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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group P. Jones 3 Internet-Draft G. Salgueiro 4 Obsoletes: 7329 (if approved) C. Pearce 5 Intended status: Standards Track P. Giralt 6 Expires: February 9, 2017 Cisco Systems, Inc. 7 August 8, 2016 9 End-to-End Session Identification in IP-Based Multimedia Communication 10 Networks 11 draft-ietf-insipid-session-id-25 13 Abstract 15 This document describes an end-to-end Session Identifier for use in 16 IP-based multimedia communication systems that enables endpoints, 17 intermediary devices, and management systems to identify a session 18 end-to-end, associate multiple endpoints with a given multipoint 19 conference, track communication sessions when they are redirected, 20 and associate one or more media flows with a given communication 21 session. While the identifier is intended to work across multiple 22 protocols, this document describes its usage in SIP. 24 This document also describes a backwards compatibility mechanism for 25 an existing session identifier implementation (RFC 7329) that is 26 sufficiently different from the procedures defined in this document. 28 This document obsoletes RFC 7329. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on February 9, 2017. 47 Copyright Notice 49 Copyright (c) 2016 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 65 2. Conventions used in this document . . . . . . . . . . . . . . 4 66 3. Session Identifier Requirements and Use Cases . . . . . . . . 4 67 4. Constructing and Conveying the Session Identifier . . . . . . 4 68 4.1. Constructing the Session Identifier . . . . . . . . . . . 4 69 4.2. Conveying the Session Identifier . . . . . . . . . . . . 5 70 5. The Session-ID Header Field . . . . . . . . . . . . . . . . . 7 71 6. Endpoint Behavior . . . . . . . . . . . . . . . . . . . . . . 8 72 7. Processing by Intermediaries . . . . . . . . . . . . . . . . 10 73 8. Handling of Remote UUID Changes . . . . . . . . . . . . . . . 13 74 9. Associating Endpoints in a Multipoint Conference . . . . . . 15 75 10. Examples of Various Call Flow Operations . . . . . . . . . . 16 76 10.1. Basic Call with 2 UUIDs . . . . . . . . . . . . . . . . 16 77 10.2. Basic Call Transfer using REFER . . . . . . . . . . . . 20 78 10.3. Basic Call Transfer using re-INVITE . . . . . . . . . . 22 79 10.4. Single Focus Conferencing . . . . . . . . . . . . . . . 24 80 10.5. Single Focus Conferencing using a web-based conference 81 service . . . . . . . . . . . . . . . . . . . . . . . . 26 82 10.6. Cascading Conference Bridges . . . . . . . . . . . . . . 28 83 10.6.1. Establishing a Cascaded Conference . . . . . . . . . 28 84 10.6.2. Calling into Cascaded Conference Bridges . . . . . . 29 85 10.7. Basic 3PCC for two UAs . . . . . . . . . . . . . . . . . 30 86 10.8. Handling in 100 Trying SIP Response and CANCEL Request . 31 87 10.8.1. Handling in a 100 Trying SIP Response . . . . . . . 31 88 10.8.2. Handling a CANCEL SIP Request . . . . . . . . . . . 33 89 10.9. Out-of-dialog REFER Transaction . . . . . . . . . . . . 34 90 11. Compatibility with a Previous Implementation . . . . . . . . 35 91 12. Security and Privacy Considerations . . . . . . . . . . . . . 36 92 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38 93 13.1. Registration of the "Session-ID" Header Field . . . . . 38 94 13.2. Registration of the "remote" Parameter . . . . . . . . . 38 96 14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 38 97 15. Dedication . . . . . . . . . . . . . . . . . . . . . . . . . 38 98 16. References . . . . . . . . . . . . . . . . . . . . . . . . . 39 99 16.1. Normative References . . . . . . . . . . . . . . . . . . 39 100 16.2. Informative References . . . . . . . . . . . . . . . . . 39 101 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41 103 1. Introduction 105 IP-based multimedia communication systems such as Session Initiation 106 Protocol (SIP) [RFC3261] and [H.323] have the concept of a "call 107 identifier" that is globally unique. The identifier is intended to 108 represent an end-to-end communication session from the originating 109 device to the terminating device. Such an identifier is useful for 110 troubleshooting, session tracking, and so forth. 112 For several reasons, however, the current call identifiers defined in 113 SIP and H.323 are not suitable for end-to-end session identification. 114 A fundamental issue in protocol interworking is the fact that the 115 syntax for the call identifier in SIP and H.323 is different. Thus, 116 if both protocols are used in a call, it is impossible to exchange 117 the call identifier end-to-end. 119 Another reason why the current call identifiers are not suitable to 120 identify a session end-to-end is that, in real-world deployments, 121 devices such as session border controllers [RFC7092] often change the 122 session signaling, including the value of the call identifier, as it 123 passes through the device. While this is deliberate and useful, it 124 makes it very difficult to track a session end-to-end. 126 This document defines a new identifier, referred to as the Session 127 Identifier, that is intended to overcome the issues that exist with 128 the currently defined call identifiers used in SIP and other IP-based 129 communication systems. The identifier defined here has been adopted 130 by the ITU ([H.460.27]) for use in H.323-based systems, allowing for 131 the ability to trace a session end-to-end for sessions traversing 132 both SIP and H.323-based systems. This document defines its use in 133 SIP. 135 The procedures specified in this document attempt to comply with the 136 requirements specified in [RFC7206]. The procedures also specify 137 capabilities not mentioned in [RFC7206], shown in call flows in 138 section 10. Additionally, the specification attempts to account for 139 a previous, pre-standard version of a SIP Session Identifier header 140 [RFC7329], specifying a backwards compatibility approach in section 141 11. 143 2. Conventions used in this document 145 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 146 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 147 document are to be interpreted as described in [RFC2119] when they 148 appear in ALL CAPS. These words may also appear in this document in 149 lower case as plain English words, absent their normative meanings. 151 The term "Session Identifier" refers to the value of the identifier, 152 whereas "Session-ID" refers to the header field used to convey the 153 identifier. The Session Identifier is a set of two Universally 154 Unique Identifiers (UUIDs) and each element of that set is simply 155 referred to herein as a UUID. 157 Throughout this document, the term "endpoint" refers to a SIP User 158 Agent (UA) that either initiates or terminates a SIP session, such as 159 a user's mobile phone or a conference server, but excludes entities 160 such as Back-to-Back User Agents (B2BUAs) that are generally located 161 along the call signaling path between endpoints. The term 162 "intermediary" refers to any entity along the call signaling path 163 between the aforementioned endpoints, including B2BUAs and SIP 164 proxies. In certain scenarios, intermediaries are allowed to 165 originate and terminate SIP messages without an endpoint being part 166 of the session or transaction. An intermediary may be performing 167 interworking between different protocols (e.g. SIP and H.323) that 168 support the Session Identifier defined in this document. 170 3. Session Identifier Requirements and Use Cases 172 Requirements and use cases for the end-to-end Session Identifier, 173 along with a definition of "session identifier" and "communication 174 session", can be found in [RFC7206]. 176 As mentioned in section 6.1 of [RFC7206], the ITU-T undertook a 177 parallel effort to define compatible procedures for an H.323 Session 178 Identifier. They are documented in [H.460.27]. 180 4. Constructing and Conveying the Session Identifier 182 4.1. Constructing the Session Identifier 184 The Session Identifier comprises two UUIDs [RFC4122], with each UUID 185 representing one of the endpoints participating in the session. 187 The version number in the UUID indicates the manner in which the UUID 188 is generated, such as using random values or using the MAC address of 189 the endpoint. To satisfy the requirement that no user or device 190 information be conveyed, endpoints MUST generate version 4 (random) 191 or version 5 (SHA-1) UUIDs to address privacy concerns related to use 192 of MAC addresses in UUIDs. 194 When generating a version 5 UUID, endpoints or intermediaries MUST 195 utilize the procedures defined in Section 4.3 of [RFC4122] and employ 196 the following "name space ID": 198 uuid_t NameSpace_SessionID = { 199 /* a58587da-c93d-11e2-ae90-f4ea67801e29 */ 200 0xa58587da, 201 0xc93d, 202 0x11e2, 203 0xae, 0x90, 0xf4, 0xea, 0x67, 0x80, 0x1e, 0x29 204 } 206 Further, the "name" to utilize for version 5 UUIDs is the 207 concatenation of the Call-ID header-value and the "tag" parameter 208 that appears on the "From" or "To" line associated with the device 209 for which the UUID is created. Once an endpoint generates a UUID for 210 a session, the UUID never changes, even if values originally used as 211 input into its construction change over time. 213 Stateless intermediaries that insert a Session-ID header field into a 214 SIP message on behalf of an endpoint MUST utilize version 5 UUIDs to 215 ensure that UUIDs for the communication session are consistently 216 generated. If a stateless intermediary does not know the tag value 217 for the endpoint (e.g., a new INVITE without a To: tag value or an 218 older SIP implementation [RFC2543] that did not include a tag 219 parameter), the intermediary MUST NOT attempt to generate a UUID for 220 that endpoint. Note that if an intermediary is stateless and the 221 endpoint on one end of the call is replaced with another endpoint due 222 to some service interaction, the values used to create the UUID 223 should change and, if so, the intermediary will compute a different 224 UUID. 226 4.2. Conveying the Session Identifier 228 The SIP User Agent (UA) initiating a new session by transmitting a 229 SIP request ("Alice"), i.e., a User Agent Client (UAC), MUST create a 230 new, previously unused, UUID and transmit that to the ultimate 231 destination UA ("Bob"). Likewise, the destination UA ("Bob"), i.e., 232 a User Agent Server (UAS), MUST create a new, previously unused, UUID 233 and transmit that to the first UA ("Alice"). These two distinct 234 UUIDs form what is referred to as the Session Identifier and is 235 represented in this document in set notation of the form {A,B}, where 236 "A" is UUID value created by UA "Alice" and "B" is the UUID value 237 created by UA "Bob". The Session Identifier {A,B} is equal to the 238 Session Identifier {B,A}. Section 6 describes how the UUIDs selected 239 by the source and destination UAs persist for the duration of the 240 session. 242 In the case where only one UUID is known, such as when a UA first 243 initiates a potentially dialog-initiating SIP request, the Session 244 Identifier would be {A,N}, where "A" represents the UUID value 245 transmitted by the UA "Alice" and "N" is what is referred to as the 246 nil UUID [RFC4122] (see section 5). 248 Since SIP sessions are subject to any number of service interactions, 249 SIP INVITE messages might be forked as sessions are established, and 250 since conferences might be established or expanded with endpoints 251 calling in or the conference focus calling out, the construction of 252 the Session Identifier as a set of UUIDs is important. 254 To understand this better, consider that an endpoint participating in 255 a communication session might be replaced with another, such as the 256 case where two "legs" of a call are joined together by a Private 257 Branch Exchange (PBX). Suppose "Alice" and "Bob" both call UA C 258 ("Carol"). There would be two distinctly identifiable Session 259 Identifiers, namely {A,C} and {B,C}. Then suppose that "Carol" uses 260 a local PBX function to join the call between herself and "Alice" 261 with the call between herself and "Bob", resulting in a single 262 remaining call between "Alice" and "Bob". This merged call can be 263 identified using two UUID values assigned by each entity in the 264 communication session, namely {A,B} in this example. 266 In the case of forking, "Alice" might send an INVITE that gets forked 267 to several different endpoints. A means of identifying each of these 268 separate communication sessions is needed and, since each of the 269 destination UAs will create its own UUID, each communication session 270 would be uniquely identified by the values {A, B1}, {A, B2}, {A, B3}, 271 and so on, where each of the Bn values refers to the UUID created by 272 the different UAs to which the SIP session is forked. 274 For conferencing scenarios, it is also useful to have a two-part 275 Session Identifier where the conference focus specifies the same UUID 276 for each conference participant. This allows for correlation among 277 the participants in a single conference. For example, in a 278 conference with three participants, the Session Identifiers might be 279 {A,M}, {B,M}, and {C,M}, where "M" is assigned by the conference 280 focus. Only a conference focus will purposely utilize the same UUID 281 for more than one SIP session and, even then, such reuse MUST be 282 restricted to the participants in the same conference. 284 How a device acting on Session Identifiers processes or utilizes the 285 Session Identifier is outside the scope of this document, however 286 devices storing a Session Identifier in a log file SHOULD follow the 287 security considerations outlined in [RFC6872]. Note that the primary 288 intent of a Session Identifier is for troubleshooting and should 289 therefore be included in logs at rest that will be used for 290 troubleshooting purposes. 292 5. The Session-ID Header Field 294 This document replaces the definition of the "Session-ID" token that 295 was added to the definition of the element "message-header" in the 296 SIP message grammar by [RFC7329]. The Session-ID header is a single- 297 instance header. 299 Each endpoint participating in a communication session has a 300 distinct, preferably locally-generated, UUID associated with it. The 301 endpoint's UUID value remains unchanged throughout the duration of 302 the communication session. Multipoint conferences can bridge 303 sessions from multiple endpoints and impose unique requirements 304 defined in Section 9. An intermediary MAY generate a UUID on behalf 305 of an endpoint that did not include a UUID of its own. 307 The UUID values for each endpoint are inserted into the "Session-ID" 308 header field of all transmitted SIP messages. The Session-ID header 309 field has the following ABNF [RFC5234] syntax: 311 session-id = "Session-ID" HCOLON session-id-value 313 session-id-value = local-uuid *(SEMI sess-id-param) 315 local-uuid = sess-uuid / nil 317 remote-uuid = sess-uuid / nil 319 sess-uuid = 32(DIGIT / %x41-46 / %x61-66) 320 ;32 chars of [0-9A-Fa-f] 322 sess-id-param = remote-param / generic-param 324 remote-param = "remote" EQUAL remote-uuid 326 nil = 32("0") 328 The productions "SEMI", "EQUAL", and "generic-param" are defined in 329 [RFC3261]. The production DIGIT is defined in [RFC5234]. 331 The Session-ID header field MUST NOT have more than one "remote" 332 parameter. In the case where an entity compliant with this 333 specification is interworking with an entity that implemented 334 [RFC7329], the "remote" parameter may be absent, but otherwise the 335 remote parameter MUST be present. The details under which those 336 conditions apply are described in Section 11. Except for backwards 337 compatibility with [RFC7329], the "remote" parameter MUST be present. 339 A special nil UUID value composed of 32 zeros is required in certain 340 situations. A nil UUID is expected as the "remote-uuid" of every 341 initial standard SIP request since the initiating endpoint would not 342 initially know the UUID value of the remote endpoint. This nil value 343 will get replaced by the ultimate destination UAS when that UAS 344 generates a response message. One caveat is explained in Section 11 345 for a possible backwards compatibility case. A nil UUID value is 346 also returned by some intermediary devices that send provisional or 347 other responses as the "local-uuid" component of the Session-ID 348 header field value, as described in Section 7. 350 The "local-uuid" in the Session-ID header field represents the UUID 351 value of the endpoint transmitting a message and the "remote-uuid" in 352 the Session-ID header field represents the UUID of the endpoint's 353 peer. For example, a Session-ID header field might appear like this: 355 Session-ID: ab30317f1a784dc48ff824d0d3715d86; 356 remote=47755a9de7794ba387653f2099600ef2 358 While this is the general form of the Session-ID header field, 359 exceptions to syntax and procedures are detailed in subsequent 360 sections. 362 The UUID values are presented as strings of lower-case hexadecimal 363 characters, with the most significant octet of the UUID appearing 364 first. 366 The Session-ID header field value is case-insensitive, but SHOULD use 367 only lowercase characters for consistency between implementations. 368 Receiving entities MUST treat sess-uuid components as case- 369 insensitive. 371 6. Endpoint Behavior 373 To comply with this specification, endpoints (non-intermediaries) 374 MUST include a Session-ID header field value in all SIP messages 375 transmitted as a part of a communication session. The locally- 376 generated UUID of the transmitter of the message MUST appear in the 377 "local-uuid" portion of the Session-ID header field value. The UUID 378 of the peer device, if known, MUST appear as the "remote" parameter 379 following the transmitter's UUID. The nil UUID value MUST be used if 380 the peer device's UUID is not known. 382 Once an endpoint allocates a UUID value for a communication session, 383 the endpoint originating the request MUST NOT change that UUID value 384 for the duration of the session, including when 386 o communication attempts are retried due to receipt of 4xx messages 387 or request timeouts; 389 o the session is redirected in response to a 3xx message; 391 o a session is transferred via a REFER message [RFC3515]; or 393 o a SIP dialog is replaced via an INVITE with Replaces [RFC3891]. 395 An endpoint that receives a Session-ID header field MUST take note of 396 any non-nil "local-uuid" value that it receives and assume that is 397 the UUID of the peer endpoint within that communications session. 398 Endpoints MUST include this received UUID value as the "remote" 399 parameter when transmitting subsequent messages, making sure not to 400 change this UUID value in the process of moving the value internally 401 from the "local-uuid" field to the "remote-uuid" field. 403 If an endpoint receives a 3xx message, receives a REFER that directs 404 the endpoint to a different peer, or receives an INVITE with Replaces 405 that also potentially results in communicating with a new peer, the 406 endpoint MUST complete any message exchanges with its current peer 407 using the existing Session Identifier, but MUST NOT use the current 408 peer's UUID value when sending the first message to what it believes 409 may be a new peer endpoint (even if the exchange results in 410 communicating with the same physical or logical entity). The 411 endpoint MUST retain its own UUID value, however, as described above. 413 It should be noted that messages received by an endpoint might 414 contain a "local-uuid" value that does not match what the endpoint 415 expected its peer's UUID to be. It is also possible for an endpoint 416 to receive a "remote-uuid" value that does not match its generated 417 UUID for the session. Either might happen as a result of service 418 interactions by intermediaries and MUST NOT affect the communication 419 session. However, the endpoint may log this event for the purposes 420 of troubleshooting. 422 An endpoint MUST assume that the UUID value of the peer endpoint may 423 change at any time due to service interactions. Section 8 discusses 424 how endpoints must handle remote UUID changes. 426 It is also important to note that if an intermediary in the network 427 forks a session, the endpoint initiating a session may receive 428 multiple responses back from different endpoints, each of which 429 contains a different UUID ("local-uuid") value. Endpoints MUST 430 ensure that the correct UUID value is returned in the "remote" 431 parameter when interacting with each endpoint. The one exception is 432 when the endpoint sends a CANCEL message, in which case the Session- 433 ID header field value MUST be identical to the Session-ID header 434 field value sent in the original request. 436 If an endpoint receives a message that does not contain a Session-ID 437 header field, that message must have no effect on what the endpoint 438 believes is the UUID value of the remote endpoint. That is, the 439 endpoint MUST NOT change the internally maintained "remote-uuid" 440 value for the peer. 442 If an endpoint receives a SIP response with a non-nil "local-uuid" 443 that is not 32 octets long, this response comes from a misbehaving 444 implementation, and its Session-ID header field MUST be discarded. 445 That said, the response might still be valid according to the rules 446 within SIP [RFC3261], and SHOULD be checked further. 448 A Multipoint Control Unit (MCU) is a special type of conferencing 449 endpoint and is discussed in Section 9. 451 7. Processing by Intermediaries 453 The following applies only to an intermediary that wishes to comply 454 with this specification and does not impose a conformance requirement 455 on intermediaries that elect to not provide any special treatment for 456 the Session-ID header field. Intermediaries that do not comply with 457 this specification might pass the header unchanged or drop it 458 entirely. 460 The Call-ID often reveals personal, device, domain or other sensitive 461 information associated with a user, which is one reason why 462 intermediaries, such as session border controllers, sometimes alter 463 the Call-ID. In order to ensure the integrity of the end-to-end 464 Session Identifier, it is constructed in a way which does not reveal 465 such information, removing the need for intermediaries to alter it. 467 When an intermediary receives messages from one endpoint in a 468 communication session that causes the transmission of one or more 469 messages toward the second endpoint in a communication session, the 470 intermediary MUST include the Session-ID header field in the 471 transmitted messages with the same UUID values found in the received 472 message, except as outlined in this section and in section 8. 474 If the intermediary aggregates several responses from different 475 endpoints, as described in Section 16.7 of [RFC3261], the 476 intermediary MUST set the local-uuid field to the nil UUID value when 477 forwarding the aggregated response to the endpoint since the true 478 UUID value of the peer is undetermined at that point. Note that an 479 intermediary that does not implement this specification might forward 480 a non-nil value, resulting in the originating endpoint receiving 481 different UUID values in the responses. It is possible for this to 482 result in the endpoint temporarily using the wrong remote UUID. 483 Subsequent messages in the dialog should resolve the temporary 484 mismatch as long as the endpoint follows the rules outlined in 485 Section 8 dealing with the handling of remote UUID changes. 487 Intermediary devices that transfer a call, such as by joining 488 together two different "call legs", MUST properly construct a 489 Session-ID header field that contains the UUID values associated with 490 the endpoints involved in the joined session and correct placement of 491 those values. As described in Section 6, the endpoint receiving a 492 message transmitted by the intermediary will assume that the first 493 UUID value belongs to its peer endpoint. 495 If an intermediary receives a SIP message without a Session-ID header 496 field or valid header field value from an endpoint for which the 497 intermediary is not storing a "remote-uuid" value, the intermediary 498 MAY assign a "local-uuid" value to represent that endpoint and, 499 having done so, MUST insert that assigned value into all signaling 500 messages on behalf of the endpoint for that dialog. In effect, the 501 intermediary becomes dialog stateful and it MUST follow the endpoint 502 procedures in Section 6 with respect to Session-ID header field value 503 treatment with itself acting as the endpoint (for the purposes of the 504 Session-ID header field) for which it inserted a component into the 505 Session-ID header field value. If the intermediary is aware of the 506 UUID value that identifies the endpoint to which a message is 507 directed, it MUST insert that UUID value into the Session-ID header 508 field value as the "remote-uuid" value. If the intermediary is 509 unaware of the UUID value that identifies the receiving endpoint, it 510 MUST use the nil UUID value as the "remote-uuid" value. 512 If an intermediary receives a SIP message without a Session-ID header 513 field or valid Session-ID header field value from an endpoint for 514 which the intermediary has previously received a Session-ID and is 515 storing a "remote-uuid" value for that endpoint, the lack of a 516 Session-ID must have no effect on what the intermediary believes is 517 the UUID value of the endpoint. That is, the intermediary MUST NOT 518 change the internally maintained "remote-uuid" value for the peer. 520 When an intermediary originates a response, such as a provisional 521 response or a response to a CANCEL request, the "remote-uuid" field 522 will contain the UUID value of the receiving endpoint. When the UUID 523 of the peer endpoint is known, the intermediary MUST insert the UUID 524 of the peer endpoint in the "local-uuid" field of the header value. 526 Otherwise, the intermediary MAY set the "local-uuid" field of the 527 header value to the "nil" UUID value. 529 When an intermediary originates a request message without first 530 having received a SIP message that triggered the transmission of the 531 message (e.g., sending a BYE message to terminate a call for policy 532 reasons), the intermediary MUST, if it has knowledge of the UUID 533 values for the two communicating endpoints, insert a Session-ID 534 header field with the "remote-uuid" field of the header value set to 535 the UUID value of the receiving endpoint and the "local-uuid" field 536 of the header value set to the UUID value of the other endpoint. 537 When the intermediary does not have knowledge of the UUID value of an 538 endpoint in the communication session, the intermediary SHOULD set 539 the unknown UUID value(s) to the "nil" UUID value. (If both are 540 unknown, the Session-ID header value SHOULD NOT be included at all, 541 since it would have no practical value.) 543 With respect to the previous two paragraphs, note that if an 544 intermediary transmits a "nil" UUID value, the receiving endpoint 545 might use that value in subsequent messages it sends. This 546 effectively violates the requirement of maintaining an end-to-end 547 Session Identifier value for the communication session if a UUID for 548 the peer endpoint had been previously conveyed. Therefore, an 549 intermediary MUST only send the "nil" UUID when the intermediary has 550 not communicated with the peer endpoint to learn its UUID. This 551 means that intermediaries SHOULD maintain state related to the UUID 552 values for both ends of a communication session if it intends to 553 originate messages (versus merely conveying messages). An 554 intermediary that does not maintain this state and that originates a 555 message as described in the previous two paragraphs MUST NOT insert a 556 Session-ID header field in order to avoid unintended, incorrect 557 reassignment of a UUID value. 559 The Session-ID header field value included in a CANCEL request MUST 560 be identical to the Session-ID header field value included in the 561 corresponding request. 563 If a SIP intermediary initiates a dialog between two endpoints in a 564 third-party call control (3PCC [RFC3725]) scenario, the SIP request 565 in the initial INVITE will have a non-nil, locally-fabricated "local- 566 uuid" value; call this temporary UUID X. The request will still have 567 a nil "remote-uuid" value; call this value N. The SIP server MUST be 568 transaction stateful. The UUID pair in the INVITE will be {X,N}. A 569 1xx or 2xx response will have a UUID pair {A,X}. This transaction 570 stateful, dialog initiating SIP server MUST replace its own UUID, 571 i.e., X, with a nil UUID (i.e., {A,N}) in the INVITE sent towards the 572 other UAS as expected (see Section 10.7 for an example). 574 Intermediaries that manipulate messages containing a Session-ID 575 header field SHOULD be aware of what UUID values it last sent towards 576 an endpoint and, following any kind of service interaction initiated 577 or affected by the intermediary, of what UUID values the receiving 578 endpoint should have knowledge to ensure that both endpoints in the 579 session have the correct and same UUID values. If an intermediary 580 can determine that an endpoint might not have received a current, 581 correct Session-ID field, the intermediary SHOULD attempt to provide 582 the correct Session-ID header field to the endpoint such as by 583 sending a re-INVITE message. Failure to take such measures may make 584 troubleshooting more difficult because of the mismatched identifiers, 585 therefore it is strongly advised that intermediaries attempt to 586 provide the correct Session Identifier if it able to do so. 588 If an intermediary receives a SIP response with a non-nil "local- 589 uuid" that is not 32 octets long, this response comes from a 590 misbehaving implementation, and its Session-ID header field MUST be 591 discarded. That said, the response might still be valid according to 592 the rules within SIP [RFC3261], and SHOULD be checked further. 594 An intermediary MUST assume that the UUID value of session peers may 595 change at any time due to service interactions and MAY itself change 596 UUID values for sessions under its control to ensure end to end 597 session identifiers are consistent for all participants in a session. 598 Section 8 discusses how intermediaries must handle remote UUID 599 changes if they maintain state of the session identifier. 601 An intermediary may perform protocol interworking between different 602 IP-based communications systems, e.g. interworking between H.323 and 603 SIP. If the intermediary supports the Session Identifier for both 604 protocols for which it is interworking, it SHOULD pass the identifier 605 between the two call legs to maintain an end-to-end identifier 606 regardless of protocol. 608 8. Handling of Remote UUID Changes 610 It is desirable to have all endpoints and intermediaries involved in 611 a session agree upon the current session identifier when these 612 changes occur. Due to race conditions or certain interworking 613 scenarios, it is not always possible to guarantee session identifier 614 consistency; however, in an attempt to ensure the highest likelihood 615 of consistency, all endpoints and intermediaries involved in a 616 session MUST accept a peer's new UUID under the following conditions: 618 o When an endpoint or intermediary receives a mid-dialog request 619 containing a new UUID from a peer, all responses to that request 620 MUST contain the new UUID value as the "remote" parameter unless a 621 subsequent successful transaction (for example, an UPDATE) 622 contains a different UUID, in which case the newest UUID MUST be 623 used. 625 o If an endpoint or intermediary sends a successful (2xx) or 626 redirection (3xx) response to the request containing the new UUID 627 value, the endpoint or intermediary MUST accept the peer's UUID 628 and include this new UUID as the "remote" parameter for any 629 subsequent messages unless the UUID from a subsequent transaction 630 has already been accepted. The one exception is a CANCEL request 631 as outlined below. 633 o If the endpoint or intermediary sends a failure (4xx, 5xx, 6xx) 634 response, it MUST NOT accept the new UUID value and any subsequent 635 messages MUST contain the previously stored UUID value in the 636 "remote" parameter for any subsequent message. Note that the 637 failure response itself will contain the new UUID value from the 638 request in the "remote" parameter. 640 o The ACK method is a special case as there is no response. When an 641 endpoint or intermediary receives an ACK for a successful (2xx) or 642 redirection (3xx) response with a new UUID value, it MUST accept 643 the peer's new UUID value and include this new UUID as the 644 "remote" parameter for any subsequent messages. If the ACK is for 645 a failure (4xx, 5xx, 6xx) response, the new value MUST NOT be 646 used. 648 o As stated in Section 6 and Section 7, the Session-ID header field 649 value included in a CANCEL request MUST be identical to the 650 Session-ID header field value included in the corresponding 651 INVITE. Upon receiving a CANCEL request, an endpoint or 652 intermediary would normally send a Request Terminated (487 - see 653 Section 15.1.2 of [RFC3261]) response which, by the rules outlined 654 above, would result in the endpoint or intermediary not storing 655 any UUID value contained in the CANCEL. Section 3.8 of [RFC6141] 656 specifies conditions where a CANCEL can result in 2xx response. 657 Because CANCEL is not passed end-to-end and will always contain 658 the UUID from the original INVITE, retaining a new UUID value 659 received in a CANCEL may result in inconsistency with the Session- 660 ID value stored on the endpoints and intermediaries involved in 661 the session. To avoid this situation, an endpoint or intermediary 662 MUST NOT accept the new UUID value received in a CANCEL and any 663 subsequent messages MUST contain the previously stored UUID value 664 in the "remote" parameter". Note that the response to the CANCEL 665 will contain the UUID value from the CANCEL request in the 666 "remote" parameter. 668 o When an endpoint or intermediary receives a response containing a 669 new UUID from a peer, the endpoint or intermediary MUST accept the 670 new UUID as the peer's UUID and include this new UUID as the 671 "remote" parameter for any subsequent messages. 673 When an intermediary accepts a new UUID from a peer, the intermediary 674 SHOULD attempt to provide the correct Session-ID header field to 675 other endpoints involved in the session, for example, by sending a 676 re-INVITE message. If an intermediary receives a message with a 677 "remote" parameter in the session identifier that does not match the 678 updated UUID, the intermediary MUST update the "remote" parameter 679 with the latest stored UUID. 681 If an intermediary is performing interworking between two different 682 protocols that both support the Session Identifier defined in this 683 document (e.g. SIP to H.323), UUID changes SHOULD be communicated 684 between protocols to maintain the end-to-end session identifier. 686 9. Associating Endpoints in a Multipoint Conference 688 Multipoint Control Units (MCUs) group two or more sessions into a 689 single multipoint conference and have a conference Focus responsible 690 for maintaining the dialogs connected to it [RFC4353]. MCUs, 691 including cascaded MCUs, MUST utilize the same UUID value ("local- 692 uuid" portion of the Session-ID header field value) with all 693 participants in the conference. In so doing, each individual session 694 in the conference will have a unique Session Identifier (since each 695 endpoint will create a unique UUID of its own), but will also have 696 one UUID in common with all other participants in the conference. 698 When creating a cascaded conference, an MCU MUST convey the UUID 699 value to utilize for a conference via the "local-uuid" portion of the 700 Session-ID header field value in an INVITE to a second MCU when using 701 SIP to establish the cascaded conference. A conference bridge, or 702 MCU, needs a way to identify itself when contacting another MCU. 703 [RFC4579] defines the "isfocus" Contact header field value parameter 704 just for this purpose. The initial MCU MUST include the UUID of that 705 particular conference in the "local-uuid" of an INVITE to the other 706 MCU(s) participating in that conference. Also included in this 707 INVITE is an "isfocus" Contact header field value parameter 708 identifying that this INVITE is coming from an MCU and that this UUID 709 is to be given out in all responses from endpoints into those MCUs 710 participating in this same conference. This ensures a single UUID is 711 common across all participating MCUs of the same conference, but is 712 unique between different conferences. 714 In the case where two existing conferences are joined, there should 715 be a session between the two MCUs where the Session Identifier is 716 comprised of the UUID values of the two conferences. This Session 717 Identifier can be used to correlate the sessions between participants 718 in the joined conference. This specification does not impose any 719 additional requirements when two existing conferences are joined. 721 Intermediary devices or network diagnostics equipment might assume 722 that when they see two or more sessions with different Session 723 Identifiers, but with one UUID in common, that the sessions are part 724 of the same conference. However, the assumption that two sessions 725 having one common UUID being part of the same conference is not 726 always correct. In a SIP forking scenario, for example, there might 727 also be what appears to be multiple sessions with a shared UUID 728 value; this is intended. The desire is to allow for the association 729 of related sessions, regardless of whether a session is forked or 730 part of a conference. 732 10. Examples of Various Call Flow Operations 734 Seeing something frequently makes understanding easier. With that in 735 mind, this section includes several call flow examples with the 736 initial UUID and the complete Session Identifier indicated per 737 message, as well as when the Session Identifier changes according to 738 the rules within this document during certain operations/functions. 740 This section is for illustrative purposes only and is non-normative. 741 In the following flows, RTP refers to the Real-time Transport 742 Protocol [RFC3550]. 744 In the examples in this section, "N" represents a nil UUID and other 745 letters represents the unique UUID values corresponding to endpoints 746 or MCUs. 748 10.1. Basic Call with 2 UUIDs 750 Session-ID 751 --- Alice B2BUA Bob Carol 752 {A,N} |---INVITE F1--->| | 753 {A,N} | |---INVITE F2--->| 754 {B,A} | |<---200 OK F3---| 755 {B,A} |<---200 OK F4---| | 756 {A,B} |-----ACK F5---->| | 757 {A,B} | |-----ACK F6---->| 758 |<==============RTP==============>| 760 Figure 1: Session-ID Creation when Alice calls Bob 762 General operation of this example: 764 o UA-Alice populates the "local-uuid" portion of the Session-ID 765 header field value. 767 o UA-Alice sends its UUID in the SIP INVITE, and populates the 768 "remote" parameter with a nil value (32 zeros). 770 o B2BUA receives an INVITE with both a "local-uuid" portion of the 771 Session-ID header field value from UA-Alice as well as the nil 772 "remote-uuid" value, and transmits the INVITE towards UA-Bob with 773 an unchanged Session-ID header field value. 775 o UA-Bob receives Session-ID and generates its "local-uuid" portion 776 of the Session-ID header field value UUID to construct the whole/ 777 complete Session-ID header field value, at the same time 778 transferring Alice's UUID unchanged to the "remote-uuid" portion 779 of the Session-ID header field value in the 200 OK SIP response. 781 o B2BUA receives the 200 OK response with a complete Session-ID 782 header field value from UA-Bob, and transmits 200 OK towards UA- 783 Alice with an unchanged Session-ID header field value. 785 o UA-Alice, upon reception of the 200 OK from the B2BUA, transmits 786 the ACK towards the B2BUA. The construction of the Session-ID 787 header field in this ACK is that of Alice's UUID is the "local- 788 uuid", and Bob's UUID populates the "remote-uuid" portion of the 789 header-value. 791 o B2BUA receives the ACK with a complete Session-ID header field 792 from UA-Alice, and transmits ACK towards UA-Bob with an unchanged 793 Session-ID header field value. 795 Below is a SIP message exchange illustrating proper use of the 796 Session-ID header field. For the sake of brevity, non-essential 797 headers and message bodies are omitted. 799 F1 INVITE Alice -> B2BUA 801 INVITE sip:bob@biloxi.example.com SIP/2.0 802 Via: SIP/2.0/UDP pc33.atlanta.example.com 803 ;branch=z9hG4bK776asdhds 804 Max-Forwards: 70 805 To: Bob 806 From: Alice ;tag=1928301774 807 Call-ID: a84b4c76e66710@pc33.atlanta.example.com 808 Session-ID: ab30317f1a784dc48ff824d0d3715d86 809 ;remote=00000000000000000000000000000000 810 CSeq: 314159 INVITE 811 Contact: 812 Content-Type: application/sdp 813 Content-Length: 142 814 (Alice's SDP not shown) 816 F2 INVITE B2BUA -> Bob 818 INVITE sip:bob@192.168.10.20 SIP/2.0 819 Via: SIP/2.0/UDP server10.biloxi.example.com 820 ;branch=z9hG4bK4b43c2ff8.1 821 Via: SIP/2.0/UDP pc33.atlanta.example.com 822 ;branch=z9hG4bK776asdhds;received=10.1.3.33 823 Max-Forwards: 69 824 To: Bob 825 From: Alice ;tag=1928301774 826 Call-ID: a84b4c76e66710@pc33.atlanta.example.com 827 Session-ID: ab30317f1a784dc48ff824d0d3715d86 828 ;remote=00000000000000000000000000000000 829 CSeq: 314159 INVITE 830 Contact: 831 Record-Route: 832 Content-Type: application/sdp 833 Content-Length: 142 835 (Alice's SDP not shown) 837 F3 200 OK Bob -> B2BUA 839 SIP/2.0 200 OK 840 Via: SIP/2.0/UDP server10.biloxi.example.com 841 ;branch=z9hG4bK4b43c2ff8.1;received=192.168.10.1 842 Via: SIP/2.0/UDP pc33.atlanta.example.com 843 ;branch=z9hG4bK776asdhds;received=10.1.3.33 844 To: Bob ;tag=a6c85cf 845 From: Alice ;tag=1928301774 846 Call-ID: a84b4c76e66710@pc33.atlanta.example.com 847 Session-ID: 47755a9de7794ba387653f2099600ef2 848 ;remote=ab30317f1a784dc48ff824d0d3715d86 849 CSeq: 314159 INVITE 850 Contact: 851 Record-Route: 852 Content-Type: application/sdp 853 Content-Length: 131 855 (Bob's SDP not shown) 857 F4 200 OK B2BUA -> Alice 858 SIP/2.0 200 OK 859 Via: SIP/2.0/UDP pc33.atlanta.example.com 860 ;branch=z9hG4bK776asdhds;received=10.1.3.33 861 To: Bob ;tag=a6c85cf 862 From: Alice ;tag=1928301774 863 Call-ID: a84b4c76e66710@pc33.atlanta.example.com 864 Session-ID: 47755a9de7794ba387653f2099600ef2 865 ;remote=ab30317f1a784dc48ff824d0d3715d86 866 CSeq: 314159 INVITE 867 Contact: 868 Record-Route: 869 Content-Type: application/sdp 870 Content-Length: 131 872 (Bob's SDP not shown) 874 F5 ACK Alice -> B2BUA 876 ACK sip:bob@192.168.10.20 SIP/2.0 877 Via: SIP/2.0/UDP pc33.atlanta.example.com 878 ;branch=z9hG4bKnashds8 879 Route: 880 Max-Forwards: 70 881 To: Bob ;tag=a6c85cf 882 From: Alice ;tag=1928301774 883 Call-ID: a84b4c76e66710@pc33.atlanta.example.com 884 Session-ID: ab30317f1a784dc48ff824d0d3715d86 885 ;remote=47755a9de7794ba387653f2099600ef2 886 CSeq: 314159 ACK 887 Content-Length: 0 889 F6 ACK B2BUA -> Bob 891 ACK sip:bob@192.168.10.20 SIP/2.0 892 Via: SIP/2.0/UDP server10.biloxi.example.com 893 ;branch=z9hG4bK4b43c2ff8.2 894 Via: SIP/2.0/UDP pc33.atlanta.example.com 895 ;branch=z9hG4bKnashds8;received=10.1.3.33 896 Max-Forwards: 70 897 To: Bob ;tag=a6c85cf 898 From: Alice ;tag=1928301774 899 Call-ID: a84b4c76e66710@pc33.atlanta.example.com 900 Session-ID: ab30317f1a784dc48ff824d0d3715d86 901 ;remote=47755a9de7794ba387653f2099600ef2 902 CSeq: 314159 ACK 903 Content-Length: 0 904 The remaining examples in this Section do not display the complete 905 SIP message exchange. Instead, they simply use the set notation 906 described in Section 4.2 to show the Session Identifier exchange 907 throughout the particular call flow being illustrated. 909 10.2. Basic Call Transfer using REFER 911 From the example built within Section 10.1, we proceed to this 'Basic 912 Call Transfer using REFER' example. Note that this is a mid-dialog 913 REFER in contrast with the out-of-dialog REFER in Section 10.9. 915 Session-ID 916 --- Alice B2BUA Bob Carol 917 | | | | 918 |<==============RTP==============>| | 919 {B,A} | |<---re-INVITE---| | 920 {B,A} |<---re-INVITE---| (puts Alice on Hold) | 921 {A,B} |-----200 OK---->| | | 922 {A,B} | |-----200 OK---->| | 923 {B,A} | |<-----ACK-------| | 924 {B,A} |<-----ACK-------| | | 925 | | | | 926 {B,A} | |<----REFER------| | 927 {B,A} |<----REFER------| | | 928 {A,B} |-----200 OK---->| | | 929 {A,B} | |-----200 OK---->| | 930 {A,B} |-----NOTIFY---->| | | 931 {A,B} | |-----NOTIFY---->| | 932 {B,A} | |<----200 OK-----| | 933 {B,A} |<----200 OK-----| | | 934 | | | | 935 {A,N} |-----INVITE---->| | 936 {A,N} | |-----INVITE-------------------->| 937 {C,A} | |<----200 OK---------------------| 938 {C,A} |<----200 OK-----| | 939 {A,C} |------ACK------>| | 940 {A,C} | |------ACK---------------------->| 941 | | | | 942 |<======================RTP======================>| 943 | | | | 944 {A,B} |-----NOTIFY---->| | | 945 {A,B} | |-----NOTIFY---->| | 946 {B,A} | |<----200 OK-----| | 947 {B,A} |<----200 OK-----| | | 948 {B,A} | |<-----BYE-------| | 949 {B,A} |<-----BYE-------| | | 950 {A,B} |-----200 OK---->| | | 951 {A,B} | |-----200 OK---->| | 952 | | | | 954 Figure 2: Call Transfer using REFER 956 General operation of this example: 958 Starting from the existing Alice/Bob call described in Figure 1 of 959 this document, which established an existing Session-ID header field 960 value: 962 o UA-Bob requests Alice to call Carol, using a REFER transaction, as 963 described in [RFC3515]. UA-Alice is initially put on hold, then 964 told in the REFER who to contact with a new INVITE, in this case 965 UA-Carol. This Alice-to-Carol dialog will have a new Call-ID, 966 therefore it requires a new Session-ID header field value. The 967 wrinkle here is we can, and will, use Alice's UUID from her 968 existing dialog with Bob in the new INVITE to Carol. 970 o UA-Alice retains her UUID from the Alice-to-Bob call {A} when 971 requesting a call with UA-Carol. This is placed in the "local- 972 uuid" portion of the Session-ID header field value, at the same 973 time inserting a nil "remote-uuid" value (because Carol's UA has 974 not yet received the UUID value). This same UUID traverses the 975 B2BUA unchanged. 977 o UA-Carol receives the INVITE with a Session Identifier UUID {A,N}, 978 replaces the A UUID value into the "remote-uuid" portion of the 979 Session-ID header field value and creates its own UUID {C} and 980 places this value in the "local-uuid" portion of the Session-ID 981 header field value, thereby removing the N (nil) value altogether. 982 This combination forms a full Session Identifier {C,A} in the 200 983 OK to the INVITE. This Session-ID header field traverses the 984 B2BUA unchanged towards UA-Alice. 986 o UA-Alice receives the 200 OK with the Session Identifier {C,A} and 987 responds to UA-Carol with an ACK (just as in Figure 1 - switches 988 places of the two UUID fields), and generates a NOTIFY to Bob with 989 a Session Identifier {A,B} indicating the call transfer was 990 successful. 992 o It does not matter which UA terminates the Alice-to-Bob call; 993 Figure 2 shows UA-Bob doing this transaction. 995 10.3. Basic Call Transfer using re-INVITE 997 From the example built within Section 10.1, we proceed to this 'Basic 998 Call Transfer using re-INVITE' example. 1000 Alice is talking to Bob. Bob pushes a button on his phone to transfer 1001 Alice to Carol via the B2BUA (using re-INVITE). 1003 Session-ID 1004 --- Alice B2BUA Bob Carol 1005 | | | | 1006 |<==============RTP==============>| | 1007 | | | | 1008 | | <--- (non-standard signaling) | 1009 {A,B} | |---re-INVITE--->| | 1010 {B,A} | |<-----200 OK----| | 1011 {A,B} | |-----ACK------->| | 1012 | | | | 1013 {A,N} | |-----INVITE-------------------->| 1014 {C,A} | |<----200 OK---------------------| 1015 {A,C} | |------ACK---------------------->| 1016 | | | | 1017 |<======================RTP======================>| 1018 | | | | 1019 {A,B} | |------BYE------>| | 1020 {B,A} | |<----200 OK-----| | 1021 | | | | 1022 {C,A} |<--re-INVITE----| | | 1023 {A,C} |----200 OK----->| | | 1024 {C,A} |<-----ACK-------| | | 1025 | (Suppose Alice modifies the session) | 1026 {A,C} |---re-INVITE--->| | | 1027 {A,C} | |---re-INVITE------------------->| 1028 {C,A} | |<---200 OK----------------------| 1029 {C,A} |<---200 OK------| | | 1030 {A,C} |------ACK------>| | | 1031 {A,C} | |------ACK---------------------->| 1032 | | | | 1034 Figure 3: Call transfer using re-INVITE 1036 General operation of this example: 1038 o We assume the call between Alice and Bob from Section 10.1 is 1039 operational with Session Identifier {A,B}. 1041 o Bob uses non-standard signaling to the B2BUA to initiate a call 1042 transfer from Alice to Carol. This could also be initiated via a 1043 REFER message from Bob, but the signaling that follows might still 1044 be similar to the above flow. In either case, Alice is completely 1045 unaware of the call transfer until a future point in time when 1046 Alice receives a message from Carol. 1048 o The B2BUA sends a re-INVITE with the Session Identifier {"local- 1049 uuid" = "A", "remote-uuid" = "B"} to re-negotiate the session with 1050 Bob. 1052 o The B2BUA sends a new INVITE with Alice's UUID {"local-uuid" = 1053 "A"} to Carol. 1055 o Carol receives the INVITE and accepts the request and adds her 1056 UUID {C} to the Session Identifier for this session {"local-uuid" 1057 = "C", "remote-uuid" = "A"}. 1059 o The B2BUA then terminates the call to Bob with a BYE using the 1060 Session Identifier {"local-uuid" = "A", "remote-uuid" = "B"}. 1062 o The B2BUA sends a re-INVITE to Alice to update Alice's view of the 1063 Session Identifier. 1065 o When Alice later attempts to modify the session with a re-INVITE, 1066 Alice will send "remote-uuid" = "C" toward Carol because it had 1067 previously received the updated UUID in the re-INVITE from the 1068 B2BUA. The B2BUA maintains the Session Identifier {"local-uuid" = 1069 "A", "remote-uuid" = "C"}. Carol replies with the "local-uuid" = 1070 "C", "remote-uuid" = "A" to reflect what was received in the 1071 INVITE (which Carol already knew from previous exchanges with the 1072 B2BUA). Alice then includes "remote-uuid" = "C" in the subsequent 1073 ACK message. 1075 10.4. Single Focus Conferencing 1077 Multiple users call into a conference server (say, an MCU) to attend 1078 one of many conferences hosted on or managed by that server. Each 1079 user has to identify which conference they want to join, but this 1080 information is not necessarily in the SIP messaging. It might be 1081 done by having a dedicated address for the conference or via an IVR, 1082 as assumed in this example and depicted with the use of M1, M2, and 1083 M3. Each user in this example goes through a two-step process of 1084 signaling to gain entry onto their conference call, which the 1085 conference focus identifies as M'. 1087 Session-ID Conference 1088 --- Alice Focus Bob Carol 1089 | | | | 1090 | | | | 1091 {A,N} |----INVITE----->| | | 1092 {M1,A} |<---200 OK------| | | 1093 {A,M1} |-----ACK------->| | | 1094 |<====RTP=======>| | | 1095 {M',A} |<---re-INVITE---| | | 1096 {A,M'} |-----200 OK---->| | | 1097 {M',A} |<-----ACK-------| | | 1098 | | | | 1099 | | | | 1100 {B,N} | |<----INVITE-----| | 1101 {M2,B} | |-----200 OK---->| | 1102 {B,M2} | |<-----ACK-------| | 1103 | |<=====RTP======>| | 1104 {M',B} | |---re-INVITE--->| | 1105 {B,M'} | |<----200 OK-----| | 1106 {M',B} | |------ACK------>| | 1107 | | | | 1108 | | | | 1109 {C,N} | |<--------------------INVITE-----| 1110 {M3,C} | |---------------------200 OK---->| 1111 {C,M3} | |<---------------------ACK-------| 1112 | |<=====================RTP======>| 1113 {M',C} | |-------------------re-INVITE--->| 1114 {C,M'} | |<--------------------200 OK-----| 1115 {M',C} | |----------------------ACK------>| 1117 Figure 4: Single Focus Conference Bridge 1119 General operation of this example: 1121 Alice calls into a conference server to attend a certain conference. 1122 This is a two-step operation since Alice cannot include the 1123 conference ID at this time and/or any passcode in the INVITE request. 1124 The first step is Alice's UA calling another UA to participate in a 1125 session. This will appear to be similar as the call-flow in Figure 1 1126 (in section 10.1). What is unique about this call is the second 1127 step: the conference server sends a re-INVITE request with its second 1128 UUID, but maintaining the UUID Alice sent in the first INVITE. This 1129 subsequent UUID from the conference server will be the same for each 1130 UA that calls into this conference server participating in this same 1131 conference bridge/call, which is generated once Alice typically 1132 authenticates and identifies which bridge she wants to participate 1133 on. 1135 o Alice sends an INVITE to the conference server with her UUID {A} 1136 and a "remote-uuid" = N. 1138 o The conference server responds with a 200 OK response which 1139 replaces the N UUID with a temporary UUID ("M1") as the "local- 1140 uuid" and a "remote-uuid" = "A". 1142 NOTE: this 'temporary' UUID is a real UUID; it is only temporary to 1143 the conference server because it knows that it is going to generate 1144 another UUID to replace the one just send in the 200 OK. 1146 o Once Alice, the user, gains access to the IVR for this conference 1147 server, she enters a specific conference ID and whatever passcode 1148 (if needed) to enter a specific conference call. 1150 o Once the conference server is satisfied Alice has identified which 1151 conference she wants to attend (including any passcode 1152 verification), the conference server re-INVITEs Alice to the 1153 specific conference and includes the Session-ID header field value 1154 component "local-uuid" = "M'" (and "remote-uuid" = "A") for that 1155 conference. All valid participants in the same conference will 1156 receive this same UUID for identification purposes and to better 1157 enable monitoring, and tracking functions. 1159 o Bob goes through this two-step process of an INVITE transaction, 1160 followed by a re-INVITE transaction to get this same UUID ("M'") 1161 for that conference. 1163 o In this example, Carol (and each additional user) goes through the 1164 same procedures and steps as Alice and Bob to get on this same 1165 conference. 1167 10.5. Single Focus Conferencing using a web-based conference service 1169 Alice, Bob and Carol call into same web-based conference. Note this 1170 this is one of many ways of implementing this functionality and 1171 should not be construed as the preferred way of establishing a web- 1172 based conference. 1174 Session-ID Conference 1175 --- Alice Focus Bob Carol 1176 | | | | 1177 |<** HTTPS *****>| | | 1178 | Transaction | | | 1179 | | | | 1180 {M,N} |<----INVITE-----| | | 1181 {A,M} |-----200 OK---->| | | 1182 {M,A} |<-----ACK-------| | | 1183 |<=====RTP======>| | | 1184 | | | | 1185 | |<** HTTPS *****>| | 1186 | | Transaction | | 1187 | | | | 1188 {M,N} | |-----INVITE---->| | 1189 {B,M} | |<----200 OK-----| | 1190 {M,B} | |------ACK------>| | 1191 | |<=====RTP======>| | 1192 | | | | 1193 | |<****************** HTTPS *****>| 1194 | | Transaction | 1195 | | | | 1196 {M,N} | |--------------------INVITE----->| 1197 {C,M} | |<-------------------200 OK------| 1198 {M,C} | |---------------------ACK------->| 1199 | |<====================RTP=======>| 1201 Figure 5: Single Focus Web-based Conference 1203 General operation of this example: 1205 o Alice communicates with web server with desire to join a certain 1206 meeting, by meeting number; also includes UA-Alice's contact 1207 information (phone number, URI and/or IP address, etc.) for each 1208 device she wants for this conference call. For example, the audio 1209 and video play-out devices could be separate units. 1211 o Conference Focus server sends INVITE (Session-ID header field 1212 value components "local-uuid" = M and a remote UUID of N, where M 1213 equals the "local-uuid" for each participant on this conference 1214 bridge) to UA-Alice to start session with that server for this A/V 1215 conference call. 1217 o Upon receiving the INVITE request from the conference focus 1218 server, Alice responds with a 200 OK. Her UA moves the "local- 1219 uuid" unchanged into the "remote-uuid" field, and generates her 1220 own UUID and places that into the "local-uuid" field to complete 1221 the Session-ID construction. 1223 o Bob and Carol perform same function to join this same A/V 1224 conference call as Alice. 1226 10.6. Cascading Conference Bridges 1228 10.6.1. Establishing a Cascaded Conference 1230 To expand conferencing capabilities requires cascading conference 1231 bridges. A conference bridge, or MCU, needs a way to identify itself 1232 when contacting another MCU. [RFC4579] defines the 'isfocus' 1233 Contact: header parameter just for this purpose. 1235 Session-ID 1236 --- MCU-1 MCU-2 MCU-3 MCU-4 1237 | | | | 1238 {M',N} |----INVITE----->| | | 1239 {J,M'} |<---200 OK------| | | 1240 {M',J} |-----ACK------->| | | 1242 Figure 6: MCUs Communicating Session Identifier UUID for Bridge 1244 Regardless of which MCU (1 or 2) a UA contacts for this conference, 1245 once the above exchange has been received and acknowledged, the UA 1246 will get the same {M',N} UUID pair from the MCU for the complete 1247 Session Identifier. 1249 A more complex form would be a series of MCUs all being informed of 1250 the same UUID to use for a specific conference. This series of MCUs 1251 can either be informed 1253 o All by one MCU (that initially generates the UUID for the 1254 conference). 1256 o The MCU that generates the UUID informs one or several MCUs of 1257 this common UUID, and they inform downstream MCUs of this common 1258 UUID that each will be using for this one conference. 1260 Session-ID 1261 --- MCU-1 MCU-2 MCU-3 MCU-4 1262 | | | | 1263 {M',N} |----INVITE----->| | | 1264 {J,M'} |<---200 OK------| | | 1265 {M',J} |-----ACK------->| | | 1266 | | | | 1267 {M',N} |---------------------INVITE----->| | 1268 {K,M'} |<--------------------200 OK------| | 1269 {M',K} |----------------------ACK------->| | 1270 | | | | 1271 {M',N} |-------------------------------------INVITE----->| 1272 {L,M'} |<------------------------------------200 OK------| 1273 {M',L} |--------------------------------------ACK------->| 1275 Figure 7: MCU Communicating Session Identifier UUID to More than One 1276 MCU 1278 General operation of this example: 1280 o The MCU generating the Session Identifier UUID communicates this 1281 in a separate INVITE, having a Contact header with the 'isfocus' 1282 header parameter. This will identify the MCU as what [RFC4579] 1283 calls a conference-aware SIP entity. 1285 o An MCU that receives this {M',N} UUID pair in an inter-MCU 1286 transaction can communicate the M' UUID in a manner in which it 1287 was received to construct a hierarchical cascade (though this time 1288 this second MCU would be the UAC MCU). 1290 o Once the conference is terminated, the cascaded MCUs will receive 1291 a BYE message to terminate the cascade. 1293 10.6.2. Calling into Cascaded Conference Bridges 1295 Here is an example of how a UA, say Robert, calls into a cascaded 1296 conference focus. Because MCU-1 has already contacted MCU-3, the MCU 1297 where Robert is going to join the conference, MCU-3 already has the 1298 Session-ID (M') for this particular conference call. 1300 Session-ID 1301 --- MCU-1 MCU-2 MCU-3 Robert 1302 | | | | 1303 {M',N} |----INVITE----->| | | 1304 {J,M'} |<---200 OK------| | | 1305 {M',J} |-----ACK------->| | | 1306 | | | | 1307 {M',N} |---------------------INVITE----->| | 1308 {K,M'} |<--------------------200 OK------| | 1309 {M',K} |----------------------ACK------->| | 1310 | | | | 1311 {R,N} | | |<---INVITE-----| 1312 (M',R} | | |----200 OK---->| 1313 {R,M'} | | |<----ACK-------| 1315 Figure 8: A UA Calling into a Cascaded MCU UUID 1317 General operation of this example: 1319 o The UA, Robert in this case, INVITEs the MCU to join a particular 1320 conference call. Robert's UA does not know anything about whether 1321 this is the main MCU of the conference call, or a cascaded MCU. 1322 Robert likely does not know MCUs can be cascaded, he just wants to 1323 join a particular call. Like as with any standard implementation, 1324 he includes a nil "remote-uuid". 1326 o The cascaded MCU, upon receiving this INVITE from Robert, replaces 1327 the nil UUID with the UUID value communicated from MCU-1 for this 1328 conference call as the "local-uuid" in the SIP response. Thus, 1329 moving Robert's UUID "R" to the "remote-uuid" value. 1331 o The ACK has the Session-ID {R,M'}, completing the 3-way handshake 1332 for this call establishment. Robert has now joined the conference 1333 call originated from MCU-1. 1335 o Once the conference is terminated, the cascaded MCUs will receive 1336 a BYE message to terminate the cascade. 1338 10.7. Basic 3PCC for two UAs 1340 An external entity sets up calls to both Alice and Bob for them to 1341 talk to each other. 1343 Session-ID 1344 --- Alice B2BUA Bob Carol 1345 | | | 1346 {X,N} |<----INVITE-----| | 1347 {A,X} |-----200 OK---->| | 1348 {A,N} | |----INVITE----->| 1349 {B,A} | |<---200 OK------| 1350 {B,A} |<-----ACK-------| | 1351 {A,B} | |------ACK------>| 1352 |<==============RTP==============>| 1354 Figure 9: 3PCC initiated call between Alice and Bob 1356 General operation of this example: 1358 o Some out of band procedure directs a B2BUA (or other SIP server) 1359 to have Alice and Bob talk to each other. In this case, the SIP 1360 server has to be transaction stateful, if not dialog stateful. 1362 o The SIP server INVITEs Alice to a session and uses a temporary 1363 UUID {X} and a nil UUID pairing. 1365 o Alice receives and accepts this call set-up and replaces the nil 1366 UUID with her UUID {A} in the Session Identifier, now {A,X}. 1368 o The transaction stateful SIP server receives Alice's UUID {A} in 1369 the local UUID portion and keeps it there, and discards its own 1370 UUID {X}, replacing this with a nil UUID value in the INVITE to 1371 Bob as if this came from Alice originally. 1373 o Bob receives and accepts this INVITE and adds his own UUID {B} to 1374 the Session Identifier, now {B,A} for the response. 1376 o The session is established. 1378 10.8. Handling in 100 Trying SIP Response and CANCEL Request 1380 The following two subsections show examples of the Session Identifier 1381 for a 100 Trying response and a CANCEL request in a single call-flow. 1383 10.8.1. Handling in a 100 Trying SIP Response 1385 The following 100 Trying response is taken from an existing RFC, from 1386 [RFC5359] Section 2.9 ("Call Forwarding - No Answer"). 1388 Session-ID Alice SIP Server Bob-1 Bob-2 1389 | | | | 1390 {A,N} |----INVITE----->| | | 1391 {A,N} | |---INVITE---->| | 1392 {N,A} |<--100 Trying---| | | 1393 {B1,A} | |<-180 Ringing-| | 1394 {B1,A} |<--180 Ringing--| | | 1395 | | | | 1396 | *Request Timeout* | 1397 | | | | 1398 {A,N} | |---CANCEL---->| | 1399 {B1,A} | |<--200 OK-----| | 1400 {B1,A} | |<---487-------| | 1401 {A,B1} | |---- ACK ---->| | 1402 | | | | 1403 {N,A} |<-181 Call Fwd--| | | 1404 | | | | 1405 {A,N} | |------------------INVITE------>| 1406 {B2,A} | |<----------------180 Ringing---| 1407 {B2,A} |<-180 Ringing---| | | 1408 {B2,A} | |<-----------------200 OK ------| 1409 {B2,A} |<--200 OK-------| | | 1410 {A,B2} |----ACK-------->| | | 1411 {A,B2} | |------------------ACK--------->| 1412 | | | | 1413 |<=========== Both way RTP Established =========>| 1414 | | | | 1415 {A,B2} |----BYE-------->| | | 1416 {A,B2} | |--------------------BYE------->| 1417 {B2,A} | |<------------------200 OK------| 1418 {B2,A} |<--200 OK-------| | | 1419 | | | | 1421 Figure 10: Session Identifier in the 100 Trying and CANCEL Messaging 1423 Below is the explanatory text from RFC 5359 Section 2.9 detailing 1424 what the desired behavior is in the above call flow (i.e., what the 1425 call-flow is attempting to achieve). 1427 "Bob wants calls to B1 forwarded to B2 if B1 is not answered 1428 (information is known to the SIP server). Alice calls B1 and no one 1429 answers. The SIP server then places the call to B2." 1431 General operation of this example: 1433 o Alice generates an INVITE request because she wants to invite Bob 1434 to join her session. She creates a UUID as described in section 1435 10.1, and places that value in the "local-uuid" field of the 1436 Session-ID header field value. Alice also generates a "remote- 1437 uuid" of nil and sends this along with the "local-uuid". 1439 o The SIP server (imagine this is a B2BUA), upon receiving Alice's 1440 INVITE, generates the optional provisional response 100 Trying. 1441 Since the SIP server has no knowledge Bob's UUID for his part of 1442 the Session Identifier value, it cannot include his "local-uuid". 1443 Rather, any 100 Trying response includes Alice's UUID in the 1444 "remote-uuid" portion of the Session-ID header-value with a nil 1445 "local-uuid" value in the response. This is consistent with what 1446 Alice's UA expects to receive in any SIP response containing this 1447 UUID. 1449 10.8.2. Handling a CANCEL SIP Request 1451 In the same call-flow example as the 100 Trying response is a CANCEL 1452 request. Please refer to Figure 10 for the CANCEL request example. 1454 General operation of this example: 1456 o In Figure 10 above, Alice generates an INVITE with her UUID value 1457 in the Session-ID header field. 1459 o Bob-1 responds to this INVITE with a 180 Ringing. In that 1460 response, he includes his UUID in the Session-ID header field 1461 value (i.e., {B1,A}); thus completing the Session-ID header field 1462 for this session, even though no final response has been generated 1463 by any of Bob's UAs. 1465 o While this means that if the SIP server were to generate a SIP 1466 request within this session it could include the complete 1467 SessionID, the server sends a CANCEL and a CANCEL always uses the 1468 same Session-ID header field as the original INVITE. Thus, the 1469 CANCEL would have a Session Identifier with the "local-uuid" = 1470 "A", and the "remote-uuid" = "N". 1472 o As it happens with this CANCEL, the SIP server intends to invite 1473 another UA of Bob (i.e., B2) for Alice to communicate with. 1475 o In this example call-flow, taken from RFC 5359, Section 2.9, a 181 1476 (Call is being Forwarded) response is sent to Alice. Since the 1477 SIP server generated this SIP request, and has no knowledge of 1478 Bob-2's UUID value, it cannot include that value in this 181. 1479 Thus, and for the exact reasons the 100 Trying including the 1480 Session Identifier value, only Alice's UUID is included in the 1481 remote-uuid component of the Session-ID header field value, with a 1482 nil UUID present in the "local-uuid" component. 1484 10.9. Out-of-dialog REFER Transaction 1486 The following call-flow was extracted from Section 6.1 of [RFC5589] 1487 ("Successful Transfer"), with the only changes being the names of the 1488 UAs to maintain consistency within this document. 1490 Alice is the transferee 1491 Bob is the transferer 1492 and Carol is the transfer-target 1494 Session-ID Bob Alice Carol 1495 | | | 1496 {A,N} |<-----INVITE--------| | 1497 {B,A} |------200 OK------->| | 1498 {A,B} |<------ACK----------| | 1499 | | | 1500 {B,A} |--INVITE {hold}---->| | 1501 {A,B} |<-200 OK------------| | 1502 {B,A} |--- ACK ----------->| | 1503 | | | 1504 {B,A} |--REFER------------>|(Refer-To:Carol) | 1505 {A,B} |<-202 Accepted------| | 1506 | | | 1507 {A,B} || | 1509 | | | 1510 {A,N} | |--INVITE------------>| 1511 {C,A} | |<-200 OK-------------| 1512 {A,C} | |---ACK-------------->| 1513 | | | 1514 {A,B} |<--NOTIFY {200 OK}--| | 1515 {B,A} |---200 OK---------->| | 1516 | | | 1517 {B,A} |--BYE-------------->| | 1518 {A,B} |<-200 OK------------| | 1519 {C,A} | |<------------BYE-----| 1520 {A,C} | |-------------200 OK->| 1522 Figure 11: Out-Of-Dialog Call Transfer 1524 General operation of this example: 1526 o Just as in Section 10.2, Figure 2, Alice invites Bob to a session, 1527 and Bob eventually transfers Alice to communicate with Carol. 1529 o What is different about the call-flow in Figure 11 is that Bob's 1530 REFER is not in-dialog. Even so, this is treated as part of the 1531 same communication session and, thus, the Session Identifier in 1532 those messages is {A,B}. 1534 o Alice will use her existing UUID and the nil UUID ({A,N}) in the 1535 INVITE towards Carol (who generates UUID "C" for this session), 1536 thus maintaining the common UUID within the Session Identifier for 1537 this new Alice-to-Carol session. 1539 11. Compatibility with a Previous Implementation 1541 There is a much earlier document that specifies the use of a Session- 1542 ID header field (namely, [RFC7329]) that we will herewith attempt to 1543 achieve backwards compatibility. Neither Session-ID header field has 1544 any versioning information, so merely adding that this document 1545 describes "version 2" is insufficient. Here are the set of rules for 1546 compatibility between the two specifications. Although the previous 1547 version was never standardized, it has been heavily implemented and 1548 adopted by other standards development organizations. For the 1549 purposes of this discussion, we will label the pre-standard 1550 specification of the Session-ID as the "old" version and this 1551 specification as the "new" version of the Session-ID. 1553 The previous (i.e., "old") version only has a single UUID value as a 1554 Session-ID header field value, but has a generic-parameter value that 1555 can be of use. 1557 In order to have an "old" version talk to an "old" version 1558 implementation, nothing needs to be done as far as the IETF is 1559 concerned. 1561 In order to have a "new" version talk to a "new" version 1562 implementation, both implementations need to follow this document (to 1563 the letter) and everything should be just fine. 1565 For this "new" implementation to work with the "old" implementation 1566 and an "old" implementation to work with "new" implementations, there 1567 needs to be a set of rules that all "new" implementations MUST follow 1568 if the "new" implementation will be communicating with devices that 1569 have implemented the "old" implementation. 1571 o Since no option tags or feature tags are to be used for 1572 distinguishing versions, the presence and order of any "remote- 1573 uuid" value within the Session-ID header field value is to be used 1574 to distinguish implementation versions. 1576 o If a SIP request has a "remote-uuid" value, this comes from a 1577 standard implementation, and not a pre-standard one. 1579 o If a SIP request has no "remote-uuid" value, this comes from a 1580 pre-standard implementation, and not a standard one. In this 1581 case, one UUID is used to identify this dialog, even if the 1582 responder is a standard implementation of this specification. 1584 o If a SIP response has a non-nil "local-uuid" that is 32 octets 1585 long and differs from the endpoint's own UUID value, this response 1586 comes from a standard implementation. 1588 o If a SIP response arrives that has the same value of Session-ID 1589 UUIDs in the same order as was sent, this comes from a pre- 1590 standard implementation, and MUST NOT be discarded for not 1591 altering the nil "remote-uuid". In this case, any new transaction 1592 within this dialog MUST preserve the order of the two UUIDs within 1593 all Session-ID header field, including the ACK, until this dialog 1594 is terminated. 1596 o If a SIP response only contains the "local-uuid" that was sent 1597 originally, this comes from a pre-standard implementation and MUST 1598 NOT be discarded for removing the nil "remote-uuid". In this 1599 case, all future transactions within this dialog MUST contain only 1600 the UUID received in the first SIP response. Any new transaction 1601 starting a new dialog from the standard Session-ID implementation 1602 MUST include a "local-uuid" and a nil "remote-uuid", even if that 1603 new dialog is between the same two UAs. 1605 o Standard implementations SHOULD NOT expect pre-standard 1606 implementations to be consistent in their implementation, even 1607 within the same dialog. For example, perhaps the first, third and 1608 tenth responses contain a "remote-uuid", but all the others do 1609 not. This behavior MUST be allowed by implementations of this 1610 specification. 1612 o The foregoing does not apply to other, presently unknown 1613 parameters that might be defined in the future. They are ignored 1614 for the purposes of interoperability with previous 1615 implementations. 1617 12. Security and Privacy Considerations 1619 The Session Identifier MUST be constructed in such a way that does 1620 not conveyed any user or device information as outlined in 1621 Section 4.1. This ensures that the data contained in the Session 1622 Identifier itself does not convey user or device information, however 1623 the Session Identifier may reveal relationships between endpoints 1624 that might not be revealed by messages without a Session Identifier. 1626 Section 4.2 requires that a UA always generate a new, previously 1627 unused, UUID when transmitting a request to initiate a new session. 1628 This ensures that two unrelated sessions originating from the same UA 1629 will never have the same UUID value, thereby removing the ability for 1630 an attacker to use the Session Identifier to identify the two 1631 unrelated sessions as being associated with the same user. 1633 Because of the inherent property that Session Identifiers are 1634 conveyed end-to-end and remain unchanged by a UA for the duration of 1635 a session, the Session Identifier could be misused to discover 1636 relationships between two or more parties when multiple parties are 1637 involved in the same session such as the case of a redirect, 1638 transfer, or conference. For example, suppose that Alice calls Bob 1639 and Bob, via his PBX (acting as a B2BUA), forwards or transfers the 1640 call to Carol. Without use of the Session Identifier, an 1641 unauthorized third party that is observing the communications between 1642 Alice and Bob might not know that Alice is actually communicating 1643 with Carol. If Alice, Bob, and Carol include the Session Identifier 1644 as a part of the signaling messages, it is possible for the third 1645 party to observe that the UA associated with Bob changed to some 1646 other UA. If the third party also has access to signaling messages 1647 between Bob and Carol, the third party can then discover that Alice 1648 is communicating with Carol. This would be true even if all other 1649 information relating to the session is changed by the PBX, including 1650 both signaling information and media address information. That said, 1651 the Session Identifier would not reveal the identity of Alice, Bob, 1652 or Carol. It would only reveal the fact that those endpoints were in 1653 associated with the same session. 1655 The Session Identifier might be utilized for logging or 1656 troubleshooting, but is not appropriate for billing purposes. 1658 This document allows for additional parameters (generic-param) to be 1659 included in the Session-ID header. This is done to allow for future 1660 extensions while preserving backward compatibility with this 1661 document. To protect privacy, the data for any generic-param 1662 included in the Session-ID header value MUST NOT include any user or 1663 device information. 1665 An intermediary implementing a privacy service that provides user 1666 privacy as per Section 5.3 of [RFC3323] MAY choose to consider the 1667 Session-ID header as being a non-essential informational header with 1668 the understanding that doing so will impair the ability to use the 1669 Session Identifier for troubleshooting purposes. 1671 13. IANA Considerations 1673 13.1. Registration of the "Session-ID" Header Field 1675 The following is the registration for the 'Session-ID' header field 1676 to the "Header Name" registry at 1678 http://www.iana.org/assignments/sip-parameters: 1680 RFC number: RFC XXXX 1682 Header name: 'Session-ID' 1684 Compact form: none 1686 Note: This document replaces the "Session-ID" header originally 1687 registered via [RFC7329]. 1689 [RFC Editor: Please replace XXXX in this section and the next with 1690 the this RFC number of this document.] 1692 13.2. Registration of the "remote" Parameter 1694 The following parameter is to be added to the "Header Field 1695 Parameters and Parameter Values" section of the SIP parameter 1696 registry: 1698 +--------------+----------------+-------------------+-----------+ 1699 | Header Field | Parameter Name | Predefined Values | Reference | 1700 +--------------+----------------+-------------------+-----------+ 1701 | Session-ID | remote | No | [RFCXXXX] | 1702 +--------------+----------------+-------------------+-----------+ 1704 14. Acknowledgements 1706 The authors would like to thank Robert Sparks, Hadriel Kaplan, 1707 Christer Holmberg, Paul Kyzivat, Brett Tate, Keith Drage, Mary 1708 Barnes, Charles Eckel, Peter Dawes, Andrew Hutton, Arun Arunachalam, 1709 Adam Gensler, Roland Jesske, and Faisal Siyavudeen for their 1710 invaluable comments during the development of this document. 1712 15. Dedication 1714 This document is dedicated to the memory of James Polk, a long-time 1715 friend and colleague. James made important contributions to this 1716 specification, including being one of its primary editors. The IETF 1717 global community mourns his loss and he will be missed dearly. 1719 16. References 1721 16.1. Normative References 1723 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1724 Requirement Levels", BCP 14, RFC 2119, 1725 DOI 10.17487/RFC2119, March 1997, 1726 . 1728 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 1729 A., Peterson, J., Sparks, R., Handley, M., and E. 1730 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 1731 DOI 10.17487/RFC3261, June 2002, 1732 . 1734 [RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer 1735 Method", RFC 3515, DOI 10.17487/RFC3515, April 2003, 1736 . 1738 [RFC3891] Mahy, R., Biggs, B., and R. Dean, "The Session Initiation 1739 Protocol (SIP) "Replaces" Header", RFC 3891, 1740 DOI 10.17487/RFC3891, September 2004, 1741 . 1743 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 1744 Unique IDentifier (UUID) URN Namespace", RFC 4122, 1745 DOI 10.17487/RFC4122, July 2005, 1746 . 1748 [RFC4579] Johnston, A. and O. Levin, "Session Initiation Protocol 1749 (SIP) Call Control - Conferencing for User Agents", 1750 BCP 119, RFC 4579, DOI 10.17487/RFC4579, August 2006, 1751 . 1753 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 1754 Specifications: ABNF", STD 68, RFC 5234, 1755 DOI 10.17487/RFC5234, January 2008, 1756 . 1758 16.2. Informative References 1760 [H.323] International Telecommunications Union, "Recommendation 1761 ITU-T H.323, Packet-based multimedia communications 1762 systems", December 2009. 1764 [H.460.27] 1765 International Telecommunications Union, "Recommendation 1766 ITU-T H.460.27, End-to-End Session Identifier for H.323 1767 Systems", November 2015. 1769 [RFC2543] Handley, M., Schulzrinne, H., Schooler, E., and J. 1770 Rosenberg, "SIP: Session Initiation Protocol", RFC 2543, 1771 DOI 10.17487/RFC2543, March 1999, 1772 . 1774 [RFC3323] Peterson, J., "A Privacy Mechanism for the Session 1775 Initiation Protocol (SIP)", RFC 3323, 1776 DOI 10.17487/RFC3323, November 2002, 1777 . 1779 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 1780 Jacobson, "RTP: A Transport Protocol for Real-Time 1781 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 1782 July 2003, . 1784 [RFC3725] Rosenberg, J., Peterson, J., Schulzrinne, H., and G. 1785 Camarillo, "Best Current Practices for Third Party Call 1786 Control (3pcc) in the Session Initiation Protocol (SIP)", 1787 BCP 85, RFC 3725, DOI 10.17487/RFC3725, April 2004, 1788 . 1790 [RFC4353] Rosenberg, J., "A Framework for Conferencing with the 1791 Session Initiation Protocol (SIP)", RFC 4353, 1792 DOI 10.17487/RFC4353, February 2006, 1793 . 1795 [RFC5359] Johnston, A., Ed., Sparks, R., Cunningham, C., Donovan, 1796 S., and K. Summers, "Session Initiation Protocol Service 1797 Examples", BCP 144, RFC 5359, DOI 10.17487/RFC5359, 1798 October 2008, . 1800 [RFC5589] Sparks, R., Johnston, A., Ed., and D. Petrie, "Session 1801 Initiation Protocol (SIP) Call Control - Transfer", 1802 BCP 149, RFC 5589, DOI 10.17487/RFC5589, June 2009, 1803 . 1805 [RFC6141] Camarillo, G., Ed., Holmberg, C., and Y. Gao, "Re-INVITE 1806 and Target-Refresh Request Handling in the Session 1807 Initiation Protocol (SIP)", RFC 6141, 1808 DOI 10.17487/RFC6141, March 2011, 1809 . 1811 [RFC6872] Gurbani, V., Ed., Burger, E., Ed., Anjali, T., Abdelnur, 1812 H., and O. Festor, "The Common Log Format (CLF) for the 1813 Session Initiation Protocol (SIP): Framework and 1814 Information Model", RFC 6872, DOI 10.17487/RFC6872, 1815 February 2013, . 1817 [RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session 1818 Initiation Protocol (SIP) Back-to-Back User Agents", 1819 RFC 7092, DOI 10.17487/RFC7092, December 2013, 1820 . 1822 [RFC7206] Jones, P., Salgueiro, G., Polk, J., Liess, L., and H. 1823 Kaplan, "Requirements for an End-to-End Session 1824 Identification in IP-Based Multimedia Communication 1825 Networks", RFC 7206, DOI 10.17487/RFC7206, May 2014, 1826 . 1828 [RFC7329] Kaplan, H., "A Session Identifier for the Session 1829 Initiation Protocol (SIP)", RFC 7329, 1830 DOI 10.17487/RFC7329, August 2014, 1831 . 1833 Authors' Addresses 1835 Paul E. Jones 1836 Cisco Systems, Inc. 1837 7025 Kit Creek Rd. 1838 Research Triangle Park, NC 27709 1839 USA 1841 Phone: +1 919 476 2048 1842 Email: paulej@packetizer.com 1844 Gonzalo Salgueiro 1845 Cisco Systems, Inc. 1846 7025 Kit Creek Rd. 1847 Research Triangle Park, NC 27709 1848 USA 1850 Phone: +1 919 392 3266 1851 Email: gsalguei@cisco.com 1852 Chris Pearce 1853 Cisco Systems, Inc. 1854 2300 East President George Bush Highway 1855 Richardson, TX 75082 1856 USA 1858 Phone: +1 972 813 5123 1859 Email: chrep@cisco.com 1861 Paul Giralt 1862 Cisco Systems, Inc. 1863 7025 Kit Creek Rd. 1864 Research Triangle Park, NC 27709 1865 USA 1867 Phone: +1 919 991 5644 1868 Email: pgiralt@cisco.com