【 Weak current college 】 building weak electricity system--the fourth section telephone communication and computer network system

First, telephone communication system telephone communication system is a smart building information transmission network of basic components. Traditional telephone systems are limited to telephone, Telegraph and other audio and low-speed data communication services, generally using the audio cable laying.　　The present building of user demand for information is not just the auditory information, more need to transmit Visual information, such as text, graphics and images, and other activities, such as non-voice, data transmission, videotex, e-mail, video phone and multimedia communications, etc. Intelligent building telephone communication systems typically include digital PABX, distribution frame, transfer box, cable boxes (boxes) and transmission lines, and other equipment.　　At present, the user switch and Nan connected with fiber-optic cable trunk lines are generally, building of transmission line performance excellent double Ridge cable. Telephone communication system installation is required in building embedded underground communication cables and pipelines, cabling, and building reserved telephone connection rooms, cable shaft, pre-buried pipe and cable wiring harness.　　If you need to set the user switches, but also in building up the telephone station. The communication aims to achieve a certain area in any two terminal information exchange between users.　　To do this, you must handle the signal send and receive, signal transmission and signal Exchange three problems.　　Telephone communication system consists of a user's terminal equipment, transmission systems and switching equipment is composed of three parts.　　1. user terminal equipment of a user's terminal equipment to complete the signal send and receive, equipment mainly in telephones, fax machines and computer terminals, etc. 2. telephone transmission system telephone transmission system as the transport medium into cable transfers (wire, cable, fiber, etc.) and wireless transmission (short-wave and microwave relay, satellite communications, etc.). Wired transfer press transfer information work is divided into analog transmission and digital transmission. Analog transmission is to convert the information with the appropriate size of the current analog transmission, phone is a simulation of voice information transmission.　　Digital transmission is information by digital encoding converted to digital signals for transmission, digital transmission a antijamming ability is strong, confidentiality and integrated circuits, etc., now the program-controlled telephone exchange is to use digital transmission of information. In the cable transmission of the telephone communication system, transmission line has a subscriber line and trunk. Subscriber line refers to the user and switch between the lines.　　Two switch between the lines is called a trunk. 3. telephone exchange equipment, program-controlled switches now widely used as a telephone switching equipment. The so-called program control refers to a control, it is the computer stored program control technology applied to the telephone switching equipment. This control is to advance the telephone exchange function compiled into the appropriate program, and program and related data are deposited into the store.　　When a user calls, the processor in accordance with the directives issued by the program to control switch, to complete the continuation function. Telephone switches according to its usage scenarios can be divided into two categories: one category is used for large switch PSTN, such as long-distance telephone switches and switch; enterprises and institutions within the telephone exchange of private branch exchange, commonly referred to as the small operator, or user switch.　　User switches General capacity, internal users can via local Council, so as to reduce the load on the local Council of telephone traffic, improve user line distance. A user switches a general-purpose and special-purpose, general-purpose user switches apply to voice service oriented unit; special switch applies to the various features of the unit, such as hotel type switch, a long distance call instant billing, message, room status, do not disturb, wake-up service and comprehensive voice capabilities.　　In addition, there are Office Automation-, banking-and network-user switch.　　Second, computer network systems, the definition of computer network: where location is different, having independent function of multiple computer systems through communication equipment and lines concatenated, separated by full-featured network management and control of the software to achieve the mutual exchange of information and sharing network resources of the system, known as a computer network system. 1. computer network function (1) information for rapid transfer and focus
Take advantage of this feature, you can use geographically dispersed units or departments connected via a computer network for mutual exchange of information and information from the parties, in order to concentrate on the units or departments for control and management. (2) resource sharing
Users on the network can share the network hardware and software resources and information resources. (3) balanced load and distribution processing
When a host of overload, you can set certain jobs over the network to the other host processing in order to balance the load and reduce local burden can improve equipment utilization. For a comprehensive, significant problems can be resolved after the job decomposition to different computers, balanced use of network resources, the purpose of achieving distributed processing.　　Today's calculation of a new trend — collaborative computing, is the use of a network of several computers to work together to complete a task. (4) comprehensive information service
Through the computer network to the whole society offers a variety of economic information, technology information and consulting services, and may transfer digital, sound and graphic images, and other information. (5) improve the reliability of your computer
In the case of stand-alone use, when a computer or a part of a failure would result in downtime, the computer will not be able to continue to use, and in computer network systems, computer and software resources available on each back-up, failure of tasks to be completed on behalf of the other computer, greatly improves the reliability of computer systems. 2. the composition of the computer network system (1) network hardware system
Composition of the LAN network hardware system can be divided into five categories: servers, workstations, network switching interconnect devices, firewall and external devices. ① Server is the personal computer (PC) or workstation or small computer. The server should have a high performance, including faster speed, more memory and a larger capacity hard disk. ② network workstations. Means to enable users in a network environment on a work planComputer (client). The role of network workstations is to let the user work in the network environment, and run from a network file server provides a variety of application software. In a LAN Server generally only store shared data or files, and on the information or document to run and processing is accomplished by the workstation. ③ network switching interconnect devices. Including network adapters, modems, network transmission media, repeaters, hubs, bridges, routers and gateways, etc. ④ Firewall. Is on the intranet and Internet of the barrier between architecture, it is differentiated and the need to distinguish between Office setting conditional isolation devices to protect the intranet information, resources, and so are not affected by illegal from Internet users. ⑤ external devices. 　　Can be networked users shared, common hardware resources, such as a laser printer, drawing equipment and mass storage systems. (2) network software system
According to the role of the network software and features that put the network software is divided into network system software and network application software. Network system software is the control and management of network operation and network resources using the network software, it provides users with access to the network and operations network into the machine interface.　　Network application software is an application for a particular purpose and the development of network software. In the network system software, the most important is the network operating system, network operating system often determines the network properties, functions, types, etc.　　There are a variety of LAN network operating system, the most widely used mainly in Microsoft Windows, Novell Netware, Banyan VINES, and the company's UNIX, LINUX, etc.　　Network application software is the use of application software development platform developed some software, such as JAVA, ASP, Perl/CGI, SQL, and other professional software applications. 3. classification of the computer network is the computer network is mainly based on a particular aspect of the feature to be classified, usually have several classifications. Press coverage of the geographical scope, divided into the wide area network (also called remote Web), LAN (local network) and Wan (City area). Press communication rate, divided into low-speed Internet, medium-speed network and high-speed Internet. The topology of the network, is divided into the star network, bus-NET, ring network, tree, mesh and hybrid network. As the transmission medium, divided into twisted-pair network, coaxial cable, fiber, wireless media network and mixed media network. According to the information exchange, split into circuit switched, packet switched networks and integrated switching network. 　　By using range, divided into public and private networks. On a computer network, coverage and communication rate is most concerned about two issues, both of which are often contradictory, that is, the larger the network coverage, communication rate lower, network coverage, the higher communication speed.　　The following provides an overview of the common press covering geographical scope to share three of the network. (1) a WAN (Wide Area Network)
Also called a remote network, its characteristics are covered range from covering several cities to a national or even global. Wide area networks are generally the use of telecommunications or utilities existing public or private communication lines as a transport media, the network consists of multiple departments or more countries combined.　　1969 United States Department of Defense Advanced research projects Agency Organization, developed by APPA network was one of the wide area network, it has been from birth till today, not only over the American continent, and spans two Ocean extending into Europe, Asia, and the rest of the world, has become the world's largest wide area network, the Internet network. (2) LAN (Local Area Network)
It is in the local scope using the computer network, features, covering geographical scope is limited, relatively small, network computers and related equipment are typically limited to one unit, of a building or even an Office. Intranet, network construction time is short, low cost, flexible, economic and social benefits significantly.

LAN generally do not use public communication line, but specialized separate laying of own communication lines. It takes the transmission medium for the twisted pair, fiber optic cables in General.　　LAN transmission distance of more recent, but data transfer rate is very high, and low error rate. (3) the man (Metropolitan Area Network)
Metropolitan area network (MAN) usually cover a city or area, between the Wan and LAN, it is in the local area network developed on the basis of a new kind of network. As Internet users growing and constantly widening the field of application, General LAN has become too great, the new application requirements to multiple LANs connected together to form a greater coverage area, and support high-speed transmission and integrated business service, suitable for large cities are using computer network, thus forming a metropolitan area network.