This read-write enumeration, applicable only to the SDM-9400 and V410 hardware, selects the voice encoding scheme, labeled aCode or bCode, used by the unit's voice processing. Because the source description is terse, an administrator relies on knowing which of the two coding options their specific card model requires for compatibility with the far-end voice equipment. For example, mismatching this encoding setting between two connected SDM-9400 units could result in garbled or unintelligible voice audio even though the link itself is up.