Internet Engineering Task Force MMUSIC WG Internet Draft Wedlund/Jiang/Schulzrinne ietf-mmusic-sdp-t38-00.txt Ericsson/Columbia U./Columbia U. December 15, 1998 Expires: June 1999 SDP Extensions for Fax over IP Using T.38 STATUS OF THIS MEMO This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as ``work in progress''. To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Distribution of this document is unlimited. ABSTRACT Fax over IP is currently using SMTP, i.e. the fax is sent as an e-mail. It would be desireable to support a fax delivery that can return status of the transmission in real time, such as whether the phone number or address was correct, whether the remote side was busy, etc. The ITU is standardizing a protocol for transferring real time fax over IP, T.38. This standard is meant to be used with the H.323 standard, but it is also possible to use it together with SIP, provided that SDP is extended to support the necessary parameters. This document defines extensions to SDP to support the use of T.38 for real-time fax. 1 Introduction Fax is a popular means for transferring documents between locations. Wedlund/Jiang/Schulzrinne [Page 1] Internet Draft T38 December 15, 1998 Traditionally, this has been done over the telephone network, as defined in the ITU specification T.30 [1]. Some of the reasons for the populatity of fax is that the sender of a fax gets a notification that the fax has been successfully sent, and that the receiver gets information on the senders telephone number and the time the fax was received. Another reason is that fax transmission over a telephone connection can not easily be eavesdropped. When introducing fax over IP, these benefits should be preserved. The ITU standard T.38 [2] defines how to transport the fax signals over IP. It is expected that the fax channel is set up by some other means, e.g., through H.323 or SIP. Annex D of H.323 [3] describes how H.323 supports fax over IP. In this document we will describe how SIP and SDP can do the same. It would probably be possible to even support the T.38 scope with SIP and SDP, but that is for future work. 2 Introduction to T.38 The ITU T.38 recommendation defines how to transfer fax in realtime between fax gateways and/or IP fax machines in an IP network. Transport of the fax signals is done either by TCP or UDP, and reliability with UDP is achieved through error control mechanisms in T.38, which can be either parity FEC or packet redundancy. The recommendation assumes that a network connection has already been established by the two (or more) peers. This is similar to traditional fax, where a phone line is allocated before the actual fax signalling starts. The issues that are left to be handled by other mechanisms are addressing, identification, authentication, and creation of the fax connection. The fax machines must also have agreed on whether to use UDP or TCP for transport, and in case of UDP, the error control scheme to use. 3 Session Initiation Protocol The Session Initiation Protocol (SIP) [4] already provides mechanisms for user (fax machine) location, caller identification, call establishment, and authentication. No additions are needed to support the use of T.38. 4 Extensions to SDP The Session Description Protocol (SDP) (RFC 2327 [5]) provides mechanisms for describing sessions. The information that needs to be represented in SDP for T.38 is o the fact that T.38 is to be used, o whether to use TCP or UDP for transport, and Wedlund/Jiang/Schulzrinne [Page 2] Internet Draft T38 December 15, 1998 o which type of error control to be used by T.38. Thus, the SDP message could be the following: v=0 o=faxgw1 2890844526 2890842807 IN IP4 128.59.19.68 s=FAX message e=faxsupport@company.com t=2873397496 0 c=IN IP4 128.59.19.68 m=application 49170 udp t38 a=t38errctl:parFEC In order to do this, "application/t38" needs to be registered as a MIME type according to the recommendations in [5]. The choice of TCP or UDP can already be represented in SDP, and the error control scheme should be represented as an attribute. 5 Security Considerations SIP provides security mechanisms for authentication of caller, and encryption of SIP messages including the SDP payload. For the T.38 flow, IP security mechanisms, as defined in RFC 1825 [6], can be used. 6 Authors' Addresses Elin Wedlund Switchlab Ericsson Telecom AB S-126 25 Stockholm SWEDEN electronic mail: elin.wedlund@etx.ericsson.se Wenyu Jiang Dept. of Computer Science Columbia University 1214 Amsterdam Avenue New York, NY 10027 USA electronic mail: wenyu@cs.columbia.edu Henning Schulzrinne Dept. of Computer Science Columbia University Wedlund/Jiang/Schulzrinne [Page 3] Internet Draft T38 December 15, 1998 1214 Amsterdam Avenue New York, NY 10027 USA electronic mail: schulzrinne@cs.columbia.edu 7 Bibliography [1] International Telecommunication Union, "Procedures for document facsimile transmission in the general switched telephone network," Recommendation T.30, Telecommunication Standardization Sector of ITU, Geneva, Switzerland, July 1996. [2] International Telecommunication Union, "Procedures for real-time group 3 facsimile communication over IP networks," Recommendation T.38, Telecommunication Standardization Sector of ITU, Geneva, Switzerland, June 1998. [3] International Telecommunication Union, "Visual telephone systems and equipment for local area networks which provide a non-guaranteed quality of service," Recommendation H.323, Telecommunication Standardization Sector of ITU, Geneva, Switzerland, May 1996. [4] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP: session initiation protocol," Internet Draft, Internet Engineering Task Force, Nov. 1998. Work in progress. [5] M. Handley and V. Jacobson, "SDP: session description protocol," RFC 2327, Internet Engineering Task Force, Apr. 1998. [6] R. Atkinson, "Security architecture for the internet protocol," RFC 1825, Internet Engineering Task Force, Aug. 1995. Wedlund/Jiang/Schulzrinne [Page 4]