单项选择题
A.Frame Relay B.HDLC C.x.25 D.PPP
Which two options are valid WAN connectivity methods?（）...
多项选择题Which two options are valid WAN connectivity methods?（）
A.PPP B.WAP C.DSL D.Ethernet E.L2TPv3
At which layer of the OSI model dose PPP perform?（）A.La...
单项选择题At which layer of the OSI model dose PPP perform?（）
A.Layer 3 B.Layer 4 C.Layer 2 D.Layer 5
Which protocol is an open standard protocol framework t...
单项选择题Which protocol is an open standard protocol framework that is commonly used in VPNs,to provid secure end-to-end communication?（）
A. L2TP B. IPsec C. PPTP D.RSA
