The FECN is the bit in the Frame Relay header that signals to anyone receiving the frame (switches and DTEs) that congestion is occurring in the same direction as the frame. Switches and DTEs can react by slowing the rate at which data is sent in that direction.

If congestion is detected on the Frame Relay network, the DE bit is turned on in the Frame Relay header. The DE bit is turned on for frames that are in excess of the CIR. The DE bit tells a switch which frames to discard if they must be discarded.

Three types of LMIs supported by Cisco routers are: Cisco, ANSI, Q933a.

Routers receive LMI information from the service provider's Frame Relay switch on a frameencapsulated interface and update the virtual circuit status to one of three different states:
Active state : Everything is up, and routers can exchange information.
Inactive state: The router's interface is up and working with a connection to the switching office, but the remote router isn't up.
Deleted state : No LMI information is being received on the interface from the switch, which could be due to a mapping problem or a line failure.

To enable Frame Relay on a Cisco router, you must first enable the serial interface for Frame Relay encapsulation with the encapsulation frame-relay interface command:
RouterB(config)#int s 0
RouterB(config-if)#ip address 192.168.1.1 255.255.255.0
RouterB(config-if)#encapsulation frame-relay