The service provided is the transfer of audio signals (voice, voiceband data, and facsimile). The data unit traversing the SAP (SSCS SDU) contains either a voice encoding or a silence encoding. Silences are conveyed across the SAP either explicitly by a Silence Insertion Descriptor (SID) data unit, or implicitly by a Null data unit. Valid values are: - enabled. - disabled. - enabledEchoCancelOff: audio service enabled with echo cancellation and silence supression off. - enabledDynamic: audio service enabled with ability to dynamically disable silence supression, silence detection, echo cancellation and compression algorithms on a per-call basis.