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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: May 21, 2013 K. Fleming 6 Digium, Inc. 7 November 17, 2012 9 Indicating Fax over IP Capability 10 in the Session Initiation Protocol (SIP) 11 draft-hanes-dispatch-fax-capability-06 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 May 21, 2013. 39 Copyright Notice 41 Copyright (c) 2012 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 . . . . . . . . . . . . . . . . . . . . . . . . . . 7 65 9.1. Normative References . . . . . . . . . . . . . . . . . . . 7 66 9.2. Informative References . . . . . . . . . . . . . . . . . . 8 67 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 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;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;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:UserY@example.com SIP/2.0 199 From: sip:UserX@operator.com 200 To: sip:UserY@example.com 201 Accept-Contact: *;+sip.fax="t38" 202 Content-Type: application/sdp 204 6. Security Considerations 206 The security considerations related to the use of media feature tags 207 from Section 11.1 of RFC 3840 [RFC3840] apply. 209 7. IANA Considerations 211 This specification adds a new media feature tag to the SIP Media 212 Feature Tag Registration Tree per the procedures defined in RFC 2506 213 [RFC2506] and RFC 3840 [RFC3840]. 215 Media feature tag name: sip.fax 217 ASN.1 Identifier: 1.3.6.1.8.4.{PH} 219 Summary of the media feature indicated by this tag: This feature tag 220 indicates whether a communications device supports the ITU-T T.38 221 [T38] fax protocol ("t38") or the passthrough method of fax 222 transmission using the ITU-T G.711 [G711] audio codec 223 ("passthrough"). 225 Values appropriate for use with this feature tag: Token with an 226 equality relationship. Values are: 228 t38: The device supports the image/t38 media type [RFC3326] and 229 implements ITU-T T.38 [T38] for transporting the ITU-T T.30 230 [T30] and ITU-T T.4 [T4] fax data over IP. 232 passthrough: The device supports the audio/pcmu and audio/pcma 233 media types [RFC4856] for transporting ITU-T T.30 [T30] and 234 ITU-T T.4 [T4] fax data using the ITU-T G.711 [G711] audio 235 codec. Additional implementation recommendations are in ITU-T 236 V.152 [V152] Sections 6 and 6.1. 238 The feature tag is intended primarily for use in the following 239 applications, protocols, services, or negotiation mechanisms: This 240 feature tag is most useful in a communications application for the 241 early identification of a Fax over IP (FoIP) call. 243 Examples of typical use: Ensuring a fax call is routed to a fax 244 capable SIP UA. 246 Related standards or documents: RFCXXXX 248 Security Considerations: The security considerations related to the 249 use of media feature tags from Section 11.1 of RFC 3840 [RFC3840] 250 apply. 252 [[NOTE TO RFC EDITOR: Please change {PH} above to the correct 253 identifier for this entry in the IANA registry for 254 iso.org.dod.internet.features.sip-tree (1.3.6.1.8.4)]] 256 [[NOTE TO RFC EDITOR: Please change XXXX to the number assigned to 257 this specification, and remove this paragraph on publication.]] 259 8. Acknowledgements 261 This document is a result of the unique cooperation between the SIP 262 Forum and the i3 Forum who embarked on a groundbreaking international 263 test program for FoIP to improve the interoperability and reliability 264 of fax communications over IP networks, especially tandem networks. 265 The authors would like to acknowledge the effort and dedication of 266 all the members of the Fax-over-IP (FoIP) Task Group in the SIP Forum 267 and the communications carriers of the I3 Forum that contributed to 268 this global effort. 270 This memo has benefited from the discussion and review of the 271 DISPATCH working group, especially the detailed and thoughtful 272 comments and corrections of Dan Wing, Paul Kyzivat, Christer 273 Holmberg, Charles Eckel, and Dale Worley. 275 The authors also thank Gonzalo Camarillo for his review and AD 276 sponsorship of this draft and DISPATCH WG chair, Mary Barnes, for her 277 review and support. 279 9. References 281 9.1. Normative References 283 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 284 Requirement Levels", BCP 14, RFC 2119, March 1997. 286 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 287 A., Peterson, J., Sparks, R., Handley, M., and E. 288 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 289 June 2002. 291 [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, 292 "Indicating User Agent Capabilities in the Session 293 Initiation Protocol (SIP)", RFC 3840, August 2004. 295 [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller 296 Preferences for the Session Initiation Protocol (SIP)", 297 RFC 3841, August 2004. 299 [T38] International Telecommunication Union, "Procedures for 300 real-time Group 3 facsimile communication over IP 301 Networks", ITU-T Recommendation T.38, October 2010. 303 9.2. Informative References 305 [G711] International Telephone and Telegraph Consultative 306 Committee, "Pulse Code Modulation (PCM) of Voice 307 Frequencies", CCITT Recommendation G.711, 1972. 309 [RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag 310 Registration Procedure", BCP 31, RFC 2506, March 1999. 312 [RFC3326] Schulzrinne, H., Oran, D., and G. Camarillo, "The Reason 313 Header Field for the Session Initiation Protocol (SIP)", 314 RFC 3326, December 2002. 316 [RFC4856] Casner, S., "Media Type Registration of Payload Formats in 317 the RTP Profile for Audio and Video Conferences", 318 RFC 4856, February 2007. 320 [T30] International Telecommunication Union, "Procedures for 321 document facsimile transmission in the general switched 322 telephone network", ITU-T Recommendation T.30, 323 September 2005. 325 [T4] International Telecommunication Union, "Standardization of 326 Group 3 facsimile terminals for document transmission", 327 ITU-T Recommendation T.4, July 2003. 329 [V152] International Telecommunication Union, "Procedures for 330 supporting voice-band data over IP networks", ITU- 331 T Recommendation V.152, September 2010. 333 Authors' Addresses 335 David Hanes 336 Cisco Systems 337 7200-10 Kit Creek Road 338 Research Triangle Park, NC 27709 339 US 341 Email: dhanes@cisco.com 343 Gonzalo Salgueiro 344 Cisco Systems 345 7200-12 Kit Creek Road 346 Research Triangle Park, NC 27709 347 US 349 Email: gsalguei@cisco.com 351 Kevin P. Fleming 352 Digium, Inc. 353 445 Jan Davis Drive NW 354 Huntsville, AL 35806 355 US 357 Email: kevin@kpfleming.us