ATM switches use the VPI/VCI fields of the cell header:

A.
To identify the QOS parameters specified in the traffic contract between the ATM end station and the network

B.
To determine if the cell should be discarded in preference to others that have not exceeded their traffic envelope

C.
To identify the next intermediate destination to which the cell should be passed

D.
To determine if the header contains a checksum error and should be discarded

E.
To determine if the cell contains user data or control data