The timing source selection for the secondary timing source. If the timing source selection is an Interface or InterfaceFixed, the interface index must be provisioned using the adGenMuxPTimingSecondarySourceInterface OID. The timing source selection options are: system(1) - When this option is selected, timing is derived from the system. interface(2) - When this option is selected as a timing source on a standalone card, timing is derived from the specified interface. When specified for a redundant pair of cards, timing is derived from the online interface and timing source will move during a failover event. interfaceFixed(3) - When this option is selected as a timing source on a standalone card or a redundant pair of cards, timing is derived from the specified interface. The timing source remains fixed and will not move during a failover event.