This read-write INTEGER controls whether VISM reads CAS-related timer parameters for this DS0 from the downloaded casAppl file (casAppl) or from this MIB's own values (mibValue), and it cannot be set on a non-CAS line. This gives an admin flexibility to override the shared CAS application file with per-endpoint timer values when different endpoints on the same CAS variant need different timing behavior. For example, if one endpoint needs a longer wink timer than the rest of the CAS variant's defaults, an admin would set ds0CasParameterSource to mibValue on that endpoint and configure the timer objects individually.