WhicharethreeadvantagesofPPPoAimplementation？（）

A.NAPandNSPprovidesecureaccesstocorporategatewayswithoutmanagingend-to-endPVCs.NAPandNSPuseLayer3routing，Layer2Forwarding，orLayer2TunnelingProtocoltunnels.Hence，theycanscaletheirbusinessmodelsforsellingwholesaleservice
B.TheNSPcanoversubscribebydeployingidleandsessiontimeoutsusinganindustrystandard
C.OnlyasinglesessionperCPEononevirtualchannel
D.Theusernameandpasswordare
E.Userscannotselectdifferentsetsofservices，althoughusingmultipleVCsandestablishing
F.IfasingleIPaddressisprovidedtotheCPE，andNATorPATisimplemented，certain
G.Additionally，ifanIP
H.PPPoAcanusethefeaturesontheCiscoServiceSelectionGateway（SSG）

【参考答案】

A, B, E