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Checking references for intended status: Informational ---------------------------------------------------------------------------- No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 CUSS WG A. Johnston 3 Internet-Draft Avaya 4 Intended status: Informational L. Liess 5 Expires: April 1, 2012 Deutsche Telekom AG 6 September 29, 2011 8 Problem Statement and Requirements for Transporting User to User Call 9 Control Information in SIP 10 draft-ietf-cuss-sip-uui-reqs-06 12 Abstract 14 This document introduces the transport of call control related User 15 to User Information (UUI) using the Session Initiation Protocol 16 (SIP), and develops several requirements for a new SIP mechanism. 17 Some SIP sessions are established by or related to a non-SIP 18 application. This application may have information that needs to be 19 transported between the SIP User Agents during session establishment. 20 In addition to interworking with the ISDN UUI Service, this extension 21 will also be used for native SIP endpoints requiring application UUI. 23 Status of this Memo 25 This Internet-Draft is submitted to IETF in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on April 1, 2012. 40 Copyright Notice 42 Copyright (c) 2011 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 2.1. User Agent to User Agent . . . . . . . . . . . . . . . . . 4 60 2.2. Proxy Retargeting . . . . . . . . . . . . . . . . . . . . 5 61 2.3. Redirection . . . . . . . . . . . . . . . . . . . . . . . 5 62 2.4. Referral . . . . . . . . . . . . . . . . . . . . . . . . . 6 63 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 7 64 4. Security Considerations . . . . . . . . . . . . . . . . . . . 9 65 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 66 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 67 7. Informative References . . . . . . . . . . . . . . . . . . . . 10 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 70 1. Overview 72 This document describes the transport of User to User Information 73 (UUI) during SIP [RFC3261] session setup. This section introduces 74 UUI and explains how it relates to SIP. 76 We define SIP UUI data as application-specific information that is 77 related to a session being established using SIP. It is assumed that 78 the application is running in both endpoints in a two party session. 79 That is, the application interacts with both the User Agents in a SIP 80 session. In order to function properly, the application needs a 81 small piece of information, the UUI, to be transported at the time of 82 session establishment. This information is essentially opaque data 83 to SIP - it is unrelated to SIP routing, authentication, or any other 84 SIP function. This application can be considered to be operating at 85 a higher layer on the protocol stack. As a result, SIP should not 86 interpret, understand, or perform any operations on the UUI. Should 87 this not be the case, then the information being transported is not 88 considered UUI, and another SIP-specific mechanism will be needed to 89 transport the information (such as a new header field). In 90 particular, this mechanism creates no requirements on intermediaries 91 such as proxies. 93 UUI is defined this way for two reasons. Firstly, this supports a 94 strict layering of protocols and data. Providing information and 95 understanding of the UUI to the transport layer (SIP in this case) 96 would not provide any benefits and instead could create cross layer 97 coupling. Secondly, it is neither feasible nor desirable for a SIP 98 User Agent (UA) to understand the information; instead the goal is 99 for the UA to simply pass the information as efficiently as possible 100 to the application which does understand the information. 102 Note that this document does not discuss the transport of non-call 103 control UUI which can be done using the SIP INFO method. 105 An important application is the interworking with User to User 106 Information (UUI) in ISDN, specifically, the transport of the call 107 control related ITU-T Q.931 User to User Information Element (UU IE) 108 [Q931] and ITU-T Q.763 User to User Information Parameter [Q763] data 109 in SIP. ISDN UUI is widely used in the PSTN today in contact centers 110 and call centers. These applications are currently transitioning 111 away from using ISDN for session establishment to using SIP. Native 112 SIP endpoints will need to implement a similar service and be able to 113 interwork with this ISDN service. 115 Note that the distinction between call control UUI and non-call 116 control UUI is very important. SIP already has a mechanism for 117 sending arbitrary UUI data between UAs during a session or dialog - 118 the SIP INFO [RFC6086] method. Call control UUI, in contrast, must 119 be exchanged at the time of setup and needs to be carried in the 120 INVITE and a few other methods and responses. Applications that 121 exchange UUI but do not have a requirement that it be transported and 122 processed during call setup can simply use SIP INFO and do not need a 123 new SIP extension. 125 In this document, four different use case call flows are discussed. 126 Next, the requirements for call control UUI transport are discussed. 128 2. Use Cases 130 This section discusses four use cases for the transport of call 131 control related user to user information. These use cases will help 132 motivate the requirements for SIP call control UUI. 134 2.1. User Agent to User Agent 136 In this scenario, the originating UA includes UUI in the INVITE sent 137 through a proxy to the terminating UA. The terminating UA can use 138 the UUI in any way. If it is an ISDN gateway, it could map the UUI 139 into the appropriate DSS1 information element or QSIG [QSIG] 140 information element or ISUP parameter. Alternatively, the using 141 application might render the information to the user, or use it 142 during alerting or as a lookup for a screen pop. In this case, the 143 proxy does not need to understand the UUI mechanism, but normal proxy 144 rules should result in the UUI being forwarded without modification. 145 This call flow is shown in Figure 1. 147 Originating UA Proxy Terminating UA 148 | | | 149 | INVITE (UUI) F1 | | 150 |------------------->| INVITE (UUI) F2 | 151 | 100 Trying F3 |------------------->| 152 |<-------------------| 200 OK F4 | 153 | 200 OK F5 |<-------------------| 154 |<-------------------| | 155 | ACK F6 | | 156 |------------------->| ACK F7 | 157 | |------------------->| 159 Figure 1. Call flow with UUI exchanged between Originating and 160 Terminating UAs. 162 2.2. Proxy Retargeting 164 In this scenario, the originating UA includes UUI in the INVITE 165 request sent through a proxy to the terminating UA. The proxy 166 retargets the INVITE request, changing its request-URI to a URI that 167 addresses the terminating UA. The UUI data is then received and 168 processed by the terminating UA. This call flow is identical to 169 Figure 1 except that the proxy retargets the request, i.e., changes 170 the Request-URI as directed by some unspecified process. The UUI in 171 the INVITE request needs to be passed unchanged through this proxy 172 retargeting operation. Note that the contents of the UUI is not used 173 by the proxy for routing, as the UUI has only end-to-end significance 174 between UAs. 176 2.3. Redirection 178 In this scenario, UUI is inserted by an application which utilizes a 179 SIP redirect server. The UUI is then included in the INVITE request 180 sent by the originating UA to the terminating UA. In this case, the 181 originating UA does not necessarily need to support the UUI mechanism 182 but does need to support the SIP redirection mechanism used to 183 include the UUI data. Two examples of UUI with redirection (transfer 184 and diversion) are defined in [ANSII] and [ETSI]. 186 Note that this case may not precisely map to an equivalent ISDN 187 service use case. This is because there is no one-to-one mapping 188 between elements in a SIP network and elements in an ISDN network. 189 Also, there is not an exact one-to-one mapping between SIP call 190 control and ISDN call control. However, this should not prevent the 191 usage of SIP call control UUI in these cases. Instead, these slight 192 differences between the SIP UUI mechanism and the ISDN service need 193 to be carefully noted and discussed in an interworking specification. 195 Figure 2 shows this scenario, with the Redirect inserting UUI which 196 is then included in the INVITE request F4 send to the terminating UA. 198 Originating UA Redirect Server Terminating UA 199 | | | 200 | INVITE F1 | | 201 |------------------->| | 202 | 302 Moved (UUI) F2 | | 203 |<-------------------| | 204 | ACK F3 | | 205 |------------------->| | 206 | INVITE (UUI) F4 | | 207 |---------------------------------------->| 208 | 200 OK F5 | 209 |<----------------------------------------| 210 | ACK F6 | 211 |---------------------------------------->| 213 Figure 2. Call flow with UUI exchanged between Redirect Server and 214 Terminating UA. 216 A common example application of this call flow is an Automatic Call 217 Distributer (ACD) in a PSTN contact center. The originator would be 218 a PSTN gateway. The ACD would act as a Redirect Server, inserting 219 UUI based on called number, calling number, time of day, and other 220 information. The resulting UUI would be passed to the agent's 221 handset which acts as the terminating UA. The UUI could be used to 222 lookup information for rendering to the agent at the time of call 223 answering. 225 This redirection scenario, and the referral scenario in the next 226 section, are the most important scenarios for contact center 227 applications. Incoming calls to a contact center almost always are 228 redirected or referred to a final destination, sometimes multiple 229 times, based on collected information and business logic. The 230 ability to pass along UUI in these call redirection scenarios is 231 critical. 233 2.4. Referral 235 In this scenario, the application uses a UA to initiate a referral, 236 which causes an INVITE request to be generated between the 237 originating UA and terminating UA with UUI data inserted by the 238 Referrer UA. Note that this REFER method [RFC3515] could be part of 239 a transfer operation or it might be unrelated to an existing call, 240 such as out-of-dialog REFER request. In some cases, this call flow 241 is used in place of the redirection call flow: the referrer 242 immediately answers the call and then sends the REFER request. This 243 scenario is shown in Figure 3. 245 Originating UA Referrer Terminating UA 246 | | | 247 | REFER (UUI) F1 | | 248 |<-------------------| | 249 | 202 Accepted F2 | | 250 |------------------->| | 251 | INVITE (UUI) F3 | | 252 |---------------------------------------->| 253 | NOTIFY (100 Trying) F4 | 254 |------------------->| | 255 | 200 OK F5 | | 256 |<-------------------| | 257 | 200 OK F6 | 258 |<----------------------------------------| 259 | ACK F7 | 260 |---------------------------------------->| 261 | NOTIFY (200 OK) F8 | | 262 |------------------->| | 263 | 200 OK F9 | | 264 |<-------------------| | 266 Figure 3. Call flow with Referral and UUI. 268 3. Requirements 270 This section states the requirements for the transport of call 271 control related user to user information (UUI). 273 REQ-1: The mechanism will allow UAs to insert and receive UUI data in 274 SIP call setup requests and responses. 276 SIP messages covered by this include INVITE requests and end-to- 277 end responses to the INVITE, i.e. 18x, 200, and 3xx responses. 279 REQ-2: The mechanism will allow UAs to insert and receive UUI data in 280 SIP dialog terminating requests and responses. 282 Q.931 UUI supports inclusion in release and release completion 283 messages. SIP messages covered by this include BYE and 200 OK 284 responses to a BYE. 286 REQ-3: The mechanism will allow UUI to be inserted and retrieved in 287 SIP redirects and referrals. 289 SIP messages covered by this include REFER requests and 3xx 290 responses to INVITE requests. 292 REQ-4: The mechanism will allow UUI to be able to survive proxy 293 retargeting or any other form of redirection of the request. 295 Retargeting is a common method of call routing in SIP, and must 296 not result in the loss of user to user information. 298 REQ-5: The mechanism should not require processing entities to 299 dereference a URL in order to retrieve the UUI data. 301 Passing a pointer or link to the UUI data will not meet the real- 302 time processing considerations and would complicate interworking 303 with the PSTN. 305 REQ-6: The mechanism will support interworking with call control 306 related DSS1 information elements or QSIG information elements and 307 ISUP parameters. 309 REQ-7: The mechanism will allow a UAC to learn that a UAS understands 310 the UUI mechanism. 312 REQ-8: The mechanism will allow a UAC to require that a UAS 313 understands the call control UUI mechanism and have a request routed 314 based on this information. If the UAS does not understand the UUI 315 mechanism, the request will fail. 317 This could be useful in ensuring that a request destined for the 318 PSTN is routed to a gateway that supports the UUI mechanism rather 319 than an otherwise equivalent PSTN gateway that does not support 320 the ISDN mechanism. Note that support of the UUI mechanism does 321 not, by itself, imply that a particular application is supported - 322 see REQ-10. 324 REQ-9: The mechanism will allow proxies to remove a particular 325 application usage of UUI data from a request or response. 327 This is a common security function provided by border elements to 328 header fields such as Alert-Info or Call-Info URIs. 330 REQ-10: The mechanism will provide the ability for a UA to discover 331 which application usages of UUI another UA understands or supports. 333 The creation of a registry of application usages for the UUI 334 mechanism is implied by this requirement. The ISDN Service 335 utilizes a field known as the protocol discriminator, which is the 336 first octet of the ISDN UUI data, for this purpose. 338 REQ-11: The UUI is a sequence of octets. The solution will provide a 339 mechanism of transporting at least 128 octets of user data and a one 340 octet protocol discriminator, i.e. 129 octets in total. 342 There is the potential for non-ISDN services to allow UUI to be 343 larger than 128 octets. However, users of the mechanism will need 344 be cognizant of the size of SIP messages and the ability of 345 parsers to handle extremely large values. 347 REQ-12: The recipient of UUI will be able to determine the entity 348 that inserted the UUI. It is acceptable that this is performed 349 implicitly where it is known that there is only one other end UA 350 involved in the dialog. Where that does not exist, some other 351 mechanism will need to be provided. 353 This requirement comes into play during redirection, retargeting, 354 and referral scenarios. 356 4. Security Considerations 358 The security requirements for the UUI mechanism are described in this 359 section. It is important to note that UUI security is jointly 360 provided at the application layer and at the SIP layer. As such, is 361 important for application users of the UUI mechanism to know the 362 level of security used and deployed in their particular SIP 363 environments, and not to assume that a standardized (but perhaps 364 rarely deployed) security mechanism is in place. 366 There are three main security models that need to be addressed by the 367 UUI mechanism. One model treats the SIP layer as untrusted and 368 requires end-to-end integrity protection and/or encryption. This 369 model can be achieved by providing these security services at a layer 370 above SIP. In this case, the application integrity protects and/or 371 encrypts the UUI data before passing it to the SIP layer. This 372 method has two advantages: it does not assume or rely on end-to-end 373 security mechanisms in SIP which have virtually no deployment, and 374 allows the application which understands the contents of the UUI to 375 apply a proper level of security. The other approach is for the 376 application to pass the UUI without any protection to the SIP layer 377 and require the SIP layer to provide this security. This approach is 378 possible in theory, although its practical use would be extremely 379 limited. The UUI mechanisim should support both of these approaches. 381 The third model utilizes a trust domain and relies on perimeter 382 security at the SIP layer. This is the security model of the PSTN 383 and ISDN where UUI is commonly used today. This approach uses hop- 384 by-hop security mechanisms and relies on border elements for 385 filtering and application of policy. This approach is used today in 386 UUI deployments. Within this approach, there is a requirement that 387 intermediary elements can detect and remove a UUI element based on 388 policy, but there is no requirement that an intermediary element be 389 able to read or interpret the UUI (as the UUI contents only have end- 390 to-end significance). 392 The next three requirements capture the UUI security requirements. 394 REQ-13: The mechanism will allow integrity protection of the UUI. 396 This allows the UAS to be able to know that the UUI has not been 397 modified or tampered with by intermediaries. This property is not 398 guaranteed by the protocol in the ISDN application. 400 REQ-14: The mechanism will allow end-to-end privacy of the UUI. 402 Some UUI may contain private or sensitive information and may 403 require different security handling from the rest of the SIP 404 message. Note that this property is not available in the ISDN 405 application. 407 REQ-15: The mechanism will allow both end-to-end and hop-by-hop 408 security models. 410 The hop-by-hop model is required by the ISDN UUI service. 412 5. IANA Considerations 414 This document has no IANA requirements. 416 6. Acknowledgements 418 Thanks to Joanne McMillen who was a co-author of earlier versions of 419 this specification. Thanks to Spencer Dawkins, Keith Drage, Dale 420 Worley, and Vijay Gurbani for their review of earlier versions of 421 this document. The authors wish to thank Christer Holmberg, 422 Frederique Forestie, Francois Audet, Denis Alexeitsev, Paul Kyzivat, 423 Cullen Jennings, and Mahalingam Mani for their comments on this 424 topic. 426 7. Informative References 428 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 429 A., Peterson, J., Sparks, R., Handley, M., and E. 430 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 431 June 2002. 433 [Q931] "ITU-T Q.931 User to User Information Element (UU IE)", 434 http://www.itu.int/rec/T-REC-Q.931-199805-I/en . 436 [Q763] "ITU-T Q.763 Signaling System No. 7 - ISDN user part 437 formats and codes", 438 http://www.itu.int/rec/T-REC-Q.931-199805-I/en . 440 [ANSII] "ANSI T1.643-1995, Telecommunications-Integrated Services 441 Digital Network (ISDN)-Explicit Call Transfer 442 Supplementary Service". 444 [ETSI] "ETSI ETS 300 207-1 Ed.1 (1994), Integrated Services 445 Digital Network (ISDN); Diversion supplementary services". 447 [QSIG] "ECMA-143 "Private Integrated Services Network (PISN) - 448 Circuit Mode Bearer Services - Inter-Exchange Signalling 449 Procedures and Protocol" December 2001". 451 [RFC6086] Holmberg, C., Burger, E., and H. Kaplan, "Session 452 Initiation Protocol (SIP) INFO Method and Package 453 Framework", RFC 6086, January 2011. 455 [RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer 456 Method", RFC 3515, April 2003. 458 Authors' Addresses 460 Alan Johnston 461 Avaya 462 St. Louis, MO 63124 464 Email: alan.b.johnston@gmail.com 466 Laura Liess 467 Deutsche Telekom AG 469 Email: laura.liess.dt@gmail.com