A.NAP and NSP provide secure access to corporate gateways without managing end-to-end PVCs.NAP and NSP use Layer 3 routing，Layer 2 Forwarding，or Layer 2 Tunneling Protocol tunnels.Hence，they can scale their business models for selling wholesale service
B.The NSP can oversubscribe by deploying idle and session timeouts using an industry standard RADIUS server for each subscriber
C.Only a single session per CPE on one virtual channel （VC).The username and password are configured on the CPE， so all users behind the CPE for that particular VC can access only one set ofservices. Users cannot select different sets of services， although using multiple VCs and establishing different PPP session on different VCs is possible
D.If a single IP address is provided to the CPE， and NAT or PAT is implemented，certain applications such as IPTV，which embed IP information in the payload， well not work. Additionally，if an IP subnet feature is used，an IP address also has to be reserved for the CPE
E.PPPoA can use the features on the Cisco Service Selection Gateway （SSG）