Real-Time Facsimile (T.38) - audio/t38 MIME Sub-type Registration
RFC 4612
Document | Type |
RFC - Historic
(August 2006; Errata)
Was draft-jones-avt-audio-t38 (individual in tsv area)
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Authors | Hiroshi Tamura , Paul Jones | ||
Last updated | 2020-01-21 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized with errata bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 4612 (Historic) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Allison Mankin | ||
Send notices to | csp@csperkins.org, magnus.westerlund@ericsson.com |
Network Working Group P. Jones Request for Comments: 4612 Cisco Systems, Inc. Category: Historic H. Tamura Ricoh Company, LTD. August 2006 Real-Time Facsimile (T.38) - audio/t38 MIME Sub-type Registration Status of This Memo This memo defines a Historic Document for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This document defines the MIME sub-type audio/t38. The usage of this MIME type, which is intended for use within Session Description Protocol (SDP), is specified within ITU-T Recommendation T.38. Table of Contents 1. Introduction ....................................................2 2. Conventions Used in This Document ...............................2 3. Mechanisms for Transporting T.38 over an IP Network .............2 4. IANA Considerations .............................................3 5. SDP Mapping of MIME Parameters ..................................5 6. Security Considerations .........................................6 7. Normative References ............................................6 8. Informative References ..........................................6 Jones & Tamura Historic [Page 1] RFC 4612 Real-time Facsimile (T.38) - audio /t38 August 2006 1. Introduction ITU-T Recommendation T.38 [1] defines the Internet Facsimile Protocol (IFP) for carriage of facsimile data over IP networks. As one option, IFP packets may be carried within an RTP [3] stream, either as the only content within the media stream or switched with other audio payload types. This memo provides rationale for using RTP as a transport for fax signaling and specifies the MIME type associated with said signaling. 2. Conventions Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [4]. 3. Mechanisms for Transporting T.38 over an IP Network When T.38 was first approved in 1998, it allowed for the transport of T.38 via UDP (using UDP Transport Layer (UDPTL), rather than RTP) or TCP. As of the time of this publication, UDPTL is the predominant means for transporting T.38 data over an IP network. In support of that, RFC 3362 [11] was published in order to allow devices to signal their desire to use UDPTL to transport T.38. A number of issues were raised with respect to the usage of UDPTL for the long-term, though. Specifically, there were concerns over the fact that UDPTL does not provide the same kind of statistics reporting as RTP Control Protocol (RTCP). Further, there are no procedures in place for encrypting and protecting the integrity of the UDPTL stream. While the latter could be addressed in UDPTL, doing so would require a lot of effort and would largely be a duplication of the security work already completed within the IETF; e.g., Secure RTP (SRTP) [10]. There are clear advantages in using RTP for T.38 today. For example, using RTP allows one to take advantage of the redundancy [12], header compression [13][14], and other RTP-related work within the IETF. Using RTP, as opposed to UDPTL, for transport provides better interoperability with a wider range of devices that know and understand RTP. This includes applications such as firewalls, Network Address Translation (NAT) devices, and gateways that bridge two IP networks, which generally support RTP before most other real- time media. Jones & Tamura Historic [Page 2] RFC 4612 Real-time Facsimile (T.38) - audio /t38 August 2006 Lastly, since today most T.38 data is generated by gateways that bridge two Public Switched Telephone Network (PSTN) networks, it is quite natural to expect that the transition from audio to fax should happen within the same media stream. The reason is that the T.38 data is simply an alternative representation of information received on the PSTN circuit. If the T.38 data is encapsulated in RTP, the gateways can easily transition from audio to fax and back again and can simply use the payload type to indicate the type of media that it is currently transmitting. With these considerations in mind, the ITU-T amended T.38 [1] to allow RTP to be used to transport T.38. With that, a new MIME registration (audio/t38) is needed to allow for T.38 to be switchedShow full document text