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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) == Missing Reference: 'RFCXXXX' is mentioned on line 565, but not defined ** Obsolete normative reference: RFC 4474 (Obsoleted by RFC 8224) ** Obsolete normative reference: RFC 5246 (Obsoleted by RFC 8446) ** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) == Outdated reference: A later version (-11) exists of draft-ietf-cuss-sip-uui-isdn-08 Summary: 3 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--).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: October 4, 2014 Human Communications 6 April 2, 2014 8 A Mechanism for Transporting User to User Call Control Information in 9 SIP 10 draft-ietf-cuss-sip-uui-15 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 syntax and semantics for the UUI data used by a specific application. 20 This UUI data is opaque to SIP and its function is unrelated to any 21 basic SIP function. This document defines a new SIP header field, 22 User-to-User, to transport UUI data, along with an extension 23 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 October 4, 2014. 42 Copyright Notice 44 Copyright (c) 2014 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 . . . . . . . . . . . . . . . . . . . 4 62 4. Normative Definition . . . . . . . . . . . . . . . . . . . . . 5 63 4.1. Syntax for UUI Header Field . . . . . . . . . . . . . . . 6 64 4.2. Hex Encoding Definition . . . . . . . . . . . . . . . . . 7 65 4.3. Source Identity of UUI data . . . . . . . . . . . . . . . 7 66 5. Guidelines for UUI Packages . . . . . . . . . . . . . . . . . 8 67 5.1. Extensibility . . . . . . . . . . . . . . . . . . . . . . 10 68 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 69 6.1. Registration of User-to-User Header Field . . . . . . . . 11 70 6.2. Registration of User-to-User Header Field Parameters . . . 11 71 6.3. Registration of UUI Packages . . . . . . . . . . . . . . . 11 72 6.4. Registration of UUI Content Parameters . . . . . . . . . . 12 73 6.5. Registration of UUI Encoding Parameters . . . . . . . . . 12 74 6.6. Registration of SIP Option Tag . . . . . . . . . . . . . . 12 75 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 76 8. Appendix - Other Possible Mechanisms . . . . . . . . . . . . . 14 77 8.1. Why INFO is Not Used . . . . . . . . . . . . . . . . . . . 14 78 8.2. Why Other Protocol Encapsulation UUI Mechanisms are 79 Not Used . . . . . . . . . . . . . . . . . . . . . . . . . 14 80 8.3. MIME body Approach . . . . . . . . . . . . . . . . . . . . 15 81 8.4. URI Parameter . . . . . . . . . . . . . . . . . . . . . . 16 82 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 83 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 84 10.1. Normative References . . . . . . . . . . . . . . . . . . . 16 85 10.2. Informative References . . . . . . . . . . . . . . . . . . 17 86 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 88 1. Overview 90 This document describes the transport of User to User Information 91 (UUI) data using SIP [RFC3261]. It defines a mechanism for the 92 transport of general application UUI data and for the transport of 93 call control related ITU-T Q.931 User to User Information Element (UU 94 IE) [Q931] and ITU-T Q.763 User to User Information Parameter [Q763] 95 data in SIP. UUI data is widely used in the PSTN today for contact 96 centers and call centers. There is also a trend for the related 97 applications to transition from ISDN to SIP. The UUI extension for 98 SIP may also be used for native SIP UAs implementing similar services 99 and to interwork with ISDN services. Note that in most cases, there 100 is an a priori understanding between the UAs in regard to what to do 101 with received UUI data. 103 The UUI mechanism is designed to meet the use cases, requirements, 104 and call flows for SIP call control UUI detailed in [RFC6567]. All 105 references to requirement numbers (REQ-N) and figure numbers refer to 106 [RFC6567]. 108 The mechanism is a new SIP header field, along with a new SIP option 109 tag. The header field carries the UUI data, along with parameters 110 indicating the encoding of the UUI data, the UUI package, and 111 optionally the content of the UUI data. The package definition 112 contains details about how a particular application can utilize the 113 UUI mechanism. The header field can be included (sometimes called 114 "escaped") into URIs supporting referral and redirection scenarios. 115 In these scenarios, the History-Info header field is used to indicate 116 the inserter of the UUI data. The SIP option tag can be used to 117 indicate support for the header field. Support for the UUI header 118 field indicates that a UA is able to extract the information in the 119 UUI data and pass it up the protocol stack. Individual packages 120 using the UUI mechanism can utilize SIP media feature tags to 121 indicate that a UA supports a particular UUI package. Guidelines for 122 defining UUI packages are provided. 124 2. Terminology 126 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 127 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 128 "OPTIONAL" in this document are to be interpreted as described in BCP 129 14, RFC 2119 [RFC2119]. 131 Note that the tag convention from SIP Torture Test 132 Messages [RFC4475] is used to show that there are no line breaks in 133 the actual message syntax. 135 3. Requirements Discussion 137 This section describes how the User-to-User header field meets the 138 requirements in [RFC6567]. The header field can be included in 139 INVITE requests and responses and BYE requests and responses, meeting 140 REQ-1 and REQ-2. 142 For redirection and referral use cases and REQ-3, the header field is 143 included (escaped) within the Contact or Refer-To URI. The details 144 of this mechanism as it applies for redirection and referral use 145 cases are covered in Section 4.1. 147 Since SIP proxy forwarding and retargeting does not affect header 148 fields, the header field meets REQ-4. 150 The UUI header field will carry the UUI data and not a pointer to the 151 data, so REQ-5 is met. 153 Since the basic design of the UUI header field is similar to the ISDN 154 UUI service, interworking with PSTN protocols is straightforward and 155 is documented in a separate specification 156 [I-D.ietf-cuss-sip-uui-isdn], meeting REQ-6. 158 Requirements REQ-7, REQ-8, and REQ-10 relate to discovery of the 159 mechanism and supported packages, and hence applications. REQ-7 160 relates to support of the UUI header field, while REQ-8 relates to 161 routing based on support of the UUI header field. REQ-7 is met by 162 defining a new SIP option tag 'uui'. The use of a Require:uui in a 163 request, or Supported:uui in an OPTIONS response could be used to 164 require or discover support of the mechanism. The presence of a 165 Supported:uui or Require:uui header field can be used by proxies to 166 route to an appropriate UA, meeting REQ-8. However, note that only 167 UAs are expected to understand the UUI data - proxies and other 168 intermediaries do not. REQ-10 is met by utilizing SIP feature tags 169 [RFC3840]. For example, the feature tag 'sip.uui-isdn' could be used 170 to indicate support of the ISDN UUI package, or 'sip.uui-pk1' could 171 be used to indicate support for a particular package, pk1. 173 Proxies commonly apply policy to the presence of certain SIP header 174 fields in requests by either passing them or removing them from 175 requests. REQ-9 is met by allowing proxies and other intermediaries 176 to remove UUI header fields in a request or response based on policy. 178 Carrying UUI data elements of at least 129 octets is trivial in the 179 UUI header field, meeting REQ-11. Note that avoiding having very 180 large UUI data elements is a good idea, as SIP header fields have 181 traditionally not been large. 183 To meet REQ-12 for the redirection and referral use cases, the 184 History-Info header field [RFC7044] can be used. In these 185 retargeting cases, the changed Request-URI will be recorded in the 186 History-Info header field along with the identity of the element that 187 performed the retargeting. 189 The requirement for integrity protection in REQ-13 could be met by 190 the use of an S/MIME signature over a subset of header fields, as 191 defined in Section 23.4 of RFC 3261 "SIP Header Privacy and Integrity 192 using S/MIME: Tunneling SIP". Note that the lack of deployment of 193 S/MIME with SIP means that in general REQ-13 is not met. The 194 requirement of REQ-14 for end-to-end privacy could be met using 195 S/MIME or using encryption at the application layer. Note that the 196 use of S/MIME to secure the UUI data will result in an additional 197 body being added to the request. Hop-wise Transport Layer Security 198 (TLS) [RFC5246] allows the header field to meet REQ-15 for hop-by-hop 199 security. 201 4. Normative Definition 203 This document defines a new SIP header field "User-to-User" to 204 transport call control UUI data to meet the requirements in 205 [RFC6567]. 207 To help tag and identify the UUI data used with this header field, 208 "purpose", "content", and "encoding" header field parameters are 209 defined. The "purpose" header field parameter identifies the package 210 which defines the generation and usage of the UUI data for a 211 particular application. The value of the "purpose" parameter is the 212 package name, as registered in the uui-packages sub-registry defined 213 in Section 6.3. For the case of interworking with the ISDN UUI 214 Service, the ISDN UUI Service interworking package is used. The 215 "content" header field parameter identifies the actual content of the 216 UUI data. If not present, the default content defined for the 217 package MUST be used. Newly defined UUI packages MUST define or 218 reference at least a default "content" value. The "encoding" header 219 field parameter indicates the method of encoding the information in 220 the UUI data associated with a particular "content" value. This 221 specification only defines "encoding=hex". If the "encoding" header 222 field parameter is not present, the default encoding defined for the 223 package MUST be used. 225 UUI data is considered an opaque series of octets. This mechanism 226 SHOULD NOT be used to convey a URL or URI, since the Call-Info header 227 field in [RFC3261] already supports this use case. 229 4.1. Syntax for UUI Header Field 231 The User-to-User (UUI) header field can be present in INVITE requests 232 and responses and in BYE requests and responses. Note that when the 233 UUI header is used in responses, it can only be utilized in end-to- 234 end responses, e.g. 1xx (excluding 100), 2xx, and 3xx responses. 236 The following syntax specification uses the Augmented Backus-Naur 237 Form (ABNF) as described in RFC 5234 and extends RFC 3261 (where 238 token and quoted-string are defined). 240 UUI = "User-to-User" HCOLON uui-value *(COMMA uui-value) 241 uui-value = uui-data *(SEMI uui-param) 242 uui-data = token / quoted-string 243 uui-param = pkg-param / cont-param / enc-param / generic-param 244 pkg-param = "purpose" EQUAL pkg-param-value 245 pkg-param-value = token 246 cont-param = "content" EQUAL cont-param-value 247 cont-param-value = token 248 enc-param = "encoding" EQUAL enc-param-value 249 enc-param-value = token / "hex" 251 The rules for how many User-to-User header fields of each package may 252 be present in a request or a response are defined for each package. 253 A sender MAY include multiple User-to-User header fields, and a 254 receiver MUST be prepared to receive multiple User-to-User header 255 fields. Consistent with the rules of SIP syntax, the syntax defined 256 in this document allows any combination of individual User-to-User 257 header fields or User-to-User header fields with multiple comma 258 separated UUI data elements. Any size limitations on the UUI data 259 for a particular purpose are to be defined by the related UUI 260 package. 262 UAs SHALL ignore UUI data from packages or encoding that they do not 263 understand. 265 For redirection use cases, the header field is included (escaped) 266 within the Contact URI. For referral use cases, the header field is 267 included (escaped) within the Refer-To URI. For example, if a UA 268 supports this specification, it SHOULD include any UUI data included 269 in a redirection URI (if the UUI data and encoding is understood). 270 Note that redirection can occur multiple times to a request. 271 Currently, UAs that support attended transfer support the ability to 272 include a Replaces header field [RFC3891] into a Refer-To URI, and 273 when acting upon this URI, add the Replaces header field to the 274 triggered INVITE. This sort of logic and behavior is utilized for 275 the UUI header field (that is, the UUI header field is included in 276 the triggered INVITE). The UA processing the REFER [RFC3515] or the 277 3xx response to the INVITE SHOULD support the UUI mechanism. If the 278 REFER or redirect target does not support UUI, the UUI header will be 279 discarded as per [RFC3261]. However, this may limit the utility of 280 use cases which depend upon the UUI being supported by all elements. 282 Here is an example of an included User-to-User header field from the 283 redirection response F2 of Figure 2: 285 286 Contact: 289 291 The resulting INVITE F4 would contain: 293 User-to-User: 56a390f3d2b7310023a2;encoding=hex;purpose=foo;content=bar 295 4.2. Hex Encoding Definition 297 This specification defines hex encoding of UUI data. When the value 298 of 'hex' is used in the 'encoding' parameter of a header field, the 299 data is encoded using base16 encoding according to Section 8 of 300 [RFC4648]. The hex-encoded value is normally represented using the 301 'token' construction from RFC 3261, although the 'quoted-string' 302 construction is permitted, in which case the quotes MUST be ignored. 304 If a canonicalized version of a normally case-insensitive hex encoded 305 UUI data object is needed for a digital signature or integrity 306 checking, then the base16 encoding with all upper case MUST be used. 308 4.3. Source Identity of UUI data 310 It is important for the recipient of UUI data to know the identity of 311 the UA that inserted the UUI data. In a request without a History- 312 Info header field, the identity of the entity which inserted the UUI 313 data will be assumed to be the source of the SIP message. For a SIP 314 request, typically this is the UA identified by the URI in the From 315 header field or a P-Asserted-Identity [RFC3325] header field. In a 316 request with a History-Info header field, the recipient needs to 317 parse the Targeted-to-URIs present (hi-targeted-to-uri defined in 318 [RFC7044]) to see if any included User-to-User header fields are 319 present. If an included User-to-User header field is present and 320 matches the UUI data in the request, this indicates that redirection 321 has taken place, resulting in the inclusion of UUI data in the 322 request. The inserter of the UUI data will be the UA identified by 323 the Targeted-to-URI of the History-Info element prior to the element 324 with the included UUI data. In a response, the inserter of the UUI 325 data will be the identity of the UA that generated the response. 326 Typically, this is the UA identified in the To header field of the 327 response. Note that any updates to this identity by use of the SIP 328 Connected Identity extension [RFC4916] or others will update this 329 information. 331 For an example of History-Info and redirection, consider Figure 2 332 from [RFC6567] where the Originating UA is Carol, the Redirector Bob, 333 and the Terminating UA Alice. The INVITE F4 containing UUI data 334 could be: 336 INVITE sips:alice@example.com SIP/2.0 337 Via: SIP/2.0/TLS lab.example.com:5061 338 ;branch=z9hG4bKnashds9 339 To: Bob 340 From: Carol ;tag=323sf33k2 341 Call-ID: dfaosidfoiwe83ifkdf 342 Max-Forwards: 70 343 Contact: 344 Supported: histinfo 345 User-to-User: 342342ef34;encoding=hex 346 History-Info: ;index=1 347 348 History-Info: ;index=1.1;rc=1 350 352 Without the redirection captured in the History-Info header field, 353 Alice would conclude the UUI data was inserted by Carol. However, 354 the History-Info containing UUI data (index=1.1) indicates that the 355 inserter was Bob (index=1). 357 To enable maintaining a record of the inserter identity of UUI data, 358 UAs supporting this mechanism SHOULD support History-Info [RFC7044] 359 and include Supported: histinfo in all requests and responses. 361 If a border element such as a proxy or a Back-to-Back User Agent 362 (B2BUA) removes a History-Info header field containing a User-to-User 363 parameter, the UA consuming the UUI data may not be able at SIP level 364 to identify the source of the UUI data. 366 5. Guidelines for UUI Packages 368 UUI packages defined using this SIP UUI mechanism MUST follow the 369 "Standards Action" guideline as defined in [RFC5226] and publish a 370 standards track RFC which describes the usage. Note that this 371 mechanism is not suitable for the transport of arbitrary data between 372 UAs. The following guidelines are provided to help determine if this 373 mechanism is appropriate or not. The SIP UUI mechanism is applicable 374 when all of the following conditions be met: 376 1. The information is generated and consumed by an application 377 during session setup using SIP, but the application is not 378 necessarily SIP aware. 380 2. The behavior of SIP entities that support it is not 381 significantly changed (as discussed in Section 4 of [RFC5727]). 383 3. User Agents (UAs) are the generators and consumers of the UUI 384 data. Proxies and other intermediaries may route based on the 385 presence of a User-to-User header field or a particular package 386 tag but do not otherwise consume or generate the UUI data. 388 4. There are no privacy issues associated with the information 389 being transported (e.g., geolocation or emergency-related 390 information are examples of inappropriate UUI data). 392 5. The UUI data is not being utilized for user-to-user Remote 393 Procedure Call (RPC) calls. 395 UUI packages define the semantics for a particular application usage 396 of UUI data. The content defines the syntax of the UUI data, while 397 the encoding defines the encoding of the UUI data for the content. 398 Each content is defined as a stream of octets, which allows multiple 399 encodings of that content. For example, packages may define: 401 1. The SIP methods and responses in which the UUI data may be 402 present. 404 2. The maximum number of UUI data elements that may be inserted 405 into a request or response. The default is one per encoding. 406 Note that a UA may still receive a request with more than this 407 maximum number due to redirection. The package needs to define 408 how to handle this situation. 410 3. The default values for content and encoding if they are not 411 present. If the same UUI data may be inserted multiple times with 412 different encodings, the package needs to state this. A package 413 may support and define multiple contents and their associated 414 encodings, and reuse contents defined by other packages. 416 4. Any size limitations on the UUI data. Size needs to be 417 specified in terms of the octet stream output of the content, 418 since the size of the resulting uui-data element will vary 419 depending on the encoding scheme. 421 A package MUST define a "purpose" header field value to identify the 422 package in the coding. A package MUST describe the new application 423 which is utilizing the UUI data and provide some use case examples. 424 The default "content" value MUST be defined or referenced in another 425 document for the package. Additional allowed contents MAY also be 426 defined or referenced. Any restrictions on the size of the UUI data 427 MUST be described. In addition, a package MAY define a Media Feature 428 tag per RFC 3840 [RFC3840] to indicate support for this UUI package. 429 For example, the media feature tag sip.uui-pk1 could be defined to 430 indicate support for a UUI package named pk1. The definition of a 431 new SIP option tag solely to identify support for a UUI package is 432 NOT RECOMMENDED unless there are additional SIP behaviors needed to 433 implement this feature. 435 For an example UUI package definition, see 436 [I-D.ietf-cuss-sip-uui-isdn]. 438 5.1. Extensibility 440 New "content" values MUST describe the semantics of the UUI data, 441 valid encodings, and give some example use cases. A previously 442 defined UUI content value can be used in a new package. In this 443 case, the semantics and usage of the content by the new package is 444 defined within the new package. New UUI content types cannot be 445 added to existing packages - instead, a new package would need to be 446 defined. New content values defined are added to the IANA registry 447 with a standards track RFC, which needs to discuss the issues in this 448 section. If no new encoding value is defined for a content, the 449 encoding defaults to "hex" as defined in this document. In this 450 case, the "hex" value will be explicitly stated via the encoding 451 parameter as the encoding for the content. 453 New "encoding" values associated with a new content MUST reference a 454 specific encoding scheme (such as "hex" which is defined in this 455 specification) or define the new encoding scheme. A previously 456 defined UUI encoding value can be used with a newly defined content. 457 In this case, the usage of the encoding is defined by the content 458 definition. New UUI encodings cannot be added to existing contents - 459 instead, a new content would need to be defined. Newly defined 460 encoding values are added to the IANA registry with a standards track 461 RFC, which needs to discuss the issues in this section. 463 6. IANA Considerations 464 6.1. Registration of User-to-User Header Field 466 This document defines a new SIP header field named "User-to-User". 468 The following row shall be added to the "Header Fields" section of 469 the SIP parameter registry: 471 +------------------+--------------+-----------+ 472 | Header Name | Compact Form | Reference | 473 +------------------+--------------+-----------+ 474 | User-to-User | | [RFCXXXX] | 475 +------------------+--------------+-----------+ 477 Editor's Note: [RFCXXXX] should be replaced with the designation of 478 this document. 480 6.2. Registration of User-to-User Header Field Parameters 482 This document defines the parameters for the header field defined in 483 the preceding section. The header field "User-to-User" can contain 484 the parameters "encoding", "content", and "purpose". 486 The following rows shall be added to the "Header Field Parameters and 487 Parameter Values" section of the SIP parameter registry: 489 +------------------+----------------+-------------------+-----------+ 490 | Header Field | Parameter Name | Predefined Values | Reference | 491 +------------------+----------------+-------------------+-----------+ 492 | User-to-User | encoding | yes | [RFCXXXX] | 493 +------------------+----------------+-------------------+-----------+ 494 | User-to-User | content | | [RFCXXXX] | 495 +------------------+----------------+-------------------+-----------+ 496 | User-to-User | purpose | | [RFCXXXX] | 497 +------------------+----------------+-------------------+-----------+ 499 Editor's Note: [RFCXXXX] should be replaced with the designation of 500 this document. 502 6.3. Registration of UUI Packages 504 This specification establishes the uui-packages sub-registry under 505 http://www.iana.org/assignments/sip-parameters. 507 The descriptive text for the table of uui-content is: 509 UUI Packages provides information about the usage of the UUI data in 510 a User-to-User header field [RFCXXXX]. 512 +------------+------------------------------------------+-----------+ 513 | Package | Description | Reference | 514 +------------+------------------------------------------+-----------+ 516 6.4. Registration of UUI Content Parameters 518 This specification establishes the uui-content sub-registry under 519 http://www.iana.org/assignments/sip-parameters. 521 The descriptive text for the table of uui-content is: 523 UUI Content provides information about the content of the UUI data in 524 a User-to-User header field [RFCXXXX]. 526 +------------+------------------------------------------+-----------+ 527 | Content | Description | Reference | 528 +------------+------------------------------------------+-----------+ 530 6.5. Registration of UUI Encoding Parameters 532 This specification establishes the uui-encoding sub-registry under 533 http://www.iana.org/assignments/sip-parameters and initiates its 534 population with the table below. 536 The descriptive text for the table of uui-encoding is: 538 UUI Encoding provides information about the encoding of the UUI data 539 in a User-to-User header field [RFCXXXX]. 541 +-----------+-------------------------------------------+-----------+ 542 | Encoding | Description | Reference | 543 +-----------+-------------------------------------------+-----------+ 544 | hex | The UUI data is encoded using hexadecimal | [RFCXXXX] | 545 +-----------+-------------------------------------------+-----------+ 547 6.6. Registration of SIP Option Tag 549 This specification registers a new SIP option tag, as per the 550 guidelines in Section 27.1 of [RFC3261]. 552 This document defines the SIP option tag "uui". 554 The following row has been added to the "Option Tags" section of the 555 SIP Parameter Registry: 557 +------------+------------------------------------------+-----------+ 558 | Name | Description | Reference | 559 +------------+------------------------------------------+-----------+ 560 | uui | This option tag is used to indicate that | [RFCXXXX] | 561 | | a UA supports and understands the | | 562 | | User-to-User header field. | | 563 +------------+------------------------------------------+-----------+ 565 Editor's Note: [RFCXXXX] should be replaced with the designation of 566 this document. 568 7. Security Considerations 570 UUI data can potentially carry sensitive information that might 571 require confidentiality protection for privacy or integrity 572 protection from third parties that may wish to read or modify the UUI 573 data. [RFC6567] describes three security models which may be 574 applicable for the UUI mechanism. 576 One model treats the SIP layer as untrusted and requires end-to-end 577 integrity protection and/or encryption. This model can be achieved 578 by providing these security services at a layer above SIP. In this 579 case, applications are encouraged to use their own integrity and/or 580 encryption mechanisms before passing it to the SIP layer. 582 The second approach is for the application to pass the UUI without 583 any protection to the SIP layer and require the SIP layer to provide 584 this security. This approach is possible in theory, although its 585 practical use would be extremely limited. To preserve multi-hop or 586 end-to-end confidentiality and integrity of UUI data, approaches 587 using S/MIME or IPsec can be used, as discussed in the review of 588 REQ-13 and REQ-14 in section 3 of this document. However, the lack 589 of deployment of these mechanisms means that applications cannot in 590 general rely on them being present. 592 The third model utilizes a trust domain and relies on perimeter 593 security at the SIP layer. This is the security model of the PSTN 594 and ISDN where UUI is commonly used today. This approach uses hop- 595 by-hop security mechanisms and relies on border elements for 596 filtering and application of policy. Standard deployed SIP security 597 mechanisms such as TLS transport, offer privacy and integrity 598 protection properties on a hop-by-hop basis at the SIP layer. 600 If the UUI data was included by the UA originator of the SIP request 601 or response, normal SIP mechanisms can be used to determine the 602 identity of the inserter of the UUI data. If the UUI data was 603 included by a UA that was not the originator of the request, a 604 History-Info header field can be used to determine the identity of 605 the inserter of the UUI data. UAs can apply policy based on the 606 origin of the UUI data using this information. In short, the UUI 607 data included in an INVITE can be trusted as much as the INVITE 608 itself can be trusted. 610 Note that it is possible that this mechanism could be used as a 611 covert communication channel between UAs, conveying information 612 unknown to the SIP network. 614 8. Appendix - Other Possible Mechanisms 616 Two other possible mechanisms for transporting UUI data will be 617 described: MIME body and URI parameter transport. 619 8.1. Why INFO is Not Used 621 Since the INFO method [RFC6086], was developed for ISUP interworking 622 of user-to-user information, it might seem to be the logical choice 623 here. For non-call control user-to-user information, INFO can be 624 utilized for end to end transport. However, for transport of call 625 control user-to-user information, INFO can not be used. As the call 626 flows in [RFC6567] show, the information is related to an attempt to 627 establish a session and needs to be passed with the session setup 628 request (INVITE), responses to that INVITE, or session termination 629 requests. As a result, it is not possible to use INFO in these 630 cases. 632 8.2. Why Other Protocol Encapsulation UUI Mechanisms are Not Used 634 Other protocols have the ability to transport UUI data. For example, 635 consider the ITU-T Q.931 User to User Information Element (UU IE) 636 [Q931] and the ITU-T Q.763 User to User Information Parameter [Q763]. 637 In addition, NSS (Narrowband Signaling System) [Q1980] is also able 638 to transport UUI data. Should one of these protocols be in use, and 639 present in both User Agents, then utilizing these other protocols to 640 transport UUI data might be a logical solution. Essentially, this is 641 just adding an additional layer in the protocol stack. In these 642 cases, SIP is not transporting the UUI data; it is encapsulating 643 another protocol, and that protocol is transporting the UUI data. 644 Once a mechanism to transport that other protocol using SIP exists, 645 the UUI data transport function is essentially obtained without any 646 additional effort or work. 648 However, the CUSS working group believes, consistent with its 649 charter, that SIP needs to have its own native UUI data transport 650 mechanism. It is not reasonable for a SIP UA to have to implement 651 another entire protocol (either ISDN or NSS, for example) just to get 652 the very simple UUI data transport service. Of course, this work 653 does not preclude anyone from using other protocols with SIP to 654 transport UUI data. 656 8.3. MIME body Approach 658 One method of transport is to use a MIME body. This is in keeping 659 with the SIP-T architecture [RFC3372] in which MIME bodies are used 660 to transport ISUP information. Since the INVITE will normally have 661 an SDP message body, the resulting INVITE with SDP and UUI data will 662 be multipart MIME. This is not ideal as many SIP UAs do not support 663 multipart MIME INVITEs. 665 A bigger problem is the insertion of a UUI message body by a redirect 666 server or in a REFER. The body would need to be encoded in the 667 Contact URI of the 3xx response or the Refer-To URI of a REFER. 668 Currently, the authors are not aware of any UAs that support this 669 capability today for any body type. As such, the complete set of 670 semantics for this operation would need to be determined and defined. 671 Some issues will need to be resolved, such as, do all the Content-* 672 header fields have to be included as well? And, what if the included 673 Content-Length does not agree with the included body? 675 Since proxies cannot remove a body from a request or response, it is 676 not clear how this mechanism could meet REQ-9. 678 The requirement for integrity protection could be met by the use of 679 an S/MIME signature over the body, as defined in Section 23.3 of RFC 680 3261 "Securing MIME bodies". Alternatively, this could be achieved 681 using RFC 4474 [RFC4474]. The requirement for end-to-end privacy 682 could be met using S/MIME encryption or using encryption at the 683 application layer. However, note that neither S/MIME or RFC 4474 684 enjoys deployment in SIP today. 686 An example: 688 689 Contact: 691 693 As such, the MIME body approach meets REQ-1, REQ-2, REQ-4, REQ-5, 694 REQ-7, REQ-11, REQ-13, and REQ-14. Meeting REQ-12 seems possible, 695 although the authors do not have a specific mechanism to propose. 696 Meeting REQ-3 is problematic, but not impossible for this mechanism. 697 However, this mechanism does not seem to be able to meet REQ-9. 699 8.4. URI Parameter 701 Another proposed approach is to encode the UUI data as a URI 702 parameter. This UUI parameter could be included in a Request-URI or 703 in the Contact URI or Refer-To URI. It is not clear how it could be 704 transported in a responses which does not have a Request-URI, or in 705 BYE requests or responses. 707 708 Contact: 710 712 An INVITE sent to this Contact URI would contain UUI data in the 713 Request-URI of the INVITE. The URI parameter has a drawback in that 714 a URI parameter carried in a Request-URI will not survive retargeting 715 by a proxy as shown in Figure 2 of [RFC6567]. That is, if the URI is 716 included with an Address of Record instead of a Contact URI, the URI 717 parameter in the Reqeuest-URI will not be copied over to the Contact 718 URI, resulting in the loss of the information. Note that if this 719 same URI was present in a Refer-To header field, the same loss of 720 information would occur. 722 The URI parameter approach would meet REQ-3, REQ-5, REQ-7, REQ-9, and 723 REQ-11. It is possible the approach could meet REQ-12 and REQ-13. 724 The mechanism does not appear to meet REQ-1, REQ-2, REQ-4, and 725 REQ-14. 727 9. Acknowledgements 729 Joanne McMillen was a major contributor and co-author of earlier 730 versions of this document. Thanks to Paul Kyzivat for his 731 contribution of hex encoding rules. Thanks to Spencer Dawkins, Keith 732 Drage, Vijay Gurbani, and Laura Liess for their review of the 733 document. The authors wish to thank Roland Jesske, Celine Serrut- 734 Valette, Francois Audet, Denis Alexeitsev, Paul Kyzivat, Cullen 735 Jennings, and Mahalingam Mani for their comments. Thanks to Scott 736 Kelly and Joel Halperin for their reviews. 738 10. References 740 10.1. Normative References 742 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 743 Requirement Levels", BCP 14, RFC 2119, March 1997. 745 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 746 A., Peterson, J., Sparks, R., Handley, M., and E. 747 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 748 June 2002. 750 [RFC4474] Peterson, J. and C. Jennings, "Enhancements for 751 Authenticated Identity Management in the Session 752 Initiation Protocol (SIP)", RFC 4474, August 2006. 754 [RFC7044] Barnes, M., Audet, F., Schubert, S., van Elburg, J., and 755 C. Holmberg, "An Extension to the Session Initiation 756 Protocol (SIP) for Request History Information", RFC 7044, 757 February 2014. 759 [RFC4916] Elwell, J., "Connected Identity in the Session Initiation 760 Protocol (SIP)", RFC 4916, June 2007. 762 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 763 "Indicating User Agent Capabilities in the Session 764 Initiation Protocol (SIP)", RFC 3840, August 2004. 766 [RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer 767 Method", RFC 3515, April 2003. 769 [RFC3891] Mahy, R., Biggs, B., and R. Dean, "The Session Initiation 770 Protocol (SIP) "Replaces" Header", RFC 3891, 771 September 2004. 773 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 774 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 776 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 777 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 778 May 2008. 780 [I-D.ietf-cuss-sip-uui-isdn] 781 Drage, K. and A. Johnston, "Interworking ISDN Call Control 782 User Information with SIP", 783 draft-ietf-cuss-sip-uui-isdn-08 (work in progress), 784 March 2014. 786 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 787 Encodings", RFC 4648, October 2006. 789 10.2. Informative References 791 [Q763] "ITU-T Q.763 Signaling System No. 7 - ISDN user part 792 formats and codes", 793 http://www.itu.int/rec/T-REC-Q.931-199805-I/en . 795 [Q931] "ITU-T Q.931 User to User Information Element (UU IE)", 796 http://www.itu.int/rec/T-REC-Q.931-199805-I/en . 798 [RFC3372] Vemuri, A. and J. Peterson, "Session Initiation Protocol 799 for Telephones (SIP-T): Context and Architectures", 800 BCP 63, RFC 3372, September 2002. 802 [RFC6086] Holmberg, C., Burger, E., and H. Kaplan, "Session 803 Initiation Protocol (SIP) INFO Method and Package 804 Framework", RFC 6086, January 2011. 806 [RFC4475] Sparks, R., Hawrylyshen, A., Johnston, A., Rosenberg, J., 807 and H. Schulzrinne, "Session Initiation Protocol (SIP) 808 Torture Test Messages", RFC 4475, May 2006. 810 [RFC5727] Peterson, J., Jennings, C., and R. Sparks, "Change Process 811 for the Session Initiation Protocol (SIP) and the Real- 812 time Applications and Infrastructure Area", BCP 67, 813 RFC 5727, March 2010. 815 [Q1980] "ITU-T Q.1980.1 The Narrowband Signalling Syntax (NSS) - 816 Syntax Definition", http://www.itu.int/itudoc/itu-t/aap/ 817 sg11aap/history/q1980.1/q1980.1.html . 819 [RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private 820 Extensions to the Session Initiation Protocol (SIP) for 821 Asserted Identity within Trusted Networks", RFC 3325, 822 November 2002. 824 [RFC6567] Johnston, A. and L. Liess, "Problem Statement and 825 Requirements for Transporting User-to-User Call Control 826 Information in SIP", RFC 6567, April 2012. 828 Authors' Addresses 830 Alan Johnston 831 Avaya 832 St. Louis, MO 63124 834 Email: alan.b.johnston@gmail.com 835 James Rafferty 836 Human Communications 837 Norfolk, MA 02056 839 Email: jay@humancomm.com