idnits 2.17.1 draft-schwarz-mmusic-sdp-for-gw-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 == The document seems to contain a disclaimer for pre-RFC5378 work, but was first submitted on or after 10 November 2008. The disclaimer is usually necessary only for documents that revise or obsolete older RFCs, and that take significant amounts of text from those RFCs. If you can contact all authors of the source material and they are willing to grant the BCP78 rights to the IETF Trust, you can and should remove the disclaimer. Otherwise, the disclaimer is needed and you can ignore this comment. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (May 2, 2016) is 2906 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) == Unused Reference: 'ITU-T H.248.49' is defined on line 349, but no explicit reference was found in the text ** Obsolete normative reference: RFC 2885 (Obsoleted by RFC 3015) ** Obsolete normative reference: RFC 3015 (Obsoleted by RFC 3525) ** Obsolete normative reference: RFC 3525 (Obsoleted by RFC 5125) ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) ** Obsolete normative reference: RFC 4572 (Obsoleted by RFC 8122) -- Duplicate reference: RFC3525, mentioned in 'RFC5125', was also mentioned in 'RFC3525'. ** Obsolete normative reference: RFC 3525 (ref. 'RFC5125') (Obsoleted by RFC 5125) -- Possible downref: Non-RFC (?) normative reference: ref. 'ITU-T H.248.x' -- Possible downref: Non-RFC (?) normative reference: ref. 'ITU-T H.248.1' -- Possible downref: Non-RFC (?) normative reference: ref. 'ITU-T H.248.15' -- Possible downref: Non-RFC (?) normative reference: ref. 'ITU-T H.248.39' -- Possible downref: Non-RFC (?) normative reference: ref. 'ITU-T H.248.49' -- Possible downref: Non-RFC (?) normative reference: ref. 'ITU-T H.248.80' -- Possible downref: Non-RFC (?) normative reference: ref. 'ITU-T H.248.90' -- Possible downref: Non-RFC (?) normative reference: ref. 'ITU-T H.248.92' -- Possible downref: Non-RFC (?) normative reference: ref. 'ITU-T H.248.93' -- Possible downref: Non-RFC (?) normative reference: ref. 'ITU-T H.248.97' -- Possible downref: Non-RFC (?) normative reference: ref. 'ITU-T H.Sup14' -- Possible downref: Non-RFC (?) normative reference: ref. 'ETSI 183046' -- Possible downref: Non-RFC (?) normative reference: ref. 'ETSI 183068' -- Obsolete informational reference (is this intentional?): RFC 1163 (Obsoleted by RFC 1267) Summary: 6 errors (**), 0 flaws (~~), 3 warnings (==), 16 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 WG MMUSIC Albrecht Schwarz (ed.) 2 Internet Draft NOKIA 3 Intended status: Standards track Christian Groves 4 Expires: November 2016 Huawei 5 May 2, 2016 7 SDP codepoints for gateway control 8 draft-schwarz-mmusic-sdp-for-gw-05.txt 10 Status of this Memo 12 This Internet-Draft is submitted in full conformance with the 13 provisions of BCP 78 and BCP 79. 15 This document may contain material from IETF Documents or IETF 16 Contributions published or made publicly available before November 17 10, 2008. The person(s) controlling the copyright in some of this 18 material may not have granted the IETF Trust the right to allow 19 modifications of such material outside the IETF Standards Process. 20 Without obtaining an adequate license from the person(s) controlling 21 the copyright in such materials, this document may not be modified 22 outside the IETF Standards Process, and derivative works of it may 23 not be created outside the IETF Standards Process, except to format 24 it for publication as an RFC or to translate it into languages other 25 than English. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF), its areas, and its working groups. Note that 29 other groups may also distribute working documents as Internet- 30 Drafts. 32 Internet-Drafts are draft documents valid for a maximum of six 33 months and may be updated, replaced, or obsoleted by other documents 34 at any time. It is inappropriate to use Internet-Drafts as 35 reference material or to cite them other than as "work in progress." 37 The list of current Internet-Drafts can be accessed at 38 http://www.ietf.org/ietf/1id-abstracts.txt 40 The list of Internet-Draft Shadow Directories can be accessed at 41 http://www.ietf.org/shadow.html 42 This Internet-Draft will expire on November 2, 2016. 44 Copyright Notice 46 Copyright (c) 2016 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 54 respect to this document. 56 Abstract 58 SDP is used in many signalling protocols at call control level (such 59 as SAP, SIP, BICC), bearer control level (such as RTSP, IPBCP) and 60 gateway control level (such as H.248/MEGACO, MGCP). Scope of this 61 RFC is related to gateway control specific SDP usage. Gateway 62 control protocols do NOT usually define and introduce any new SDP 63 parameters, however, gateway control protocols need specific SDP 64 parameter values in addition to those defined at call or bearer 65 control level. Such SDP codepoints are collected by this RFC with 66 the purpose of registration with IANA. 68 Table of Contents 70 1. Introduction...................................................3 71 1.1. Motivation................................................3 72 1.2. Scope.....................................................3 73 2. Conventions used in this document..............................4 74 2.1. Prescriptive language.....................................4 75 2.2. Terminology used..........................................4 76 2.3. Abbreviations used........................................5 77 3. Security Considerations........................................6 78 4. IANA Considerations............................................6 79 4.1. Registration aspects of "m="-line element.........6 80 4.2. SDP codepoints related to "m="-line element.......7 81 5. References.....................................................7 82 5.1. Normative References......................................7 83 5.2. Informative References....................................9 84 6. Acknowledgments................................................9 85 Appendix A. Background - Gateway control protocols in scope...11 86 A.1. Introduction............................................11 87 A.2. Background - SDP usage in gateway control protocol(s)...11 88 A.3. Motivation - Why gateway control specific SDP?..........12 89 Appendix B. Decomposed gateways - usage of SDP................13 90 B.1. SDP for bearer type indication..........................13 91 B.2. SDP for controlling the mode of operation of a gateway..13 92 Appendix C. SDP codepoints related to "c="-line...............13 93 C.1. SDP codepoints related to "c="-line element..13 94 Appendix D. SDP codepoints related to "m="-line...............13 95 D.1. SDP codepoints related to "m="-line element.....13 96 D.1.1. Purpose...........................................13 97 D.1.2. Application-agnostic indications..................14 98 D.1.3. Protocol individual indications...................14 99 D.1.4. Gateway specific SDP codepoints...................15 100 D.2. SDP codepoints related to "m="-line element......15 101 Appendix E. SDP codepoints related to "a="-lines (SDP attrib.)15 102 E.1. SDP attribute "ITU-T H.248 package".....................15 103 7. CHANGE LOG....................................................16 104 7.1. Initial draft name "draft-schwarz-sdp-for-gw"............16 105 7.1.1. Changes against "-00"...............................16 106 7.1.2. Changes against "-01"...............................16 107 7.1.3. Changes against "-02"...............................16 108 7.2. WG draft name "draft-schwarz-mmusic-sdp-for-gw"..........16 109 7.2.1. Version "-00".......................................16 110 7.2.2. Changes against "-00"...............................16 111 7.2.3. Changes against "-01"...............................17 112 7.2.4. Changes against "-02"...............................17 113 7.2.5. Changes against "-03"...............................17 114 7.2.6. Changes against "-04"...............................17 116 1. Introduction 118 1.1. Motivation 120 There is a gap concerning the registration of some specific SDP 121 codepoints, which are primarily required for gateway control. 122 Detailed background information is summarized in Appendix A. 124 1.2. Scope 126 The purpose of this document is to collect SDP codepoints, which are 127 specific to gateway control protocols in order to identify any 128 additional codepoints that require reqistration with IANA. The focus 129 is (but not limited to) on SDP codepoints related to the SDP "m="- 130 line. 132 These SDP codepoints for gateway control are defined by ITU-T in the 133 ITU-T H.248.x-series of Recommendations [ITU-T H.248.x]. The 134 individual "H.248.x" documents define specific gateway control 135 applications. 137 Appendices C, D and E provide SDP line specific considerations 138 ("c="-, "m="- and "a="-lines) from gateway perspective. 140 Clause 4 on "IANA consideration" addresses the SDP information as in 141 scope of this document ("which is inter alia the result of such 142 gateway control aspect as discussed in above referred Appendices). 144 2. Conventions used in this document 146 2.1. Prescriptive language 148 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 149 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 150 document are to be interpreted as described in RFC-2119 [RFC2119]. 152 2.2. Terminology used 154 APPLICATION: 156 This term, when used in the context of "application-agnostic" or 157 "application-aware", refers to the IP application protocol on top 158 of a "L4 transport protocol" (e.g., "TCP", "UDP") with or without 159 a "transport security protocol" (e.g., "TLS", "DTLS"). 161 NOTE - The notion of application includes (if present) also the 162 associated protocol layer of "application level framing protocol" 163 (e.g., "RTP"). 165 BORDER GATEWAY: 167 A H.248 packet-to-packet (media) gateway, such as an IP-to-IP 168 gateway, with scope on two-party communication services. 169 NOTE: not to be confused with border gateway entities in the 170 native IP router space, such as a border router with support of 171 border gateway protocols (such as BGP, e.g. [RFC1163]). 173 CODEPOINT: 175 The combination of a "signalling parameter" plus assigned "value" 176 in protocol engineering. The "value" represents a codepoint (or 177 code position) in the code space. 179 X-AGNOSTIC / X-AWARE: 181 Placeholder 'X' denotes a protocol layer, a protocol stack or an 182 abstracted model such as "application", "media", "transport", etc. 183 This term indicates whether the controlled entity (here: H.248 MG) 184 is aware or not about information concerning 'X'. 186 2.3. Abbreviations used 188 B2BUA Back-to-Back User Agent 190 BGF Bearer Gateway Function 192 BGP Border Gateway Protocol 194 BICC Bearer Independent Call Control 196 DTLS Datagram Transport Layer Security 198 GCP Gateway Control Protocol 200 IPBCP (ITU-T) IP Bearer Control Protocol 202 ITU-T International Telecommunication Union Telecommunication 203 Standardization Sector 205 IWF Interworking Function 207 MEGACO Media Gateway Control 209 MG (H.248) Media Gateway 211 MGC (H.248) Media Gateway Controller 213 RTP Real-time Transport Protocol 215 RTSP Real-Time Streaming Protocol 217 SAP Session Announcement Protocol 219 SCTP Stream Control Transmission Protocol 221 SDP Session Description Protocol 223 SIP Session Initiation Protocol 225 TCP Transmission Control Protocol 226 TLS Transport Layer Security 228 UA User Agent 230 UDP User Datagram Protocol 232 3. Security Considerations 234 This RFC is related to the registration of protocol codepoints, thus 235 outside any security aspects. 237 4. IANA Considerations 239 4.1. Registration aspects of "m="-line element 241 The usual registration process is described in Section 8.2.2 of 242 [RFC4566]. Usage of such SDP codepoints for gateway control is 243 specific (as outlined in Appendix B and section D.1), therefore 244 leads to following considerations related to the registration 245 process: 247 a) [RFC4566], 8.2.2: The "proto" field describes the transport 248 protocol used. 250 Comment from gateway control: the notion of "transport protocol" 251 translates to either single protocol layer or protocol stack segment 252 (see section D.1). 254 b) [RFC4566], 8.2.2: New transport protocols SHOULD be registered 255 with IANA. Registrations MUST reference an RFC describing the 256 protocol. 258 Comment from gateway control: there are not any new IP transport 259 protocols defined by ITU-T for gateway control, hence, there will be 260 not any correspondent RFC. There will be rather a reference to an 261 ITU-T document which specifies the usage of that SDP codepoint in 262 the application-specific context of gateway control. 264 c) [RFC4566], 8.2.2: Registrations MUST also define the rules by 265 which their "fmt" namespace is managed. 267 Comment from gateway control: not applicable because there are not 268 any new IP transport protocols defined by ITU-T for gateway control, 269 hence existing rules are used. 271 4.2. SDP codepoints related to "m="-line element 273 This document updates the "Session Description Protocol (SDP) 274 Parameters" registry as specified in Section 8.2.2 of [RFC4566]. 275 Specifically, it adds the values in Table 1 to the table for the SDP 276 "proto" field registry. 278 +-------+----------------------+-------------------------+ 279 | Type | SDP Name | Reference | 280 +-------+----------------------+-------------------------+ 281 | proto | "TLS" | [ITU-T H.248.90] | 282 +-------+----------------------+-------------------------+ 283 | proto | "TCP/TLS" | [ITU-T H.248.90] Note 1 | 284 +-------+----------------------+-------------------------+ 285 | proto | "SCTP/TLS" | [ITU-T H.248.90] | 286 +-------+----------------------+-------------------------+ 287 | proto | "DTLS" | [ITU-T H.248.93] | 288 +-------+----------------------+-------------------------+ 289 | proto | "UDP/DTLS" | [ITU-T H.248.93] | 290 +-------+----------------------+-------------------------+ 291 | proto | "DCCP/DTLS" | [ITU-T H.248.93] | 292 +-------+----------------------+-------------------------+ 293 | proto | "SCTP" | [ITU-T H.248.97] Note2 | 294 +-------+----------------------+-------------------------+ 295 | proto | "SCTP/DTLS" | [ITU-T H.248.97] Note2 | 296 +-------+----------------------+-------------------------+ 297 | proto | "DTLS/SCTP" | [ITU-T H.248.97] Note2 | 298 +-------+----------------------+-------------------------+ 300 Table 1: SDP "proto" field values 302 Note 1 - Codepoint "TCP/TLS" already registered [RFC4572]. 304 Note 2 - Table entry may be deleted again dependent on progress of 305 IETF draft "draft-ietf-mmusic-sctp-sdp" 306 (http://tools.ietf.org/wg/mmusic/draft-ietf-mmusic-sctp-sdp/). 308 5. References 310 5.1. Normative References 312 [RFC2119] RFC 2119 (03/1997), "Key words for use in RFCs to Indicate 313 Requirement Levels", BCP 14. 315 [RFC2885] RFC 2885 (08/2000), "Megaco Protocol version 0.8". 317 [RFC3015] RFC 3015 (11/2000), "Megaco Protocol Version 1.0". 319 [RFC3525] RFC 3525 (06/2003), "Gateway Control Protocol Version 1". 321 [RFC4566] RFC 4566 (07/2006), "SDP: Session Description Protocol". 323 [RFC4572] RFC 4572 (07/2006), "Connection-Oriented Media Transport 324 over the Transport Layer Security (TLS) Protocol in the 325 Session Description Protocol (SDP)". 327 [RFC5125] RFC 5125 (02/2008), "Reclassification of RFC 3525 to 328 Historic". 330 [ITU-T H.248.x] The ITU-T H.248.x-series of Recommendations 331 (Gateway Control Protocol). 332 Website: http://www.itu.int/rec/T-REC-H/e 334 [ITU-T H.248.1] Recommendation ITU-T H.248.1 (03/2013), "Gateway 335 control protocol: Version 3". 336 Free copy via: http://www.itu.int/rec/T-REC-H.248.1- 337 201303-I/en 339 [ITU-T H.248.15] Recommendation ITU-T H.248.15 (03/2013), "Gateway 340 control protocol: SDP ITU-T H.248 package attribute". 341 Free copy via: http://www.itu.int/rec/T-REC-H.248.15- 342 201303-I/en 344 [ITU-T H.248.39] Recommendation ITU-T H.248.39 (10/2014), "Gateway 345 control protocol: H.248 SDP parameter identification and 346 wildcarding". 347 Free copy via: http://www.itu.int/rec/T-REC-H.248.39/en 349 [ITU-T H.248.49] Recommendation ITU-T H.248.49 (08/2007), "Gateway 350 control protocol: Session description protocol RFC and 351 capabilities packages". 352 Free copy via: http://www.itu.int/rec/T-REC-H.248.49/en 354 [ITU-T H.248.80] Recommendation ITU-T H.248.80 (01/2014), "Usage of 355 the revised SDP offer / answer model with H.248". 356 Free copy via: http://www.itu.int/rec/T-REC-H.248.80/en 358 [ITU-T H.248.90] Recommendation ITU-T H.248.90 (10/2014), "Gateway 359 control protocol: H.248 packages for control of transport 360 security using TLS". 361 Free copy via: http://www.itu.int/rec/T-REC-H.248.90/en 363 [ITU-T H.248.92] Recommendation ITU-T H.248.92 (10/2014), "Gateway 364 control protocol: Stream endpoint interlinkage package". 365 Free copy via: http://www.itu.int/rec/T-REC-H.248.92/en 367 [ITU-T H.248.93] Recommendation ITU-T H.248.93 (10/2014), "Gateway 368 control protocol: H.248 packages for control of transport 369 security using DTLS". 370 Free copy via: http://www.itu.int/rec/T-REC-H.248.93/en 372 [ITU-T H.248.97] Recommendation ITU-T H.248.97 (11/2015), "Gateway 373 control protocol: H.248 support for control of SCTP bearer 374 connections". 375 Free copy via: http://www.itu.int/rec/T-REC-H.248.97- 376 201511-P/en 378 [ITU-T H.Sup14] Supplement ITU-T H.Sup14 (10/2015), "Gateway 379 Control Protocol: ITU-T H.248.x-series - SDP codepoints 380 for gateway control - Release 2". 381 Free copy via: http://www.itu.int/rec/T-REC-H.Sup14- 382 201510-I/en 384 [ETSI 183046] ETSI TR 183 046 V3.3.1 (2009-08), "Telecommunications 385 and Internet converged Services and Protocols for Advanced 386 Networking (TISPAN); SDP Interworking between Call/Session 387 Control Protocols (SIP/SDP, RTSP/SDP; etc.) and the 388 Gateway Control Protocol (H.248/SDP)". 390 [ETSI 183068] ETSI TR 183 068 V3.1.1 (2009-08), "Telecommunications 391 and Internet converged Services and Protocols for Advanced 392 Networking (TISPAN); Guidelines on using Ia H.248 profile 393 for control of Border Gateway Functions (BGF); Border 394 Gateway Guidelines". 396 5.2. Informative References 398 [RFC1163] RFC 1163 (06/1990), "A Border Gateway Protocol (BGP)". 400 [RFC7092] RFC 7092 (12/2013), "A Taxonomy of Session Initiation 401 Protocol (SIP) Back-to-Back User Agents". 403 6. Acknowledgments 405 The work origins in ITU-T Study Group 16 Question 3 "Multimedia 406 gateway control architectures and protocols" in cooperation with 407 3GPP CT4 (Technical Specification Group "Core Network and 408 Terminals", Working Group 4). The authors like to thank all 409 delegates for comments, review and contributions. 411 Authors' Addresses 413 Dr. Albrecht Schwarz (editor) 414 NOKIA 415 Lorenzstrasse 10 416 D-70435 Stuttgart 417 GERMANY 419 Email: Albrecht.Schwarz@nokia.com 421 Christian Groves 422 Huawei 423 Melbourne 424 AUSTRALIA 426 Email: Christian.Groves@nteczone.com 428 Appendix A. Background - Gateway control protocols in scope 430 A.1. Introduction 432 Gateway control protocols are required for decomposed network 433 elements which separate media plane and signalling plane related 434 network functions (see e.g., [RFC7092] concerning a decomposed B2BUA 435 with a SIP specific signalling B2BUA plus a media plane B2BUA 436 entity). 438 The gateway control interface between the controlling entity (known 439 as media gateway controller, MGC) and controlled entity (known as 440 media gateway) follows a disclosed, open, standardized protocol. 442 This RFC considers such gateway control protocols which use the SDP 443 [RFC4566] as embedded signalling for media-related characteristics. 445 This RFC focuses on following gateway control protocol, known as 446 "H.248", as standardized within the ITU-T H.248.x-series of 447 Recommendations [ITU-T H.248.x]. The core protocol is defined by 448 H.248.1 [ITU-T H.248.1], which actually originates in the IETF, 449 known as MEGACO (media gateway control): 451 IETF history: 453 o Closed working group "MEGACO" (since technology was transferred 454 to ITU-T); 456 o IETF MEGACO protocol versions: see [RFC2885], [RFC3015], 457 [RFC3525]; 459 o Transfer IETF to ITU-T: "Reclassification of RFC 3525 to 460 Historic", [RFC5125]. 462 A.2. Background - SDP usage in gateway control protocol(s) 464 Gateway control protocol H.248 supports two message encoding modes: 465 binary and text. Gateway deployments in IP network environments use 466 primarily H.248 text encoding mode in order to benefit from SDP 467 usage at call control signalling level. For instance, the SIP level 468 SDP information is mapped by the H.248 MGC entity to SDP information 469 as used in H.248 gateway control signaling. The following list 470 indicates areas where SDP is used in H.248 gateway control: 472 o SDP in H.248: clause 7.1.8 "Local and Remote Descriptors" and 473 particularly clause 7.1.8.1.1.2 "Summary - ITU-T H.248 usage of 474 SDP" in [ITU-T H.248.1]; 476 o Wildcarding in SDP: "H.248 SDP parameter identification and 477 wildcarding" [ITU-T H.248.39]; 479 o SDP versioning: "SDP RFC and capabilities packages", [ITU-T 480 H.248.49]; 482 o SDP profiling: the allowed SDP elements and codespace could be 483 limited by H.248 profile specifications, see "ITU-T H.248 profile 484 definition template" in Appendix III/[ITU-T H.248.1] (profile 485 template clauses 6.15 and 6.16 are related to SDP); 487 o SDP offer/answer models: "Usage of the revised SDP offer / answer 488 model with H.248", [ITU-T H.248.80]; 490 o SDP mapping between call control and H.248: "SDP Interworking 491 between Call/Session Control Protocols (SIP/SDP, RTSP/SDP; etc.) 492 and the Gateway Control Protocol (H.248/SDP)" [ETSI 183046]. 494 o SDP for mode control in border gateways: see Annex G 495 "Illustration of BGF modes of operation" and particularily Annex 496 G.2 "BGF modes driven by particular SDP lines" [ETSI 183068]. 498 A.3. Motivation - Why gateway control specific SDP? 500 Gateway control protocol (GCP) specific SDP codepoints are primarily 501 required in two areas: 503 1. SDP for bearer type indication 505 2. SDP for controlling the mode of operation of a gateway 507 Clause 3 provides detailed background and [ETSI 183068], Annex G 508 illustrates several examples in the area of IP-to-IP gateways (also 509 known as border gateways). 511 Appendix B. Decomposed gateways - usage of SDP 513 Gateway control protocol (GCP) specific SDP codepoints are primarily 514 required in two areas: 516 B.1. SDP for bearer type indication 518 The bearer connection endpoint at media gateway level needs to be 519 specified concerning the required bearer protocol or protocol stack 520 segment respectively. This relates essentially to the SDP "m="line 521 element. However, media gateways require in addition so 522 called "agnostic" type of SDP codepoints, which is in contrast to 523 the so called application-aware, transport protocol type aware SDP 524 codepoints used by communication endpoints (such as a SIP UA located 525 in an IP host entity). 527 B.2. SDP for controlling the mode of operation of a gateway 529 A media gateway (MG) typically internally interconnects multiple 530 bearer connection endpoints. A plethora of interworking functions 531 (IWF) may be supported in the media plane by the MG. The type of IWF 532 is known as mode of operation. The mode of operation is typically 533 controlled via SDP. The semantic is actually the result of the SDP 534 information of ALL involved bearer connection endpoints (in H.248: 535 terminations / stream endpoints). The operation may be traffic 536 directions specific. 538 Appendix C. SDP codepoints related to "c="-line 540 C.1. SDP codepoints related to "c="-line element 542 H.248 may utilise the existing elements as defined in the 543 IANA registry "http://www.iana.org/assignments/sdp-parameters/sdp- 544 parameters.xhtml#sdp-parameters-5". No additional registrations are 545 required. 547 Appendix D. SDP codepoints related to "m="-line 549 D.1. SDP codepoints related to "m="-line element 551 D.1.1. Purpose 552 The SDP "m=" line element allows the indication of 554 a) a single protocol (layer) or 556 b) a protocol stack (i.e., multiple, consecutive protocol layers). 558 The protocol stack based value is inherently ambiguous in case of 559 the requirement in indicating a particular protocol layer out of the 560 stack. This is a well-known issue of this element. 562 Example: = "x/y/z", i.e., indicates a protocol stack segment 563 with protocol layering "z-over-y-over-x". The MGC wants to trigger a 564 bearer control procedure for protocol 'y' at MG level and uses such 565 an SDP codepoint. However, there are also the options of bearer 566 control procedures at protocol layers 'x' or 'z'. Consequently, the 567 SDP codepoint "x/y/z" can't be used because semantically ambigous. 568 What would be required here are separate SDP codepoints "x", "y" and 569 "z". 571 The example illustrates that there are not any new IP transport 572 protocols invented for gateway control. 574 D.1.2. Application-agnostic indications 576 Application-agnostic, - or X-agnostic in general -, indications are 577 typically realized by using character "-" instead of a concrete 578 value in SDP fields (see [ITU-T H.248.39]). Such an SDP value is 579 basically out of scope of IANA registration. 581 D.1.3. Protocol individual indications 583 There is the so-called "interlinkage" capability defined for gateway 584 control, see [ITU-T H.248.92]. This functionality allows to 585 interlink connection/session oriented transport protocol endpoints 586 within a media gateway. If two transport protocol endpoints are 587 interlinked the establishment and/or release of a connection/session 588 at the source transport protocol endpoint will trigger an MG- 589 autonomous establishment and/or release of the interlinked transport 590 protocol endpoint. 592 The configuration of the gateway internal interlinkage topology is 593 defined in section 7.1.1/[ITU-T H.248.92] and uses the SDP 594 element for the indication of interlinked protocol layers. However, 595 the SDP codepoints are limited to single protocol layers only. 597 Reference: [ITU-T H.248.92] section 7.1.1: "Value proto is as per 598 clause 9/[IETF RFC 4566], with the restriction that a single 599 transport protocol value should be selected when the IANA proto 600 codepoint represents a protocol stack segment (format e.g. "x/y/z"), 601 rather than a single individual protocol layer (format "x")." 603 D.1.4. Gateway specific SDP codepoints 605 See [ITU-T H.Sup14]. 607 D.2. SDP codepoints related to "m="-line element 609 No specific from H.248 perspective. 611 Appendix E. SDP codepoints related to "a="-lines (SDP attrib.) 613 E.1. SDP attribute "ITU-T H.248 package" 615 ITU-T Recommendation [ITU-T H.248.15] defines an ITU-T specific 616 extension for SDP. The SDP attribute "a=h248item:" allows for the 617 carriage of general ITU-T H.248 properties in the local and remote 618 descriptor in the textual ITU-T H.248 protocol encoding mode. This 619 attribute has already been registered with IANA (see: 620 http://www.iana.org/assignments/sdp-parameters/sdp- 621 parameters.xhtml#sdp-parameters-5). 623 7. CHANGE LOG 625 7.1. Initial draft name "draft-schwarz-sdp-for-gw" 627 7.1.1. Changes against "-00" 629 o Replace Draft ITU-T Recommandation work item name by "H.248.x" 630 number (H.248.90 (TLS), H.248.92 (SEPLINK)) 632 o Correction of clause 5: addition of ITU-T specific SDP attribute 633 "a=h248item:" 635 o Editorial: update of abbreviation list 637 7.1.2. Changes against "-01" 639 o addition of SDP "c=" line information 641 o complementary information on registration status (clauses 4.1 and 642 6.1) 644 o Missing reference (RFC 4572) to codepoint "TCP/TLS" added. 646 o Editorial: review & update of abbreviation list 648 7.1.3. Changes against "-02" 650 o correction of draft name from "draft-schwarz-sdp-for-gw-..." to 651 "draft-schwarz-mmusic-sdp-for-gw-...", i.e., a restart with 652 version number 00 required 654 o update of references 656 7.2. WG draft name "draft-schwarz-mmusic-sdp-for-gw" 658 7.2.1. Version "-00" 660 The June 2014 draft. 662 7.2.2. Changes against "-00" 664 o clause 1.4 'scope': addition of complementary information 666 o clause 5.1.1: there was still information solicited, which is 667 added here 669 o clause 5.1.3: there was still information solicited, dependent on 670 progress of H.248.92, which is added here 672 o clause 8.1: clarification of registration aspects related to RFC 673 4566 675 o editorials: update of references due to recent approval of 676 Recommendations (rev.) H.248.39, H.248.90, H.248.92 and H.248.93, 677 and Supplement H.Sup14 by ITU-T. 679 7.2.3. Changes against "-01" 681 o nearly all informative text of the main body was moved in 682 Appendices in order to narrow and limit the normative text on the 683 prime subject of this draft, thus, "-02" does provide only 684 editorial updates, - in more detail: 685 new Appendix A = old sections 1.1, 1.2 and 1.3; 686 new Appendix B = old section 3; 687 new Appendix C = old section 4; 688 new Appendix D = old section 5; 689 new Appendix E = old section 6. 691 7.2.4. Changes against "-02" 693 o editorial error corrected: section 1.1 was splitted again in 694 sections 1.1 "Motivation" and "Scope". 696 7.2.5. Changes against "-03" 698 o Reference update I: ITU-T H.248.SCTP => H.248.97 700 o Reference update II: ITU-T H.Sup14 Release 1 => H.Sup14 Release 2 702 7.2.6. Changes against "-04" 704 o missing URLs inserted in two ITU-T references