Network Working Group A. Li Request for Comments: 3558 UCLA Category: Standards Track July 2003 RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV) 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 (2003). All Rights Reserved. Abstract This document describes the RTP payload format for Enhanced Variable Rate Codec (EVRC) Speech and Selectable Mode Vocoder (SMV) Speech. Two sub-formats are specified for different application scenarios. A bundled/interleaved format is included to reduce the effect of packet loss on speech quality and amortize the overhead of the RTP header over more than one speech frame. A non-bundled format is also supported for conversational applications. Table of Contents 1. Introduction ................................................... 2 2. Background ..................................................... 2 3. The Codecs Supported ........................................... 3 3.1. EVRC ...................................................... 3 3.2. SMV ....................................................... 3 3.3. Other Frame-Based Vocoders ................................ 4 4. RTP/Vocoder Packet Format ...................................... 4 4.1. Interleaved/Bundled Packet Format ......................... 5 4.2. Header-Free Packet Format ................................. 6 4.3. Determining the Format of Packets ......................... 7 5. Packet Table of Contents Entries and Codec Data Frame Format ... 7 5.1. Packet Table of Contents entries .......................... 7 5.2. Codec Data Frames ......................................... 8 6. Interleaving Codec Data Frames ................................. 9 7. Bundling Codec Data Frames .................................... 12 8. Handling Missing Codec Data Frames ............................ 12 Li Standards Track