K.3 Computation of RTP payload size

26.1143GPPIP Multimedia Subsystem (IMS)Media handling and interactionMultimedia telephonyRelease 18TS

When the b=AS bandwidth is computed it is assumed that the codec is using the highest allowed coded mode for each frame.

The RTP payload size for the bandwidth-efficient payload format mode and 1 frame/packet is calculated from the following components:

– 4 bits for the payload header (=CMR)

– 6 bits for the Table of Contents (ToC)

– N bits for the speech frame (size depends on codec mode)

– Padding bits at the end of the RTP payload to give an integer number of octets

The RTP payload size for the octet-aligned payload format mode and 1 frame/packet is calculated from the following components:

– 4 bits for the payload header (=CMR) + 4 bits padding

– 6 bits for the Table of Contents (ToC) + 2 bits padding

– N bits for the speech frame (size depends on codec mode) + padding bits to give an integer number of octets

– No padding in the end of the RTP payload is needed since each item is already an integer number of octets

The RTP payload size for the bandwidth-efficient payload format mode and 2 frames per packet is calculated from the following components:

– 4 bits for the payload header (=CMR)

– 6 bits for the Table of Contents (ToC) for speech frame 1

– 6 bits for the Table of Contents (ToC) for speech frame 2

– N1 bits for the speech frame 1 (size depends on codec mode)

– N2 bits for the speech frame 2 (size depends on codec mode)

– Padding bits at the end of the RTP payload to give an integer number of octets

The RTP payload size for the octet-aligned payload format mode and 2 frames per packet is calculated from the following components:

– 4 bits for the payload header (=CMR) + 4 bits padding

– 6 bits for the Table of Contents (ToC) for speech frame 1 + 2 bits padding

– 6 bits for the Table of Contents (ToC) for speech frame 2 + 2 bits padding

– N1 bits for the speech frame 1 (size depends on codec mode) + padding bits to give an integer number of octets

– N2 bits for the speech frame 2 (size depends on codec mode) + padding bits to give an integer number of octets

– No padding in the end of the RTP payload is needed since each item is already an integer number of octets