idnits 2.17.1 draft-ietf-cuss-sip-uui-isdn-05.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 824 has weird spacing: '...ats and codes...' -- The document date (August 4, 2013) is 3917 days in the past. Is this intentional? 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to lower-maturity documents in RFCs) == Missing Reference: 'RFCXXXX' is mentioned on line 582, but not defined == Outdated reference: A later version (-17) exists of draft-ietf-cuss-sip-uui-10 -- Possible downref: Non-RFC (?) normative reference: ref. 'Q931' Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group K. Drage, Ed. 3 Internet-Draft Alcatel-Lucent 4 Intended status: Standards Track A. Johnston 5 Expires: February 5, 2014 Avaya 6 August 4, 2013 8 Interworking ISDN Call Control User Information with SIP 9 draft-ietf-cuss-sip-uui-isdn-05 11 Abstract 13 The motivation and use cases for interworking and transporting ITU-T 14 DSS1 User-user information element data in SIP are described in the 15 "Problem Statement and Requirements for Transporting User to User 16 Call Control Information in SIP" document. As networks move to SIP 17 it is important that applications requiring this data can continue to 18 function in SIP networks as well as the ability to interwork with 19 this ISDN service for end-to- end transparency. This document 20 defines a usage (a new package) of the User-to-User header field to 21 enable interworking with this ISDN service. 23 This document covers the interworking with both public ISDN and 24 private ISDN capabilities, so the potential interworking with QSIG 25 will also be addressed. 27 The package is identified by a new value "isdn-uui" of the "purpose" 28 header field parameter. 30 Status of this Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on February 5, 2014. 47 Copyright Notice 48 Copyright (c) 2013 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 65 3. Summary of the ISDN User-to-User Service . . . . . . . . . . . 3 66 3.1. The service . . . . . . . . . . . . . . . . . . . . . . . 3 67 3.2. Impacts of the ISDN service on SIP operation . . . . . . . 5 68 4. Relation to SIP-T . . . . . . . . . . . . . . . . . . . . . . 6 69 5. Transition away from ISDN . . . . . . . . . . . . . . . . . . 6 70 6. ISDN Usage of the User-to-User Header Field . . . . . . . . . 7 71 7. UAC requirements . . . . . . . . . . . . . . . . . . . . . . . 8 72 8. UAS requirements . . . . . . . . . . . . . . . . . . . . . . . 9 73 9. UUI contents . . . . . . . . . . . . . . . . . . . . . . . . . 10 74 10. Considerations for ISDN interworking gateways . . . . . . . . 11 75 11. Coding requirements . . . . . . . . . . . . . . . . . . . . . 11 76 12. Media Feature Tag . . . . . . . . . . . . . . . . . . . . . . 12 77 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 78 14. Security Considerations . . . . . . . . . . . . . . . . . . . 13 79 15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 80 16. Changes since previous versions . . . . . . . . . . . . . . . 14 81 17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 82 17.1. Normative References . . . . . . . . . . . . . . . . . . . 18 83 17.2. Informative References . . . . . . . . . . . . . . . . . . 18 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 86 1. Terminology 88 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 89 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 90 document are to be interpreted as described in BCP 14, RFC 2119 91 [RFC2119]. 93 2. Overview 95 This document describes a usage of the User-to-User header field 96 defined in [I-D.ietf-cuss-sip-uui] to enable the transport of User to 97 User Information (UUI) in ISDN interworking scenarios using SIP 98 [RFC3261]. Specifically, this document discusses the interworking of 99 call control related ITU-T DSS1 User-user information element [Q931], 100 [Q957.1] and ITU-T Q.763 User-to-user information parameter [Q763] 101 data in SIP. UUI is widely used in the PSTN today in contact centers 102 and call centers which are transitioning away from ISDN to SIP. 104 This usage is not limited to scenarios where interworking will occur. 105 Rather it describes a usage where interworking is possible if 106 interworking is met. That does not preclude its usage directly 107 between two SIP terminals. 109 3. Summary of the ISDN User-to-User Service 111 3.1. The service 113 ISDN defines a number of related services. Firstly there is a user 114 signalling bearer service, which uses the information elements / 115 parameters in the signalling channel to carry the data, and does not 116 establish a related circuit-switched connection. For DSS1, this is 117 specified in ITU-T Recommendation Q.931 section 3.3 and section 7 118 [Q931]. It also defines a user-to-user signalling supplementary 119 service, which uses the information elements / parameters in the 120 signalling channel to carry additional data, but which is used in 121 conjunction with the establishment of a related circuit-switched 122 connection. This reuses the same information elements / parameters 123 as the user signalling bearer service, with the addition of other 124 signalling information, and for DSS1 this is specified in ITU-T 125 Recommendation Q.957.1 [Q957.1]. 127 ISDN defines three variants of the user-to-user signalling 128 supplementary service as follows: 130 UUS1: User-to-user information exchanged during the setup and 131 clearing phases of a call, by transporting User-to-user 132 information element within call control messages. This in itself 133 has two subvariants, UUS1 implicit and UUS1 explicit. UUS1 134 explicit uses additional supplementary service control information 135 to control the request and granting of the service, as in UUS2 and 136 UUS3. In UUS1 implicit, it is the presence of the user signalling 137 data itself that constitutes the request for the service. UUS1 138 explicit as a result also allows the requester to additionally 139 specify whether the parallel circuit-switched connection should 140 proceed if the UUS1 service cannot be provided (preferred or 141 required); 143 UUS2: User-to-user information exchanged from the sender's point of 144 view during call establishment, between the DSS1 ALERTING and DSS1 145 CONNECT messages, within DSS1 USER INFORMATION messages; and 147 UUS3: User-to-user information exchanged while a call is in the 148 Active state, within DSS1 USER INFORMATION messages. 150 The service is always requested by the calling user. 152 This document defines only the provision of the ISDN UUS1 implicit 153 supplementary service to interworking scenarios, this being the most 154 widely deployed and used of the various ISDN user-to-user services, 155 and indeed the one that matches the requirements specified in RFC 156 6567 [RFC6567]. 158 The above come from the ISDN specifications defined for public 159 networks. There are a parallel set of ISDN specifications defined 160 for private networks (QSIG}. These specifications do not define a 161 UUS1 implicit supplementary service. However, implementation of such 162 a UUS1 implicit supplementary service for private networks can 163 readily be constructed in a proprietary fashion based on the 164 specifications for public networks, and evidence suggests that some 165 vendors have done so. On this basis, there is no reason why this 166 package cannot also be used to support interworking with such a 167 private network service, on the assumption that the constraints are 168 exactly the same as those for the public network. 170 The ISDN UUS1 service has the following additional characteristics as 171 to the data that can be transported: 173 The maximum number of octets of user information that can be 174 transported in 128 octets plus a protocol discriminator. It is 175 noted that some early ISDN implementations had a limitation of 32 176 octets, but it is understood that these are not currently 177 deployed. While this package does not prohibit longer data 178 fields, the mechanism at any interworking point is to discard data 179 elements that are too long to handle. The handled length can 180 normally be assumed to be 128 octets. 182 The content of the user information octets is described by a 183 single octet protocol discriminator (see table 4-26 of ITU-T 184 Recommendation Q.931) [Q931]. That protocol descriminator may 185 describe the protocol used within the user data, the structure of 186 the user data, or leave it entirely open. Note that not all 187 values within the protocol discriminator necessarily make sense 188 for use in the user to user service, as the content is aligned 189 with the protocol discriminator that appears at the start of all 190 DSS1 messages (see table 4-1 of ITU-T Recommendation Q.931) 191 [Q931]. The protocol discriminator value has no impact on the 192 interworking capability. 194 Only a single user information can be transported in each message. 196 The ISDN service works without encryption or integrity protection. 197 The user trusts the intermediate network elements, and therefore 198 the operator of those elements, not to modify the data, and to 199 deliver all the data to the remote user. On a link by link basis, 200 message contents are protected at layer 2 by standard CRC 201 mechanisms - this allows loss on a link level basis to be 202 detected, but does not guard against fraudulent attacks on the 203 link itself. This does not prevent the use of additional 204 encryption or integrity protection within the UUI data itself, 205 although the limit on the size of the UUI data (protocol 206 discriminator plus 128 octets) will restrict this. 208 3.2. Impacts of the ISDN service on SIP operation 210 The ISDN service has the following impacts that need to be understood 211 within the SIP environment. 213 Call transfer ISDN call transfer cancels all user-to-user 214 supplementary services. In the ISDN, if user-to-user data is 215 required after call transfer, then UUS3 has to be renegotiated, 216 which is not provided by this SIP extension. The impact of this 217 restriction on the SIP environment is that UUI header fields 218 cannot be exchanged in transactions clearing down the SIP dialog 219 after call transfer has occurred. 221 Conference ISDN conferencing allows the user to still exchange user- 222 to-user data after the conference is created. As far as UUS1 is 223 concerned, it is not permitted. 225 The ISDN three-party supplementary service is similar in many ways 226 to conferencing, but is signalled using a different mechanism. 227 This means that on clearing, the controller using UUS1 implicit 228 does have the choice of sending data to either or both remote 229 users. Because SIP conferencing cannot completely emulate the 230 ISDN three-party supplementary service at the served user, UUS1 231 implicit is not possible. 233 Diversion When ISDN diversion occurs, any UUS1 user-to-user data is 234 sent to the forwarded-to-user (assuming that the call meets 235 requirements for providing the service - this is impacted by the 236 explicit service only). If the type of diversion is such that the 237 call is also delivered to the forwarding user, they will also 238 receive any UUS1 user-to-user data. 240 4. Relation to SIP-T 242 A method of transport of ISDN UUI is to use SIP-T [RFC3372] and 243 transport the UUI information end-to-end, as part of an ISUP message 244 or QSIG message) as a MIME body. If the SIP-T method of 245 encapsulation of ISDN instead of interworking is used, this is a 246 reasonable mechanism and does not require any extensions to existing 247 SIP-T. However, if true ISDN interworking is being done, this 248 approach is not reasonable. Instead, the better approach is to 249 interwork the ISDN UUI using the native SIP UUI transport mechanism, 250 the User-to-User header field. The rest of this document describes 251 this approach. 253 5. Transition away from ISDN 255 This interworking usage of the SIP UUI mechanism will likely begin 256 with one User Agent being an ISDN gateway while the other User Agent 257 is a native SIP endpoint. As networks transition away from ISDN, it 258 is possible that both User Agents could become native SIP endpoints. 259 In this case, there is an opportunity to transition away from this 260 ISDN usage to a more general usage of [I-D.ietf-cuss-sip-uui]. 262 The SIP UUI mechanism provides a way to achieve this transition. As 263 an endpoint moves from being an ISDN gateway to a native SIP 264 endpoint, and a package for some form of enhanced UUI has been 265 standardized, the endpoint can carry the UUI data both as ISDN and as 266 some other package in parallel, and in the same messages or in 267 different messages depending on the needs of the application. This 268 will permit the other endpoint to use the UUI according to the ISDN 269 package if it is an ISDN gateway or the enhanced package if it is a 270 native SIP endpoint. 272 6. ISDN Usage of the User-to-User Header Field 274 This document defines the package for the ISDN interworking of UUI 275 which is to interoperate with ISDN User to User Signaling (UUS), a 276 supplementary service in which the user is able to send/receive a 277 limited amount of information to/from another ISDN user over the 278 signalling channel in association with a call to the other ISDN user. 280 Two examples of ISDN UUI with redirection (transfer and diversion) 281 are defined in [ANSII] and [ETSI]. 283 One objective of the design of this package has been to keep the 284 functionality at the interworking point as simple as possible. 285 Therefore responsibility for respecting the limits has been 286 transferred to the end UA. If an interworking point is reached, and 287 the limitations are not met, then the UUI data will not be 288 transferred, although the SIP request will otherwise be interworked. 289 As a result there is also only one encoding value specified. 291 The general principals of this package of the UUI mechanism are 292 therefore as follows: 294 That the sending application is expected to limit their sending 295 requirements to the subset provided by the ISDN UUI service. 297 That the SIP UA will not allow the reception of more that one 298 User-to-User header field relating to the "isdn-uui" package in 299 the same SIP request or response, and will only allow it in a 300 request or response of the appropriate method (INVITE or BYE). 301 What happens to User-to-User header fields relating to different 302 packages is outside the scope of this document. 304 That an interworking point trying to interwork UUI data that is 305 too long will discard the UUI data, but proceed with the 306 interworking. There is no notification of such discard back to 307 the sending user. If the SIP user knows that it is interworking 308 with the ISDN, then the UUI application at the SIP endpoint should 309 limit its communication to 128 octet packets plus the protocol 310 discriminator, in the knowledge that discard will occur if it does 311 not. The UUI application at the SIP endpoint has complete control 312 over what occurs. It should be noted that this was exactly the 313 envisaged operation when early ISDN implementations that only 314 supported 32 octets interworked with those supporting 128 octets. 315 It also corresponds to the interworking with ISDNs that do not 316 support the supplementary service at all, as discard will occur in 317 these circumstances as well. Note that failure to include the 318 user-user data into the ISDN SETUP message (when discard occurs) 319 will result in the service being unavailable for the remainder of 320 the call when UUS1 implicit operation is used. 322 7. UAC requirements 324 The UAC MUST meet the requirements of [I-D.ietf-cuss-sip-uui] in 325 addition to the requirements defined in this document. 327 The UAC MUST only use this package of the UUI mechanism extension in 328 association with the initial INVITE method and the BYE method 329 relating to an INVITE dialog. Usage on transactions associated with 330 any other type of dialog, or on methods not associated with a dialog 331 is precluded. Usage on other methods within the INVITE dialog, and 332 on re-INVITE transactions with the INVITE dialog, is also precluded. 334 If the UAC wishes to use or permit the sending of UUI data at any 335 point in the dialog, the UAC MUST include in the INVITE request for 336 that dialog a User-to-User header field. The UAC SHOULD set the 337 "purpose" header field parameter to "isdn-uui". Non-inclusion of the 338 "purpose" header field parameter is permitted, but this is primarily 339 to allow earlier implementations to support this package. This 340 initial header field constitutes the implicit request to use the UUI 341 service, and is therefore included even when there is no data except 342 the protocol discriminator octet to send at that point in time. 344 The UAC MUST NOT include the User-to-User header field with a 345 "purpose" header field parameter set to "isdn-uui", or with no 346 "purpose" header field parameter", in any message of an INVITE dialog 347 if the original INVITE request did not include the User-to-User 348 header field, either with a "purpose" header field parameter set to 349 "isdn-uui", or with no "purpose" header field parameter included. 351 When sending UUI for the ISDN package, if the "purpose" header field 352 is included, the UAC MUST set the User-to-User "purpose" header field 353 parameter to "isdn-uui". The UAC MUST NOT include more than one 354 User-to-User header field for this package in any SIP request or 355 response. 357 When receiving UUI, when multiple User-to-User header fields are 358 received in the same response with the "purpose" header field 359 parameter to "isdn-uui", or with no "purpose" header field parameter, 360 or with some combination of these, the UAS MUST discard all these 361 header fields. There are no mechanisms for determining which was the 362 intended data packet so all are discarded. 364 The application designer will need to take into account the ISDN 365 service restrictions; failure to do so can result in information 366 being discarded at any interworking point with the ISDN. This 367 document makes no further normative requirements based on those 368 constraints, because those constraints may vary from one ISDN to 369 another. It is reasonable to expect that a limitation of 128 octets 370 (plus a protocol discriminator) can be imposed by the ISDN, and 371 therefore UUI data longer than this will never reach the destination 372 if such interworking occurs. Note that the 128 octet limit (plus a 373 protocol discriminator) applies before the encoding (or after the 374 decoding) using the "hex" encoding. The "hex" encoding is defined in 375 [I-D.ietf-cuss-sip-uui]. 377 [I-D.ietf-cuss-sip-uui] defines a "uui" option tag for use with the 378 UUI mechanism extension. Because for the ISDN UUI service, the 379 service is service 1 implicit, the inclusion of the "uui" option tag 380 in a Supported header field conveys no additional information over 381 and above the presence of the User-to-User header field with the 382 "purpose" header field parameter to "isdn-uui" in the INVITE request. 383 While there is no harm in including the "uui" option tag, and 384 strictly it should be included if the extension is supported, it 385 performs no function. The presence of the "uui" option tag in the 386 Require header field of an INVITE request will cause the request to 387 fail if it reaches a UAS or ISDN interworking gateway that does not 388 support this extension; such a usage is not precluded although it 389 does not form part of the package. 391 8. UAS requirements 393 The UAS MUST meet the requirements of [I-D.ietf-cuss-sip-uui] in 394 addition to the requirements defined in this document. 396 The UAS MUST only use this package of the UUI mechanism extension in 397 association with the initial INVITE method and the BYE method 398 relating to an INVITE dialog. Usage on transactions associated with 399 any other type of dialog, or on methods not associated with a dialog 400 is precluded. Usage on other methods within the INVITE dialog, and 401 on re-INVITE transactions with the INVITE dialog, is also precluded. 403 The UAS MUST NOT include the User-to-User header field with a 404 "purpose" header field parameter set to "isdn-uui", or with no 405 "purpose" header field parameter", in any message of an INVITE dialog 406 if the original INVITE request did not include the User-to-User 407 header field, either with a "purpose" header field parameter set to 408 "isdn-uui", or with no "purpose" header field parameter included. 410 The UAS MAY include the User-to-User header field in responses to the 411 initial INVITE request, or the BYE requests or responses for the 412 dialog, only where the original INVITE request included a User-to- 413 User header field with the "purpose" header field parameter to "isdn- 414 uui", or where no "purpose" header field parameter was included. 415 When sending UUI for the ISDN package, the UAS SHOULD set the User- 416 to-User "purpose" header field parameter to "isdn-uui". Non- 417 inclusion of the "purpose" header field parameter is permitted, but 418 this is primarily to allow earlier implementations to support this 419 package. The UAS MUST NOT include more than one User-to-User header 420 field for this package in any SIP request or response. 422 Where the UAS is acting as a redirect server, the UAS MUST NOT 423 include the User-to-User header field in the header URI parameter in 424 a 3xx response to an incoming request. 426 When receiving UUI, when a User-to-User header field is received in a 427 request that is not from the originating user with the "purpose" 428 header field parameter to "isdn-uui", or with no "purpose" header 429 field parameter, the UAC MUST discard this header field. 431 When receiving UUI, when multiple User-to-User header fields are 432 received from the originating user in the same request with the 433 "purpose" header field parameter to "isdn-uui", or with no "purpose" 434 header field parameter, or with some combination of these, the UAC 435 MUST discard all these header fields. There are no mechanisms for 436 determining which was the intended data packet so all are discarded. 438 9. UUI contents 440 These requirements apply when the "purpose" header field parameter is 441 set to "isdn-uui", or with no "purpose" header field parameter. 442 Processing for User-to-User header fields sent or received with 443 values other than this value are outside the scope of this document, 444 and the appropriate package document for that value applies. 446 The default and only content defined for this package is "isdn-uui". 447 When sending UUI, the sending SIP entity MAY, but need not, include a 448 "content" header field with a value set to "isdn-uui". A receiving 449 SIP entity MUST ignore a received User-to-User header field if the 450 "content" header field parameter is present and the value is some 451 other value that "isdn-uui". 453 The default and only encoding defined for this package is "hex". 454 When sending UUI, the sending SIP entity MAY, but need not, include 455 an "encoding" header field with a value set to "hex". A receiving 456 SIP entity MUST ignore a received User-to-User header field if the 457 "encoding" header field parameter is present and the value is some 458 other value that "hex". 460 When sending UUI, the sending application MUST include a protocol 461 discriminator octet, conforming to table 4-26 of ITU-T Recommendation 462 Q.931 [Q931] as the first octet of the UUI data. It is up to the 463 receiving application what it does with this value. This document 464 places no other normative requirement on the use of the protocol 465 discriminator; it is required at interworking gateways to allow 466 mapping into the appropriate fields in the ISDN protocols, but 467 otherwise the usage is entirely up to the application, and outside 468 the scope of this document. Valid values are identified and 469 documented by ITU-T, and there is no IANA registry for these values. 471 10. Considerations for ISDN interworking gateways 473 ISDN interworking gateways MUST support the requirements defined for 474 UAS and UAC operation. 476 ISDN interworking gateways MUST support only the "isdn-uui" package 477 on dialogs that are interworked. 479 ISDN interworking gateways will take octet structured data from the 480 ISDN side and encode it using the "hex" encoding scheme defined in 481 [I-D.ietf-cuss-sip-uui] for inclusion as the uui-data in the User-to- 482 User header field. In the reverse direction, it will take valid uui- 483 data according to the "hex" encoding scheme, and decode it to octet 484 structured data for sending to the ISDN side. 486 When mapping data content from the ISDN to the SIP signalling, or 487 from SIP signalling to the ISDN, the gateway needs to assume that all 488 content is octet structured binary, irrespective of the value of the 489 received protocol discriminator. There are no requirements in the 490 ISDN to ensure that the content matches the value of the protocol 491 discriminator, and it is for the application usage to sort out any 492 discrepancy. The same applies to the ISDN protocol discrimination 493 defined table 4-26 of ITU-T Recommendation Q.931 [Q931] as the first 494 octet of the UUI data; the interworking gateway will not perform any 495 additional checking of this value. 497 [I-D.ietf-cuss-sip-uui] defines a "uui" option tag for use with the 498 UUI mechanism extension. The option tag is not interworked at an 499 ISDN interworking gateway. The ISDN interworking gateways MUST NOT 500 take the omission of the "uui" option tag in a received INVITE 501 request to indicate that interworking of a received header field is 502 not to be performed. 504 11. Coding requirements 506 This document defines "isdn-uui" as a new value of the User-to-User 507 "purpose" header field parameter. The following ABNF adds to the 508 production in [I-D.ietf-cuss-sip-uui] 510 pkg-param-value =/ "isdn-uui" 512 This document defines "isdn-uui" as a new value of the User-to-User 513 "content" header field parameter. A content value of "isdn-uui" 514 indicates that the contents have a first octet that is a protocol 515 discriminator (see table 4-26 of ITU-T Recommendation Q.931) [Q931] 516 followed by uui-data that can be subject to a length limitation 517 (before encoding or after decoding) that is generally 128 octets. 518 The following ABNF adds to the production in [I-D.ietf-cuss-sip-uui] 520 cont-param-value =/ "isdn-uui" 522 12. Media Feature Tag 524 This document defines a new media feature tag "sip.uui-isdn". This 525 feature tag indicates that this UUI package is supported by the 526 sender, and its usage is entirely in accordance with RFC 3840 527 [RFC3840]. This document makes no additional provisions for the use 528 of this feature tag. 530 13. IANA Considerations 532 This document adds the following row to the "UUI packages" sub- 533 registry of the SIP parameter registry: 535 Value: isdn-uui 537 Description: The associated application is being used with 538 constraints suitable for interworking with the ISDN user-to-user 539 service, and therefore can be interworked at ISDN gateways. 541 Reference: RFCXXXX 543 Contact: 545 This document adds the following row to the "UUI content" subregistry 546 of the SIP parameter registry: 548 Value: isdn-uui 550 Description: The associated contents conforms to the content 551 associated with the ISDN user-to-user service. In the presence of 552 the "purpose" header field parameter set to "isdn-uui" (or the 553 absence of any "purpose" header field parameter) this is the 554 default meaning and therefore need not be included in this case. 556 Reference: RFCXXXX 558 Contact: 560 This document defines the following media feature tag which is added 561 to the features.sip-tree of the Media Feature tags registry: 563 Media feature-tag name: sip.uui-isdn 565 ASN.1 Identifier: 1.3.6.1.8.4.x 567 Summary of the media feature indicated by this tag: This media 568 feature-tag when used in a Contact header field of a SIP request 569 or a SIP response indicates that the entity sending the SIP 570 message supports the UUI package "uui-isdn". 572 Values appropriate for use with this feature-tag: none 574 Examples of typical use: Indicating that a mobile phone supports 575 SRVCC for calls in alerting phase. 577 Related standards or documents: RFCXXXX 579 Security Considerations: Security considerations for this media 580 feature-tag are discussed in section 11.1 of RFC 3840 [RFC3840] 582 Editor's Note: [RFCXXXX] should be replaced with the designation of 583 this document. 585 14. Security Considerations 587 This document contains no specific requirements in regard to security 588 over and above those specified in [I-D.ietf-cuss-sip-uui]. The 589 overlying use case will define the security measures required. The 590 underlying user-to-user extension provides a number of tools that can 591 meet certain security requirements. As a level of guidance, data 592 that is used to assist in selecting which SIP UA should respond to 593 the call would not be expected to carry any higher level of security 594 than a media feature tag. Information that might otherwise reveal 595 private information about an individual, or where a level of 596 authenticity needs to be guaranteed, may need a higher level of 597 protection, and may indeed not be suitable for this package, 598 particularly taking into account the statement in the following 599 paragraph. 601 As this capability is defined to interwork with the ISDN, if the ISDN 602 forms part of the route, any usage needs to assume that the security 603 level of the ISDN is the highest level of security available. As the 604 ISDN security is itself not definable on an end-to-end basis, this 605 can be an unknown quantity. This is because ISDN security exists on 606 a hop-by-hop basis, and is only as secure as the least secure 607 component. This can be high in some places (e.g. it can require 608 physical access to a secure building) and in other places it can be 609 low (e.g. the point where an ISDN access enters a building). If this 610 level of security is not sufficient, then either a different user-to- 611 user package, or indeed, a different method of data transfer, needs 612 to be selected by the application user. 614 15. Acknowledgements 616 Joanne McMillen was a major contributor and co-author of earlier 617 versions of this document. 619 Thanks to Spencer Dawkins, Vijay Gurbani, and Laura Liess for their 620 review of earlier versions of this document. The authors wish to 621 thank Francois Audet, Denis Alexeitsev, Paul Kyzivat, Cullen 622 Jennings, Mahalingam Mani and Celine Serrut-Valette for their 623 comments. 625 16. Changes since previous versions 627 Note to RFC editor: This section is to be deleted before final 628 publication. 630 Changes since made in the creation of the 631 draft-ietf-cuss-sip-uui-isdn-05 version from the 632 draft-ietf-cuss-sip-uui-isdn-04 version. 634 ABNF provided for definition of values of package and content to 635 correspond to ABNF in current version of [I-D.ietf-cuss-sip-uui] 637 Changes since made in the creation of the 638 draft-ietf-cuss-sip-uui-isdn-04 version from the 639 draft-ietf-cuss-sip-uui-isdn-03 version. 641 Change of the "package" header field parameter back to the 642 "purpose" header field parameter in alignment with change in 643 draft-ietf-cuss-sip-uui. 645 Identification of the package name in the abstract. 647 Minor change to IANA registration of "content" header field 648 parameter value to align with main text such that absence of 649 "package" header field parameter and absence of "content" header 650 field parameter implies this package and therefore this content, 651 as a default. 653 Changes since made in the creation of the 654 draft-ietf-cuss-sip-uui-isdn-03 version from the 655 draft-ietf-cuss-sip-uui-isdn-02 version. 657 Clarification added that the default content is "isdn-uui". 659 Clarification added that the default encoding is "hex". 661 Changeout of "payload" terminology to "UUI data". 663 Changes since made in the creation of the 664 draft-ietf-cuss-sip-uui-isdn-02 version from the 665 draft-ietf-cuss-sip-uui-isdn-01 version. 667 The inclusion of the "package" header field parameter has be 668 downgraded to "RECOMMENDED", with the purpose stated as being for 669 interworking. Changes have been made to the procedures at the 670 receiving side to allow for the non-inclusion of the "package" 671 header field parameter. The effect of this is that the absence of 672 the "package" header field parameter means by default the use of 673 the "uui-isdn" package. 675 Clarification that the package is not to be used on re-INVITE 676 transactions or on other transations within an INVITE dialog. 678 Further clarification on using this package in conjunction with 679 other packages. 681 Closure of the remaining open issue relating to use of UUS1 in 682 conjunction with the ISDN conference service - UUS1 is not 683 possible after the conference is created. 685 A number of editorial changes have been made. 687 Changes since made in the creation of the 688 draft-ietf-cuss-sip-uui-isdn-01 version from the 689 draft-ietf-cuss-sip-uui-isdn-00 version. 691 QSIG does not define a UUS service. As such changes are made to 692 indicate that it is possible to support a proprietary service on 693 QSIG based on the public ISDN standards, and interworking with 694 such proprietary versions is supported. The associated 695 contributors note regarding interactions with other QSIG services 696 has therefore been removed with this amendment. 698 Added additional paragraph above the objectives of the 699 interworking design. 701 Made clear that the 128 octets apply before encoding in "hex". 702 Reference added to the generic UUI document for the ecoding of 703 "hex". 705 Indicated that it is the "content" header field parameter set to 706 "isdn-uui" that defines the structure of the uui-data, with the 707 first octet being a protocol discriminator and the remaining 708 octets potentially being limited to 128 octets. 710 Aligned the IANA registration section with the registries created 711 by the generic UUI document. 713 Added reference to the generic UUI document to the security 714 considerations section. 716 Changes since made in the creation of the 717 draft-ietf-cuss-sip-uui-isdn-00 version from the 718 draft-drage-cuss-sip-uui-isdn-01 version. 720 Removed overburdening of the word "application". Changed the name 721 of the "app" header field parameter in the mechanism draft to 722 "package" header field parameter. This had a consequential impact 723 on the ISDN document. The word "application" is now solely 724 reserved for the name of the functionality that passes the UUI to 725 the SIP functionality to send, and to which the UUI is delivered 726 on receipt by the SIP functionality. As well as the change of the 727 name of the header field parameter, this resulted in a number of 728 instances of the word "application" becoming "package". A couple 729 of instances relating to the coding of the "content" header field 730 parameter have become "SIP entity". 732 Section 5 needed substantial rewording as it no longer applied in 733 this manner. Modified the text to indicate that if one wants to 734 use an enhanced UUI where both endpoints are SIP, but still work 735 with the ISDN, then one will have to same information using two 736 different packages, one the ISDN one, and the other some enhanced 737 package. 739 In section 8, a couple of requirements relating to the "content" 740 header field parameter really related to the "package" header 741 field parameter (formerly "app" header field parameter). These 742 are corrected. 744 Updated references from "draft-johnston-cuss-sip-uui" to 745 "draft-ietf-cuss-sip-uui". 747 Made clear throughout the document that the UUI payload is a 748 protocol discriminator plus 128 octets of data. 750 Made clearer that it is the initial INVITE request and responses 751 and the BYE request and responses only that carry the information 752 in this package. 754 Made clear that there are no normative requirements on the 755 protocol discriminator. In particular text is added to the end of 756 section 9. 758 Removed the following text from section 7, as it is a duplicate of 759 the text in section 9: 761 " When sending UUI, the sending application MUST include a 762 protocol discriminator octet, conforming to table 4-26 of ITU-T 763 Recommendation Q.931 [Q931] as the first octet of the payload 764 information." 766 Defined a media feature tag specific for the package. It has been 767 proposed to do this for all packages. "sip.uui-isdn" has been 768 added. 770 Corrected the short title for the draft. 772 Changes since made in the creation of the 773 draft-drage-cuss-sip-uui-isdn-01 version from the 774 draft-drage-cuss-sip-uui-isdn-00 version. 776 Closure of a number of open issues identified in the -00 version 777 and the creation of appropriate procedures for the UAC, the UAS, 778 and the ISDN interworking gateway. 780 17. References 781 17.1. Normative References 783 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 784 Requirement Levels", BCP 14, RFC 2119, March 1997. 786 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 787 A., Peterson, J., Sparks, R., Handley, M., and E. 788 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 789 June 2002. 791 [RFC3372] Vemuri, A. and J. Peterson, "Session Initiation Protocol 792 for Telephones (SIP-T): Context and Architectures", 793 BCP 63, RFC 3372, September 2002. 795 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 796 "Indicating User Agent Capabilities in the Session 797 Initiation Protocol (SIP)", RFC 3840, August 2004. 799 [I-D.ietf-cuss-sip-uui] 800 Johnston, A. and J. Rafferty, "A Mechanism for 801 Transporting User to User Call Control Information in 802 SIP", draft-ietf-cuss-sip-uui-10 (work in progress), 803 April 2013. 805 [Q931] "ITU-T Recommendation Q.931: Digital subscriber Signalling 806 System No. 1 - Network layer; ISDN user-network interface 807 layer 3 specification for basic call control", 808 http://www.itu.int/rec/T-REC-Q.931-199805-I/en . 810 17.2. Informative References 812 [RFC6567] Johnston, A. and L. Liess, "Problem Statement and 813 Requirements for Transporting User-to-User Call Control 814 Information in SIP", RFC 6567, April 2012. 816 [Q957.1] "ITU-T Recommendation Q.957.1: Digital subscriber 817 Signalling System No. 1 - Stage 3 description for 818 supplementary services using DSS 1; Stage 3 description 819 for additional information transfer supplementary services 820 using DSS 1: User-to-User Signalling (UUS)", 821 http://www.itu.int/rec/T-REC-Q.957.1-199607-I . 823 [Q763] "ITU-T Q.763 Signaling System No. 7 - ISDN user part 824 formats and codes", 825 http://www.itu.int/rec/T-REC-Q.931-199805-I/en . 827 [ANSII] "ANSI T1.643-1995, Telecommunications-Integrated Services 828 Digital Network (ISDN)-Explicit Call Transfer 829 Supplementary Service". 831 [ETSI] "ETSI ETS 300 207-1 Ed.1 (1994), Integrated Services 832 Digital Network (ISDN); Diversion supplementary 833 services". 835 Authors' Addresses 837 Keith Drage (editor) 838 Alcatel-Lucent 839 Quadrant, Stonehill Green, Westlea 840 Swindon 841 UK 843 Email: keith.drage@alcatel-lucent.com 845 Alan Johnston 846 Avaya 847 St. Louis, MO 63124 848 United States 850 Email: alan.b.johnston@gmail.com