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）

A.trunk admission control
B.forwarding traffic to tunnel
C.information distribution
D.path selection， calculation， and setup
E.traffic patterns prediction

A.MPLS is required between the PE and CE routers that connect the backbone carrier to the customer carrier.
B.The backbone carrier must enable the PE router to check that the packets it receives from the CErouter contain only the labels that the PE router advertised to the CE router.
C.Every packet that crosses the backbone carrier must be encapsulated so that the packet includes MPLS labels
D.AII PE routers that link the backbone carrier to the customer carrier must run Route Target Rewrite.
E.Arouting protocol is required between the PE and CE routers that connect the backbone carrierto thecustomer carrier. The routing protocol enables the customer carrier to exchange IGP routing information with the backbone carrier.

A.immediately after receiving the first packet on the shared tree for a given （S，G）
B.after receiving over 1 kb/s traffic onthe shared tree for a given （S，G）
C.10 seconds after receiving the first packet on the shared tree for a given （S，G）
D.30 seconds after receiving the first packet on the shared tree for a given （S，G）
E.after receiving over 10 kb/s traffic onthe shared tree for a given （S，G）

A.MAC over MPLS
B.L2TPV3
C.802.1 QinQ
D.Ethernet over MPLS
E.GRE