An RTP Payload Format for EVRC Speech draft-3gpp2-avt-evrc-01.txt

1
An RTP Payload Format for EVRC Speechdraft-3gpp2
-avt-evrc-01.txt

• by
• Lucent, Nokia, Qualcomm, Samsung and UCLA

(alphabetic ordered)
2
EVRC codec

• Speech codec
• EIA / TIA IS-127
• Used in cdma2000 applications
• Three different sizes of output frames
• Full rate (171 bits)
• 1/2 rate (80 bits)
• 1/8 rate (16 bits)

3
Application

• cdma2000 wireless voice telephone services
• cdma2000 video streaming services
• cdma2000 video conferencing services

The packet-switched mode of the later two
services requires an RTP payload format to be
defined for EVRC codec data.
4
Combined Draft

• The differences with the submitted draft
• Some textual clarifications
• Octet 0 of EVRC payload now has bit to support
  rate reduction
• Incorporated section from Lucent draft on MIME
  types and SDP parameters

5
Proposed payload format

• Follows format of RFC 2658 for PureVoiceä (13K
  celp) codec.
• Included format specifically for non-interleaved
  case (one codec data in each RTP packet) save
  the 1 byte overhead.
• Included Rate Reduction bits to signal requests
  for reducing the codec rate for the reverse
  direction.

6
RTP payload format for EVRC
1. Interleaving / bundling 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 interleaving byte RR Reserved (2 bits,
must be 00) LLL Interleave (3 bits) NNN
Interleave index (3 bits)
7
Codec data format
0 1 2 3 4 5 6 7 -------- IR frame
type --------
codec data
I Interleaving disabled (1 bit) R Reduce rate
(1 bit) Frame type (6 bits)
Value RATE TOTAL CODEC data frame size
(in octets) --------------------------------------
------------------- 0 Blank 1
1 1/8 3 3 1/2 11
4 1 23 14 Erasure 1
(SHOULD NOT be transmitted by sender)
8
Single codec data format
2. Single codec data format Interleaving/bundlin
g disabled
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



one codec data frames
--------
----------------
--------
The interleaving byte is not present.
9
Misc issues

• The receiver can determine if the payload is
  interleaved by detecting the presence of 1 at the
  first bit of the RTP payload.
• The sender must not increasing the interleaving
  size LLL without changing SSRC.
• The sender must not switch from non-interleaved
  format to interleaved format without changing
  SSRC.

10
Comments, questions?