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(74)was designed many years ago，with a goal in mind：transmitting the human voice in a more-or-less recognizable form．

In 8011 terminology．all communication was to go through the base station, called an(75)

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In the data link layer, the data unit is called(71)．

The(72)is a system for linking hypertext documents Originally, each document was a page written in(73)with hyperlinks to other documents．Nowadays，XML is gradually starting to take over from(73)．

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TCP/IP是一个协议簇，它的体系结构分为4层：应用层、网际层、网络接口层和(47)，其中，ARP属于(48)。为了在源主机和目的主机之间传送数据，IP需要确定源主机和目的主机是否在同一个网络中。如果不在同一网络时，则必须通过(49)进行通信。

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