A Real-time Transport Protocol (RTP) Header Extension for Client-to-Mixer Audio Level Indication
RFC 6464

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Internet Engineering Task Force (IETF)                    J. Lennox, Ed.
Request for Comments: 6464                                         Vidyo
Category: Standards Track                                        E. Ivov
ISSN: 2070-1721                                                    Jitsi
                                                              E. Marocco
                                                          Telecom Italia
                                                           December 2011

       A Real-time Transport Protocol (RTP) Header Extension for
                 Client-to-Mixer Audio Level Indication

Abstract

   This document defines a mechanism by which packets of Real-time
   Transport Protocol (RTP) audio streams can indicate, in an RTP header
   extension, the audio level of the audio sample carried in the RTP
   packet.  In large conferences, this can reduce the load on an audio
   mixer or other middlebox that wants to forward only a few of the
   loudest audio streams, without requiring it to decode and measure
   every stream that is received.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6464.

Lennox, et al.               Standards Track                    [Page 1]
RFC 6464         Client-to-Mixer Audio Level Indication    December 2011

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................3
   3. Audio Levels ....................................................3
   4. Signaling (Setup) Information ...................................5
   5. Considerations on Use ...........................................6
   6. Security Considerations .........................................6
   7. IANA Considerations .............................................7
   8. References ......................................................7
      8.1. Normative References .......................................7
      8.2. Informative References .....................................8

1.  Introduction

   In a centralized Real-time Transport Protocol (RTP) [RFC3550] audio
   conference, an audio mixer or forwarder receives audio streams from
   many or all of the conference participants.  It then selectively
   forwards some of them to other participants in the conference.  In
   large conferences, it is possible that such a server might be
   receiving a large number of streams, of which only a few are intended
   to be forwarded to the other conference participants.

   In such a scenario, in order to pick the audio streams to forward, a
   centralized server needs to decode, measure audio levels, and
   possibly perform voice activity detection on audio data from a large
   number of streams.  The need for such processing limits the size or
   number of conferences such a server can support.

   As an alternative, this document defines an RTP header extension
   [RFC5285] through which senders of audio packets can indicate the
   audio level of the packets' payload, reducing the processing load for
   a server.

Lennox, et al.               Standards Track                    [Page 2]
RFC 6464         Client-to-Mixer Audio Level Indication    December 2011

   The header extension in this document is different than, but
   complementary with, the one defined in [RFC6465], which defines a
   mechanism by which audio mixers can indicate to clients the levels of
   the contributing sources that made up the mixed audio.

2.  Terminology

   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 [RFC2119] and
   indicate requirement levels for compliant implementations.