In order to realize data communication, data transmission is necessary, that is, data information sent by a data source in one place is transmitted to a data receiving device in another place through a transmission channel. The channel used for data transmission can be a solid-state baseband circuit, a frequency division analog circuit or a time division digital circuit.

Because of its long development history, large communication capacity and wide coverage, telephone network is economically and technically suitable and is a common way to provide data transmission channels. However, when using telephone circuit as data transmission channel, some measures must be taken to adapt it to the requirements of transmitting data signals.

2. Data exchange and communication protocols

In a data communication system or a computer network, the transmission channel used can be fixed or provided by a switching network. There are two main ways of data exchange: circuit switching and packet switching, among which packet switching is more commonly used in actual data networks.

In packet-switched data networks, in addition to the functions required by data transmission and data link control regulations between adjacent switching nodes, it is also necessary to store and forward data packets at each switching node. Routing, flow control, congestion control, user network connection and network maintenance and management. Therefore, some related functions need to be implemented in the terminal system connected to the data exchange network.

All these functions related to the formation of data exchange network are stipulated in the form of communication protocols, including the interface protocol between the terminal system and the network. The so-called agreement is the rules and agreements that both parties must abide by in order to communicate accurately and effectively. They are of great significance in data communication. The data link control process mentioned above is actually a data communication protocol.

Extended data

The development trend of data communication is as follows:

1. With the expansion of application scope and scale, new application services such as electronic data interchange (EDI) and multimedia communication are constantly emerging.

2. With the increase of business volume, the network is developing towards high speed, broadband, digital transmission and comprehensive utilization. For example, many new technologies such as fiber-optic high-speed local area network, metropolitan area network, broadband integrated service digital network, relay and fast packet switching have developed rapidly, and some of them have entered the practical stage.

3. With the development of mobile communication, mobile data communication has developed rapidly.

4. With the continuous expansion of the scale of networks and systems, the interconnection of different types of networks and systems (including the operation and management of Internet) becomes more and more important.

5. The communication protocol standards have been greatly increased, and the protocol engineering technology is also developing day by day.