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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Possible downref: Non-RFC (?) normative reference: ref. 'T38' Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DISPATCH D. Hanes 3 Internet-Draft G. Salgueiro 4 Intended status: Standards Track Cisco Systems 5 Expires: July 19, 2013 K. Fleming 6 Digium, Inc. 7 January 15, 2013 9 Indicating Fax over IP Capability 10 in the Session Initiation Protocol (SIP) 11 draft-hanes-dispatch-fax-capability-07 13 Abstract 15 This document defines and registers with IANA the new 'fax' media 16 feature tag for use with SIP. Currently, fax calls are 17 indistinguishable from voice at call initiation. Consequently, fax 18 calls can be routed to SIP user agents that are not fax capable. A 19 'fax' media feature tag implemented in conjunction with caller 20 preferences allows for more accurate fax call routing. 22 Status of this Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on July 19, 2013. 39 Copyright Notice 41 Copyright (c) 2013 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 4. Usage of the sip.fax Parameter . . . . . . . . . . . . . . . . 4 60 5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 61 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 62 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 63 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 64 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 65 9.1. Normative References . . . . . . . . . . . . . . . . . . . 8 66 9.2. Informative References . . . . . . . . . . . . . . . . . . 8 67 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 69 1. Introduction 71 Fax communications in the Session Initiation Protocol (SIP) [RFC3261] 72 are handled in a "voice first" manner. Indications that a user 73 desires to use a fax transport protocol, such as ITU-T T.38 [T38], to 74 send a fax are not known when the initial INVITE message is sent. 75 The call is set up as a voice call first and then only after it is 76 connected, does a switchover to the T.38 [T38] protocol occur. This 77 is problematic in that fax calls can be routed inadvertently to SIP 78 user agents (UAs) that are not fax capable. 80 To ensure that fax calls are routed to fax capable SIP user agents, 81 an implementation of caller preferences defined in RFC 3841 [RFC3841] 82 can be used. Feature preferences are a part of RFC 3841 [RFC3841] 83 that would allow UAs to express their preference for receiving fax 84 communications. Subsequently SIP servers take these preferences into 85 account to increase the likelihood that fax calls are routed to fax 86 capable SIP user agents. 88 This document defines the 'fax' media feature tag for use in the SIP 89 tree as per Section 12.1 of RFC 3840 [RFC3840]. This feature tag 90 will be applied per RFC 3841 [RFC3841] as a feature preference for 91 fax capable UAs. 93 2. Terminology 95 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 96 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 97 document are to be interpreted as described in [RFC2119]. 99 3. Motivation 101 In the majority of circumstances, it is preferred that capabilities 102 be handled in the Session Description Protocol (SDP) portion of the 103 SIP [RFC3261] communication. However, fax is somewhat unique in that 104 the ultimate intention of the call is not accurately signaled in the 105 initial SDP exchange. Specifically, indications of T.38 [T38] or any 106 other fax transport protocol in the call are not known when the call 107 is initiated by an INVITE message. Fax calls are always considered 108 voice calls until after they are connected. This results in the 109 possibility of fax calls being received by SIP user agents not 110 capable of handling fax transmissions. 112 For example, Alice wants to send a fax to Bob. Bob has registered two 113 SIP UAs. The first SIP UA is not fax capable but the second one 114 supports the T.38 [T38] fax protocol. Currently, SIP servers are 115 unable to know when the call starts that Alice prefers a fax capable 116 SIP UA to handle her call. Additionally, the SIP servers are also 117 not aware of which of Bob's SIP UAs are fax capable. 119 To resolve this issue of calls not arriving at a UA supporting fax, 120 this document defines a new media feature tag specific to fax per RFC 121 3840 [RFC3840]. Caller preferences as defined in RFC3841 [RFC3841] 122 can then be used for registering UAs that support fax and routing fax 123 calls to these UAs. Thus, Alice can express up front that she 124 prefers a T.38 [T38] fax capable SIP UA for this call. At the same 125 time, Bob's SIP UAs have expressed their fax capabilities as well 126 during registration. Now when Alice places a fax call to Bob, the 127 call is appropriately routed to Bob's fax capable SIP UA. 129 4. Usage of the sip.fax Parameter 131 The sip.fax media feature tag is a new string parameter, defined in 132 this document, that allows a call to indicate a fax preference. A UA 133 preferring the reception of fax calls MUST include the "sip.fax" 134 media feature tag in the Contact header field of REGISTER messages. 135 To confirm the registration of this preference, a SIP [RFC3261] 136 Registrar MUST then include this tag in the Contact header field of 137 its 200 OK response. 139 If a calling UA wants to ensure that a call is routed to a fax 140 capable UA, then the UA MUST include the "sip.fax" media feature tag 141 in the Contact header field of an INVITE request. Otherwise, without 142 this tag, fax call determination is not possible until after the call 143 is connected. 145 This parameter has two allowed values: "t38" and "passthrough". The 146 "t38" value indicates that the impending call will utilize the ITU-T 147 T.38 [T38] protocol for the fax transmission. The "passthrough" 148 value indicates that the ITU-T G.711 [G711] codec will be used to 149 transport the fax call. 151 5. Example 153 Bob registers with the fax media feature tag. The message flow is 154 shown in Figure 1: 156 SIP Registrar Bob's SIP UA 157 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 158 | | 159 | REGISTER F1 | 160 |<------------------------------| 161 | | 162 | 200 OK F2 | 163 |------------------------------>| 164 | | 166 Figure 1: Fax Media Feature Tag SIP Registration Example 168 F1 REGISTER Bob -> Registrar 170 REGISTER sip:example.com SIP/2.0 171 Via: SIP/2.0/TCP bob-TP.example.com:5060;branch=z9hG4bK309475a2 172 From: ;tag=a6c85cf 173 To: 174 Call-ID: a84b4c76e66710 175 Max-Forwards: 70 176 CSeq: 116 REGISTER 177 Contact: ;+sip.fax="t38" 178 Expires: 3600 180 The registrar responds with a 200 OK: 182 F2 200 OK Registrar -> Bob 184 SIP/2.0 200 OK 185 From: ;tag=a6c85cf 186 To: ;tag=1263390604 187 Contact: ;+sip.fax="t38" 188 Expires: 120 189 Call-ID: a84b4c76e66710 190 Via: SIP/2.0/TCP bob-TP.example.com:5060;branch=z9hG4bK309475a2 191 CSeq: 116 REGISTER 192 Expires: 3600 194 Callers desiring to express a preference for fax will include the 195 sip.fax media feature tag in the Accept-Contact header of their 196 INVITE. 198 INVITE sip:bob@biloxi.example.com SIP/2.0 199 Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b43 200 Max-Forwards: 70 201 From: Alice ;tag=9fxced76sl 202 To: Bob 203 Accept-Contact: *;+sip.fax="t38" 204 Call-ID: 3848276298220188511@atlanta.example.com 205 CSeq: 1 INVITE 206 Contact: 207 Content-Type: application/sdp 208 Content-Length: 151 210 6. Security Considerations 212 The security considerations related to the use of media feature tags 213 from Section 11.1 of RFC 3840 [RFC3840] apply. 215 7. IANA Considerations 217 This specification adds a new media feature tag to the SIP Media 218 Feature Tag Registration Tree per the procedures defined in RFC 2506 219 [RFC2506] and RFC 3840 [RFC3840]. 221 Media feature tag name: sip.fax 223 ASN.1 Identifier: 1.3.6.1.8.4.{PH} 225 Summary of the media feature indicated by this tag: This feature tag 226 indicates whether a communications device supports the ITU-T T.38 227 [T38] fax protocol ("t38") or the passthrough method of fax 228 transmission using the ITU-T G.711 [G711] audio codec 229 ("passthrough"). 231 Values appropriate for use with this feature tag: Token with an 232 equality relationship. Values are: 234 t38: The device supports the image/t38 media type [RFC3326] and 235 implements ITU-T T.38 [T38] for transporting the ITU-T T.30 236 [T30] and ITU-T T.4 [T4] fax data over IP. 238 passthrough: The device supports the audio/pcmu and audio/pcma 239 media types [RFC4856] for transporting ITU-T T.30 [T30] and 240 ITU-T T.4 [T4] fax data using the ITU-T G.711 [G711] audio 241 codec. Additional implementation recommendations are in ITU-T 242 V.152 [V152] Sections 6 and 6.1. 244 The feature tag is intended primarily for use in the following 245 applications, protocols, services, or negotiation mechanisms: This 246 feature tag is most useful in a communications application for the 247 early identification of a Fax over IP (FoIP) call. 249 Examples of typical use: Ensuring a fax call is routed to a fax 250 capable SIP UA. 252 Related standards or documents: RFCXXXX 254 Security Considerations: The security considerations related to the 255 use of media feature tags from Section 11.1 of RFC 3840 [RFC3840] 256 apply. 258 [[NOTE TO RFC EDITOR: Please change {PH} above to the correct 259 identifier for this entry in the IANA registry for 260 iso.org.dod.internet.features.sip-tree (1.3.6.1.8.4)]] 262 [[NOTE TO RFC EDITOR: Please change XXXX to the number assigned to 263 this specification, and remove this paragraph on publication.]] 265 8. Acknowledgements 267 This document is a result of the unique cooperation between the SIP 268 Forum and the i3 Forum who embarked on a groundbreaking international 269 test program for FoIP to improve the interoperability and reliability 270 of fax communications over IP networks, especially tandem networks. 271 The authors would like to acknowledge the effort and dedication of 272 all the members of the Fax-over-IP (FoIP) Task Group in the SIP Forum 273 and the communications carriers of the I3 Forum that contributed to 274 this global effort. 276 This memo has benefited from the discussion and review of the 277 DISPATCH working group, especially the detailed and thoughtful 278 comments and corrections of Dan Wing, Paul Kyzivat, Christer 279 Holmberg, Charles Eckel, Hadriel Kaplan, Tom Yu and Dale Worley. 281 The authors also thank Gonzalo Camarillo for his review and AD 282 sponsorship of this draft and DISPATCH WG chair, Mary Barnes, for her 283 review and support. 285 9. References 286 9.1. Normative References 288 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 289 Requirement Levels", BCP 14, RFC 2119, March 1997. 291 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 292 A., Peterson, J., Sparks, R., Handley, M., and E. 293 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 294 June 2002. 296 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 297 "Indicating User Agent Capabilities in the Session 298 Initiation Protocol (SIP)", RFC 3840, August 2004. 300 [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller 301 Preferences for the Session Initiation Protocol (SIP)", 302 RFC 3841, August 2004. 304 [T38] International Telecommunication Union, "Procedures for 305 real-time Group 3 facsimile communication over IP 306 Networks", ITU-T Recommendation T.38, October 2010. 308 9.2. Informative References 310 [G711] International Telephone and Telegraph Consultative 311 Committee, "Pulse Code Modulation (PCM) of Voice 312 Frequencies", CCITT Recommendation G.711, 1972. 314 [RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag 315 Registration Procedure", BCP 31, RFC 2506, March 1999. 317 [RFC3326] Schulzrinne, H., Oran, D., and G. Camarillo, "The Reason 318 Header Field for the Session Initiation Protocol (SIP)", 319 RFC 3326, December 2002. 321 [RFC4856] Casner, S., "Media Type Registration of Payload Formats in 322 the RTP Profile for Audio and Video Conferences", 323 RFC 4856, February 2007. 325 [T30] International Telecommunication Union, "Procedures for 326 document facsimile transmission in the general switched 327 telephone network", ITU-T Recommendation T.30, 328 September 2005. 330 [T4] International Telecommunication Union, "Standardization of 331 Group 3 facsimile terminals for document transmission", 332 ITU-T Recommendation T.4, July 2003. 334 [V152] International Telecommunication Union, "Procedures for 335 supporting voice-band data over IP networks", ITU- 336 T Recommendation V.152, September 2010. 338 Authors' Addresses 340 David Hanes 341 Cisco Systems 342 7200-10 Kit Creek Road 343 Research Triangle Park, NC 27709 344 US 346 Email: dhanes@cisco.com 348 Gonzalo Salgueiro 349 Cisco Systems 350 7200-12 Kit Creek Road 351 Research Triangle Park, NC 27709 352 US 354 Email: gsalguei@cisco.com 356 Kevin P. Fleming 357 Digium, Inc. 358 445 Jan Davis Drive NW 359 Huntsville, AL 35806 360 US 362 Email: kevin@kpfleming.us