AMR AMR-WB octet-align Parameter
AMR/AMR-WB sessions can be established in either bandwidth-efficient or octet-aligned format. Octet-aligned format increases processing efficiency, and is required for AMR’s robust sorting, interleaving and frame CRC capabilities. With octet-aligned format, all fields in the AMR/AMR-WB header are individually aligned to octet boundaries by the addition of padding bits. With bandwidth-efficient format, only the full payload is octet aligned resulting in the addition of fewer padding bits.
Format usage is specified by the optional AMR/AMR-WB octet-align parameter, which assumes one of two values: 0 (the default), indicating bandwidth-efficient format, or 1 indicating octet-aligned format. In the absence of the octet-align parameter, bandwidth-efficient format is employed.
A mismatch of offer/answer octet-align values requires transcoding as shown in the following table, where N/P indicates the absence of the octet-align parameter.
octet-align
Values
Offer Answer Format Transcoding Required
0 0 bandwidth-efficient No
1 1 octet-aligned No
0 1 mismatch Yes
1 0 mismatch Yes
N/P N/P bandwidth-efficient No
N/P 0 bandwidth-efficient No
N/P 1 mismatch Yes
0 N/P bandwidth-efficient No
1 N/P mismatch Yes