Resolution
If issuing the show version command on the router does not list the hardware installed on the router module and if the show diag command does not clearly specify the name of this module, but instead lists the Unknown module or Unknown card, ensure that you have the correct Cisco IOS Software features. You must have the Plus feature set installed, which is noted by the "-s" in the Flash file name.
If you have the correct features and still cannot see the module, make sure the module is seated properly in the slot. To make certain, turn off the router after saving your configuration and reseat the Voice Interface Card (VIC) in the network module (depending if it applies on your platform) and then reseat the module (VIC or Network Module [NM]-2V) in the router slot. Restart the router and make sure the orange lights disappear and then see if you can identify the hardware correctly.
The basic method to test a Foreign Exchange Station (FXS) port is to connect an analog phone and see if the dial tone is heard when the phone goes off-hook. If it does not, check that the port is not in a shutdown state. If it is in a shutdown state, issue the no shutdown command.
For more information, refer to these documents:
