Communication Manager sends SUBSCRIBE messages to the primary Multi-Function Soft Switch (MFSS) and the backup MFSS and accepts subscription requests from the primary MFSS. The backup MFSS and primary MFSS use SIP OPTION messages to support failover and failback processing. When the primary MFSS fails, the control moves to the backup MFSS. However, when the primary MFSS becomes active, the control comes back to the primary MFSS.