idnits 2.17.1 draft-ietf-sipping-early-disposition-01.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** Looks like you're using RFC 2026 boilerplate. This must be updated to follow RFC 3978/3979, as updated by RFC 4748. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- == No 'Intended status' indicated for this document; assuming Proposed Standard Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack a Security Considerations section. == There are 3 instances of lines with non-RFC2606-compliant FQDNs in the document. == There are 4 instances of lines with non-RFC6890-compliant IPv4 addresses in the document. If these are example addresses, they should be changed. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the RFC 3978 Section 5.4 Copyright Line does not match the current year == Line 282 has weird spacing: '...session the ...' == The document seems to lack the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords. (The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (January 13, 2004) is 7409 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) -- Obsolete informational reference (is this intentional?): RFC 2327 (ref. '5') (Obsoleted by RFC 4566) Summary: 2 errors (**), 0 flaws (~~), 6 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SIPPING Working Group G. Camarillo 3 Internet-Draft Ericsson 4 Expires: July 13, 2004 January 13, 2004 6 The Early Session Disposition Type for the Session Initiation 7 Protocol (SIP) 8 draft-ietf-sipping-early-disposition-01.txt 10 Status of this Memo 12 This document is an Internet-Draft and is in full conformance with 13 all provisions of Section 10 of RFC2026. 15 Internet-Drafts are working documents of the Internet Engineering 16 Task Force (IETF), its areas, and its working groups. Note that other 17 groups may also distribute working documents as Internet-Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six months 20 and may be updated, replaced, or obsoleted by other documents at any 21 time. It is inappropriate to use Internet-Drafts as reference 22 material or to cite them other than as "work in progress." 24 The list of current Internet-Drafts can be accessed at http:// 25 www.ietf.org/ietf/1id-abstracts.txt. 27 The list of Internet-Draft Shadow Directories can be accessed at 28 http://www.ietf.org/shadow.html. 30 This Internet-Draft will expire on July 13, 2004. 32 Copyright Notice 34 Copyright (C) The Internet Society (2004). All Rights Reserved. 36 Abstract 38 This document defines a new disposition type (early-session) for the 39 Content-Disposition header field in SIP. The treatment of 40 "early-session" bodies is similar to the treatment of "session" 41 bodies. That is, they follow the offer/answer model. Their only 42 difference is that session descriptions whose disposition type is 43 "early-session" are used to establish early media sessions within 44 early dialogs, as opposed to regular sessions within regular dialogs. 46 Table of Contents 48 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3 49 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 50 3. Issues Related to Early Media Session Establishment . . . . . . 3 51 4. The Early Session Disposition Type . . . . . . . . . . . . . . . 4 52 5. Preconditions . . . . . . . . . . . . . . . . . . . . . . . . . 5 53 6. Option tag . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 54 7. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 55 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 56 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8 57 Normative References . . . . . . . . . . . . . . . . . . . . . . 8 58 Informational References . . . . . . . . . . . . . . . . . . . . 8 59 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 60 Intellectual Property and Copyright Statements . . . . . . . . . 9 62 1. Introduction 64 A SIP [2] user agent establishing an INVITE dialog may need to 65 exchange media with the destination user agent (or user agents if the 66 INVITE forks) or with application servers in the path before the 67 dialog is established. Media exchanged this way is referred to as 68 early media. 70 Section 3 describes the current approach to establish early media 71 sessions in SIP and discusses its problems. Section 4 defines the 72 "early-session" disposition type to resolve those problems. 74 2. Terminology 76 In this document, the key words "MUST", "MUST NOT", "REQUIRED", 77 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT 78 RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as 79 described in BCP 14, RFC 2119 [1] and indicate requirement levels for 80 compliant implementations. 82 3. Issues Related to Early Media Session Establishment 84 Traditionally, early media sessions have been established in the same 85 way as regular sessions. That is, using an offer/answer exchange 86 where the disposition type of the session descriptions is "session". 87 Application servers perform an offer/answer exchange with the UAC to 88 exchange early media exclusively, while UASs use the same offer/ 89 answer exchange, first to exchange early media, and once the regular 90 dialog is established, to exchange regular media. There are issues 91 related to both, application servers and UASs using this mechanism. 93 Application servers may not be able to generate an answer for an 94 offer received in the INVITE. The UAC created the offer for the UAS, 95 and so, it may have applied end-to-end encryption or have included 96 information (e.g., related to key management) that the application 97 server is not supposed to use. Therefore, application servers need a 98 means to perform an offer/answer exchange with the UAC which is 99 independent from the offer/answer exchange between both UAs. 101 UASs using the offer/answer exchange that will carry regular media to 102 send and receive early media can cause media clipping, as described 103 in Section 2.1.1 of [6]. Some UACs cannot receive early media from 104 different UASs at the same time. So, when an INVITE forks and several 105 UASs start sending early media, the UAC mutes all the UASs but one 106 (which is usually randomly chosen). If the UAS that accepts the 107 INVITE (i.e., sends a 200 OK) was muted, a new offer/answer exchange 108 is needed to unmute it. This usually causes media clipping. 109 Therefore, UASs need a means to perform an offer/answer exchange with 110 the UAC to exchange early media which is independent from the offer/ 111 answer exchanged used to exchange regular media. 113 A potential solution to this need would be to establish a different 114 dialog using a globally routable URI to perform an independent offer/ 115 answer exchange. This dialog would be labelled as a dialog for early 116 media and would be related to the original dialog somehow at the UAC. 117 However, performing all the offer/answer exchanges within the 118 original dialog has many advantages: 120 It is simpler. 122 It does not have synchronization problems, because all the early 123 dialogs are terminated when the session is accepted. 125 It does not require globally routable URIs. 127 It does not introduce service interaction issues related to 128 services that may be wrongly applied to the new dialog. 130 It makes firewall management easier. 132 4. The Early Session Disposition Type 134 We define a new disposition type for the Content-Disposition header 135 field: early-session. User agents MUST use early-session bodies to 136 establish early media sessions in the same way as they use session 137 bodies to establish regular sessions, as described in RFC 3261 [2] 138 and in RFC 3264 [3]. Particularly, early-session bodies MUST follow 139 the offer/answer model and MAY appear in the same messages as session 140 bodies do with the exceptions of 2xx responses for an INVITE and 141 ACKs. Nevertheless, it is NOT RECOMMENDED to include early offers in 142 INVITEs because they can fork, and the UAC could receive multiple 143 early answers establishing early media streams at roughly the same 144 time. It is also NOT RECOMMENDED to use the same transport address 145 (IP address plus port) in a session body and in an early-session 146 body. Using different transport addresses (e.g., different ports) to 147 receive early and regular media makes it easy to detect the start of 148 the regular media. 150 If a UA needs to refuse an early-session offer, it MUST to so by 151 refusing all the media streams in it. When SDP [5] is used, this is 152 done by setting the port number of all the media streams to zero. 154 This is the same mechanism that UACs use to refuse regular offers 155 that arrive in a response to an empty INVITE. 157 An early media session established using early-session bodies MUST be 158 terminated when its corresponding early dialog is terminated or it 159 transitions to a regular dialog. 161 It is RECOMMENDED that UAs generating regular and early session 162 descriptions use, as long as it is possible, the same codecs in both. 163 This way, the remote UA does not need to change codecs when the early 164 session transitions to a regular session. 166 5. Preconditions 168 RFC 3312 [4] defines a framework for preconditions for SDP. 169 Early-sessions MAY contain preconditions, which are treated in the 170 same way as preconditions in regular sessions. That is, the UAs do 171 not exchange media and the called user is not alerted until the 172 preconditions are met. 174 6. Option tag 176 We define an option tag to be used in Require and Supported header 177 fields. Its name is early-session. A UA adding the early-session 178 option tag to a message indicates that it understands the 179 early-session disposition type. 181 7. Example 183 Figure 1 shows the message flow between two UAs. INVITE (1) has an 184 early-session option tag in its Supported header field and the body 185 shown in Figure 2. The UAS sends back a response with two body parts 186 ,as shown in Figure 3; one of disposition type session and the other 187 early-session. The session body part is the answer to the offer in 188 the INVITE. The early-session body part is an offer to establish an 189 early media session. When the UAC receives the 183 (Session Progress) 190 response, it sends the answer to the early-session offer in a PRACK, 191 as shown in Figure 4. This early media session is terminated when the 192 early dialog transitions to a regular dialog. That is, when the UAS 193 sends the (5) 200 (OK) response for the INVITE. 195 A B 196 | | 197 |--------(1) INVITE-------->| 198 | offer | 199 | | 200 |<--(2) Session Progress----| 201 | early-offer | 202 | answer | 203 | | 204 |---------(3) PRACK-------->| 205 | early-answer | 206 | | 207 |<--------(4) 200 OK--------| 208 | | 209 | * * | 210 | ************************* | 211 |* Early Media *| 212 | ************************* | 213 | * * | 214 | | 215 |<--------(5) 200 OK--------| 216 | | 217 |----------(6) ACK--------->| 218 | | 220 Figure 1: Message flow 222 Content-Type: application/sdp 223 Content-Disposition: session 225 v=0 226 o=alice 2890844730 2890844731 IN IP4 host.example.com 227 s= 228 c=IN IP4 192.0.0.1 229 t=0 0 230 m=audio 20000 RTP/AVP 0 232 Figure 2: Offer 234 Content-Type: multipart/mixed; boundary="boundary1" 235 Content-Length: 401 237 --boundary1 238 Content-Type: application/sdp 239 Content-Disposition: session 241 v=0 242 o=Bob 2890844725 2890844725 IN IP4 host.example2.com 243 s= 244 c=IN IP4 192.0.0.2 245 t=0 0 246 m=audio 30000 RTP/AVP 0 248 --boundary1 249 Content-Type: application/sdp 250 Content-Disposition: early-session 252 v=0 253 o=Bob 2890844714 2890844714 IN IP4 host.example2.com 254 s= 255 c=IN IP4 192.0.0.2 256 t=0 0 257 m=audio 30002 RTP/AVP 0 259 --boundary1-- 261 Figure 3: Early offer and answer 263 Content-Type: application/sdp 264 Content-Disposition: early-session 266 v=0 267 o=alice 2890844717 2890844717 IN IP4 host.example.com 268 s= 269 c=IN IP4 192.0.0.1 270 t=0 0 271 m=audio 20002 RTP/AVP 0 273 Figure 4: Answer 275 8. IANA Considerations 277 This document defines a new Content-Disposition header field 278 disposition type (early-session) in Section 4. This value should be 279 registered in the IANA registry for Content-Dispositions with the 280 following description: 282 early-session the body describes an early communications 283 session, for example, an RFC 2327 SDP body 285 This document defines a SIP option tag (early-session) in Section 6. 286 It should be registered in the SIP parameters registry (http:// 287 www.iana.org/assignments/sip-parameters) under "Option Tags", with 288 the following description. 290 A UA adding the early-session option tag to a message indicates 291 that it understands the early-session content disposition. 293 9. Acknowledgements 295 Francois Audet and Christer Holmberg provided useful comments on this 296 document. 298 Normative References 300 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 301 Levels", BCP 14, RFC 2119, March 1997. 303 [2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., 304 Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: 305 Session Initiation Protocol", RFC 3261, June 2002. 307 [3] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with 308 Session Description Protocol (SDP)", RFC 3264, June 2002. 310 [4] Camarillo, G., Marshall, W. and J. Rosenberg, "Integration of 311 Resource Management and Session Initiation Protocol (SIP)", RFC 312 3312, October 2002. 314 Informational References 316 [5] Handley, M. and V. Jacobson, "SDP: Session Description 317 Protocol", RFC 2327, April 1998. 319 [6] Camarillo, G. and H. Schulzrinne, "Early Media and Ringback Tone 320 Generation in the Session Initiation Protocol", 321 draft-camarillo-sipping-early-media-02 (work in progress), July 322 2003. 324 Author's Address 326 Gonzalo Camarillo 327 Ericsson 328 Hirsalantie 11 329 Jorvas 02420 330 Finland 332 EMail: Gonzalo.Camarillo@ericsson.com 334 Intellectual Property Statement 336 The IETF takes no position regarding the validity or scope of any 337 intellectual property or other rights that might be claimed to 338 pertain to the implementation or use of the technology described in 339 this document or the extent to which any license under such rights 340 might or might not be available; neither does it represent that it 341 has made any effort to identify any such rights. Information on the 342 IETF's procedures with respect to rights in standards-track and 343 standards-related documentation can be found in BCP-11. Copies of 344 claims of rights made available for publication and any assurances of 345 licenses to be made available, or the result of an attempt made to 346 obtain a general license or permission for the use of such 347 proprietary rights by implementors or users of this specification can 348 be obtained from the IETF Secretariat. 350 The IETF invites any interested party to bring to its attention any 351 copyrights, patents or patent applications, or other proprietary 352 rights which may cover technology that may be required to practice 353 this standard. Please address the information to the IETF Executive 354 Director. 356 Full Copyright Statement 358 Copyright (C) The Internet Society (2004). All Rights Reserved. 360 This document and translations of it may be copied and furnished to 361 others, and derivative works that comment on or otherwise explain it 362 or assist in its implementation may be prepared, copied, published 363 and distributed, in whole or in part, without restriction of any 364 kind, provided that the above copyright notice and this paragraph are 365 included on all such copies and derivative works. However, this 366 document itself may not be modified in any way, such as by removing 367 the copyright notice or references to the Internet Society or other 368 Internet organizations, except as needed for the purpose of 369 developing Internet standards in which case the procedures for 370 copyrights defined in the Internet Standards process must be 371 followed, or as required to translate it into languages other than 372 English. 374 The limited permissions granted above are perpetual and will not be 375 revoked by the Internet Society or its successors or assignees. 377 This document and the information contained herein is provided on an 378 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 379 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 380 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 381 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 382 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 384 Acknowledgment 386 Funding for the RFC Editor function is currently provided by the 387 Internet Society.