外文资料

computer network

The definition of computer network

Computer network refers to the geographical position of having individual functions, different sets of computer and peripheral equipment, communication lines through the link in the network operating system, network management software and network communications protocol management and coordination, resource sharing and messaging computer system.

On the computer network of the most simple definition is: a number of mutually connected to share resources for the purpose, a collection of autonomous computers.

The simplest computer network is only two computers and connect them to a link, that is, two nodes and a link. Because there is no third computer, and there is no exchange problems.

The largest computer network is the Internet. It consists of a lot of interconnected computer networks formed through many routers. So the Internet is also known as "network of networks."

In addition, media from a network point of view, the computer network can be viewed by multiple computers through a specific device and software to connect up a new media.

Development of computer network

The first generation of online computer networks --- remote terminal stage.

Second-generation computer --- computer network stage.

Third-generation computer network computer network interconnection stage.

Fourth-generation computer networks --- the Internet and information highway stage.

1, the first phase of 50 years can be traced back to the 20th century. Then people began to develop independently of each other's computer technology and communication technology combine to complete the data communication and computer communication network research, for the computer network and prepared the technical preparation, laid the theoretical foundation.

Second, the generation packet switching:

60 years of the 20th century, the Soviet Union during the Cold War, the U.S. Department of Defense Advanced Research Planning Agency-led proposal to develop a new ARPA network against attacks from the former Soviet Union's nuclear threat. Because at that time, the traditional circuit-switched

telecommunications network has been extending in all directions while, but during the war, once the communication circuit is a switch or link the bombing, then we must interrupt the communication circuit, such as to immediately switch to bypass the circuit, but also must re-dial a connection, it will be delayed for some time.

The new network must meet some basic requirements:

1, not to call, but for data transfer between computers.

2, can connect different types of computer.

3, all nodes are equally important, and this greatly enhanced network survivability.

4, computer communications, there must be circuitous route. When the link or node is destroyed, the circuitous route ongoing communication can automatically find the right route.

5, the network structure should be as simple as possible, but very reliable transmission of data.

According to these requirements, a group of experts to design a new computer using the packet switching network. Moreover, the use of circuit switching to the transmission of computer data, the lines are often very low transmission rate. Because computer data is a burst mode to appear in the

transmission line, For example, when users read the information on the terminal screen or keyboard input and edit a file or when the computer under processing and the results are not yet returned, valuable lines of communication resources will be wasted.

Store and forward packet switching technology is used. To send a message to one by one into the "group" in the network transmission. The first group is important to control information, so the

characteristics of packet switching is based on the tag.Packet switched network nodes by the number of switches and links connecting these switches form. Conceptually, a node switch is a small computer, but the host is for users of information processing, the node switches to packet switching. Each node has a two-port switch, one group is on the computer connected to the lower speed link. One group is in the high-speed link and the network switch is connected to other nodes. Note that, since the switch node is a computer, input and output ports that there is no direct connection between its process is: first, the

received packet into the cache, a temporary node switch is a short packet, while not the long message, short packet buffer memory in switches (ie, memory) instead of stored in the disk, which guarantees a high exchange rate. Then look forwarding to identify to a destination address from the port forwarding, then the exchange of bodies and handed the packet out the appropriate port forwarding. Between each node switches have regular exchange of routing information, but it is to carry out routing, when a certain link of communication is too big or interrupted, the switch node to run the routing protocol to automatically find another path forward group. Communication line utilization rate of resources to improve: When

grouped in a link, the other segment of the communication link is not being currently occupied by the two sides to communicate, even this link, this link only if the group is occupied only when sending In the idle time between packet transmission, the link can send a packet by the other host. Shows using store and forward packet switching is essentially used in the process of data communication bandwidth dynamic allocation strategy.

Third, the Internet age

Internet infrastructure has undergone three stages of evolution, these three stages overlap in time there.

1, from a single network ARPAnet to the development of the Internet: U.S. Department of Defense in 1969 founded the first ARPAnet packet switching network is only a single packet switching network to connect all its hosts are directly connected to the nearest switch node, it scale up quickly to mid-70s, it was recognized that using only a single network can not meet all the communication problems. Then began to study a lot of ARPA network interconnect technology, which led to the subsequent emergence of the Internet. 1983 TCP / IP protocol known as the ARPAnet standard protocols. In the same year, ARPAnet into two networks, a pilot study with the research network ARPAnet, the other is the military's computer network MILnet. 1990, ARPAnet officially announced the completion of the task by trial closure. 2, the establishment of the tertiary structure of the Internet: In 1985, the United States National Science Foundation NSF recognized the importance of scientific research computer network. In 1986,

NSF computer centers around the six large computer network NSFnet, it is a three network,

sub-backbone, regional network, campus network. It replaces the ARPAnet as the main part of the internet. 1991, NSF and the U.S. government recognized that the Internet will not be limited to

universities and research institutions, thus supporting local network access, many companies have

joined the network dramatically increase the amount of information the U.S. government decided to turn the Internet's backbone network to private company, and began a unit on Internet access charges. 3, the formation of multi-level structure of the Internet: In 1993, the U.S. government-funded

NSFnet on gradually a number of commercial Internet backbone substitution, This is also called Internet backbone providers, supporting ISP. Taking into account the possible commercialization of the Internet a lot of ISP, in order to run different ISP interconnection between networks, created in 1994, the network access point NAP 4 4 telecom companies were operating, Beginning of this century, the United States NAP reached a dozen. NAP is the most senior of the access point, it is mainly a different ISP to provide switching equipment, is that they communicate with each other. Now the Internet has been very difficult to give a very fine network structure of its description, but can be divided into five access levels: network access point NAP, a number of countries operated backbone, regional ISP, local ISP, the campus network, business or home PC, Internet users.