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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-09) exists of draft-ietf-sipcore-rfc3265bis-04 == Outdated reference: A later version (-14) exists of draft-ietf-salud-alert-info-urns-04 == Outdated reference: A later version (-15) exists of draft-worley-service-example-08 Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 BLISS A. Johnston, Ed. 3 Internet-Draft Avaya 4 Updates: 3261, 4235 (if approved) M. Soroushnejad 5 Intended status: Standards Track V. Venkataramanan 6 Expires: July 2, 2012 Sylantro Systems Corp 7 December 30, 2011 9 Shared Appearances of a Session Initiation Protocol (SIP) Address of 10 Record (AOR) 11 draft-ietf-bliss-shared-appearances-09 13 Abstract 15 This document describes the requirements and implementation of a 16 group telephony feature commonly known as Bridged Line Appearance 17 (BLA) or Multiple Line Appearance (MLA), or Shared Call/Line 18 Appearance (SCA). When implemented using the Session Initiation 19 Protocol (SIP), it is referred to as shared appearances of an Address 20 of Record (AOR) since SIP does not have the concept of lines. This 21 feature is commonly offered in IP Centrex services and IP-PBX 22 offerings and is likely to be implemented on SIP IP telephones and 23 SIP feature servers used in a business environment. This feature 24 allows several user agents (UAs) to share a common AOR, learn about 25 calls placed and received by other UAs in the group, and pick up or 26 join calls within the group. This document discusses use cases, 27 lists requirements and defines extensions to implement this feature. 29 Status of this Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at http://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on July 2, 2012. 46 Copyright Notice 48 Copyright (c) 2011 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 This document may contain material from IETF Documents or IETF 62 Contributions published or made publicly available before November 63 10, 2008. The person(s) controlling the copyright in some of this 64 material may not have granted the IETF Trust the right to allow 65 modifications of such material outside the IETF Standards Process. 66 Without obtaining an adequate license from the person(s) controlling 67 the copyright in such materials, this document may not be modified 68 outside the IETF Standards Process, and derivative works of it may 69 not be created outside the IETF Standards Process, except to format 70 it for publication as an RFC or to translate it into languages other 71 than English. 73 Table of Contents 75 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 76 2. Conventions used in this document . . . . . . . . . . . . . . 6 77 3. Usage Scenarios . . . . . . . . . . . . . . . . . . . . . . . 6 78 3.1. Executive/Assistant Arrangement . . . . . . . . . . . . . 6 79 3.2. Call Group . . . . . . . . . . . . . . . . . . . . . . . 7 80 3.3. Single Line Extension . . . . . . . . . . . . . . . . . . 7 81 3.4. Changing UAs . . . . . . . . . . . . . . . . . . . . . . 7 82 4. Requirements and Implementation . . . . . . . . . . . . . . . 7 83 4.1. Requirements . . . . . . . . . . . . . . . . . . . . . . 7 84 4.2. Implementation . . . . . . . . . . . . . . . . . . . . . 9 85 5. Normative Description . . . . . . . . . . . . . . . . . . . . 11 86 5.1. Elements . . . . . . . . . . . . . . . . . . . . . . . . 11 87 5.2. Shared Appearance Dialog Package Extensions . . . . . . . 12 88 5.2.1. The element . . . . . . . . . . . . . . . 12 89 5.2.2. The element . . . . . . . . . . . . . . . 12 90 5.2.3. The element . . . . . . . . . . . . . 13 91 5.2.4. The element . . . . . . . . . . . . 14 92 5.3. Shared Appearance User Agents . . . . . . . . . . . . . . 14 93 5.3.1. Appearance Numbers and Call Context . . . . . . . . . 17 94 5.3.2. Appearance Numbers and Call Control . . . . . . . . . 17 95 5.3.3. Appearance Numbers and Transfer . . . . . . . . . . . 18 96 5.4. Appearance Agent . . . . . . . . . . . . . . . . . . . . 19 97 6. XML Schema Definition . . . . . . . . . . . . . . . . . . . . 21 98 7. Alert-Info Appearance Parameter Definition . . . . . . . . . . 23 99 8. User Interface Considerations . . . . . . . . . . . . . . . . 24 100 8.1. Appearance Number Rendering . . . . . . . . . . . . . . . 24 101 8.1.1. Single Appearance UAs . . . . . . . . . . . . . . . . 24 102 8.1.2. Dual Appearance UAs . . . . . . . . . . . . . . . . . 24 103 8.1.3. Shared Appearance UAs with Fixed Appearance Number . . 24 104 8.1.4. Shared Appearance UAs with Variable Appearance 105 Number . . . . . . . . . . . . . . . . . . . . . . . . 25 106 8.1.5. Example User Interface Issues . . . . . . . . . . . . 25 107 8.2. Call State Rendering . . . . . . . . . . . . . . . . . . 26 108 9. Interoperability with non-Shared Appearance UAs . . . . . . . 26 109 9.1. Appearance Assignment . . . . . . . . . . . . . . . . . . 26 110 9.2. Appearance Release . . . . . . . . . . . . . . . . . . . 27 111 9.3. UAs Supporting Dialog Events but Not Shared Appearance . 27 112 10. Provisioning Considerations . . . . . . . . . . . . . . . . . 27 113 11. Example Message Flows . . . . . . . . . . . . . . . . . . . . 28 114 11.1. Registration and Subscription . . . . . . . . . . . . . . 28 115 11.2. Appearance Selection for Incoming Call . . . . . . . . . 32 116 11.3. Outgoing Call without Appearance Seizure . . . . . . . . 35 117 11.4. Outgoing Call with Appearance Seizure . . . . . . . . . . 38 118 11.5. Outgoing Call without using an Appearance Number . . . . 42 119 11.6. Appearance Release . . . . . . . . . . . . . . . . . . . 44 120 11.7. Appearance Pickup . . . . . . . . . . . . . . . . . . . . 45 121 11.8. Calls between UAs within the Group . . . . . . . . . . . 49 122 11.9. Consultation Hold with Appearances . . . . . . . . . . . 52 123 11.10. Joining or Bridging an Appearance . . . . . . . . . . . . 55 124 11.11. Appearance Allocation - Loss of Appearance . . . . . . . 57 125 11.12. Appearance Seizure Contention Race Condition . . . . . . 58 126 11.13. Appearance Agent Subscription to UAs . . . . . . . . . . 60 127 11.14. Appearance Pickup Race Condition Failure . . . . . . . . 61 128 11.15. Appearance Seizure Incoming/Outgoing Contention Race 129 Condition . . . . . . . . . . . . . . . . . . . . . . . . 64 130 12. Security Considerations . . . . . . . . . . . . . . . . . . . 65 131 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 66 132 13.1. SIP Event Package Parameter: shared . . . . . . . . . . . 66 133 13.2. URN Sub-Namespace Registration: sa-dialog-info . . . . . 67 134 13.3. XML Schema Registration . . . . . . . . . . . . . . . . . 67 135 14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 68 136 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 68 137 15.1. Normative References . . . . . . . . . . . . . . . . . . 68 138 15.2. Informative References . . . . . . . . . . . . . . . . . 69 139 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 70 141 1. Introduction 143 The feature and functionality requirements for SIP user agents (UAs) 144 supporting business telephony applications differ greatly from basic 145 SIP user agents, both in terms of services and end user experience. 146 In addition to basic SIP support [RFC3261], many of the services in a 147 business environment require the support for SIP extensions such as 148 REFER [RFC3515], SUBSCRIBE/NOTIFY primitives 149 [I-D.ietf-sipcore-rfc3265bis] PUBLISH [RFC3903], the SIP Replaces 150 [RFC3891], and Join [RFC3911] header fields, etc. Many of the 151 popular business services have been documented in the SIP Service 152 Examples [RFC5359]. 154 This specification details a method for implementing a group 155 telephony feature known variously in telephony as Bridged Line 156 Appearance (BLA) or Multiple Line Appearances (MLA), one of the more 157 popular advanced features expected of SIP IP telephony devices in a 158 business environment. Other names for this feature include Shared 159 Call/Line Appearance (SCA), Shared Call Status and Multiple Call 160 Appearance (MCA). A variant of this feature is known as Single Line 161 Extension. 163 This document looks at how this feature can be implemented using 164 standard SIP [RFC3261] in conjunction with SIP events 165 [I-D.ietf-sipcore-rfc3265bis] and publication [RFC3903] (carrying the 166 SIP dialog state event package [RFC4235]) for exchanging status among 167 user agents. 169 In traditional telephony, the line is physical. A common scenario in 170 telephony is for a number of business telephones to share a single or 171 a small number of lines. The sharing or appearance of these lines 172 between a number of phones is what gives this feature its name. A 173 common scenario in SIP is for a number of business telephones to 174 share a single or a small number of Address of Record (AOR) URIs. 176 In addition, an AOR can have multiple appearances on a single UA in 177 terms of the user interface. The appearance number relates to the 178 user interface for the telephone - typically each appearance of an 179 AOR has a visual display (lamp that can change color or blink or a 180 screen icon) and a button (used to select the appearance) where each 181 appearance number is associated with a different dialog to/from the 182 AOR. The telephony concept of line appearance is still relevant to 183 SIP due to the user interface considerations. It is important to 184 keep the appearance number construct because: 186 1. Human users are used to the concept and will expect it in 187 replacement systems (e.g. an overhead page announcement says "Joe 188 pickup line 3"). 190 2. It is a useful structure for user interface representation. 192 The purpose of the appearance number is to identify active calls to 193 facilitate sharing between users (e.g. passing a call from one user 194 to another). If a telephone has enough buttons/lamps, the appearance 195 number could be the positional sequence number of the button. If 196 not, it may still be desirable to present the call state, but the 197 appearance number should be displayed so that users know which call, 198 for example, is on hold on which key. 200 In this document, except for the usage scenarios in the next section, 201 we will use the term "appearance" rather than "line appearance" since 202 SIP does not have the concept of lines. Note that this does not mean 203 that a conventional telephony user interface (lamps and buttons) must 204 be used - implementations may use another metaphor as long as the 205 appearance number is readily apparent to the user. Each AOR has a 206 separate appearance numbering space. As a result, a given UA user 207 interface may have multiple occurrences of the same appearance 208 number, but they will be for different AORs. 210 2. Conventions used in this document 212 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 213 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 214 document are to be interpreted as described in RFC-2119 [RFC2119] and 215 indicate requirement levels for compliant mechanisms. 217 3. Usage Scenarios 219 The following examples are common applications of the Shared 220 Appearances feature and are mentioned here as informative use cases. 221 All these example usages can be supported by the Shared Appearances 222 feature described in this document. The main differences relate to 223 the user interface considerations of the device. 225 3.1. Executive/Assistant Arrangement 227 The appearances on the executive's UA also appear on the assistant's 228 UA. The assistant may answer incoming calls to the executive and 229 then place the call on hold for the executive to pick up. The 230 assistant can always see the state of all calls on the executive's 231 UA. 233 3.2. Call Group 235 Users with similar business needs or tasks can be assigned to 236 specific groups and share an AOR. For example, an IT department 237 staff of five might answer a help line which has three appearances on 238 each phone in the IT work area. A call answered on one phone can be 239 put on hold and picked up on another phone. A shout or an IM to 240 another staff member can result in them taking over a call on a 241 particular appearance. Another phone can request to be added/joined/ 242 bridged to an existing appearance resulting in a conference call. 244 3.3. Single Line Extension 246 In this scenario, incoming calls are offered to a group of UAs. When 247 one answers, the other UAs are informed. If another UA in the group 248 seizes the line (i.e. goes off hook), it is immediately bridged or 249 joined in with the call. This mimics the way residential telephone 250 extensions usually operate. 252 3.4. Changing UAs 254 A user is on a call on one UA and wishes to change devices and 255 continue the call on another UA. They place the call on hold, note 256 the appearance number of the call, then walk to another UA. They are 257 able to identify the same appearance number on the other UA, pickup 258 the call, and continue the conversation. 260 4. Requirements and Implementation 262 The next section details the requirements and discusses the 263 implementation of the shared appearances of an AOR feature. 265 4.1. Requirements 267 The basic requirements of the shared appearance feature can be 268 summarized as follows: 270 REQ-1 Incoming calls to the AOR must be offered to a group of UAs and 271 can be answered by any of them. 273 REQ-2 Each UA in the group must be able to learn the call status of 274 the others in the group for the purpose of rendering this information 275 to the user. 277 REQ-3 A UA must be able to join (also called bridge or conference 278 together) or pick up (take) an active call of another UA in the group 279 in a secure way. 281 REQ-4 The mechanism should require the minimal amount of 282 configuration. UAs registering against the group AOR should be able 283 to participate in the appearance group without manual configuration 284 of group members. 286 REQ-5 The mechanism must scale for large numbers of appearances, n, 287 and large numbers of UAs, N, without introducing excessive messaging 288 traffic. 290 REQ-6 Each call or session (incoming or outgoing) should be assigned 291 a common "appearance" number from a managed pool administered for the 292 AOR group. Once the session has terminated, the appearance number is 293 released back into the pool and can be reused by another incoming or 294 outgoing session. 296 REQ-7 Each UA in the group must be able to learn the status of all 297 appearances of the group. 299 REQ-8 There must be mechanisms to resolve appearance contention among 300 the UAs in the group. 302 REQ-9 The mechanism must allow all UAs receiving an incoming session 303 request to utilize the same appearance number at the time of 304 alerting. 306 REQ-10 The mechanism must have a way of reconstructing appearance 307 state after an outage that does not result in excessive traffic and 308 processing. 310 REQ-11 The mechanism must have backwards compatibility such that a UA 311 which is unaware of the feature can still register against the group 312 AOR and make and receive calls. 314 REQ-12 The mechanism must not allow UAs outside the group to select, 315 seize or manipulate appearance numbers. 317 REQ-13 For privacy reasons, there must be a mechanism so that 318 appearance information is not leaked outside the group of UAs. (e.g. 319 "So who do you have on line 1?") 321 REQ-14 The mechanism must support a way for UAs to request 322 exclusivity on a line appearance. Exclusivity means that the UA 323 requesting it desires to have a private conversation with the 324 external party and other UAs must not be allowed to join or take the 325 call. Exclusivity may be requested at the start of an incoming or 326 outgoing session or during the session. An exclusivity request may 327 be accepted or rejected by the entity providing the shared appearance 328 service. Therefore, the mechanism must provide a way of 329 communicating the result back to the requester UA. 331 REQ-15 The mechanism should support a way for a UA to seize a 332 particular appearance number for outgoing requests prior to sending 333 the actual request. This is often called seizure. 335 REQ-16 The mechanism should support a way for a UA to seize a 336 particular appearance number and also send the request at the same 337 time. This is needed when an automatic ringdown feature (a telephone 338 configured to immediately dial a phone number when it goes off hook) 339 is combined with shared appearances - in this case, seizing the line 340 is the same thing as dialing. 342 4.2. Implementation 344 This section non-normatively discusses the implementation of the 345 shared appearance feature. The normative description is in 346 Section 5. Many of the requirements for this service can be met 347 using standard SIP mechanisms such as: 349 - A SIP Forking Proxy and Registrar/Location Service meets REQ-1. 351 - The SIP Dialog Package meets REQ-2. 353 - The SIP Replaces and Join header fields meets REQ-3. 355 - The use of a State Agent for the Dialog Package meets REQ-4 and 356 REQ-5. 358 REQ-6 suggests the need for an entity which manages the appearance 359 resource. Just as conferencing systems commonly have a single point 360 of control, known as a focus, a Shared Appearance group has a single 361 point of control of the appearance shared resource. This is defined 362 as an Appearance Agent for a group. While an Appearance Agent can be 363 part of a centralized server, it could also be co-resident in a 364 member User Agent that has taken on this functionality for a group. 365 The Appearance Agent knows or is able to determine the dialog state 366 of all members of the group. 368 While the appearance resource could be managed co-operatively by a 369 group of UAs without any central control, this is outside the scope 370 of this draft. It is also possible that the Appearance Agent logic 371 could be distributed in all UAs in the group. For example, rules 372 that govern assigning appearance numbers for incoming requests (e.g. 373 lowest available appearance number) and rules for contention handling 374 (e.g. when two UAs request the use of the same appearance number, 375 hash dialog identifiers and compare with the lowest hash winning) 376 would need to be defined and implemented. 378 To best meet REQ-9, the appearance number for an incoming INVITE 379 needs to be contained in the INVITE, in addition to being delivered 380 in the dialog package NOTIFY. Otherwise, if the NOTIFY is delayed or 381 lost, a UA in the group might receive an incoming INVITE but might 382 not know which appearance number to render during alerting. 384 This specification defines an extension parameter for the Alert-Info 385 header field in RFC 3261 to carry the appearance number: 387 Alert-Info: ;appearance=1 389 The next section discusses the operations used to implement parts of 390 the shared appearance feature. 392 1. A UA is configured with the AOR of a shared appearance group. It 393 registers against the AOR, then attempts a dialog state 394 subscription to the AOR. If the subscription fails, loops back 395 to itself, or returns an error, it knows there is no State Agent, 396 and hence no Appearance Agent and this feature is not 397 implemented. 398 2. If the subscription receives a 200 OK, the UA knows there is a 399 State Agent and that the feature is implemented. The UA then 400 follows the steps in this list. 401 3. Information learned about the dialog state of other UAs in the 402 group is rendered to the user. 403 4. Incoming calls are forked to all UAs in the group, and any may 404 answer. UAs receive the appearance number to use in rendering 405 the incoming call in a NOTIFY from the Appearance Agent and in 406 the INVITE itself. The UA will also receive a notification if 407 the call is answered by another UA in the group so this 408 information can be rendered to the user. 409 5. For outgoing calls, the operation depends on the implementation. 410 If the user seizes a particular appearance number for the call, 411 the UA publishes the trying state dialog information with the 412 desired appearance number and waits for a 2xx response before 413 sending the INVITE. 414 6. For outgoing calls, if the user does not seize a particular 415 appearance or does not care, the INVITE can be sent immediately, 416 and the appearance number learned as the call progresses from a 417 notification from the Appearance Agent. 418 7. For outgoing calls, if the user does not want an appearance 419 number assigned (such as during a consultation call or if a UA is 420 fetching 'service media' such as music on hold 421 [I-D.worley-service-example]), the UA also publishes prior to 422 sending the INVITE but does not include an appearance number in 423 the publication. 425 8. Established calls within the group may be joined (bridged) or 426 taken (picked) by another UA. Information in the dialog package 427 notifications can be used to construct Join or Replaces header 428 fields. Since the same appearance number is used for these types 429 of operations, this information is published prior to sending the 430 INVITE Join or INVITE Replaces. 431 9. The Appearance Agent may not have direct access to the complete 432 dialog state of some or all of the UAs in the group. If this is 433 the case, the Appearance Agent will subscribe to the dialog state 434 of individual UAs in the group to obtain this information. In 435 any case, the Appearance Agent will send normal notifications 436 (via the subscriptions established by the UAs in step 1) every 437 time the aggregate dialog state of the AOR changes, including 438 when calls are placed, answered, placed on and off hold, and hung 439 up. 441 5. Normative Description 443 This section normatively describes the shared appearance feature 444 extensions. The following definitions are used throughout this 445 document: 447 Appearance number: An appearance number is a positive integer 448 associated with one or more dialogs of an AOR. Appearance numbers 449 are managed by an Appearance Agent and displayed and rendered to the 450 user by UAs that support this specification. When an appearance 451 number is assigned or requested, generally the assigned number is the 452 smallest positive integer that is not currently assigned as an 453 appearance number to a dialog for this AOR. 455 Seizing: An appearance can be reserved prior to a call being placed 456 by seizing the appearance. An appearance can be seized by 457 communicating an artificial state of "trying" prior to actually 458 initiating a dialog (i.e. sending the INVITE), in order to appear as 459 if it was already initiating a dialog. 461 Selecting(or Not-Seizing): An appearance is merely selected (i.e., 462 not seized) if there is no such communication of artificial state of 463 "trying" prior to initiating a dialog: i.e., the state is 464 communicated when the dialog is actually initiated. The appearance 465 number is learned after the INVITE is sent. 467 5.1. Elements 469 A complete system to implement this feature consists of: 471 1. User Agents that support publications, subscriptions, and 472 notifications for the SIP dialog event package, and the shared 473 appearance dialog package extensions and behavior. 474 2. An Appearance Agent consisting of a State Agent for the dialog 475 event package that implements an Event State Compositor (ESC) and 476 the shared appearance dialog package extensions and behavior. 477 The Appearance Agent also has logic for assigning and releasing 478 appearance numbers, and resolving appearance number contention. 479 3. A forking proxy server that can communicate with the State Agent 480 4. A registrar that supports the registration event package. 482 The behavior of these elements is described normatively in the 483 following sections after the definitions of the dialog package 484 extensions. 486 5.2. Shared Appearance Dialog Package Extensions 488 This specification defines four new elements as extensions to the SIP 489 Dialog Event package [RFC4235]. The schema is defined in Section 6. 490 The elements are , , , and 491 which are sub-elements of the element. 493 5.2.1. The element 495 The element, a child of the element, is used to 496 convey the appearance number of the dialog described by the parent 497 element. When sent by a UA in a PUBLISH with parent 498 with state attribute "trying" to the Appearance Agent, the 499 UA is requesting assignment of the given appearance number to the 500 current or future dialog with the given dialog identifiers. When an 501 element is sent by the Appearance Agent in a NOTIFY, it 502 indicates that the appearance number has been assigned to the 503 specified dialog. 505 Note that a element describes the contained dialogs 506 from the point of view of the UA (named by the "entity" attribute), 507 regardless of whether the containing request is sent by the UA or the 508 Appearance Agent. In particular, if the UA sent a request within the 509 described dialog, the To header field URI would match the 510 value and the to-tag parameter would match the remote-tag 511 attribute. Similarly, the From header field URI would match the 512 value and the from-tag parameter would match the 513 local-tag attribute. 515 5.2.2. The element 517 The element, a child of the element, is a 518 boolean, which when true, indicates that the UA is willing to accept 519 an INVITE with a Join or Replaces header field targeted to the dialog 520 described by the element that is the parent of the 521 element. For example, some shared appearance systems 522 only allow call pickup when the call is on hold. In this case, the 523 element should be set to "true" when the call is held and 524 "false" when the call is not held, rather than having the "exclusive" 525 value implied by the hold state. 527 It is important to note that this element is a hint. In order to 528 prevent another UA from taking or joining a call, a UA can, in 529 addition to setting the tag, not report full dialog 530 information to the Appearance Agent. Not having the full dialog 531 information (Call-ID, remote-tag, and local-tag) prevents another UA 532 from constructing a Join or Replaces header field. Although a UA may 533 set exclusive to true, the UA must still be ready to reject an INVITE 534 Join relating to this dialog. If these dialog identifiers have 535 already been shared with the Appearance Agent, the UA could send an 536 INVITE Replaces to change them and then not report the new ones to 537 the Appearance Agent. 539 If the proxy knows which dialogs are marked exclusive, the proxy MAY 540 enforce this exclusivity by rejecting INVITE Join and INVITE Replaces 541 requests containing those dialog identifiers with a 403 Forbidden 542 response. 544 Note that exclusivity has nothing to do with appearance number 545 selection or seizing - instead, it is about call control 546 operations that can be performed on a dialog. 548 If the element is not present, it is assumed to be true. 550 5.2.3. The element 552 The element, a child of the element, is used 553 to convey dialog identifiers of any other dialogs which are joined 554 (mixed or bridged) with the dialog. Only the UA which is the common 555 endpoint of the mixed dialogs (and thus controlling the mixing 556 operation) should include this element in publications to the 557 Appearance Agent. Note that this element should still be used even 558 when the Join header field was not used to join the dialogs. For 559 example, two separate dialogs on a UA could be joined without any SIP 560 call control operations. Joined dialogs will share the same 561 appearance number. 563 If the element is not present, it is assumed that the 564 dialog is not joined or to be joined to any other dialog. 566 5.2.4. The element 568 The element, a child of the element, is 569 used to convey dialog identifiers of any other dialogs which will be 570 or have been replaced with this dialog. For example, a UA in the 571 group picking up a call on another UA by sending an INVITE with 572 Replaces would include this element for the replacing dialog. 573 Replaced dialogs will share the same appearance number. 575 If the element is not present, it is assumed that 576 the dialog has not replaced or is not to replace to any other dialog. 578 5.3. Shared Appearance User Agents 580 User Agents that support the Shared Appearance feature MUST support 581 the dialog state package [RFC4235] with the shared appearance 582 extensions and the 'shared' dialog event package parameter defined in 583 Section 13. 585 User Agents MUST support the dialog package extensions in Section 5.2 586 along with SUBSCRIBE and NOTIFY [I-D.ietf-sipcore-rfc3265bis] and 587 PUBLISH [RFC3903]. SUBSCRIBE, NOTIFY, and PUBLISH requests for the 588 dialog event package MUST include the 'shared' Event header field 589 parameter. 591 The presence of the 'shared' Event package parameter tells the 592 Appearance Agent that this UA supports this specification. 594 Upon initialization, the UA MUST subscribe to the dialog event 595 package of the AOR and refresh the subscription per the SIP Events 596 Framework. If the SUBSCRIBE request fails, then no Appearance Agent 597 may be present and this feature is not active for this AOR. The UA 598 MAY periodically retry the subscription to see if conditions have 599 changed at intervals no shorter than 4 hours. 601 Four hours was chosen to limit the subscription test to 6 per day 602 per UA. Increading this interval would reduce this failure 603 traffic but take longer for a newly activated Appearance Agent to 604 be discovered. 606 User Agents which implement the shared appearances feature and call 607 pickup, joining and bridging MUST support sending an INVITE with 608 Replaces [RFC3891] or Join [RFC3911]. The User Agent Client needs to 609 include the to-tag and from-tag information in the Replaces or Join 610 header so that the correct dialog will be matched by the User Agent 611 Server per the rules in RFC 3891 and RFC 3911. 613 All User Agents which implement the shared appearances feature and 614 support INVITE MUST support receiving an INVITE with a Replaces 615 [RFC3891] or a Join [RFC3911] header field. 617 When publishing or notifying dialog package information, a UA MUST 618 include all dialog identification available at the time of 619 publication, with the exception that a UA may omit information if it 620 wishes to prevent other UAs from joining or picking up a call. 621 Dialog identification includes local and remote target URIs, call-id, 622 to-tag, and from-tag. When calls are placed on hold, the 623 "+sip.rendering=no" feature tag MUST be included in dialog package 624 notifications. 626 The accurate rendering of the idle/active/alerting/hold state of 627 other UAs in the group is an important part of the shared 628 appearance feature. 630 In the following cases, before sending the INVITE, A UA MUST send a 631 dialog package PUBLISH request and wait for a 2xx response before 632 proceeding: 634 1. When the user seizes a particular appearance number for an 635 outgoing call (e.g. seizing the appearance and going "off-hook", 636 if the UA's user interface uses this metaphor). 637 2. When the user has requested that an appearance number not be used 638 for an outgoing call (i.e. during a consultation call, a 'service 639 media' call such as for music on hold 640 [I-D.worley-service-example] or for a call not considered part of 641 the shared appearance group). 642 3. When the user has selected to join (or bridge) an existing call. 643 4. When the user has selected to replace (or take) an existing call. 645 An exception is an emergency call, when a UA MUST never wait for a 646 confirmed seizure before sending an INVITE. Instead, the emergency 647 call MUST proceed without waiting for the PUBLISH transaction. 649 Note that when a UA seizes an appearance prior to establishment of a 650 dialog (#1 and #2 in above list), not all dialog information will be 651 available. In particular, when a UA publishes an attempt to seize an 652 appearance prior to knowing the destination URI, minimal or no dialog 653 information may be available. For example, in some cases, only the 654 local target URI for the call will be known and no dialog 655 information. If the From tag and Call-ID were not present in the 656 initial PUBLISH, a new PUBLISH MUST be sent as soon as this 657 information is available. 659 The first publication will cause the Appearance Agent to reserve 660 the appearance number for this UA. If the publication does not 661 have any dialog identifiers (e.g. Call-ID, or local tag) the 662 Appearance Agent cannot assign the appearance number to a 663 particular dialog of the UA until the second publication which 664 will contain some dialog identifiers. 666 This publication state is refreshed as described in [RFC3903] during 667 the early dialog state or the Appearance Agent may reassign the 668 appearance number. Once the dialog has transitioned to the confirmed 669 state, no publication refreshes are necessary. 671 This specification assumes that the Appearance Agent has other 672 means besides UA publication to learn about the state of UA 673 dialogs. In this specification, PUBLISH is used to indicate 674 desired and intended appearance number operations. Once a dialog 675 transitions from early to confirmed, this role is over, and hence 676 no publication refreshes are needed. 678 Appearance numbers are a shorthand label for active and pending 679 dialogs related to an AOR. Many of the features and services built 680 using this extension rely on the correct rendering of this 681 information to the human user. In addition, the group nature of the 682 feature means that the rendering must be similar between different 683 vendors and different models. Failure to do so will greatly reduce 684 the value and usefulness of these protocol extensions. The 685 appearances number for each active and pending dialog SHOULD be 686 explicitly (i.e. by appearance number) or implicitly (using a user 687 interface metaphor that makes the numbering and ordering clear to the 688 user) rendered to the user. The far end identity of each dialog 689 (e.g. the remote party identity) MUST NOT be rendered in place of the 690 appearance number. The state of each appearance SHOULD also be 691 rendered (idle, active, busy, joined, etc.). UAs can tell that a set 692 of dialogs are joined (bridged or mixed) together by the presence of 693 one or more elements containing other SIP dialog 694 identifiers. Appearance numbers of dialogs can be learned by dialog 695 package notifications containing the element from the 696 Appearance Agent or from the 'appearance' Alert-Info parameter in an 697 incoming INVITE. Should they conflict, the dialog package 698 notification takes precedence. 700 A UA that does not need to seize a particular appearance number (or 701 doesn't care) would just send an INVITE as normal to place an 702 outbound call. 704 A user may select an appearance number but then abandon placing a 705 call (go back on hook). In this case, the UA MUST free up the 706 appearance number by removing the event state with a PUBLISH as 707 described in [RFC3903]. 709 A UA SHOULD register against the AOR only if it is likely the UA will 710 be answering incoming calls. If the UA is mainly going to be 711 monitoring the status of the shared appearance group calls and 712 picking or joining calls, the UA SHOULD only subscribe to the AOR and 713 not register against the AOR. 715 All subscribed UAs will receive dialog package NOTIFYs of trying 716 state for incoming INVITEs. 718 5.3.1. Appearance Numbers and Call Context 720 There are cases where two separate dialogs at a UA are not mixed but 721 share the same 'context'. That is, they relate to each other and 722 should not be treated the same as any other two dialogs within the 723 group. One example of this is a 'consultation call' where a user 724 puts an existing dialog on hold, then calls another user, before 725 switching back to the original dialog. Another case, described 726 below, occurs during transfer operations, where for a transient 727 period, a UA is invovled in dialogs with two other UAs, but the 728 dialogs are related, and should not be treated as independent 729 dialogs. These cases are best handled by not assigning an appearance 730 number to a newly-created dialog when it shares a context with an 731 existing dialog. But if the pre-existing dialog is terminated, its 732 appearance number should be reassigned to the newly-created dialog. 734 A UA wanting to place a call but not have an appearance number 735 assigned publishes before sending the INVITE without an 'appearance' 736 element but with the 'shared' event package parameter present. If 737 the Appearance Agent policy does not allow calls without an assigned 738 appearance number, a 400 response is sent by the Appearance Agent and 739 the UA will republish either selecting/seizing an appearance number 740 or send the INVITE without publishing, in which case the Appearance 741 Agent will assign one. 743 Note that if an Appearance Agent rejects calls without an 744 appearance number, certain operations such as consultation calls, 745 transfer, and music on hold may be negatively impacted. 747 5.3.2. Appearance Numbers and Call Control 749 When an INVITE is generated to attempt to bridge or take a call (i.e. 750 contains Join or Replaces with a dialog identifier of another dialog 751 in the shared appearance group), the UA MUST first send a PUBLISH to 752 the Appearance Agent. This PUBLISH will contain: 754 1. The appearance number of the joined or replaced call in the 755 element 757 2. If the dialog is being joined, the element will 758 contain the dialog information from the Join header field 759 3. If the dialog is being replaced, the element 760 will contain the dialog information from the Replaces header 761 field 763 Note that this information is provided to the Appearance Agent so 764 that it can provide proper appearance assignment behavior. If the 765 INVITE Join or Replaces was sent without publishing first, the 766 Appearance Agent might assign a new appearance number to this 767 INVITE, which would be a mistake. With Join, the publication has 768 the element to prevent the Appearance Agent from 769 generating a 400 response due to the reuse of an appearance 770 number. For Replaces, the purpose of the is to 771 prevent a race condition where the BYE could cause the appearance 772 number to be released when it should stay with the replacing 773 dialog. 775 5.3.3. Appearance Numbers and Transfer 777 During a transfer operation, it is important that the appearance 778 number not change during the operation. Consider the example of 779 Alice, a member of an appearance group, who is talking to Carol, who 780 is outside the appearance group. Carol transfers Alice to David, who 781 is also outside the appearance group. For example, if Alice is using 782 appearance 3 for the session with Carol, the resulting session with 783 David should also use appearance number 3. Otherwise, an appearance 784 number change can cause a "jump" on the UI and confusion to the user. 785 There are two possible scenarios using the terminology of RFC 5589: 786 Alice is the transferee in any type of transfer (receives the REFER) 787 or the transfer target in an attended transfer (receives the INVITE 788 with Replaces). 790 If Alice is the transferee, the triggered INVITE from the REFER is 791 treated as a consultation call. Alice SHOULD publish requesting that 792 the Appearance Agent not assign an appearance number for this INVITE. 793 When the transfer completes, Alice SHOULD publish again to move the 794 appearance number from the dialog with Carol to the dialog with 795 David. Note that this publication MUST be sent prior to sending the 796 BYE to Carol to avoid a race condition where the Appearance Agent 797 reassigns the appearance number after seeing the BYE. 799 If Alice is the target, the incoming INVITE will contain a Replaces 800 header field. As a result, the Appearance Agent will have reused the 801 appearance number of the dialog with Carol, and this appearance 802 number will continue to be used after the dialog with Carol has been 803 terminated. 805 5.4. Appearance Agent 807 An Appearance Agent defined in this specification MUST implement a 808 dialog package state agent for the UAs registered against the AOR. 809 The Appearance Agent MUST support the appearance dialog package 810 extensions defined in Section 5.2. The Appearance Agent MUST support 811 publications and subscriptions for this event package. 813 The Appearance Agent MUST have a way of discovering the state of all 814 dialogs associated with the AOR. If this information is not 815 available from a call stateful proxy or B2BUA, the Appearance Agent 816 MAY use the registration event package [RFC3680] to learn of UAs 817 associated with the AOR and MAY subscribe to their dialog event 818 state. Also, an Appearance Agent MAY subscribe to a UAs dialog event 819 state in order to reconstruct state. As a result, the registrar MUST 820 support the registration event package. Dialog package notifications 821 are recommended by RFC 4235 to "only contain information on the 822 dialogs whose state or participation information has changed." This 823 specification extends RFC 4235 as follows. The Appearance Agent 824 SHOULD send dialog event state notifications whenever the following 825 events happen to UAs in the AOR group: 827 1. A call is received, placed, answered, or terminated. 828 2. A call is placed on or off hold. 829 3. A call is joined or replaced. 830 4. An appearance number is reserved or released. 832 The Appearance Agent MUST allocate an appearance number for all 833 incoming calls and send immediate notifications to the UAs subscribed 834 to the shared group AOR. A new appearance number is allocated except 835 for an incoming INVITE with a Join or Replaces header field. For 836 this case, the appearance number should match the appearance number 837 of the dialog being joined or replaced. If the INVITE Replaces or 838 Join comes from outside the appearance group, the Appearance Agent 839 will include a or element in the 840 NOTIFY containing the dialog information from the Replaces or Joined 841 header field. 843 The Appearance Agent MUST be able to communicate with the forking 844 proxy to learn about incoming calls and also to pass the appearance 845 number to the proxy to insert in the Alert-Info header field. 847 Note that UAs need to be able to handle incoming INVITEs without 848 an appearance number assigned. This could be caused by a failure 849 of the Appearance Agent or other error condition. Although the 850 proper rendering of the INVITE may not be possible, this is better 851 than ignoring or failing the INVITE. 853 An Appearance Agent SHOULD assign an appearance number to an outgoing 854 dialog if a PUBLISH has not been received selecting/seizing a 855 particular appearance number. 857 Note that if the appearance group has appearance-unaware UAs 858 making calls, the Appearance Agent will still allocate appearance 859 numbers for INVITEs sent by those UAs. 861 An Appearance Agent receiving a PUBLISH with an appearance number 862 checks to make sure the publication is valid. An appearance number 863 can be assigned to only one dialog unless there is a 864 or element indicating that the dialog will be/has 865 been replaced or joined. A 400 response is returned if the chosen 866 appearance number is invalid, and an immediate NOTIFY should be sent 867 to the UA containing full dialog event state. 869 An Appearance Agent receiving a PUBLISH without an appearance number 870 but with the 'shared' event package parameter present interprets this 871 as a request by the UA to not assign an appearance number. If the 872 Appearance Agent policy does not allow this, a 400 response is 873 returned. If policy does allow this, a 200 OK response is returned 874 and no appearance number is allocated. An Appearance Agent does not 875 have to share this dialog information (i.e. send a NOTIFY) with other 876 UAs in the group as the information will not be rendered by the other 877 UAs. 879 The Appearance Agent allocates an apperance number to a dialog from 880 the time the appearance is requested via a PUBLISH or from the 881 receipt of an INVITE, to the time when the last dialog associated 882 with the appearance is terminated, including all dialogs which are 883 joined or replaced. During the early dialog state, the Appearance 884 Agent controls the rate of dialog state publication using the Expires 885 header field in 200 OK responses to PUBLISH requests. An interval of 886 3 minutes is RECOMMENDED. After the dialog associated with the 887 publication has been confirmed, the expiration of the publication 888 state has no effect on the appearance allocation. If the publication 889 contains no dialog state information, the Appearance Agent MUST 890 reserve the appearance number for the UA but can not assign the 891 appearance to any particular dialog of the UA. When the publication 892 state is updated with any dialog information, the appearance number 893 can then be assigned to the particular dialog. A UA which has been 894 allocated an appearance number using a PUBLISH MAY free up the 895 appearance number by removing the event state with a PUBLISH as 896 described in [RFC3903]. 898 If an INVITE is sent by a member of the group using the shared AOR or 899 sent to the shared AOR and no appearance number is available, the 900 proxy MAY reject the INVITE with a 403 Forbidden response code. 902 Appearance numbers are only used for dialogs in which one UA 903 associated with the group AOR is a participant. If an incoming 904 INVITE to the group AOR is forwarded to another AOR, the appearance 905 number is immediately freed up and can be assigned to another dialog. 907 6. XML Schema Definition 909 The 'appearance', 'joined-dialog', 'replaced-dialog', and 'exclusive' 910 elements are defined within a new XML namespace URI. This namespace 911 is "urn:ietf:params:xml:ns:sa-dialog-info". The schema for these 912 elements is: 914 915 921 923 924 926 928 930 931 933 935 936 938 940 942 943 945 946 947 948 950 951 952 953 954 956 7. Alert-Info Appearance Parameter Definition 958 This specification extends RFC 3261 [RFC3261] to add an 'appearance' 959 parameter to the Alert-Info header field, and to also allow proxies 960 to modify or delete the Alert-Info header field. 962 The changes to RFC 3261 ABNF are: 964 alert-param = LAQUOT absoluteURI RAQUOT *( SEMI 965 (generic-param / appearance-param) ) 966 appearance-param = "appearance" EQUAL 1*DIGIT 968 A proxy inserting an 'appearance' Alert-Info parameter follows normal 969 policies Alert-Info policies. If an Alert-Info is already present, 970 the proxy either removes the Alert-Info if it is not trusted, or adds 971 the 'appearance' parameter to the Alert-Info header field. If an 972 appearance number parameter is already present (associated with 973 another AOR or by mistake), the value is rewritten adding the new 974 appearance number. There MUST NOT be more than one appearance 975 parameter in an Alert-Info header field. 977 If no special ringtone is desired, a normal ringtone should be 978 indicated using the urn:alert:service:normal in the Alert-Info, as 979 per [I-D.ietf-salud-alert-info-urns]. The appearance number present 980 in an Alert-Info header field SHOULD be rendered by the UA to the 981 user, following the guidelines in Section 5.3. If the INVITE is 982 forwarded to another AOR, the appearance parameter in the Alert-Info 983 SHOULD be removed before forwarding outside the group. 985 The determination as to what value to use in the appearance parameter 986 can be done at the proxy that forks the incoming request to all the 987 registered UAs. 989 There are a variety of ways the proxy can use to determine what 990 value it should use to populate this parameter. For example, the 991 proxy could fetch this information by initiating a SUBSCRIBE 992 request with Expires: 0 to the Appearance Agent for the AOR to 993 fetch the list of lines that are in use. Alternatively, it could 994 act like a UA that is a part of the appearance group and SUBSCRIBE 995 to the State-Agent like any other UA. This would ensure that the 996 active dialog information is available without having to poll on a 997 need basis. It could keep track of the list of active calls for 998 the appearance AOR based on how many unique INVITE requests it has 999 forked to or received from the appearance AOR. Another approach 1000 would be for the Proxy to first send the incoming INVITE to the 1001 Appearance Agent which would redirect to the appearance group URI 1002 and escape the proper Alert-Info header field for the Proxy to 1003 recurse and distribute to the other UAs in the group. 1005 The Appearance Agent needs to know about all incoming requests to 1006 the AOR in order to seize the appearance number. One way in which 1007 this could be done is for the Appearance Agent to register against 1008 the AOR with a higher q value. This will result in the INVITE 1009 being sent to the Appearance Agent first, then being offered to 1010 the UAs in the group. 1012 8. User Interface Considerations 1014 The "appearance number" allocated to a call is an important concept 1015 that enables calls to be handled by multiple devices with 1016 heterogeneous user interfaces in a manner that still allows users to 1017 see a consistent model. Careful treatment of the appearance number 1018 is essential to meet the expectations of the users. Also, rendering 1019 the correct call/appearance state to users is also important. 1021 8.1. Appearance Number Rendering 1023 Since different UAs have different user interface capabilities, it is 1024 usual to find that some UAs have restrictions that others do not. 1025 Perfect interoperability across all UAs is clearly not possible, but 1026 by careful design, interoperability up to the limits of each UA can 1027 be achieved. 1029 The following guidelines suggest how the appearance number should be 1030 handled in three typical user interface implementations. 1032 8.1.1. Single Appearance UAs 1034 These devices are constrained by only having the capability of 1035 displaying status indications for a single appearance. The UA should 1036 still send messages annotated with appearance number "1". Any call 1037 indications for appearances other than for number "1" should be 1038 rejected with a 486 or 480 response. 1040 8.1.2. Dual Appearance UAs 1042 These devices are essentially single appearance phones that implement 1043 call waiting. They have a very simple user interface that allows 1044 them to switch between two appearances (toggle or flash hook) and 1045 perhaps audible tones to indicate the status of the other appearance. 1046 Only appearance numbers "1" and "2" will be used by these UAs. 1048 8.1.3. Shared Appearance UAs with Fixed Appearance Number 1050 This UA is the typical 'business-class' hard-phone. A number of 1051 appearances are typically configured statically and labeled on 1052 buttons, and calls may be managed using these configured appearances. 1053 Any calls outside this range should be rejected, and not mapped to a 1054 free button. Users of these devices often seize specific appearance 1055 numbers for outgoing calls, and the UA will need to seize the 1056 appearance number and wait for confirmation from the Appearance Agent 1057 before proceeding with calls. 1059 8.1.4. Shared Appearance UAs with Variable Appearance Number 1061 This UA is typically a soft-phone or graphically rich user interface 1062 hard-phone. In these cases, even the idea of an appearance index may 1063 seem unnecessary. However, for these phones to be able to interwork 1064 successfully with other phone types, it is important that they still 1065 use the appearance index to govern the order of appearance of calls 1066 in progress. No specific guidance on presentation is given except 1067 that the order should be consistent. These devices can typically 1068 make calls without waiting for confirmation from the Appearance Agent 1069 on the appearance number. 1071 8.1.5. Example User Interface Issues 1073 The problems faced by each style of user interface are readily seen 1074 in this example: 1076 1. A call arrives at the shared appearance group, and is assigned an 1077 appearance number of "1". All UAs should be able to render to 1078 the user the arrival of this call. 1079 2. Another call arrives at the shared appearance group, and is 1080 assigned an appearance number of "2". The single appearance UA 1081 should not present this call to the user. Other user agents 1082 should have no problems presenting this call distinctly from the 1083 first call. 1084 3. The first call clears, releasing appearance number "1". The 1085 single appearance UA should now be indicating no calls since it 1086 is unable to manage calls other than on the first appearance. 1087 Both shared appearance UAs should clearly show that appearance 1088 number "1" is now free, but that there is still a call on 1089 appearance number "2". 1090 4. A third call arrives, and is assigned the appearance number of 1091 "1". All UAs should be able to render the arrival of this new 1092 call to the user. Multiple appearance UAs should continue to 1093 indicate the presence of the second call, and should also ensure 1094 that the presentation order is related to the appearance number 1095 and not the order of call arrival. 1097 8.2. Call State Rendering 1099 UAs that implement the shared appearance feature typically have a 1100 user interface that provides the state of other appearances in the 1101 group. As dialog state NOTIFYs from the Appearance Agent are 1102 processed, this information can be rendered. Even the simplest user 1103 interface typically has three states: idle, active, and hold. The 1104 idle state, usually indicated by lamp off, is indicated for an 1105 appearance when the appearance number is not associated with any 1106 dialogs, as reported by the Appearance Agent. The active state, 1107 usually indicated by a lamp on, is indicated by an appearance number 1108 being associated with at least one dialog, as reported by the 1109 Appearance Agent. The hold state, often indicated by a blinking 1110 lamp, means the call state from the perspective of the UA in the 1111 shared appearance group is hold. This can be determined by the 1112 presence of the "+sip.rendering=no" feature tag [RFC3840] with the 1113 local target URI. Note that the hold state of the remote target URI 1114 is not relevant to this display. For joined dialogs, the state is 1115 rendered as hold only if all local target URIs are indicated with the 1116 "+sip.rendering=no" feature tag. 1118 9. Interoperability with non-Shared Appearance UAs 1120 It is desirable to allow a basic UA that does not directly support 1121 shared appearance to be part of a shared appearance group. To 1122 support this the Proxy must collaborate with the Appearance Agent. 1123 This is not required in the basic shared appearance architecture, 1124 consequently shared appearance interoperability with non-shared 1125 appearance UAs will not be available in all shared appearance 1126 deployments. 1128 First, a UA which does not support dialog events or the shared 1129 appearance feature will be discussed. Then, a UA which does support 1130 dialog events but not the shared appearance feature will be 1131 discussed. 1133 9.1. Appearance Assignment 1135 A UA that has no knowledge of appearances must will only have 1136 appearance numbers for outgoing calls if assigned by the Appearance 1137 Agent. If the non-shared appearance UA does not support Join or 1138 Replaces, all dialogs could be marked "exclusive" to indicate that 1139 these options are not available. 1141 9.2. Appearance Release 1143 In all cases the Appearance Agent must be aware of dialog lifetime to 1144 release appearances back into the group. 1146 It is also desirable that any dialog state changes (such as hold, 1147 etc) be made available to other UAs in the group through the Dialog 1148 Event Package. If the Appearance Agent includes a proxy which 1149 Record-Routes for dialogs from the non-shared appearance aware UA, 1150 the Appearance Agent will know about the state of dialogs including 1151 hold, etc. This information could be determined from inspection of 1152 non-end-to-end-encrypted INVITE and re-INVITE messages and added to 1153 the dialog information conveyed to other UAs. 1155 9.3. UAs Supporting Dialog Events but Not Shared Appearance 1157 Interoperability with UAs which support dialog events but not the 1158 shared appearance feature is more straightforward. As before, all 1159 appearance number assignment must be done by the Appearance Agent. 1160 The Appearance Agent can include appearance information in NOTIFYs - 1161 this UA will simply ignore this extra information. This type of UA 1162 will ignore appearance number limitations and may attempt to Join or 1163 Replace dialogs marked exclusive. As a result, the Proxy or UAs need 1164 to reject such requests or the dialogs will get joined or taken. 1166 10. Provisioning Considerations 1168 UAs can automatically discover if this feature is active for an AOR 1169 by looking for the 'shared' Event header parameter in a response to a 1170 dialog package SUBSCRIBE to the AOR, so no provisioning for this is 1171 needed. 1173 The registrar will need to be provisioned to accept either first or 1174 third party registrations for the shared AOR. First party 1175 registration means the To and From URIs in the REGISTER request are 1176 the shared AOR URI. Third party registration means the To URI is the 1177 shared AOR URI and the From URI is a different AOR, perhaps that of 1178 the individual user. Either the credentials of the shared AOR or the 1179 user MUST be accepted by the registrar and the Appearance Agent, 1180 depending on the authorization policy in place for the domain. 1182 If the Appearance Agent needs to subscribe to the dialog state of the 1183 UAs, then the Appearance Agent and the UAs need to be provisioned 1184 with credentials so the UAs can authenticate the Appearance Agent. 1186 In some cases, UAs in the shared appearance group might have a UI 1187 limitation on the number of appearances that can be rendered. 1189 Typically this will be hard phones with buttons/lamps instead of more 1190 flexible UIs. In this case, it can be useful for the Appearance 1191 Agent to know this maximum number. This can allow the Appearance 1192 Agent to apply policy when this limit is reached, e.g. deny a call. 1193 However, this mechanism does not provide any way to discover this by 1194 protocol means. 1196 11. Example Message Flows 1198 The next section shows call flow and message examples. The flows and 1199 descriptions are non-normative. Note that in these examples, all 1200 INVITEs sent by a UA in the group will be From the shared AOR 1201 (sip:HelpDesk@example.com in this case), and all INVITES sent to the 1202 group will have a Request-URI of the shared AOR. Any other requests 1203 would not apply to this feature and would be handled using normal SIP 1204 mechanisms. 1206 Note that the first twelve examples assume the Appearance Agent is 1207 aware of dialog state events. The example in Section 11.13 shows the 1208 case where this is not the case and as a result the Appearance Agent 1209 initiates a subscription to users of the shared AOR. Any of the 1210 other call flow examples could have shown this mode of operation as 1211 it is equally valid. 1213 11.1. Registration and Subscription 1215 Bob and Alice are in an appearance group identified by the shared 1216 appearance AOR sip:HelpDesk@example.com. Bob REGISTERs using contact 1217 sip:bob@ua2.example.com. Alice REGISTERs with contact 1218 sip:alice@ua1.example.com. 1220 User Agents for Alice and Bob subscribe to the dialog package for the 1221 appearance AOR and publish dialog state to the Appearance Agent. 1222 Message exchanges between the Registrar, Appearance Agent, Alice, and 1223 Bob are shown below. The call flow examples below do not show the 1224 authentication of subscriptions, publications, and notifications. It 1225 should be noted that for security purposes, all subscriptions must be 1226 authorized before the SUBSCRIBE is accepted. 1228 Also note that registrations and subscriptions must all be refreshed 1229 by Alice at intervals determined by the expiration intervals returned 1230 by the Registrar or Appearance Agent. 1232 Registrar Appearance Agent Alice Bob 1233 | | | | 1234 | | | | 1235 |<--------------------------- REGISTER F1<| | 1236 | | | | 1237 |>F2 200 OK ----------------------------->| | 1238 | | | | 1239 | |<----- SUBSCRIBE F3<| | 1240 | | | | 1241 | |>F4 200 OK -------->| | 1242 | | | | 1243 | |>F5 NOTIFY -------->| | 1244 | | | | 1245 | |<-------- 200 OK F6<| | 1246 | | | | 1247 |<-------------------------------------------- REGISTER F7<| 1248 | | | | 1249 |>F8 200 OK ---------------------------------------------->| 1250 | | | | 1251 | |<---------------------- SUBSCRIBE F9<| 1252 | | | | 1253 | |>F10 200 OK ------------------------>| 1254 | | | | 1255 | |>F11 NOTIFY ------------------------>| 1256 | | | | 1257 | |<------------------------ 200 OK F12<| 1258 | | | | 1260 Figure 1. 1262 F1-F2: Alice registers AOR with 1263 contact: 1265 F1 Alice ----> Registrar 1267 REGISTER sip:registrar.example.com SIP/2.0 1268 Via: SIP/2.0/UDP ua1.example.com;branch=z9hG4bK527b54da8ACC7B09 1269 From: ;tag=CDF9A668-909E2BDD 1270 To: 1271 CSeq: 2 REGISTER 1272 Call-ID: d3281184-518783de-cc23d6bb 1273 Contact: 1274 Max-Forwards: 70 1275 Expires: 3600 1276 Content-Length: 0 1278 F2 Registrar ----> Alice 1280 SIP/2.0 200 OK 1281 Via: SIP/2.0/UDP ua1.example.com;branch=z9hG4bK527b54da8ACC7B09 1282 CSeq: 2 REGISTER 1283 Call-ID: d3281184-518783de-cc23d6bb 1284 From: ;tag=CDF9A668-909E2BDD 1285 To: ;tag=1664573879820199 1286 Contact: ;expires=3600 1287 Content-Length: 0 1289 F3 to F6: Alice also subscribes to the events associated with the 1290 Appearance AOR. Appearance Agent notifies Alice of the status. 1292 F3 Alice ----> Appearance Agent 1294 SUBSCRIBE sip:HelpDesk@example.com SIP/2.0 1295 Via: SIP/2.0/UDP ua1.example.com;branch=z9hG4bKf10fac97E7A76D6A 1296 From: ;tag=925A3CAD-CEBB276E 1297 To: 1298 CSeq: 91 SUBSCRIBE 1299 Call-ID: ef4704d9-bb68aa0b-474c9d94 1300 Contact: 1301 Event: dialog;shared 1302 Accept: application/dialog-info+xml 1303 Max-Forwards: 70 1304 Expires: 3700 1305 Content-Length: 0 1307 F4 Appearance Agent ----> Alice 1309 SIP/2.0 200 OK 1310 Via: SIP/2.0/UDP ua1.example.com;branch=z9hG4bKf10fac97E7A76D6A 1311 CSeq: 91 SUBSCRIBE 1312 Call-ID: ef4704d9-bb68aa0b-474c9d94 1313 From: ;tag=925A3CAD-CEBB276E 1314 To: ;tag=1636248422222257 1315 Allow-Events: dialog 1316 Expires: 3700 1317 Contact: 1318 Content-Length: 0 1320 F5 Appearance Agent ----> Alice 1322 NOTIFY sip:alice@ua1.example.com SIP/2.0 1323 From: ;tag=1636248422222257 1324 To: ;tag=925A3CAD-CEBB276E 1325 Call-ID: ef4704d9-bb68aa0b-474c9d94 1326 CSeq: 232 NOTIFY 1327 Via: SIP/2.0/UDP appearanceagent.example.com;branch=z9hG4bK1846 1328 Max-Forwards: 70 1329 Content-Type: application/dialog-info+xml 1330 Event: dialog;shared 1331 Subscription-State: active;expires=3000 1332 Contact: 1333 Content-Length: ... 1335 1336 1340 1342 F6 Alice ----> Appearance Agent 1344 SIP/2.0 200 OK 1345 Via: SIP/2.0/UDP appearanceagent.example.com;branch=z9hG4bK1846 1346 From: ;tag=1636248422222257 1347 To: ;tag=925A3CAD-CEBB276E 1348 CSeq: 232 NOTIFY 1349 Call-ID: ef4704d9-bb68aa0b-474c9d94 1350 Contact: 1351 Content-Length: 0 1353 F7 Bob ----> Registrar 1355 REGISTER sip:registrar.example.com SIP/2.0 1356 Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4b53b54d87B 1357 From: ;tag=34831131 1358 To: 1359 CSeq: 72 REGISTER 1360 Call-ID: 139490230230249348 1361 Contact: 1362 Max-Forwards: 70 1363 Expires: 3600 1364 Content-Length: 0 1366 F8 Registrar ----> Bob 1368 SIP/2.0 200 OK 1369 Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4b53b54d87B 1370 From: ;tag=34831131 1371 To: ;tag=fkwlwqi1 1372 CSeq: 72 REGISTER 1373 Call-ID: 139490230230249348 1374 Contact: ;expires=3200 1375 Contact: ;expires=3600 1376 Content-Length: 0 1378 11.2. Appearance Selection for Incoming Call 1380 In the call flow below Bob and Alice are in an appearance group. 1381 Carol places a call to the appearance group AOR. The Appearance 1382 Agent sends NOTIFYs to Alice and Bob telling them what appearance the 1383 call is using. Both Alice and Bob's devices are alerted of the 1384 incoming call. Bob answers the call. 1386 Note that it is possible that both Alice and Bob answer the call and 1387 send 200 OK responses to Carol. It is up to Carol to resolve this 1388 situation. Typically, Carol will send ACKs to both 200 OKs but send 1389 a BYE to terminate one of the dialogs. As a result, either Alice or 1390 Bob will receive the BYE and publish that their dialog is over. 1391 However, if Carol answers both Alice and Bob and keeps both dialogs 1392 active, then the Appearance Agent will need to resolve the situation 1393 by moving either Alice or Bob's dialog to a different appearance. 1395 All NOTIFY messages in the call flow below carry dialog events and 1396 only dialog states are mentioned for simplicity. For brevity, the 1397 details of some messages are not shown below. Note that the order of 1398 F2 - F5 and F7 - F8 could be reversed. 1400 Forking Appearance 1401 Carol Proxy Agent Alice Bob 1402 | | | | | 1403 |>F1 INVITE >| | | | 1404 | |< - - - - - >| | | 1405 | | |>F2 NOTIFY ----------->| 1406 | | | | | 1407 | | |F4 NOTIFY ->| | 1410 | | | | | 1411 | | |<-200 OK F5-<| | 1412 |<- 100 F6 -<| | | | 1413 | |>F7 INVITE (appearance=1) ---------->| 1414 | | | | | 1415 | |>F8 INVITE (appearance=1) >| | 1416 | | | | | 1417 | |<-------------------- Ringing 180 F9<| 1418 |< 180 F10 -<| | | | 1419 | |<--------- 180 Ringing F11<| | 1420 |< 180 F12 -<| | | | 1421 | | | | | 1422 | |<------------------------ 200 OK F13<| 1423 |< 200 F14 -<| | | | 1424 | | | | | 1425 | |>F15 CANCEL -------------->| | 1426 | | | | | 1427 | |<-------------- 200 OK F16<| | 1428 | | | | | 1429 | |F18 ACK ----------------->| | 1432 |>F19 ACK -->| | | | 1433 | |>F20 ACK --------------------------->| 1434 | | | | | 1435 |<=============Both way RTP established===========>| 1436 | | | | | 1437 | |< - - - - - >| | | 1438 | | | | | 1439 | | |>F21 NOTIFY >| | 1440 | | | | | 1441 | | |<- 200 F22 -<| | 1442 | | | | | 1443 | | |>F23 NOTIFY ---------->| 1444 | | | | | 1445 | | | Alice 1452 NOTIFY sip:alice@ua1.example.com SIP/2.0 1453 From: ;tag=151702541050937 1454 To: ;tag=18433323-C3D237CE 1455 Call-ID: 1e361d2f-a9f51109-bafe31d4 1456 CSeq: 12 NOTIFY 1457 Via: SIP/2.0/UDP appearanceagent.example.com;branch=z9hG4bK1403 1458 Max-Forwards: 70 1459 Content-Type: application/dialog-info+xml 1460 Event: dialog;shared 1461 Subscription-State: active;expires=2800 1462 Contact: 1463 Content-Length: ... 1465 1466 1471 1475 1 1476 trying 1477 1478 sip:carol@ua.example.com 1479 1480 1481 1483 F7 Proxy ----> Bob 1485 INVITE sip:bob@ua2.example.com SIP/2.0 1486 Via: SIP/2.0/UDP ua3.example.com;branch=z9hG4bK4324ea 1487 Via: SIP/2.0/UDP proxy.example.com;branch=z9hG4bK38432ji 1488 From: ;tag=44BAD75D-E3128D42 1489 To: 1490 CSeq: 106 INVITE 1491 Call-ID: 14-1541707345 1492 Contact: 1493 Max-Forwards: 69 1494 Alert-Info: ;appearance=1 1495 Content-Type: application/sdp 1496 Content-Length: ... 1498 v=0 1499 o=- 1102980499 1102980499 IN IP4 ua3.example.com 1500 s= 1501 c=IN IP4 ua3.example.com 1502 t=0 0 1503 m=audio 2238 RTP/AVP 0 8 101 1504 a=rtpmap:0 PCMU/8000 1505 a=rtpmap:8 PCMA/8000 1506 a=rtpmap:101 telephone-event/8000 1508 F21 Appearance Agent ----> Alice 1510 NOTIFY sip:alice@ua1.example.com SIP/2.0 1511 From: ;tag=151702541050937 1512 To: ;tag=18433323-C3D237CE 1513 Call-ID: 1e361d2f-a9f51109-bafe31d4 1514 CSeq: 13 NOTIFY 1515 Via: SIP/2.0/UDP appearanceagent.example.com;branch=z9hG4bK4164F03j 1516 Max-Forwards: 70 1517 Content-Type: application/dialog-info+xml 1518 Event: dialog;shared 1519 Subscription-State: active;expires=2500 1520 Contact: 1521 Content-Length: ... 1523 1524 1529 1534 1 1535 confirmed 1536 1537 sip:bob@ua2.example.com 1538 1539 1540 sip:carol@ua.example.com 1541 1542 1543 1545 11.3. Outgoing Call without Appearance Seizure 1547 In this scenario, Bob's UA places a call without first selecting/ 1548 seizing an appearance number. After Bob sends the INVITE, the 1549 appearance assigns an appearance number for it and notifies both 1550 Alice and Bob. 1552 Carol Proxy Alice Appearance Agent Bob 1553 | | | | | 1554 | | | | | 1555 | |<------------------------------------- INVITE F1<| 1556 | | | | | 1557 | |>F2 100 Trying --------------------------------->| 1558 |<-- INVITE F3<| | | | 1559 | |< - - - - - - - - - - - - - ->| | 1560 | | | | | 1561 | | |<-- NOTIFY F4<| | 1562 | | | | | 1563 | | |>F5 200 OK -->| | 1564 | | | |------- NOTIFY F6>| 1565 | | | | | 1566 | | | |F8 180 ---->| | | | 1568 | |>F9 180 Ringing -------------------------------->| 1569 | | | | | 1570 | |< - - - - - - - - - - - - - ->| | 1571 | | | | | 1572 | | |<- NOTIFY F10<| | 1573 | | | | | 1574 | | |>F11 200 OK ->| | 1575 | | | |------ NOTIFY F12>| 1576 | | | | | 1577 | | | |F14 200 OK ->| | | | 1579 | |>F15 200 OK ------------------------------------>| 1580 | | | | | 1581 | |<--------------------------------------- ACK F16<| 1582 |<---- ACK F17<| | | | 1583 | | | | | 1584 |<================= Both way RTP established ===================>| 1585 | | | | | 1586 | |< - - - - - - - - - - - - - ->| | 1587 | | | | | 1588 | | |<- NOTIFY F18<| | 1589 | | | | | 1590 | | |>F19 200 OK ->| | 1591 | | | |------ NOTIFY F20>| 1592 | | | | | 1593 | | | | Proxy 1600 INVITE sip:carol@example.com SIP/2.0 1601 Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bK98c87c52123A08BF 1602 From: ;tag=15A3DE7C-9283203B 1603 To: 1604 CSeq: 1 INVITE 1605 Call-ID: f3b3cbd0-a2c5775e-5df9f8d5 1606 Contact: 1607 Max-Forwards: 70 1608 Content-Type: application/sdp 1609 Content-Length: 223 1611 v=0 1612 o=- 1102980499 1102980499 IN IP4 ua2.example.com 1613 s=IP SIP UA 1614 c=IN IP4 ua2.example.com 1615 t=0 0 1616 a=sendrecv 1617 m=audio 2236 RTP/AVP 0 8 101 1618 a=rtpmap:0 PCMU/8000 1619 a=rtpmap:8 PCMA/8000 1620 a=rtpmap:101 telephone-event/8000 1622 F4 Appearance Agent ----> Alice 1624 NOTIFY sip:alice@ua1.example.com SIP/2.0 1625 Via: SIP/2.0/UDP appearanceagent.example.com;branch=z9hG4bK81d84f62 1626 From: ;tag=1636248422222257 1627 To: ;tag=925A3CAD-CEBB276E 1628 Call-ID: ef4704d9-bb68aa0b-474c9d94 1629 CSeq: 233 NOTIFY 1630 Max-Forwards: 70 1631 Content-Type: application/dialog-info+xml 1632 Event: dialog;shared 1633 Subscription-State: active;expires=2200 1634 Contact: 1635 Content-Length: ... 1637 1638 1643 1646 1 1647 false 1648 trying 1649 1650 1651 1652 1653 1654 1656 F6 Appearance Agent ----> Bob 1658 NOTIFY sip:bob@ua1.example.com SIP/2.0 1659 From: ;tag=497585728578386 1660 To: ;tag=633618CF-B9C2EDA4 1661 Call-ID: a7d559db-d6d7dcad-311c9e3a 1662 CSeq: 7 NOTIFY 1663 Via: SIP/2.0/UDP appearanceagent.example.com 1664 ;branch=z9hG4bK1711759878512309 1665 Max-Forwards: 70 1666 Content-Type: application/dialog-info+xml 1667 Event: dialog;shared 1668 Subscription-State: active;expires=2000 1669 Contact: 1670 Content-Length: ... 1672 1673 1678 1681 1 1682 false 1683 trying 1684 1685 1686 1687 1688 1689 1691 11.4. Outgoing Call with Appearance Seizure 1693 In this scenario, Bob's UA sends out a dialog event PUBLISH with 1694 state (trying) selecting/seizing an appearance number before sending 1695 the INVITE. After receiving the 200 OK from the Appearance Agent 1696 confirming the appearance number, Bob's UA sends the INVITE to Carol 1697 and establishes a session. For brevity, details of some of the 1698 messages are not included in the message flows. 1700 Carol Proxy Alice Appearance Agent Bob 1701 | | | | | 1702 | | | |<----- PUBLISH F1<| 1703 | | | | | 1704 | | | |>F2 200 OK ------>| 1705 | | | | | 1706 | | |<-- NOTIFY F3<| | 1707 | | | | | 1708 | | |>F4 200 OK -->| | 1709 | | | |------- NOTIFY F5>| 1710 | | | | | 1711 | | | |F8 100 Trying --------------------------------->| 1716 |<-- INVITE F9<| | | | 1717 | | | |<---- PUBLISH F10<| 1718 | | | | | 1719 | | | |>F11 200 OK ----->| 1720 | | | | | 1721 |>F12 180 --->| | | | 1722 | |>F13 180 Ringing ------------------------------->| 1723 | | | | | 1724 | |< - - - - - - - - - - - - - ->| | 1725 | | | | | 1726 | | |<- NOTIFY F14<| | 1727 | | | | | 1728 | | |>F15 200 OK ->| | 1729 | | | |------ NOTIFY F16>| 1730 | | | | | 1731 | | | |F18 200 OK ->| | | | 1733 | |>F19 200 OK ------------------------------------>| 1734 | | | | | 1735 | |<--------------------------------------- ACK F20<| 1736 |<---- ACK F21<| | | | 1737 | | | | | 1738 |<================= Both way RTP established ===================>| 1739 | | | | | 1740 | |< - - - - - - - - - - - - - ->| | 1741 | | | | | 1742 | | |<- NOTIFY F22<| | 1743 | | | | | 1744 | | |>F23 200 OK ->| | 1745 | | | |------ NOTIFY F24>| 1746 | | | | | 1747 | | | | Appearance Agent 1760 PUBLISH sip:HelpDesk@example.com SIP/2.0 1761 Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bK61314d6446383E79 1762 From: ;tag=44150CC6-A7B7919D 1763 To: 1764 CSeq: 7 PUBLISH 1765 Call-ID: 44fwF144-F12893K38424 1766 Contact: 1767 Event: dialog;shared 1768 Max-Forwards: 70 1769 Content-Type: application/dialog-info+xml 1770 Content-Length: ... 1772 1773 1778 1779 1 1780 false 1781 trying 1782 1783 1784 1785 1786 1787 1789 F2 Appearance Agent ----> Bob 1791 SIP/2.0 200 OK 1792 Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bK61314d6446383E79 1793 From: ;tag=44150CC6-A7B7919D 1794 To: 1795 CSeq: 7 PUBLISH 1796 Call-ID: 44fwF144-F12893K38424 1797 Contact: 1798 Event: dialog;shared 1799 SIP-Etag: 482943245 1800 Allow-Events: dialog 1801 Expires: 60 1802 Content-Length: 0 1804 F7 Bob ---> Proxy 1806 INVITE sip:carol@example.com SIP/2.0 1807 Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bK342122 1808 Max-Forwards: 70 1809 From: ;tag=15A3DE7C-9283203B 1810 To: 1811 Call-ID: f3b3cbd0-a2c5775e-5df9f8d5 1812 CSeq: 31 INVITE 1813 Contact: 1814 Content-Type: application/sdp 1815 Content-Length: ... 1817 (SDP Not Shown) 1819 F10 Bob ----> Appearance Agent 1821 PUBLISH sip:HelpDesk@example.com SIP/2.0 1822 Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bK6d644638E7 1823 From: ;tag=0CCf6-A7FdsB79D 1824 To: 1825 CSeq: 437 PUBLISH 1826 Call-ID: fwF14d4-F1FFF2F2893K38424 1827 Contact: 1828 Event: dialog;shared 1829 Max-Forwards: 70 1830 Content-Type: application/dialog-info+xml 1831 Content-Length: ... 1833 1834 1839 1843 1 1844 false 1845 trying 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1857 11.5. Outgoing Call without using an Appearance Number 1859 In this scenario, Bob's UA sends out a dialog event PUBLISH with 1860 state (trying) indicating that he does not want to utilize an 1861 appearance number for this dialog. The PUBLISH does not have an 1862 appearance element but does have the 'shared' dialog event parameter. 1863 As a result, the Appearance Agent knows the UA does not wish to use 1864 an appearance number for this call. If the Appearance Agent does not 1865 wish to allow this, it would reject the PUBLISH with a 400 response 1866 and the UA would know to re-PUBLISH selecting/seizing an appearance 1867 number. 1869 Carol Proxy Alice Appearance Agent Bob 1870 | | | | | 1871 | | | |<----- PUBLISH F1<| 1872 | | | | | 1873 | | | |>F2 200 OK ------>| 1874 | | | | | 1875 | | |<-- NOTIFY F3<| | 1876 | | | | | 1877 | | |>F4 200 OK -->| | 1878 | | | |------- NOTIFY F5>| 1879 | | | | | 1880 | | | |F8 100 Trying --------------------------------->| 1885 |<-- INVITE F9<| | | | 1886 | | | |<---- PUBLISH F10<| 1887 | | | | | 1888 | | | |>F11 200 OK ----->| 1889 | | | | | 1890 |>F12 180 --->| | | | 1891 | |>F13 180 Ringing ------------------------------->| 1892 | | | | | 1893 | |< - - - - - - - - - - - - - ->| | 1894 | | | | | 1895 | | |<- NOTIFY F14<| | 1896 | | | | | 1897 | | |>F15 200 OK ->| | 1898 | | | |------ NOTIFY F16>| 1899 | | | | | 1900 | | | |F18 200 OK ->| | | | 1902 | |>F19 200 OK ------------------------------------>| 1903 | | | | | 1904 | |<--------------------------------------- ACK F20<| 1905 |<---- ACK F21<| | | | 1906 | | | | | 1907 |<================= Both way RTP established ===================>| 1908 | | | | | 1909 | |< - - - - - - - - - - - - - ->| | 1910 | | | | | 1911 | | |<- NOTIFY F22<| | 1912 | | | | | 1913 | | |>F23 200 OK ->| | 1914 | | | |------ NOTIFY F24>| 1915 | | | | | 1916 | | | | Appearance Agent 1923 PUBLISH sip:appearanceagent.example.com SIP/2.0 1924 Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bK61314d6446383E79 1925 From: ;tag=4415df82k39sf 1926 To: 1927 CSeq: 7 PUBLISH 1928 Call-ID: 44fwF144-F12893K38424 1929 Contact: 1930 Event: dialog;shared 1931 Max-Forwards: 70 1932 Content-Type: application/dialog-info+xml 1933 Content-Length: ... 1935 1936 1941 1942 false 1943 trying 1944 1945 1946 1947 1948 1949 1951 Note that F7 would be the same as the previous example. 1953 11.6. Appearance Release 1955 Bob and Carol are in a dialog, created, for example as in 1956 Section 11.3. Carol sends a BYE to Bob to terminate the dialog and 1957 the Appearance Agent de-allocates the appearance number used, sending 1958 notifications out to the UAs in the shared group. 1960 Carol Proxy Alice Appearance Agent Bob 1961 | | | | | 1962 | | | | | 1963 |<================= Both way RTP established ===================>| 1964 | | | | | 1965 |>F22 BYE ---->| | | | 1966 | |>F23 BYE --------------------------------------->| 1967 | | | | | 1968 | |<------------------------------------ 200 OK F24<| 1969 |<--200 OK F25<| | | | 1970 | |< - - - - - - - - - - - - - ->| | 1971 | | | | | 1972 | | |<- NOTIFY F26<| | 1973 | | | | | 1974 | | |>F27 200 OK ->| | 1975 | | | |------ NOTIFY F28>| 1976 | | | | | 1977 | | | | Bob 1983 NOTIFY sip:bob@ua1.example.com SIP/2.0 1984 From: ;tag=497585728578386 1985 To: 1986 Call-ID: a7d559db-d6d7dcad-311c9e3a 1987 CSeq: 7 NOTIFY 1988 Via: SIP/2.0/UDP appearanceagent.example.com 1989 ;branch=z9hG4bK759878512309 1990 Max-Forwards: 70 1991 Content-Type: application/dialog-info+xml 1992 Event: dialog;shared 1993 Subscription-State: active;expires=1800 1994 Contact: 1995 Content-Length: ... 1997 1998 2003 2008 1 2009 false 2010 terminated 2011 2012 2013 2014 2015 2016 2018 11.7. Appearance Pickup 2020 In this scenario, Bob has an established dialog with Carol created 2021 using the call flows of Figure 1 or Figure 2. Bob then places Carol 2022 on hold. Alice receives a notification of this and renders this on 2023 Alice's UI. Alice subsequently picks up the held call and has a 2024 established session with Carol. Finally, Carol hangs up. Alice must 2025 PUBLISH F32 to indicate that the INVITE F38 will be an attempt to 2026 pickup the dialog between Carol and Bob, and hence may use the same 2027 appearance number. 2029 Carol Proxy Alice Appearance Agent Bob 2030 | | | | | 2031 |<================= Both way RTP established ===================>| 2032 | | | | | 2033 | |<------------------------------(hold) INVITE F22<| 2034 |<- INVITE F23<| | | | 2035 | | | | | 2036 |>F24 200 OK ->| | | | 2037 | |>F25 200 OK ------------------------------------>| 2038 | | | | | 2039 | |<--------------------------------------- ACK F26<| 2040 |<---- ACK F27<| | | | 2041 | |< - - - - - - - - - - - - - ->| | 2042 | | | | | 2043 | | |<- NOTIFY F28<| | 2044 | | | | | 2045 | | |>F29 200 OK ->| | 2046 | | | |>F30 NOTIFY ----->| 2047 | | | | | 2048 | | | |<----- 200 OK F31<| 2049 | | | | | 2050 | | Alice decides to pick up the call | 2051 | | | | | 2052 | | |>F32 PUBLISH->| | 2053 | | | | | 2054 | | |<- 200 OK F33<| | 2055 | | | | | 2056 | | |<- NOTIFY F34<| | 2057 | | | | | 2058 | | |>F35 200 OK ->| | 2059 | | | |>F36 NOTIFY ----->| 2060 | | | | | 2061 | | | |<----- 200 OK F37<| 2062 | |<-- INVITE F38<| | | 2063 |<- INVITE F39<|(w/ Replaces) | | | 2064 |( w/ Replaces)| | | | 2065 |>F40 200 OK ->| | | | 2066 | |>F41 200 OK -->| | | 2067 | | | | | 2068 | |< - - - - - - - - - - - - - ->| | 2069 | | | | | 2070 | | | |>F42 NOTIFY ----->| 2071 | | | | | 2072 | | | |<----- 200 OK F43<| 2073 | | |<- NOTIFY F44<| | 2074 | | | | | 2075 | | |>F45 200 OK ->| | 2076 | | | | | 2077 | |<----- ACK F46<| | | 2078 |<---- ACK F47<| | | | 2079 | | | | | 2080 |<= Both way RTP established =>| | | 2081 | | | | | 2082 |>F48 BYE ---->| | | | 2083 | |>F49 BYE --------------------------------------->| 2084 | | | | | 2085 | |<------------------------------------ OK 200 F50<| 2086 |<- 200 OK F51<| | | | 2087 | | | | | 2088 | |< - - - - - - - - - - - - - ->| | 2089 | | | | | 2090 | | |<- NOTIFY F52<| | 2091 | | | | | 2092 | | |>F53 200 OK ->| | 2093 | | | | | 2094 | | | |>F54 NOTIFY ----->| 2095 | | | | | 2096 | | | |<----- 200 OK F55<| 2098 Figure 7. 2100 F28 Appearance ----> Alice 2102 NOTIFY sip:alice@ua1.example.com SIP/2.0 2103 From: ;tag=151702541050937 2104 To: ;tag=18433323-C3D237CE 2105 Call-ID: 1e361d2f-a9f51109-bafe31d4 2106 CSeq: 12 NOTIFY 2107 Via: SIP/2.0/UDP appearanceagent.example.com 2108 ;branch=z9hG4bK1403 2109 Max-Forwards: 70 2110 Content-Type: application/dialog-info+xml 2111 Event: dialog;shared 2112 Subscription-State: active;expires=1800 2113 Contact: 2114 Content-Length: ... 2116 2117 2122 2127 1 2128 false 2129 active 2130 2131 2132 2133 2134 2135 2136 sip:carol@example.com 2137 2138 2139 2140 2142 F32 Alice ----> Appearance Agent 2144 PUBLISH sip:HelpDesk@example.com SIP/2.0 2145 Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bKa5d6cf61F5FBC05A 2146 From: ;tag=44150CC6-A7B7919D 2147 To: ;tag=428765950880801 2148 CSeq: 11 PUBLISH 2149 Call-ID: 87837Fkw87asfds 2150 Contact: 2151 Event: dialog;shared 2152 Max-Forwards: 70 2153 Content-Type: application/dialog-info+xml 2154 Content-Length: ... 2156 2157 2162 2165 1 2166 false 2167 2172 trying 2173 2174 2175 2176 2177 2178 2179 2180 2181 2182 2184 F38 Alice ----> Proxy 2186 INVITE sip:carol@example.com SIP/2.0 2187 Via: SIP/2.0/UDP ua1.example.com;branch=z9hG4bK4ea695b5B376A60C 2188 From: ;tag=8C4183CB-BCEAB710 2189 To: 2190 CSeq: 1 INVITE 2191 Call-ID: 3d57cd17-47deb849-dca8b6c6 2192 Contact: 2193 2194 Replaces: f3b3cbd0-a2c5775e-5df9f8d5;to-tag=65a98f7c 2195 -1dd2-11b2-88c6-b03162323164+65a98f7c;from-tag=15A3DE7C-9283203B 2196 2197 Max-Forwards: 70 2198 Content-Type: application/sdp 2199 Content-Length: 223 2201 v=0 2202 o=- 1102980497 1102980497 IN IP4 ua1.example.com 2203 s=IP SIP UA 2204 c=IN IP4 ua1.example.com 2205 t=0 0 2206 a=sendrecv 2207 m=audio 2238 RTP/AVP 0 8 101 2208 a=rtpmap:0 PCMU/8000 2209 a=rtpmap:8 PCMA/8000 2210 a=rtpmap:101 telephone-event/8000 2212 11.8. Calls between UAs within the Group 2214 In this scenario, Bob calls Alice who is also in the Appearance 2215 group. Only one appearance number is used for this dialog. This 2216 example also shows the use of the 'exclusive' tag to indicate that 2217 other UAs in the group can not join or take this dialog. 2219 Carol Proxy Alice Appearance Agent Bob 2220 | | | | | 2221 | |<-------------------- INVITE (to Alice's UA) F1<| 2222 | | | | | 2223 | |< - - - - - - - - - - - - - ->| | 2224 | | | | | 2225 | | | | | 2226 | | |<-- NOTIFY F2<| | 2227 | | | | | 2228 | | |>F3 200 OK -->| | 2229 | | | |>F4 NOTIFY ------>| 2230 | | | | | 2231 | | | |<------ 200 OK F5<| 2232 | |>F6 INVITE --->| | | 2233 | | (appearance=1)| | | 2234 | | | | | 2235 | |<------ 180 F7<| | | 2236 | | | | | 2237 | |>F8 180 --------------------------------------->| 2238 | | | | | 2239 | |< - - - - - - - - - - - - - ->| | 2240 | | | | | 2241 | | |<-- NOTIFY F9<| | 2242 | | | | | 2243 | | |>F10 200 OK ->| | 2244 | | | |>F11 NOTIFY ----->| 2245 | | | | | 2246 | | | |<----- 200 OK F12<| 2247 | |<-- 200 OK F13<| | | 2248 | | | | | 2249 | |>F14 200 OK ------------------------------------>| 2250 | | | | | 2251 | |<--------------------------------------- ACK F15<| 2252 | | | | | 2253 | |>F16 ACK ----->| | | 2254 | | | | | 2255 | | |<======= RTP established =======>| 2256 | | | | | 2257 | |< - - - - - - - - - - - - - ->| | 2258 | | | | | 2259 | | |<- NOTIFY F17<| | 2260 | | | | | 2261 | | |>F18 200 OK ->| | 2262 | | | |>F19 NOTIFY ----->| 2263 | | | | | 2264 | | | |<----- 200 OK F24<| 2265 | | | | | 2267 Figure 8. 2269 F19 Appearance Agent ----> Bob 2271 NOTIFY sip:bob@ua1.example.com SIP/2.0 2272 From: ;tag=497585728578386 2273 To: ;tag=633618CF-B9C2EDA4 2274 Call-ID: a7d559db-d6d7dcad-311c9e3a 2275 CSeq: 7 NOTIFY 2276 Via: SIP/2.0/UDP appearanceagent.example.com 2277 ;branch=z9hG4bK1711759878512309 2278 Max-Forwards: 70 2279 Content-Type: application/dialog-info+xml 2280 Event: dialog;shared 2281 Subscription-State: active;expires=1500 2282 Contact: 2283 Content-Length: ... 2285 2286 2291 2296 true 2297 1 2298 confirmed 2299 2300 2301 2302 2303 2304 sip:HelpDesk@example.com 2305 2306 2307 2309 2314 true 2315 1 2316 confirmed 2317 2318 2319 2320 2321 sip:HelpDesk@example.com 2322 2323 2324 2326 2328 11.9. Consultation Hold with Appearances 2330 In this scenario, Bob has a call with Carol. Bob makes a 2331 consultation call to Alice by putting Carol on hold and calling 2332 Alice. Bob chooses not to have an appearance number for the call to 2333 Alice since he is treating it as part of the call to Carol. He 2334 indicates this in his PUBLISH F32 which contains the 'shared' Event 2335 parameter but no element. The PUBLISH is sent before 2336 the INVITE to Alice to ensure no appearance number is assigned by the 2337 Appearance Agent. Finally, Bob hangs up with Alice and resumes the 2338 call with Carol. Dialog notifications of the consultation call are 2339 not shown, as they are not used. 2341 Note that if Carol hangs up while Bob is consulting with Alice, Bob 2342 can decide if he wants to reuse the appearance number used with Carol 2343 for the call with Alice. If not, Bob publishes the termination of 2344 the dialog with Carol and the Appearance Agent will re-allocate the 2345 appearance. If he wants to keep the appearance, Bob will publish the 2346 termination of the dialog with Carol and also publish the appearance 2347 with the dialog with Alice. This will result in Bob keeping the 2348 appearance number until he reports the dialog with Alice terminated. 2350 Note that the call flow would be similar if Bob called a music on 2351 hold server instead of Alice to implement a music on hold service as 2352 described in [I-D.worley-service-example]. 2354 Carol Proxy Alice Appearance Agent Bob 2355 | | | | | 2356 |<================= Both way RTP established ===================>| 2357 | | | | | 2358 | |<------------------------------(hold) INVITE F22<| 2359 |<- INVITE F23<| | | | 2360 | | | | | 2361 |>F24 200 OK ->| | | | 2362 | |>F25 200 OK ------------------------------------>| 2363 | | | | | 2364 | |<--------------------------------------- ACK F26<| 2365 |<---- ACK F27<| | | | 2366 | |< - - - - - - - - - - - - - ->| | 2367 | | | | | 2368 | | |<- NOTIFY F28<| | 2369 | | | | | 2370 | | |>F29 200 OK ->| | 2371 | | | |>F30 NOTIFY ----->| 2372 | | | | | 2373 | | | |<----- 200 OK F31<| 2374 | | | | | 2375 | | Bob makes a consultation call to Alice | 2376 | | | | | 2377 | | | |<---- PUBLISH F32<| 2378 | | | | | 2379 | | | |>F33 200 OK ----->| 2380 | | | | | 2381 | |<------------------------------------ INVITE F34<| 2382 | | | | | 2383 | |>F35 INVITE -->| | | 2384 | | | | | 2385 | |<-- 200 OK F36<| | | 2386 | | | | | 2387 | |>F37 200 OK ------------------------------------>| 2388 | | | | | 2389 | |<--------------------------------------- ACK F38<| 2390 | | | | | 2391 | |>F39 ACK ----->| | | 2392 | | | | | 2393 | | |<======= RTP established =======>| 2394 | | | | | 2395 | | Bob hangs up with Alice | 2396 | | | | | 2397 | |<--------------------------------------- BYE F40<| 2398 | | | | | 2399 | |>F41 BYE ----->| | | 2400 | | | | | 2401 | |<-- 200 OK F42<| | | 2402 | | | | | 2403 | |>F43 200 OK ------------------------------------>| 2404 | | | | | 2405 | |<----------------------------(unhold) INVITE F44<| 2406 |<- INVITE F45<| | | | 2407 | | | | | 2408 |>F46 200 OK ->| | | | 2409 | |>F47 200 OK ------------------------------------>| 2410 | | | | | 2411 | |<--------------------------------------- ACK F48<| 2412 |<---- ACK F49<| | | | 2413 | |< - - - - - - - - - - - - - ->| | 2414 | | | | | 2415 | | |<- NOTIFY F50<| | 2416 | | | | | 2417 | | |>F51 200 OK ->| | 2418 | | | |>F52 NOTIFY ----->| 2419 | | | | | 2420 | | | |<----- 200 OK F53<| 2421 | | | | | 2422 |<================= Both way RTP established ===================>| 2423 | | | | | 2425 Figure 9. 2427 F32 Bob ----> Appearance Agent 2429 PUBLISH sip:HelpDesk@example.com SIP/2.0 2430 Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bKa5d6cf61F5FBC05A 2431 From: ;tag=44150CC6-A7B7919D 2432 To: ;tag=428765950880801 2433 CSeq: 11 PUBLISH 2434 Call-ID: 44fwF144-F12893K38424 2435 Contact: 2436 Event: dialog;shared 2437 Max-Forwards: 70 2438 Content-Type: application/dialog-info+xml 2439 Content-Length: ... 2441 2442 2447 2451 true 2452 trying 2453 2454 2455 2457 2458 2459 sip:HelpDesk@example.com 2460 2461 2462 2463 2465 11.10. Joining or Bridging an Appearance 2467 In this call flow, a call answered by Bob is joined by Alice or 2468 "bridged". The Join header field is used by Alice to request this 2469 bridging. If Bob did not support media mixing, Bob could obtain 2470 conferencing resources as described in [RFC4579]. 2472 Carol Forking Proxy Appearance Agent Alice Bob 2473 | | | | | 2474 |<=============Both way RTP established===========>| 2475 | | | | | 2476 | | |< PUBLISH F22| | 2477 | | | | | 2478 | | |>F23 200 OK >| | 2479 | | | | | 2480 | |<---- INVITE (w/ Join) F24<| | 2481 | | | | | 2482 | |>F25 INVITE (w/Join)---------------->| 2483 | | | | | 2484 | |<---- OK 200 Contact:Bob;isfocus F26<| 2485 | | | | | 2486 | |< - - - - - >| | | 2487 | | | | | 2488 | | |>F27 NOTIFY >| | 2489 | | | | | 2490 | | |< 200 OK F28<| | 2491 | | | | | 2492 | | |>F29 NOTIFY ---------->| 2493 | | | | | 2494 | | |F31 200 OK Contact:B----->| | 2497 | | | | | 2498 | |<----------------- ACK F32<| | 2499 | | | | | 2500 | |>ACK F33---------------------------->| 2501 | | | | | 2502 | |<-----INVITE Contact:Bob;isfocus F34<| 2503 |<-INVITE F35| | | | 2504 | | | | | 2505 |>F26 200 -->| | | | 2506 | |>F37 200 OK ------------------------>| 2507 | | | | | 2508 | |<--------------------------- ACK F38<| 2509 |<--- ACK F39| | | | 2510 | | | |<==RTP==>| 2511 |<=============Both way RTP established===========>| 2512 | | | | | 2513 | |< - - - - - >| | | 2514 | | | | | 2515 | | |>F40 NOTIFY >| | 2516 | | | | | 2517 | | |< 200 OK F41<| | 2518 | | | | | 2519 | | |>F42 NOTIFY ---------->| 2520 | | | | | 2521 | | | Appearance Agent 2528 PUBLISH sip:HelpDesk@example.com SIP/2.0 2529 Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bKa5d6cf61F5FBC05A 2530 From: ;tag=44150CC6-A7B7919D 2531 To: ;tag=428765950880801 2532 CSeq: 11 PUBLISH 2533 Call-ID: 87837Fkw87asfds 2534 Contact: 2535 Event: dialog;shared 2536 Max-Forwards: 70 2537 Content-Type: application/dialog-info+xml 2538 Content-Length: ... 2540 2541 2546 2549 1 2550 false 2551 2555 trying 2556 2557 2558 2559 2560 2561 2562 2563 2564 2566 F24 Alice ----> Proxy 2568 INVITE sip:bob@ua.example.com SIP/2.0 2569 Via: SIP/2.0/UDP ua1.example.com;branch=z9hG4bKcc9d727c2C29BE31 2570 From: ;tag=605AD957-1F6305C2 2571 To: 2572 CSeq: 2 INVITE 2573 Call-ID: dc95da63-60db1abd-d5a74b48 2574 Contact: 2575 2576 Join: 14-1541707345;to-tag=d3b06488-1dd1-11b2-88c5 2577 -b03162323164+d3e48f4c;from-tag=44BAD75D-E3128D42 2578 2579 Max-Forwards: 70 2580 Content-Type: application/sdp 2581 Content-Length: 223 2583 v=0 2584 o=- 1103061265 1103061265 IN IP4 ua1.example.com 2585 s=IP SIP UA 2586 c=IN IP4 ua1.example.com 2587 t=0 0 2588 a=sendrecv 2589 m=audio 2236 RTP/AVP 0 8 101 2590 a=rtpmap:0 PCMU/8000 2591 a=rtpmap:8 PCMA/8000 2592 a=rtpmap:101 telephone-event/8000 2594 11.11. Appearance Allocation - Loss of Appearance 2596 Bob reserves an appearance with a PUBLISH, sends an INVITE to Carol, 2597 then becomes unreachable. When he fails to refresh his publication 2598 to the appearance agent, the Appearance Agent declares the dialog 2599 terminated and frees up the appearance using NOTIFYs F14 and F16. 2601 After retransmitting the NOTIFY to Bob (in not shown messages F17, 2602 F18, etc.), the subscription is terminated. 2604 Carol Proxy Alice Appearance Agent Bob 2605 | | | | | 2606 | | | |<----- PUBLISH F1<| 2607 | | | | | 2608 | | | |>F2 200 OK ------>| 2609 | | | | | 2610 | | |<-- NOTIFY F3<| | 2611 | | | | | 2612 | | |>F4 200 OK -->| | 2613 | | | |------- NOTIFY F5>| 2614 | | | | | 2615 | | | |F8 100 Trying --------------------------------->| 2620 |<-- INVITE F9<| | | | 2621 | | | |<---- PUBLISH F10<| 2622 | | | | | 2623 | | | |>F11 200 OK ----->| 2624 | | | | | 2625 |>F12 180 --->| | | | 2626 | |>F13 180 Ringing ------------------------------->| 2627 | | | | | 2628 | | | | Bob goes offline | 2629 | | | | | 2630 | | | Appearance selection times out | 2631 | | | | | 2632 | | |<- NOTIFY F14<| | 2633 | | | | | 2634 | | |>F15 200 OK ->| | 2635 | | | |------ NOTIFY F16>| 2636 | | | | | 2637 | | | NOTIFY is retransmitted | 2639 Figure 11. 2641 11.12. Appearance Seizure Contention Race Condition 2643 Bob and Alice both try to reserve appearance 2 by publishing at the 2644 same time. The Appearance Agent allocates the appearance to Bob by 2645 sending a 200 OK and denies it to Alice by sending a 400 response. 2646 After the NOTIFY F5, Alice learns that Bob is using appearance 2. 2647 Alice then attempts to reserve appearance 3 by publishing, which is 2648 then accepted. 2650 Carol Proxy Alice Appearance Agent Bob 2651 | | | | | 2652 | | | |<----- PUBLISH F1<| 2653 | | | | (appearance=2) 2654 | | |>F2 PUBLISH ->| | 2655 | | | (appearance=2) | 2656 | | | | | 2657 | | | |>F3 200 OK ------>| 2658 | | |<---- F4 400 <| | 2659 | | | | | 2660 | | |<-- NOTIFY F5<| | 2661 | | | | | 2662 | | |>F6 200 OK -->| | 2663 | | | |------- NOTIFY F7>| 2664 | | | | | 2665 | | | |F10 100 Trying -------------------------------->| 2670 |<- INVITE F11<| | | | 2671 | | | |<---- PUBLISH F12<| 2672 | | | | (appearance=2) 2673 | | | |>F13 200 OK ----->| 2674 | | |>F14 PUBLISH->| | 2675 | | | (appearance=3) | 2676 | | | | | 2677 | | |<--- F15 200 <| | 2678 | | | | | 2679 | | |<- NOTIFY F16<| | 2680 | | | | | 2681 | |>F17 200 OK ->| | 2682 Dave | | |------ NOTIFY F18>| 2683 | | | | | 2684 | | | |F21 100 ----->| | | 2688 |<- INVITE F22<| | | | 2690 Figure 12. 2692 11.13. Appearance Agent Subscription to UAs 2694 In this scenario, the Appearance Agent does not have any way of 2695 knowing Bob's dialog state information, except through Bob. This 2696 could be because the Appearance Agent is not part of a B2BUA, or 2697 perhaps Bob is remotely registering. When Bob registers, the 2698 Appearance Agent receives a registration event package notification 2699 from the registrar. The Appearance Agent then SUBSCRIBEs to Bob's 2700 dialog event state using Event:dialog in the SUBSCRIBE. Whenever 2701 Bob's dialog state changes, Bob's UA sends a NOTIFY to the Appearance 2702 Agent which then notifies the other other UAs in the group. 2704 Carol Proxy Alice Appearance Agent Bob 2705 | | | | | 2706 | |<----------------------------------- REGISTER F1<| 2707 | | | | | 2708 | |>F2 200 OK ------------------------------------->| 2709 | | | | | 2710 | |>F3 NOTIFY ------------------>| | 2711 | | | | | 2712 | |<------------------ 200 OK F4<| | 2713 | | | |---- SUBSCRIBE F5>| 2714 | | | | | 2715 | | | |F8 200 OK ------>| 2720 | | | | | 2721 | | | |<--- SUBSCRIBE F9<| 2722 | | | | | 2723 | | | |>F10 200 OK ----->| 2724 | | | | | 2725 | | | |------ NOTIFY F11>| 2726 | | | | | 2727 | | | |F14 100 Trying -------------------------------->| 2732 |<- INVITE F15<| | | | 2733 | | | |<----- NOTIFY F16<| 2734 | | | | | 2735 | | | |>F17 200 OK ----->| 2736 | | |<- NOTIFY F18<| | 2737 | | | | | 2738 | | |>F19 200 OK ->| | 2739 | | | |------ NOTIFY F20>| 2740 | | | | | 2741 | | | |F22 180 --->| | | | 2743 | |>F23 180 Ringing ------------------------------->| 2744 | | | | | 2745 | | | |<----- NOTIFY F24<| 2746 | | | | | 2747 | | | |>F25 200 OK ----->| 2748 | | |<- NOTIFY F26<| | 2749 | | | | | 2750 | | |>F27 200 OK ->| | 2751 | | | |------ NOTIFY F28>| 2752 | | | | | 2753 | | | |F30 200 OK ->| | | | 2755 | |>F31 200 OK ------------------------------------>| 2756 | | | | | 2757 | | | |<----- NOTIFY F32<| 2758 | | | | | 2759 | | | |>F33 200 OK ----->| 2760 | | | | | 2761 | |<--------------------------------------- ACK F34<| 2762 |<---- ACK F35<| | | | 2763 | | | | | 2764 |<================= Both way RTP established ===================>| 2765 | | | | | 2766 | | |<- NOTIFY F36<| | 2767 | | | | | 2768 | | |>F37 200 OK ->| | 2769 | | | |------ NOTIFY F38>| 2770 | | | | | 2771 | | | || 2789 | | | | | 2790 | |<------------------------------(hold) INVITE F22<| 2791 |<- INVITE F23<| | | | 2792 | | | | | 2793 |>F24 200 OK ->| | | | 2794 | |>F25 200 OK ------------------------------------>| 2795 | | | | | 2796 | |<--------------------------------------- ACK F26<| 2797 |<---- ACK F27<| | | | 2798 | | | | | 2799 | |< - - - - - - - - - - - - - ->| | 2800 | | | | | 2801 | | |<- NOTIFY F28<| | 2802 | | | | | 2803 | | |>F29 200 OK ->| | 2804 | | | |>F30 NOTIFY ----->| 2805 | | | | | 2806 | | | |<----- 200 OK F31<| 2807 | | | | | 2808 | | Alice decides to pick up the call | 2809 | | | | | 2810 | | |>F32 PUBLISH->| | 2811 | | | | | 2812 | | |<- 200 OK F33<| | 2813 | | | | | 2814 | | |<- NOTIFY F34<| | 2815 | | | | | 2816 | | |>F35 200 OK ->| | 2817 | | | |>F36 NOTIFY ----->| 2818 | | | | | 2819 | | | |<----- 200 OK F37<| 2820 |>F38 BYE ---->| | | | 2821 | |>F39 BYE --------------------------------------->| 2822 | | | | | 2823 | |<------------------------------------ OK 200 F40<| 2824 |<- 200 OK F41<| | | | 2825 | |<-- INVITE F42<| | | 2826 |<- INVITE F43<|(w/ Replaces) | | | 2827 |( w/ Replaces)| | | | 2828 | | | | | 2829 |>F44 481 ---->| | | | 2830 | |>F45 481 ----->| | | 2831 |<---- ACK F46<| | | | 2832 | |<----- ACK F47<| | | 2833 | | |>F48 PUBLISH->| | 2834 | | | | | 2835 | | |<- 200 OK F49<| | 2836 | | | | | 2837 | | |<- NOTIFY F50<| | 2838 | | | | | 2839 | | |>F51 200 OK ->| | 2840 | | | |>F52 NOTIFY ----->| 2841 | | | | | 2842 | | | |<----- 200 OK F53<| 2844 Figure 14. 2846 F48 Alice ----> Appearance Agent 2848 PUBLISH sip:HelpDesk@example.com SIP/2.0 2849 Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bKa5d6cf61F5FBC05A 2850 From: ;tag=44150CC6-A7B7919D 2851 To: ;tag=428765950880801 2852 CSeq: 11 PUBLISH 2853 Call-ID: 87837Fkw87asfds 2854 Contact: 2855 Event: dialog;shared 2856 Max-Forwards: 70 2857 Content-Type: application/dialog-info+xml 2858 Content-Length: ... 2860 2861 2866 2869 1 2870 false 2871 2875 terminated 2876 2877 2878 2879 2880 2881 2882 2884 2885 2887 11.15. Appearance Seizure Incoming/Outgoing Contention Race Condition 2889 Alice tries to seize appearance 2 at the same time appearance 2 is 2890 allocated to an incoming call. The Appearance Agent resolves the 2891 conflict by sending a 400 to Alice. After the NOTIFY F6, Alice 2892 learns that the incoming call is using appearance 2. Alice 2893 republishes for appearance 3, which is accepted. Note that this 2894 example shows the INVITE being received before the NOTIFY from the 2895 Appearance Agent. 2897 Carol Proxy Alice Appearance Agent Bob 2898 | | | | | 2899 |>-- INVITE F1>| | | | 2900 | |< - - - - - - - - - - - - - ->| | 2901 | | | | | 2902 | | |>F2 PUBLISH ->| | 2903 | | | (appearance=2) | 2904 | | | | | 2905 | |>F3 INVITE (appearance=2) ---------------------->| 2906 | | | | | 2907 | |>F4 INVITE | | | 2908 | |(appearance=2)>| | | 2909 | | |<---- F5 400 <| | 2910 | | | | | 2911 | | |<-- NOTIFY F6<| | 2912 | | | | | 2913 | | |>F7 200 OK -->| | 2914 | | | |------- NOTIFY F8>| 2915 | | | | | 2916 | | | |F10 PUBLISH->| | 2919 | | | (appearance=3) | 2920 | | | | | 2921 | | |< F11 200 OK <| | 2922 | | | | | 2923 | | |<- NOTIFY F12<| | 2924 | | | | | 2925 | |>F13 200 OK ->| | 2926 Dave | | |------ NOTIFY F14>| 2927 | | | | | 2928 | | | |F17 100 ----->| | | 2932 |<- INVITE F18<| | | | 2934 Figure 15. 2936 12. Security Considerations 2938 Since multiple line appearance features are implemented using 2939 semantics provided by [RFC3261], Event Package for Dialog State as 2940 define in , and Event Notification [I-D.ietf-sipcore-rfc3265bis], 2941 [RFC3903], security considerations in these documents apply to this 2942 draft as well. 2944 NOTIFY or PUBLISH message bodies that provide the dialog state 2945 information and the dialog identifiers MAY be encrypted end-to-end 2946 using the standard mechanisms. All SUBSCRIBES between the UA's and 2947 the Appearance Agent MUST be authenticated. 2949 For an emergency call, a UA MUST never wait for a confirmed seizure 2950 of an appearance before sending an INVITE. Instead, the emergency 2951 call MUST proceed regardless of the status of the PUBLISH 2952 transaction. 2954 13. IANA Considerations 2956 This section registers the SIP event package parameter 'shared', the 2957 SIP Alert-Info header field parameter "appearance" and the XML 2958 namespace extensions to the SIP Dialog Package. 2960 13.1. SIP Event Package Parameter: shared 2962 This specification defines a new event parameter 'shared' for the 2963 Dialog Package. When used in a NOTIFY, it indicates that the 2964 notifier supports the shared appearance feature. When used in a 2965 PUBLISH, it indicates that the publisher has explicit appearance 2966 information contained in the message body. If not present in a 2967 PUBLISH, the Appearance Agent MAY assign an appearance number to any 2968 new dialogs in the message body. 2970 13.2. URN Sub-Namespace Registration: sa-dialog-info 2972 This section registers a new XML namespace per the procedures 2973 in [RFC3688]. 2975 URI: urn:ietf:params:xml:ns:sa-dialog-info. 2977 Registrant Contact: IETF BLISS working group, , 2978 Alan Johnston 2980 XML: 2982 BEGIN 2983 2984 2986 2987 2988 2990 Shared Appearance Dialog Information Namespace 2991 2992 2993

Namespace for Shared Appearance Dialog Information

2994

urn:ietf:params:xml:ns:dialog-info

2995

See 2996 RFCXXXX.

2997 2998 2999 END 3001 13.3. XML Schema Registration 3003 This section registers an XML schema per the procedures in 3004 [RFC3688]. 3006 URI: urn:ietf:params:xml:schesa:sa-dialog-info. 3008 Registrant Contact: IETF BLISS working group, , 3009 Alan Johnston 3011 The XML for this schema can be found in Section 6. 3013 14. Acknowledgements 3015 The following individuals were part of the shared appearance Design 3016 team and have provided input and text to the document (in 3017 alphabetical order): 3019 Martin Dolly, Andrew Hutton, Raj Jain, Fernando Lombardo, Derek 3020 MacDonald, Bill Mitchell, Michael Procter, Theo Zowzouvillys. 3022 Thanks to Chris Boulton for helping with the XML schema. 3024 Much of the material has been drawn from previous work by Mohsen 3025 Soroushnejad, Venkatesh Venkataramanan, Paul Pepper and Anil Kumar, 3026 who in turn received assistance from: 3028 Kent Fritz, John Weald, and Sunil Veluvali of Sylantro Systems, Steve 3029 Towlson, and Michael Procter of Citel Technologies, Rob Harder and 3030 Hong Chen of Polycom Inc, John Elwell, J D Smith of Siemens 3031 Communications, Dale R. Worley of Pingtel, Graeme Dollar of Yahoo 3032 Inc. 3034 Also thanks to Geoff Devine, Paul Kyzivat, Jerry Yin, John Elwell, 3035 Dan York, Spenser Dawkins, Martin Dolly, and Brett Tate for their 3036 comments. 3038 Thanks to Carolyn Beeton, Francois Audet, Andy Hutton, Tim Ross, Raji 3039 Chinnappa, and Harsh Mendiratta for their detailed review of the 3040 document. 3042 15. References 3044 15.1. Normative References 3046 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3047 Requirement Levels", BCP 14, RFC 2119, March 1997. 3049 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 3050 A., Peterson, J., Sparks, R., Handley, M., and E. 3051 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 3052 June 2002. 3054 [RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer 3055 Method", RFC 3515, April 2003. 3057 [I-D.ietf-sipcore-rfc3265bis] 3058 Roach, A., "SIP-Specific Event Notification", 3059 draft-ietf-sipcore-rfc3265bis-04 (work in progress), 3060 October 2011. 3062 [RFC3903] Niemi, A., "Session Initiation Protocol (SIP) Extension 3063 for Event State Publication", RFC 3903, October 2004. 3065 [RFC3891] Mahy, R., Biggs, B., and R. Dean, "The Session Initiation 3066 Protocol (SIP) "Replaces" Header", RFC 3891, 3067 September 2004. 3069 [RFC4235] Rosenberg, J., Schulzrinne, H., and R. Mahy, "An INVITE- 3070 Initiated Dialog Event Package for the Session Initiation 3071 Protocol (SIP)", RFC 4235, November 2005. 3073 [RFC3911] Mahy, R. and D. Petrie, "The Session Initiation Protocol 3074 (SIP) "Join" Header", RFC 3911, October 2004. 3076 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 3077 "Indicating User Agent Capabilities in the Session 3078 Initiation Protocol (SIP)", RFC 3840, August 2004. 3080 [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, 3081 January 2004. 3083 [I-D.ietf-salud-alert-info-urns] 3084 Liess, L., Jesske, R., Johnston, A., Worley, D., and P. 3085 Kyzivat, "Alert-Info URNs for the Session Initiation 3086 Protocol (SIP)", draft-ietf-salud-alert-info-urns-04 (work 3087 in progress), December 2011. 3089 15.2. Informative References 3091 [RFC5359] Johnston, A., Sparks, R., Cunningham, C., Donovan, S., and 3092 K. Summers, "Session Initiation Protocol Service 3093 Examples", BCP 144, RFC 5359, October 2008. 3095 [RFC4579] Johnston, A. and O. Levin, "Session Initiation Protocol 3096 (SIP) Call Control - Conferencing for User Agents", 3097 BCP 119, RFC 4579, August 2006. 3099 [RFC3680] Rosenberg, J., "A Session Initiation Protocol (SIP) Event 3100 Package for Registrations", RFC 3680, March 2004. 3102 [I-D.worley-service-example] 3103 Worley, D., "Session Initiation Protocol Service Example 3104 -- Music on Hold", draft-worley-service-example-08 (work 3105 in progress), August 2011. 3107 Authors' Addresses 3109 Alan Johnston (editor) 3110 Avaya 3111 St. Louis, MO 63124 3113 Email: alan.b.johnston@gmail.com 3115 Mohsen Soroushnejad 3116 Sylantro Systems Corp 3118 Email: mohsen.soroush@sylantro.com 3120 Venkatesh Venkataramanan 3121 Sylantro Systems Corp 3123 Email: vvenkatar@gmail.com