The simplest definition of computer network is: a collection of interconnected and autonomous computers for the purpose of * * * enjoying resources [TANE96]. The simplest computer network has only two computers and a link connecting them, namely, two nodes and a link. Because there is no third computer, there is no replacement problem. The largest computer network is the Internet. It consists of many computer networks interconnected by many routers. [1] Therefore, the Internet is also called "the network of networks". In addition, from the perspective of network media, computer network can be regarded as a new media that is connected by multiple computers through specific equipment and software.

Edit this development process

The first generation computer network-remote terminal online stage, the second generation computer-computer network stage, the third generation computer network-computer network interconnection stage, the fourth generation computer network-Internet and information superhighway stage.

The first stage can be traced back to the 1950s.

At that time, people began to combine computer technology and communication technology, which developed independently from each other, and completed the research on data communication and computer communication network, which made technical preparations for the emergence of computer network and laid a theoretical foundation.

Generation of double packet switching

In the 1960s, during the Cold War between the United States and the Soviet Union, ARPA, a forward-looking research and planning agency led by the US Department of Defense, proposed to develop a brand-new network to deal with the threat of nuclear attack from the former Soviet Union. Because at that time, although the traditional circuit-switched telecommunications network had extended in all directions, during the war, once a switch or link of the circuit being communicated was blown up, the whole communication circuit would be interrupted. If you want to use other circuitous circuits immediately, you must redial to establish the connection, which will delay some time. This new network must meet some basic requirements: 1: It is not used for telephone calls, but for data transmission between computers. 2. You can connect different types of computers. 3. All network nodes are equally important, which greatly improves the survivability of the network. Computers must have circuitous routes when communicating. When a link or node is broken, circuitous routing can make the ongoing communication automatically find a suitable route. 5. The network structure should be as simple as possible, but the data transmission should be very reliable. According to these requirements, a group of experts designed a new computer network using packet switching. Moreover, the computer data transmission rate of circuit switching is often very low. Because computer data suddenly appears on the transmission line, for example, when the user reads the information on the terminal screen or inputs and edits files with the keyboard, or when the computer is processing and the result has not returned, valuable communication line resources are wasted. Packet switching adopts store-and-forward technology. Messages to be sent are divided into "packets" and transmitted in the network. The header of a packet is important control information, so the characteristics of packet switching are label-based. A packet-switched network consists of several node switches and links connecting these switches. Conceptually, a node switch is a small computer, but the host handles information for users and the node switch performs packet switching. Each node switch has two groups of ports, one is connected to the computer, and the link speed is low. A group of switches connected to other nodes in the network through high-speed links. Note that since the node switch is a computer, there is no direct connection between the input and output ports. The processing process is as follows: firstly, the received message is put into the cache, and the node switch temporarily stores the short message instead of the long message, and the short message is temporarily stored in the memory of the switch instead of the disk, thus ensuring a high switching rate. Then look up the forwarding table to find out which port to forward to the destination address, and then the switching organization will hand over the packet to the appropriate port for forwarding. Node switches also need to exchange routing information frequently, but this is for routing. When the traffic of a link is too large or interrupted, the routing protocol running on the node switch can automatically find other paths to forward packets. The utilization ratio of communication line resources is improved: when the data packet is on a certain link, the communication links of other segments are not occupied by the two parties currently communicating, and even the link is occupied only when the data packet is transmitted on this link, and the link can still be sent by other hosts during the idle time of data packet transmission. It can be seen that the essence of packet switching using store-and-forward is the strategy of dynamically allocating transmission bandwidth during data communication.

Third, the Internet age.

The basic structure of the Internet has generally experienced three stages of evolution, and these three stages overlap in time. internet

1: From a single network ARPAnet to the Internet: 1969 The U.S. Department of Defense created the first packet-switched network ARPAnet, which is just a single packet-switched network. All the hosts that want to connect to it are directly connected to the nearest node switch, and its scale is growing rapidly. By the mid-1970s, people realized that only a single network could not meet all communication problems. So ARPA began to study many technologies of network interconnection, which led to the emergence of the Internet. 1983 TCP/IP protocol is called the standard protocol of ARPAnet. In the same year, ARPAnet was divided into two networks, ARPAnet is a scientific research network for experimental research and MILnet is a military computer network. 1990, ARPAnet was officially closed due to the completion of the test task. 2. Establish a three-tier structure of the Internet: Starting from 1985, the National Science Foundation NSF of the United States recognized the importance of computer networks to scientific research. 1986, NSF built a computer network NSFnet around six large computer centers, which is a three-layer network, divided into backbone network, regional network and campus network. It has replaced ARPANET as the main part of the Internet. 199 1, NSF and the US government realize that the Internet will not be limited to universities and research institutions, so they support local network access. Many companies have joined in, greatly increasing the amount of information on the network. The U.S. government decided to hand over the backbone of the Internet to private companies, and began to charge units that access the Internet. 3. Formation of multi-level Internet: Since 1993, NSFnet funded by the US government has been gradually replaced by several commercial Internet backbones, also known as Internet auxiliary providers. Considering that there may be many ISPs after the commercialization of the Internet, in order to make the networks operated by different ISPs interoperable, four network access points NAP were established at 1994, which were operated by four telecom companies respectively. At the beginning of this century, NAP was the most advanced access point, which mainly provided switching equipment to different ISPs so that they could communicate with each other. It is difficult to describe its network structure in detail now, but it can be roughly divided into five access levels: network access point NAP, national backbone network operated by several companies, regional ISP, local ISP, campus network, enterprise or home PC users.

Edit this paragraph function

The function of computer network is mainly manifested in three aspects: hardware resource sharing, software resource sharing and information exchange between users. (1) Hardware resources * * *. It can provide exclusive access to expensive equipment such as processing resources, storage resources, input and output resources and so on. In the whole network, users can save investment, and it is also convenient for centralized management and balanced load sharing. (2) Software resources * * *. Users on the Internet are allowed to remotely access various large databases, and they can obtain network file transfer service, remote process management service and remote file access service, thus avoiding repeated labor and data resources storage in software development and facilitating centralized management. (3) Information exchange between users. Computer network provides powerful communication means for users distributed everywhere. Users can send emails, publish news messages and conduct e-commerce activities through computer networks. Computer Network Overview Computer network refers to a computer system that connects multiple computers with independent functions in different geographical locations and their external devices under the management and coordination of network operating system, network management software and network communication protocol to realize resource sharing and information transmission. Simply put, a computer network is a collection of two or more computers interconnected by cables, telephone lines or wireless communication. The development of computer network has gone through three stages: terminal-oriented single-stage computer network, computer-to-computer network and open standardized computer network. Generally speaking, a computer network is formed by physically (or logically) connecting multiple computers (or other computer network devices) through transmission media and software. Generally speaking, the composition of computer network basically includes four parts: computer, network operating system, transmission medium (tangible or intangible, such as invisible electromagnetic waves in wireless network) and corresponding application software. The definition is very simple: a network is a group of computers connected in some form. A network can consist of two computers or thousands of computers and users in the same building. We usually call such a network a local area network, which extends to a larger area, such as the whole city or even the whole country. Such a network is called a wide area network. Of course, if you want to divide it carefully, there can also be MAN (Metropolitan Area Network) and ANC (Metropolitan Area Network), and these networks need to be maintained by special managers. And the Internet, which we contact most often, is composed of countless local area networks and wide area networks. Internet only provides the connection between them, and there is no special person to manage it (except for maintaining the connection and formulating the use standard). It can be said that the Internet is the freest and most unregulated place. There is no distinction between national boundaries and races on the Internet. As long as you are connected to the internet, the computer on the other side of the world is actually no different from your roommate's computer. Because we still use the local area network most often (even if we connect to the Internet from home, we actually connect to the ISP's local area network first), so here we mainly discuss the local area network. Local area network can be said to be the most basic unit in many networks. When you have a certain understanding of the local area network, it will be easier to understand the wide area network and the Internet, but you just need to know more and more complicated communication means. Internet? Intranet? External network? Friends who have been exposed to the internet should have heard the above nouns more or less, right? However, do you know the difference between them and how to define them? In fact, the earliest term should be Internet. Later, people introduced the concept and skills of Internet into the internal private network, which can be an independent local area network or a dedicated wide area network, so it was called Intranet. The biggest difference between the two is openness. The Internet is open and belongs to no one. As long as you can connect, you belong to one of them, and you will also get the open resources on it. Relatively speaking, the intranet is exclusive and non-open. It often exists on the private network, but its structure, service mode and design all refer to the model of the Internet.

Edit the composition and classification of this paragraph.

Generally speaking, a computer network is formed by physically (or logically) connecting multiple computers (or other computer network devices) through transmission media and software. Generally speaking, the composition of computer network basically includes four parts: computer, network operating system, transmission medium (which can be tangible or intangible, such as the transmission medium of wireless network is air) and corresponding application software. To learn the network, we must first understand the current main network types, and distinguish which ones are necessary for our junior scholars and which ones are the current mainstream network types.