RFC 2833 (rfc2833) - Page 1 of 30

RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals

Alternative Format: Original Text Document
Next >
Network Working Group                                      H. Schulzrinne
Request for Comments: 2833                            Columbia University
Category: Standards Track                                      S. Petrack
                                                                  MetaTel
                                                                 May 2000


   RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals

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 (2000).  All Rights Reserved.

Abstract

   This memo describes how to carry dual-tone multifrequency (DTMF)
   signaling, other tone signals and telephony events in RTP packets.

1 Introduction

   This memo defines two payload formats, one for carrying dual-tone
   multifrequency (DTMF) digits, other line and trunk signals (Section
   3), and a second one for general multi-frequency tones in RTP [1]
   packets (Section 4). Separate RTP payload formats are desirable since
   low-rate voice codecs cannot be guaranteed to reproduce these tone
   signals accurately enough for automatic recognition. Defining
   separate payload formats also permits higher redundancy while
   maintaining a low bit rate.

   The payload formats described here may be useful in at least three
   applications: DTMF handling for gateways and end systems, as well as
   "RTP trunks". In the first application, the Internet telephony
   gateway detects DTMF on the incoming circuits and sends the RTP
   payload described here instead of regular audio packets. The gateway
   likely has the necessary digital signal processors and algorithms, as
   it often needs to detect DTMF, e.g., for two-stage dialing. Having
   the gateway detect tones relieves the receiving Internet end system
   from having to do this work and also avoids that low bit-rate codecs
   like G.723.1 render DTMF tones unintelligible. Secondly, an Internet




Schulzrinne & Petrack       Standards Track
Next >