数据通信的基础知识概述入设备通信。
其本地管理接口（LMI）可大大简化帧中继网的配置和管理。
⑤局域网（LAN）与广域网（WAN）的高速连接。
⑥LAN与LAN的互联。
⑦远程计算机辅助设计/制造文件的传送、图像查询以及图像监视、会议电视等2．无线数据通信的应用无线数据通信也称为移动数据通信。
它的业务范围很广，也有广泛的应前景。
（1）移动数据通信在业务上的应用。
移动数据通信的业务，通常分为基本数据业务和专用数据业务两种：基本数据业务的应用有电子信箱、传真、信息广播、局域网（LAN）接入等。
•专用业务的应用有个人移动数据通信、计算机辅助调度、车、船、舰队管理、ＧPS汽车卫星定位、远程数据接入等。
（2）移动数据通信在工业及其它领域的应用。
移动数据通信在这些领域的应用可分为固定式应用、移动式应用和个人应用三种类型。
①固定式应用是指通过无线接入公用数据网的固定式应用系统及网络。
如边远山区的计算机入网、交警部门的交通监测与控制、收费停车场、加油站以及灾害的遥测和告警系统等。
②移动式应用是指野外勘探、施工、设计部门及交通运输部门的运输车、船队和快递公司为发布指示或记录实时事件，通过无线数据网络实现业务调度、远程数据访问、报告输入、通知联络、数据收集等均需采用移动式数据终端。
移动数据终端在公安部门的刑警、巡警、交警也开始应用。
③个人应用是指专业性很强的业务技术人员、公安外线侦察破案人员等需要在外办公时，通过无线数据终端进行远程打印、传真、访问主机、数据库查询、查证。
股票交易商也可以通过无线数据终端随时随地跟踪查询股票信息，即使度假也可以从远程参加股票交易。
Rudimentary knowledge summary of data communicationThe communication technology and computer technology that data communication is combine but a kind of new communication way that produce . Must transmit the channel while transmitting information between two places, according to transmitting the difference of medias, difference of wired data communication and wireless data communication. But they all connect data terminal and computer through transmitting the channel , and make the data terminal of different places realize the sharing of software and hardware and information resources.The pattern of exchanging of data communication and scope of application1. Usually there are three kinds of patterns of exchanging in data communication for the pattern of exchanging of data communication:(1) The circuit exchangingIt means two computers or terminal stations are while communicating each other that the circuit exchanges the circuit and exchanges, use the same real physics chain, use this chain to carry on the information transmission from start to finish in communication, allow other computer or terminal station henries of this circuit altogether at the same time.(2)Newspaper document exchangenewspaper document exchange is it store among memory of exchanger newspaper document of user to exchange (whether memory or outside deposit), as is it when circuit idle , mail exchanger or terminal station received toneed to this newspaper document and then to output while being necessary. This kind of memory - the way to transmit can improve the utilization ratio of junction line and circuit .(3)Dividing into groups exchangesit make long data piece on piece to cut whole copies of newspaper document that user send apart into to exchange to divide into groups to exchange to divide into groups (is it divide into groups or bale to call), divide into groups in order to store these - way that transmit transmit in network. The first message of dividing into groups has identifications receiving the address and sending the address in succession . In the packet switching network, different users' grouping data adopt the technology transfer that is replied and used dynamically , namely the network has routes to choose, there can be different users' grouping to convey in the same route, so the utilization ratio of the circuit is relatively high.2. Scope of application of different patterns of exchanging(1)Circuit pattern of exchanging apply public telephone network, public telegram network and public datum network(cSPDN) that circuit exchange,etc. among the communication networks usually. Department's traditional way of pattern of exchanging of first two kinds of circuit; The last way and public telephone network are similar basically, but itjoins users in Line four or way of Line two, suitable for the data interchange of higher speed . Data network not public on it is to be special-purpose in it,putting through rate, speed , the user line not working of it from, circuit terms not balanced ,etc. last telephone network not public . Its advantage is that real-time character is strong, delay very small and exchanging the cost relatively low; Its shortcoming is that a utilization ratio of a circuit is low. The circuit exchanges and is suitable for once after continuing, the communication of the long message.(2)The gentle pattern of exchanging of the newspaper is suitable for realizing different speed , different agreements , terminal stations or the one point to many point one , with storing the data communication that is transmitted for the unit gentlies of different codes terminal station. Because of way this, network prolong heavy when transmitting, take a large amount of memory and outside check space, not suitable to prolong while requiring the system security high , network smaller data communication.(3)Is it store - transmit foundation of the way not to develop to exchange to divide into groups, but it has advantage that circuit exchanges and the newspaper document exchange concurrently. It is suitable for conversational compunication , for instance the database is searched , picture and textinformation depositting and withdraw , E-mail transmitting and such different fields as communication ,etc. among the computers, it is relatively low to transmit the cost high in quality, and in the communication among different speed terminal station. Its shortcoming is not to suitable for expecting much , business use very great in amount of information of real-time character .1. Wired data communication(1)Digital Data Net (DDN)Digital Data Net is controlled the administrative center to make up by user cycle , DDN node , digital channel and network. DDN utilizes such digital channels as optic fibre or digital microwave , satellite ,etc. and figure to reply the digital data transmission net made up of equipment alternately. We can say too DDN connect data communication technology , digital communication technology , fiber optic communication technology and figure alternately digital communication networks that technology conbined together. The digital channel should include users to the connection circuit of the network , the transmission of the namely users cycle should be the the figure one, but there are ordinary cables and paired line in fact, but before transmitting quality and is not so good as.(2)The packet switching networkpacket switching network (PSPDN ) iswith ccITT X. Based on 25 suggestions, so also called X. 25 networks . It adopts storing- transmit the way, • divides the newspaper document which users sent here into having data section which uses certain length, control information on the section in each data , form a grouping with address make the colony up, transmit on the net. Packet switching network most outstanding advantage to can open large timid thorough fares at the same time at one circuit, use at the same time for a lot of user, network have dynamic route choose function and a advanced one yard examine function by mistake by mistake, but the performance of the network is relatively bad.(3)Frame relaying networkframe relaying network deposit and withdraw by frame relaying equipment , frame relaying exchange equipment and public frame relaying service network 3 part make up usually. The frame relaying network is developed from the swapper of dividing into groups. Frame relaying technology pairs of different user data group in bigger frame relaying frame seal of length, in addition, transmit on the net after seeking the location and controlling information.2. Wireless data communicationwireless data communication call the mobile data communication too, it develops on the basis of wired data communication. Wired data communication depends on transmittingwiredly, is only suitable for the communication between regular terminal station and the computer or the computer. And the mobile data communication conveyed the data through the spread of the radiowave, therefore may realize moving mobile communication under the state . Narrow sense say mobile data communication computer computer and wireless communication of people sometimes. It passes with the wired data network interconnectedly, expands the application of the networking of the wired data to moving and portable users.puter network (Computer Network), entangle telephone wire or have , • wireless channel two the above-mentioned computer interconnected set through optical cable , pair. Can realize network resource-sharing through network every user, for instance file , procedure , printer and modem ,etc.. Computer network divide according to geographical position , can divide into Internet , WAN , city land network and LAN 4 kinds. Internet is the biggest Internet in the world; WAN generally means that joins the network of each area in a country, WAN is generally distributed in the distance among 100-1000 kilometers; City land net is call city net, its coverage is generally a city, do not have an area of 10-100 kilometers; The geographical distribution of the LAN is relatively small , such as a building, or a unit , a school, even a largeroom ,etc..The LAN is a computer network used most at present, a unit can use a lot of LANs , if financial department use LAN is it manage financial account to come, personnel department use LAN is it manage personal file , various kinds of talent message to come, public security men criminal investigation department use LAN is it manage crime information system , traffic police department use LAN is it manage motor vehicle , driver message ,etc. to come to come.2. ProcotolProcotol whether two computer carry on language that network's talking use, there are a lot of procotols, there are agreements facing agreement , facing bit of the character , the agreement that • still faces bytes and counts, but the most frequently used one is TCP/IP agreement in •. It is suitable for the large-scale network composed of a lot of LANs and small-scale network not needing the route to choose . The characteristic of TCP/IP agreement has open system structure, and very manageable.。
