数据通信实际上是把电子计算机和通信结合在一起,用来完成各种数据业务和数据交换,也就是包括计算机在内的各种终端相互间传递数据的通信。它可以是终端和计算机通过通信线路连接起来的在线系统,也可以是由通信线路连结多台计算机组成的共享资源的计算机网络。计算机参加通信是数据通信的重要特征。为了保证终端和终端之间、终端和中心之间正确传递信息,需要对数据传输过程进行控制,即传输控制。为了实现传输控制,制定了一系列的规则,这些规 Data communication is actually a combination of electronic computers and communications, used to complete a variety of data services and data exchange, that is, including computers, including a variety of terminals to communicate data transfer between each other. It can be an online system in which a terminal and a computer are connected by a communication line, or a computer network in which a plurality of computers are connected by a communication line to share resources. Computer participation in communications is an important feature of data communications. In order to ensure that the information is correctly transferred between the terminal and the terminal, between the terminal and the center, the data transmission process needs to be controlled, that is, transmission control. In order to achieve transmission control, a series of rules and regulations have been drawn up