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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force Jean-Francois Mule 3 Internet Draft CableLabs 4 Document: Jieying Li 5 Category: Informational iVox Networks 6 Expires: February 2002 August 2002 8 SIP Support for Real-time Fax: 9 Call Flow Examples 10 And 11 Best Current Practices 13 Status of this Memo 15 This document is an Internet-Draft and is in full conformance with 16 all provisions of Section 10 of RFC2026 [1]. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six 24 months and may be updated, replaced, or obsoleted by other documents 25 at any time. It is inappropriate to use Internet- Drafts as 26 reference material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 1. Abstract 35 The Session Initiation Protocol (SIP) allows the establishment of 36 real-time Internet fax communications. Real-time facsimile 37 communications over IP may follow 2 modes of operation: T.38 fax 38 relay as defined by the ITU-T T.38 recommendation or fax pass- 39 through. 40 This document clarifies the options available to Internet telephony 41 gateway vendors to handle real-time fax calls using SIP. While our 42 primary focus is to address the more reliable real-time T.38 Group 3 43 fax mode, we briefly cover the fax pass-through mode to enable 44 fallback operations and super G3 fax communications using SIP. We 45 also give examples of SIP call flows for real-time Internet fax 46 gateways or SIP proxy redirect servers. Elements in these call 47 flows include SIP User Agents, SIP Proxy Servers, and Gateways to 48 the PSTN (Public Switch Telephone Network). 49 This document introduces best current practices for SIP T.38 fax and 50 SIP fax pass-through sessions. A session starts with audio 51 capabilities, and, upon fax tone detection, T.38 fax capabilities 52 are negotiated; upon successful negotiation, the session continues 53 with fax capabilities and the media termination hosts exchange T.38 54 Internet fax packets. The T.38 fax call scenarios include various 56 J-F. Mule/J. Li SIPPING WG 1 57 SIP T.38 Call Flows February 2002 59 aspects of the call sequence: the detection of fax transmission, the 60 usage of the T.38 session description attributes, the optional 61 fallback into fax pass-through mode and the session termination. The 62 fax pass-through call scenarios involve some specific SDP media 63 attributes to enable proper fax transmission. 64 Fax transmission can be detected by the receiving side, the emitting 65 side or both (in the latter case, a 'glare' effect may appear). 66 This document only covers the case when the fax transmission is 67 detected by the receiving side: it is the most common practice and 68 the other cases do not represent any particular challenges and are 69 therefore left for future discussions). Call flow diagrams and 70 message details are shown. A list of IANA defined SDP attribute 71 names for T.38 is summarized in section 7. 73 Table of Contents 75 Status of this Memo.......................................................1 76 1. Abstract...............................................................1 77 2. Conventions used in this document......................................3 78 3. Overview...............................................................3 79 3.1. General Assumptions.................................................3 80 3.2 Legend for Message Flows..............................................3 81 3.3 Changes to previous drafts............................................4 82 4 Handling of real-time fax communication using SIP.......................4 83 4.1 Internet telephony gateways and fax detection.........................5 84 4.2 Internet telephony gateways and T.38 fax media connections............5 85 4.3 SIP session and fax termination.......................................6 86 4.4 Internet telephony gateways and fax pass-through mode.................6 87 4.5 Responses to SIP OPTIONS request......................................7 88 4.6 Beyond Internet telephony gateways....................................7 89 5 Successful SIP T.38 fax Call Scenarios..................................7 90 5.1 Internet fax device � fax only support................................7 91 5.1.1 Sequence Diagram....................................................7 92 5.1.2 Message Details.....................................................8 93 5.2 SIP T.38 fax call � fax stream replaces voice stream.................13 94 5.2.1 Sequence Diagram...................................................13 95 5.2.2 Message Details....................................................15 96 5.3 SIP T.38 fax call � fax stream added to voice stream.................25 97 5.3.1 Sequence Diagram...................................................26 98 5.3.2 Message Details....................................................27 99 5.4 SIP T.38 fax call � fax stream forced to replace voice stream........37 100 5.4.1 Sequence Diagram...................................................37 101 5.4.2 Message Details....................................................37 102 6. Unsuccessful Scenarios................................................41 103 6.1. Unsuccessful T.38 fax scenario � no support for T.38................41 104 6.1.1. Sequence Diagram..................................................41 105 6.1.2. Message Details...................................................42 106 6.2. Unsuccessful T.38 fax scenario � 488/606 response & G.711 fallback..43 107 6.2.1. Sequence Diagram..................................................44 108 6.2.2. Message Details...................................................45 109 7. SDP Attribute Table for T.38 sessions.................................50 110 8. Considerations........................................................51 111 8.1. Level of requirements for Internet gateways.........................51 112 8.2. Negotiation of UDP ports for T.38 transmission......................51 114 J-F. Mule/J. Li 2 115 SIP T.38 Call Flows February 2002 117 8.3. Adding a fax stream to SIP session vs. Replacing audio stream.......51 118 8.4. Adding text to make use of SIP OPTIONS: in progress in draft-02.....51 119 8.5. Use of IP addresses in SDP connection information...................52 120 8.6. Unsuccessful scenario: 606 or 488...................................52 121 9. Security Considerations...............................................52 122 10. References...........................................................52 123 11. Acknowledgments......................................................53 124 12. Author's Addresses...................................................53 125 Full Copyright Statement.................................................53 127 2. Conventions used in this document 129 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 130 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 131 this document are to be interpreted as described in RFC-2119 [2]. 133 3. Overview 135 The Session Initiation Protocol (SIP) is defined by RFC2543 [3] and 136 T.38 is the ITU-T Recommendation defining the procedures for real- 137 time Group 3 facsimile communications over IP networks [4]. This 138 document deals with the handling of real-time fax communications 139 using the SIP protocol for T.38 fax and fax pass-through modes. 140 For T.38, this document deals primarily with one transport protocol 141 for the media: T.38 over UDP/UDPTL; T.38 fax packet transport over 142 TCP using SIP session establishment can easily be extrapolated. 143 These T.38 call flows were developed in the design of carrier-class 144 SIP Telephony products supporting voice and real-time fax traffic. 145 It is the hope of the authors that this document will be useful for 146 the SIP community, SIP implementors of T.38 fax products, designers. 147 Call flows shown in this document complement the main SIP call flow 148 Internet-Draft [5]. These call flows are based on the current 149 version 2.0 of SIP in RFC2543[3], the ITU-T T.38 Amendment 2 [6] and 150 an ITU-T SG8 liaison to IANA. Note: IANA registration of the T.38 151 SDP attributes is currently a work in progress. 153 3.1. General Assumptions 155 Internet telephony gateways with T.38 support MAY pass various fax 156 tones (T.30 CNG, CED, etc.) or flag sequence (like V.21 Preamble) in 157 the RTP audio streams before those tones or flag sequence are 158 detected. Once detected by the DSP resources, T.38 fax-capable 159 devices switch from audio to fax mode and initiate a T.38 fax packet 160 transmission. 161 These best current practices MAY apply to "Network Gateway", 162 "Enterprise Gateway" and Internet-aware fax devices or terminals. 164 3.2 Legend for Message Flows 166 J-F. Mule/J. Li 3 167 SIP T.38 Call Flows February 2002 169 The legend defined [5] also applies in this document. 170 Dashed lines (---) represent control messages that are mandatory to 171 the call scenario. These control messages can be SIP or PSTN 172 signaling. Double dashed lines (===) represent media paths between 173 network elements. Messages with parenthesis around name represent 174 optional control messages. Messages are identified in the Figures 175 as F1, F2, etc. This references the message details in the table 176 that follows the Figure. Comments in the message details are shown 177 in the following form: /* Comments. */ 179 3.3 Changes to previous drafts 181 o Changes to draft-01 182 The changes between the current draft and draft-01 are: 183 - Major updates: 184 + additions based on SIPit fax testing event 8/2001: added 185 text regarding the negotiation of T38MaxBitRate in 4.2, 186 + added more general text for the handling of real-time 187 fax pass-through, 188 + added of echo cancellation & silence suppression SDP 189 attributes and usage recommendations in 6.2, 190 + correction of the session version number in SDP when 191 issuing re-INVITE with updated SDP information as per 192 draft-ietf-sip-rfc2543bis-05, 193 + started a section on the use of the OPTIONS method to 194 determine the support of T.38 capabilities (work-in- 195 progress), 196 - Minor editorial updates (added tag fields in To and From header 197 lines as well as Contact header lines as per draft-ietf-sip- 198 rfc2543bis-05, added proper reference to T.38 Amendment 2 pre- 199 published version, exact case matching for T38MaxBitRate, etc.) 201 o Changes to draft-00 202 The major changes between draft-01 and draft-00 are listed below: 203 - Major updates: 204 + new text in fax handling section 4.2 based on sip list: 205 clarified text for fax detection, capability negotiation 206 and termination 207 + additions of new successful call flows in section 5 208 + additions of unsuccessful call flows in section 6 209 - Added Record-Route header, modified Cseq numbers, 210 - Added T38FaxMaxDatagram attribute in SDP and corrected 211 the sample value for T38FaxMaxBuffer, 212 - Minor editorial changes (e.g. removed references in Abstract). 213 4 Handling of real-time fax communication using SIP 215 The handling of real-time fax sessions using SIP involves the 216 initial session establishment, the modification or negotiation of 217 session capabilities upon fax detection, the optional fallback into 218 fax pass-through mode and the session termination. 220 J-F. Mule/J. Li 4 221 SIP T.38 Call Flows February 2002 223 Some variants of these best current practices MAY apply depending on 224 the nature or the configuration of Internet telephony gateways. Two 225 distinct cases are considered in this document: 226 o The Internet telephony gateway only supports T.38 real-time 227 fax communications (by design or by configuration). In this case, 228 the Internet fax gateway SHOULD initiate the SIP session with T.38 229 SDP capabilities (this is typically the case of Internet fax 230 terminals, also called Internet-aware fax devices or the case of 231 gateways statically configured to support T.38 fax calls only); 232 o The Internet telephony gateway supports voice and real-time 233 fax communications. In this case, the Internet telephony gateway 234 initiates the SIP session with audio capabilities, and, upon fax 235 detection, the switchover to T.38 fax capabilities is triggered. 236 The fax media connection may replace or be added to the audio 237 connection depending on the target applications. 239 4.1 Internet telephony gateways and fax detection 241 Two possible ways exist for an Internet telephony gateway to detect 242 a facsimile communication: 244 1. On the emitting gateway (the one sending the facsimile document), 245 the T.30 calling tone (CNG) is detected. The CNG tone is however an 246 optional signal [7]; 247 2. On the receiving gateway, the V.21 Preamble flag sequence is 248 detected. The Preamble is always present and follows the called 249 station identification tone (CED) when CED is present. 250 Note that even though the CED tone may be detected on the receiving 251 gateway, since the fax CED tone is similar to V.25 ANS modem tones, 252 it SHOULD NOT be used to trigger the fax switchover. 254 In conclusion, several conditions can trigger fax detection. 255 Internet telephony gateways supporting T.38 real-time facsimile MUST 256 support the detection of fax transmission on the V.21 Preamble flag 257 sequence; Internet telephony gateways MAY support the detection of 258 fax on CNG tone. The authors recommend that a facsimile 259 transmission SHOULD be detected on the receiving Internet telephony 260 gateway. 262 4.2 Internet telephony gateways and T.38 fax media connections 264 Upon successful fax detection, the description of the media 265 connection(s) is modified using the SDP protocol [8] as described in 266 SIP (see sections in chapter 5). 268 Several cases should be considered: 269 - In the case of Internet fax devices (supporting T.38 fax only 270 communications), the SIP session is established with SDP description 271 containing the T.38 media attributes; refer to section 5.1 for a 272 sample call flow for Internet fax devices. 274 J-F. Mule/J. Li 5 275 SIP T.38 Call Flows February 2002 277 - In the case of Internet telephony gateways, the SIP/SDP session is 278 modified and the T.38 fax media connection SHOULD replace the 279 existing audio media connection. The SIP UAC triggering the 280 modification of the session description MUST indicate all of its 281 T.38 media attributes in SDP. This is the recommended behavior for 282 gateways; refer to section 5.2 for a sample call flow illustrating 283 this scenario. 284 Some implementations MAY choose to add the fax media connection to 285 the existing audio connection and in that case, they SHOULD mute the 286 audio connection while fax is transmitted. Refer to section 5.3 for 287 a sample call flow illustrating this optional scenario. 289 Note: 290 Among the SDP T.38 media attributes being exchanged after fax 291 detection, implementors should particularly pay attention to 292 T38MaxBitRate, the maximum T.38 bit rate for the media connection. 293 It is recommended to implement the following rule when responding to 294 a maximum bit rate proposal. If the remote peer's SDP description 295 contains a maximum fax bit rate of X and the local host is set to a 296 maximum bit rate of Y (either by fax protocol detection or 297 configuration), the local host MUST propose a maximum fax rate of 298 min (X,Y) in the SIP response to the re-INVITE in order to 299 facilitate the negotiation. This note is exemplified in section 300 5.2.1. in messages F11-F14. Failures to implement this rule MAY 301 imply call teardown in some cases. 303 4.3 SIP session and fax termination 305 Upon completion of the fax transmission, any audio connection 306 successfully established prior to fax detection SHOULD be restored 307 or the session MUST be terminated. 309 4.4 Internet telephony gateways and fax pass-through mode 311 This section deals real-time facsimile communications over IP using 312 fax pass-through instead of T.38 fax relay. In this mode, the 313 facsimile communication is handled as a PCM audio call (PCMA/PCMU as 314 specified in ITU-T recommendation G.711). 316 The fax pass-through mode is important to prevent call failures, for 317 example in cases when one of the SIP communication peers does not 318 support T.38. For Internet telephony gateways with support for 319 PCM/G.711 audio but no support for T.38 real-time fax, it is 320 recommended to switch the session to fax pass-through mode. 321 Internet telephony gateways SHOULD handle the fall back mode to fax 322 pass-through by recognizing the SDP T.38 connection and proposing to 323 switch to a new audio connection. The new audio connection SHOULD 324 have the following characteristics: at a minimum, specify PCM G.711 325 codec, silence suppression OFF, echo cancellation ON. The telephony 326 gateway that originated the failed T.38 re-INVITE SHOULD initiate 327 the subsequent re-INVITE to fax pass-through mode. 329 J-F. Mule/J. Li 6 330 SIP T.38 Call Flows February 2002 332 Refer to section 6.2 for a sample call flow illustrating this 333 scenario. 335 4.5 Responses to SIP OPTIONS request 336 Suggestion currently logged in section 8.4, just a placeholder for 337 now; <> 339 4.6 Beyond Internet telephony gateways 341 This document may also serve to vendors of SIP redirect servers or 342 other SIP UA types like SIP phones. Such SIP entities may recognize 343 the fax nature of the sessions and redirect the flows to the proper 344 real-time fax-capable devices or to other fax service providers. 346 5 Successful SIP T.38 fax Call Scenarios 348 5.1 Internet fax device � fax only support 350 This section represents a SIP call flow for a T.38 fax session 351 between 2 Internet fax terminals. It is also applicable to Internet 352 telephony gateways when telephony ports are statically configured to 353 support fax only (case of analog IP telephony gateways where a 354 specific port is connected to a fax terminal). 355 A session starts with fax capabilities (t.38/udptl). The mechanism 356 for supporting T.38 in SIP & SDP is detailed in T.38 Annex D [9], a 357 temporary document that proposes an amendment to T.38 describing SIP 358 call establishment procedures. 360 5.1.1 Sequence Diagram 362 Internet Fax UA Proxy IFTGW UA 364 Fax | | | 365 ------->| F1 INVITE | | 366 emitted |------------------->| | 367 | | F2 INVITE | 368 | |------------------->| 369 | F3 100 Trying | | 370 |<-------------------| F4 100 Trying | 371 | |<-------------------| 372 | | | 373 | | F5 180 Ringing | 374 | F6 180 Ringing |<-------------------| 375 |<-------------------| | 376 | | F7 200 OK | 377 | F8 200 OK |<-------------------| 378 |<-------------------| | 380 J-F. Mule/J. Li 7 381 SIP T.38 Call Flows February 2002 383 | F9 ACK | | 384 |------------------->| F10 ACK | 385 | |------------------->| 386 | | 387 | T.38/UDPTL Fax Flow Established | 388 |<=======================================>| 389 End of | | 390 fax | | | 391 detected| | | 392 ------->| | | 393 | F11 BYE | | 394 |------------------->| | 395 | | F12 BYE | 396 | |------------------->| 397 | | F13 200 OK | 398 | |<-------------------| 399 | F14 200 OK | | 400 |<-------------------| | 402 5.1.2 Message Details 404 F1 INVITE I.FAX UA -> PROXY 406 INVITE sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 407 Via: SIP/2.0/UDP ifax.here.com:5060 408 From: sip:+1-303-555-1111@ifax.here.com;user=phone;tag=ab111 409 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone 410 Call-ID: 1717@ifax.here.com 411 CSeq: 17 INVITE 412 Contact: 413 Content-Type: application/sdp 414 Content-Length: 320 416 v=0 417 o=ifaxgw1 2890846527 2890846527 IN IP4 ifax.here.com 418 s=Session SDP 419 c=IN IP4 ifaxmg.here.com 420 t=0 0 421 m=image 15002 udptl t38 422 a=T38FaxVersion:0 423 a=T38MaxBitRate:14400 424 a=T38FaxFillBitRemoval:0 425 a=T38FaxTranscodingMMR:0 426 a=T38FaxTranscodingJBIG:0 427 a=T38FaxRateManagement:transferredTCF 428 a=T38FaxMaxBuffer:72 429 a=T38FaxMaxDatagram:316 430 a=T38FaxUdpEC:t38UDPFEC 431 a=T38FaxUdpEC:t38UDPRedundancy 433 J-F. Mule/J. Li 8 434 SIP T.38 Call Flows February 2002 436 F2 INVITE PROXY -> IFTGW UA 438 INVITE sip:+1-650-555-2222@iftgw.there.com;user=phone SIP/2.0 439 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 440 Via: SIP/2.0/UDP ifax.here.com:5060 441 Record-Route: 443 From: sip:+1-303-555-1111@ifax.here.com;user=phone;tag=ab111 444 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone 445 Call-ID: 1717@ifax.here.com 446 CSeq: 17 INVITE 447 Contact: 448 Content-Type: application/sdp 449 Content-Length: 320 451 v=0 452 o=ifaxgw1 2890846527 2890846527 IN IP4 ifax.here.com 453 s=Session SDP 454 c=IN IP4 ifaxmg.here.com 455 t=0 0 456 m=image 15002 udptl t38 457 a=T38FaxVersion:0 458 a=T38MaxBitRate:14400 459 a=T38FaxFillBitRemoval:0 460 a=T38FaxTranscodingMMR:0 461 a=T38FaxTranscodingJBIG:0 462 a=T38FaxRateManagement:transferredTCF 463 a=T38FaxMaxBuffer:72 464 a=T38FaxMaxDatagram:316 465 a=T38FaxUdpEC:t38UDPFEC 466 a=T38FaxUdpEC:t38UDPRedundancy 468 F3 (100 Trying) PROXY -> I.FAX UA 470 SIP/2.0 100 Trying 471 Via: SIP/2.0/UDP ifax.here.com:5060 472 From: sip:+1-303-555-1111@ifax.here.com;user=phone;tag=ab111 473 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone 474 Call-ID: 1717@ifax.here.com 475 CSeq: 17 INVITE 476 Content-Length: 0 478 F4 (100 Trying) IFTGW UA -> PROXY 480 SIP/2.0 100 Trying 481 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 482 Via: SIP/2.0/UDP ifax.here.com:5060 483 From: sip:+1-303-555-1111@ifax.here.com;user=phone;tag=ab11 485 J-F. Mule/J. Li 9 486 SIP T.38 Call Flows February 2002 488 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 489 Call-ID: 1717@ifax.here.com 490 CSeq: 17 INVITE 491 Contact: 492 Content-Length: 0 494 F5 180 Ringing IFTGW UA -> PROXY 496 SIP/2.0 180 Ringing 497 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 498 Via: SIP/2.0/UDP ifax.here.com:5060 499 From: sip:+1-303-555-1111@ifax.here.com;user=phone;tag=ab11 500 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 501 Call-ID: 1717@ifax.here.com 502 CSeq: 17 INVITE 503 Contact: 504 Content-Length: 0 506 F6 180 Ringing PROXY -> I.FAX UA 508 SIP/2.0 180 Ringing 509 Via: SIP/2.0/UDP ifax.here.com:5060 510 From: sip:+1-303-555-1111@ifax.here.com;user=phone;tag=ab11 511 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 512 Call-ID: 1717@ifax.here.com 513 CSeq: 17 INVITE 514 Contact: 515 Content-Length: 0 517 F7 200 OK IFTGW UA -> PROXY 519 SIP/2.0 200 OK 520 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 521 Via: SIP/2.0/UDP ifax.here.com:5060 522 From: sip:+1-303-555-1111@ifax.here.com;user=phone;tag=ab11 523 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 524 Call-ID: 1717@ifax.here.com 525 CSeq: 17 INVITE 526 Contact: 527 Content-Type: application/sdp 528 Content-Length: 320 530 v=0 531 o=faxgw1 2890844527 2890844527 IN IP4 iftgw.there.com 532 s=Session SDP 533 c=IN IP4 iftmg.there.com 534 t=0 0 535 m=image 49172 udptl t38 536 a=T38FaxVersion:0 537 a=T38MaxBitRate:14400 539 J-F. Mule/J. Li 10 540 SIP T.38 Call Flows February 2002 542 a=T38FaxFillBitRemoval:0 543 a=T38FaxTranscodingMMR:0 544 a=T38FaxTranscodingJBIG:0 545 a=T38FaxRateManagement:transferredTCF 546 a=T38FaxMaxBuffer:72 547 a=T38FaxMaxDatagram:316 548 a=T38FaxUdpEC:t38UDPRedundancy 550 F8 200 OK PROXY -> I.FAX UA 552 SIP/2.0 200 OK 553 Via: SIP/2.0/UDP ifax.here.com:5060 554 Record-Route: 556 From: sip:+1-303-555-1111@ifax.here.com;user=phone;tag=ab11 557 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 558 Call-ID: 1717@ifax.here.com 559 CSeq: 17 INVITE 560 Contact: 561 Content-Type: application/sdp 562 Content-Length: 320 564 v=0 565 o=faxgw1 2890844527 2890844527 IN IP4 iftgw.there.com 566 s=Session SDP 567 c=IN IP4 iftmg.there.com 568 t=0 0 569 m=image 49172 udptl t38 570 a=T38FaxVersion:0 571 a=T38MaxBitRate:14400 572 a=T38FaxFillBitRemoval:0 573 a=T38FaxTranscodingMMR:0 574 a=T38FaxTranscodingJBIG:0 575 a=T38FaxRateManagement:transferredTCF 576 a=T38FaxMaxBuffer:72 577 a=T38FaxMaxDatagram:316 578 a=T38FaxUdpEC:t38UDPRedundancy 580 F9 ACK I.FAX UA -> PROXY 582 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 583 Via: SIP/2.0/UDP ifax.here.com:5060 584 Route: 586 From: sip:+1-303-555-1111@ifax.here.com;user=phone;tag=ab11 587 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 588 Call-ID: 1717@ifax.here.com 589 CSeq: 17 ACK 590 Content-Length: 0 592 J-F. Mule/J. Li 11 593 SIP T.38 Call Flows February 2002 595 F10 ACK PROXY -> IFTGW UA 597 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 598 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 599 Via: SIP/2.0/UDP ifax.here.com:5060 600 Record-Route: 602 From: sip:+1-303-555-1111@ifax.here.com;user=phone;tag=ab11 603 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 604 Call-ID: 1717@ifax.here.com 605 CSeq: 17 ACK 606 Content-Length: 0 608 /* T.38 fax streams are established. */ 610 F11 BYE I.FAX UA -> PROXY 612 BYE sip:+1-650-555-2222@obelix.wcom.com SIP/2.0 613 Via: SIP/2.0/UDP ifax.here.com:5060 614 Route: 616 From: sip:+1-303-555-1111@ifax.here.com;user=phone;tag=ab22 617 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone 618 Call-ID: 1717@ifax.here.com 619 CSeq: 18 BYE 620 Content-Length: 0 622 F12 BYE PROXY -> IFTGW UA 624 BYE sip:+1-650-555-2222@obelix.wcom.com SIP/2.0 625 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d009.1 626 Via: SIP/2.0/UDP ifax.here.com:5060 627 Record-Route: 629 From: sip:+1-303-555-1111@ifax.here.com;user=phone;tag=ab22 630 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone 631 Call-ID: 1717@ifax.here.com 632 CSeq: 18 BYE 633 Content-Length: 0 635 F13 200 OK IFTGW UA -> PROXY 637 SIP/2.0 200 OK 638 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 639 Via: SIP/2.0/UDP ifax.here.com:5060 640 From: sip:+1-303-555-1111@ifax.here.com;user=phone;tag=ab22 642 J-F. Mule/J. Li 12 643 SIP T.38 Call Flows February 2002 645 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde34 646 Call-ID: 1717@ifax.here.com 647 CSeq: 18 BYE 648 Content-Type: application/sdp 649 Content-Length: 0 651 F14 200 OK PROXY -> I.FAX UA 653 SIP/2.0 200 OK 654 Via: SIP/2.0/UDP ifax.here.com:5060 655 Record-Route: 657 From: sip:+1-303-555-1111@ifax.here.com;user=phone;tag=ab22 658 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde34 659 Call-ID: 1717@ifax.here.com 660 CSeq: 18 BYE 661 Content-Type: application/sdp 662 Content-Length: 0 664 5.2 SIP T.38 fax call � fax stream replaces voice stream 666 This section represents the SIP call flow for a T.38 fax session 667 between 2 Internet telephony gateways (fax detection on terminating 668 side). 669 A session starts with audio capabilities, and then the session is 670 modified to switch to t38 fax mode (t.38/udptl). 672 Scenario: 673 1. A SIP INVITE is sent to the called party requesting a voice 674 connection per RFC2543; our scenario involves 1 SIP proxy. An audio 675 connection is established, 676 2. Upon detection of Preamble by the terminating gateway, a SIP re- 677 INVITE request is sent to the emitting gateway to modify the 678 parameters of the session to allow a T.38 fax media connection. 679 This INVITE request contains new SDP information detailing T.38 680 capabilities, 681 3. Upon successful acknowledgments, T.38 IFP fax packets are 682 sent/received on UDP ports, which may be the same UDP ports used for 683 audio RTP, 684 4. Once the fax transmission is terminated, audio capabilities are 685 �restored� or the call is terminated. 687 5.2.1 Sequence Diagram 688 In our example, we illustrate the fact that Internet telephony 689 gateways may use multiple network interfaces for signaling and/or 690 media streaming or one network interface with multiple IP addresses. 691 Typically, our example shows: 693 J-F. Mule/J. Li 13 694 SIP T.38 Call Flows February 2002 696 - one interface for SIP signaling 697 (ingress gateway = ift.here.com, egress gateway = iftgw.there.com) 698 - one or multiple interface(s) for media transport: 699 (ingress gateway = iftmg.here.com, egress gateway = iftmg.there.com) 700 A proxy is acting as a pure SIP signaling proxy (obelix.wcom.com). 702 IFT UA Proxy IFTGW UA 703 | | | 704 | F1 INVITE | | 705 |------------------->| | 706 | | F2 INVITE | 707 | |------------------->| 708 | F3 100 Trying | | 709 |<-------------------| F4 100 Trying | 710 | |<-------------------| 711 | | | 712 | | F5 180 Ringing | 713 | F6 180 Ringing |<-------------------| 714 |<-------------------| | 715 | | F7 200 OK | 716 | F8 200 OK |<-------------------| 717 |<-------------------| | 718 | | | 719 | F9 ACK | | 720 |------------------->| F10 ACK | 721 | ------------------->| 722 | | 723 | Both Way RTP Media Established | 724 Fax |<=======================================>| 725 ------->| | 726 emitted | | | 727 | | | Preamble 728 | | |<--------- 729 | | F11 INVITE | detected 730 | |<-------------------| 731 | F12 INVITE | | 732 |<-------------------| | 733 | | | 734 | F13 200 OK | | 735 |------------------->| | 736 | | F14 200 OK | 737 | |------------------->| 738 | | | 739 | | F15 ACK | 740 | |<-------------------| 741 | F16 ACK | | 742 |<-------------------| | 743 | | 744 | T.38/UDPT Fax Flow Established | 745 |<=======================================>| 746 End of | | 747 fax | | | 749 J-F. Mule/J. Li 14 750 SIP T.38 Call Flows February 2002 752 detected| | | 753 ------->| | | 754 | | | End of fax 755 | | |<---------- 756 | | | detected 758 | | F17 INVITE | 759 | |<-------------------| 760 | F18 INVITE | | 761 |<-------------------| | 762 | | | 763 | F19 200 OK | | 764 |------------------->| | 765 | | F20 200 OK | 766 | |------------------->| 767 | | | 768 | | F21 ACK | 769 | |<-------------------| 770 | F22 ACK | | 771 |<-------------------| | 773 | Both Way RTP Media Re-Established | 774 |<=======================================>| 775 | F23 BYE | | 776 |------------------->| | 777 | | F24 BYE | 778 | |------------------->| 779 | | | 780 | | F25 200 OK | 781 | |<-------------------| 782 | F26 200 OK | | 783 |<-------------------| | 785 5.2.2 Message Details 787 F1 INVITE IFT UA -> PROXY 789 INVITE sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 790 Via: SIP/2.0/UDP ift.here.com:5060 791 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 792 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone 793 Call-ID: 1717@ift.here.com 794 CSeq: 17 INVITE 795 Contact: 796 Content-Type: application/sdp 797 Content-Length: 146 799 v=0 800 o=IFAXTERMINAL01 2890844527 2890844527 IN IP4 ift.here.com 801 s=Session SDP 802 c=IN IP4 iftmg.here.com 804 J-F. Mule/J. Li 15 805 SIP T.38 Call Flows February 2002 807 t=0 0 808 m=audio 3456 RTP/AVP 0 809 a=rtpmap:0 PCMU/8000 811 F2 INVITE PROXY -> IFTGW UA 813 INVITE sip:+1-650-555-2222@iftgw.there.com;user=phone SIP/2.0 814 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 815 Via: SIP/2.0/UDP ift.here.com:5060 816 Record-Route: 818 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 819 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone 820 Call-ID: 1717@ift.here.com 821 CSeq: 17 INVITE 822 Contact: 823 Content-Type: application/sdp 824 Content-Length: 146 826 v=0 827 o=IFAXTERMINAL01 2890844527 2890844527 IN IP4 ift.here.com 828 s=Session SDP 829 c=IN IP4 iftmg.here.com 830 t=0 0 831 m=audio 3456 RTP/AVP 0 832 a=rtpmap:0 PCMU/8000 834 F3 (100 Trying) PROXY -> IFT UA 836 SIP/2.0 100 Trying 837 Via: SIP/2.0/UDP ift.here.com:5060 838 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 839 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone 840 Call-ID: 1717@ift.here.com 841 CSeq: 17 INVITE 842 Content-Length: 0 844 F4 100 Trying IFTGW UA -> PROXY 846 SIP/2.0 100 Trying 847 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 848 Via: SIP/2.0/UDP ift.here.com:5060 849 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 850 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 851 Call-ID: 1717@ift.here.com 852 CSeq: 17 INVITE 853 Contact: 854 Content-Length: 0 856 J-F. Mule/J. Li 16 857 SIP T.38 Call Flows February 2002 859 F5 180 Ringing IFTGW UA -> PROXY 861 SIP/2.0 180 Ringing 862 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 863 Via: SIP/2.0/UDP ift.here.com:5060 864 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 865 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 866 Call-ID: 1717@ift.here.com 867 CSeq: 17 INVITE 868 Contact: 869 Content-Length: 0 871 F6 180 Ringing PROXY -> IFT UA 873 SIP/2.0 180 Ringing 874 Via: SIP/2.0/UDP ift.here.com:5060 875 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 876 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 877 Call-ID: 1717@ift.here.com 878 CSeq: 17 INVITE 879 Contact: 880 Content-Length: 0 882 F7 200 OK IFTGW UA -> PROXY 884 SIP/2.0 200 OK 885 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 886 Via: SIP/2.0/UDP ift.here.com:5060 887 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 888 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 889 Call-ID: 1717@ift.here.com 890 CSeq: 17 INVITE 891 Contact: 892 Content-Type: application/sdp 893 Content-Length: 150 895 v=0 896 o=IFAXTERMINAL01 2890844527 171089 IN IP4 iftgw.there.com 897 s=Session SDP 898 c=IN IP4 iftmg.there.com 899 t=0 0 900 m=audio 12322 RTP/AVP 0 901 a=rtpmap:0 PCMU/8000 903 F8 200 OK PROXY -> IFT UA 905 SIP/2.0 200 OK 906 Via: SIP/2.0/UDP ift.here.com:5060 907 Record-Route: 913 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 914 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 915 Call-ID: 1717@ift.here.com 916 CSeq: 17 INVITE 917 Contact: 918 Content-Type: application/sdp 919 Content-Length: 150 921 v=0 922 o=IFAXTERMINAL01 2890844527 171089 IN IP4 iftgw.there.com 923 s=Session SDP 924 c=IN IP4 iftmg.there.com 925 t=0 0 926 m=audio 12322 RTP/AVP 0 927 a=rtpmap:0 PCMU/8000 929 F9 ACK IFT UA -> PROXY 931 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 932 Via: SIP/2.0/UDP ift.here.com:5060 933 Route: 935 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 936 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 937 Call-ID: 1717@ift.here.com 938 CSeq: 17 ACK 939 Content-Length: 0 941 F10 ACK PROXY -> IFTGW UA 943 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 944 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 945 Via: SIP/2.0/UDP ift.here.com:5060 946 Record-Route: 948 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 949 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 950 Call-ID: 1717@ift.here.com 951 CSeq: 17 ACK 952 Content-Length: 0 954 /* RTP streams are established. The CNG fax tone is sent in-band if 955 it is present. The receiving side IFT gateway DSP detects the 956 Preamble sequence. A new UDP port is open on IFTGW for T.38 IFP 957 packets and the IFTGW signals the switch over to fax mode by send a 958 re-INVITE with the new UDP port in the SDP. 960 J-F. Mule/J. Li 18 961 SIP T.38 Call Flows February 2002 963 Note: the IFTGW has a T38MaxBitRate configured to 9600 */ 965 F11 INVITE IFTGW UA -> PROXY 967 INVITE sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 968 Via: SIP/2.0/UDP iftgw.there.com:5060 969 Route: 971 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 972 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 973 Call-ID: 1717@ift.here.com 974 CSeq: 18 INVITE 975 Contact: 976 Content-Type: application/sdp 977 Content-Length: 320 979 v=0 980 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com 981 s=Session SDP 982 c=IN IP4 iftmg.there.com 983 t=0 0 984 m=image 49172 udptl t38 985 a=T38FaxVersion:0 986 a=T38MaxBitRate:9600 987 a=T38FaxFillBitRemoval:0 988 a=T38FaxTranscodingMMR:0 989 a=T38FaxTranscodingJBIG:0 990 a=T38FaxRateManagement:transferredTCF 991 a=T38FaxMaxBuffer:72 992 a=T38FaxMaxDatagram:316 993 a=T38FaxUdpEC:t38UDPFEC 994 a=T38FaxUdpEC:t38UDPRedundancy 996 F12 INVITE PROXY -> IFT UA 998 INVITE sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 999 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d008.1 1000 Via: SIP/2.0/UDP iftgw.there.com:5060 1001 Record-Route: 1003 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1004 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1005 Call-ID: 1717@ift.here.com 1006 CSeq: 18 INVITE 1007 Contact: 1008 Content-Type: application/sdp 1009 Content-Length: 320 1011 v=0 1012 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com 1013 s=Session SDP 1015 J-F. Mule/J. Li 19 1016 SIP T.38 Call Flows February 2002 1018 c=IN IP4 iftmg.there.com 1019 t=0 0 1020 m=image 49172 udptl t38 1021 a=T38FaxVersion:0 1022 a=T38MaxBitRate:9600 1023 a=T38FaxFillBitRemoval:0 1024 a=T38FaxTranscodingMMR:0 1025 a=T38FaxTranscodingJBIG:0 1026 a=T38FaxRateManagement:transferredTCF 1027 a=T38FaxMaxBuffer:72 1028 a=T38FaxMaxDatagram:316 1029 a=T38FaxUdpEC:t38UDPFEC 1030 a=T38FaxUdpEC:t38UDPRedundancy 1032 /* Note: the IFT has a T38MaxBitRate configured to 14400 but since 1033 it received a T38MaxBitRate proposal of 9600, it replies with 1034 T38MaxBitRate = min (9600,14400) */ 1036 F13 200 OK IFT UA -> PROXY 1038 SIP/2.0 200 OK 1039 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d008.1 1040 Via: SIP/2.0/UDP iftgw.there.com:5060 1041 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1042 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1043 Call-ID: 1717@ift.here.com 1044 CSeq: 18 INVITE 1045 Contact: 1046 Content-Type: application/sdp 1047 Content-Length: 320 1049 v=0 1050 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com 1051 s=Session SDP 1052 c=IN IP4 iftmg.here.com 1053 t=0 0 1054 m=image 15002 udptl t38 1055 a=T38FaxVersion:0 1056 a=T38MaxBitRate:9600 1057 a=T38FaxFillBitRemoval:0 1058 a=T38FaxTranscodingMMR:0 1059 a=T38FaxTranscodingJBIG:0 1060 a=T38FaxRateManagement:transferredTCF 1061 a=T38FaxMaxBuffer:72 1062 a=T38FaxMaxDatagram:316 1063 a=T38FaxUdpEC:t38UDPRedundancy 1065 F14 200 OK PROXY -> IFT UA 1067 SIP/2.0 200 OK 1068 Via: SIP/2.0/UDP iftgw.there.com:5060 1069 Record-Route: 1075 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1076 To: sip:+1-650-555-2222@obelix.wcom.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 1084 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com 1085 s=Session SDP 1086 c=IN IP4 iftmg.here.com 1087 t=0 0 1088 m=image 15002 udptl t38 1089 a=T38FaxVersion:0 1090 a=T38MaxBitRate:9600 1091 a=T38FaxFillBitRemoval:0 1092 a=T38FaxTranscodingMMR:0 1093 a=T38FaxTranscodingJBIG:0 1094 a=T38FaxRateManagement:transferredTCF 1095 a=T38FaxMaxBuffer:72 1096 a=T38FaxMaxDatagram:316 1097 a=T38FaxUdpEC:t38UDPRedundancy 1099 F15 ACK IFTGW UA -> PROXY 1101 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1102 Via: SIP/2.0/UDP iftgw.there.com:5060 1103 Route: 1105 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1106 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1107 Call-ID: 1717@ift.here.com 1108 CSeq: 18 ACK 1109 Content-Length: 0 1111 F16 ACK PROXY -> IFT UA 1113 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1114 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d008.1 1115 Via: SIP/2.0/UDP iftgw.there.com:5060 1116 Record-Route: 1118 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1119 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1120 Call-ID: 1717@ift.here.com 1121 CSeq: 18 ACK 1122 Content-Length: 0 1124 J-F. Mule/J. Li 21 1125 SIP T.38 Call Flows February 2002 1127 /* T.38 fax transmission established both ways */ 1129 /* Then, the end of the fax transmission is detected on ingress side 1130 and sent to the egress side (IFTGW). IFTGW initiates the switch 1131 back to voice communication */ 1133 F17 INVITE IFTGW UA -> PROXY 1135 INVITE sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1136 Via: SIP/2.0/UDP iftgw.there.com:5060 1137 Route: 1139 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1140 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1141 Call-ID: 1717@ift.here.com 1142 CSeq: 19 INVITE 1143 Contact: 1144 Content-Type: application/sdp 1145 Content-Length: 181 1147 v=0 1148 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com 1149 s=Session SDP 1150 c=IN IP4 iftmg.there.com 1151 t=0 0 1152 m=audio 12322 RTP/AVP 0 1153 a=rtpmap:0 PCMU/8000 1155 F18 INVITE PROXY -> IFT UA 1157 INVITE sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1158 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d009.1 1159 Via: SIP/2.0/UDP iftgw.there.com:5060 1160 Record-Route: 1162 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1163 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1164 Call-ID: 1717@ift.here.com 1165 CSeq: 19 INVITE 1166 Contact: 1167 Content-Type: application/sdp 1168 Content-Length: 181 1170 v=0 1171 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com 1172 s=Session SDP 1173 c=IN IP4 iftmg.there.com 1174 t=0 0 1175 m=audio 12322 RTP/AVP 0 1176 a=rtpmap:0 PCMU/8000 1178 J-F. Mule/J. Li 22 1179 SIP T.38 Call Flows February 2002 1181 F19 200 OK IFT UA -> PROXY 1183 SIP/2.0 200 OK 1184 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d008.1 1185 Via: SIP/2.0/UDP iftgw.there.com:5060 1186 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1187 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1188 Call-ID: 1717@ift.here.com 1189 CSeq: 19 INVITE 1190 Contact: 1191 Content-Type: application/sdp 1192 Content-Length: 150 1194 v=0 1195 o=faxgw1 2890844527 2890844529 IN IP4 ift.here.com 1196 s=Session SDP 1197 c=IN IP4 iftmg.here.com 1198 t=0 0 1199 m=audio 3456 RTP/AVP 0 1200 a=rtpmap:0 PCMU/8000 1202 F20 200 OK PROXY -> IFTGW UA 1204 SIP/2.0 200 OK 1205 Via: SIP/2.0/UDP iftgw.there.com:5060 1206 Record-Route: 1208 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1209 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1210 Call-ID: 1717@ift.here.com 1211 CSeq: 19 INVITE 1212 Contact: 1213 Content-Type: application/sdp 1214 Content-Length: 150 1216 v=0 1217 o=faxgw1 2890844527 2890844529 IN IP4 ift.here.com 1218 s=Session SDP 1219 c=IN IP4 iftmg.here.com 1220 t=0 0 1221 m=audio 3456 RTP/AVP 0 1222 a=rtpmap:0 PCMU/8000 1224 F21 ACK IFTGW UA -> PROXY 1226 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1227 Via: SIP/2.0/UDP iftgw.there.com:5060 1228 Route: 1234 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1235 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1236 Call-ID: 1717@ift.here.com 1237 CSeq: 19 ACK 1238 Content-Length: 0 1240 F22 ACK PROXY -> IFT UA 1242 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1243 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d009.1 1244 Via: SIP/2.0/UDP iftgw.there.com:5060 1245 Record-Route: 1247 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1248 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1249 Call-ID: 1717@ift.here.com 1250 CSeq: 19 ACK 1251 Content-Length: 0 1253 /* Voice streams re-established both ways */ 1255 F23 BYE IFT UA -> PROXY 1257 BYE sip:+1-650-555-2222@obelix.wcom.com SIP/2.0 1258 Via: SIP/2.0/UDP ift.here.com:5060 1259 Route: 1261 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1262 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone 1263 Call-ID: 1717@ift.here.com 1264 CSeq: 20 BYE 1265 Content-Length: 0 1267 F24 BYE PROXY -> IFTGW UA 1269 BYE sip:+1-650-555-2222@obelix.wcom.com SIP/2.0 1270 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d009.1 1271 Via: SIP/2.0/UDP ift.here.com:5060 1272 Record-Route: 1274 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1275 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone 1276 Call-ID: 1717@ift.here.com 1277 CSeq: 20 BYE 1278 Content-Length: 0 1280 F25 200 OK IFTGW UA -> PROXY 1282 J-F. Mule/J. Li 24 1283 SIP T.38 Call Flows February 2002 1285 SIP/2.0 200 OK 1286 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 1287 Via: SIP/2.0/UDP ift.here.com:5060 1288 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1289 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde24 1290 Call-ID: 1717@ift.here.com 1291 CSeq: 20 BYE 1292 Content-Type: application/sdp 1293 Content-Length: 0 1295 F26 200 OK PROXY -> IFT UA 1297 SIP/2.0 200 OK 1298 Via: SIP/2.0/UDP ift.here.com:5060 1299 Record-Route: 1301 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1302 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde24 1303 Call-ID: 1717@ift.here.com 1304 CSeq: 20 BYE 1305 Content-Type: application/sdp 1306 Content-Length: 0 1308 5.3 SIP T.38 fax call � fax stream added to voice stream 1310 This section represents the SIP call flow for a T.38 fax session 1311 between 2 Internet telephony gateways. It shows the detection of 1312 the fax communication on terminating or receiving side. 1313 A session starts with one audio stream in SDP, and, upon detection 1314 of fax, an additional fax stream is added to the session while the 1315 voice stream is muted. After the fax communication is terminated, 1316 the fax stream is terminated and the voice stream is restored. 1318 Scenario: 1319 1. A SIP INVITE is sent to the called party requesting a voice 1320 connection per RFC2543; our scenario involves 1 SIP proxy. An audio 1321 connection is established, 1322 2. Upon detection of Preamble by the terminating gateway, a SIP 1323 re�INVITE request is sent to the emitting gateway to modify the 1324 parameters of the session to add a T.38 fax connection. The 1325 connection data is specified per media description and not at the 1326 session-level. This allows the audio stream and t.38 fax stream to 1327 be controlled independently (i.e., placing the audio on hold while 1328 the t.38 fax transmission is active). Also note that the t.38 fax 1329 media stream has been added to the session. This re-INVITE request 1330 contains SDP information detailing the additional T.38 capabilities, 1331 3. It is suggested that the voice pipe be muted while the fax 1332 session is in progress. Upon successful acknowledgments, T.38 IFP 1333 fax packets are sent/received on different UDP ports than the one 1334 used for audio RTP, 1336 J-F. Mule/J. Li 25 1337 SIP T.38 Call Flows February 2002 1339 4. Once the fax transmission is terminated, audio capabilities are 1340 �restored� or the call is terminated. 1342 5.3.1 Sequence Diagram 1344 IFT UA Proxy IFTGW UA 1345 | | | 1346 | F1 INVITE | | 1347 |------------------->| | 1348 | | F2 INVITE | 1349 | |------------------->| 1350 | F3 100 Trying | | 1351 |<-------------------| F4 100 Trying | 1352 | |<-------------------| 1353 | | | 1354 | | F5 180 Ringing | 1355 | F6 180 Ringing |<-------------------| 1356 |<-------------------| | 1357 | | F7 200 OK | 1358 | F8 200 OK |<-------------------| 1359 |<-------------------| | 1360 | | | 1361 | F9 ACK | | 1362 |------------------->| F10 ACK | 1363 | ------------------->| 1364 | | 1365 | Both Way RTP Media Established | 1366 Fax |<=======================================>| 1367 ------->| | 1368 emitted | | | 1369 | | | Preamble 1370 | | |<--------- 1371 | | F11 INVITE | detected 1372 | |<-------------------| 1373 | F12 INVITE | | 1374 |<-------------------| | 1375 | | | 1376 | F13 200 OK | | 1377 |------------------->| | 1378 | | F14 200 OK | 1379 | |------------------->| 1380 | | F15 ACK | 1381 | |<-------------------| 1382 | F16 ACK | | 1383 |<-------------------| | 1384 | | 1385 | T.38/UDPT Fax Flow Established | 1386 | Voice connection muted | 1387 |<=======================================>| 1388 End of | | 1389 fax | | | 1391 J-F. Mule/J. Li 26 1392 SIP T.38 Call Flows February 2002 1394 detected| | | 1395 ------->| | | 1396 | | 1397 | | | End of fax 1398 | | |<---------- 1399 | | | detected 1400 | | F17 INVITE | 1401 | |<-------------------| 1402 | F18 INVITE | | 1403 |<-------------------| | 1404 | | | 1405 | F19 200 OK | | 1406 |------------------->| | 1407 | | F20 200 OK | 1408 | |------------------->| 1409 | | | 1410 | | F21 ACK | 1411 | |<-------------------| 1412 | F22 ACK | | 1413 |<-------------------| | 1414 | | 1415 | Both way RTP Flow restored | 1416 |<=======================================>| 1417 | | 1418 | F23 BYE | | 1419 |------------------->| | 1420 | | F24 BYE | 1421 | |------------------->| 1422 | | | 1423 | | F25 200 OK | 1424 | |<-------------------| 1425 | F26 200 OK | | 1426 |<-------------------| | 1428 5.3.2 Message Details 1430 F1 INVITE IFT UA -> PROXY 1432 INVITE sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1433 Via: SIP/2.0/UDP ift.here.com:5060 1434 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1435 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone 1436 Call-ID: 1717@ift.here.com 1437 CSeq: 17 INVITE 1438 Contact: 1439 Content-Type: application/sdp 1440 Content-Length: 146 1442 v=0 1443 o=IFAXTERMINAL01 2890844527 2890844527 IN IP4 ift.here.com 1444 s=Session SDP 1446 J-F. Mule/J. Li 27 1447 SIP T.38 Call Flows February 2002 1449 c=IN IP4 iftmg.here.com 1450 t=0 0 1451 m=audio 3456 RTP/AVP 0 1452 a=rtpmap:0 PCMU/8000 1454 F2 INVITE PROXY -> IFTGW UA 1456 INVITE sip:+1-650-555-2222@iftgw.there.com;user=phone SIP/2.0 1457 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 1458 Via: SIP/2.0/UDP ift.here.com:5060 1459 Record-Route: 1461 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1462 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone 1463 Call-ID: 1717@ift.here.com 1464 CSeq: 17 INVITE 1465 Contact: 1466 Content-Type: application/sdp 1467 Content-Length: 146 1469 v=0 1470 o=IFAXTERMINAL01 2890844527 2890844527 IN IP4 ift.here.com 1471 s=Session SDP 1472 c=IN IP4 iftmg.here.com 1473 t=0 0 1474 m=audio 3456 RTP/AVP 0 1475 a=rtpmap:0 PCMU/8000 1477 F3 (100 Trying) PROXY -> IFT UA 1479 SIP/2.0 100 Trying 1480 Via: SIP/2.0/UDP ift.here.com:5060 1481 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1482 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone 1483 Call-ID: 1717@ift.here.com 1484 CSeq: 17 INVITE 1485 Content-Length: 0 1487 F4 100 Trying IFTGW UA -> PROXY 1489 SIP/2.0 100 Trying 1490 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 1491 Via: SIP/2.0/UDP ift.here.com:5060 1492 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1493 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1494 Call-ID: 1717@ift.here.com 1495 CSeq: 17 INVITE 1496 Contact: 1497 Content-Length: 0 1499 J-F. Mule/J. Li 28 1500 SIP T.38 Call Flows February 2002 1502 F5 180 Ringing IFTGW UA -> PROXY 1504 SIP/2.0 180 Ringing 1505 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 1506 Via: SIP/2.0/UDP ift.here.com:5060 1507 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1508 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1509 Call-ID: 1717@ift.here.com 1510 CSeq: 17 INVITE 1511 Contact: 1512 Content-Length: 0 1514 F6 180 Ringing PROXY -> IFT UA 1516 SIP/2.0 180 Ringing 1517 Via: SIP/2.0/UDP ift.here.com:5060 1518 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1519 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1520 Call-ID: 1717@ift.here.com 1521 CSeq: 17 INVITE 1522 Contact: 1523 Content-Length: 0 1525 F7 200 OK IFTGW UA -> PROXY 1527 SIP/2.0 200 OK 1528 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 1529 Via: SIP/2.0/UDP ift.here.com:5060 1530 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1531 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1532 Call-ID: 1717@ift.here.com 1533 CSeq: 17 INVITE 1534 Contact: 1535 Content-Type: application/sdp 1536 Content-Length: 150 1538 v=0 1539 o=IFAXTERMINAL01 2890844527 171089 IN IP4 iftgw.there.com 1540 s=Session SDP 1541 c=IN IP4 iftmg.there.com 1542 t=0 0 1543 m=audio 12322 RTP/AVP 0 1544 a=rtpmap:0 PCMU/8000 1546 F8 200 OK PROXY -> IFT UA 1548 SIP/2.0 200 OK 1549 Via: SIP/2.0/UDP ift.here.com:5060 1551 J-F. Mule/J. Li 29 1552 SIP T.38 Call Flows February 2002 1554 Record-Route: 1556 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1557 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1558 Call-ID: 1717@ift.here.com 1559 CSeq: 17 INVITE 1560 Contact: 1561 Content-Type: application/sdp 1562 Content-Length: 150 1564 v=0 1565 o=IFAXTERMINAL01 2890844527 171089 IN IP4 iftgw.there.com 1566 s=Session SDP 1567 c=IN IP4 iftmg.there.com 1568 t=0 0 1569 m=audio 12322 RTP/AVP 0 1570 a=rtpmap:0 PCMU/8000 1572 F9 ACK IFT UA -> PROXY 1574 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1575 Via: SIP/2.0/UDP ift.here.com:5060 1576 Route: 1578 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1579 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1580 Call-ID: 1717@ift.here.com 1581 CSeq: 17 ACK 1582 Content-Length: 0 1584 F10 ACK PROXY -> IFTGW UA 1586 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1587 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 1588 Via: SIP/2.0/UDP ift.here.com:5060 1589 Record-Route: 1591 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1592 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1593 Call-ID: 1717@ift.here.com 1594 CSeq: 17 ACK 1595 Content-Length: 0 1597 /* RTP streams are established. The CNG fax tone is sent in-band if 1598 it is present. The receiving side IFT gateway DSP detects the 1599 Preamble. A new UDP port is open on IFTGW for T.38 IFP packets and 1600 the IFTGW signals the switch over to fax mode by send a re-INVITE 1601 with the new UDP port in the SDP */ 1603 J-F. Mule/J. Li 30 1604 SIP T.38 Call Flows February 2002 1606 F11 INVITE IFTGW UA -> PROXY 1608 INVITE sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1609 Via: SIP/2.0/UDP iftgw.there.com:5060 1610 Route: 1612 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1613 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1614 Call-ID: 1717@ift.here.com 1615 CSeq: 18 INVITE 1616 Contact: 1617 Content-Type: application/sdp 1618 Content-Length: 320 1620 v=0 1621 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com 1622 s=Session SDP 1623 t=0 0 1624 m=audio 12322 RTP/AVP 0 1625 c=IN IP4 0.0.0.0 1626 m=image 49172 udptl t38 1627 c=IN IP4 iftmg.there.com 1628 a=T38FaxVersion:0 1629 a=T38MaxBitRate:14400 1630 a=T38FaxFillBitRemoval:0 1631 a=T38FaxTranscodingMMR:0 1632 a=T38FaxTranscodingJBIG:0 1633 a=T38FaxRateManagement:transferredTCF 1634 a=T38FaxMaxBuffer:72 1635 a=T38FaxMaxDatagram:316 1636 a=T38FaxUdpEC:t38UDPFEC 1637 a=T38FaxUdpEC:t38UDPRedundancy 1639 F12 INVITE PROXY -> IFT UA 1641 INVITE sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1642 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d008.1 1643 Via: SIP/2.0/UDP iftgw.there.com:5060 1644 Record-Route: 1646 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1647 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1648 Call-ID: 1717@ift.here.com 1649 CSeq: 18 INVITE 1650 Contact: 1651 Content-Type: application/sdp 1652 Content-Length: 320 1654 v=0 1655 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com 1656 s=Session SDP 1657 t=0 0 1659 J-F. Mule/J. Li 31 1660 SIP T.38 Call Flows February 2002 1662 m=audio 12322 RTP/AVP 0 1663 c=IN IP4 0.0.0.0 1664 m=image 49172 udptl t38 1665 c=IN IP4 iftmg.there.com 1666 a=T38FaxVersion:0 1667 a=T38MaxBitRate:14400 1668 a=T38FaxFillBitRemoval:0 1669 a=T38FaxTranscodingMMR:0 1670 a=T38FaxTranscodingJBIG:0 1671 a=T38FaxRateManagement:transferredTCF 1672 a=T38FaxMaxBuffer:72 1673 a=T38FaxMaxDatagram:316 1674 a=T38FaxUdpEC:t38UDPFEC 1675 a=T38FaxUdpEC:t38UDPRedundancy 1677 F13 200 OK IFT UA -> PROXY 1679 SIP/2.0 200 OK 1680 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d008.1 1681 Via: SIP/2.0/UDP iftgw.there.com:5060 1682 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1683 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1684 Call-ID: 1717@ift.here.com 1685 CSeq: 18 INVITE 1686 Contact: 1687 Content-Type: application/sdp 1688 Content-Length: 320 1690 v=0 1691 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com 1692 s=Session SDP 1693 t=0 0 1694 m=audio 3456 RTP/AVP 0 1695 c=IN IP4 0.0.0.0 1696 m=image 15002 udptl t38 1697 c=IN IP4 iftmg.here.com 1698 a=T38FaxVersion:0 1699 a=T38MaxBitRate:14400 1700 a=T38FaxFillBitRemoval:0 1701 a=T38FaxTranscodingMMR:0 1702 a=T38FaxTranscodingJBIG:0 1703 a=T38FaxRateManagement:transferredTCF 1704 a=T38FaxMaxBuffer:72 1705 a=T38FaxMaxDatagram:316 1706 a=T38FaxUdpEC:t38UDPRedundancy 1708 F14 200 OK PROXY -> IFT UA 1710 SIP/2.0 200 OK 1711 Via: SIP/2.0/UDP iftgw.there.com:5060 1712 Record-Route: 1718 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1719 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1720 Call-ID: 1717@ift.here.com 1721 CSeq: 18 INVITE 1722 Contact: 1723 Content-Type: application/sdp 1724 Content-Length: 320 1726 v=0 1727 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com 1728 s=Session SDP 1729 t=0 0 1730 m=audio 3456 RTP/AVP 0 1731 c=IN IP4 0.0.0.0 1732 m=image 15002 udptl t38 1733 c=IN IP4 iftmg.here.com 1734 a=T38FaxVersion:0 1735 a=T38MaxBitRate:14400 1736 a=T38FaxFillBitRemoval:0 1737 a=T38FaxTranscodingMMR:0 1738 a=T38FaxTranscodingJBIG:0 1739 a=T38FaxRateManagement:transferredTCF 1740 a=T38FaxMaxBuffer:72 1741 a=T38FaxMaxDatagram:316 1742 a=T38FaxUdpEC:t38UDPRedundancy 1744 F15 ACK IFTGW UA -> PROXY 1746 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1747 Via: SIP/2.0/UDP iftgw.there.com:5060 1748 Route: 1750 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1751 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1752 Call-ID: 1717@ift.here.com 1753 CSeq: 18 ACK 1754 Content-Length: 0 1756 F16 ACK PROXY -> IFT UA 1758 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1759 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d008.1 1760 Via: SIP/2.0/UDP iftgw.there.com:5060 1761 Record-Route: 1763 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1764 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1765 Call-ID: 1717@ift.here.com 1766 CSeq: 18 ACK 1767 Content-Length: 0 1769 J-F. Mule/J. Li 33 1770 SIP T.38 Call Flows February 2002 1772 /* T.38 fax transmission established both ways and the voice stream 1773 is muted */ 1774 /* Then, the end of the fax transmission is detected on ingress side 1775 and sent to the egress side (IFTGW). IFTGW initiates the switch back 1776 to voice communication */ 1778 F17 INVITE IFTGW UA -> PROXY 1780 INVITE sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1781 Via: SIP/2.0/UDP iftgw.there.com:5060 1782 Route: 1784 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1785 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1786 Call-ID: 1717@ift.here.com 1787 CSeq: 19 INVITE 1788 Contact: 1789 Content-Type: application/sdp 1790 Content-Length: 181 1792 v=0 1793 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com 1794 s=Session SDP 1795 c=IN IP4 iftmg.there.com 1796 t=0 0 1797 m=audio 12322 RTP/AVP 0 1798 a=rtpmap:0 PCMU/8000 1800 F18 INVITE PROXY -> IFT UA 1802 INVITE sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1803 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d009.1 1804 Via: SIP/2.0/UDP iftgw.there.com:5060 1805 Record-Route: 1807 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1808 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1809 Call-ID: 1717@ift.here.com 1810 CSeq: 19 INVITE 1811 Contact: 1812 Content-Type: application/sdp 1813 Content-Length: 181 1815 v=0 1816 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com 1817 s=Session SDP 1818 c=IN IP4 iftmg.there.com 1819 t=0 0 1820 m=audio 12322 RTP/AVP 0 1822 J-F. Mule/J. Li 34 1823 SIP T.38 Call Flows February 2002 1825 a=rtpmap:0 PCMU/8000 1827 F19 200 OK IFT UA -> PROXY 1829 SIP/2.0 200 OK 1830 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d008.1 1831 Via: SIP/2.0/UDP iftgw.there.com:5060 1832 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1833 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1834 Call-ID: 1717@ift.here.com 1835 CSeq: 19 INVITE 1836 Contact: 1837 Content-Type: application/sdp 1838 Content-Length: 150 1840 v=0 1841 o=faxgw1 2890844527 2890844529 IN IP4 ift.here.com 1842 s=Session SDP 1843 c=IN IP4 iftmg.here.com 1844 t=0 0 1845 m=audio 3456 RTP/AVP 0 1846 a=rtpmap:0 PCMU/8000 1848 F20 200 OK PROXY -> IFTGW UA 1850 SIP/2.0 200 OK 1851 Via: SIP/2.0/UDP iftgw.there.com:5060 1852 Record-Route: 1854 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1855 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1856 Call-ID: 1717@ift.here.com 1857 CSeq: 19 INVITE 1858 Contact: 1859 Content-Type: application/sdp 1860 Content-Length: 150 1862 v=0 1863 o=faxgw1 2890844527 2890844529 IN IP4 ift.here.com 1864 s=Session SDP 1865 c=IN IP4 iftmg.here.com 1866 t=0 0 1867 m=audio 3456 RTP/AVP 0 1868 a=rtpmap:0 PCMU/8000 1870 F21 ACK IFTGW UA -> PROXY 1872 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1873 Via: SIP/2.0/UDP iftgw.there.com:5060 1874 Route: 1877 J-F. Mule/J. Li 35 1878 SIP T.38 Call Flows February 2002 1880 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1881 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1882 Call-ID: 1717@ift.here.com 1883 CSeq: 19 ACK 1884 Content-Length: 0 1886 F22 ACK PROXY -> IFT UA 1888 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1889 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d009.1 1890 Via: SIP/2.0/UDP iftgw.there.com:5060 1891 Record-Route: 1893 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1894 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1895 Call-ID: 1717@ift.here.com 1896 CSeq: 19 ACK 1897 Content-Length: 0 1899 F23 BYE IFT UA -> PROXY 1901 BYE sip:+1-650-555-2222@obelix.wcom.com SIP/2.0 1902 Via: SIP/2.0/UDP ift.here.com:5060 1903 Route: 1905 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1906 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone 1907 Call-ID: 1717@ift.here.com 1908 CSeq: 20 BYE 1909 Content-Length: 0 1911 F24 BYE PROXY -> IFTGW UA 1913 BYE sip:+1-650-555-2222@obelix.wcom.com SIP/2.0 1914 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d009.1 1915 Via: SIP/2.0/UDP ift.here.com:5060 1916 Record-Route: 1918 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1919 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone 1920 Call-ID: 1717@ift.here.com 1921 CSeq: 20 BYE 1922 Content-Length: 0 1924 F25 200 OK IFTGW UA -> PROXY 1926 SIP/2.0 200 OK 1927 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 1928 Via: SIP/2.0/UDP ift.here.com:5060 1929 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1931 J-F. Mule/J. Li 36 1932 SIP T.38 Call Flows February 2002 1934 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde24 1935 Call-ID: 1717@ift.here.com 1936 CSeq: 20 BYE 1937 Content-Type: application/sdp 1938 Content-Length: 0 1940 F26 200 OK PROXY -> IFT UA 1942 SIP/2.0 200 OK 1943 Via: SIP/2.0/UDP ift.here.com:5060 1944 Record-Route: 1946 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 1947 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde24 1948 Call-ID: 1717@ift.here.com 1949 CSeq: 20 BYE 1950 Content-Type: application/sdp 1951 Content-Length: 0 1953 5.4 SIP T.38 fax call � fax stream forced to replace voice stream 1955 This section illustrates the following scenario: 1956 1. A SIP INVITE is sent to the called party requesting a voice 1957 connection per RFC2543; our scenario involves 1 SIP proxy. An audio 1958 connection is established, 1959 2. Upon detection of Preamble by the terminating gateway, a SIP 1960 re�INVITE request is sent to the emitting gateway to modify the 1961 parameters of the session to add a T.38 fax connection. This re- 1962 INVITE request contains SDP information detailing the additional 1963 T.38 capabilities. It is also suggested that the voice pipe be 1964 muted while the fax session is in progress. 1965 3. The emitting gateway does not have the resources to maintain both 1966 the audio & fax streams and replies by allowing the fax media 1967 stream. Upon successful acknowledgments, the audio stream is 1968 terminated and T.38 IFP fax packets are exchanged, 1969 4. Once the fax transmission is terminated, audio capabilities are 1970 �re-negotiated� and the call is terminated. 1972 5.4.1 Sequence Diagram 1973 Refer to section 5.3.1; sequence diagram is unchanged. 1975 5.4.2 Message Details 1976 See section 5.3.2 for the complete set of messages. We only 1977 indicate the changed messages based on the emitting gateway�s 1978 decline to support both voice and fax streams. 1980 ... 1981 F11 INVITE IFTGW UA -> PROXY 1983 J-F. Mule/J. Li 37 1984 SIP T.38 Call Flows February 2002 1986 INVITE sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 1987 Via: SIP/2.0/UDP iftgw.there.com:5060 1988 Route: 1990 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 1991 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 1992 Call-ID: 1717@ift.here.com 1993 CSeq: 18 INVITE 1994 Contact: 1995 Content-Type: application/sdp 1996 Content-Length: 320 1998 v=0 1999 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com 2000 s=Session SDP 2001 t=0 0 2002 m=audio 12322 RTP/AVP 0 2003 c=IN IP4 0.0.0.0 2004 m=image 49172 udptl t38 2005 c=IN IP4 iftmg.there.com 2006 a=T38FaxVersion:0 2007 a=T38MaxBitRate:14400 2008 a=T38FaxFillBitRemoval:0 2009 a=T38FaxTranscodingMMR:0 2010 a=T38FaxTranscodingJBIG:0 2011 a=T38FaxRateManagement:transferredTCF 2012 a=T38FaxMaxBuffer:72 2013 a=T38FaxMaxDatagram:316 2014 a=T38FaxUdpEC:t38UDPFEC 2015 a=T38FaxUdpEC:t38UDPRedundancy 2017 F12 INVITE PROXY -> IFT UA 2019 INVITE sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 2020 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d008.1 2021 Via: SIP/2.0/UDP iftgw.there.com:5060 2022 Record-Route: 2024 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2025 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 2026 Call-ID: 1717@ift.here.com 2027 CSeq: 18 INVITE 2028 Contact: 2029 Content-Type: application/sdp 2030 Content-Length: 320 2032 v=0 2033 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com 2034 s=Session SDP 2035 t=0 0 2036 m=audio 12322 RTP/AVP 0 2038 J-F. Mule/J. Li 38 2039 SIP T.38 Call Flows February 2002 2041 c=IN IP4 0.0.0.0 2042 m=image 49172 udptl t38 2043 c=IN IP4 iftmg.there.com 2044 a=T38FaxVersion:0 2045 a=T38MaxBitRate:14400 2046 a=T38FaxFillBitRemoval:0 2047 a=T38FaxTranscodingMMR:0 2048 a=T38FaxTranscodingJBIG:0 2049 a=T38FaxRateManagement:transferredTCF 2050 a=T38FaxMaxBuffer:72 2051 a=T38FaxMaxDatagram:316 2052 a=T38FaxUdpEC:t38UDPFEC 2053 a=T38FaxUdpEC:t38UDPRedundancy 2055 F13 200 OK IFT UA -> PROXY 2057 SIP/2.0 200 OK 2058 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d008.1 2059 Via: SIP/2.0/UDP iftgw.there.com:5060 2060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2061 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 2062 Call-ID: 1717@ift.here.com 2063 CSeq: 18 INVITE 2064 Contact: 2065 Content-Type: application/sdp 2066 Content-Length: 320 2068 v=0 2069 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com 2070 s=Session SDP 2071 t=0 0 2072 m=audio 0 RTP/AVP 0 2073 c=IN IP4 0.0.0.0 2074 m=image 15002 udptl t38 2075 c=IN IP4 iftmg.here.com 2076 a=T38FaxVersion:0 2077 a=T38MaxBitRate:14400 2078 a=T38FaxFillBitRemoval:0 2079 a=T38FaxTranscodingMMR:0 2080 a=T38FaxTranscodingJBIG:0 2081 a=T38FaxRateManagement:transferredTCF 2082 a=T38FaxMaxBuffer:72 2083 a=T38FaxMaxDatagram:316 2084 a=T38FaxUdpEC:t38UDPRedundancy 2086 F14 200 OK PROXY -> IFT UA 2088 SIP/2.0 200 OK 2089 Via: SIP/2.0/UDP iftgw.there.com:5060 2090 Record-Route: 2096 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2097 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 2098 Call-ID: 1717@ift.here.com 2099 CSeq: 18 INVITE 2100 Contact: 2101 Content-Type: application/sdp 2102 Content-Length: 320 2104 v=0 2105 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com 2106 s=Session SDP 2107 t=0 0 2108 m=audio 0 RTP/AVP 0 2109 c=IN IP4 0.0.0.0 2110 m=image 15002 udptl t38 2111 c=IN IP4 iftmg.here.com 2112 a=T38FaxVersion:0 2113 a=T38MaxBitRate:14400 2114 a=T38FaxFillBitRemoval:0 2115 a=T38FaxTranscodingMMR:0 2116 a=T38FaxTranscodingJBIG:0 2117 a=T38FaxRateManagement:transferredTCF 2118 a=T38FaxMaxBuffer:72 2119 a=T38FaxMaxDatagram:316 2120 a=T38FaxUdpEC:t38UDPRedundancy 2122 F15 ACK IFTGW UA -> PROXY 2124 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 2125 Via: SIP/2.0/UDP iftgw.there.com:5060 2126 Route: 2128 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2129 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 2130 Call-ID: 1717@ift.here.com 2131 CSeq: 18 ACK 2132 Content-Length: 0 2134 F16 ACK PROXY -> IFT UA 2136 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 2137 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d008.1 2138 Via: SIP/2.0/UDP iftgw.there.com:5060 2139 Record-Route: 2141 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2142 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 2143 Call-ID: 1717@ift.here.com 2144 CSeq: 18 ACK 2145 Content-Length: 0 2147 J-F. Mule/J. Li 40 2148 SIP T.38 Call Flows February 2002 2150 6. Unsuccessful Scenarios 2152 6.1. Unsuccessful T.38 fax scenario � no support for T.38 2153 This section represents a SIP T.38 call failure because the emitting 2154 gateway does not support T.38. 2156 Scenario: 2157 1. A SIP INVITE is sent to the called party requesting a voice 2158 connection per RFC2543; our scenario involves 1 SIP proxy. An audio 2159 connection is established, 2160 2. Upon detection of Preamble by the terminating gateway, a SIP 2161 re�INVITE request is sent to the emitting gateway to modify the 2162 parameters of the session to allow a T.38 fax connection. This re- 2163 INVITE request contains SDP information detailing T.38 capabilities, 2164 3. The emitting gateway rejects the re�INVITE with a 415 Unsupported 2165 Media Type response. 2166 4. Upon reception of the reject, the call is terminated. 2168 6.1.1. Sequence Diagram 2170 The messages F1 to F12 are identical to section 5.2. 2172 IFT UA Proxy IFTGW UA 2173 | | | 2174 | F1 INVITE | | 2175 |------------------->| | 2176 | | F2 INVITE | 2177 | |------------------->| 2178 | F3 100 Trying | | 2179 |<-------------------| F4 100 Trying | 2180 | |<-------------------| 2181 | | | 2182 | | F5 180 Ringing | 2183 | F6 180 Ringing |<-------------------| 2184 |<-------------------| | 2185 | | F7 200 OK | 2186 | F8 200 OK |<-------------------| 2187 |<-------------------| | 2188 | F9 ACK | | 2189 |------------------->| F10 ACK | 2190 | ------------------->| 2191 | | 2192 | Both Way RTP Media Established | 2193 Fax |<=======================================>| 2194 ------->| | 2195 emitted | | | 2196 | | | Preamble 2197 | | |<--------- 2198 | | F11 INVITE | detected 2200 J-F. Mule/J. Li 41 2201 SIP T.38 Call Flows February 2002 2203 | |<-------------------| 2204 | F12 INVITE | | 2205 |<-------------------| | 2206 | | | 2207 | F13 415 | | 2208 |------------------->| | 2209 | | F14 415 | 2210 | |------------------->| 2211 | | | 2212 | | F15 BYE | 2213 | |<-------------------| 2214 | F16 BYE | | 2215 |<-------------------| | 2216 | | | 2217 | F17 200 OK | | 2218 |------------------->| | 2219 | | F18 200 OK | 2220 | |------------------->| 2222 6.1.2. Message Details 2224 Messages F1 to F12 are identical to section 5.2; refer to 5.2. 2226 F13 415 Unsupported Media Type IFT UA -> PROXY 2228 SIP/2.0 415 Unsupported Media Type 2229 Via: SIP/2.0/UDP ift.here.com:5060 2230 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2231 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 2232 Call-ID: 1717@ift.here.com 2233 CSeq: 18 INVITE 2234 Contact: 2235 Content-Length: 0 2237 F14 415 Unsupported Media Type PROXY -> IFTGW UA 2239 SIP/2.0 415 Unsupported Media Type 2240 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d010.1 2241 Via: SIP/2.0/UDP ift.here.com:5060 2242 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2243 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 2244 Call-ID: 1717@ift.here.com 2245 CSeq: 18 INVITE 2246 Contact: 2247 Content-Length: 0 2249 F15 BYE IFTGW UA -> PROXY 2251 BYE sip:+1-650-555-2222@obelix.wcom.com SIP/2.0 2253 J-F. Mule/J. Li 42 2254 SIP T.38 Call Flows February 2002 2256 Via: SIP/2.0/UDP iftgw.there.com:5060 2257 Route: 2259 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2260 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde34 2261 Call-ID: 1717@ift.here.com 2262 CSeq: 19 BYE 2263 Content-Length: 0 2265 F16 BYE PROXY -> IFT UA 2267 BYE sip:+1-650-555-2222@obelix.wcom.com SIP/2.0 2268 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d010.1 2269 Via: SIP/2.0/UDP iftgw.there.com:5060 2270 Record-Route: 2272 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2273 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde34 2274 Call-ID: 1717@ift.here.com 2275 CSeq: 19 BYE 2276 Content-Length: 0 2278 F17 200 OK IFT UA -> PROXY 2280 SIP/2.0 200 OK 2281 Via: SIP/2.0/UDP ift.here.com:5060 2282 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2283 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde34 2284 Call-ID: 1717@ift.here.com 2285 CSeq: 19 BYE 2286 Content-Type: application/sdp 2287 Content-Length: 0 2289 F18 200 OK PROXY -> IFTGW UA 2291 SIP/2.0 200 OK 2292 Via: SIP/2.0/UDP obelix.wcom.com:5060 2293 Via: SIP/2.0/UDP ift.here.com:5060 2294 Record-Route: 2296 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2297 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde34 2298 Call-ID: 1717@ift.here.com 2299 CSeq: 19 BYE 2300 Content-Type: application/sdp 2301 Content-Length: 0 2303 6.2. Unsuccessful T.38 fax scenario � 488/606 response & G.711 fallback 2305 J-F. Mule/J. Li 43 2306 SIP T.38 Call Flows February 2002 2308 This section represents an unsuccessful SIP T.38 fax call: when the 2309 emitting gateway does not support T.38 fax relay, it SHOULD respond 2310 with either a �488 Not Acceptable Here� response or a �606 Not 2311 Acceptable� response to indicate that some aspects of the session 2312 description are not acceptable. The terminating gateway SHOULD 2313 react by proposing a fallback to G.711 fax pass-through with special 2314 codec characteristics � echo cancellation ON, silence suppression 2315 OFF. The message details in this section make use of the generic 2316 SDP attributes ecan and silenceSupp, defined in RFC3108 [10]. 2318 Scenario: 2319 1. A SIP INVITE is sent to the called party requesting a voice 2320 connection per RFC2543; our scenario involves 1 SIP proxy. An audio 2321 connection is established, 2322 2. Upon detection of Preamble by the terminating gateway, a SIP 2323 re�INVITE request is sent to the emitting gateway to modify the 2324 parameters of the session to allow a T.38 fax connection. This re- 2325 INVITE request contains SDP information detailing T.38 capabilities, 2326 3. The emitting gateway rejects the re-INVITE with a 488 or 606 2327 response. Upon reception of the reject, the terminating gateway 2328 proposes to use plain G.711 to carry the fax stream. 2329 4. The call is terminated. 2331 6.2.1. Sequence Diagram 2332 The messages F1 to F12 are identical to section 5.2. 2334 IFT UA Proxy IFTGW UA 2335 | | | 2336 | F1 INVITE | | 2337 |------------------->| | 2338 | | F2 INVITE | 2339 | |------------------->| 2340 | F3 100 Trying | | 2341 |<-------------------| F4 100 Trying | 2342 | |<-------------------| 2343 | | | 2344 | | F5 180 Ringing | 2345 | F6 180 Ringing |<-------------------| 2346 |<-------------------| | 2347 | | F7 200 OK | 2348 | F8 200 OK |<-------------------| 2349 |<-------------------| | 2350 | F9 ACK | | 2351 |------------------->| F10 ACK | 2352 | ------------------->| 2353 | | 2354 | Both Way RTP Media Established | 2355 Fax |<=======================================>| 2356 ------->| | 2357 emitted | | | 2358 | | | Preamble 2359 | | |<--------- 2361 J-F. Mule/J. Li 44 2362 SIP T.38 Call Flows February 2002 2364 | | F11 INVITE | detected 2365 | |<-------------------| 2366 | F12 INVITE | | 2367 |<-------------------| | 2368 | | | 2369 | F13 606 | | 2370 |------------------->| | 2371 | | F14 606 (or 488) | 2372 | |------------------->| 2373 | | F15 INVITE | 2374 | |<-------------------| 2375 | F16 INVITE | | 2376 |<-------------------| | 2377 | F17 200 OK | | 2378 |------------------->| | 2379 | | F18 200 OK | 2380 | |------------------->| 2381 | | | 2382 | | F19 ACK | 2383 | |<-------------------| 2384 | F20 ACK | | 2385 |<-------------------| | 2386 | | 2387 | G.711 RTP Flow Established | 2388 |<=======================================>| 2389 | for fax pass-through | 2390 | | 2391 | F21 BYE | | 2392 |------------------->| | 2393 | | F22 BYE | 2394 | |------------------->| 2395 | | | 2396 | | F23 200 OK | 2397 | |<-------------------| 2398 | F24 200 OK | | 2399 |<-------------------| | 2401 6.2.2. Message Details 2403 Messages F1 to F12 are identical to section 5.2; refer to 5.2. 2405 F13 606 Not Acceptable IFT UA -> PROXY 2407 SIP/2.0 606 Not Acceptable 2408 Via: SIP/2.0/UDP ift.here.com:5060 2409 Warning: 304 Media type not available: One or more media types 2410 contained in the session description are not available. 2411 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2412 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 2413 Call-ID: 1717@ift.here.com 2414 CSeq: 18 INVITE 2416 J-F. Mule/J. Li 45 2417 SIP T.38 Call Flows February 2002 2419 Content-Length: 0 2421 F14 606 Not Acceptable PROXY -> IFTGW UA 2423 SIP/2.0 606 Not Acceptable 2424 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d010.1 2425 Via: SIP/2.0/UDP ift.here.com:5060 2426 Warning: 304 Media type not available: One or more media types 2427 contained in the session description are not available. 2428 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2429 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 2430 Call-ID: 1717@ift.here.com 2431 CSeq: 18 INVITE 2432 Content-Length: 0 2434 F15 INVITE IFTGW UA -> PROXY 2436 INVITE sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 2437 Via: SIP/2.0/UDP iftgw.there.com:5060 2438 Route: 2440 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2441 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 2442 Call-ID: 1717@ift.here.com 2443 CSeq: 19 INVITE 2444 Contact: 2445 Content-Type: application/sdp 2446 Content-Length: 181 2448 v=0 2449 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com 2450 s=Session SDP 2451 c=IN IP4 iftmg.there.com 2452 t=0 0 2453 m=audio 12322 RTP/AVP 0 2454 a=rtpmap:0 PCMU/8000 2455 a=ecan:fb on - 2456 a=silenceSupp:off - - - - 2458 F16 INVITE PROXY -> IFT UA 2460 INVITE sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 2461 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d009.1 2462 Via: SIP/2.0/UDP iftgw.there.com:5060 2463 Record-Route: 2465 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2466 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 2468 J-F. Mule/J. Li 46 2469 SIP T.38 Call Flows February 2002 2471 Call-ID: 1717@ift.here.com 2472 CSeq: 19 INVITE 2473 Contact: 2474 Content-Type: application/sdp 2475 Content-Length: 181 2477 v=0 2478 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com 2479 s=Session SDP 2480 c=IN IP4 iftmg.there.com 2481 t=0 0 2482 m=audio 12322 RTP/AVP 0 2483 a=rtpmap:0 PCMU/8000 2484 a=ecan:fb on - 2485 a=silenceSupp:off - - - - 2487 F17 200 OK IFT UA -> PROXY 2489 SIP/2.0 200 OK 2490 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d008.1 2491 Via: SIP/2.0/UDP iftgw.there.com:5060 2492 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2493 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 2494 Call-ID: 1717@ift.here.com 2495 CSeq: 19 INVITE 2496 Contact: 2497 Content-Type: application/sdp 2498 Content-Length: 150 2500 v=0 2501 o=faxgw1 2890844527 2890844528 IN IP4 ift.here.com 2502 s=Session SDP 2503 c=IN IP4 iftmg.here.com 2504 t=0 0 2505 m=audio 3456 RTP/AVP 0 2506 a=rtpmap:0 PCMU/8000 2507 a=ecan:fb on - 2508 a=silenceSupp:off - - - - 2510 F18 200 OK PROXY -> IFTGW UA 2512 SIP/2.0 200 OK 2513 Via: SIP/2.0/UDP iftgw.there.com:5060 2514 Record-Route: 2516 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2517 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 2518 Call-ID: 1717@ift.here.com 2519 CSeq: 19 INVITE 2520 Contact: 2521 Content-Type: application/sdp 2523 J-F. Mule/J. Li 47 2524 SIP T.38 Call Flows February 2002 2526 Content-Length: 150 2528 v=0 2529 o=faxgw1 2890844527 2890844528 IN IP4 ift.here.com 2530 s=Session SDP 2531 c=IN IP4 iftmg.here.com 2532 t=0 0 2533 m=audio 3456 RTP/AVP 0 2534 a=rtpmap:0 PCMU/8000 2535 a=ecan:fb on - 2536 a=silenceSupp:off - - - - 2538 F19 ACK IFTGW UA -> PROXY 2540 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 2541 Via: SIP/2.0/UDP iftgw.there.com:5060 2542 Route: 2544 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2545 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 2546 Call-ID: 1717@ift.here.com 2547 CSeq: 19 ACK 2548 Content-Length: 0 2550 F20 ACK PROXY -> IFT UA 2552 ACK sip:+1-650-555-2222@obelix.wcom.com;user=phone SIP/2.0 2553 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d009.1 2554 Via: SIP/2.0/UDP iftgw.there.com:5060 2555 Record-Route: 2557 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 2558 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde17 2559 Call-ID: 1717@ift.here.com 2560 CSeq: 19 ACK 2561 Content-Length: 0 2563 /* G.711 audio streams established both ways for fax pass through */ 2565 F21 BYE IFT UA -> PROXY 2567 BYE sip:+1-650-555-2222@obelix.wcom.com SIP/2.0 2568 Via: SIP/2.0/UDP ift.here.com:5060 2569 Route: 2571 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2572 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde34 2573 Call-ID: 1717@ift.here.com 2574 CSeq: 20 BYE 2576 J-F. Mule/J. Li 48 2577 SIP T.38 Call Flows February 2002 2579 Content-Length: 0 2581 F22 BYE PROXY -> IFTGW UA 2583 BYE sip:+1-650-555-2222@obelix.wcom.com SIP/2.0 2584 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d009.1 2585 Via: SIP/2.0/UDP ift.here.com:5060 2586 Record-Route: 2588 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2589 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde34 2590 Call-ID: 1717@ift.here.com 2591 CSeq: 20 BYE 2592 Content-Length: 0 2594 F23 200 OK IFTGW UA -> PROXY 2596 SIP/2.0 200 OK 2597 Via: SIP/2.0/UDP obelix.wcom.com:5060; branch=2d007.1 2598 Via: SIP/2.0/UDP ift.here.com:5060 2599 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2600 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde34 2601 Call-ID: 1717@ift.here.com 2602 CSeq: 20 BYE 2603 Content-Type: application/sdp 2604 Content-Length: 0 2606 F24 200 OK PROXY -> IFT UA 2608 SIP/2.0 200 OK 2609 Via: SIP/2.0/UDP ift.here.com:5060 2610 Record-Route: 2612 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 2613 To: sip:+1-650-555-2222@obelix.wcom.com;user=phone;tag=cde34 2614 Call-ID: 1717@ift.here.com 2615 CSeq: 20 BYE 2616 Content-Type: application/sdp 2617 Content-Length: 0 2619 J-F. Mule/J. Li 49 2620 SIP T.38 Call Flows February 2002 2622 7. SDP Attribute Table for T.38 sessions 2623 For a detailed description of these attributes, refer to IANA. The 2624 tables below are replicated here for reference only. 2626 +-----------------------+---------------------+--------------+ 2627 | SDP Attribute Name | Appropriate values | Example | 2628 | ("att-field") | | | 2629 +-----------------------+---------------------+--------------+ 2630 | | | | 2631 | T38FaxVersion | 1*DIGIT | 0 | 2632 | | | | 2633 | T38MaxBitRate | 1*(DIGIT) | 14400 | 2634 | | | | 2635 | T38FaxFillBitRemoval | boolean | 0 | 2636 | | | | 2637 | T38FaxTranscodingMMR | boolean | 0 | 2638 | | | | 2639 | T38FaxTranscodingJBIG | boolean | 0 | 2640 | | | | 2641 | T38FaxRateManagement | localTCF | |transferredTCF| 2642 | | transferredTCF | | 2643 | | | | 2644 | T38FaxMaxBuffer | 1*(DIGIT); optional | 72 | 2645 | | | (bytes) | 2646 | | | | 2647 | T38FaxMaxDatagram | 1*(DIGIT); | Depends on | 2648 | | optional | redundancy; | 2649 | | | 316 (bytes)| 2650 | | | | 2651 | T38FaxUdpEC | t38UDPFEC | | T38UDPRedund | 2652 | | t38UDPRedundancy | ancy | 2653 +-----------------------+---------------------+--------------+ 2655 Registered SDP Protocol �proto� for T.38: 2657 +-----------------+ 2658 | Name | 2659 | | 2660 +-----------------+ 2661 | | 2662 | UDPTL | 2663 | | 2664 | TCP | 2665 | | 2666 +-----------------+ 2668 Registered SDP Protocol �fmt�, MIME media type image/t38: 2669 MIME media type name: image 2670 MIME subtype name: t38 2672 J-F. Mule/J. Li 50 2673 SIP T.38 Call Flows February 2002 2675 8. Considerations 2677 In this temporary section, we log the open items for discussion as 2678 well as issues that have been solved on the mailing list: 2680 8.1. Level of requirements for Internet gateways 2681 --- Status: closed, solved by old draft01 text in section 4.2 2682 Based on the comments received on old draft-00, the authors 2683 recommend that: T.38 Internet fax gateways MUST trigger a SIP re- 2684 INVITE upon detection of the V.21 Preamble flag sequence on the 2685 receiving side. Emitting gateways MAY trigger session modification 2686 upon CNG. 2688 8.2. Negotiation of UDP ports for T.38 transmission 2689 --- Status: not an issue, just logged here 2690 When switching to T.38 mode, Internet fax gateways specify a new set 2691 of parameters for the media connection in SDP. Some gateways may 2692 choose the UDP/RTP port used in audio mode for UDP/UDPTL/T.38 2693 traffic. Some gateways may choose to open a new UDP port for 2694 UDPTL/T.38 fax (and keep the previous UDP/RTP port open for the 2695 switch back to audio). 2696 SDP provides the mechanism to precisely define in SIP all cases: 2697 - if an Internet Fax gateway desires to re-use the UDP/RTP port for 2698 UDP/UDPTL/T.38, put 1 �m=� line in the re-INVITE. 2699 m=image udptl t38 2700 - if an Internet Fax gateway desires to release the RTP port and 2701 open a new UDP port for T.38: 2702 m=image udptl t38 2703 - if an Internet Fax gateway desires to keep the RTP port for future 2704 use in the session and open a new UDP port for T.38, we need to 2705 repeat the RTP/AVP port: 2706 m=audio RTP/AVP 0 2707 m=image udptl t38 2709 8.3. Adding a fax stream to SIP session vs. Replacing audio stream 2710 --- Status: closed, see flows 5.2 and 5.3 2711 Based on the mailing list discussion, it is recommended in section 2712 5.2 to replace an existing audio media connection with a fax one. 2713 We however kept section 5.3 to illustrate what adding a fax stream 2714 would entail. 2716 8.4. Adding text to make use of SIP OPTIONS: in progress in draft-02 2717 --- Status: Open for discussion 2718 As discussed with Bill Sulzen, the SIP OPTIONS response could be 2719 used to assert that real-time fax communications using either T.38 2720 or fax-passthrough are supported. This could certainly improve the 2721 negotiation phases and reduce the number of SIP messages. It is 2722 also key to get the capabilities of the Internet-aware fax device or 2723 gateway other than on a per call basis. 2724 What needs to be added: 2725 - add text in sub-section in section 4.5 2726 - specify how the Accept header line should be populated (do we 2727 want to specify t.38 and/or fax pass-through (meaning ability to 2729 J-F. Mule/J. Li 51 2730 SIP T.38 Call Flows February 2002 2732 support ecan and silencesuppression), and within t.38, do we want to 2733 specify whether it is t.38 over tcp, udptl, both, etc. 2735 8.5. Use of IP addresses in SDP connection information 2736 --- Status: Open for discussion 2737 Comment from Christer Holmberg: SDP connection information should 2738 use IP addresses instead of domain names (as per draft-ietf-mmusic- 2739 sdp-new-03) 2741 8.6. Unsuccessful scenario: 606 or 488 2742 --- Status: closed 2743 Comment from Bill Sulzen: it is acceptable or even preferable to 2744 reject with a 488 Not Acceptable Media? 2745 Resolution: treat 606 and 488 as equally appropriate. 2747 9. Security Considerations 2749 The security mechanisms provided in RFC2543 apply: message 2750 authentication can be performed on SIP INVITEs and also BYE. 2752 10. References 2754 1 S. Bradner, "The Internet Standards Process -- Revision 3", BCP 2755 9, RFC 2026, October 1996. 2757 2 S. Bradner, "Key words for use in RFCs to Indicate Requirement 2758 Levels", BCP 14, RFC 2119, March 1997. 2760 3 M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP: 2761 Session Initiation Protocol", RFC 2543, March 1999. 2763 4 ITU-T Recommendation T.38, �Procedures for real-time Group 3 2764 facsimile communication over IP networks�, June 1998. 2766 5 Johnston, et al, �SIP Telephony Call Flow Examples�, Internet- 2767 Draft draft-ietf-sip-call-flows-05.txt, June 2001. 2769 6 ITU-T Recommendation T.38 Amendment 2, �Procedures for real-time 2770 Group 3 facsimile communication over IP networks�, February 2000. 2772 7 ITU-T Recommendation T.30, �Procedures for document facsimile 2773 transmission in the general switched telephone network�, March 2774 1993. 2776 8 M. Handley, V. Jacobson, "SDP: session description protocol", 2777 RFC 2327, April 1998. 2779 9 ITU-T Recommendation T.38 Amendment 2 Annex D, �SIP/SDP Call 2780 Establishment Procedures�, February 2000. 2782 J-F. Mule/J. Li 52 2783 SIP T.38 Call Flows February 2002 2785 10 R. Kumar, M. Mostafa, �Conventions for the use of the Session 2786 Description Protocol (SDP) for ATM Bearer Connections�, RFC3108, 2787 May 2001. 2789 11. Acknowledgments 2791 This document would not have been possible without the help of the 2792 following development engineers and fax experts, in particular 2793 Stanley Khouw, Bill Michalek, and George Maphis of Clarent 2794 Corporation. 2796 The authors would like to thank Bill Sulzen of Cisco Systems for his 2797 continued support and critical comments. We also acknowledge the 2798 valuable contributions from Flemming Andreasen of Cisco Systems, 2799 Christer Holmberg of Ericsson, and Bert Culpepper of InterVoice- 2800 Brite. 2801 Many thanks to the reviewers of the previous document for their 2802 comments: Jim Renkel of 3COM, Sudipto Mukherjee of Cisco Systems, 2803 Arjun Roychowdhury of Hughes Software Systems. 2805 12. Author's Addresses 2807 Jieying Li 2808 iVox Networks 2809 26701 West Agoura Road 2810 Calabasa, CA 91302 2811 email:jieying.li@ivoxnetworks.com 2813 Jean-Francois Mule� 2814 CableLabs 2815 400 Centennial Parkway 2816 Louisville, CO 80027 2817 USA 2818 email: jf.mule@cablelabs.com 2820 Full Copyright Statement 2822 "Copyright (C) The Internet Society (2002). All Rights Reserved. 2823 This document and translations of it may be copied and furnished to 2824 others, and derivative works that comment on or otherwise explain it 2825 or assist in its implementation may be prepared, copied, published 2826 and distributed, in whole or in part, without restriction of any 2827 kind, provided that the above copyright notice and this paragraph 2828 are included on all such copies and derivative works. However, this 2829 document itself may not be modified in any way, such as by removing 2830 the copyright notice or references to the Internet Society or other 2831 Internet organizations, except as needed for the purpose of 2832 developing Internet standards in which case the procedures for 2833 copyrights defined in the Internet Standards process must be 2834 followed, or as required to translate it into 2836 J-F. Mule/J. Li 53