RTP Payload for DTMF Digits, Telephony Tones, and Telephony Signals
RFC 4733

Network Working Group                                     H. Schulzrinne
Request for Comments: 4733                                   Columbia U.
Obsoletes: 2833                                                T. Taylor
Category: Standards Track                                         Nortel
                                                           December 2006

  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 IETF Trust (2006).

Abstract

   This memo describes how to carry dual-tone multifrequency (DTMF)
   signalling, other tone signals, and telephony events in RTP packets.
   It obsoletes RFC 2833.

   This memo captures and expands upon the basic framework defined in
   RFC 2833, but retains only the most basic event codes.  It sets up an
   IANA registry to which other event code assignments may be added.
   Companion documents add event codes to this registry relating to
   modem, fax, text telephony, and channel-associated signalling events.
   The remainder of the event codes defined in RFC 2833 are
   conditionally reserved in case other documents revive their use.

   This document provides a number of clarifications to the original
   document.  However, it specifically differs from RFC 2833 by removing
   the requirement that all compliant implementations support the DTMF
   events.  Instead, compliant implementations taking part in
   out-of-band negotiations of media stream content indicate what events
   they support.  This memo adds three new procedures to the RFC 2833
   framework: subdivision of long events into segments, reporting of
   multiple events in a single packet, and the concept and reporting of
   state events.

Schulzrinne & Taylor        Standards Track                     [Page 1]
RFC 4733               Telephony Events and Tones          December 2006

Table of Contents

   1. Introduction ....................................................4
      1.1. Terminology ................................................4
      1.2. Overview ...................................................4
      1.3. Potential Applications .....................................5
      1.4. Events, States, Tone Patterns, and Voice-Encoded Tones .....6
   2. RTP Payload Format for Named Telephone Events ...................8
      2.1. Introduction ...............................................8
      2.2. Use of RTP Header Fields ...................................8
           2.2.1. Timestamp ...........................................8
           2.2.2. Marker Bit ..........................................8
      2.3. Payload Format .............................................8
           2.3.1. Event Field .........................................9
           2.3.2. E ("End") Bit .......................................9
           2.3.3. R Bit ...............................................9
           2.3.4. Volume Field ........................................9
           2.3.5. Duration Field ......................................9
      2.4. Optional Media Type Parameters ............................10
           2.4.1. Relationship to SDP ................................10
      2.5. Procedures ................................................11
           2.5.1. Sending Procedures .................................11
           2.5.2. Receiving Procedures ...............................16
      2.6. Congestion and Performance ................................19
           2.6.1. Performance Requirements ...........................20
           2.6.2. Reliability Mechanisms .............................20
           2.6.3. Adjusting to Congestion ............................22
   3. Specification of Event Codes for DTMF Events ...................23
      3.1. DTMF Applications .........................................23
      3.2. DTMF Events ...............................................25
      3.3. Congestion Considerations .................................25
   4. RTP Payload Format for Telephony Tones .........................26
      4.1. Introduction ..............................................26
      4.2. Examples of Common Telephone Tone Signals .................27
      4.3. Use of RTP Header Fields ..................................27
           4.3.1. Timestamp ..........................................27
           4.3.2. Marker Bit .........................................27