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Johnston 5 Expires: April 3, 2012 Avaya 6 October 2011 8 Interworking ISDN Call Control User Information with SIP 9 draft-ietf-cuss-sip-uui-isdn-01 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 of the User-to-User header field to enable 21 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 Status of this Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at http://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on April 3, 2012. 44 Copyright Notice 46 Copyright (c) 2011 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (http://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 62 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 63 3. Summary of the ISDN User-to-User Service . . . . . . . . . . . 3 64 3.1. The service . . . . . . . . . . . . . . . . . . . . . . . 3 65 3.2. Impacts of the ISDN service on SIP operation . . . . . . . 5 66 4. Relation to SIP-T . . . . . . . . . . . . . . . . . . . . . . 6 67 5. Transition away from ISDN . . . . . . . . . . . . . . . . . . 6 68 6. ISDN Usage of the User-to-User Header Field . . . . . . . . . 7 69 7. UAC requirements . . . . . . . . . . . . . . . . . . . . . . . 8 70 8. UAS requirements . . . . . . . . . . . . . . . . . . . . . . . 9 71 9. UUI contents . . . . . . . . . . . . . . . . . . . . . . . . . 10 72 10. Considerations for ISDN interworking gateways . . . . . . . . 11 73 11. Coding requirements . . . . . . . . . . . . . . . . . . . . . 11 74 12. Media Feature Tag . . . . . . . . . . . . . . . . . . . . . . 12 75 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 76 14. Security Considerations . . . . . . . . . . . . . . . . . . . 13 77 15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 78 16. Changes since previous versions . . . . . . . . . . . . . . . 14 79 17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 80 17.1. Normative References . . . . . . . . . . . . . . . . . . . 16 81 17.2. Informative References . . . . . . . . . . . . . . . . . . 16 82 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 84 1. Terminology 86 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 87 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 88 document are to be interpreted as described in BCP 14, RFC 2119 89 [RFC2119]. 91 2. Overview 93 This document describes a usage of the User-to-User header field 94 defined in [I-D.ietf-cuss-sip-uui] to enable the transport of User to 95 User Information (UUI) in ISDN interworking scenarios using SIP 96 [RFC3261]. Specifically, this document discuss the interworking of 97 call control related ITU-T DSS1 User-user information element [Q931], 98 [Q957.1] and ITU-T Q.763 User-to-user information parameter [Q763] 99 data in SIP. UUI is widely used in the PSTN today in contact centers 100 and call centers which are transitioning away from ISDN to SIP. 102 This usage is not limited to scenarios where interworking will occur. 103 Rather it describes a usage where interworking is possible if 104 interworking is met. That does not preclude its usage directly 105 between two SIP terminals. 107 3. Summary of the ISDN User-to-User Service 109 3.1. The service 111 ISDN defines a number of related services. Firstly there is a user 112 signalling bearer service, which uses the information elements / 113 parameters in the signalling channel to carry the data, and does not 114 establish a related circuit-switched connection. For DSS1, this is 115 specified in ITU-T Recommendation Q.931 section 3.3 and section 7 116 [Q931]. It also defines a user-to-user signalling supplementary 117 service, which uses the information elements / parameters in the 118 signalling channel to carry additional data, but which is used in 119 conjunction with the establishment of a related circuit-switched 120 connection. This reuses the same information elements / parameters 121 as the user signalling bearer service, with the addition of other 122 signalling information, and for DSS1 this is specified in ITU-T 123 Recommendation Q.957.1 [Q957.1]. 125 ISDN defines three variants of the user-to-user signalling 126 supplementary service as follows: 128 UUS1: User-to-user information exchanged during the setup and 129 clearing phases of a call, by transporting User-to-user 130 information element within call control messages. This in itself 131 has two subvariants, UUS1 implicit and UUS1 explicit. UUS1 132 explicit uses additional supplementary service control information 133 to control the request and granting of the service, as in USS2 and 134 UUS3. In UUS1 implicit, it is the presence of the user signalling 135 data itself that constitutes the request for the service. UUS1 136 explicit as a result also allows the requester to additionally 137 specify whether the parallel circuit-switched connection should 138 proceed if the UUS1 service cannot be provided (preferred or 139 required). 141 UUS2: User-to-user information exchanged from the sender's point of 142 view during call establishment, between the DSS1 ALERTING and DSS1 143 CONNECT messages, within DSS1 USER INFORMATION messages; and 145 UUS3: User-to-user information exchanged while a call is in the 146 Active state, within DSS1 USER INFORMATION messages. 148 The service is always requested by the calling user. 150 This document defines only the provision of the ISDN UUS1 implicit 151 supplementary service to interworking scenarios, this being the most 152 widely deployed and used of the various ISDN user-to-user services, 153 and indeed the one that matches the requirements specified in 154 draft-ietf-cuss-sip-uui-reqs [I-D.ietf-cuss-sip-uui-reqs]. 156 The above come from the ISDN specifications defined for public 157 networks. There are a parallel set of ISDN specifications defined 158 for private networks (QSIG}. These specifications do not define a 159 UUS1 implicit supplementary service. However, implementation of such 160 a UUS1 implicit supplementary service for private networks can 161 readily be constructed in a proprietary fashion based on the 162 specifications for public networks, and evidence suggests that some 163 vendors have done so. On this basis, there is not reason why this 164 package cannot also be used to support interworking with such a 165 private network service, on the assumption that the constraints are 166 exactly the same as those for the public network. 168 The ISDN UUS1 service has the following additional characteristics as 169 to the data that can be transported: 171 The maximum number of octets of user information that can be 172 transported in 128 octets plus a protocol discriminator. It is 173 noted that some early ISDN implementations had a limitation of 32 174 octets, but it is understood that these are not currently 175 deployed. While this package does not prohibit longer data 176 fields, the mechanism at any interworking point is to discard data 177 elements that are too long to handle. The handled length can 178 normally be assumed to be 128 octets. 180 The content of the user information octets is described by a 181 single octet protocol discriminator (see table 4-26 of ITU-T 182 Recommendation Q.931) [Q931]. That protocol descriminator may 183 describe the protocol used within the user data, the structure of 184 the user data, or leave it entirely open. Note that not all 185 values within the protocol discriminator necessarily make sense 186 for use in the user to user service, as the content is aligned 187 with the protocol discriminator that appears at the start of all 188 DSS1 messages (see table 4-1 of ITU-T Recommendation Q.931) 189 [Q931]. The protocol discriminator value has no impact on the 190 interworking capability. 192 Only a single user information package can be transported in each 193 message. 195 The ISDN service works without encryption or integrity protection. 196 The user trusts the intermediate network elements, and therefore 197 the operator of those elements, not to modify the data, and to 198 deliver all the data to the remote user. On a link by link basis, 199 message contents are protected at layer 2 by standard CRC 200 mechanisms - this allows loss on a link level basis to be 201 detected, but does not guard against fraudulent attacks on the 202 link itself. This does not prevent the use of additional 203 encryption or integrity protection within the payload itself, 204 although the limit on the size of the payload (128 octets) will 205 restrict this. 207 3.2. Impacts of the ISDN service on SIP operation 209 The ISDN service has the following impacts that need to be understood 210 within the SIP environment. 212 Call transfer ISDN call transfer cancels all user-to-user 213 supplementary services. In the ISDN, if user-to-user data is 214 required after call transfer, then UUS3 has to be renegotiated, 215 which is not provided by this SIP extension. The impact of this 216 restriction on the SIP environment is that UUI header fields 217 cannot be exchanged in transactions clearing down the SIP dialog 218 after call transfer has occurred. 220 Conference ISDN conferencing allows the user to still exchange user- 221 to-user data after the conference is created. As far as UUS1 is 222 concerned, this means that when an individual party clears, those 223 clearing messages can still contain user-to-user data. As a 224 conferee this is sent to the conference controller. As the 225 conference controller, as this effectively clears the conference, 226 it can be broadcast to all conferees, or sent to individual 227 conferees [OPEN ISSUE - CHECK THIS IN THE PROTOCOL - DOES IT 228 REQUIRE EXPLICIT]. 230 The ISDN three-party supplementary service is similar in many ways 231 to conferencing, but is signalled using a different mechanism. 232 This means that on clearing, the controller using UUS1 implicit 233 does have the choice of sending data to either or both remote 234 users. 236 Diversion When ISDN diversion occurs, any UUS1 user-to-user data is 237 sent to the forwarded-to-user (assuming that the call meets 238 requirements for providing the service - this is impacted by the 239 explicit service only). If the type of diversion is such that the 240 call is also delivered to the forwarding user, they will also 241 receive any UUS1 user-to-user data. 243 4. Relation to SIP-T 245 A method of transport of ISDN UUI is to use SIP-T [RFC3372] and 246 transport the UUI information end-to-end, as part of an ISUP message 247 or QSIG message) as a MIME body. If the SIP-T method of 248 encapsulation of ISDN instead of interworking is used, this is a 249 reasonable mechanism and does not require any extensions to existing 250 SIP-T. However, if true ISDN interworking is being done, this 251 approach is not reasonable. Instead, the better approach is to 252 interwork the ISDN UUI using the native SIP UUI transport mechanism, 253 the User-to-User header field. The rest of this document describes 254 this approach. 256 5. Transition away from ISDN 258 This interworking usage of the SIP UUI mechanism will likely begin 259 with one User Agent being an ISDN gateway while the other User Agent 260 is a native SIP endpoint. As networks transition away from ISDN, it 261 is possible that both User Agents could become native SIP endpoints. 262 In this case, there is an opportunity to transition away from this 263 ISDN usage to a more general usage of [I-D.ietf-cuss-sip-uui]. 265 The SIP UUI mechanism provides a way to achieve this transition. As 266 an endpoint moves from being an ISDN gateway to a native SIP 267 endpoint, and a package for some form of enhanced UUI has been 268 standardized, the endpoint can carry the UUI data both as ISDN and as 269 some other package in parallel. This will permit the other endpoint 270 to use the UUI according to the ISDN package if it is an ISDN gateway 271 or the enhanced package if it is a native SIP endpoint. 273 6. ISDN Usage of the User-to-User Header Field 275 This document defines the package for the ISDN interworking of UUI 276 which is to interoperate with ISDN User to User Signaling (UUS), a 277 supplementary service in which the user is able to send/receive a 278 limited amount of information to/from another ISDN user over the 279 signalling channel in association with a call to the other ISDN 280 user.. 282 Two examples of ISDN UUI with redirection (transfer and diversion) 283 are defined in [ANSII] and [ETSI]. 285 One objective of the design of this package has been to keep the 286 functionality at the interworking point as simple as possible. 287 Therefore responsibility for respecting the limits has been 288 transferred to the end UA. If an interworking point is reached, and 289 the limitations are not met, then the UUI data will not be 290 transferred, although he SIP request will otherwise be interworked. 291 As a result there is also only one encoding value specified. 293 The general principals of this package of the UUI mechanism are 294 therefore as follows: 296 That the sending application is expected limit their sending 297 requirements to the subset provided by the ISDN UUI service. 299 That the SIP UA will not allow the reception of more that one 300 User-to-User header field of the "isdn-uui" package in the same 301 SIP request or response, and will only allow it in a request or 302 response of the appropriate method (INVITE or BYE). What happens 303 to User-to-User header fields relating to different packages is 304 outside the scope of this document. 306 That an interworking point trying to interwork UUI data that is 307 too long will discard the UUI data, but proceed with the 308 interworking. There is no notification of such discard back to 309 the sending user. If the SIP user knows that it is interworking 310 with the ISDN, then the UUI application at the SIP endpoint should 311 limit its communication to 128 octet packets plus the protocol 312 discriminator, in the knowledge that discard will occur if it does 313 not. The UUI application at the SIP endpoint has complete control 314 over what occurs. It should be noted that this was exactly the 315 envisaged operation when early ISDN implementations that only 316 supported 32 octets interworked with those supporting 128 octets. 318 It also corresponds to the interworking with ISDNs that do not 319 support the supplementary service at all, as discard will occur in 320 these circumstances as well. Note that failure to include the 321 user-user data into the ISDN SETUP message (when discard occurs) 322 will result in the service being unavailable for the remainder of 323 the call when UUS1 implicit operation is used. 325 7. UAC requirements 327 The UAC MUST meet the requirements of [I-D.ietf-cuss-sip-uui] in 328 addition to the requirements defined in this document. 330 The UAC MUST only use this package of the UUI mechanism extension in 331 association with the initial INVITE method and the BYE method 332 relating to an INVITE dialog. Usage on transactions associated with 333 any other type of dialog, or on methods not associated with a dialog 334 is precluded. 336 If the UAC wishes to user or permit the sending of UUI data at any 337 point in the dialog, the UAC MUST include in the INVITE request for 338 that dialog a User-to-User header field with an "package" header 339 field parameter set to "isdn-uui". This initial header field 340 constitutes the implicit request to use the UUI service, and is 341 therefore included even when there is no data except the protocol 342 discriminator octet to send at that point in time. 344 The UAC MUST NOT include the User-to-User header field with an 345 "package" header field parameter set to "isdn-uui" in any message of 346 an INVITE dialog if the original INVITE request did not include the 347 User-to-User header field with an "package" header field parameter 348 set to "isdn-uui" 350 When sending UUI for the ISDN package, the UAC MUST set the User-to- 351 User "package" header field parameter to "isdn-uui". The UAC MUST 352 NOT include more than one User-to-User header field for this package 353 in any SIP request or response. 355 When receiving UUI, when multiple User-to-User header fields are 356 received in the same response with the "package" header field 357 parameter to "isdn-uui", the UAS MUST discard all these header 358 fields. There are no mechanisms for determining which was the 359 intended data packet so all are discarded. 361 The application designer will need to take into account the ISDN 362 service restrictions; failure to do so can result in information 363 being discarded at any interworking point with the ISDN. This 364 document makes no further normative requirements based on those 365 constraints, because those constraints may vary from one ISDN to 366 another. It is reasonable to expect that a limitation of 128 octets 367 (plus a protocol discriminator) can be imposed by the ISDN, and 368 therefore payloads longer than this will never reach the destination 369 if such interworking occurs. Note that the 128 octet limit (plus a 370 protocol discriminator) applies before the encoding (or after the 371 decoding) using the "hex" encoding. The "hex" encoding is defined in 372 [I-D.ietf-cuss-sip-uui]. 374 [I-D.ietf-cuss-sip-uui] defines a "uui" option tag for use with the 375 UUI mechanism extension. Because for the ISDN UUI service, the 376 service is service 1 implicit, the inclusion of the "uui" option tag 377 in a Supported header field conveys no additional information over 378 and above the presence of the User-to-User header field with the 379 "package" header field parameter to "isdn-uui" in the INVITE request. 380 While there is no harm in including the "uui" option tag, and 381 strictly it should be included if the extension is supported, it 382 performs no function. The presence of the "uui" option tag in the 383 Require header field of an INVITE request will cause the request to 384 fail if it reaches a UAS or ISDN interworking gateway that does not 385 support this extension; such a usage is not precluded although it 386 does not form part of the package. 388 8. UAS requirements 390 The UAS MUST meet the requirements of [I-D.ietf-cuss-sip-uui] in 391 addition to the requirements defined in this document. 393 The UAS MUST only use this package of the UUI mechanism extension in 394 association with the initial INVITE method and the BYE method 395 relating to an INVITE dialog. Usage on transactions associated with 396 any other type of dialog, or on methods not associated with a dialog 397 is precluded. 399 The UAS MUST NOT include the User-to-User header field with an 400 "package" header field parameter set to "isdn-uui" in any message of 401 an INVITE dialog if the original INVITE request did not include the 402 User-to-User header field with an "package" header field parameter 403 set to "isdn-uui" 405 The UAS MAY include the User-to-User header field in responses to the 406 initial INVITE request, or the BYE requests or responses for the 407 dialog, only where the original INVITE request included a User-to- 408 User header field with the "package" header field parameter to "isdn- 409 uui". When sending UUI for the ISDN package, the UAS MUST set the 410 User-to-User "package" header field parameter to "isdn-uui". The UAS 411 MUST NOT include more than one User-to-User header field for this 412 package in any SIP request or response. 414 Where the UAS is acting as a redirect server, the UAS MUST NOT 415 include the User-to-User header field in the header URI parameter in 416 a 3xx response to an incoming request. 418 When receiving UUI, when a User-to-User header field is received in a 419 request that is not from the originating user with the "package" 420 header field parameter to "isdn-uui", the UAC MUST discard this 421 header fields. 423 When receiving UUI, when multiple User-to-User header fields are 424 received from the originating user in the same request with the 425 "package" header field parameter to "isdn-uui", the UAC MUST discard 426 all these header fields. There are no mechanisms for determining 427 which was the intended data packet so all are discarded. 429 9. UUI contents 431 These requirements apply when the "package" header field parameter is 432 set to "isdn-uui". Processing for User-to-User header fields sent or 433 received with values other than this value are outside the scope of 434 this document, and the appropriate package document for that value 435 applies. 437 When sending UUI, the sending SIP entity MAY, but need not, include a 438 "content" header field with a value set to "isdn-uui". A receiving 439 SIP entity MUST ignore a received User-to-User header field if the 440 "content" header field parameter is present and the value is some 441 other value that "isdn-uui". 443 When sending UUI, the sending SIP entity MAY, but need not, include 444 an "encoding" header field with a value set to "hex". A receiving 445 SIP entity MUST ignore a received User-to-User header field if the 446 "encoding" header field parameter is present and the value is some 447 other value that "hex". 449 When sending UUI, the sending application MUST include a protocol 450 discriminator octet, conforming to table 4-26 of ITU-T Recommendation 451 Q.931 [Q931] as the first octet of the payload information. It is up 452 to the receiving application what it does with this value. This 453 document places no other normative requirement on the use of the 454 protocol discriminator; it is required at interworking gateways to 455 allow mapping into the appropriate fields in the ISDN protocols, but 456 otherwise the usage is entirely up to the application, and outside 457 the scope of this document. Valid values are identified and 458 documented by ITU-T, and there is no IANA registry for these values. 460 10. Considerations for ISDN interworking gateways 462 ISDN interworking gateways MUST support the requirements defined for 463 UAS and UAC operation. 465 ISDN interworking gateways MUST support only the "isdn-uui" package 466 on dialogs that are interworked. 468 ISDN interworking gateways will take octet structured data from the 469 ISDN side and encode it using the "hex" encoding scheme defined in 470 [I-D.ietf-cuss-sip-uui] for inclusion as the uui-data in the User-to- 471 User header field. In the reverse direction, it will take valid uui- 472 data according to the "hex" encoding scheme, and decode it to octet 473 structured data for sending to the ISDN side. 475 When mapping data content from the ISDN to the SIP signalling, or 476 from SIP signalling to the ISDN, the gateway needs to assume that all 477 content is octet structured binary, irrespective of the value of the 478 received protocol discriminator. There are no requirements in the 479 ISDN to ensure that the content matches the value of the protocol 480 discriminator, and it is for the application usage to sort out any 481 discrepancy. The same applies to the ISDN protocol discrimination 482 defined table 4-26 of ITU-T Recommendation Q.931 [Q931] as the first 483 octet of the payload information; the interworking gateway will not 484 perform any additional checking of this value. 486 [I-D.ietf-cuss-sip-uui] defines a "uui" option tag for use with the 487 UUI mechanism extension. The option tag is not interworked at an 488 ISDN interworking gateway. The ISDN interworking gateways MUST NOT 489 take the omission of the "uui" option tag in a received INVITE 490 request to indicate that interworking of a received header field is 491 not to be performed. 493 11. Coding requirements 495 This document defines "isdn-uui" as a new value of the User-to-User 496 "package" header field parameter. 498 This document defines "isdn-uui" as a new value of the User-to-User 499 "content" header field parameter. A content value of "isdn-uui" 500 indicates that the contents have a first octet that is a protocol 501 discriminator (see table 4-26 of ITU-T Recommendation Q.931) [Q931] 502 followed by uui-data that can be subject to a length limitation 503 (before encoding or after decoding) that is generally 128 octets. 505 12. Media Feature Tag 507 This document defines a new media feature tag "sip.uui-isdn". This 508 feature tag indicates that this UUI package is supported by the 509 sender, and its usage is entirely in accordance with RFC 3840 510 [RFC3840]. This document makes no additional provisions for the use 511 of this feature tag. 513 13. IANA Considerations 515 This document adds the following row to the "UUI packages" sub- 516 registry of the SIP parameter registry: 518 Value: isdn-uui 520 Description: The associated application is being used with 521 constraints suitable for interworking with the ISDN user-to-user 522 service, and therefore can be interworked at ISDN gateways. 524 Reference: RFCXXXX 526 Contact: 528 This document adds the following row to the "UUI content" subregistry 529 of the SIP parameter registry: 531 Value: isdn-uui 533 Description: The associated contents conforms to the content 534 associated with the ISDN user-to-user service. In the presence of 535 the "package" header field parameter set to "isdn-uui" this is the 536 default meaning and therefore need not be included in this case. 538 Reference: RFCXXXX 540 Contact: 542 This document defines the following media feature tag which is added 543 to the features.sip-tree of the Media Feature tags registry: 545 Media feature-tag name: sip.uui-isdn 547 ASN.1 Identifier: 1.3.6.1.8.4.x 549 Summary of the media feature indicated by this tag: This media 550 feature-tag when used in a Contact header field of a SIP request 551 or a SIP response indicates that the entity sending the SIP 552 message supports the UUI package "uui-isdn". 554 Values appropriate for use with this feature-tag: none 556 Examples of typical use: Indicating that a mobile phone supports 557 SRVCC for calls in alerting phase. 559 Related standards or documents: RFCXXXX 561 Security Considerations: Security considerations for this media 562 feature-tag are discussed in section 11.1 of RFC 3840 [RFC3840] 564 Editor's Note: [RFCXXXX] should be replaced with the designation of 565 this document. 567 14. Security Considerations 569 This document contains no specific requirements in regard to security 570 over and above those specified in [I-D.ietf-cuss-sip-uui]. The 571 overlying use case will define the security measures required. The 572 underlying user-to-user extension provides a number of tools that can 573 meet certain security requirements. As a level of guidance, data 574 that is used to assist in selecting which SIP UA should respond to 575 the call would not be expected to carry any higher level of security 576 than a media feature tag. Information that might otherwise reveal 577 private information about an individual, or where a level of 578 authenticity needs to be guaranteed, may need a higher level of 579 protection, and may indeed not be suitable for this package, 580 particularly taking into account the statement in the following 581 paragraph. 583 As this capability to is defined to interwork with the ISDN, if the 584 ISDN forms part of the route, any usage needs to assume that the 585 security level of the ISDN is the highest level of security 586 available. As the ISDN security is itself not definable on an end- 587 to-end basis, this can be an unknown quantity. This is because ISDN 588 security exists on a hop-by-hop basis, and is only as secure as the 589 least secure component. This can be high in some places (e.g. it can 590 require physical access to a secure building) and in other places it 591 can be low (e.g. the point where an ISDN access enters a building). 592 If this level of security is not sufficient, then either a different 593 user-to-user package, or indeed, a different method of data transfer, 594 needs to be selected by the application user. 596 15. Acknowledgements 598 Joanne McMillen was a major contributor and co-author of earlier 599 versions of this document. 601 Thanks to Spencer Dawkins, Vijay Gurbani, and Laura Liess for their 602 review of earlier versions of this document. The authors wish to 603 thank Francois Audet, Denis Alexeitsev, Paul Kyzivat, Cullen 604 Jennings, and Mahalingam Mani for their comments. 606 16. Changes since previous versions 608 Note to RFC editor: This section is to be deleted before final 609 publication. 611 Changes since made in the creation of the 612 draft-ietf-cuss-sip-uui-isdn-01 version from the 613 draft-ietf-cuss-sip-uui-isdn-00 version. 615 QSIG does not define a UUS service. As such changes are made to 616 indicate that it is possible to support a proprietary service on 617 QSIG based on the public ISDN standards, and interworking with 618 such proprietary versions is supported. The associated 619 contributors note regarding interactions with other QSIG services 620 has therefore been removed with this amendment. 622 Added additional paragraph above the objectives of the 623 interworking design. 625 Made clear that the 128 octets apply before encoding in "hex". 626 Reference added to the generic UUI document for the ecoding of 627 "hex". 629 Indicated that it is the "content" header field parameter set to 630 "isdn-uui" that defines the structure of the uui-data, with the 631 first octet being a protocol discriminator and the remaining 632 octets potentially being limited to 128 octets. 634 Aligned the IANA registration section with the registries created 635 by the generic UUI document. 637 Added reference to the generic UUI document to the security 638 considerations section. 640 Changes since made in the creation of the 641 draft-ietf-cuss-sip-uui-isdn-00 version from the 642 draft-drage-cuss-sip-uui-isdn-01 version. 644 Removed overburdening of the word "application". Changed the name 645 of the "app" header field parameter in the mechanism draft to 646 "package" header field parameter. This had a consequential impact 647 on the ISDN document. The word "application" is now solely 648 reserved for the name of the functionality that passes the UUI to 649 the SIP functionality to send, and to which the UUI is delivered 650 on receipt by the SIP functionality. As well as the change of the 651 name of the header field parameter, this resulted in a number of 652 instances of the word "application" becoming "package". A couple 653 of instances relating to the coding of the "content" header field 654 parameter have become "SIP entity". 656 Section 5 needed substantial rewording as it no longer applied in 657 this manner. Modified the text to indicate that if one wants to 658 use an enhanced UUI where both endpoints are SIP, but still work 659 with the ISDN, then one will have to same information using two 660 different packages, one the ISDN one, and the other some enhanced 661 package. 663 In section 8, a couple of requirements relating to the "content" 664 header field parameter really related to the "package" header 665 field parameter (formerly "app" header field parameter). These 666 are corrected. 668 Updated references from "draft-johnston-cuss-sip-uui" to 669 "draft-ietf-cuss-sip-uui". 671 Made clear throughout the document that the UUI payload is a 672 protocol discriminator plus 128 octets of data. 674 Made clearer that it is the initial INVITE request and responses 675 and the BYE request and responses only that carry the information 676 in this package. 678 Made clear that there are no normative requirements on the 679 protocol discriminator. In particular text is added to the end of 680 section 9. 682 Removed the following text from section 7, as it is a duplicate of 683 the text in section 9: 685 " When sending UUI, the sending application MUST include a 686 protocol discriminator octet, conforming to table 4-26 of ITU-T 687 Recommendation Q.931 [Q931] as the first octet of the payload 688 information." 690 Defined a media feature tag specific for the package. It has been 691 proposed to do this for all packages. "sip.uui-isdn" has been 692 added. 694 Corrected the short title for the draft. 696 Changes since made in the creation of the 697 draft-drage-cuss-sip-uui-isdn-01 version from the 698 draft-drage-cuss-sip-uui-isdn-00 version. 700 Closure of a number of open issues identified in the -00 version 701 and the creation of appropriate procedures for the UAC, the UAS, 702 and the ISDN interworking gateway. 704 17. References 706 17.1. Normative References 708 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 709 Requirement Levels", BCP 14, RFC 2119, March 1997. 711 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 712 A., Peterson, J., Sparks, R., Handley, M., and E. 713 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 714 June 2002. 716 [RFC3372] Vemuri, A. and J. Peterson, "Session Initiation Protocol 717 for Telephones (SIP-T): Context and Architectures", 718 BCP 63, RFC 3372, September 2002. 720 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 721 "Indicating User Agent Capabilities in the Session 722 Initiation Protocol (SIP)", RFC 3840, August 2004. 724 [I-D.ietf-cuss-sip-uui] 725 Johnston, A. and J. Rafferty, "A Mechanism for 726 Transporting User to User Call Control Information in 727 SIP", draft-ietf-cuss-sip-uui-04 (work in progress), 728 October 2011. 730 [Q931] "ITU-T Recommendation Q.931: Digital subscriber Signalling 731 System No. 1 - Network layer; ISDN user-network interface 732 layer 3 specification for basic call control", 733 http://www.itu.int/rec/T-REC-Q.931-199805-I/en . 735 17.2. Informative References 737 [I-D.ietf-cuss-sip-uui-reqs] 738 Johnston, A. and L. Liess, "Problem Statement and 739 Requirements for Transporting User to User Call Control 740 Information in SIP", draft-ietf-cuss-sip-uui-reqs-07 (work 741 in progress), October 2011. 743 [Q957.1] "ITU-T Recommendation Q.957.1: Digital subscriber 744 Signalling System No. 1 - Stage 3 description for 745 supplementary services using DSS 1; Stage 3 description 746 for additional information transfer supplementary services 747 using DSS 1: User-to-User Signalling (UUS)", 748 http://www.itu.int/rec/T-REC-Q.957.1-199607-I . 750 [Q763] "ITU-T Q.763 Signaling System No. 7 - ISDN user part 751 formats and codes", 752 http://www.itu.int/rec/T-REC-Q.931-199805-I/en . 754 [ANSII] "ANSI T1.643-1995, Telecommunications-Integrated Services 755 Digital Network (ISDN)-Explicit Call Transfer 756 Supplementary Service". 758 [ETSI] "ETSI ETS 300 207-1 Ed.1 (1994), Integrated Services 759 Digital Network (ISDN); Diversion supplementary 760 services". 762 Authors' Addresses 764 Keith Drage (editor) 765 Alcatel-Lucent 766 Quadrant, Stonehill Green, Westlea 767 Swindon 768 UK 770 Email: keith.drage@alcatel-lucent.com 772 Alan Johnston 773 Avaya 774 St. Louis, MO 63124 775 United States 777 Email: alan.b.johnston@gmail.com