A.1 RTP Header Usage

26.4453GPPCodec for Enhanced Voice Services (EVS)Detailed algorithmic descriptionRelease 15TS

The format of the RTP header is specified in RFC 3550 [30]. This EVS RTP payload format uses the fields of the RTP header in a manner consistent with the usages in RFC 3550 [30].

The timestamp clock frequency for the EVS codec is 16 kHz, regardless of the audio bandwidth. The duration of one speech frame-block is 20 ms for both EVS Primary and EVS AMR-WB IO modes. Thus, the timestamp is increased by 320 for each consecutive frame-block.

The RTP header marker bit (M) shall be set to 1, if the first frame-block carried in the RTP packet contains a speech frame, which is the first in a talkspurt. For all other RTP packets the marker bit shall be set to zero (M=0).