RTP Payload Format for a 64 kbit/s Transparent Call
RFC 4040

Document Type RFC - Proposed Standard (April 2005; No errata)
Last updated 2013-03-02
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IESG IESG state RFC 4040 (Proposed Standard)
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Responsible AD Allison Mankin
Send notices to csp@csperkins.org, magnus.westerlund@ericsson.com, mankin@psg.com
Network Working Group                                         R. Kreuter
Request for Comments: 4040                                    Siemens AG
Category: Standards Track                                     April 2005

          RTP Payload Format for a 64 kbit/s Transparent Call

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document describes how to carry 64 kbit/s channel data
   transparently in RTP packets, using a pseudo-codec called
   "Clearmode".  It also serves as registration for a related MIME type
   called "audio/clearmode".

   "Clearmode" is a basic feature of VoIP Media Gateways.

Table of Contents

   1.  Introduction..................................................  2
   2.  Conventions Used in This Document.............................  2
   3.  64 kbit/s Data Stream Handling and RTP Header Parameters......  3
   4.  IANA Considerations...........................................  3
   5.  Mapping to Session Description Protocol (SDP) Parameters......  5
   6.  Security Considerations.......................................  5
   7.  References....................................................  6
       7.1. Normative References.....................................  6
       7.2. Informative References...................................  6
   8.  Acknowledgements..............................................  7

Kreuter                     Standards Track                     [Page 1]
RFC 4040             64 kbit/s Voice Band Data Call           April 2005

1.  Introduction

   Voice over IP (VoIP) Media Gateways need to carry all possible data
   streams generated by analog terminals or integrated services digital
   network (ISDN) terminals via an IP network.  Within this document a

   VoIP Media Gateway is a device that converts a (digital or analog)
   linear data stream to a digital packetized data stream or vice versa.
   Refer to RFC 2719 [10] for an introduction into the basic
   architecture of a Media Gateway based network.

   Usually a VoIP Media Gateway does some processing on the data it
   converts besides packetization or depacketization; i.e. echo
   cancellation or dual tone multifrequency (DTMF) detection, and
   especially a coding/decoding.  But there is a class of data streams
   that does not rely on or allow any data processing within the VoIP
   Media Gateway except for packetization or depacketization.  ISDN data
   terminals i.e. will produce data streams that are not compatible with
   a non-linear encoding as used for voice.

   For such applications, there is a necessity for a transparent relay
   of 64 kbit/s data streams in real-time transport protocol (RTP) [4]
   packets.  This mode is often referred to as "clear-channel data" or
   "64 kbit/s unrestricted".  No encoder/decoder is needed in that case,
   but a unique RTP payload type is necessary and a related MIME type is
   to be registered for signaling purposes.

   Clearmode is not restricted to the examples described above.  It can
   be used by any application, that does not need a special
   encoding/decoding for transfer via a RTP connection.

   This payload format document describes a pseudo-codec called
   "Clearmode", for sample oriented 64 kbit/s data streams with 8 bits
   per sample.  It is in accordance with RFC 2736 [1], which provides a
   guideline for the specification of new RTP payload formats.

   Examples for the current use of Clearmode are the transfer of "ISDN 7
   kHz voice" and "ISDN data" in VoIP Media Gateways.

   This document also serves as the MIME type registration according to
   RFC 2045 [2] and RFC 2048 [3], which defines procedures for
   registration of new MIME types within the IETF tree.

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 [8].

Kreuter                     Standards Track                     [Page 2]
RFC 4040             64 kbit/s Voice Band Data Call           April 2005

3.  64 kbit/s Data Stream Handling and RTP Header Parameters
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