An RTP Payload Format for EVRC Speech

draft-3gpp2-avt-evrc-01.txt

byLucent, Nokia, Qualcomm, Samsung and UCLA (alphabetic ordered)

EVRC codec

Speech codecEIA / TIA IS-127Used in cdma2000 applicationsThree different sizes of output frames Full rate (171 bits) 1/2 rate (80 bits) 1/8 rate (16 bits)

Application

cdma2000 wireless voice telephone servicescdma2000 video streaming servicescdma2000 video conferencing services

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

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

Proposed payload format

Follows format of RFC 2658 for PureVoice13K 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.

RTP payload format for EVRC

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 +| .... |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

1. Interleaving / bundling format

The interleaving byte :

RR – Reserved (2 bits, must be 00)LLL – Interleave (3 bits)NNN – Interleave index (3 bits)

Codec data format 0 1 2 3 4 5 6 7+-+-+-+-+-+-+-+-+|I|R| 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)

Single codec data 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] |+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+| |+ one codec data frames +-+-+-+-+-+-+-+-+| |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

2. Single codec data format – Interleaving/bundling disabled

The interleaving byte is not present.

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.

Comments, questions?