Data communication is a new communication method produced by the combination of communication technology and computer technology. To transmit information between the two places, there must be a transmission channel. According to different transmission media, there are wired data communication and wireless data communication. But they all connect the data terminal with the computer through the transmission channel, and enable the data terminal in different locations to realize the sharing of software, hardware and information resources.
1. Data communication exchange method and scope of application 1. Data communication exchange methods There are generally three types of data communication exchange methods:
(1) Circuit switching Circuit switching means that two computers or terminals use the same actual physical link when communicating with each other. This link is used for information transmission throughout the communication, and other computers or terminals are not allowed to share the circuit at the same time. .
(2) Message exchange Message exchange is to store the user's message in the switch's memory (memory or external storage). When the required output circuit is idle, the message is then sent to the switch or terminal to be received. This store-and-forward approach can improve the utilization of trunks and circuits.
(3) Packet switching Packet switching divides the entire message sent by the user into several fixed-length data blocks (called packets or packets), and transmits these packets in a network in a store-and-forward manner.
2. Scope of application of various switching methods (1) Circuit switching methods are commonly used in communication networks such as public telephone networks, public telegraph networks, and circuit-switched public data networks (CSPDN). The first two circuit switching methods are traditional methods, and the latter method is basically similar to the public telephone network, but it uses four-wire or two-wire methods to connect users and is suitable for higher-speed data exchange. Because it is a dedicated public data network, its connection rate, working rate, subscriber line distance, line balance conditions, etc. are better than the public telephone network.
(2) The message exchange method is suitable for data communication that realizes store-and-forward between terminals with different rates, different protocols, and different code terminals or one-to-multipoint same-text units. In this way, the network transmission delay is large, and a large amount of memory and external storage space is occupied, so it is not suitable for data communication that requires high system security and a small network delay.
(3) Packet switching is developed on the basis of store-and-forward mode, but it has the advantages of circuit switching and message switching. It is suitable for conversational computer communication, such as database retrieval, graphic information access, e-mail transmission, and inter-computer communication. It has high transmission quality, low cost, and can communicate between terminals of different rates. The disadvantage is that it is not suitable for business applications that require high real-time performance and a large amount of information.
Second, the network and its protocol 1. The computer network (computer network) is a collection of two or more computers interconnected by optical cables, twisted-pair telephone lines, or wireless channels. Network users can share network resources through the network. Computer networks are divided according to geographic location and can be divided into four types: Internet, WAN, MAN, and LAN.
2. Network protocol Network protocol is the language used for network conversation between two computers. There are many network protocols, including character-oriented protocol, bit-oriented protocol, and byte-oriented protocol, but the most commonly used is TCP / IP protocol. It is suitable for large networks composed of many LANs and small networks that do not require routing. The TCP / IP protocol is characterized by an open architecture and is very easy to manage.
TCP / IP is actually a standard network protocol, which is a collection of related protocols, including transmission control protocol and Internet protocol. The TCP protocol is used to transfer data between applications, and the IP protocol is used to transfer data between the program and the host. Because TCP / IP is cross-platform, it has become the standard connection protocol of the Internet. The network protocol is divided into the following four layers:
(1) Network interface layer: responsible for receiving and sending physical frames;
(2) Network layer: responsible for communication between adjacent nodes;
(3) Transport layer: responsible for the communication from the starting point to the terminal;
(4) Application layer: provide applications such as file transfer, e-mail, etc. to transfer data from one computer to another in T c P / IP protocol. The data needs to be processed by the above four-layer communication software. Transmission in the physical network.
The current IP protocol is composed of 32 binary digits. For example, 202.0.96.133 indicates the IP address used by the computer connected to the Internet. The IP address is unique on the entire Internet.
Third, the application prospects of data communication 1, the application of wired data communication (1) the application scope of digital data circuit (DDN) are:
â‘ Set up a public digital data communication network;
â‘¡It can be public data exchange network, various private networks, wireless paging system, video teletext system, high-speed data transmission, conference TV, I SDN (2 B + D channel or 30B + D channel), postal storage computer The network etc. provides relay or data channels;
â‘¢ Provide Internet connection for Frame Relay, Virtual Private Network, LAN, and different types of networks;
â‘£Using DDN to realize the LAN connection of large users; for example, the professional banks, education, scientific research in our district, and the LAN interconnection between the Public Security Department of the autonomous region and the Urban Public Security Bureau.
⑤Provide leased lines to allow large users to set up a dedicated digital data transmission network;
â‘¥ Use DDN as a transmission method for centralized operation and maintenance, or interconnect the l 1 O alarm service desks of cities and towns in the whole district to realize the unified command of public security organs in the whole district.
(2) Application of packet switching network â‘ Electronic mailbox business Electronic mailbox system is also called e-mail. It is a communication method that exchanges information in a store-and-forward manner. On the packet switching network platform, the user sends the information to be sent to the storage space of the e-mail box in a prescribed format, which is processed and transmitted by the e-mail box system and sent to the e-mail box of the receiving user to notify the recipient.
â‘¡Electronic data exchange business Electronic data interchange (EDI) is the product of the combination of computers, communications and modern management technologies, and is also known as "paperless trade". EDI replaces paper documents with electronic documents, and the traditional multipoint-to-multipoint connection has become a network information transfer. EDI technology is an extremely important tool for future business development. Now it is widely used at home and abroad.
â‘¢ Fax storage and forwarding business Fax storage and forwarding is the combination of computer and communication technology to establish an intelligent fax network. The network uses the computer's store-and-forward technology to realize various new service items required by the vast number of users. The core of the store-and-forward technology is the fax switch.
â‘£Video service is a new, public and open information service system developed using the existing public telecommunications network. The business types of videotex mainly include public database services and dedicated database services.
(3) Application of frame relay technology â‘ Form a frame relay public network to provide frame relay services.
â‘¡ Install a frame relay interface on the packet switch to provide services.
â‘¢Users provide low-cost virtual broadband services.
â‘£In the private network, the use of multiplexed physical interfaces can reduce the number of ports required by bridges, routers and controllers during LAN interconnection, and reduce the number of communication facilities required for interconnected devices.
⑤High-speed connection between local area network (LAN) and wide area network (wAN).
â‘¥ LAN and LAN interconnection.
⑦ Remote computer-aided design / manufacturing file transmission, image query and image monitoring, conference TV, etc.
2. Application of wireless data communication (1) Application of mobile data communication in business.
The business of mobile data communication is usually divided into two kinds of basic data service and special data service: the application of basic data service includes electronic mailbox, fax, information broadcasting, local area network (LAN) access and so on. Applications for dedicated services include personal mobile data communications, computer-aided dispatch, vehicle, ship, fleet management, GPS vehicle satellite positioning, and remote data access.
(2) The application of mobile data communication in industry and other fields.
â‘ Fixed applications refer to fixed application systems and networks that access public data networks through wireless.
â‘¡Mobile application refers to transport vehicles, fleets and courier companies in the field exploration, construction, design and transportation departments to issue instructions or record real-time events, realize business scheduling, remote data access, report input, notification through wireless data network Mobile data terminals are required for communication and data collection.
â‘¢Personal applications refer to highly professional business technicians, outside security investigation personnel, etc. who need to work outside, remote printing, faxing, accessing the host computer, database query, verification, etc. through wireless data terminals.
4. Concluding remarks Digital data network (DDN) began to be applied in the public security private communication network, promoting the rapid development of the public security private communication network, and gradually developing towards digitalization, integration, and broadband. Public security organs have a lot of social information, and to realize the sharing of information resources, they must gradually develop in this direction. The information superhighway will integrate various communication services such as telephone, fax, data, and dynamic images through high-capacity optical fiber and multimedia technologies such as synchronous digital system (SDH), adopt computer comprehensive processing, apply ATM technology, and interact quickly Transmission, connecting the public security organs at all levels in the country cc I c, so that various types of public security information can communicate with each other at different levels to achieve the sharing of information resources.
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