在七十年代末，国际标准化组织ISO提出了开放系统互连参考模型。协议分层大大简化了网络协议的复杂性，在OSI7层模型中，网络层的功能主要是（）。

A.Dead
B.Establish
C.Network
D.Terminate

A.Organization for Standards Institute
B.Organization for Internet Standards
C.Open Standards Institute
D.Open Systems Interconnection

A.to map a known DLCI to an IP address
B.to mapa known IP address to a MAC address
C.to map known SPID toa MAC address
D.to map a known DLCI to a MAC address
E.to map a known IP address to a SPID
F.to mapa known MAC address to an IP address