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