one. Computer network concept:
With the development of the computer network itself, people have put forward various different views.
Early computer systems were highly centralized, all devices were installed in separate large rooms, and later batch processing and time-sharing systems appeared, and multiple terminals connected to the time-sharing system must follow the host computer. In the mid-to-late 1950s, many systems connected geographically dispersed terminals to a central computer through communication lines, thus gaining the first generation of computer networks.
The first generation of computer networks are remote online systems centered on a single computer. A typical application is an aircraft ticketing system consisting of a computer and more than 2,000 terminals across the United States.
Terminal: The external devices of a computer include a CRT controller and a keyboard, without GPU memory.
With the increase of remote terminals, front-end FEP was added in front of the host. At that time, people defined the computer network as a system that connects to transmit information to realize telematics or achieve resource sharing in a near future, but such communication systems have already had the prototype of communication.
The second-generation computer network is interconnected through communication lines to provide services to users. It emerged in the late 1960s. It is typical of the ARPAnet developed by the U.S. Department of Defense Advanced Research Projects Agency.
The hosts are not directly connected by lines, but are interconnected after the interface message processor IMP is forwarded. IMP and the interconnected communication lines are responsible for communication tasks between the hosts, forming a communication subnet. The host of the communication subnet interconnection is responsible for running programs, providing resource sharing, and forming a resource subnet.
The understanding of the content of the transmitted information when communicating between two hosts, the information representation form and the response signals in various situations must abide by a common agreement, called a protocol.
In the ARPA network, protocols are divided into several levels according to their functions, how to layer them, and the sum of the protocols specifically adopted in each layer are called network architecture. Architecture is an abstract concept, and its specific implementation is completed through specific hardware and software.
The second-generation network developed rapidly from the 1970s to the mid-1980s.
The second generation network is centered on the communication subnet. During this period, the concept of network was "a collection of independent functions connected to the purpose of sharing resources with each other", forming the basic concept of computer networks.
The third generation computer network is an open and standardized network with a unified network architecture and complies with international standards.
IS0 promulgated 0SI/RM in 1984. This model is divided into seven levels, also known as the 0SI seven-layer model, which is recognized as the basis of the new generation of computer network architecture. Laid the foundation for popularizing LANs.
After the 1970s, due to the emergence of large-scale integrated circuits, local area networks have been widely used and developed rapidly due to their low investment and flexibility. Compared with wide area networks, such as hierarchical architectures and different characteristics. For example, LANs do not use storage and forwarding to save costs, but connect online computers by a single broadcast channel.
The fourth-generation computer network began in the late 1980s, and local area network technology developed maturely, with fiber optic and high-speed network technologies, multimedia, and intelligent networks emerging. The entire network is like a large computer system that is transparent to users, and has developed into an Internet represented by the Internet. Computer network: A system that realizes resource sharing and data communication through multiple computer systems with independent working capabilities through communication equipment and network software with complete line functions.
From the definition, there are three issues involved:
(1) At least two computers are connected.
(2) Communication equipment and line media.
(3) Network software, communication protocol and NOS
two. Category of computer networks:
There are many standards used for computer network classification, such as topology structure, application protocols, etc. However, these standards can only reflect the characteristics of a certain aspect of the network. The classification standard that best reflects the essential characteristics of network technology is distribution distance, which is divided into LAN, MAN, WAN, and INTERNET according to the distribution distance.
1. local area network:
A few meters - 10 kilometers. A small computer developed after a large number of promotions of microcomputers. It has easy configuration and high speed, 4Mbps - 2GbpS. Located in a building or unit, there is no path search problem and does not include the network layer.
2. Urban Network:
10 kilometers - 100 kilometers For a city's LAN interconnection, it adopts IEEE802.6 standard, 50Kbps - l00Kbps, located in a city.
3. WAN:
Also known as a remote network, hundreds of kilometers - thousands of kilometers. It developed earlier, rented dedicated lines, connected by IMP and line, forming a mesh structure, solving the diameter problem, with a speed of 9.6Kbps-45Mbps, such as: CHINANET, CHINAPAC, and CHINADDN networks of the Ministry of Posts and Telecommunications.
4. internet:
It is not a specific network technology, it is a high-level technology that unifies different physical network technologies according to a certain protocol.