外文资料(2)

The functions of computer network

The main function of the performance of the computer network resource sharing in hardware, software, resource sharing and information exchange between the three aspects of the user.

(1) hardware resource sharing. In the context of the entire network can provide processing

resources, storage resources, input and output resources, the sharing of expensive equipment, allowing users to save investment, but also easy to manage and share the load balanced.

(2) software resources sharing. Allows Internet users to get remote access to all major databases, can be the network file transfer services, remote process management services and remote file access service, thus avoiding duplication of software development on the duplication of storage and data resources, but also easy to focus on management.

(3) information exchange between users. Distributed computer network users around the powerful means of communication. Users can send email through computer networks, publishing news and e-commerce activities.

The composition and classification of computer network

More simply by a computer network is more than one computer (or other computer network equipment) and software through the transmission medium physical (or logical) connection with the composition. The composition is basically the whole computer network, including: computer, network operating systems, transmission media (which can be tangible or intangible, such as wireless network transmission medium is air) and the corresponding four-part applications. Although a variety of network types of classification standards, but from the geographical area is divided into a common network we all recognized criteria for the classification. By this standard can be divided into a variety of network types LAN, MAN, WAN and the Internet of four. Generally only a small local area network within the region, metropolitan area networking is different, but at this point to note here is that the network division is not strictly geographic distinction, can only be a qualitative concept. The following are brief details of these computer network.

1, LAN (Local Area Network; LAN)

Usually we often "LAN" means local area network, this is our most common, most widely used kind of network. Now the entire local area network computer network technology with the development and full

application and popularity of almost every unit has its own local area network, and some even have their own small home LAN. Obviously, the so-called local area network, that is localized within the network area it covered a smaller range. LAN configuration in the number of computers without much restrictions, little can be only two, and more up to several hundred. In general in the enterprise LAN, the number of stations to 200 units in dozens of times around. In the network the geographical distances involved in general can be a few meters to 10 kilometers. LAN are generally located within a building or a unit, there is no routing problems, the application does not include the network layer.

This network is characterized by: connecting narrow, less the number of users, configuration is easy, high speed connection. Currently the fastest rate of LAN today's 10G Ethernet to be considered a. IEEE 802 standards committee defined a variety of major LAN network: Ethernet (Ethernet), Token Ring (Token Ring), Fiber Distributed Interface Network (FDDI), Asynchronous Transfer Mode network (ATM) and the latest wireless local area network (WLAN).

2, MAN (Metropolitan Area Network; MAN)

This network is generally in a city, but not in the same geographical district within the computer Internet. The network connection can be 10-100 km distance, which is used in IEEE802.6 standard. MAN and LAN extension of the range compared to longer, more number of computers connected in the

geographical scope can be said to extend LAN network. In a large city or urban areas, a MAN network is usually connected to multiple LAN networks. Government agencies such as the connection LAN, the hospital's LAN, Telecom, LAN, the LAN, etc. companies. Since the introduction of fiber-optic connection to MAN in the high-speed LAN interconnection possible.

MAN uses ATM technology to do more backbone. ATM is used for data, voice, video and multimedia applications, high-speed network transmission method. ATM includes an interface and a protocol that can be a conventional transmission channel, bit rate change and changes in the traffic to switch between. ATM also includes hardware, software and protocol standards in line with the ATM

media. ATM backbone to provide a scalable infrastructure to be able to adapt to different size, speed and address of the Network. ATM's biggest drawback is the cost too high, it is generally in the MAN government applications, such as postal services, banks and hospitals.

3, the WAN (Wide Area Network; WAN)

This network is also known as remote network, the coverage ratio of MAN (MAN) wider, which is generally between different cities in the LAN or MAN network interconnection, geographic range from a few hundred kilometers to several thousand kilometers. Because of distance, information decay more serious, so this is generally to be leased-line network through the IMP (Interface Information Processing) protocol and the line connected to form network structure to solve the problem through the path. This MAN is because many users are connected, the total export of limited bandwidth, so the user's terminal connection rates generally lower, usually 9.6Kbps-45Mbps.

4, the Internet (Internet)

Internet has its English word "Internet" of harmonics, also known as "Internet." Internet applications such development today, it is our every day dealings with a network, whether from the geographical area, or from the network in terms of its size are the largest in a network is that we often say that the "Web" , "WWW" and "World Wide Web" and so it is called. From the geographical scope, it can be a global computer's Internet, this network is characterized by the greatest uncertainty, the entire network of computers all the time as people access the network in constant change. When you connect to the Internet when your computer can be part of the Internet, but once when you disconnect the Internet connection, your computer is not part of the Internet was. But its advantage is very clear is that large

amount of information, dissemination, regardless of where you are, as long as the Alliance on the Internet you can send to any available Internet users to your letters and advertising. Because of the complexity of this network, so this network of technology is very complex.

5, wireless network

With the laptop (Cnotebook compnter) and personal digital assistants (Personal Digital Assistant, PDA) such as the increasing popularity of portable computers and development of people on the road often receive phone calls, send faxes and e-mail read on-line information and log on to the remote machinery. However, in the car or the plane is not possible with the unit through the cable medium connected to the network, this time the wireless network may be interested. Although the wireless network and mobile communications are often linked, but the two concepts are not the same. For

example, when the portable computer PCMCIA card access through the phone jack, it becomes part of cable network. . On the other hand, some connected via the wireless network location of the computer may then be fixed, if not easy to connect by cable through the building the wireless network between two buildings will be connected to the computer.

Wireless networks, especially wireless LANs have many advantages, such as easy to install and use. But the wireless LAN is also much to be desired: If it's data transfer rate generally low, much lower than the wired LAN; other wireless LAN is also relatively high error rate, but also more serious mutual interference between sites. Users of wireless networks have different ways of realization. Some foreign universities in their campus to install a number of antennas, allowing students to sit under the tree view libraries. This situation is directly between two computers through a wireless LAN to communicate digitally implemented. Another possible way is to use a traditional analog modem to communicate