Frame Relay Cheat Sheet

Frame Relay Discard Eligability (DE)

The DE bit is used to indicate the frame has a lower importance than other frames. The DE bit is part of the address field in the address header. Sending devices can set the DE bit to 1 to indicate lower importance.

FECN - Forward-Explicit Notification for the receiver that the path is congested

BECN - Backward-Explicit Notification for the sender that the path is congested

PVC Status

The DCE(switch) reports the status and the DTE (router) recieves the status. The status is exchanged via the LMI protocol. The statuses are:

• Active - PVC configured correctly 
• Inactive - PVC configured correctly at local switch but down at the other end
• Deleted - PVC is not present

LMI is the signalling between the frame relay switch and the router. The 3 types of LMI are Cisco(default), ANSI and Q933A

Sub Interfaces

Two types of sub interfaces can be created for frame relay.

Multipoint and point-to-point. A multipoint sub interface can handle multiple PVCs

Point-to-point sub interface turns every PVC into a point-to-point network with its own network addressing. Using point-to-point sub interfaces gives greater control over our frame relay network.

Troubleshooting

When performing a loopback test put the interface encapsulation to HDLC

• < Prev
• Next >