Which of these is a Layer 2 transport architecture that provides packet-based transmission optimized for data based on a dual （counter-rotating） ring topology？（）

单项选择题WhichoftheseLayer2accessdesignsdoesnotsupportVLANextensions？（）

A.FlexLinks
B.loop-free U
C.looped square
D.looped triangle
E.loop-free inverted U

单项选择题For acceptable voice calls, the packet error rate should be less than（）%

A.0.01
B.0.1
C.1
D.2.5

多项选择题What are three primary activities in the cycle of building an enterprise security strategy?（）

A. activity audit
B. administration
C. policy establishment
D. technology implementation

多项选择题Which two of these are recommended practices with trunks? （）

A. use ISL encapsulation
B. use 802.1q encapsulation
C. set ISL to desirable and auto with encapsulation negotiate to support ILS protocol negotiation
D. use VTP server mode to support dynamic propagation of VLAN information across the network
E. set DTP to desirable and desirable with encapsulation negotiate to support DTP protocol negotiation.

单项选择题When is the site-to-site remote access model appropriate? （）

A. for multiple ISDN connections
B. for modem concentrated dial-up connections
C. for a group of users in the same vicinity sharing a connection
D. for use by mobile users