Networks can be interconnected by different devices.In the physical layer,networks can be connected by (64) or Hubs, which just move the bits from one network to an identical net-work. One layer up we find bridgas and swiehes, which operate at data link layer. They can accept (65) , examine the MAC address, and forward the frames to a different network while doing minor protocol translation in the process. In the network layer, we have routers that can connect two netwoks. If two networks have (66) network layer, the router may be able to translate between the packet formats. In the transport layer we find transport gateway, which can interface between the two transport connections. Finally, in the application layer, application gateways translate message
(67) . As an example, gateways between Internet e-mail and X.400 e-mail must (68) the e-mail message and change various header fields.
A.syntax
B.semantics
C.languages
D.format
A.数据
B.地址
C.校验电路
D.刷新电路
A.目标网络
B.源地址
C.路由权值
D.下一跳
A.5年
B.10年
C.15年
D.20年
A.管理员
B.管理代理
C.管理信息数据库
D.代理服务设备
A.TCP
B.UDP
C.IP
D.IPX
A.基站
B.远程站
C.用户本地网
D.移动台
A.编码
B.数据缓冲
C.数据转换
D.路由选择