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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SIPPING Working Group Jean-Francois Mule 3 Internet Engineering Task Force CableLabs 4 Internet Draft 5 Document: draft-ietf-sipping-realtimefax-01.txt 6 Category: Informational Jieying Li 7 Expires: February 2003 August 2003 9 SIP Support for Real-time Fax: 10 Call Flow Examples 11 And 12 Best Current Practices 14 Status of this Memo 16 This document is an Internet-Draft and is in full conformance with 17 all provisions of Section 10 of RFC2026 [1]. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six 25 months and may be updated, replaced, or obsoleted by other documents 26 at any time. It is inappropriate to use Internet- Drafts as 27 reference material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 1. Abstract 36 The Session Initiation Protocol (SIP) allows the establishment of 37 real-time Internet fax communications. Real-time facsimile 38 communications over IP may follow 2 modes of operation: T.38 fax 39 relay as defined by the ITU-T T.38 recommendation or fax pass- 40 through. 41 This document clarifies the options available to Internet telephony 42 gateway vendors to handle real-time fax calls using SIP. While our 43 primary focus is to address the more reliable real-time T.38 Group 3 44 fax mode, we briefly cover the fax pass-through mode to enable 45 fallback operations and super G3 fax communications using SIP. We 46 also give examples of SIP call flows for real-time Internet fax 47 gateways or SIP proxy redirect servers. Elements in these call 48 flows include SIP User Agents, SIP Proxy Servers, and Gateways to 49 the PSTN (Public Switch Telephone Network). 50 This document introduces best current practices for SIP T.38 fax and 51 SIP fax pass-through sessions. A session starts with audio 52 capabilities, and, upon fax tone detection, T.38 fax capabilities 53 are negotiated; upon successful negotiation, the session continues 55 J-F. Mule/J. Li SIPPING WG 1 56 SIP T.38 Call Flows February 2003 58 with fax capabilities and the media termination hosts exchange T.38 59 Internet fax packets. The T.38 fax call scenarios include various 60 aspects of the call sequence: the detection of fax transmission, the 61 usage of the T.38 session description attributes, the optional 62 fallback into fax pass-through mode and the session termination. The 63 fax pass-through call scenarios involve some specific SDP media 64 attributes to enable proper fax transmission. 65 Fax transmission can be detected by the receiving side, the emitting 66 side or both (in the latter case, a 'glare' effect may appear). 67 This document only covers the case when the fax transmission is 68 detected by the receiving side: it is the most common practice and 69 the other cases do not represent any particular challenges and are 70 therefore left for future discussions). Call flow diagrams and 71 message details are shown. A list of IANA defined SDP attribute 72 names for T.38 is summarized in section 7. 74 J-F. Mule/J. Li 2 75 SIP T.38 Call Flows February 2003 77 Table of Contents 79 Status of this Memo...................................................1 80 1. Abstract...........................................................1 81 2. Conventions used in this document..................................4 82 3. Overview...........................................................4 83 3.1. General Assumptions.............................................4 84 3.2 Legend for Message Flows..........................................4 85 3.3 Changes to previous drafts........................................5 86 4 Handling of real-time fax communication using SIP...................5 87 4.1 Internet telephony gateways and fax detection.....................6 88 4.2 Internet telephony gateways and T.38 fax media connections........6 89 4.3 SIP session and fax termination...................................7 90 4.4 Internet telephony gateways and fax pass-through mode.............7 91 4.5 Responses to SIP OPTIONS request..................................8 92 4.6 Beyond Internet telephony gateways................................8 93 5 Successful SIP T.38 fax Call Scenarios..............................8 94 5.1 Internet fax device - fax only support............................8 95 5.1.1 Sequence Diagram................................................8 96 5.1.2 Message Details.................................................9 97 5.2 SIP T.38 fax call -fax stream replaces voice stream..............14 98 5.2.1 Sequence Diagram...............................................15 99 5.2.2 Message Details................................................17 100 5.3 SIP T.38 fax call - fax stream added to voice stream.............26 101 5.3.1 Sequence Diagram...............................................27 102 5.3.2 Message Details................................................29 103 5.4 SIP T.38 fax call - fax stream forced to replace voice stream....38 104 5.4.1 Sequence Diagram...............................................39 105 5.4.2 Message Details................................................39 106 6. Unsuccessful Scenarios............................................42 107 6.1. Unsuccessful T.38 fax scenario - no support for T.38............42 108 6.1.1. Sequence Diagram..............................................42 109 6.1.2. Message Details...............................................43 110 6.2. Unsuccessful T.38 fax scenario -488/606 rsp & G.711 fallback....45 111 6.2.1. Sequence Diagram..............................................46 112 6.2.2. Message Details...............................................47 113 7. SDP Attribute Table for T.38 sessions.............................52 114 8. Considerations....................................................53 115 8.1. Level of requirements for Internet gateways.....................53 116 8.2. Negotiation of UDP ports for T.38 transmission..................53 117 8.3. Adding a fax stream to SIP session vs. Replacing audio stream...53 118 8.4. Adding text to make use of SIP OPTIONS: in progress in draft-02.53 119 8.5. Use of IP addresses in SDP connection information...............54 120 8.6. Unsuccessful scenario: 606 or 488...............................54 121 8.7. SIP re-INVITE or UPDATE?........................................54 122 9. Security Considerations...........................................54 123 10. References.......................................................54 124 11. Acknowledgments..................................................55 125 12. Author's Addresses...............................................55 126 Full Copyright Statement.............................................56 127 Acknowledgement......................................................56 129 J-F. Mule/J. Li 3 130 SIP T.38 Call Flows February 2003 132 2. Conventions used in this document 134 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 135 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 136 this document are to be interpreted as described in RFC-2119 [2]. 138 3. Overview 140 The Session Initiation Protocol (SIP) is defined by RFC3261 [3] and 141 T.38 is the ITU-T Recommendation defining the procedures for real- 142 time Group 3 facsimile communications over IP networks [4]. This 143 document deals with the handling of real-time fax communications 144 using the SIP protocol for T.38 fax and fax pass-through modes. 145 For T.38, this document deals primarily with one transport protocol 146 for the media: T.38 over UDP/UDPTL; T.38 fax packet transport over 147 TCP using SIP session establishment can easily be extrapolated. 148 These T.38 call flows were developed in the design of carrier-class 149 SIP Telephony products supporting voice and real-time fax traffic. 150 It is the hope of the authors that this document will be useful for 151 the SIP community, SIP implementors of T.38 fax products, designers. 152 Call flows shown in this document complement the main SIP call flow 153 Internet-Draft [5]. These call flows are based on the current 154 version 2.0 of SIP in RFC3261[3], the ITU-T T.38 Amendment 2 [6] and 155 an ITU-T SG8 liaison to IANA. Note: IANA registration of the T.38 156 SDP attributes is currently a work in progress. 158 3.1. General Assumptions 160 Internet telephony gateways with T.38 support MAY pass various fax 161 tones (T.30 CNG, CED, etc.) or flag sequence (like V.21 Preamble) in 162 the RTP audio streams before those tones or flag sequence are 163 detected. Once detected by the DSP resources, T.38 fax-capable 164 devices switch from audio to fax mode and initiate a T.38 fax packet 165 transmission. 166 These best current practices MAY apply to "Network Gateway", 167 "Enterprise Gateway" and Internet-aware fax devices or terminals. 169 3.2 Legend for Message Flows 171 The legend defined [5] also applies in this document. 172 Dashed lines (---) represent control messages that are mandatory to 173 the call scenario. These control messages can be SIP or PSTN 174 signaling. Double dashed lines (===) represent media paths between 175 network elements. Messages with parenthesis around name represent 176 optional control messages. Messages are identified in the Figures 177 as F1, F2, etc. This references the message details in the table 178 that follows the Figure. Comments in the message details are shown 179 in the following form: /* Comments. */ 181 J-F. Mule/J. Li 4 182 SIP T.38 Call Flows February 2003 184 3.3 Changes to previous drafts 186 o Changes to sipping-draft-01 187 The changes between the current draft and the expired sipping draft- 188 00 are: 189 - removed ecan which is a local param and removed all text 190 - started realignment with rfc3261 (tags, branch, Max-Forward): 191 this remains unfinished and it has not been proof-read; look 192 for more rigorous updates in the next draft 193 - realigned with T.38 recommendation from 3/2002 194 + corrected T38FaxFillBitRemoval, T38FaxTranscodingMMR, 195 T38FaxTranscodingJBIG 196 - edits: updated reference section (to do: need to split it into 197 normative vs. informative) 199 o Changes to draft-01 200 The changes between the current draft and draft-01 are: 201 - Major updates: 202 + additions based on SIPit fax testing event 8/2001: added 203 text regarding the negotiation of T38MaxBitRate in 4.2, 204 + added more general text for the handling of real-time 205 fax pass-through, 206 + added of echo cancellation & silence suppression SDP 207 attributes and usage recommendations in 6.2, 208 + correction of the session version number in SDP when 209 issuing re-INVITE with updated SDP information as per 210 draft-ietf-sip-rfc2543bis-05, 211 + started a section on the use of the OPTIONS method to 212 determine the support of T.38 capabilities (work-in- 213 progress), 214 - Minor editorial updates (added tag fields in To and From header 215 lines as well as Contact header lines as per draft-ietf-sip- 216 rfc2543bis-05, added proper reference to T.38 Amendment 2 pre- 217 published version, exact case matching for T38MaxBitRate, etc.) 219 o Changes to draft-00 220 The major changes between draft-01 and draft-00 are listed below: 221 - Major updates: 222 + new text in fax handling section 4.2 based on sip list: 223 clarified text for fax detection, capability negotiation 224 and termination 225 + additions of new successful call flows in section 5 226 + additions of unsuccessful call flows in section 6 227 - Added Record-Route header, modified Cseq numbers, 228 - Added T38FaxMaxDatagram attribute in SDP and corrected 229 the sample value for T38FaxMaxBuffer, 230 - Minor editorial changes (e.g. removed references in Abstract). 231 4 Handling of real-time fax communication using SIP 233 The handling of real-time fax sessions using SIP involves the 234 initial session establishment, the modification or negotiation of 236 J-F. Mule/J. Li 5 237 SIP T.38 Call Flows February 2003 239 session capabilities upon fax detection, the optional fallback into 240 fax pass-through mode and the session termination. 242 Some variants of these best current practices MAY apply depending on 243 the nature or the configuration of Internet telephony gateways. Two 244 distinct cases are considered in this document: 245 o The Internet telephony gateway only supports T.38 real-time 246 fax communications (by design or by configuration). In this case, 247 the Internet fax gateway SHOULD initiate the SIP session with T.38 248 SDP capabilities (this is typically the case of Internet fax 249 terminals, also called Internet-aware fax devices or the case of 250 gateways statically configured to support T.38 fax calls only); 251 o The Internet telephony gateway supports voice and real-time 252 fax communications. In this case, the Internet telephony gateway 253 initiates the SIP session with audio capabilities, and, upon fax 254 detection, the switchover to T.38 fax capabilities is triggered. 255 The fax media connection may replace or be added to the audio 256 connection depending on the target applications. 258 4.1 Internet telephony gateways and fax detection 260 Two possible ways exist for an Internet telephony gateway to detect 261 a facsimile communication: 263 1. On the emitting gateway (the one sending the facsimile document), 264 the T.30 calling tone (CNG) is detected. The CNG tone is however an 265 optional signal [7]; 266 2. On the receiving gateway, the V.21 Preamble flag sequence is 267 detected. The Preamble is always present and follows the called 268 station identification tone (CED) when CED is present. 269 Note that even though the CED tone may be detected on the receiving 270 gateway, since the fax CED tone is similar to V.25 ANS modem tones, 271 it SHOULD NOT be used to trigger the fax switchover. 273 In conclusion, several conditions can trigger fax detection. 274 Internet telephony gateways supporting T.38 real-time facsimile MUST 275 support the detection of fax transmission on the V.21 Preamble flag 276 sequence; Internet telephony gateways MAY support the detection of 277 fax on CNG tone. The authors recommend that a facsimile 278 transmission SHOULD be detected on the receiving Internet telephony 279 gateway. 281 4.2 Internet telephony gateways and T.38 fax media connections 283 Upon successful fax detection, the description of the media 284 connection(s) is modified using the SDP protocol [8] as described in 285 SIP (see sections in chapter 5). 287 Several cases should be considered: 288 - In the case of Internet fax devices (supporting T.38 fax only 289 communications), the SIP session is established with SDP description 291 J-F. Mule/J. Li 6 292 SIP T.38 Call Flows February 2003 294 containing the T.38 media attributes; refer to section 5.1 for a 295 sample call flow for Internet fax devices. 296 - In the case of Internet telephony gateways, the SIP/SDP session is 297 modified and the T.38 fax media connection SHOULD replace the 298 existing audio media connection. The SIP UAC triggering the 299 modification of the session description MUST indicate all of its 300 T.38 media attributes in SDP. This is the recommended behavior for 301 gateways; refer to section 5.2 for a sample call flow illustrating 302 this scenario. 303 Some implementations MAY choose to add the fax media connection to 304 the existing audio connection and in that case, they SHOULD mute the 305 audio connection while fax is transmitted. Refer to section 5.3 for 306 a sample call flow illustrating this optional scenario. 308 Note: 309 Among the SDP T.38 media attributes being exchanged after fax 310 detection, implementors should particularly pay attention to 311 T38MaxBitRate, the maximum T.38 bit rate for the media connection. 312 It is recommended to implement the following rule when responding to 313 a maximum bit rate proposal. If the remote peer's SDP description 314 contains a maximum fax bit rate of X and the local host is set to a 315 maximum bit rate of Y (either by fax protocol detection or 316 configuration), the local host MUST propose a maximum fax rate of 317 min (X,Y) in the SIP response to the re-INVITE in order to 318 facilitate the negotiation. This note is exemplified in section 319 5.2.1. in messages F11-F14. Failures to implement this rule MAY 320 imply call teardown in some cases. 322 4.3 SIP session and fax termination 324 Upon completion of the fax transmission, any audio connection 325 successfully established prior to fax detection SHOULD be restored 326 or the session MUST be terminated. 328 4.4 Internet telephony gateways and fax pass-through mode 330 This section deals real-time facsimile communications over IP using 331 fax pass-through instead of T.38 fax relay. In this mode, the 332 facsimile communication is handled as a PCM audio call (PCMA/PCMU as 333 specified in ITU-T recommendation G.711). 335 The fax pass-through mode is important to prevent call failures, for 336 example in cases when one of the SIP communication peers does not 337 support T.38. For Internet telephony gateways with support for 338 PCM/G.711 audio but no support for T.38 real-time fax, it is 339 recommended to switch the session to fax pass-through mode. 340 Internet telephony gateways SHOULD handle the fall back mode to fax 341 pass-through by recognizing the SDP T.38 connection and proposing to 342 switch to a new audio connection. The new audio connection SHOULD 343 have the following characteristics: at a minimum, specify PCM G.711 344 codec, silence suppression OFF. The telephony gateway that 346 J-F. Mule/J. Li 7 347 SIP T.38 Call Flows February 2003 349 originated the failed T.38 re-INVITE SHOULD initiate the subsequent 350 re-INVITE to fax pass-through mode. 351 Refer to section 6.2 for a sample call flow illustrating this 352 scenario. 354 4.5 Responses to SIP OPTIONS request 355 Suggestion currently logged in section 8.4, just a placeholder for 356 now; <> 358 4.6 Beyond Internet telephony gateways 360 This document may also serve to vendors of SIP redirect servers or 361 other SIP UA types like SIP phones. Such SIP entities may recognize 362 the fax nature of the sessions and redirect the flows to the proper 363 real-time fax-capable devices or to other fax service providers. 365 5 Successful SIP T.38 fax Call Scenarios 367 5.1 Internet fax device - - fax only support 369 This section represents a SIP call flow for a T.38 fax session 370 between 2 Internet fax terminals. It is also applicable to Internet 371 telephony gateways when telephony ports are statically configured to 372 support fax only (case of analog IP telephony gateways where a 373 specific port is connected to a fax terminal). 374 A session starts with fax capabilities (t.38/udptl). The mechanism 375 for supporting T.38 in SIP & SDP is detailed in T.38 Annex D [9], a 376 temporary document that proposes an amendment to T.38 describing SIP 377 call establishment procedures. 379 5.1.1 Sequence Diagram 381 Internet Fax UA Proxy IFTGW UA 383 Fax | | | 384 ------->| F1 INVITE | | 385 emitted |------------------->| | 386 | | F2 INVITE | 387 | |------------------->| 388 | F3 100 Trying | | 389 |<-------------------| F4 100 Trying | 390 | |<-------------------| 391 | | | 392 | | F5 180 Ringing | 393 | F6 180 Ringing |<-------------------| 394 |<-------------------| | 395 | | F7 200 OK | 397 J-F. Mule/J. Li 8 398 SIP T.38 Call Flows February 2003 400 | F8 200 OK |<-------------------| 401 |<-------------------| | 402 | F9 ACK | | 403 |------------------->| F10 ACK | 404 | |------------------->| 405 | | 406 | T.38/UDPTL Fax Flow Established | 407 |<=======================================>| 408 End of | | 409 fax | | | 410 detected| | | 411 ------->| | | 412 | F11 BYE | | 413 |------------------->| | 414 | | F12 BYE | 415 | |------------------->| 416 | | F13 200 OK | 417 | |<-------------------| 418 | F14 200 OK | | 419 |<-------------------| | 421 5.1.2 Message Details 423 F1 INVITE I.FAX UA -> PROXY 425 INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 426 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 427 Max-Forwards: 70 428 From: iFax 429 ;tag=ab111 430 To: fax Bob 431 Call-ID: 1717@ifax.here.com 432 CSeq: 17 INVITE 433 Contact: 434 Content-Type: application/sdp 435 Content-Length: 320 437 v=0 438 o=ifaxgw1 2890846527 2890846527 IN IP4 ifax.here.com 439 s=Session SDP 440 c=IN IP4 ifaxmg.here.com 441 t=0 0 442 m=image 15002 udptl t38 443 a=T38FaxVersion:0 444 a=T38MaxBitRate:14400 445 a=T38FaxRateManagement:transferredTCF 446 a=T38FaxMaxBuffer:72 447 a=T38FaxMaxDatagram:316 448 a=T38FaxUdpEC:t38UDPFEC 449 a=T38FaxUdpEC:t38UDPRedundancy 451 J-F. Mule/J. Li 9 452 SIP T.38 Call Flows February 2003 454 F2 INVITE PROXY -> IFTGW UA 456 INVITE sip:+1-650-555-2222@iftgw.there.com;user=phone SIP/2.0 457 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 458 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 459 Max-Forwards: 69 460 Record-Route: 462 From: iFax 463 ;tag=ab111 464 To: fax Bob 465 Call-ID: 1717@ifax.here.com 466 CSeq: 17 INVITE 467 Contact: 468 Content-Type: application/sdp 469 Content-Length: 320 471 v=0 472 o=ifaxgw1 2890846527 2890846527 IN IP4 ifax.here.com 473 s=Session SDP 474 c=IN IP4 ifaxmg.here.com 475 t=0 0 476 m=image 15002 udptl t38 477 a=T38FaxVersion:0 478 a=T38MaxBitRate:14400 479 a=T38FaxRateManagement:transferredTCF 480 a=T38FaxMaxBuffer:72 481 a=T38FaxMaxDatagram:316 482 a=T38FaxUdpEC:t38UDPFEC 483 a=T38FaxUdpEC:t38UDPRedundancy 485 F3 (100 Trying) PROXY -> I.FAX UA 487 SIP/2.0 100 Trying 488 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 489 From: iFax 490 ;tag=ab111 491 To: fax Bob 492 Call-ID: 1717@ifax.here.com 493 CSeq: 17 INVITE 494 Content-Length: 0 496 F4 (100 Trying) IFTGW UA -> PROXY 498 SIP/2.0 100 Trying 499 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 500 Via: SIP/2.0/UDP ifax.here.com:5060 502 J-F. Mule/J. Li 10 503 SIP T.38 Call Flows February 2003 505 From: iFax 506 ;tag=ab111 507 To: fax Bob 508 Call-ID: 1717@ifax.here.com 509 CSeq: 17 INVITE 510 Contact: 511 Content-Length: 0 513 F5 180 Ringing IFTGW UA -> PROXY 515 SIP/2.0 180 Ringing 516 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 517 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 518 From: iFax 519 ;tag=ab111 520 To: fax Bob 521 Call-ID: 1717@ifax.here.com 522 CSeq: 17 INVITE 523 Contact: 524 Content-Length: 0 526 F6 180 Ringing PROXY -> I.FAX UA 528 SIP/2.0 180 Ringing 529 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 530 From: iFax 531 ;tag=ab111 532 To: fax Bob 533 Call-ID: 1717@ifax.here.com 534 CSeq: 17 INVITE 535 Contact: 536 Content-Length: 0 538 F7 200 OK IFTGW UA -> PROXY 540 SIP/2.0 200 OK 541 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 542 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 543 From: iFax 544 ;tag=ab111 545 To: fax Bob 546 Call-ID: 1717@ifax.here.com 547 CSeq: 17 INVITE 548 Contact: 549 Content-Type: application/sdp 550 Content-Length: 320 552 v=0 554 J-F. Mule/J. Li 11 555 SIP T.38 Call Flows February 2003 557 o=faxgw1 2890844527 2890844527 IN IP4 iftgw.there.com 558 s=Session SDP 559 c=IN IP4 iftmg.there.com 560 t=0 0 561 m=image 49172 udptl t38 562 a=T38FaxVersion:0 563 a=T38MaxBitRate:14400 564 a=T38FaxRateManagement:transferredTCF 565 a=T38FaxMaxBuffer:72 566 a=T38FaxMaxDatagram:316 567 a=T38FaxUdpEC:t38UDPRedundancy 569 F8 200 OK PROXY -> I.FAX UA 571 SIP/2.0 200 OK 572 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 573 Record-Route: 575 From: iFax 576 ;tag=ab111 577 To: fax Bob 578 Call-ID: 1717@ifax.here.com 579 CSeq: 17 INVITE 580 Contact: 581 Content-Type: application/sdp 582 Content-Length: 320 584 v=0 585 o=faxgw1 2890844527 2890844527 IN IP4 iftgw.there.com 586 s=Session SDP 587 c=IN IP4 iftmg.there.com 588 t=0 0 589 m=image 49172 udptl t38 590 a=T38FaxVersion:0 591 a=T38MaxBitRate:14400 592 a=T38FaxRateManagement:transferredTCF 593 a=T38FaxMaxBuffer:72 594 a=T38FaxMaxDatagram:316 595 a=T38FaxUdpEC:t38UDPRedundancy 597 F9 ACK I.FAX UA -> PROXY 599 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 600 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 601 Max-Forwards: 70 602 Route: 604 From: iFax 605 ;tag=ab111 606 To: fax Bob 607 Call-ID: 1717@ifax.here.com 609 J-F. Mule/J. Li 12 610 SIP T.38 Call Flows February 2003 612 CSeq: 17 ACK 613 Content-Length: 0 615 F10 ACK PROXY -> IFTGW UA 617 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 618 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 619 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 620 Max-Forwards: 69 621 Route: 623 From: iFax 624 ;tag=ab111 625 To: fax Bob 626 Call-ID: 1717@ifax.here.com 627 CSeq: 17 ACK 628 Content-Length: 0 630 /* T.38 fax streams are established. */ 632 F11 BYE I.FAX UA -> PROXY 634 BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 635 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 636 Max-Forwards: 70 637 Route: 639 From: iFax 640 ;tag=ab22 641 To: fax Bob 642 ;tag=cde34 643 Call-ID: 1717@ifax.here.com 644 CSeq: 18 BYE 645 Content-Length: 0 647 F12 BYE PROXY -> IFTGW UA 649 BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 650 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 651 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 652 Max-Forwards: 69 653 Record-Route: 655 From: iFax 656 ;tag=ab22 657 To: fax Bob 658 ;tag=cde34 659 Call-ID: 1717@ifax.here.com 660 CSeq: 18 BYE 662 J-F. Mule/J. Li 13 663 SIP T.38 Call Flows February 2003 665 Content-Length: 0 667 F13 200 OK IFTGW UA -> PROXY 669 SIP/2.0 200 OK 670 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 671 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 672 From: iFax 673 ;tag=ab22 674 To: fax Bob 675 ;tag=cde34 676 Call-ID: 1717@ifax.here.com 677 CSeq: 18 BYE 678 Content-Type: application/sdp 679 Content-Length: 0 681 F14 200 OK PROXY -> I.FAX UA 683 SIP/2.0 200 OK 684 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 685 Record-Route: 687 From: iFax 688 ;tag=ab22 689 To: fax Bob 690 ;tag=cde34 691 Call-ID: 1717@ifax.here.com 692 CSeq: 18 BYE 693 Content-Type: application/sdp 694 Content-Length: 0 696 5.2 SIP T.38 fax call - - fax stream replaces voice stream 698 This section represents the SIP call flow for a T.38 fax session 699 between 2 Internet telephony gateways (fax detection on terminating 700 side). 701 A session starts with audio capabilities, and then the session is 702 modified to switch to t38 fax mode (t.38/udptl). 704 Scenario: 705 1. A SIP INVITE is sent to the called party requesting a voice 706 connection per RFC3261; our scenario involves 1 SIP proxy. An audio 707 connection is established, 708 2. Upon detection of Preamble by the terminating gateway, a SIP re- 709 INVITE request is sent to the emitting gateway to modify the 710 parameters of the session to allow a T.38 fax media connection. 712 J-F. Mule/J. Li 14 713 SIP T.38 Call Flows February 2003 715 This INVITE request contains new SDP information detailing T.38 716 capabilities, 717 3. Upon successful acknowledgments, T.38 IFP fax packets are 718 sent/received on UDP ports, which may be the same UDP ports used for 719 audio RTP, 720 4. Once the fax transmission is terminated, audio capabilities are 721 ��restored�� or the call is terminated. 723 5.2.1 Sequence Diagram 724 In our example, we illustrate the fact that Internet telephony 725 gateways may use multiple network interfaces for signaling and/or 726 media streaming or one network interface with multiple IP addresses. 727 Typically, our example shows: 728 - one interface for SIP signaling 729 (ingress gateway = ift.here.com, egress gateway = iftgw.there.com) 730 - one or multiple interface(s) for media transport: 731 (ingress gateway = iftmg.here.com, egress gateway = iftmg.there.com) 732 A proxy is acting as a pure SIP signaling proxy 733 (obelix.banyuls.com). 735 IFT UA Proxy IFTGW UA 736 | | | 737 | F1 INVITE | | 738 |------------------->| | 739 | | F2 INVITE | 740 | |------------------->| 741 | F3 100 Trying | | 742 |<-------------------| F4 100 Trying | 743 | |<-------------------| 744 | | | 745 | | F5 180 Ringing | 746 | F6 180 Ringing |<-------------------| 747 |<-------------------| | 748 | | F7 200 OK | 749 | F8 200 OK |<-------------------| 750 |<-------------------| | 751 | | | 752 | F9 ACK | | 753 |------------------->| F10 ACK | 754 | ------------------->| 755 | | 756 | Both Way RTP Media Established | 757 Fax |<=======================================>| 758 ------->| | 759 emitted | | | 760 | | | Preamble 761 | | |<--------- 762 | | F11 INVITE | detected 763 | |<-------------------| 765 J-F. Mule/J. Li 15 766 SIP T.38 Call Flows February 2003 768 | F12 INVITE | | 769 |<-------------------| | 770 | | | 771 | F13 200 OK | | 772 |------------------->| | 773 | | F14 200 OK | 774 | |------------------->| 775 | | | 776 | | F15 ACK | 777 | |<-------------------| 778 | F16 ACK | | 779 |<-------------------| | 780 | | 781 | T.38/UDPT Fax Flow Established | 782 |<=======================================>| 783 End of | | 784 fax | | | 785 detected| | | 786 ------->| | | 787 | | | End of fax 788 | | |<---------- 789 | | | detected 791 | | F17 INVITE | 792 | |<-------------------| 793 | F18 INVITE | | 794 |<-------------------| | 795 | | | 796 | F19 200 OK | | 797 |------------------->| | 798 | | F20 200 OK | 799 | |------------------->| 800 | | | 801 | | F21 ACK | 802 | |<-------------------| 803 | F22 ACK | | 804 |<-------------------| | 806 | Both Way RTP Media Re-Established | 807 |<=======================================>| 808 | F23 BYE | | 809 |------------------->| | 810 | | F24 BYE | 811 | |------------------->| 812 | | | 813 | | F25 200 OK | 814 | |<-------------------| 815 | F26 200 OK | | 816 |<-------------------| | 818 J-F. Mule/J. Li 16 819 SIP T.38 Call Flows February 2003 821 5.2.2 Message Details 823 << NOTE: WIP - ALIGNMENT with RFC3261 req. incomplete for the rest 824 of the document.>> 826 F1 INVITE IFT UA -> PROXY 828 INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 829 Via: SIP/2.0/UDP ift.here.com:5060 830 Max-Forwards: 70 831 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 832 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone 833 Call-ID: 1717@ift.here.com 834 CSeq: 17 INVITE 835 Contact: 836 Content-Type: application/sdp 837 Content-Length: 146 839 v=0 840 o=IFAXTERMINAL01 2890844527 2890844527 IN IP4 ift.here.com 841 s=Session SDP 842 c=IN IP4 iftmg.here.com 843 t=0 0 844 m=audio 3456 RTP/AVP 0 845 a=rtpmap:0 PCMU/8000 847 F2 INVITE PROXY -> IFTGW UA 849 INVITE sip:+1-650-555-2222@iftgw.there.com;user=phone SIP/2.0 850 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 851 Via: SIP/2.0/UDP ift.here.com:5060 852 Max-Forwards: 69 853 Record-Route: 855 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 856 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone 857 Call-ID: 1717@ift.here.com 858 CSeq: 17 INVITE 859 Contact: 860 Content-Type: application/sdp 861 Content-Length: 146 863 v=0 864 o=IFAXTERMINAL01 2890844527 2890844527 IN IP4 ift.here.com 865 s=Session SDP 866 c=IN IP4 iftmg.here.com 867 t=0 0 868 m=audio 3456 RTP/AVP 0 869 a=rtpmap:0 PCMU/8000 871 F3 (100 Trying) PROXY -> IFT UA 873 J-F. Mule/J. Li 17 874 SIP T.38 Call Flows February 2003 876 SIP/2.0 100 Trying 877 Via: SIP/2.0/UDP ift.here.com:5060 878 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 879 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone 880 Call-ID: 1717@ift.here.com 881 CSeq: 17 INVITE 882 Content-Length: 0 884 F4 100 Trying IFTGW UA -> PROXY 886 SIP/2.0 100 Trying 887 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 888 Via: SIP/2.0/UDP ift.here.com:5060 889 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 890 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 891 Call-ID: 1717@ift.here.com 892 CSeq: 17 INVITE 893 Contact: 894 Content-Length: 0 896 F5 180 Ringing IFTGW UA -> PROXY 898 SIP/2.0 180 Ringing 899 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 900 Via: SIP/2.0/UDP ift.here.com:5060 901 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 902 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 903 Call-ID: 1717@ift.here.com 904 CSeq: 17 INVITE 905 Contact: 906 Content-Length: 0 908 F6 180 Ringing PROXY -> IFT UA 910 SIP/2.0 180 Ringing 911 Via: SIP/2.0/UDP ift.here.com:5060 912 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 913 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 914 Call-ID: 1717@ift.here.com 915 CSeq: 17 INVITE 916 Contact: 917 Content-Length: 0 919 F7 200 OK IFTGW UA -> PROXY 921 SIP/2.0 200 OK 922 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 923 Via: SIP/2.0/UDP ift.here.com:5060 925 J-F. Mule/J. Li 18 926 SIP T.38 Call Flows February 2003 928 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 929 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 930 Call-ID: 1717@ift.here.com 931 CSeq: 17 INVITE 932 Contact: 933 Content-Type: application/sdp 934 Content-Length: 150 936 v=0 937 o=IFAXTERMINAL01 2890844527 171089 IN IP4 iftgw.there.com 938 s=Session SDP 939 c=IN IP4 iftmg.there.com 940 t=0 0 941 m=audio 12322 RTP/AVP 0 942 a=rtpmap:0 PCMU/8000 944 F8 200 OK PROXY -> IFT UA 946 SIP/2.0 200 OK 947 Via: SIP/2.0/UDP ift.here.com:5060 948 Record-Route: 950 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 951 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 952 Call-ID: 1717@ift.here.com 953 CSeq: 17 INVITE 954 Contact: 955 Content-Type: application/sdp 956 Content-Length: 150 958 v=0 959 o=IFAXTERMINAL01 2890844527 171089 IN IP4 iftgw.there.com 960 s=Session SDP 961 c=IN IP4 iftmg.there.com 962 t=0 0 963 m=audio 12322 RTP/AVP 0 964 a=rtpmap:0 PCMU/8000 966 F9 ACK IFT UA -> PROXY 968 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 969 Via: SIP/2.0/UDP ift.here.com:5060 970 Max-Forwards: 70 971 Route: 973 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 974 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 975 Call-ID: 1717@ift.here.com 976 CSeq: 17 ACK 977 Content-Length: 0 979 J-F. Mule/J. Li 19 980 SIP T.38 Call Flows February 2003 982 F10 ACK PROXY -> IFTGW UA 984 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 985 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 986 Via: SIP/2.0/UDP ift.here.com:5060 987 Max-Forwards: 69 988 Record-Route: 990 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 991 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 992 Call-ID: 1717@ift.here.com 993 CSeq: 17 ACK 994 Content-Length: 0 996 /* RTP streams are established. The CNG fax tone is sent in-band if 997 it is present. The receiving side IFT gateway DSP detects the 998 Preamble sequence. A new UDP port is open on IFTGW for T.38 IFP 999 packets and the IFTGW signals the switch over to fax mode by send a 1000 re-INVITE with the new UDP port in the SDP. 1001 Note: the IFTGW has a T38MaxBitRate configured to 9600 */ 1003 F11 INVITE IFTGW UA -> PROXY 1005 INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1006 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1007 Max-Forwards: 70 1008 Route: 1010 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1011 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1012 Call-ID: 1717@ift.here.com 1013 CSeq: 18 INVITE 1014 Contact: 1015 Content-Type: application/sdp 1016 Content-Length: 320 1018 v=0 1019 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com 1020 s=Session SDP 1021 c=IN IP4 iftmg.there.com 1022 t=0 0 1023 m=image 49172 udptl t38 1024 a=T38FaxVersion:0 1025 a=T38MaxBitRate:9600 1026 a=T38FaxRateManagement:transferredTCF 1027 a=T38FaxMaxBuffer:72 1029 J-F. Mule/J. Li 20 1030 SIP T.38 Call Flows February 2003 1032 a=T38FaxMaxDatagram:316 1033 a=T38FaxUdpEC:t38UDPFEC 1034 a=T38FaxUdpEC:t38UDPRedundancy 1036 F12 INVITE PROXY -> IFT UA 1038 INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1039 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 1040 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1041 Max-Forwards: 69 1042 Record-Route: 1044 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1045 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1046 Call-ID: 1717@ift.here.com 1047 CSeq: 18 INVITE 1048 Contact: 1049 Content-Type: application/sdp 1050 Content-Length: 320 1052 v=0 1053 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com 1054 s=Session SDP 1055 c=IN IP4 iftmg.there.com 1056 t=0 0 1057 m=image 49172 udptl t38 1058 a=T38FaxVersion:0 1059 a=T38MaxBitRate:9600 1060 a=T38FaxRateManagement:transferredTCF 1061 a=T38FaxMaxBuffer:72 1062 a=T38FaxMaxDatagram:316 1063 a=T38FaxUdpEC:t38UDPFEC 1064 a=T38FaxUdpEC:t38UDPRedundancy 1066 /* Note: the IFT has a T38MaxBitRate configured to 14400 but since 1067 it received a T38MaxBitRate proposal of 9600, it replies with 1068 T38MaxBitRate = min (9600,14400) */ 1070 F13 200 OK IFT UA -> PROXY 1072 SIP/2.0 200 OK 1073 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 1074 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1075 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1076 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1077 Call-ID: 1717@ift.here.com 1078 CSeq: 18 INVITE 1079 Contact: 1080 Content-Type: application/sdp 1081 Content-Length: 320 1083 v=0 1085 J-F. Mule/J. Li 21 1086 SIP T.38 Call Flows February 2003 1088 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com 1089 s=Session SDP 1090 c=IN IP4 iftmg.here.com 1091 t=0 0 1092 m=image 15002 udptl t38 1093 a=T38FaxVersion:0 1094 a=T38MaxBitRate:9600 1095 a=T38FaxRateManagement:transferredTCF 1096 a=T38FaxMaxBuffer:72 1097 a=T38FaxMaxDatagram:316 1098 a=T38FaxUdpEC:t38UDPRedundancy 1100 F14 200 OK PROXY -> IFT UA 1102 SIP/2.0 200 OK 1103 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1104 Record-Route: 1106 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1107 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1108 Call-ID: 1717@ift.here.com 1109 CSeq: 18 INVITE 1110 Contact: 1111 Content-Type: application/sdp 1112 Content-Length: 320 1114 v=0 1115 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com 1116 s=Session SDP 1117 c=IN IP4 iftmg.here.com 1118 t=0 0 1119 m=image 15002 udptl t38 1120 a=T38FaxVersion:0 1121 a=T38MaxBitRate:9600 1122 a=T38FaxRateManagement:transferredTCF 1123 a=T38FaxMaxBuffer:72 1124 a=T38FaxMaxDatagram:316 1125 a=T38FaxUdpEC:t38UDPRedundancy 1127 F15 ACK IFTGW UA -> PROXY 1129 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1130 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1131 Max-Forwards: 70 1132 Route: 1134 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1135 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1136 Call-ID: 1717@ift.here.com 1137 CSeq: 18 ACK 1138 Content-Length: 0 1140 J-F. Mule/J. Li 22 1141 SIP T.38 Call Flows February 2003 1143 F16 ACK PROXY -> IFT UA 1145 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1146 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 1147 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1148 Max-Forwards: 69 1149 Record-Route: 1151 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1152 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1153 Call-ID: 1717@ift.here.com 1154 CSeq: 18 ACK 1155 Content-Length: 0 1157 /* T.38 fax transmission established both ways */ 1159 /* Then, the end of the fax transmission is detected on ingress side 1160 and sent to the egress side (IFTGW). IFTGW initiates the switch 1161 back to voice communication */ 1163 F17 INVITE IFTGW UA -> PROXY 1165 INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1166 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1167 Max-Forwards: 70 1168 Route: 1170 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1171 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1172 Call-ID: 1717@ift.here.com 1173 CSeq: 19 INVITE 1174 Contact: 1175 Content-Type: application/sdp 1176 Content-Length: 181 1178 v=0 1179 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com 1180 s=Session SDP 1181 c=IN IP4 iftmg.there.com 1182 t=0 0 1183 m=audio 12322 RTP/AVP 0 1184 a=rtpmap:0 PCMU/8000 1186 F18 INVITE PROXY -> IFT UA 1188 INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1189 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 1190 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1192 J-F. Mule/J. Li 23 1193 SIP T.38 Call Flows February 2003 1195 Max-Forwards: 69 1196 Record-Route: 1198 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1199 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1200 Call-ID: 1717@ift.here.com 1201 CSeq: 19 INVITE 1202 Contact: 1203 Content-Type: application/sdp 1204 Content-Length: 181 1206 v=0 1207 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com 1208 s=Session SDP 1209 c=IN IP4 iftmg.there.com 1210 t=0 0 1211 m=audio 12322 RTP/AVP 0 1212 a=rtpmap:0 PCMU/8000 1214 F19 200 OK IFT UA -> PROXY 1216 SIP/2.0 200 OK 1217 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 1218 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1219 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1220 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1221 Call-ID: 1717@ift.here.com 1222 CSeq: 19 INVITE 1223 Contact: 1224 Content-Type: application/sdp 1225 Content-Length: 150 1227 v=0 1228 o=faxgw1 2890844527 2890844529 IN IP4 ift.here.com 1229 s=Session SDP 1230 c=IN IP4 iftmg.here.com 1231 t=0 0 1232 m=audio 3456 RTP/AVP 0 1233 a=rtpmap:0 PCMU/8000 1235 F20 200 OK PROXY -> IFTGW UA 1237 SIP/2.0 200 OK 1238 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1239 Record-Route: 1241 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1242 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1243 Call-ID: 1717@ift.here.com 1244 CSeq: 19 INVITE 1245 Contact: 1247 J-F. Mule/J. Li 24 1248 SIP T.38 Call Flows February 2003 1250 Content-Type: application/sdp 1251 Content-Length: 150 1253 v=0 1254 o=faxgw1 2890844527 2890844529 IN IP4 ift.here.com 1255 s=Session SDP 1256 c=IN IP4 iftmg.here.com 1257 t=0 0 1258 m=audio 3456 RTP/AVP 0 1259 a=rtpmap:0 PCMU/8000 1261 F21 ACK IFTGW UA -> PROXY 1263 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1264 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1265 Max-Forwards: 70 1266 Route: 1268 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1269 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1270 Call-ID: 1717@ift.here.com 1271 CSeq: 19 ACK 1272 Content-Length: 0 1274 F22 ACK PROXY -> IFT UA 1276 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1277 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 1278 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1279 Max-Forwards: 69 1280 Record-Route: 1282 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1283 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1284 Call-ID: 1717@ift.here.com 1285 CSeq: 19 ACK 1286 Content-Length: 0 1288 /* Voice streams re-established both ways */ 1290 F23 BYE IFT UA -> PROXY 1292 BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 1293 Via: SIP/2.0/UDP ift.here.com:5060 1294 Max-Forwards: 70 1295 Route: 1298 J-F. Mule/J. Li 25 1299 SIP T.38 Call Flows February 2003 1301 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1302 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone 1303 Call-ID: 1717@ift.here.com 1304 CSeq: 20 BYE 1305 Content-Length: 0 1307 F24 BYE PROXY -> IFTGW UA 1309 BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 1310 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 1311 Via: SIP/2.0/UDP ift.here.com:5060 1312 Max-Forwards: 69 1313 Record-Route: 1315 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1316 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone 1317 Call-ID: 1717@ift.here.com 1318 CSeq: 20 BYE 1319 Content-Length: 0 1321 F25 200 OK IFTGW UA -> PROXY 1323 SIP/2.0 200 OK 1324 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 1325 Via: SIP/2.0/UDP ift.here.com:5060 1326 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1327 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde24 1328 Call-ID: 1717@ift.here.com 1329 CSeq: 20 BYE 1330 Content-Type: application/sdp 1331 Content-Length: 0 1333 F26 200 OK PROXY -> IFT UA 1335 SIP/2.0 200 OK 1336 Via: SIP/2.0/UDP ift.here.com:5060 1337 Record-Route: 1339 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1340 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde24 1341 Call-ID: 1717@ift.here.com 1342 CSeq: 20 BYE 1343 Content-Type: application/sdp 1344 Content-Length: 0 1346 5.3 SIP T.38 fax call - - fax stream added to voice stream 1348 J-F. Mule/J. Li 26 1349 SIP T.38 Call Flows February 2003 1351 This section represents the SIP call flow for a T.38 fax session 1352 between 2 Internet telephony gateways. It shows the detection of 1353 the fax communication on terminating or receiving side. 1354 A session starts with one audio stream in SDP, and, upon detection 1355 of fax, an additional fax stream is added to the session while the 1356 voice stream is muted. After the fax communication is terminated, 1357 the fax stream is terminated and the voice stream is restored. 1359 Scenario: 1360 1. A SIP INVITE is sent to the called party requesting a voice 1361 connection per RFC3261; our scenario involves 1 SIP proxy. An audio 1362 connection is established, 1363 2. Upon detection of Preamble by the terminating gateway, a SIP 1364 re�INVITE request is sent to the emitting gateway to modify the 1365 parameters of the session to add a T.38 fax connection. The 1366 connection data is specified per media description and not at the 1367 session-level. This allows the audio stream and t.38 fax stream to 1368 be controlled independently (i.e., placing the audio on hold while 1369 the t.38 fax transmission is active). Also note that the t.38 fax 1370 media stream has been added to the session. This re-INVITE request 1371 contains SDP information detailing the additional T.38 capabilities, 1372 3. It is suggested that the voice pipe be muted while the fax 1373 session is in progress. Upon successful acknowledgments, T.38 IFP 1374 fax packets are sent/received on different UDP ports than the one 1375 used for audio RTP, 1376 4. Once the fax transmission is terminated, audio capabilities are 1377 ��restored�� or the call is terminated. 1379 5.3.1 Sequence Diagram 1381 IFT UA Proxy IFTGW UA 1382 | | | 1383 | F1 INVITE | | 1384 |------------------->| | 1385 | | F2 INVITE | 1386 | |------------------->| 1387 | F3 100 Trying | | 1388 |<-------------------| F4 100 Trying | 1389 | |<-------------------| 1390 | | | 1391 | | F5 180 Ringing | 1392 | F6 180 Ringing |<-------------------| 1393 |<-------------------| | 1394 | | F7 200 OK | 1395 | F8 200 OK |<-------------------| 1396 |<-------------------| | 1397 | | | 1398 | F9 ACK | | 1399 |------------------->| F10 ACK | 1400 | ------------------->| 1401 | | 1403 J-F. Mule/J. Li 27 1404 SIP T.38 Call Flows February 2003 1406 | Both Way RTP Media Established | 1407 Fax |<=======================================>| 1408 ------->| | 1409 emitted | | | 1410 | | | Preamble 1411 | | |<--------- 1412 | | F11 INVITE | detected 1413 | |<-------------------| 1414 | F12 INVITE | | 1415 |<-------------------| | 1416 | | | 1417 | F13 200 OK | | 1418 |------------------->| | 1419 | | F14 200 OK | 1420 | |------------------->| 1421 | | F15 ACK | 1422 | |<-------------------| 1423 | F16 ACK | | 1424 |<-------------------| | 1425 | | 1426 | T.38/UDPT Fax Flow Established | 1427 | Voice connection muted | 1428 |<=======================================>| 1429 End of | | 1430 fax | | | 1431 detected| | | 1432 ------->| | | 1433 | | 1434 | | | End of fax 1435 | | |<---------- 1436 | | | detected 1437 | | F17 INVITE | 1438 | |<-------------------| 1439 | F18 INVITE | | 1440 |<-------------------| | 1441 | | | 1442 | F19 200 OK | | 1443 |------------------->| | 1444 | | F20 200 OK | 1445 | |------------------->| 1446 | | | 1447 | | F21 ACK | 1448 | |<-------------------| 1449 | F22 ACK | | 1450 |<-------------------| | 1451 | | 1452 | Both way RTP Flow restored | 1453 |<=======================================>| 1454 | | 1455 | F23 BYE | | 1456 |------------------->| | 1457 | | F24 BYE | 1459 J-F. Mule/J. Li 28 1460 SIP T.38 Call Flows February 2003 1462 | |------------------->| 1463 | | | 1464 | | F25 200 OK | 1465 | |<-------------------| 1466 | F26 200 OK | | 1467 |<-------------------| | 1469 5.3.2 Message Details 1471 F1 INVITE IFT UA -> PROXY 1473 INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1474 Via: SIP/2.0/UDP ift.here.com:5060 1475 Max-Forwards: 70 1476 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1477 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone 1478 Call-ID: 1717@ift.here.com 1479 CSeq: 17 INVITE 1480 Contact: 1481 Content-Type: application/sdp 1482 Content-Length: 146 1484 v=0 1485 o=IFAXTERMINAL01 2890844527 2890844527 IN IP4 ift.here.com 1486 s=Session SDP 1487 c=IN IP4 iftmg.here.com 1488 t=0 0 1489 m=audio 3456 RTP/AVP 0 1490 a=rtpmap:0 PCMU/8000 1492 F2 INVITE PROXY -> IFTGW UA 1494 INVITE sip:+1-650-555-2222@iftgw.there.com;user=phone SIP/2.0 1495 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 1496 Via: SIP/2.0/UDP ift.here.com:5060 1497 Max-Forwards: 69 1498 Record-Route: 1500 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1501 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone 1502 Call-ID: 1717@ift.here.com 1503 CSeq: 17 INVITE 1504 Contact: 1505 Content-Type: application/sdp 1506 Content-Length: 146 1508 v=0 1509 o=IFAXTERMINAL01 2890844527 2890844527 IN IP4 ift.here.com 1510 s=Session SDP 1512 J-F. Mule/J. Li 29 1513 SIP T.38 Call Flows February 2003 1515 c=IN IP4 iftmg.here.com 1516 t=0 0 1517 m=audio 3456 RTP/AVP 0 1518 a=rtpmap:0 PCMU/8000 1520 F3 (100 Trying) PROXY -> IFT UA 1522 SIP/2.0 100 Trying 1523 Via: SIP/2.0/UDP ift.here.com:5060 1524 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1525 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone 1526 Call-ID: 1717@ift.here.com 1527 CSeq: 17 INVITE 1528 Content-Length: 0 1530 F4 100 Trying IFTGW UA -> PROXY 1532 SIP/2.0 100 Trying 1533 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 1534 Via: SIP/2.0/UDP ift.here.com:5060 1535 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1536 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1537 Call-ID: 1717@ift.here.com 1538 CSeq: 17 INVITE 1539 Contact: 1540 Content-Length: 0 1542 F5 180 Ringing IFTGW UA -> PROXY 1544 SIP/2.0 180 Ringing 1545 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 1546 Via: SIP/2.0/UDP ift.here.com:5060 1547 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1548 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1549 Call-ID: 1717@ift.here.com 1550 CSeq: 17 INVITE 1551 Contact: 1552 Content-Length: 0 1554 F6 180 Ringing PROXY -> IFT UA 1556 SIP/2.0 180 Ringing 1557 Via: SIP/2.0/UDP ift.here.com:5060 1558 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1559 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1560 Call-ID: 1717@ift.here.com 1561 CSeq: 17 INVITE 1562 Contact: 1563 Content-Length: 0 1565 J-F. Mule/J. Li 30 1566 SIP T.38 Call Flows February 2003 1568 F7 200 OK IFTGW UA -> PROXY 1570 SIP/2.0 200 OK 1571 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 1572 Via: SIP/2.0/UDP ift.here.com:5060 1573 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1574 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1575 Call-ID: 1717@ift.here.com 1576 CSeq: 17 INVITE 1577 Contact: 1578 Content-Type: application/sdp 1579 Content-Length: 150 1581 v=0 1582 o=IFAXTERMINAL01 2890844527 171089 IN IP4 iftgw.there.com 1583 s=Session SDP 1584 c=IN IP4 iftmg.there.com 1585 t=0 0 1586 m=audio 12322 RTP/AVP 0 1587 a=rtpmap:0 PCMU/8000 1589 F8 200 OK PROXY -> IFT UA 1591 SIP/2.0 200 OK 1592 Via: SIP/2.0/UDP ift.here.com:5060 1593 Record-Route: 1595 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1596 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1597 Call-ID: 1717@ift.here.com 1598 CSeq: 17 INVITE 1599 Contact: 1600 Content-Type: application/sdp 1601 Content-Length: 150 1603 v=0 1604 o=IFAXTERMINAL01 2890844527 171089 IN IP4 iftgw.there.com 1605 s=Session SDP 1606 c=IN IP4 iftmg.there.com 1607 t=0 0 1608 m=audio 12322 RTP/AVP 0 1609 a=rtpmap:0 PCMU/8000 1611 F9 ACK IFT UA -> PROXY 1613 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1614 Via: SIP/2.0/UDP ift.here.com:5060 1615 Max-Forwards: 70 1617 J-F. Mule/J. Li 31 1618 SIP T.38 Call Flows February 2003 1620 Route: 1622 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1623 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1624 Call-ID: 1717@ift.here.com 1625 CSeq: 17 ACK 1626 Content-Length: 0 1628 F10 ACK PROXY -> IFTGW UA 1630 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1631 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 1632 Via: SIP/2.0/UDP ift.here.com:5060 1633 Max-Forwards: 69 1634 Record-Route: 1636 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1637 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1638 Call-ID: 1717@ift.here.com 1639 CSeq: 17 ACK 1640 Content-Length: 0 1642 /* RTP streams are established. The CNG fax tone is sent in-band if 1643 it is present. The receiving side IFT gateway DSP detects the 1644 Preamble. A new UDP port is open on IFTGW for T.38 IFP packets and 1645 the IFTGW signals the switch over to fax mode by send a re-INVITE 1646 with the new UDP port in the SDP */ 1648 F11 INVITE IFTGW UA -> PROXY 1650 INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1651 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1652 Max-Forwards: 70 1653 Route: 1655 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1656 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1657 Call-ID: 1717@ift.here.com 1658 CSeq: 18 INVITE 1659 Contact: 1660 Content-Type: application/sdp 1661 Content-Length: 320 1663 v=0 1664 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com 1665 s=Session SDP 1666 t=0 0 1667 m=audio 12322 RTP/AVP 0 1668 c=IN IP4 0.0.0.0 1669 m=image 49172 udptl t38 1670 c=IN IP4 iftmg.there.com 1672 J-F. Mule/J. Li 32 1673 SIP T.38 Call Flows February 2003 1675 a=T38FaxVersion:0 1676 a=T38MaxBitRate:14400 1677 a=T38FaxRateManagement:transferredTCF 1678 a=T38FaxMaxBuffer:72 1679 a=T38FaxMaxDatagram:316 1680 a=T38FaxUdpEC:t38UDPFEC 1681 a=T38FaxUdpEC:t38UDPRedundancy 1683 F12 INVITE PROXY -> IFT UA 1685 INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1686 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 1687 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1688 Max-Forwards: 69 1689 Record-Route: 1691 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1692 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1693 Call-ID: 1717@ift.here.com 1694 CSeq: 18 INVITE 1695 Contact: 1696 Content-Type: application/sdp 1697 Content-Length: 320 1699 v=0 1700 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com 1701 s=Session SDP 1702 t=0 0 1703 m=audio 12322 RTP/AVP 0 1704 c=IN IP4 0.0.0.0 1705 m=image 49172 udptl t38 1706 c=IN IP4 iftmg.there.com 1707 a=T38FaxVersion:0 1708 a=T38MaxBitRate:14400 1709 a=T38FaxRateManagement:transferredTCF 1710 a=T38FaxMaxBuffer:72 1711 a=T38FaxMaxDatagram:316 1712 a=T38FaxUdpEC:t38UDPFEC 1713 a=T38FaxUdpEC:t38UDPRedundancy 1715 F13 200 OK IFT UA -> PROXY 1717 SIP/2.0 200 OK 1718 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 1719 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1720 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1721 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1722 Call-ID: 1717@ift.here.com 1723 CSeq: 18 INVITE 1724 Contact: 1725 Content-Type: application/sdp 1727 J-F. Mule/J. Li 33 1728 SIP T.38 Call Flows February 2003 1730 Content-Length: 320 1732 v=0 1733 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com 1734 s=Session SDP 1735 t=0 0 1736 m=audio 3456 RTP/AVP 0 1737 c=IN IP4 0.0.0.0 1738 m=image 15002 udptl t38 1739 c=IN IP4 iftmg.here.com 1740 a=T38FaxVersion:0 1741 a=T38MaxBitRate:14400 1742 a=T38FaxRateManagement:transferredTCF 1743 a=T38FaxMaxBuffer:72 1744 a=T38FaxMaxDatagram:316 1745 a=T38FaxUdpEC:t38UDPRedundancy 1747 F14 200 OK PROXY -> IFT UA 1749 SIP/2.0 200 OK 1750 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1751 Record-Route: 1753 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1754 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1755 Call-ID: 1717@ift.here.com 1756 CSeq: 18 INVITE 1757 Contact: 1758 Content-Type: application/sdp 1759 Content-Length: 320 1761 v=0 1762 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com 1763 s=Session SDP 1764 t=0 0 1765 m=audio 3456 RTP/AVP 0 1766 c=IN IP4 0.0.0.0 1767 m=image 15002 udptl t38 1768 c=IN IP4 iftmg.here.com 1769 a=T38FaxVersion:0 1770 a=T38MaxBitRate:14400 1771 a=T38FaxRateManagement:transferredTCF 1772 a=T38FaxMaxBuffer:72 1773 a=T38FaxMaxDatagram:316 1774 a=T38FaxUdpEC:t38UDPRedundancy 1776 F15 ACK IFTGW UA -> PROXY 1778 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1779 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1780 Max-Forwards: 70 1782 J-F. Mule/J. Li 34 1783 SIP T.38 Call Flows February 2003 1785 Route: 1787 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1788 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1789 Call-ID: 1717@ift.here.com 1790 CSeq: 18 ACK 1791 Content-Length: 0 1793 F16 ACK PROXY -> IFT UA 1795 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1796 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 1797 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1798 Max-Forwards: 69 1799 Record-Route: 1801 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1802 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1803 Call-ID: 1717@ift.here.com 1804 CSeq: 18 ACK 1805 Content-Length: 0 1807 /* T.38 fax transmission established both ways and the voice stream 1808 is muted */ 1809 /* Then, the end of the fax transmission is detected on ingress side 1810 and sent to the egress side (IFTGW). IFTGW initiates the switch back 1811 to voice communication */ 1813 F17 INVITE IFTGW UA -> PROXY 1815 INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1816 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1817 Max-Forwards: 70 1818 Route: 1820 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1821 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1822 Call-ID: 1717@ift.here.com 1823 CSeq: 19 INVITE 1824 Contact: 1825 Content-Type: application/sdp 1826 Content-Length: 181 1828 v=0 1829 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com 1830 s=Session SDP 1831 c=IN IP4 iftmg.there.com 1832 t=0 0 1833 m=audio 12322 RTP/AVP 0 1834 a=rtpmap:0 PCMU/8000 1836 J-F. Mule/J. Li 35 1837 SIP T.38 Call Flows February 2003 1839 F18 INVITE PROXY -> IFT UA 1841 INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1842 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 1843 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1844 Max-Forwards: 69 1845 Record-Route: 1847 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1848 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1849 Call-ID: 1717@ift.here.com 1850 CSeq: 19 INVITE 1851 Contact: 1852 Content-Type: application/sdp 1853 Content-Length: 181 1855 v=0 1856 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com 1857 s=Session SDP 1858 c=IN IP4 iftmg.there.com 1859 t=0 0 1860 m=audio 12322 RTP/AVP 0 1861 a=rtpmap:0 PCMU/8000 1863 F19 200 OK IFT UA -> PROXY 1865 SIP/2.0 200 OK 1866 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 1867 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1868 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1869 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1870 Call-ID: 1717@ift.here.com 1871 CSeq: 19 INVITE 1872 Contact: 1873 Content-Type: application/sdp 1874 Content-Length: 150 1876 v=0 1877 o=faxgw1 2890844527 2890844529 IN IP4 ift.here.com 1878 s=Session SDP 1879 c=IN IP4 iftmg.here.com 1880 t=0 0 1881 m=audio 3456 RTP/AVP 0 1882 a=rtpmap:0 PCMU/8000 1884 F20 200 OK PROXY -> IFTGW UA 1886 SIP/2.0 200 OK 1887 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1889 J-F. Mule/J. Li 36 1890 SIP T.38 Call Flows February 2003 1892 Record-Route: 1894 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1895 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1896 Call-ID: 1717@ift.here.com 1897 CSeq: 19 INVITE 1898 Contact: 1899 Content-Type: application/sdp 1900 Content-Length: 150 1902 v=0 1903 o=faxgw1 2890844527 2890844529 IN IP4 ift.here.com 1904 s=Session SDP 1905 c=IN IP4 iftmg.here.com 1906 t=0 0 1907 m=audio 3456 RTP/AVP 0 1908 a=rtpmap:0 PCMU/8000 1910 F21 ACK IFTGW UA -> PROXY 1912 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1913 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1914 Max-Forwards: 70 1915 Route: 1917 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1918 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1919 Call-ID: 1717@ift.here.com 1920 CSeq: 19 ACK 1921 Content-Length: 0 1923 F22 ACK PROXY -> IFT UA 1925 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 1926 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 1927 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 1928 Max-Forwards: 69 1929 Record-Route: 1931 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1932 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 1933 Call-ID: 1717@ift.here.com 1934 CSeq: 19 ACK 1935 Content-Length: 0 1937 F23 BYE IFT UA -> PROXY 1939 BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 1940 Via: SIP/2.0/UDP ift.here.com:5060 1941 Max-Forwards: 70 1942 Route: 1948 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1949 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone 1950 Call-ID: 1717@ift.here.com 1951 CSeq: 20 BYE 1952 Content-Length: 0 1954 F24 BYE PROXY -> IFTGW UA 1956 BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 1957 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 1958 Via: SIP/2.0/UDP ift.here.com:5060 1959 Max-Forwards: 69 1960 Record-Route: 1962 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1963 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone 1964 Call-ID: 1717@ift.here.com 1965 CSeq: 20 BYE 1966 Content-Length: 0 1968 F25 200 OK IFTGW UA -> PROXY 1970 SIP/2.0 200 OK 1971 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 1972 Via: SIP/2.0/UDP ift.here.com:5060 1973 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1974 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde24 1975 Call-ID: 1717@ift.here.com 1976 CSeq: 20 BYE 1977 Content-Type: application/sdp 1978 Content-Length: 0 1980 F26 200 OK PROXY -> IFT UA 1982 SIP/2.0 200 OK 1983 Via: SIP/2.0/UDP ift.here.com:5060 1984 Record-Route: 1986 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1987 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde24 1988 Call-ID: 1717@ift.here.com 1989 CSeq: 20 BYE 1990 Content-Type: application/sdp 1991 Content-Length: 0 1993 5.4 SIP T.38 fax call - - fax stream forced to replace voice stream 1995 This section illustrates the following scenario: 1997 J-F. Mule/J. Li 38 1998 SIP T.38 Call Flows February 2003 2000 1. A SIP INVITE is sent to the called party requesting a voice 2001 connection per RFC3261; our scenario involves 1 SIP proxy. An audio 2002 connection is established, 2003 2. Upon detection of Preamble by the terminating gateway, a SIP 2004 re�INVITE request is sent to the emitting gateway to modify the 2005 parameters of the session to add a T.38 fax connection. This re- 2006 INVITE request contains SDP information detailing the additional 2007 T.38 capabilities. It is also suggested that the voice pipe be 2008 muted while the fax session is in progress. 2009 3. The emitting gateway does not have the resources to maintain both 2010 the audio & fax streams and replies by allowing the fax media 2011 stream. Upon successful acknowledgments, the audio stream is 2012 terminated and T.38 IFP fax packets are exchanged, 2013 4. Once the fax transmission is terminated, audio capabilities are 2014 ��re-negotiated�� and the call is terminated. 2016 5.4.1 Sequence Diagram 2017 Refer to section 5.3.1; sequence diagram is unchanged. 2019 5.4.2 Message Details 2020 See section 5.3.2 for the complete set of messages. We only 2021 indicate the changed messages based on the emitting gateway�s 2022 decline to support both voice and fax streams. 2024 ... 2025 F11 INVITE IFTGW UA -> PROXY 2027 INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 2028 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 2029 Max-Forwards: 70 2030 Route: 2032 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2033 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 2034 Call-ID: 1717@ift.here.com 2035 CSeq: 18 INVITE 2036 Contact: 2037 Content-Type: application/sdp 2038 Content-Length: 320 2040 v=0 2041 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com 2042 s=Session SDP 2043 t=0 0 2044 m=audio 12322 RTP/AVP 0 2045 c=IN IP4 0.0.0.0 2046 m=image 49172 udptl t38 2047 c=IN IP4 iftmg.there.com 2048 a=T38FaxVersion:0 2049 a=T38MaxBitRate:14400 2051 J-F. Mule/J. Li 39 2052 SIP T.38 Call Flows February 2003 2054 a=T38FaxRateManagement:transferredTCF 2055 a=T38FaxMaxBuffer:72 2056 a=T38FaxMaxDatagram:316 2057 a=T38FaxUdpEC:t38UDPFEC 2058 a=T38FaxUdpEC:t38UDPRedundancy 2060 F12 INVITE PROXY -> IFT UA 2062 INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 2063 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 2064 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 2065 Max-Forwards: 69 2066 Record-Route: 2068 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2069 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 2070 Call-ID: 1717@ift.here.com 2071 CSeq: 18 INVITE 2072 Contact: 2073 Content-Type: application/sdp 2074 Content-Length: 320 2076 v=0 2077 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com 2078 s=Session SDP 2079 t=0 0 2080 m=audio 12322 RTP/AVP 0 2081 c=IN IP4 0.0.0.0 2082 m=image 49172 udptl t38 2083 c=IN IP4 iftmg.there.com 2084 a=T38FaxVersion:0 2085 a=T38MaxBitRate:14400 2086 a=T38FaxRateManagement:transferredTCF 2087 a=T38FaxMaxBuffer:72 2088 a=T38FaxMaxDatagram:316 2089 a=T38FaxUdpEC:t38UDPFEC 2090 a=T38FaxUdpEC:t38UDPRedundancy 2092 F13 200 OK IFT UA -> PROXY 2094 SIP/2.0 200 OK 2095 Via: SIP/2.0/UDP obelix.banyuls.com:5060; 2096 branch=z9hG4bK2d008.1 2097 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 2098 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2099 To: sip:+1-650-555- 2100 2222@obelix.banyuls.com;user=phone;tag=cde17 2101 Call-ID: 1717@ift.here.com 2102 CSeq: 18 INVITE 2103 Contact: 2105 J-F. Mule/J. Li 40 2106 SIP T.38 Call Flows February 2003 2108 Content-Type: application/sdp 2109 Content-Length: 320 2111 v=0 2112 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com 2113 s=Session SDP 2114 t=0 0 2115 m=audio 0 RTP/AVP 0 2116 c=IN IP4 0.0.0.0 2117 m=image 15002 udptl t38 2118 c=IN IP4 iftmg.here.com 2119 a=T38FaxVersion:0 2120 a=T38MaxBitRate:14400 2121 a=T38FaxRateManagement:transferredTCF 2122 a=T38FaxMaxBuffer:72 2123 a=T38FaxMaxDatagram:316 2124 a=T38FaxUdpEC:t38UDPRedundancy 2126 F14 200 OK PROXY -> IFT UA 2128 SIP/2.0 200 OK 2129 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 2130 Record-Route: 2132 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2133 To: sip:+1-650-555- 2134 2222@obelix.banyuls.com;user=phone;tag=cde17 2135 Call-ID: 1717@ift.here.com 2136 CSeq: 18 INVITE 2137 Contact: 2138 Content-Type: application/sdp 2139 Content-Length: 320 2141 v=0 2142 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com 2143 s=Session SDP 2144 t=0 0 2145 m=audio 0 RTP/AVP 0 2146 c=IN IP4 0.0.0.0 2147 m=image 15002 udptl t38 2148 c=IN IP4 iftmg.here.com 2149 a=T38FaxVersion:0 2150 a=T38MaxBitRate:14400 2151 a=T38FaxRateManagement:transferredTCF 2152 a=T38FaxMaxBuffer:72 2153 a=T38FaxMaxDatagram:316 2154 a=T38FaxUdpEC:t38UDPRedundancy 2156 F15 ACK IFTGW UA -> PROXY 2158 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 2160 J-F. Mule/J. Li 41 2161 SIP T.38 Call Flows February 2003 2163 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 2164 Max-Forwards: 70 2165 Route: 2167 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2168 To: sip:+1-650-555- 2169 2222@obelix.banyuls.com;user=phone;tag=cde17 2170 Call-ID: 1717@ift.here.com 2171 CSeq: 18 ACK 2172 Content-Length: 0 2174 F16 ACK PROXY -> IFT UA 2176 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 2177 Via: SIP/2.0/UDP obelix.banyuls.com:5060; 2178 branch=z9hG4bK2d008.1 2179 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 2180 Max-Forwards: 69 2181 Record-Route: 2183 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2184 To: sip:+1-650-555- 2185 2222@obelix.banyuls.com;user=phone;tag=cde17 2186 Call-ID: 1717@ift.here.com 2187 CSeq: 18 ACK 2188 Content-Length: 0 2190 6. Unsuccessful Scenarios 2192 6.1. Unsuccessful T.38 fax scenario - - no support for T.38 2193 This section represents a SIP T.38 call failure because the emitting 2194 gateway does not support T.38. 2196 Scenario: 2197 1. A SIP INVITE is sent to the called party requesting a voice 2198 connection per RFC3261; our scenario involves 1 SIP proxy. An audio 2199 connection is established, 2200 2. Upon detection of Preamble by the terminating gateway, a SIP 2201 re�INVITE request is sent to the emitting gateway to modify the 2202 parameters of the session to allow a T.38 fax connection. This re- 2203 INVITE request contains SDP information detailing T.38 capabilities, 2204 3. The emitting gateway rejects the re�INVITE with a 415 Unsupported 2205 Media Type response. 2206 4. Upon reception of the reject, the call is terminated. 2208 6.1.1. Sequence Diagram 2210 The messages F1 to F12 are identical to section 5.2. 2212 J-F. Mule/J. Li 42 2213 SIP T.38 Call Flows February 2003 2215 IFT UA Proxy IFTGW UA 2216 | | | 2217 | F1 INVITE | | 2218 |------------------->| | 2219 | | F2 INVITE | 2220 | |------------------->| 2221 | F3 100 Trying | | 2222 |<-------------------| F4 100 Trying | 2223 | |<-------------------| 2224 | | | 2225 | | F5 180 Ringing | 2226 | F6 180 Ringing |<-------------------| 2227 |<-------------------| | 2228 | | F7 200 OK | 2229 | F8 200 OK |<-------------------| 2230 |<-------------------| | 2231 | F9 ACK | | 2232 |------------------->| F10 ACK | 2233 | ------------------->| 2234 | | 2235 | Both Way RTP Media Established | 2236 Fax |<=======================================>| 2237 ------->| | 2238 emitted | | | 2239 | | | Preamble 2240 | | |<--------- 2241 | | F11 INVITE | detected 2242 | |<-------------------| 2243 | F12 INVITE | | 2244 |<-------------------| | 2245 | | | 2246 | F13 415 | | 2247 |------------------->| | 2248 | | F14 415 | 2249 | |------------------->| 2250 | | | 2251 | | F15 BYE | 2252 | |<-------------------| 2253 | F16 BYE | | 2254 |<-------------------| | 2255 | | | 2256 | F17 200 OK | | 2257 |------------------->| | 2258 | | F18 200 OK | 2259 | |------------------->| 2261 6.1.2. Message Details 2263 Messages F1 to F12 are identical to section 5.2; refer to 5.2. 2265 F13 415 Unsupported Media Type IFT UA -> PROXY 2267 J-F. Mule/J. Li 43 2268 SIP T.38 Call Flows February 2003 2270 SIP/2.0 415 Unsupported Media Type 2271 Via: SIP/2.0/UDP ift.here.com:5060 2272 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2273 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 2274 Call-ID: 1717@ift.here.com 2275 CSeq: 18 INVITE 2276 Contact: 2277 Content-Length: 0 2279 F14 415 Unsupported Media Type PROXY -> IFTGW UA 2281 SIP/2.0 415 Unsupported Media Type 2282 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=2d010.1 2283 Via: SIP/2.0/UDP ift.here.com:5060 2284 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2285 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 2286 Call-ID: 1717@ift.here.com 2287 CSeq: 18 INVITE 2288 Contact: 2289 Content-Length: 0 2291 F15 BYE IFTGW UA -> PROXY 2293 BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 2294 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 2295 Max-Forwards: 70 2296 Route: 2298 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2299 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 2300 Call-ID: 1717@ift.here.com 2301 CSeq: 19 BYE 2302 Content-Length: 0 2304 F16 BYE PROXY -> IFT UA 2306 BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 2307 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=2d010.1 2308 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 2309 Max-Forwards: 69 2310 Record-Route: 2312 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2313 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 2314 Call-ID: 1717@ift.here.com 2315 CSeq: 19 BYE 2316 Content-Length: 0 2318 J-F. Mule/J. Li 44 2319 SIP T.38 Call Flows February 2003 2321 F17 200 OK IFT UA -> PROXY 2323 SIP/2.0 200 OK 2324 Via: SIP/2.0/UDP ift.here.com:5060 2325 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2326 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 2327 Call-ID: 1717@ift.here.com 2328 CSeq: 19 BYE 2329 Content-Type: application/sdp 2330 Content-Length: 0 2332 F18 200 OK PROXY -> IFTGW UA 2334 SIP/2.0 200 OK 2335 Via: SIP/2.0/UDP obelix.banyuls.com:5060 2336 Via: SIP/2.0/UDP ift.here.com:5060 2337 Record-Route: 2339 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2340 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 2341 Call-ID: 1717@ift.here.com 2342 CSeq: 19 BYE 2343 Content-Type: application/sdp 2344 Content-Length: 0 2346 6.2. Unsuccessful T.38 fax scenario - - 488/606 rsp & G.711 fallback 2348 This section represents an unsuccessful SIP T.38 fax call: when the 2349 emitting gateway does not support T.38 fax relay, it SHOULD respond 2350 with either a ��488 Not Acceptable Here�� response or a ��606 Not 2351 Acceptable�� response to indicate that some aspects of the session 2352 description are not acceptable. The terminating gateway SHOULD 2353 react by proposing a fallback to G.711 fax pass-through with special 2354 codec characteristics - -silence suppression OFF. The message details 2355 in this section make use of the generic SDP attribute silenceSupp 2356 defined in RFC3108 [10]. 2358 Scenario: 2359 1. A SIP INVITE is sent to the called party requesting a voice 2360 connection per RFC3261; our scenario involves 1 SIP proxy. An audio 2361 connection is established, 2362 2. Upon detection of Preamble by the terminating gateway, a SIP 2363 re�INVITE request is sent to the emitting gateway to modify the 2364 parameters of the session to allow a T.38 fax connection. This re- 2365 INVITE request contains SDP information detailing T.38 capabilities, 2366 3. The emitting gateway rejects the re-INVITE with a 488 or 606 2367 response. Upon reception of the reject, the terminating gateway 2368 proposes to use plain G.711 to carry the fax stream. 2369 4. The call is terminated. 2371 J-F. Mule/J. Li 45 2372 SIP T.38 Call Flows February 2003 2374 6.2.1. Sequence Diagram 2375 The messages F1 to F12 are identical to section 5.2. 2377 IFT UA Proxy IFTGW UA 2378 | | | 2379 | F1 INVITE | | 2380 |------------------->| | 2381 | | F2 INVITE | 2382 | |------------------->| 2383 | F3 100 Trying | | 2384 |<-------------------| F4 100 Trying | 2385 | |<-------------------| 2386 | | | 2387 | | F5 180 Ringing | 2388 | F6 180 Ringing |<-------------------| 2389 |<-------------------| | 2390 | | F7 200 OK | 2391 | F8 200 OK |<-------------------| 2392 |<-------------------| | 2393 | F9 ACK | | 2394 |------------------->| F10 ACK | 2395 | ------------------->| 2396 | | 2397 | Both Way RTP Media Established | 2398 Fax |<=======================================>| 2399 ------->| | 2400 emitted | | | 2401 | | | Preamble 2402 | | |<--------- 2403 | | F11 INVITE | detected 2404 | |<-------------------| 2405 | F12 INVITE | | 2406 |<-------------------| | 2407 | | | 2408 | F13 606 | | 2409 |------------------->| | 2410 | | F14 606 (or 488) | 2411 | |------------------->| 2412 | | F15 INVITE | 2413 | |<-------------------| 2414 | F16 INVITE | | 2415 |<-------------------| | 2416 | F17 200 OK | | 2417 |------------------->| | 2418 | | F18 200 OK | 2419 | |------------------->| 2420 | | | 2421 | | F19 ACK | 2422 | |<-------------------| 2423 | F20 ACK | | 2424 |<-------------------| | 2425 | | 2427 J-F. Mule/J. Li 46 2428 SIP T.38 Call Flows February 2003 2430 | G.711 RTP Flow Established | 2431 |<=======================================>| 2432 | for fax pass-through | 2433 | | 2434 | F21 BYE | | 2435 |------------------->| | 2436 | | F22 BYE | 2437 | |------------------->| 2438 | | | 2439 | | F23 200 OK | 2440 | |<-------------------| 2441 | F24 200 OK | | 2442 |<-------------------| | 2444 6.2.2. Message Details 2446 Messages F1 to F12 are identical to section 5.2; refer to 5.2. 2448 F13 606 Not Acceptable IFT UA -> PROXY 2450 SIP/2.0 606 Not Acceptable 2451 Via: SIP/2.0/UDP ift.here.com:5060 2452 Warning: 304 Media type not available: One or more media types 2453 contained in the session description are not available. 2454 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2455 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 2456 Call-ID: 1717@ift.here.com 2457 CSeq: 18 INVITE 2458 Content-Length: 0 2460 F14 606 Not Acceptable PROXY -> IFTGW UA 2462 SIP/2.0 606 Not Acceptable 2463 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=2d010.1 2464 Via: SIP/2.0/UDP ift.here.com:5060 2465 Warning: 304 Media type not available: One or more media types 2466 contained in the session description are not available. 2467 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2468 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 2469 Call-ID: 1717@ift.here.com 2470 CSeq: 18 INVITE 2471 Content-Length: 0 2473 F15 INVITE IFTGW UA -> PROXY 2475 INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 2476 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 2477 Max-Forwards: 70 2478 Route: 2484 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2485 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 2486 Call-ID: 1717@ift.here.com 2487 CSeq: 19 INVITE 2488 Contact: 2489 Content-Type: application/sdp 2490 Content-Length: 181 2492 v=0 2493 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com 2494 s=Session SDP 2495 c=IN IP4 iftmg.there.com 2496 t=0 0 2497 m=audio 12322 RTP/AVP 0 2498 a=rtpmap:0 PCMU/8000 2499 a=silenceSupp:off - - - - 2501 F16 INVITE PROXY -> IFT UA 2503 INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 2504 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 2505 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 2506 Max-Forwards: 69 2507 Record-Route: 2509 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2510 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 2511 Call-ID: 1717@ift.here.com 2512 CSeq: 19 INVITE 2513 Contact: 2514 Content-Type: application/sdp 2515 Content-Length: 181 2517 v=0 2518 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com 2519 s=Session SDP 2520 c=IN IP4 iftmg.there.com 2521 t=0 0 2522 m=audio 12322 RTP/AVP 0 2523 a=rtpmap:0 PCMU/8000 2524 a=silenceSupp:off - - - - 2526 F17 200 OK IFT UA -> PROXY 2528 SIP/2.0 200 OK 2529 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 2530 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 2531 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2533 J-F. Mule/J. Li 48 2534 SIP T.38 Call Flows February 2003 2536 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 2537 Call-ID: 1717@ift.here.com 2538 CSeq: 19 INVITE 2539 Contact: 2540 Content-Type: application/sdp 2541 Content-Length: 150 2543 v=0 2544 o=faxgw1 2890844527 2890844528 IN IP4 ift.here.com 2545 s=Session SDP 2546 c=IN IP4 iftmg.here.com 2547 t=0 0 2548 m=audio 3456 RTP/AVP 0 2549 a=rtpmap:0 PCMU/8000 2550 a=silenceSupp:off - - - - 2552 F18 200 OK PROXY -> IFTGW UA 2554 SIP/2.0 200 OK 2555 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 2556 Record-Route: 2558 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2559 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 2560 Call-ID: 1717@ift.here.com 2561 CSeq: 19 INVITE 2562 Contact: 2563 Content-Type: application/sdp 2564 Content-Length: 150 2566 v=0 2567 o=faxgw1 2890844527 2890844528 IN IP4 ift.here.com 2568 s=Session SDP 2569 c=IN IP4 iftmg.here.com 2570 t=0 0 2571 m=audio 3456 RTP/AVP 0 2572 a=rtpmap:0 PCMU/8000 2573 a=silenceSupp:off - - - - 2575 F19 ACK IFTGW UA -> PROXY 2577 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 2578 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 2579 Max-Forwards: 70 2580 Route: 2582 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2583 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 2584 Call-ID: 1717@ift.here.com 2585 CSeq: 19 ACK 2586 Content-Length: 0 2588 J-F. Mule/J. Li 49 2589 SIP T.38 Call Flows February 2003 2591 F20 ACK PROXY -> IFT UA 2593 ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 2594 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 2595 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 2596 Max-Forwards: 69 2597 Record-Route: 2599 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2600 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 2601 Call-ID: 1717@ift.here.com 2602 CSeq: 19 ACK 2603 Content-Length: 0 2605 /* G.711 audio streams established both ways for fax pass through */ 2607 F21 BYE IFT UA -> PROXY 2609 BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 2610 Via: SIP/2.0/UDP ift.here.com:5060 2611 Max-Forwards: 70 2612 Route: 2614 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2615 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 2616 Call-ID: 1717@ift.here.com 2617 CSeq: 20 BYE 2618 Content-Length: 0 2620 F22 BYE PROXY -> IFTGW UA 2622 BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 2623 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 2624 Via: SIP/2.0/UDP ift.here.com:5060 2625 Max-Forwards: 69 2626 Record-Route: 2628 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2629 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 2630 Call-ID: 1717@ift.here.com 2631 CSeq: 20 BYE 2632 Content-Length: 0 2634 F23 200 OK IFTGW UA -> PROXY 2636 SIP/2.0 200 OK 2637 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 2639 J-F. Mule/J. Li 50 2640 SIP T.38 Call Flows February 2003 2642 Via: SIP/2.0/UDP ift.here.com:5060 2643 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2644 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 2645 Call-ID: 1717@ift.here.com 2646 CSeq: 20 BYE 2647 Content-Type: application/sdp 2648 Content-Length: 0 2650 F24 200 OK PROXY -> IFT UA 2652 SIP/2.0 200 OK 2653 Via: SIP/2.0/UDP ift.here.com:5060 2654 Record-Route: 2656 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2657 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 2658 Call-ID: 1717@ift.here.com 2659 CSeq: 20 BYE 2660 Content-Type: application/sdp 2661 Content-Length: 0 2663 J-F. Mule/J. Li 51 2664 SIP T.38 Call Flows February 2003 2666 7. SDP Attribute Table for T.38 sessions 2667 For a detailed description of these attributes, refer to IANA�s SDP 2668 parameters registration page. The tables below are replicated here 2669 for information only. 2671 +-----------------------+---------------------+---------------+ 2672 | SDP Attribute Name | Appropriate values | Example | 2673 | ("att-field") | | | 2674 +-----------------------+---------------------+---------------+ 2675 | | | | 2676 | T38FaxVersion | 1*DIGIT | 0 | 2677 | | | | 2678 | T38MaxBitRate | 1*(DIGIT) | 14400 | 2679 | | | | 2680 | T38FaxFillBitRemoval | boolean |true if present| 2681 | | | | 2682 | T38FaxTranscodingMMR | boolean |true if present| 2683 | | | | 2684 | T38FaxTranscodingJBIG | boolean |true if present| 2685 | | | | 2686 | T38FaxRateManagement | localTCF | |transferredTCF | 2687 | | transferredTCF | | 2688 | | | | 2689 | T38FaxMaxBuffer | 1*(DIGIT); optional | 72 | 2690 | | | (bytes) | 2691 | | | | 2692 | T38FaxMaxDatagram | 1*(DIGIT); | Depends on | 2693 | | optional | redundancy; | 2694 | | | 316 (bytes) | 2695 | | | | 2696 | T38FaxUdpEC | t38UDPFEC | | T38UDPRedund | 2697 | | t38UDPRedundancy | ancy | 2698 +-----------------------+---------------------+---------------+ 2700 Registered SDP Protocol ��proto�� for T.38: 2702 +-----------------+ 2703 | Name | 2704 | | 2705 +-----------------+ 2706 | | 2707 | UDPTL | 2708 | | 2709 | TCP | 2710 | | 2711 +-----------------+ 2713 Registered SDP Protocol ��fmt��, MIME media type image/t38: 2714 Registered Real-time Facsimile (T.38) - image/t38 MIME Sub-type is 2715 defined in [11]; 2716 MIME media type name: image 2717 MIME subtype name: t38 2719 J-F. Mule/J. Li 52 2720 SIP T.38 Call Flows February 2003 2722 8. Considerations 2724 In this temporary section, we log the open items for discussion as 2725 well as issues that have been solved on the mailing list: 2727 8.1. Level of requirements for Internet gateways 2728 --- Status: closed, solved by old draft01 text in section 4.2 2729 Based on the comments received on old draft-00, the authors 2730 recommend that: T.38 Internet fax gateways MUST trigger a SIP re- 2731 INVITE upon detection of the V.21 Preamble flag sequence on the 2732 receiving side. Emitting gateways MAY trigger session modification 2733 upon CNG. 2735 8.2. Negotiation of UDP ports for T.38 transmission 2736 --- Status: not an issue, just logged here 2737 When switching to T.38 mode, Internet fax gateways specify a new set 2738 of parameters for the media connection in SDP. Some gateways may 2739 choose the UDP/RTP port used in audio mode for UDP/UDPTL/T.38 2740 traffic. Some gateways may choose to open a new UDP port for 2741 UDPTL/T.38 fax (and keep the previous UDP/RTP port open for the 2742 switch back to audio). 2743 SDP provides the mechanism to precisely define in SIP all cases: 2744 - if an Internet Fax gateway desires to re-use the UDP/RTP port for 2745 UDP/UDPTL/T.38, put 1 ��m=�� line in the re-INVITE. 2746 m=image udptl t38 2747 - if an Internet Fax gateway desires to release the RTP port and 2748 open a new UDP port for T.38: 2749 m=image udptl t38 2750 - if an Internet Fax gateway desires to keep the RTP port for future 2751 use in the session and open a new UDP port for T.38, we need to 2752 repeat the RTP/AVP port: 2753 m=audio RTP/AVP 0 2754 m=image udptl t38 2756 8.3. Adding a fax stream to SIP session vs. Replacing audio stream 2757 --- Status: closed, see flows 5.2 and 5.3 2758 Based on the mailing list discussion, it is recommended in section 2759 5.2 to replace an existing audio media connection with a fax one. 2760 We however kept section 5.3 to illustrate what adding a fax stream 2761 would entail. 2763 8.4. Adding text to make use of SIP OPTIONS: in progress in draft-02 2764 --- Status: Open for discussion 2765 As discussed with Bill Sulzen, the SIP OPTIONS response could be 2766 used to assert that real-time fax communications using either T.38 2767 or fax-passthrough are supported. This could certainly improve the 2768 negotiation phases and reduce the number of SIP messages. It is 2769 also key to get the capabilities of the Internet-aware fax device or 2770 gateway other than on a per call basis. 2771 What needs to be added: 2773 J-F. Mule/J. Li 53 2774 SIP T.38 Call Flows February 2003 2776 - add text in sub-section in section 4.5 2777 - specify how the Accept header line should be populated (do we 2778 want to specify t.38 and/or fax pass-through (meaning ability to 2779 support silencesuppression), and within t.38, do we want to specify 2780 whether it is t.38 over tcp, udptl, both, etc. 2782 8.5. Use of IP addresses in SDP connection information 2783 --- Status: Closed, remains unchanged per sipping call flow ID 2784 Comment from Christer Holmberg: SDP connection information should 2785 use IP addresses instead of domain names (as per draft-ietf-mmusic- 2786 sdp-new-03) 2788 8.6. Unsuccessful scenario: 606 or 488 2789 --- Status: Closed 2790 Comment from Bill Sulzen: it is acceptable or even preferable to 2791 reject with a 488 Not Acceptable Media? 2792 Resolution: treat 606 and 488 as equally appropriate. 2794 8.7. SIP re-INVITE or UPDATE? 2795 --- Status: open with the following recommendation 2796 In most cases, the SIP dialog is established when the codec changes 2797 occur so the use of UPDATE is not required. Also the re-INVITE is 2798 more standard so we propose to use re-INVITE. 2800 9. Security Considerations 2802 This document contains examples of SIP session establishment of 2803 particular media types. The security considerations in RFC 3261 [3] 2804 apply. There is no known additional security threats because of the 2805 nature of the media descriptors exchanged in these call flows. 2807 RFC 3261 describes the basic threats including server impersonation, 2808 message body tampering, session modifying or teardown, and denial of 2809 service and amplification attacks. 2810 The use of TLS and the Secure SIP (sips) URI scheme provides a 2811 better level of security including two-way authentication. IPsec can 2812 also improve security. 2813 S/MIME can provide end-to-end confidentiality and integrity 2814 protection of message bodies, as described in RFC 3261. 2816 10. References 2818 1 S. Bradner, "The Internet Standards Process -- Revision 3", BCP 2819 9, RFC 2026, October 1996. 2821 2 S. Bradner, "Key words for use in RFCs to Indicate Requirement 2822 Levels", BCP 14, RFC 2119, March 1997. 2824 3 Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., 2825 Peterson, J., Sparks, R., Handley, M., and Schooler, E., "SIP: 2827 J-F. Mule/J. Li 54 2828 SIP T.38 Call Flows February 2003 2830 Session Initiation Protocol", RFC 3261, June 2002. 2832 4 ITU-T Recommendation T.38, ��Procedures for real-time Group 3 2833 facsimile communication over IP networks��, June 1998. 2835 5 Johnston, et al, ��SIP Basic Call Flow Examples��, Internet-Draft 2836 draft-ietf-sipping-basic-call-flows-01.txt, October 2002. 2838 6 ITU-T Recommendation T.38, ��Procedures for real-time Group 3 2839 facsimile communication over IP networks��, March 2002. 2841 7 ITU-T Recommendation T.30, ��Procedures for document facsimile 2842 transmission in the general switched telephone network��, March 2843 1993. 2845 8 M. Handley, V. Jacobson, "SDP: session description protocol", 2846 RFC 2327, April 1998. 2848 9 ITU-T Recommendation T.38 Amendment 2 Annex D, ��SIP/SDP Call 2849 Establishment Procedures��, February 2000. 2851 10 R. Kumar, M. Mostafa, ��Conventions for the use of the Session 2852 Description Protocol (SDP) for ATM Bearer Connections��, RFC3108, 2853 May 2001. 2855 11 G. Parsons, ��Real-time Facsimile (T.38) - image/t38 MIME Sub-type 2856 Registration��, RFC3362, August 2002. 2858 1. Acknowledgments 2860 This document would not have been possible without the help of the 2861 following development engineers and fax experts, in particular 2862 Stanley Khouw, Bill Michalek, and George Maphis of Clarent 2863 Corporation. 2865 The authors would like to thank Bill Sulzen of Cisco Systems for his 2866 continued support and critical comments. We also acknowledge the 2867 valuable contributions from Flemming Andreasen of Cisco Systems, 2868 Christer Holmberg of Ericsson, and Bert Culpepper of InterVoice- 2869 Brite. 2870 Many thanks to the reviewers of the previous document for their 2871 comments: Jim Renkel of 3COM, Sudipto Mukherjee of Cisco Systems, 2872 Arjun Roychowdhury of Hughes Software Systems. 2874 2. Author's Addresses 2876 Jieying Li 2877 email:jieying.li@ivoxnetworks.com 2879 Jean-Francois Mule� 2880 CableLabs 2882 J-F. Mule/J. Li 55 2883 SIP T.38 Call Flows February 2003 2885 400 Centennial Parkway 2886 Louisville, CO 80027 2887 USA 2888 email: jfm@cablelabs.com 2890 ull Copyright Statement 2892 "Copyright (C) The Internet Society 2003. All Rights Reserved. 2894 This document and translations of it may be copied and furnished to 2895 others, and derivative works that comment on or otherwise explain it 2896 or assist in its implementation may be prepared, copied, published 2897 and distributed, in whole or in part, without restriction of any 2898 kind, provided that the above copyright notice and this paragraph 2899 are included on all such copies and derivative works. However, this 2900 document itself may not be modified in any way, such as by removing 2901 the copyright notice or references to the Internet Society or other 2902 Internet organizations, except as needed for the purpose of 2903 developing Internet standards in which case the procedures for 2904 copyrights defined in the Internet Standards process must be 2905 followed, or as required to translate it into languages other than 2906 English. 2908 The limited permissions granted above are perpetual and will not be 2909 revoked by the Internet Society or its successors or assigns. 2911 This document and the information contained herein is provided on an 2912 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 2913 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 2914 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 2915 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 2916 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 2918 cknowledgement 2920 Funding for the RFC Editor function is currently provided by the 2921 Internet Society. 2923 -F. Mule/J. Li 56