网络协议的3个关键要素是语法、语义和同步，其中(24)说明控制信息或数据的结构和格式：(25)指出发出何种控制信息，完成何种动作。

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Networks can be interconnected by different devices in the physical layer networks can be connected by (71) or hubs．which just move the bits from one network to an identical network．One layer up we find bridges and switches which operate at data link layer．They can accept (72) ，examine the MAC address and forward the frames to a different network while doing minor protocol translation in the process in me network layer，we have routers that can connect two networks，If two networks have (73) network layer，the router may be able to translate betweenthe packer formats．In the transport layer we find transport gateway，which can interface between two transport connections Finally，in the application layer，application gateways translate message (74) ．As an example，gateways between Internet e-mail and X，400 e-mail must (75) thee-mail message and change various header fields．

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配置WWW服务器是Linux操作平台的重要工作之一，而Apache是目前应用最为广泛的Web服务器产品之一，(48)是Apache的主要配置文件。如果允许以“http://www.xxx.edu.cn/-usemame”方式访问用户的个人主页，必须通过(49)指令设置个人主页文档所在的目录。

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若FTP地址写为ftp://test:123@222.18.8.241:8901，则该地址中的“test”的含义是FTP服务器的(42)。若FTP地址为ftp://222.18.8.241，则该地址对应连接的FTP服务器用户名字为(43)。

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