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RTP Payload Format for PureVoice(tm) Audio (RFC2658) Disclosure Number: IPCOM000003247D
Original Publication Date: 1999-Aug-01
Included in the Prior Art Database: 2019-Feb-11
Document File: 10 page(s) / 14K

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Internet Society Requests For Comment (RFCs)

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10.17487/RFC2658: DOI


This document describes the RTP payload format for PureVoice(tm) Audio. [STANDARDS-TRACK]

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 16% of the total text.

Network Working Group K. McKay Request for Comments: 2658 QUALCOMM Incorporated Category: Standards Track August 1999

RTP Payload Format for PureVoice(tm) Audio

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 (1999). All Rights Reserved.


This document describes the RTP payload format for PureVoice(tm) Audio. The packet format supports variable interleaving to reduce the effect of packet loss on audio quality.

1 Introduction

This document describes how compressed PureVoice audio as produced by the Qualcomm PureVoice CODEC [1] may be formatted for use as an RTP payload type. A method is provided to interleave the output of the compressor to reduce quality degradation due to lost packets. Furthermore, the sender may choose various interleave settings based on the importance of low end-to-end delay versus greater tolerance for lost packets.

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 [3].

2 Background

The Electronic Industries Association (EIA) & Telecommunications Industry Association (TIA) standard IS-733 [1] defines an audio compression algorithm for use in CDMA applications. In addition to being the standard CODEC for all wireless CDMA terminals, the Qualcomm PureVoice CODEC (a.k.a. Qcelp) is used in several Internet applications most notably JFax(tm), Apple(r) QuickTime(tm), and Eudora(r).

K. McKay Standards Track [Page 1]

RFC 2658 RTP Payload Format for PureVoice(tm) Audio August 1999

The Qcelp CODEC [1] compresses each 20 milliseconds of 8000 Hz, 16- bit sampled input speech into one of four different size output frames: Rate 1 (266 bits), Rate 1/2 (124 bits), Rate 1/4 (54 bits) or Rate 1/8 (20 bits). The CODEC chooses the output frame rate based on analysis of the input speech and the current operating mode (either normal or reduced rate). For typical speech patterns, this results in an average output of 6.8 k bits/sec for normal mode and 4.7 k bits/sec for reduced rate mode.

3 RTP/Qcelp Packet Format

The RTP timestamp is in 1/8000 of a second units. The RTP payload data for the Qcelp CODEC has the following format:

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RTP Header [2] | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ |RR | LLL | NNN | | +-+-+-+-+-+-+-+-+ one or more codec data frames | | .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The RTP header has the expected values as described in...