This Annex contains examples of computing b=AS for AMR and AMR-WB when ptime=20 and when ptime=40. In these examples, it is assumed that no extra bandwidth is allocated for redundancy.

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.

When redundancy is used then the RTP payload contains several frames, both non-redundant and redundant. For example, for 100% redundancy each RTP payload contains one non-redundant frame and one redundant frame, giving 2 frames per packet. The packet rate is however still 50 frames per packet. If the SDP includes multiple codecs and/or configurations then the bandwidth is calculated for each configuration and the b=AS bandwidth is set to the highest of the bandwidths.

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

The tables below give a detailed description of the bandwidth computation. The b=AS bandwidth is not defined for SID. Since a SID is rarely encapsulated with a speech frame or another SID, Tables K.9-16 do not include the computation procedure for the comfort noise frame.