A.for trail trace identification
B.as the backward defect indicator
C.to transmit information between OTU termination points
D.to extend command and management functions over several frames
E.General communication channels 1 and 2 （GCC1/GCC2） do not belong to OTU OH

A.PPPoE can provide a host with access to a destination over Ethernet. You can have only one  PPPoE session per PVC
B.You must install PPPoE client software on all hosts that connect to the Ethernet segment. This means that the access provider must maintain a CPE
C.You cannot use PPPoE with Cisco Service Selection Gateway
D.PPPoE implementation is susceptible to broadcast storms and possible denial-of-service attacks
E.Per-session accounting is possible， which allows the service provider to charge the subscriber based on session time for various services offered. The service provider can also require a minimum access charge