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