(1) is used to ensure the confidentiality,integrity and authenticity of the two end points in the private network． (2) ，an application—layer protocol，authenticates each peer in an IPSec transaction．IKE negotiates security policy，determining which algorithm may be used to set up the tunnel．it alsohandles the exchange of session keys used for that one transaction．

Networks that use (3) to secure data traffic can automatically authenticate devices by using (4) ，which verify the identities of the two users who are sending information back and forth．IPSeccan be ideal way to secure data in large networks that require secure connections among many devices．

Users deploying IPSec can (5) their network infrastructure without affecting the applications on individual computer．The protocol suite is available as a software-only upgrade to the networkinfrastructure．This alows security to be implemented without costly changes to each computer．Mostimportant，IPSec allows interoperability among different network devices，PCs and other computingsystems．

2（）

A．IPSec

B．SSL

C．L2TP

D．The Internet Key Exchange

关于膝关节正位，侧位影像的标准片不正确的是（）

A.正位包括股骨两髁，胫骨两髁及腓骨小头

B.膝关节正位关节间平行等距，位于照片正中

C.膝关节正位、腓骨小头与胫骨应分开2cm

D.侧位股骨两髁重叠，关节位于照片正中

E.侧位髌骨呈侧位