26.1143GPPIP Multimedia Subsystem (IMS)Media handling and interactionMultimedia telephonyRelease 18TS
The bandwidth is calculated using the following procedure when no extra bandwidth is allocated for redundancy:
1) Calculate the size of the RTP payload, see below.
2) Calculate the size of the IP packets by taking the RTP payload size (in bytes) and adding the IP/UDP/RTP overhead: 20 bytes for IPv4; 40 bytes for IPv6; 8 bytes for UDP; 12 bytes for RTP.
3) Convert the IP packet size to bits.
4) Calculate the required bit-rate (bps) given the packet size and the packet rate: 50 packets per second for 1 frame per packet; 25 packets per second for 2 frames per packet.
5) The b=AS bandwidth is then calculated by converting the required bit-rate to kbps and rounding to the nearest higher integer value.
If the SDP includes multiple codecs and/or configurations, the bandwidth is calculated for each configuration and the b=AS bandwidth is set to the highest of the bandwidths.