The PSM (protection switch module) provides trunk fiber protection for Cisco ONS 15530 systems configured in point-to-point topologies. The PSM sends the DWDM signal from the OADM module to both the west and east directions. It receives both the west and east signals and selects one to send to the OADM module. When a trunk fiber cut occurs on the active path, the PSM switches the received signal to the standby path. Since the PSM occupies one of the OADM subslots in the shelf, it protects a maximum of four channels and the OSC in a single shelf configuration.The PSM also has an optical monitor port for testing the west and east receive signals. This port samples one percent of these signals, which can be monitored with an optical power meter, or optical spectrum analyzer. A PSM can be installed in subslots 0/0 and 0/1 of the Cisco ONS 15530 chassis. The PSM for the Cisco ONS 15530 has a front panel with four MU connector pairs.