The DE bit is used for what purpose?

A.
To identify congestion in the network.

B.
To inform the CPE that frames have been discarded because of congestion.

C.
To identify a frame that should be transmitted through the network on a best effort case.

D.
All of the above.

Explanation:
Discard eligibility (DE) is set by the DTE device, such as a router, to indicate that the marked frame is of lesser importance relative to other frames being transmitted. Frames that are marked as “discard eligible” should be discarded before other frames in a congested network. This allows for a basic prioritization mechanism in Frame Relay networks.