., Wing, D., and E. Rescorla, 1940 "Guidelines for Choosing RTP Control Protocol (RTCP) 1941 Canonical Names (CNAMEs)", RFC 7022, September 2013. 1943 [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, 1944 "Recommendations for Secure Use of Transport Layer 1945 Security (TLS) and Datagram Transport Layer Security 1946 (DTLS)", BCP 195, RFC 7525, May 2015. 1948 Authors' Addresses 1949 Leon Portman 1950 NICE Systems 1951 22 Zarhin Street 1952 P.O. Box 690 1953 Ra'anana 4310602 1954 Israel 1956 Email: leon.portman@gmail.com 1958 Henry Lum (editor) 1959 Genesys 1960 1380 Rodick Road, Suite 201 1961 Markham, Ontario L3R4G5 1962 Canada 1964 Email: henry.lum@genesyslab.com 1966 Charles Eckel 1967 Cisco 1968 170 West Tasman Drive 1969 San Jose, CA 95134 1970 United States 1972 Email: eckelcu@cisco.com 1974 Alan Johnston 1975 Avaya 1976 St. Louis, MO 63124 1978 Email: alan.b.johnston@gmail.com 1980 Andrew Hutton 1981 Unify 1982 Brickhill Street 1983 Milton Keynes MK15 0DJ 1984 United Kingdom 1986 Email: andrew.hutton@unify.com