Definition
Communication network terminal, namely computer display terminal, is the input and output device of computer system. The computer display terminal is produced with the centralized processing mode of the mainframe era, and continues to develop with the development of computing technology. So far, computing technology has experienced three development periods: the host era, the PC era, and the network computing era. The terminal is adapted to the three stages of computing technology development, and the application has also experienced the three stages of character dumb terminals, graphic terminals and network terminals. Form.
Terminal equipment is divided into two types: general-purpose and special-purpose. General-purpose terminal equipment refers to general-purpose computer input and output devices with communication processing and control functions. The type and quantity of configuration depends on needs. The input and output devices that can usually be selected are: keyboard, card reader, paper tape reader, optical character or mark recognition machine, voice recognizer, serial or line printer, display, card punching machine, paper tape punching Machines, voice synthesizers, floppy disk drives, tape drives, disk drives, etc. General-purpose terminal equipment is roughly divided into two types: remote batch processing terminal and interactive terminal according to the variety and quantity of configuration.
Main categories
Common client devices are divided into two categories: one is a thick client and the other is a thin client. Then, the devices based on the open industry standard architecture and more powerful functions represented by the PC are called "fat clients", and the others are classified as "thin clients." The space and scale of the thin client industry is also very large, no less than the scale of the PC.
1. From a technical perspective, the data processing mode will be decentralized to centralized, the user interface will be more user-friendly, manageability and security will be greatly improved; at the same time, communication and information processing methods will also be fully networked, and can achieve unprecedented System scalability and cross-platform capabilities.
2. In terms of application form, network terminal equipment will not be limited to the traditional desktop application environment. With the diversification of connection methods, it can be used as a desktop device, and it can also be used in mobile and portable ways. There will be diversified terminal devices. Product form: In addition, with the expansion of cross-platform capabilities, in order to meet the needs of different system applications, network terminal devices will also appear in many faces: Unix terminals, Windows terminals, Linux terminals, Web terminals, Java terminals, and so on.
3. In terms of application areas, terminal devices in the era of character dumb terminals and graphic terminals can only be used in window service industries and counter services will be gone forever, and non-counter services such as online banking, online securities, and bank low-counter services will be extensive Adopt network terminal equipment, and the application field of network terminal equipment will also rapidly expand to emerging non-financial industries such as telecommunications, electricity, taxation, education, and government.
Main applications
Audio communication terminal equipment
Audio communication terminal is the most widely used type of communication terminal in the communication system. It can be used in ordinary telephones. The ordinary analog telephones, dictaphones, coin-operated telephones, magnetic card telephones, IC card telephones of the switching network PSTN can also be digital telephones used in ISDN networks and wireless mobile phones used in mobile communication networks.
Generally speaking, a telephone with the most basic functions is composed of a call module, a dialing module, a ringing module, and a line interface. Most telephones are push-button telephones, and their number issuing modules mainly include push-button dials and dual tone signal/pulse signal generators. The ringing module is composed of a tone ringing circuit, a piezoelectric ceramic ringer or a speaker. Its function is to detect the signal status on the telephone line in the standby state, and drive the piezoelectric when the ringing signal sent from the telephone exchange is received. The ceramic ringer or speaker emits a ringing tone. The call module is composed of a receiver composed of electric/acoustic devices, a microphone composed of sound/electric conversion devices, and a signal amplifier. Its function is to complete the acoustic-electric conversion and signal amplification of the voice signal when speaking, as well as the amplification of the received signal and the voice signal The electro-acoustic transformation.
Graphic and image communication terminal
Fax is a graphic and image communication service that has been widely used. It is to record text, icons, photos and other information on paper media. , Through the photoelectric scanning method into electrical signals, after transmission through the public telephone switching network, at the receiving end in a hard copy way to obtain the paper medium information similar to the sending end.
The three most widely used communication terminal facsimile machines that work in ordinary telephone switching networks are composed of CCD image sensors, video processing circuits, motor drive circuits, recording control circuits, codecs, and system controllers. , Modem, network controller, operation panel and power supply system.
Video communication terminal
The main video communication terminals used in the communication system are various TV cameras, cameras for multimedia computers, TV receivers, video monitors, and computer monitors.
Color cameras are mainly composed of optical systems, camera tubes (or solid urban and rural devices), video processing circuits, synchronization signal generators and color signal encoders.
Compared with color cameras, multimedia computer cameras have a simple structure but lower technical indicators. The optical system generally uses a relatively inexpensive plastic lens, and the imaging device uses a single-chip CCD or CMOS solid-state imaging device. According to its signal output form, it can be divided into two categories: analog camera and digital camera.
Color TV receivers, video monitors and computer monitors are the main video communication terminal equipment. Among them, color TV receivers are mainly used to receive and display broadcast TV signals, cable TV signals, and video TV signals output by various video playback equipment; video monitors are mainly used in various professional fields to monitor video image signals. Its various technical performance indicators are higher than TV receivers, but generally do not have the function of receiving high-frequency TV signals; computer monitors are mainly used for the display of computer graphics and images, because it does not have high-frequency demodulation and full-color TV signal decoding Circuit, so it cannot be used directly to display TV signals. Computer monitors are much higher than TV receivers in terms of display resolution and screen refresh rate, and they work in a progressive scan state.
Data communication terminal
There are many types of ISDN terminal equipment, and the most commonly used terminal equipment mainly includes the following:
The network terminal is the terminal device of the user's transmission line, it is the joint device for digital signal transmission and reception on the ordinary telephone line, and the interface device between the telephone office program-controlled exchange and the user's terminal device. This device is installed at the user's place and is an essential terminal for N-ISDN function. Network terminals are divided into basic rate network terminals and primary group rate network terminals.
ISDN user terminal There are many types of equipment, including ISDN video conference system, PC desktop system (including video phone), ISDN small switchboard, TA adapter , ISDN routers, ISDN dial-up servers, digital telephones, four types of fax machines, etc.