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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 579, 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reference: RFC 5246 (Obsoleted by RFC 8446) ** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) == Outdated reference: A later version (-11) exists of draft-ietf-cuss-sip-uui-isdn-08 Summary: 3 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--).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: November 1, 2014 Human Communications 6 April 30, 2014 8 A Mechanism for Transporting User to User Call Control Information in 9 SIP 10 draft-ietf-cuss-sip-uui-16 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 are defined by a UUI package. This UUI data is opaque to SIP and its 21 function is unrelated to any basic SIP function. This document 22 defines a new SIP header field, User-to-User, to transport UUI data, 23 along with an 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 November 1, 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 . . . . . . . . . . . . . . . . . . . . . 11 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 . . . . . . . . . . . . . . 13 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 . . . . . . . . . . . . . . . . . . . . . . . . . . 17 84 10.1. Normative References . . . . . . . . . . . . . . . . . . . 17 85 10.2. Informative References . . . . . . . . . . . . . . . . . . 18 86 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 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. If the 215 "purpose" header field parameter is not present, interworking with 216 the ISDN UUI Service MUST be assumed. The "content" header field 217 parameter identifies the actual content of the UUI data. If not 218 present, the default content defined for the package MUST be used. 219 Newly defined UUI packages MUST define or reference at least a 220 default "content" value. The "encoding" header field parameter 221 indicates the method of encoding the information in the UUI data 222 associated with a particular "content" value. This specification 223 only defines "encoding=hex". If the "encoding" header field 224 parameter is not present, the default encoding defined for the 225 package MUST be used. 227 UUI data is considered an opaque series of octets. This mechanism 228 SHOULD NOT be used to convey a URL or URI, since the Call-Info header 229 field in [RFC3261] already supports this use case. 231 4.1. Syntax for UUI Header Field 233 The User-to-User (UUI) header field can be present in INVITE requests 234 and responses and in BYE requests and responses. Note that when the 235 UUI header is used in responses, it can only be utilized in end-to- 236 end responses, e.g. 1xx (excluding 100), 2xx, and 3xx responses. 238 The following syntax specification uses the Augmented Backus-Naur 239 Form (ABNF) as described in RFC 5234 and extends RFC 3261 (where 240 token and quoted-string are defined). 242 UUI = "User-to-User" HCOLON uui-value *(COMMA uui-value) 243 uui-value = uui-data *(SEMI uui-param) 244 uui-data = token / quoted-string 245 uui-param = pkg-param / cont-param / enc-param / generic-param 246 pkg-param = "purpose" EQUAL pkg-param-value 247 pkg-param-value = token 248 cont-param = "content" EQUAL cont-param-value 249 cont-param-value = token 250 enc-param = "encoding" EQUAL enc-param-value 251 enc-param-value = token / "hex" 253 The rules for how many User-to-User header fields of each package may 254 be present in a request or a response are defined for each package. 255 A sender MAY include multiple User-to-User header fields, and a 256 receiver MUST be prepared to receive multiple User-to-User header 257 fields. Consistent with the rules of SIP syntax, the syntax defined 258 in this document allows any combination of individual User-to-User 259 header fields or User-to-User header fields with multiple comma 260 separated UUI data elements. Any size limitations on the UUI data 261 for a particular purpose are to be defined by the related UUI 262 package. 264 UAs SHALL ignore UUI data from packages or encoding that they do not 265 understand. 267 For redirection use cases, the header field is included (escaped) 268 within the Contact URI. For referral use cases, the header field is 269 included (escaped) within the Refer-To URI. For example, if a UA 270 supports this specification, it SHOULD include any UUI data included 271 in a redirection URI (if the UUI data and encoding is understood). 272 Note that redirection can occur multiple times to a request. 273 Currently, UAs that support attended transfer support the ability to 274 include a Replaces header field [RFC3891] into a Refer-To URI, and 275 when acting upon this URI, add the Replaces header field to the 276 triggered INVITE. This sort of logic and behavior is utilized for 277 the UUI header field (that is, the UUI header field is included in 278 the triggered INVITE). The UA processing the REFER [RFC3515] or the 279 3xx response to the INVITE SHOULD support the UUI mechanism. If the 280 REFER or redirect target does not support UUI, the UUI header will be 281 discarded as per [RFC3261]. However, this may limit the utility of 282 use cases which depend upon the UUI being supported by all elements. 284 Here is an example of an included User-to-User header field from the 285 redirection response F2 of Figure 2: 287 288 Contact: 291 293 The resulting INVITE F4 would contain: 295 User-to-User: 56a390f3d2b7310023a2;encoding=hex;purpose=foo;content=bar 297 4.2. Hex Encoding Definition 299 This specification defines hex encoding of UUI data. When the value 300 of 'hex' is used in the 'encoding' parameter of a header field, the 301 data is encoded using base16 encoding according to Section 8 of 302 [RFC4648]. The hex-encoded value is normally represented using the 303 'token' construction from RFC 3261, although the 'quoted-string' 304 construction is permitted, in which case the quotes MUST be ignored. 306 If a canonicalized version of a normally case-insensitive hex encoded 307 UUI data object is needed for a digital signature or integrity 308 checking, then the base16 encoding with all upper case MUST be used. 310 4.3. Source Identity of UUI data 312 It is important for the recipient of UUI data to know the identity of 313 the UA that inserted the UUI data. In a request without a History- 314 Info header field, the identity of the entity which inserted the UUI 315 data will be assumed to be the source of the SIP message. For a SIP 316 request, typically this is the UA identified by the URI in the From 317 header field or a P-Asserted-Identity [RFC3325] header field. In a 318 request with a History-Info header field, the recipient needs to 319 parse the Targeted-to-URIs present (hi-targeted-to-uri defined in 320 [RFC7044]) to see if any included User-to-User header fields are 321 present. If an included User-to-User header field is present and 322 matches the UUI data in the request, this indicates that redirection 323 has taken place, resulting in the inclusion of UUI data in the 324 request. The inserter of the UUI data will be the UA identified by 325 the Targeted-to-URI of the History-Info element prior to the element 326 with the included UUI data. In a response, the inserter of the UUI 327 data will be the identity of the UA that generated the response. 328 Typically, this is the UA identified in the To header field of the 329 response. Note that any updates to this identity by use of the SIP 330 Connected Identity extension [RFC4916] or others will update this 331 information. 333 For an example of History-Info and redirection, consider Figure 2 334 from [RFC6567] where the Originating UA is Carol, the Redirector Bob, 335 and the Terminating UA Alice. The INVITE F4 containing UUI data 336 could be: 338 INVITE sips:alice@example.com SIP/2.0 339 Via: SIP/2.0/TLS lab.example.com:5061 340 ;branch=z9hG4bKnashds9 341 To: Bob 342 From: Carol ;tag=323sf33k2 343 Call-ID: dfaosidfoiwe83ifkdf 344 Max-Forwards: 70 345 Contact: 346 Supported: histinfo 347 User-to-User: 342342ef34;encoding=hex 348 History-Info: ;index=1 349 350 History-Info: ;index=1.1;rc=1 352 354 Without the redirection captured in the History-Info header field, 355 Alice would conclude the UUI data was inserted by Carol. However, 356 the History-Info containing UUI data (index=1.1) indicates that the 357 inserter was Bob (index=1). 359 To enable maintaining a record of the inserter identity of UUI data, 360 UAs supporting this mechanism SHOULD support History-Info [RFC7044] 361 and include Supported: histinfo in all requests and responses. 363 If a border element such as a proxy or a Back-to-Back User Agent 364 (B2BUA) removes a History-Info header field containing a User-to-User 365 parameter, the UA consuming the UUI data may not be able at SIP level 366 to identify the source of the UUI data. 368 5. Guidelines for UUI Packages 370 UUI packages defined using this SIP UUI mechanism MUST follow the 371 "Standards Action" guideline as defined in [RFC5226] and publish a 372 standards track RFC which describes the usage. The WG chose to adopt 373 this conservative policy while it considers other potential 374 registration policies. Note that this mechanism is not suitable for 375 the transport of arbitrary data between UAs. The following 376 guidelines are provided to help determine if this mechanism is 377 appropriate or not. The SIP UUI mechanism is applicable when all of 378 the following conditions be met: 380 1. The information is generated and consumed by an application 381 during session setup using SIP, but the application is not 382 necessarily SIP aware. 384 2. The behavior of SIP entities that support it is not 385 significantly changed (as discussed in Section 4 of [RFC5727]). 387 3. User Agents (UAs) are the generators and consumers of the UUI 388 data. Proxies and other intermediaries may route based on the 389 presence of a User-to-User header field or a particular package 390 tag but do not otherwise consume or generate the UUI data. 392 4. There are no privacy issues associated with the information 393 being transported (e.g., geolocation or emergency-related 394 information are examples of inappropriate UUI data). 396 5. The UUI data is not being utilized for user-to-user Remote 397 Procedure Call (RPC) calls. 399 UUI packages define the semantics for a particular application usage 400 of UUI data. The content defines the syntax of the UUI data, while 401 the encoding defines the encoding of the UUI data for the content. 402 Each content is defined as a stream of octets, which allows multiple 403 encodings of that content. For example, packages may define: 405 1. The SIP methods and responses in which the UUI data may be 406 present. 408 2. The maximum number of UUI data elements that may be inserted 409 into a request or response. The default is one per encoding. 410 Note that a UA may still receive a request with more than this 411 maximum number due to redirection. The package needs to define 412 how to handle this situation. 414 3. The default values for content and encoding if they are not 415 present. If the same UUI data may be inserted multiple times with 416 different encodings, the package needs to state this. A package 417 may support and define multiple contents and their associated 418 encodings, and reuse contents defined by other packages. 420 4. Any size limitations on the UUI data. Size needs to be 421 specified in terms of the octet stream output of the content, 422 since the size of the resulting uui-data element will vary 423 depending on the encoding scheme. 425 A package MUST define a "purpose" header field value to identify the 426 package in the coding. A package MUST describe the new application 427 which is utilizing the UUI data and provide some use case examples. 428 The default "content" value MUST be defined or referenced in another 429 document for the package. Additional allowed contents MAY also be 430 defined or referenced. Any restrictions on the size of the UUI data 431 MUST be described. In addition, a package MAY define a Media Feature 432 tag per RFC 3840 [RFC3840] to indicate support for this UUI package. 433 For example, the media feature tag sip.uui-pk1 could be defined to 434 indicate support for a UUI package named pk1. The definition of a 435 new SIP option tag solely to identify support for a UUI package is 436 NOT RECOMMENDED unless there are additional SIP behaviors needed to 437 implement this feature. 439 For an example UUI package definition, see 440 [I-D.ietf-cuss-sip-uui-isdn]. 442 5.1. Extensibility 444 New "content" values MUST describe the semantics of the UUI data, 445 valid encodings, and give some example use cases. A previously 446 defined UUI content value can be used in a new package. In this 447 case, the semantics and usage of the content by the new package is 448 defined within the new package. New UUI content types cannot be 449 added to existing packages - instead, a new package would need to be 450 defined. New content values defined are added to the IANA registry 451 with a standards track RFC, which needs to discuss the issues in this 452 section. If no new encoding value is defined for a content, the 453 encoding defaults to "hex" as defined in this document. In this 454 case, the "hex" value will be explicitly stated via the encoding 455 parameter as the encoding for the content. 457 New "encoding" values associated with a new content MUST reference a 458 specific encoding scheme (such as "hex" which is defined in this 459 specification) or define the new encoding scheme. A previously 460 defined UUI encoding value can be used with a newly defined content. 461 In this case, the usage of the encoding is defined by the content 462 definition. New UUI encodings cannot be added to existing contents - 463 instead, a new content would need to be defined. Newly defined 464 encoding values are added to the IANA registry with a standards track 465 RFC, which needs to discuss the issues in this section. 467 6. IANA Considerations 469 6.1. Registration of User-to-User Header Field 471 This document defines a new SIP header field named "User-to-User". 473 The following row shall be added to the "Header Fields" section of 474 the SIP parameter registry: 476 +------------------+--------------+-----------+ 477 | Header Name | Compact Form | Reference | 478 +------------------+--------------+-----------+ 479 | User-to-User | | [RFCXXXX] | 480 +------------------+--------------+-----------+ 482 Editor's Note: [RFCXXXX] should be replaced with the designation of 483 this document. 485 6.2. Registration of User-to-User Header Field Parameters 487 This document defines the parameters for the header field defined in 488 the preceding section. The header field "User-to-User" can contain 489 the parameters "encoding", "content", and "purpose". 491 The following rows shall be added to the "Header Field Parameters and 492 Parameter Values" section of the SIP parameter registry: 494 +------------------+----------------+-------------------+-----------+ 495 | Header Field | Parameter Name | Predefined Values | Reference | 496 +------------------+----------------+-------------------+-----------+ 497 | User-to-User | encoding | yes | [RFCXXXX] | 498 +------------------+----------------+-------------------+-----------+ 499 | User-to-User | content | | [RFCXXXX] | 500 +------------------+----------------+-------------------+-----------+ 501 | User-to-User | purpose | | [RFCXXXX] | 502 +------------------+----------------+-------------------+-----------+ 504 Editor's Note: [RFCXXXX] should be replaced with the designation of 505 this document. 507 6.3. Registration of UUI Packages 509 This specification establishes the uui-packages sub-registry under 510 http://www.iana.org/assignments/sip-parameters. 512 The descriptive text for the table of uui-content is: 514 UUI Packages provides information about the usage of the UUI data in 515 a User-to-User header field [RFCXXXX]. 517 The registration policy for this registry is "Standards Action" as 518 defined in [RFC5226]. 520 +------------+------------------------------------------+-----------+ 521 | Package | Description | Reference | 522 +------------+------------------------------------------+-----------+ 524 6.4. Registration of UUI Content Parameters 526 This specification establishes the uui-content sub-registry under 527 http://www.iana.org/assignments/sip-parameters. 529 The descriptive text for the table of uui-content is: 531 UUI Content provides information about the content of the UUI data in 532 a User-to-User header field [RFCXXXX]. 534 The registration policy for this registry is "Standards Action" as 535 defined in [RFC5226]. 537 +------------+------------------------------------------+-----------+ 538 | Content | Description | Reference | 539 +------------+------------------------------------------+-----------+ 541 6.5. Registration of UUI Encoding Parameters 543 This specification establishes the uui-encoding sub-registry under 544 http://www.iana.org/assignments/sip-parameters and initiates its 545 population with the table below. 547 The descriptive text for the table of uui-encoding is: 549 UUI Encoding provides information about the encoding of the UUI data 550 in a User-to-User header field [RFCXXXX]. 552 The registration policy for this registry is "Standards Action" as 553 defined in [RFC5226]. 555 +-----------+-------------------------------------------+-----------+ 556 | Encoding | Description | Reference | 557 +-----------+-------------------------------------------+-----------+ 558 | hex | The UUI data is encoded using hexadecimal | [RFCXXXX] | 559 +-----------+-------------------------------------------+-----------+ 561 6.6. Registration of SIP Option Tag 563 This specification registers a new SIP option tag, as per the 564 guidelines in Section 27.1 of [RFC3261]. 566 This document defines the SIP option tag "uui". 568 The following row has been added to the "Option Tags" section of the 569 SIP Parameter Registry: 571 +------------+------------------------------------------+-----------+ 572 | Name | Description | Reference | 573 +------------+------------------------------------------+-----------+ 574 | uui | This option tag is used to indicate that | [RFCXXXX] | 575 | | a UA supports and understands the | | 576 | | User-to-User header field. | | 577 +------------+------------------------------------------+-----------+ 579 Editor's Note: [RFCXXXX] should be replaced with the designation of 580 this document. 582 7. Security Considerations 584 UUI data can potentially carry sensitive information that might 585 require confidentiality protection for privacy or integrity 586 protection from third parties that may wish to read or modify the UUI 587 data. [RFC6567] describes three security models which may be 588 applicable for the UUI mechanism. 590 One model treats the SIP layer as untrusted and requires end-to-end 591 integrity protection and/or encryption. This model can be achieved 592 by providing these security services at a layer above SIP. In this 593 case, applications are encouraged to use their own integrity and/or 594 encryption mechanisms before passing it to the SIP layer. 596 The second approach is for the application to pass the UUI without 597 any protection to the SIP layer and require the SIP layer to provide 598 this security. This approach is possible in theory, although its 599 practical use would be extremely limited. To preserve multi-hop or 600 end-to-end confidentiality and integrity of UUI data, approaches 601 using S/MIME or IPsec can be used, as discussed in the review of 602 REQ-13 and REQ-14 in section 3 of this document. However, the lack 603 of deployment of these mechanisms means that applications cannot in 604 general rely on them being present. 606 The third model utilizes a trust domain and relies on perimeter 607 security at the SIP layer. This is the security model of the PSTN 608 and ISDN where UUI is commonly used today. This approach uses hop- 609 by-hop security mechanisms and relies on border elements for 610 filtering and application of policy. Standard deployed SIP security 611 mechanisms such as TLS transport, offer privacy and integrity 612 protection properties on a hop-by-hop basis at the SIP layer. 614 If the UUI data was included by the UA originator of the SIP request 615 or response, normal SIP mechanisms can be used to determine the 616 identity of the inserter of the UUI data. If the UUI data was 617 included by a UA that was not the originator of the request, a 618 History-Info header field can be used to determine the identity of 619 the inserter of the UUI data. UAs can apply policy based on the 620 origin of the UUI data using this information. In short, the UUI 621 data included in an INVITE can be trusted as much as the INVITE 622 itself can be trusted. 624 Note that it is possible that this mechanism could be used as a 625 covert communication channel between UAs, conveying information 626 unknown to the SIP network. 628 8. Appendix - Other Possible Mechanisms 630 Two other possible mechanisms for transporting UUI data will be 631 described: MIME body and URI parameter transport. 633 8.1. Why INFO is Not Used 635 Since the INFO method [RFC6086], was developed for ISUP interworking 636 of user-to-user information, it might seem to be the logical choice 637 here. For non-call control user-to-user information, INFO can be 638 utilized for end to end transport. However, for transport of call 639 control user-to-user information, INFO can not be used. As the call 640 flows in [RFC6567] show, the information is related to an attempt to 641 establish a session and needs to be passed with the session setup 642 request (INVITE), responses to that INVITE, or session termination 643 requests. As a result, it is not possible to use INFO in these 644 cases. 646 8.2. Why Other Protocol Encapsulation UUI Mechanisms are Not Used 648 Other protocols have the ability to transport UUI data. For example, 649 consider the ITU-T Q.931 User to User Information Element (UU IE) 650 [Q931] and the ITU-T Q.763 User to User Information Parameter [Q763]. 651 In addition, NSS (Narrowband Signaling System) [Q1980] is also able 652 to transport UUI data. Should one of these protocols be in use, and 653 present in both User Agents, then utilizing these other protocols to 654 transport UUI data might be a logical solution. Essentially, this is 655 just adding an additional layer in the protocol stack. In these 656 cases, SIP is not transporting the UUI data; it is encapsulating 657 another protocol, and that protocol is transporting the UUI data. 658 Once a mechanism to transport that other protocol using SIP exists, 659 the UUI data transport function is essentially obtained without any 660 additional effort or work. 662 However, the CUSS working group believes, consistent with its 663 charter, that SIP needs to have its own native UUI data transport 664 mechanism. It is not reasonable for a SIP UA to have to implement 665 another entire protocol (either ISDN or NSS, for example) just to get 666 the very simple UUI data transport service. Of course, this work 667 does not preclude anyone from using other protocols with SIP to 668 transport UUI data. 670 8.3. MIME body Approach 672 One method of transport is to use a MIME body. This is in keeping 673 with the SIP-T architecture [RFC3372] in which MIME bodies are used 674 to transport ISUP information. Since the INVITE will normally have 675 an SDP message body, the resulting INVITE with SDP and UUI data will 676 be multipart MIME. This is not ideal as many SIP UAs do not support 677 multipart MIME INVITEs. 679 A bigger problem is the insertion of a UUI message body by a redirect 680 server or in a REFER. The body would need to be encoded in the 681 Contact URI of the 3xx response or the Refer-To URI of a REFER. 682 Currently, the authors are not aware of any UAs that support this 683 capability today for any body type. As such, the complete set of 684 semantics for this operation would need to be determined and defined. 685 Some issues will need to be resolved, such as, do all the Content-* 686 header fields have to be included as well? And, what if the included 687 Content-Length does not agree with the included body? 689 Since proxies cannot remove a body from a request or response, it is 690 not clear how this mechanism could meet REQ-9. 692 The requirement for integrity protection could be met by the use of 693 an S/MIME signature over the body, as defined in Section 23.3 of RFC 694 3261 "Securing MIME bodies". Alternatively, this could be achieved 695 using RFC 4474 [RFC4474]. The requirement for end-to-end privacy 696 could be met using S/MIME encryption or using encryption at the 697 application layer. However, note that neither S/MIME or RFC 4474 698 enjoys deployment in SIP today. 700 An example: 702 703 Contact: 705 707 As such, the MIME body approach meets REQ-1, REQ-2, REQ-4, REQ-5, 708 REQ-7, REQ-11, REQ-13, and REQ-14. Meeting REQ-12 seems possible, 709 although the authors do not have a specific mechanism to propose. 710 Meeting REQ-3 is problematic, but not impossible for this mechanism. 711 However, this mechanism does not seem to be able to meet REQ-9. 713 8.4. URI Parameter 715 Another proposed approach is to encode the UUI data as a URI 716 parameter. This UUI parameter could be included in a Request-URI or 717 in the Contact URI or Refer-To URI. It is not clear how it could be 718 transported in a responses which does not have a Request-URI, or in 719 BYE requests or responses. 721 722 Contact: 724 726 An INVITE sent to this Contact URI would contain UUI data in the 727 Request-URI of the INVITE. The URI parameter has a drawback in that 728 a URI parameter carried in a Request-URI will not survive retargeting 729 by a proxy as shown in Figure 2 of [RFC6567]. That is, if the URI is 730 included with an Address of Record instead of a Contact URI, the URI 731 parameter in the Reqeuest-URI will not be copied over to the Contact 732 URI, resulting in the loss of the information. Note that if this 733 same URI was present in a Refer-To header field, the same loss of 734 information would occur. 736 The URI parameter approach would meet REQ-3, REQ-5, REQ-7, REQ-9, and 737 REQ-11. It is possible the approach could meet REQ-12 and REQ-13. 738 The mechanism does not appear to meet REQ-1, REQ-2, REQ-4, and 739 REQ-14. 741 9. Acknowledgements 743 Joanne McMillen was a major contributor and co-author of earlier 744 versions of this document. Thanks to Paul Kyzivat for his 745 contribution of hex encoding rules. Thanks to Spencer Dawkins, Keith 746 Drage, Vijay Gurbani, and Laura Liess for their review of the 747 document. The authors wish to thank Roland Jesske, Celine Serrut- 748 Valette, Francois Audet, Denis Alexeitsev, Paul Kyzivat, Cullen 749 Jennings, and Mahalingam Mani for their comments. Thanks to Scott 750 Kelly and Joel Halperin for their reviews. 752 10. References 754 10.1. Normative References 756 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 757 Requirement Levels", BCP 14, RFC 2119, March 1997. 759 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 760 A., Peterson, J., Sparks, R., Handley, M., and E. 761 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 762 June 2002. 764 [RFC4474] Peterson, J. and C. Jennings, "Enhancements for 765 Authenticated Identity Management in the Session 766 Initiation Protocol (SIP)", RFC 4474, August 2006. 768 [RFC7044] Barnes, M., Audet, F., Schubert, S., van Elburg, J., and 769 C. Holmberg, "An Extension to the Session Initiation 770 Protocol (SIP) for Request History Information", RFC 7044, 771 February 2014. 773 [RFC4916] Elwell, J., "Connected Identity in the Session Initiation 774 Protocol (SIP)", RFC 4916, June 2007. 776 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 777 "Indicating User Agent Capabilities in the Session 778 Initiation Protocol (SIP)", RFC 3840, August 2004. 780 [RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer 781 Method", RFC 3515, April 2003. 783 [RFC3891] Mahy, R., Biggs, B., and R. Dean, "The Session Initiation 784 Protocol (SIP) "Replaces" Header", RFC 3891, 785 September 2004. 787 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 788 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 790 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 791 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 792 May 2008. 794 [I-D.ietf-cuss-sip-uui-isdn] 795 Drage, K. and A. Johnston, "Interworking ISDN Call Control 796 User Information with SIP", 797 draft-ietf-cuss-sip-uui-isdn-08 (work in progress), 798 March 2014. 800 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 801 Encodings", RFC 4648, October 2006. 803 10.2. Informative References 805 [Q763] "ITU-T Q.763 Signaling System No. 7 - ISDN user part 806 formats and codes", 807 http://www.itu.int/rec/T-REC-Q.931-199805-I/en . 809 [Q931] "ITU-T Q.931 User to User Information Element (UU IE)", 810 http://www.itu.int/rec/T-REC-Q.931-199805-I/en . 812 [RFC3372] Vemuri, A. and J. Peterson, "Session Initiation Protocol 813 for Telephones (SIP-T): Context and Architectures", 814 BCP 63, RFC 3372, September 2002. 816 [RFC6086] Holmberg, C., Burger, E., and H. Kaplan, "Session 817 Initiation Protocol (SIP) INFO Method and Package 818 Framework", RFC 6086, January 2011. 820 [RFC4475] Sparks, R., Hawrylyshen, A., Johnston, A., Rosenberg, J., 821 and H. Schulzrinne, "Session Initiation Protocol (SIP) 822 Torture Test Messages", RFC 4475, May 2006. 824 [RFC5727] Peterson, J., Jennings, C., and R. Sparks, "Change Process 825 for the Session Initiation Protocol (SIP) and the Real- 826 time Applications and Infrastructure Area", BCP 67, 827 RFC 5727, March 2010. 829 [Q1980] "ITU-T Q.1980.1 The Narrowband Signalling Syntax (NSS) - 830 Syntax Definition", http://www.itu.int/itudoc/itu-t/aap/ 831 sg11aap/history/q1980.1/q1980.1.html . 833 [RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private 834 Extensions to the Session Initiation Protocol (SIP) for 835 Asserted Identity within Trusted Networks", RFC 3325, 836 November 2002. 838 [RFC6567] Johnston, A. and L. Liess, "Problem Statement and 839 Requirements for Transporting User-to-User Call Control 840 Information in SIP", RFC 6567, April 2012. 842 Authors' Addresses 844 Alan Johnston 845 Avaya 846 St. Louis, MO 63124 848 Email: alan.b.johnston@gmail.com 850 James Rafferty 851 Human Communications 852 Norfolk, MA 02056 854 Email: jay@humancomm.com