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'I-D.ietf-cuss-sip-uui-reqs') ** Obsolete normative reference: RFC 4474 (Obsoleted by RFC 8224) == Outdated reference: A later version (-12) exists of draft-ietf-sipcore-rfc4244bis-05 Summary: 3 errors (**), 0 flaws (~~), 7 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group A. Johnston 3 Internet-Draft Avaya 4 Intended status: Standards Track J. Rafferty 5 Expires: January 12, 2012 Dialogic 6 July 11, 2011 8 A Mechanism for Transporting User to User Call Control Information in 9 SIP 10 draft-ietf-cuss-sip-uui-01 12 Abstract 14 There is a need for applications using SIP to exchange User to User 15 Information (UUI) data during session establishment. This 16 information, known as call control UUI, is a small piece of data 17 inserted by an application initiating the session, and utilized by an 18 application accepting the session. This data is opaque to SIP and 19 its function is unrelated to any basic SIP function. This document 20 defines a new SIP header field, User-to-User, to transport UUI, along 21 with an extension mechanism. 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 January 12, 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 3. Requirements Discussion . . . . . . . . . . . . . . . . . . . 3 60 4. Normative Definition . . . . . . . . . . . . . . . . . . . . . 5 61 4.1. Syntax for UUI Header Field . . . . . . . . . . . . . . . 5 62 4.2. Definition of New Parameter Values . . . . . . . . . . . . 6 63 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 64 5.1. Registration of Header Field . . . . . . . . . . . . . . . 6 65 5.2. Registration of Header Field Parameters . . . . . . . . . 7 66 5.3. Registration of SIP Option Tag . . . . . . . . . . . . . . 7 67 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 68 7. Appendix - Other Possible Mechanisms . . . . . . . . . . . . . 8 69 7.1. Why INFO is Not Used . . . . . . . . . . . . . . . . . . . 8 70 7.2. Why Other Protocol Encapsulation UUI Mechanisms are 71 Not Used . . . . . . . . . . . . . . . . . . . . . . . . . 8 72 7.3. MIME body Approach . . . . . . . . . . . . . . . . . . . . 9 73 7.4. URI Parameter . . . . . . . . . . . . . . . . . . . . . . 10 74 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 75 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 76 9.1. Informative References . . . . . . . . . . . . . . . . . . 10 77 9.2. Normative References . . . . . . . . . . . . . . . . . . . 11 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 80 1. Overview 82 This document describes the transport of User to User Information 83 (UUI) using SIP [RFC3261]. Specifically, we discuss a mechanism for 84 the transport of general application UUI and also for the transport 85 of call control related ITU-T Q.931 User to User Information Element 86 (UU IE) [Q931] and ITU-T Q.763 User to User Information Parameter 87 [Q763] data in SIP. UUI is widely used in the PSTN today in contact 88 centers and call centers which are transitioning away from ISDN to 89 SIP. This extension will also be used for native SIP endpoints 90 implementing similar services and interworking with ISDN services. 92 This mechanism was designed to meet the use cases, requirements, and 93 call flows for SIP call control UUI detailed in 94 [I-D.ietf-cuss-sip-uui-reqs]. All references to requirement numbers 95 (REQ-N) and figure numbers refer to this document. 97 The mechanism chosen is a new SIP header field, along with a new SIP 98 option tag and media feature tag. The header field carries the UUI 99 information, along with parameters indicating the encoding of the 100 UUI, the application user of the UUI, and optionally the content of 101 the UUI. The header field can be escaped into URIs supporting 102 referral and redirection scenarios. In these scenarios, History-Info 103 is used to indicate the inserter of the UUI. The SIP option tag is 104 used to indicate support for the header field. Support for the 105 header field indicates that a UA is able to extract the information 106 in the UUI and pass it up the protocol stack. The media feature tag 107 is used to indicate that a UA supports a particular application user 108 of UUI. 110 2. Terminology 112 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 113 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 114 document are to be interpreted as described in BCP 14, RFC 2119 115 [RFC2119]. 117 3. Requirements Discussion 119 This section describes how the User-to-User header field meets the 120 requirements in [I-D.ietf-cuss-sip-uui-reqs]. The header field can 121 be included in INVITE requests and responses and BYE requests and 122 responses, meeting REQ-1 and REQ-2. 124 For redirection and referral use cases and REQ-3, the header field 125 would be escaped into the Contact or Refer-To URI. Currently, UAs 126 that support attended transfer support the ability to escape a 127 Replaces header field into a Refer-To URI, and when acting upon this 128 URI add the Replaces header field to the triggered INVITE. This 129 logic and behavior is identical for the UUI header field. The UA 130 processing the REFER or the 3xx to the INVITE will need to support 131 the UUI mechanism, as UAs in general do not process unknown escaped 132 header fields. 134 Since SIP proxy forwarding and retargeting does not affect header 135 fields, the header field meets REQ-4. 137 The UUI header field will carry the UUI data and not a pointer to the 138 data, so REQ-5 is met. 140 Since the basic design of the UUI header field is similar to the ISDN 141 UUI service, interworking with PSTN protocols will be straightforward 142 and will be documented in a separate specification, meeting REQ-6 144 Requirements REQ-7, REQ-8, and REQ-10 relate to discovery of the 145 mechanism and supported applications. REQ-7 relates to support of 146 the UUI header field, while REQ-8 relates to routing based on support 147 of the UUI header field. REQ-7 is met by defining a new SIP option 148 tag 'uui'. The use of a 'Require: uui' in a request, or 'Supported: 149 uui' in an OPTIONS response could be used to require or discover 150 support of the mechanism. The presence of a Supported:uui or 151 Require:uui header field can be used by proxies to route to an 152 appropriate UA, meeting REQ-8. REQ-10 is met by creating a new class 153 of SIP feature tags. For example, the feature tag 'sip.uui.isdn' 154 could be used to indicate support of the ISDN UUI service, or 155 'sip.uui.app1' could be used to indicate support for a particular 156 application, app1. 158 Proxies commonly apply policy to the presence of certain SIP header 159 fields in requests by either passing them or removing them from 160 requests. REQ-9 is met by allowing proxies and other intermediaries 161 to remove UUI header fields in a request or response based on policy. 163 Carrying UUI data elements of at least 129 octets is trivial in the 164 UUI header field, meeting REQ-11. Note that very large UUI elements 165 should be avoided, as SIP header fields have traditionally not been 166 large. 168 To meet REQ-12 in redirection and referral use cases, History-Info 169 [I-D.ietf-sipcore-rfc4244bis] can be used. In these retargeting 170 cases, the changed Request-URI will be recorded in the History-Info 171 header field along with the identity of the element that performed 172 the retargeting. 174 The requirement for integrity protection in REQ-13 could be met by 175 the use of an S/MIME signature over a subset of header fields, as 176 defined in Section 23.4 of RFC 3261 "SIP Header Privacy and Integrity 177 using S/MIME: Tunneling SIP". The requirement of REQ-14 for end-to- 178 end privacy could be met using S/MIME or using encryption at the 179 application layer. Note that the use of S/MIME to secure the UUI 180 will result in an additional body being added to the request. 181 Hopwise TLS allows the header field to meet REQ-15 for hop-by-hop 182 security. 184 4. Normative Definition 186 This document defines a new SIP header field "User-to-User" to 187 transport call control UUI to meet the requirements in 188 [I-D.ietf-cuss-sip-uui-reqs]. 190 To help tag and identify the UUI used with this header field, "app", 191 "content", and "encoding" parameters are defined. The "app" 192 parameter identifies the application which generates and consumes the 193 UUI information. For the case of interworking with the ISDN UUI 194 Service, the application is unknown, so a value to indicate ISDN UUI 195 Service interworking will be defined. If the "app" parameter is not 196 present, interworking with the ISDN UUI Service MUST be assumed. The 197 "content" parameter identifies the actual content of the UUI data. 198 If not present, the content MUST be assumed to be unknown as it is in 199 the ISDN UUI Service. For newly defined applications using the SIP 200 UUI service, a "content" value MUST be defined and SHOULD be used. 201 The "encoding" parameter indicates the method of encoding the 202 information in the UUI. This specification only defines 203 "encoding=hex". If the "encoding" parameter is not present, "hex" 204 MUST be assumed. 206 4.1. Syntax for UUI Header Field 208 The User-to-User header field can be present in INVITE requests and 209 responses only and in BYE requests and responses. 211 The following syntax specification uses the augmented Backus-Naur 212 Form (BNF) as described in RFC 2234 and extends RFC 3261. 214 UUI = "User-to-User" HCOLON uui-data *(SEMI uui-param) 215 uui-data = token 216 uui-param = enc-param | cont-param | app-param | generic-param 217 enc-param = "encoding="("hex" | token) 218 cont-param = "content=" token 219 app-param = "app=" token 221 User-to-User header fields with different "app" parameters MAY be 222 present in a request or response. The number of User-to-User header 223 fields which may be present in a request or response is defined for a 224 particular application. Any size limitations on the UUI for a 225 particular purpose must be defined by that application. 227 4.2. Definition of New Parameter Values 229 This specification defines only the value of "hex" for the "encoding" 230 parameter. New values can be defined and added to the IANA registry 231 with a standards track RFC, which needs to discuss the issues in this 232 section. 234 New "encoding" values must reference a common encoding scheme or 235 define the exact new encoding scheme. 237 New "content" values must describe the content of the UUI and give 238 some example use cases. The default "encoding" and other allowed 239 encoding methods must be defined for this new content. 241 New "app" values must describe the new application which is utilizing 242 the UUI data and give some example use cases. The default "content" 243 value and other allowed contents must be defined for this new 244 purpose. Any restrictions on the size of the UUI data must be 245 described for the new application. 247 5. IANA Considerations 249 5.1. Registration of Header Field 251 This document defines a new SIP header field named "User-to-User". 253 The following row shall be added to the "Header Fields" section of 254 the SIP parameter registry: 256 +------------------+--------------+-----------+ 257 | Header Name | Compact Form | Reference | 258 +------------------+--------------+-----------+ 259 | User-to-User | | [RFCXXXX] | 260 +------------------+--------------+-----------+ 262 Editor's Note: [RFCXXXX] should be replaced with the designation of 263 this document. 265 5.2. Registration of Header Field Parameters 267 This document defines the parameters for the header field defined in 268 the preceding section. The header field "User-to-User" can contain 269 the parameters "encoding", "content", and "purpose". 271 The following rows shall be added to the "Header Field Parameters and 272 Parameter Values" section of the SIP parameter registry: 274 +------------------+----------------+-------------------+-----------+ 275 | Header Field | Parameter Name | Predefined Values | Reference | 276 +------------------+----------------+-------------------+-----------+ 277 | User-to-User | encoding | hex | [RFCXXXX] | 278 +------------------+----------------+-------------------+-----------+ 280 Editor's Note: [RFCXXXX] should be replaced with the designation of 281 this document. 283 5.3. Registration of SIP Option Tag 285 This specification registers a new SIP option tag, as per the 286 guidelines in Section 27.1 of [RFC3261]. 288 This document defines the SIP option tag "uui". 290 The following row has been added to the "Option Tags" section of the 291 SIP Parameter Registry: 293 +------------+------------------------------------------+-----------+ 294 | Name | Description | Reference | 295 +------------+------------------------------------------+-----------+ 296 | uui | This option tag is used to indicate that | [RFCXXXX] | 297 | | a UA supports and understands the | | 298 | | User-to-User header field. | | 299 +------------+------------------------------------------+-----------+ 301 Editor's Note: [RFCXXXX] should be replaced with the designation of 302 this document. 304 Registration of SIP media feature tag is TBD. 306 6. Security Considerations 308 User to user information can potentially carry sensitive information 309 that might require privacy or integrity protection. Standard 310 deployed SIP security mechanisms such as TLS transport, offer these 311 properties on a hop-by-hop basis. To preserve multi-hop or end-to- 312 end confidentiality and integrity of UUI, approaches using S/MIME can 313 be used, as discussed in the draft. However, the lack of deployment 314 of these mechanisms means that applications can not in general rely 315 on them. As such, applications are encouraged to utilize their own 316 security mechanisms. 318 7. Appendix - Other Possible Mechanisms 320 Two other possible mechanisms for transporting UUI will be described: 321 MIME body and URI parameter transport. 323 7.1. Why INFO is Not Used 325 Since the INFO method [RFC2976], was developed for ISUP interworking 326 of user-to-user information, it might seem to be the logical choice 327 here. For non-call control user-to-user information, INFO can be 328 utilized for end to end transport. However, for transport of call 329 control user-to-user information, INFO can not be used. As the call 330 flows in [I-D.ietf-cuss-sip-uui-reqs] show, the information is 331 related to an attempt to establish a session and must be passed with 332 the session setup request (INVITE), responses to that INVITE, or 333 session termination requests. As a result, it is not possible to use 334 INFO in these cases. 336 7.2. Why Other Protocol Encapsulation UUI Mechanisms are Not Used 338 Other protocols have the ability to transport UUI information. For 339 example, consider the ITU-T Q.931 User to User Information Element 340 (UU IE) [Q931] and the ITU-T Q.763 User to User Information Parameter 341 [Q763]. In addition, NSS (Narrowband Signaling System) [Q1980] is 342 also able to transport UUI information. Should one of these 343 protocols be in use, and present in both User Agents, then utilizing 344 these other protocols to transport UUI might be a logical solution. 345 Essentially, this is just adding an additional layer in the protocol 346 stack. In these cases, SIP is not transporting the UUI; it is 347 encapsulating another protocol, and that protocol is transporting the 348 UUI. Once a mechanism to transport that other protocol using SIP 349 exists, the UUI transport function is essentially obtained without 350 any additional effort or work. 352 However, the authors believe that SIP needs to have its own native 353 UUI transport mechanism. It is not reasonable for a SIP UA to have 354 to implement another entire protocol (either ISDN or NSS, for 355 example) just to get the very simple UUI transport service. Of 356 course, this work does not preclude anyone from using other protocols 357 with SIP to transport UUI information. 359 7.3. MIME body Approach 361 One method of transport is to use a MIME body. This is in keeping 362 with the SIP-T architecture [RFC3372] in which MIME bodies are used 363 to transport ISUP information. Since the INVITE will normally have 364 an SDP message body, the resulting INVITE with SDP and UUI will be 365 multipart MIME. This is not ideal as many SIP UAs do not support 366 multipart MIME INVITEs. 368 A bigger problem is the insertion of a UUI message body by a redirect 369 server or in a REFER. The body would need to be encoded in the 370 Contact URI of the 3xx response or the Refer-To URI of a REFER. 371 Currently, the authors are not aware of any UAs that support this 372 capability today for any body type. As such, the complete set of 373 semantics for this operation would need to be determined and defined. 374 Some issues will need to be resolved, such as, do all the Content-* 375 header fields have to be escaped as well? And, what if the escaped 376 Content-Length does not agree with the escaped body? 378 Since proxies cannot remove a body from a request or response, it is 379 not at all clear how this mechanism could meet REQ-9. 381 The requirement for integrity protection could be met by the use of 382 an S/MIME signature over the body, as defined in Section 23.3 of RFC 383 3261 "Securing MIME bodies". Alternatively, this could be achieved 384 using RFC 4474 [RFC4474]. The requirement for end-to-end privacy 385 could be met using S/MIME encryption or using encryption at the 386 application layer. However, note that neither S/MIME or RFC 4474 387 enjoys deployment in SIP today. 389 An example: 391 392 Contact: 394 396 Note that the tag convention from SIP Torture Test 397 Messages [RFC4475] is used to show that there are no line breaks in 398 the actual message syntax. 400 As such, the MIME body approach meets REQ-1, REQ-2, REQ-4, REQ-5, 401 REQ-7, REQ-11, REQ-13, and REQ-14. Meeting REQ-12 seems possible, 402 although the authors do not have a specific mechanism to propose. 403 Meeting REQ-3 is problematic, but not impossible for this mechanism. 404 However, this mechanism does not seem to be able to meet REQ-9. 406 7.4. URI Parameter 408 Another proposed approach is to encode the UUI as a URI parameter. 409 This UUI parameter could be included in a Request-URI or in the 410 Contact URI or Refer-To URI. It is not clear how it could be 411 transported in a responses which does not have a Request-URI, or in 412 BYE requests or responses. 414 415 Contact: 417 419 An INVITE sent to this Contact URI would contain UUI in the Request- 420 URI of the INVITE. The URI parameter has a drawback in that a URI 421 parameter carried in a Request-URI will not survive retargeting by a 422 proxy as shown in Figure 2 of [I-D.ietf-cuss-sip-uui-reqs]. That is, 423 if the URI is included with an Address of Record instead of a Contact 424 URI, the URI parameter in the Reqeuest-URI will not be copied over to 425 the Contact URI, resulting in the loss of the information. Note that 426 if this same URI was present in a Refer-To header field, the same 427 loss of information would occur. 429 The URI parameter approach would meet REQ-3, REQ-5, REQ-7, REQ-9, and 430 REQ-11. It is possible the approach could meet REQ-12 and REQ-13. 431 The mechanism does not appear to meet REQ-1, REQ-2, REQ-4, and 432 REQ-14. 434 8. Acknowledgements 436 Joanne McMillen was a major contributor and co-author of earlier 437 versions of this document. Thanks to Spencer Dawkins, Keith Drage, 438 Vijay Gurbani, and Laura Liess for their review of the document. The 439 authors wish to thank Francois Audet, Denis Alexeitsev, Paul Kyzivat, 440 Cullen Jennings, and Mahalingam Mani for their comments. 442 9. References 444 9.1. Informative References 446 [Q763] "ITU-T Q.763 Signaling System No. 7 - ISDN user part 447 formats and codes", 448 http://www.itu.int/rec/T-REC-Q.931-199805-I/en . 450 [Q931] "ITU-T Q.931 User to User Information Element (UU IE)", 451 http://www.itu.int/rec/T-REC-Q.931-199805-I/en . 453 [ETSI] "ETSI ETS 300 207-1 Ed.1 (1994), Integrated Services 454 Digital Network (ISDN); Diversion supplementary 455 services". 457 [RFC3372] Vemuri, A. and J. Peterson, "Session Initiation Protocol 458 for Telephones (SIP-T): Context and Architectures", 459 BCP 63, RFC 3372, September 2002. 461 [RFC2976] Donovan, S., "The SIP INFO Method", RFC 2976, 462 October 2000. 464 [RFC4475] Sparks, R., Hawrylyshen, A., Johnston, A., Rosenberg, J., 465 and H. Schulzrinne, "Session Initiation Protocol (SIP) 466 Torture Test Messages", RFC 4475, May 2006. 468 [Q1980] "ITU-T Q.1980.1 The Narrowband Signalling Syntax (NSS) - 469 Syntax Definition", http://www.itu.int/itudoc/itu-t/aap/ 470 sg11aap/history/q1980.1/q1980.1.html . 472 9.2. Normative References 474 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 475 Requirement Levels", BCP 14, RFC 2119, March 1997. 477 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 478 A., Peterson, J., Sparks, R., Handley, M., and E. 479 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 480 June 2002. 482 [RFC3324] Watson, M., "Short Term Requirements for Network Asserted 483 Identity", RFC 3324, November 2002. 485 [I-D.ietf-cuss-sip-uui-reqs] 486 Johnston, A. and L. Liess, "Problem Statement and 487 Requirements for Transporting User to User Call Control 488 Information in SIP", draft-ietf-cuss-sip-uui-reqs-02 (work 489 in progress), May 2011. 491 [RFC4474] Peterson, J. and C. Jennings, "Enhancements for 492 Authenticated Identity Management in the Session 493 Initiation Protocol (SIP)", RFC 4474, August 2006. 495 [I-D.ietf-sipcore-rfc4244bis] 496 Barnes, M., Audet, F., Schubert, S., Gmbh, D., and C. 497 Holmberg, "An Extension to the Session Initiation Protocol 498 (SIP) for Request History Information", 499 draft-ietf-sipcore-rfc4244bis-05 (work in progress), 500 April 2011. 502 Authors' Addresses 504 Alan Johnston 505 Avaya 506 St. Louis, MO 63124 508 Email: alan.b.johnston@gmail.com 510 James Rafferty 511 Dialogic 513 Email: james.rafferty@dialogic.com