WAN Practice Questions

Frame Relay FECN and BECN

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Q8. A frame is received at the destination router over Frame Relay network with FECN bit value set to 1. What does this indicate?

A. That there is traffic congestion in the direction of source to destination.

B. That there is traffic congestion in the direction of destination to source.

C. That there is no traffic congestion in the direction of source to destination.

D. That there is no traffic congestion in the direction of destination to source.

Correct Answer: A

Explanation:

Frame Relay has two types of congestion notification mechanisms:

FECN: Forward-Explicit Congestion Notification, and

BECN: Backward-Explicit Congestion Notification.

If the network is congested in the direction of source to destination, FR switches set the value of the frames FECN to 1(one). DTE devices may implement flow control based on this information. FR switches set the value of BECN bit to 1 (one) in frames traveling in the opposite direction of frames with their FECN bit set. This will enable to DTE device to initiate appropriate flow control in the direction in which the frame has arrived.

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