An RTP Payload Format for EVRC Speech draft-3gpp2-avt-evrc-01.txt by Lucent, Nokia, Qualcomm, Samsung and UCLA (alphabetic ordered)

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)

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.

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 PureVoice   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.

RTP payload format for EVRC | RTP Header [2] | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ |RR | LLL | NNN | | one or more codec data frames + |.... | 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 |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) Blank 1 1 1/ / Erasure 1 (SHOULD NOT be transmitted by sender)

Single codec data format | RTP Header [2] | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | + one codec data frames | 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.

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