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  3. The network layer is concerned with gett

The network layer is concerned with gett

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问题 The network layer is concerned with getting (71) from the source all the way to the destination. Getting to the destination may require making many hops at intermediate routers along the way. This function clearly contrasts with that of the data link layer, which has the more modest goal of just moving (72) from one end of a wire to the other. Thus, the network layer is the (73) layer that deals with end-to-end transmission. To achieve its goals, the network layer must know about the (74) of the network (i.e., the set of all routers and links) and choose (75) paths through it, even for large networks. It must also take care when choosing routes to avoid overloading some of the communication lines and routers while leaving others idle. Finally, when the source and destination are in different networks, new problems occur. It is up to the network layer to deal with them.A.appropriateB.longC.undefinedD.incomplete
选项
答案 A
解析 网络层关注的是如何将源端数据包一路送到接收方。为了将数据包送到接收方，可能沿途要经过许多跳（hop）中间路由器。这种功能显然与数据链路层的功能不同，数据链路层的目标没那么宏伟，只是将帧从线路一边传送到另一边。因此，网络层是处理端到端数据传输的最底层。为了实现这个目标，网络层必须知道网络拓扑结构（即所有路由器和链路的集合），并从中选择出适当的路径，即使是大型网络也要选出一条好路经。同时，网络层还必须仔细选择路由器，避免某些通信线路和路由器负载过重，而其他线路和路由器空闲。最后，当源端和接收方位于不同网络时，还会出现新的问题，这些问题都需要由网络层来解决。
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中级 网络工程师

软件水平考试初中高级

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