Computer Network (1)-Basic Concepts of Computer Network

1. Introduction to Computer Network

1.1 Concept

Networks include many types, such as computer networks, telephone networks, and human neural networks.

Computer network : It is a decentralized computer system with independent functions , which is connected with lines through communication equipment, and a system that realizes resource sharing and information transmission by software with perfect functions.

A computer network is a collection of interconnected, autonomous computers.
Interconnection : interconnection, communication link
autonomy : no master-slave relationship

1.2 Function

Data communication (connectivity): transfer files, pictures
Resource sharing : hardware, software, and data sharing
Distributed processing: Multiple computers each undertake different parts of the same task, such as the Hadoop distributed platform.
Improve reliability: Use alternative machines to ensure high availability.
Load balancing: All computers work together to complete the same task.

1.3 Composition

Classified by composition : hardware (host, link, communication equipment), software (qq, WeChat, Kugou, ftp), protocol (core of computer network)

Classified by working method : edge part (users directly use [C/S mode P2P method]), core part (provide services for the edge part)

Classified by functional composition : resource subnet (to realize resource sharing and data processing), communication subnet (to realize data communication)

OSI seven-layer network model: physical layer, data link layer, network layer, transport layer, session layer, presentation layer, application layer

The first three layers : belong to the communication subnet, which consists of various transmission media, communication equipment, and corresponding network protocols.
The last four layers : a collection of equipment and software that belong to the resource subnet and realize resource sharing functions.

1.4 Classification

Classified by distribution range : wide area network WAN (switching technology) [transnational], metropolitan area network MAN [city], local area network WAN (broadcasting technology) [about 1km], personal area network PAN [smart phones, smart watches]

Classified by user : public network [China Telecom China Mobile], private network [military, government]

Classified by switching technology : circuit switching, message switching, packet switching

Classified by topology : bus type, star type, ring, mesh type [commonly used in wide area networks]

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Classified by transmission technology : broadcast network ( shared common communication channel , one-to-many), point-to-point network (using packet storage and forwarding and routing mechanism, one-to-one)

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2. Standardization of computer networks

To realize the interconnection between the hardware and software of different manufacturers, a unified standard must be followed.

① Statutory standards : formal and legal standards formulated by authoritative organizations. Such as OSI.

②De facto standards : As certain companies' products occupy the mainstream in the competition, the technologies and agreements in the products form standards. Such as TCP/IP protocol.

RFC (request for comments) rose to an Internet standard procedure:
① draft (Internet Draft) Internet : from their own draft, send mail.
② proposed standard (Proposed Standard) : receive a reply, draft a standard recommendations. This is an RFC document.
③Draft Standard (Draft Standard) : Public comments on revisions and corrections. [This step is now canceled]
④Internet Standard (Internet Standard) : It is reviewed and published as an Internet standard by IETF and IAB.

Related organizations:
①International Organization for Standardization IOS : OSI reference model, HDLC protocol
②International Telecommunication Union ITU : designated communication rules ③International
Institute of Electrical and Electronic Engineers IEEE : academic institutions, IEEE802 series standards, 5G
④Internet Engineering Task Force IETF : responsible for Internet related standards The designation determines whether the RFC document becomes an Internet standard.