Overview of computer networks

1. What is a computer network?

The computer network connects two or more computers through cables or network devices, and information exchange and resource sharing between them has been achieved.

There are other ways to exchange information between computers. Most people have used the most primitive "manual network" approach, that is, copying files to a USB flash drive and then copying them to other computers, the problem with "manual network" is that the speed is too slow, coupled with the use of an increasingly large U disk to copy files. One day, computer players found that networking was much faster than copying files between computers using USB flash drives. As a result, modern computers are born.

So what is computer network? Connect the communication devices and lines in different geographic locations, operate relatively independent computers, and configure the corresponding system and application software, A computer network is a system formed by sharing hardware resources and transferring information between independent computers.

A network is a virtual platform for information transmission, receiving, and sharing. It associates information of various points, faces, and bodies to share these resources. It is a tool used by people to communicate information. As a tool, it will become increasingly useful. There will be more and more functions and more content. The network uses software tools such as text reading, image viewing, audio and video playback, download and transmission, and game chat, and other aspects to bring people an extremely rich and beautiful use and enjoyment. The Network is also a channel for resource sharing, but it is a tool for humans after all. I believe that one day, with the help of software tools, the network will bring people extremely beautiful and even better than what the human body can bring. For example, with the help of software tools, people can enter the network platform with an extremely real appearance, feel the health and death, play and entertainment, get married and have children, etc. But these are just enriching people's lives and cannot replace people's lives. They can only imitate people's feelings, not replace people's feelings. Online transactions of virtual products can be directly realized, such as the purchase, transmission, transmission, and receipt of text and audio/video. However, even things larger than sesame seeds must be delivered by people. This is the limit of network development. It can surpass people in terms of virtual and sensory aspects, but it will never replace people in terms of physical feelings.

1. Data Communication

In modern society, the amount of information is surging and information exchange is also increasing. The use of networks to transmit various types of information and data is more resource-saving and efficient than traditional methods. In addition, voice can also be transmitted through networks, images and videos for multimedia communication.

2. Resource Sharing

There are many expensive resources in computer networks, such as large databases and giant computers, which are not owned by every user. Therefore, resource sharing must be implemented. Resource Sharing includes hardware sharing, such as printers and large-capacity disks, as well as software resource sharing, such as programs and data. The purpose of resource sharing is to avoid repeated investment and labor, thus improving the resource utilization and improving the overall cost-effectiveness of the system.

3. Increased reliability

In a system, the temporary failure of a single part or computer must be maintained by replacing resources, but in the computer network, each resource, especially the program and data, can be stored in multiple points, and users can access a certain resource in the network through multiple channels, this avoids the impact of spof on users.

4. Improve system processing capability

The processing capability of a single machine is limited. After multiple computers are connected, the idle time between computers is uneven due to various reasons (such as time difference. Theoretically speaking. Multiple computers in the same network can improve the processing capability of the entire system through collaborative operations and parallel processing, so that various computers in the network can achieve load balancing.

Ii. History of computing network development

1. The first phase of Computer Network Development

In 1960s, standard technology: group exchange technology.

2. The second stage of computing Development

In late 1970s and early 1980s, standard technology: TCP/IP protocol.

3. The third stage of computer development

In the middle of 1990s, standard technology: Web technology.

III. Basic concepts of computer networks

Network protocols and standards

1. Protocol

Protocols and standards. protocols can be understood as rules, and standards can be understood as rules of consistent acceptance.

Syntax: refers to the structure and form of data, that is, the sequence of data transmission.

Semantics: Meaning refers to the meaning of each part. It defines how each part of data is interpreted and how to act based on this interpretation.

Synchronization: determines when data is sent and how often data is sent,

2. Standards

We can understand network communication protocols as dialects and standards as Mandarin.

Most of these standards are developed by organizations in North America, including:

ISO (International Standardization Organization)

Ansl (US National Standardization Administration)

ITU-T (International Telecommunication Union-Telecommunications Standardization Bureau)

IEEE (Institute of Electrical and Electronics Engineers)

Network protocols and standards are of great guiding significance and must be observed by people in the industry.

3. The IEEE802 LAN Standard defines how the network adapter accesses the transmission media, such as the commonly used twisted pair wires, optical fiber cables, and unlimited data transmission methods,

1. 802.3

It defines four 10 Mbps Ethernet specifications for different media, including Ethernet standards using twisted pair wires-10base-t, which will soon become the preferred Ethernet standard for office automation applications

In the next few years, the rapid development of Ethernet, and the exit of 802.3, are as follows:

IEEE 802.3u standard and 10-Gigabit Ethernet standard

IEEE 802.3z standard, fiber optic medium for Gigabit Ethernet specifications

IEEE 802.3ab standard and twisted pair wires enable Gigabit Ethernet standard specifications

Eee802.3ae standard optical fiber medium for 10 Gigabit Ethernet specifications

IEEE 802.3an standard, twisted pair wires enable 10-Gigabit Ethernet specifications

802.11

He became the first wireless LAN Standard mainly used for wireless access between office and campus LAN user terminals.

With the development of IEEE, a series of new standards are introduced as follows:

The IEEE 802.11aeee802.11 standard has a carrier frequency of 5 GHz and a communication rate of up to 54 Mb/s. Currently, this standard is basically not used in wireless networks.

IEEE802.11b is a widely used wireless LAN standard. Most wireless devices still support this standard, with a carrier rate of 2.4 GHz and a communication rate of up to 11 Mb/s.

 

Ieee802.11g is currently widely used in Wireless LAN standards, with a carrier rate of 2.4 GHz and a maximum communication rate of 54 Mb/s. It can be compatible with IEEE802.11b.

Ieee802.11n is a standard widely used in the draft phase. Many products that support the ieee802.11n standard come out of "premature birth. This is mainly because it has the following three advantages:

1. In terms of transmission rate, thanks to the development of MMO [multiple inputs and multiple outputs] technology, ieee802.11n can reach up to 600 Mb/s, 50 times that of IEEE802.11b, and more than 10 times that of ieee802.11g.

2. In terms of coverage, ieee802.11n uses smart antenna technology to improve signal stability, reduce signal interference, and expand its coverage to several thousands of meters.

3. in terms of compatibility, ieee802.11n adopts a software-based wireless technology to achieve interoperability and compatibility with different software. Currently, ieee802.11n is not only compatible with the standards of all wireless LAN, in addition, it can be combined with wireless wide area networks (WANs), such as 3G.

This article is from the blog of "Liu Jinhua's blog" and will not be reproduced!