RTP Payload Format for PureVoice(tm) Audio (RFC2658)
Original Publication Date: 1999-Aug-01
Included in the Prior Art Database: 2019-Feb-11
Internet Society Requests For Comment (RFCs)
This document describes the RTP payload format for PureVoice(tm) Audio. [STANDARDS-TRACK]
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 (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.
This document describes how compressed PureVoice audio as produced by the Qualcomm PureVoice CODEC  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 .
The Electronic Industries Association (EIA) & Telecommunications Industry Association (TIA) standard IS-733  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  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  | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ |RR | LLL | NNN | | +-+-+-+-+-+-+-+-+ one or more codec data frames | | .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The RTP header has the expected values as described in...