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'I-D.ietf-cuss-sip-uui-reqs') ** Obsolete normative reference: RFC 4474 (Obsoleted by RFC 8224) == Outdated reference: A later version (-12) exists of draft-ietf-sipcore-rfc4244bis-06 Summary: 5 errors (**), 0 flaws (~~), 7 warnings (==), 1 comment (--). 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: September 13, 2012 Dialogic 6 March 12, 2012 8 A Mechanism for Transporting User to User Call Control Information in 9 SIP 10 draft-ietf-cuss-sip-uui-05 12 Abstract 14 There is a class of applications which benefit from using SIP to 15 exchange User to User Information (UUI) data during session 16 establishment. This information, known as call control UUI data, is 17 a small piece of data inserted by an application initiating the 18 session, and utilized by an application accepting the session. The 19 rules which apply for a certain application are defined by a UUI 20 package. This UUI data is opaque to SIP and its function is 21 unrelated to any basic SIP function. This document defines a new SIP 22 header field, User-to-User, to transport UUI data, along with an 23 extension mechanism. 25 Status of this Memo 27 This Internet-Draft is submitted to IETF in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on September 13, 2012. 42 Copyright Notice 44 Copyright (c) 2012 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 60 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 61 3. Requirements Discussion . . . . . . . . . . . . . . . . . . . 3 62 4. Normative Definition . . . . . . . . . . . . . . . . . . . . . 5 63 4.1. Syntax for UUI Header Field . . . . . . . . . . . . . . . 5 64 4.2. Source Identity of UUI data . . . . . . . . . . . . . . . 6 65 5. Guidelines for UUI Packages . . . . . . . . . . . . . . . . . 8 66 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 67 6.1. Registration of User-to-User Header Field . . . . . . . . 10 68 6.2. Registration of User-to-User Header Field Parameters . . . 10 69 6.3. Registration of UUI Packages . . . . . . . . . . . . . . . 10 70 6.4. Registration of UUI Content Parameters . . . . . . . . . . 11 71 6.5. Registration of UUI Encoding Parameters . . . . . . . . . 11 72 6.6. Registration of SIP Option Tag . . . . . . . . . . . . . . 11 73 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 74 8. Appendix - Other Possible Mechanisms . . . . . . . . . . . . . 12 75 8.1. Why INFO is Not Used . . . . . . . . . . . . . . . . . . . 12 76 8.2. Why Other Protocol Encapsulation UUI Mechanisms are 77 Not Used . . . . . . . . . . . . . . . . . . . . . . . . . 13 78 8.3. MIME body Approach . . . . . . . . . . . . . . . . . . . . 13 79 8.4. URI Parameter . . . . . . . . . . . . . . . . . . . . . . 14 80 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15 81 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 82 10.1. Informative References . . . . . . . . . . . . . . . . . . 15 83 10.2. Normative References . . . . . . . . . . . . . . . . . . . 16 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 86 1. Overview 88 This document describes the transport of User to User Information 89 (UUI) data using SIP [RFC3261]. A mechanism is defined for the 90 transport of general application UUI data and for the transport of 91 call control related ITU-T Q.931 User to User Information Element (UU 92 IE) [Q931] and ITU-T Q.763 User to User Information Parameter [Q763] 93 data in SIP. UUI data is widely used in the PSTN today for contact 94 centers and call centers. There is also a trend for the related 95 applications to transition from ISDN to SIP. The UUI extension for 96 SIP may also be used for native SIP UAs implementing similar services 97 and to interwork with ISDN services. Note that in most cases, there 98 is an a priori understanding between the UAs in regard to what to do 99 with received UUI data. 101 This mechanism was designed to meet the use cases, requirements, and 102 call flows for SIP call control UUI detailed in 103 [I-D.ietf-cuss-sip-uui-reqs]. All references to requirement numbers 104 (REQ-N) and figure numbers refer to this document. 106 The mechanism is a new SIP header field, along with a new SIP option 107 tag. The header field carries the UUI data, along with parameters 108 indicating the encoding of the UUI data, the UUI package, and 109 optionally the content of the UUI data. The package definition 110 contains details about how a particular application can utilize the 111 UUI mechanism. The header field can be included (sometimes called 112 "escaped") into URIs supporting referral and redirection scenarios. 113 In these scenarios, History-Info is used to indicate the inserter of 114 the UUI data. The SIP option tag can be used to indicate support for 115 the header field. Support for the UUI header field indicates that a 116 UA is able to extract the information in the UUI data and pass it up 117 the protocol stack. Individual packages using the UUI mechanism can 118 utlize SIP media feature tags to indicate that a UA supports a 119 particular UUI package. Guidelines for defining UUI packages are 120 provided. 122 2. Terminology 124 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 125 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 126 document are to be interpreted as described in BCP 14, RFC 2119 127 [RFC2119]. 129 3. Requirements Discussion 131 This section describes how the User-to-User header field meets the 132 requirements in [I-D.ietf-cuss-sip-uui-reqs]. The header field can 133 be included in INVITE requests and responses and BYE requests and 134 responses, meeting REQ-1 and REQ-2. 136 For redirection and referral use cases and REQ-3, the header field 137 shall be included (escaped) into the Contact or Refer-To URI. 138 Currently, UAs that support attended transfer support the ability to 139 include a Replaces header field into a Refer-To URI, and when acting 140 upon this URI add the Replaces header field to the triggered INVITE. 141 This logic and behavior is identical for the UUI header field. The 142 UA processing the REFER or the 3xx to the INVITE will need to support 143 the UUI mechanism, as UAs in general do not process unknown included 144 header fields. 146 Since SIP proxy forwarding and retargeting does not affect header 147 fields, the header field meets REQ-4. 149 The UUI header field will carry the UUI data and not a pointer to the 150 data, so REQ-5 is met. 152 Since the basic design of the UUI header field is similar to the ISDN 153 UUI service, interworking with PSTN protocols will be straightforward 154 and will be documented in a separate specification, meeting REQ-6. 156 Requirements REQ-7, REQ-8, and REQ-10 relate to discovery of the 157 mechanism and supported packages, and hence applications. REQ-7 158 relates to support of the UUI header field, while REQ-8 relates to 159 routing based on support of the UUI header field. REQ-7 is met by 160 defining a new SIP option tag 'uui'. The use of a Require:uui in a 161 request, or Supported:uui in an OPTIONS response could be used to 162 require or discover support of the mechanism. The presence of a 163 Supported:uui or Require:uui header field can be used by proxies to 164 route to an appropriate UA, meeting REQ-8. However, note that only 165 UAs are expected to understand the UUI data - proxies and other 166 intermediaries do not. REQ-10 is met by utlizing SIP feature tags 167 [RFC3840]. For example, the feature tag 'sip.uui-isdn' could be used 168 to indicate support of the ISDN UUI package, or 'sip.uui-pk1' could 169 be used to indicate support for a particular package, pk1. 171 Proxies commonly apply policy to the presence of certain SIP header 172 fields in requests by either passing them or removing them from 173 requests. REQ-9 is met by allowing proxies and other intermediaries 174 to remove UUI header fields in a request or response based on policy. 176 Carrying UUI data elements of at least 129 octets is trivial in the 177 UUI header field, meeting REQ-11. Note that very large UUI data 178 elements should be avoided, as SIP header fields have traditionally 179 not been large. 181 To meet REQ-12 for the redirection and referral use cases, History- 182 Info [I-D.ietf-sipcore-rfc4244bis] can be used. In these retargeting 183 cases, the changed Request-URI will be recorded in the History-Info 184 header field along with the identity of the element that performed 185 the retargeting. 187 The requirement for integrity protection in REQ-13 could be met by 188 the use of an S/MIME signature over a subset of header fields, as 189 defined in Section 23.4 of RFC 3261 "SIP Header Privacy and Integrity 190 using S/MIME: Tunneling SIP". The requirement of REQ-14 for end-to- 191 end privacy could be met using S/MIME or using encryption at the 192 application layer. Note that the use of S/MIME to secure the UUI 193 data will result in an additional body being added to the request. 194 Hopwise TLS allows the header field to meet REQ-15 for hop-by-hop 195 security. 197 4. Normative Definition 199 This document defines a new SIP header field "User-to-User" to 200 transport call control UUI data to meet the requirements in 201 [I-D.ietf-cuss-sip-uui-reqs]. 203 To help tag and identify the UUI data used with this header field, 204 "package", "content", and "encoding" parameters are defined. The 205 "package" parameter identifies the package which defines the 206 generation and usage of the UUI data for a particular application. 207 For the case of interworking with the ISDN UUI Service, the ISDN UUI 208 Service interworking package is used. If the "package" parameter is 209 not present, interworking with the ISDN UUI Service MUST be assumed. 210 The "content" parameter identifies the actual content of the UUI 211 data. If not present, the content MUST be assumed to be unknown as 212 it is in the ISDN UUI Service. Newly defined UUI packages MUST 213 define a new "content" value. The "encoding" parameter indicates the 214 method of encoding the information in the UUI data. This 215 specification only defines "encoding=hex". If the "encoding" 216 parameter is not present, "hex" MUST be assumed. 218 UUI data is considered an opaque series of octets. This mechanism 219 SHOULD NOT be used to convey a URL or URI; the Call-Info header field 220 [RFC3261] is used for this purpose. 222 4.1. Syntax for UUI Header Field 224 The User-to-User header field can be present in INVITE requests and 225 responses only and in BYE requests and responses. Note that only 226 end-to-end responses can be used, e.g. 1xx (excluding 100), 2xx, and 227 3xx responses. 229 The following syntax specification uses the augmented Backus-Naur 230 Form (BNF) as described in RFC 5234 and extends RFC 3261. 232 UUI = "User-to-User" HCOLON uui-value *(COMMA uui-value) 233 uui-value = uui-data *(SEMI uui-param) 234 uui-data = token / quoted-string 235 uui-param = pkg-param / cont-param / enc-param / generic-param 236 pkg-param = "package" EQUAL token 237 cont-param = "content" EQUAL token 238 enc-param = "encoding" EQUAL ("hex" / token) 240 The rules for how many User-to-User header field of each package may 241 be present in a request or a response are defined for each package. 242 The syntax allows any combination of individual User-to-User header 243 fields or User-to-User header fields with multiple comma separated 244 UUI data elements. Multiple User-to-User header fields MAY be 245 present in a request or response. Any size limitations on the UUI 246 data for a particular purpose must be defined by the related UUI 247 package. 249 UAs SHOULD ignore UUI data from packages or encoding that they do not 250 understand. 252 If an element supports this specification, it SHOULD include any UUI 253 data included in a redirection URI. Note that redirection can occur 254 multiple times to a request. 256 Here is an example of an included User-to-User header field from the 257 redirection response F2 of Figure 3: 259 260 Contact: 263 265 The resulting INVITE F5 would contain: 267 User-to-User: 56a390f3d2b7310023a;encoding=hex;purpose=foo;content=bar 269 4.2. Source Identity of UUI data 271 It is important for the recipient of UUI data to know the identity of 272 the UA that inserted the UUI data. In a request without a History- 273 Info [I-D.ietf-sipcore-rfc4244bis] header field, the identity of the 274 entity which inserted the UUI data will be assumed to be the source 275 of the SIP message. For a SIP request, typically this is the UA 276 identified by the URI in the From header field or a P-Asserted- 277 Identity [RFC3325] header field. In a request with a History-Info 278 header field, the recipient needs to parse the Targeted-to-URIs 279 present (hi-targeted-to-uri) to see if any included User-to-User 280 header fields are present. If an included User-to-User header field 281 is present and matches the UUI data in the request, this indicates 282 that redirection has taken place, resulting in the inclusion of UUI 283 data in the request. The inserter of the UUI data will be the UA 284 identified by the Targeted-to-URI of the History-Info element prior 285 to the element with the included UUI data. In a response, the 286 inserter of the UUI data will be the identity of the UA that 287 generated the response. Typically, this is the UA identified in the 288 To header field of the response. Note that any updates to this 289 identity by use of the SIP Connected Identity extension [RFC4916] or 290 others will update this information. 292 For an example of History-Info and redirection, consider Figure 2 293 from [I-D.ietf-cuss-sip-uui-reqs] where the Originating UA is Carol, 294 the Redirector Bob, and the Terminating UA Alice. The INVITE F4 295 containing UUI data could be: 297 INVITE sips:alice@example.com SIP/2.0 298 Via: SIP/2.0/TLS lab.example.com:5061 299 ;branch=z9hG4bKnashds9 300 To: Bob 301 From: Carol ;tag=323sf33k2 302 Call-ID: dfaosidfoiwe83ifkdf 303 Max-Forwards: 70 304 Contact: 305 Supported: histinfo 306 User-to-User: 342342ef34;encoding=hex 307 History-Info: ;index=1 308 309 History-Info: ;index=1.1;rc=1 311 313 Without the redirection captured in the History-Info, Alice would 314 conclude the UUI data was inserted by Carol. However, the History- 315 Info containing UUI data (index=1.1) indicates that the inserter was 316 Bob (index=1). 318 Note that the tag convention from SIP Torture Test 319 Messages [RFC4475] is used to show that there are no line breaks in 320 the actual message syntax. 322 To enable maintaining a record of the inserter identity of UUI data, 323 UAs supporting this mechanism SHOULD support History-Info 324 [I-D.ietf-sipcore-rfc4244bis] and include Supported: histinfo in all 325 requests and responses. 327 5. Guidelines for UUI Packages 329 UUI packages defined using this SIP UUI mechanism MUST publish a 330 standards track RFC which describes the usage. Note that this 331 mechanism is not suitable for the transport of arbitrary data between 332 UAs. The following guidelines are provided to help determine if this 333 mechanism is appropriate or some other SIP mechanism should be used. 334 The SIP UUI mechanism is applicable when all of the following 335 conditions be met: 337 1. The information is generated and consumed by an application 338 during session setup using SIP, but the application is not 339 necessarily SIP aware. 341 2. The behavior of SIP entities that support it is not 342 significantly changed (as discussed in Section 4 of [RFC5727]). 344 3. User Agents (UAs) are the generators and consumers of the UUI 345 data. Proxies and other intermediaries may route based on the 346 presence of a User-to-User header field or a particular package 347 tag but do not otherwise consume or generate the UUI data. 349 4. There are no overriding privacy issues associated with the 350 information being transported (e.g., geolocation or emergency- 351 related information are examples of inappropriate UUI data). 353 5. The UUI data is not being utilized for user-to-user Remote 354 Procedure Call (RPC) calls. 356 UUI packages define the semantics for a particular application usage 357 of UUI data. The content defines the syntax of the UUI data, while 358 the encoding defines the encoding of the UUI data. Each content is 359 defined as a stream of octets, which allows multiple encodings of 360 that content. For example, packages may define: 362 1. The SIP methods and responses in which the UUI data may be 363 present. 365 2. The maximum number of UUI data elements that may be inserted 366 into a request or response. (The default is one per encoding.) 367 Note that a UA may still receive a request with more than this 368 maximum number due to redirection. The package must define how to 369 handle this situation. 371 3. The default values for content and encoding if they are not 372 present. If the same UUI data may be inserted multiple times with 373 different encodings, the packages must state this. A package may 374 support and define multiple encodings and contents, and reuse 375 encodings and contents defined by other packages. 377 4. Any size limitations on the UUI data. Size should be 378 specified in terms of the octet stream output of the content, 379 since the size of the resulting uui-data element will vary 380 depending on the encoding scheme. 382 New "package" values MUST describe the new application which is 383 utilizing the UUI data and provide some use case examples. The 384 default "content" value and other allowed contents MUST be defined or 385 referenced in another document for the package. Any restrictions on 386 the size of the UUI data must be described. In addition, a package 387 may define a Media Feature tag per RFC 3840 [RFC3840] to indicate 388 support for this UUI package. For example, the media feature tag 389 sip.uui-pk1 could be defined to indicate support for a UUI package 390 named pk1. The definition of a new SIP option tag solely to identify 391 support for a UUI package is NOT RECOMMENDED unless there are 392 additional SIP behaviors needed to implement this feature. 394 For an example UUI package definition, see 395 [I-D.drage-cuss-sip-uui-isdn]. 397 This specification defines only the value of "hex" for the "encoding" 398 parameter. Hex encoding, as used for UUI data is defined to use only 399 the characters 0-9, A-F, or a-f. Hex encoded UUI data MUST have an 400 even number of octets, and is considered invalid if has an odd 401 number. Hex encoding is normally done as a token, although quoted- 402 string is permitted, in which case the quotes are ignored. Hex 403 encoding yields a sequence of octets, one octet per two hex digits, 404 in the same order, with the first digit of each pair defining the 405 high order four bits of the octet and the second digit providing the 406 low order four bits. 408 New "encoding" values MUST reference a common encoding scheme or 409 define the exact new encoding scheme. New values can be defined and 410 added to the IANA registry with a standards track RFC, which needs to 411 discuss the issues in this section. 413 New "content" values MUST describe the content of the UUI data and 414 give some example use cases. The default "encoding" and other 415 allowed encoding methods must be defined for this new content. Note 416 that a content value can be used by multiple UUI packages. In this 417 case, the semantics and usage of the content is defined by the 418 package. 420 6. IANA Considerations 422 6.1. Registration of User-to-User Header Field 424 This document defines a new SIP header field named "User-to-User". 426 The following row shall be added to the "Header Fields" section of 427 the SIP parameter registry: 429 +------------------+--------------+-----------+ 430 | Header Name | Compact Form | Reference | 431 +------------------+--------------+-----------+ 432 | User-to-User | | [RFCXXXX] | 433 +------------------+--------------+-----------+ 435 Editor's Note: [RFCXXXX] should be replaced with the designation of 436 this document. 438 6.2. Registration of User-to-User Header Field Parameters 440 This document defines the parameters for the header field defined in 441 the preceding section. The header field "User-to-User" can contain 442 the parameters "encoding", "content", and "package". 444 The following rows shall be added to the "Header Field Parameters and 445 Parameter Values" section of the SIP parameter registry: 447 +------------------+----------------+-------------------+-----------+ 448 | Header Field | Parameter Name | Predefined Values | Reference | 449 +------------------+----------------+-------------------+-----------+ 450 | User-to-User | encoding | hex | [RFCXXXX] | 451 +------------------+----------------+-------------------+-----------+ 452 | User-to-User | content | | [RFCXXXX] | 453 +------------------+----------------+-------------------+-----------+ 454 | User-to-User | package | | [RFCXXXX] | 455 +------------------+----------------+-------------------+-----------+ 457 Editor's Note: [RFCXXXX] should be replaced with the designation of 458 this document. 460 6.3. Registration of UUI Packages 462 This specification establishes the uui-packages sub-registry under 463 http://www.iana.org/assignments/sip-parameters. New uui-packages 464 shall be registered by standards track RFC publication. 466 The descriptive text for the table of uui-content is: 468 UUI Packages provides information about the usage of the UUI data in 469 a User-to-User header field [RFCXXXX]. 471 +------------+-------------------------------------------+-----------+ 472 | Package | Description | Reference | 473 +------------+-------------------------------------------+-----------+ 475 6.4. Registration of UUI Content Parameters 477 This specification establishes the uui-content sub-registry under 478 http://www.iana.org/assignments/sip-parameters. New uui-content 479 values shall be registered by standards track RFC publication. 481 The descriptive text for the table of uui-content is: 483 UUI Content provides information about the content of the UUI data in 484 a User-to-User header field [RFCXXXX]. 486 +------------+-------------------------------------------+-----------+ 487 | Content | Description | Reference | 488 +------------+-------------------------------------------+-----------+ 490 6.5. Registration of UUI Encoding Parameters 492 This specification establishes the uui-encoding sub-registry under 493 http://www.iana.org/assignments/sip-parameters and initiates its 494 population with the table below. Additional uui-encoding values 495 shall be registered by a standards track RFC publication. 497 The descriptive text for the table of uui-encoding is: 499 UUI Encoding provides information about the encoding of the UUI data 500 in a User-to-User header field [RFCXXXX]. 502 +------------+-------------------------------------------+-----------+ 503 | Encoding | Description | Reference | 504 +------------+-------------------------------------------+-----------+ 505 | hex | The UUI data is encoded using hexadecimal | | 506 +------------+-------------------------------------------+-----------+ 508 6.6. Registration of SIP Option Tag 510 This specification registers a new SIP option tag, as per the 511 guidelines in Section 27.1 of [RFC3261]. 513 This document defines the SIP option tag "uui". 515 The following row has been added to the "Option Tags" section of the 516 SIP Parameter Registry: 518 +------------+------------------------------------------+-----------+ 519 | Name | Description | Reference | 520 +------------+------------------------------------------+-----------+ 521 | uui | This option tag is used to indicate that | [RFCXXXX] | 522 | | a UA supports and understands the | | 523 | | User-to-User header field. | | 524 +------------+------------------------------------------+-----------+ 526 Editor's Note: [RFCXXXX] should be replaced with the designation of 527 this document. 529 7. Security Considerations 531 User to user information can potentially carry sensitive information 532 that might require privacy or integrity protection. Standard 533 deployed SIP security mechanisms such as TLS transport, offer these 534 properties on a hop-by-hop basis. To preserve multi-hop or end-to- 535 end confidentiality and integrity of UUI data, approaches using 536 S/MIME or IPSec can be used, as discussed in the draft. However, the 537 lack of deployment of these mechanisms means that applications can 538 not in general rely on them. As such, applications are encouraged to 539 utilize their own security mechanisms. 541 If the UUI data was included by the UA originator of the SIP request 542 or response, normal SIP mechanisms can be used to determine the 543 identity of the inserter of the UUI data. If the UUI data was 544 included by a UA that was not the originator of the request, History- 545 Info can be used to determine the indentity of the inserter of the 546 UUI data. UAs can apply policy based on the origin of the UUI data 547 using this information. 549 8. Appendix - Other Possible Mechanisms 551 Two other possible mechanisms for transporting UUI data will be 552 described: MIME body and URI parameter transport. 554 8.1. Why INFO is Not Used 556 Since the INFO method [RFC6086], was developed for ISUP interworking 557 of user-to-user information, it might seem to be the logical choice 558 here. For non-call control user-to-user information, INFO can be 559 utilized for end to end transport. However, for transport of call 560 control user-to-user information, INFO can not be used. As the call 561 flows in [I-D.ietf-cuss-sip-uui-reqs] show, the information is 562 related to an attempt to establish a session and must be passed with 563 the session setup request (INVITE), responses to that INVITE, or 564 session termination requests. As a result, it is not possible to use 565 INFO in these cases. 567 8.2. Why Other Protocol Encapsulation UUI Mechanisms are Not Used 569 Other protocols have the ability to transport UUI data. For example, 570 consider the ITU-T Q.931 User to User Information Element (UU IE) 571 [Q931] and the ITU-T Q.763 User to User Information Parameter [Q763]. 572 In addition, NSS (Narrowband Signaling System) [Q1980] is also able 573 to transport UUI data. Should one of these protocols be in use, and 574 present in both User Agents, then utilizing these other protocols to 575 transport UUI data might be a logical solution. Essentially, this is 576 just adding an additional layer in the protocol stack. In these 577 cases, SIP is not transporting the UUI data; it is encapsulating 578 another protocol, and that protocol is transporting the UUI data. 579 Once a mechanism to transport that other protocol using SIP exists, 580 the UUI data transport function is essentially obtained without any 581 additional effort or work. 583 However, the authors believe that SIP needs to have its own native 584 UUI data transport mechanism. It is not reasonable for a SIP UA to 585 have to implement another entire protocol (either ISDN or NSS, for 586 example) just to get the very simple UUI data transport service. Of 587 course, this work does not preclude anyone from using other protocols 588 with SIP to transport UUI data. 590 8.3. MIME body Approach 592 One method of transport is to use a MIME body. This is in keeping 593 with the SIP-T architecture [RFC3372] in which MIME bodies are used 594 to transport ISUP information. Since the INVITE will normally have 595 an SDP message body, the resulting INVITE with SDP and UUI data will 596 be multipart MIME. This is not ideal as many SIP UAs do not support 597 multipart MIME INVITEs. 599 A bigger problem is the insertion of a UUI message body by a redirect 600 server or in a REFER. The body would need to be encoded in the 601 Contact URI of the 3xx response or the Refer-To URI of a REFER. 602 Currently, the authors are not aware of any UAs that support this 603 capability today for any body type. As such, the complete set of 604 semantics for this operation would need to be determined and defined. 605 Some issues will need to be resolved, such as, do all the Content-* 606 header fields have to be included as well? And, what if the included 607 Content-Length does not agree with the included body? 609 Since proxies cannot remove a body from a request or response, it is 610 not clear how this mechanism could meet REQ-9. 612 The requirement for integrity protection could be met by the use of 613 an S/MIME signature over the body, as defined in Section 23.3 of RFC 614 3261 "Securing MIME bodies". Alternatively, this could be achieved 615 using RFC 4474 [RFC4474]. The requirement for end-to-end privacy 616 could be met using S/MIME encryption or using encryption at the 617 application layer. However, note that neither S/MIME or RFC 4474 618 enjoys deployment in SIP today. 620 An example: 622 623 Contact: 625 627 As such, the MIME body approach meets REQ-1, REQ-2, REQ-4, REQ-5, 628 REQ-7, REQ-11, REQ-13, and REQ-14. Meeting REQ-12 seems possible, 629 although the authors do not have a specific mechanism to propose. 630 Meeting REQ-3 is problematic, but not impossible for this mechanism. 631 However, this mechanism does not seem to be able to meet REQ-9. 633 8.4. URI Parameter 635 Another proposed approach is to encode the UUI data as a URI 636 parameter. This UUI parameter could be included in a Request-URI or 637 in the Contact URI or Refer-To URI. It is not clear how it could be 638 transported in a responses which does not have a Request-URI, or in 639 BYE requests or responses. 641 642 Contact: 644 646 An INVITE sent to this Contact URI would contain UUI data in the 647 Request-URI of the INVITE. The URI parameter has a drawback in that 648 a URI parameter carried in a Request-URI will not survive retargeting 649 by a proxy as shown in Figure 2 of [I-D.ietf-cuss-sip-uui-reqs]. 650 That is, if the URI is included with an Address of Record instead of 651 a Contact URI, the URI parameter in the Reqeuest-URI will not be 652 copied over to the Contact URI, resulting in the loss of the 653 information. Note that if this same URI was present in a Refer-To 654 header field, the same loss of information would occur. 656 The URI parameter approach would meet REQ-3, REQ-5, REQ-7, REQ-9, and 657 REQ-11. It is possible the approach could meet REQ-12 and REQ-13. 659 The mechanism does not appear to meet REQ-1, REQ-2, REQ-4, and 660 REQ-14. 662 9. Acknowledgements 664 Joanne McMillen was a major contributor and co-author of earlier 665 versions of this document. Thanks to Paul Kyzivat for his 666 contribution of hex encoding rules. Thanks to Spencer Dawkins, Keith 667 Drage, Vijay Gurbani, and Laura Liess for their review of the 668 document. The authors wish to thank Francois Audet, Denis 669 Alexeitsev, Paul Kyzivat, Cullen Jennings, and Mahalingam Mani for 670 their comments. 672 10. References 674 10.1. Informative References 676 [Q763] "ITU-T Q.763 Signaling System No. 7 - ISDN user part 677 formats and codes", 678 http://www.itu.int/rec/T-REC-Q.931-199805-I/en . 680 [Q931] "ITU-T Q.931 User to User Information Element (UU IE)", 681 http://www.itu.int/rec/T-REC-Q.931-199805-I/en . 683 [ETSI] "ETSI ETS 300 207-1 Ed.1 (1994), Integrated Services 684 Digital Network (ISDN); Diversion supplementary 685 services". 687 [RFC3372] Vemuri, A. and J. Peterson, "Session Initiation Protocol 688 for Telephones (SIP-T): Context and Architectures", 689 BCP 63, RFC 3372, September 2002. 691 [RFC6086] Holmberg, C., Burger, E., and H. Kaplan, "Session 692 Initiation Protocol (SIP) INFO Method and Package 693 Framework", RFC 6086, January 2011. 695 [RFC4475] Sparks, R., Hawrylyshen, A., Johnston, A., Rosenberg, J., 696 and H. Schulzrinne, "Session Initiation Protocol (SIP) 697 Torture Test Messages", RFC 4475, May 2006. 699 [RFC5727] Peterson, J., Jennings, C., and R. Sparks, "Change Process 700 for the Session Initiation Protocol (SIP) and the Real- 701 time Applications and Infrastructure Area", BCP 67, 702 RFC 5727, March 2010. 704 [I-D.drage-cuss-sip-uui-isdn] 705 Drage, K. and A. Johnston, "Interworking ISDN Call Control 706 User Information with SIP", 707 draft-drage-cuss-sip-uui-isdn-01 (work in progress), 708 September 2011. 710 [Q1980] "ITU-T Q.1980.1 The Narrowband Signalling Syntax (NSS) - 711 Syntax Definition", http://www.itu.int/itudoc/itu-t/aap/ 712 sg11aap/history/q1980.1/q1980.1.html . 714 10.2. Normative References 716 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 717 Requirement Levels", BCP 14, RFC 2119, March 1997. 719 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 720 A., Peterson, J., Sparks, R., Handley, M., and E. 721 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 722 June 2002. 724 [RFC3324] Watson, M., "Short Term Requirements for Network Asserted 725 Identity", RFC 3324, November 2002. 727 [RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private 728 Extensions to the Session Initiation Protocol (SIP) for 729 Asserted Identity within Trusted Networks", RFC 3325, 730 November 2002. 732 [I-D.ietf-cuss-sip-uui-reqs] 733 Johnston, A. and L. Liess, "Problem Statement and 734 Requirements for Transporting User to User Call Control 735 Information in SIP", draft-ietf-cuss-sip-uui-reqs-09 (work 736 in progress), January 2012. 738 [RFC4474] Peterson, J. and C. Jennings, "Enhancements for 739 Authenticated Identity Management in the Session 740 Initiation Protocol (SIP)", RFC 4474, August 2006. 742 [I-D.ietf-sipcore-rfc4244bis] 743 Holmberg, C., Audet, F., Barnes, M., Elburg, H., and S. 744 Schubert, "An Extension to the Session Initiation Protocol 745 (SIP) for Request History Information", 746 draft-ietf-sipcore-rfc4244bis-06 (work in progress), 747 October 2011. 749 [RFC4916] Elwell, J., "Connected Identity in the Session Initiation 750 Protocol (SIP)", RFC 4916, June 2007. 752 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 753 "Indicating User Agent Capabilities in the Session 754 Initiation Protocol (SIP)", RFC 3840, August 2004. 756 Authors' Addresses 758 Alan Johnston 759 Avaya 760 St. Louis, MO 63124 762 Email: alan.b.johnston@gmail.com 764 James Rafferty 765 Dialogic 767 Email: james.rafferty@dialogic.com