RFC 3267 (rfc3267) - Page 2 of 49

Real-Time Transport Protocol (RTP) Payload Format and File Storage Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio Codecs

Alternative Format: Original Text Document


RFC 3267        RTP Payload Format for AMR and AMR-WB          June 2002


Table of Contents

   1. Introduction.................................................... 3
   2. Conventions and Acronyms........................................ 3
   3. Background on AMR/AMR-WB and Design Principles.................. 4
     3.1. The Adaptive Multi-Rate (AMR) Speech Codec.................. 4
     3.2. The Adaptive Multi-Rate Wideband (AMR-WB) Speech Codec...... 5
     3.3. Multi-rate Encoding and Mode Adaptation..................... 5
     3.4. Voice Activity Detection and Discontinuous Transmission..... 6
     3.5. Support for Multi-Channel Session........................... 6
     3.6. Unequal Bit-error Detection and Protection.................. 7
       3.6.1. Applying UEP and UED in an IP Network................... 7
     3.7. Robustness against Packet Loss.............................. 9
       3.7.1. Use of Forward Error Correction (FEC)................... 9
       3.7.2. Use of Frame Interleaving...............................11
     3.8. Bandwidth Efficient or Octet-aligned Mode...................11
     3.9. AMR or AMR-WB Speech over IP scenarios......................12
   4. AMR and AMR-WB RTP Payload Formats..............................14
     4.1. RTP Header Usage............................................14
     4.2. Payload Structure...........................................16
     4.3. Bandwidth-Efficient Mode....................................16
       4.3.1. The Payload Header......................................16
       4.3.2. The Payload Table of Contents...........................17
       4.3.3. Speech Data.............................................19
       4.3.4. Algorithm for Forming the Payload.......................20
       4.3.5 Payload Examples.........................................21
            4.3.5.1. Single Channel Payload Carrying a Single Frame...21
            4.3.5.2. Single Channel Payload Carrying Multiple Frames..22
            4.3.5.3. Multi-Channel Payload Carrying Multiple Frames...23
     4.4. Octet-aligned Mode..........................................25
       4.4.1. The Payload Header......................................25
       4.4.2. The Payload Table of Contents and Frame CRCs............26
         4.4.2.1. Use of Frame CRC for UED over IP....................28
       4.4.3. Speech Data.............................................30
       4.4.4. Methods for Forming the Payload.........................30
       4.4.5. Payload Examples........................................32
            4.4.5.1. Basic Single Channel Payload Carrying
                     Multiple Frames..................................32
         4.4.5.2. Two Channel Payload with CRC, Interleaving,
                     and Robust-sorting...............................32
     4.5. Implementation Considerations...............................33
   5. AMR and AMR-WB Storage Format...................................34
     5.1. Single Channel Header.......................................34
     5.2. Multi-channel Header........................................35
     5.3. Speech Frames...............................................36
   6. Congestion Control..............................................37
   7. Security Considerations.........................................37
     7.1. Confidentiality.............................................37



Sjoberg, et. al.            Standards Track

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