Basic knowledge and terminology of computer network (1)

1. Overview of Computer Networks

1.1 Definition

Computer network : Also called computer communication network. It is a decentralized and independently functionalcomputer system, implemented by well-functioning network software and protocolsResource SharingandInformation transfersystem.

Simply put, a computer network is a collection of autonomous computers that interconnect two or more computers through communication links (cables, phone lines, or wireless communications) for the purpose of sharing resources.

1.2 Function

1. Data communication (data transmission): One of the basic functions of computer networks, used to realize data transmission between computers, the transmission of information and files, etc.

2.Resource Sharing: Other computers on the same computer network can use the resources of a certain computer and can be shared

• Hardware (typical server rental, cloud computing, printer usage, etc.)
• Software (remotely access the host using various APPs or client applications, etc.)
• Data resources (such as Baidu Library resources use)

3. load balancing: Work is evenly distributed to each computer system on the network.

Multiple servers form a server set in a symmetrical manner. Each server has an equal status and can provide external services independently without the assistance of other servers. Through some kind of load sharing technology, requests sent from the outside are evenly distributed to a certain server in the symmetric structure, and the server that receives the request responds to the customer's request independently.

Features:
1. Ability to automatically detect system load conditions, server failures , and remove corresponding tasks from failed servers . 2. Ability to support multiple load balancing strategies , such as polling, weighted polling, least connections, etc. 3. It can improve the availability and reliability of the system , because even if one of the servers fails, the other servers can still continue to provide services (replacement machines).

distributed processing: In a network system, several structurally independent computers can cooperate with each other to complete the processing of the same task.

Features:
1. Distributed processingCan improve the operating efficiency of the system.
2. Compared with parallel systems, it hasHigher resource utilization and throughput, because parallel systems can only use at most one set of processors, while distributed systems can use multiple processors.
3. More efficient than parallel systemsEasy to expand, because parallel systems can only scale up to a certain number of processors (e.g., 8), while distributed systems can connect a large number of processors (e.g., thousands).
4. More efficient than parallel systemseasy to build, because parallel systems require high-speed interconnection and synchronization mechanisms, while distributed systems can use existing communication networks.

4. Centralized management: Through various management systems, daily work management and information organization and storage are realized. Reduces management difficulty and management costs.

5. Comprehensive information services
By improving performance, distributed processing and rational selection of network resources, computer networks provide the most essential functions for network users, avoid system paralysis and improve system reliability.

develop:

1.3 Phase 1

1.3.1 ARPANET

A computer network established in 1969 by the U.S. Department of Defense's Advanced Research Projects Agency (ARPA)The earliest global packet switching network. Initially there were only four nodes,
features :
1. Basically aWan, is the ancestor of the global Internet.
2. usedpacket switched networkthe concept of.
3.UseInterface Message Processor (IMP) for subnetting.
4.ARPANETs software is divided into two parts - host and subnet.
For collaboration via email.
Advances have been made in the transfer of important documents and defense data.
5. Multiple nodes communicate together (decentralized command system). Each node is connected to many different terminals. The damage of a certain node will not affect the communication of the entire network.

Limitations :
Increasing number of local area network (LAN) connections leads to processing difficulties.
Can only connect to the same type of network

1.3.2 Internet

Developed on the basis of ARPANET, it is a global network collection composed of many networks, including ARPANET. Realized the interconnection of different networks.

1.3.3 Internet

A larger, broader concept that includes all of the Internet, as well as some internal private networks. The Internet is often used to represent a global, open collection of networks. The World's Largest Internet
Technically, the Internet is a type of Internet, but the Internet is larger than the Internet in terms of size and influence.

In short, ARPANET is the predecessor of the Internet, and the Internet was developed on the basis of ARPANET and the Internet and includes all network collections.

1.4 The second stage----Three-layer network structure

1.5 The third stage—multi-level ISP structure

1.5.1 Definition (ISP and ICP)

The full name of ISP is Internet Service Provider. Internet service provider/provider is a company that comprehensively provides Internet access services, information services and value-added services to a wide range of users. Such as China Telecom, China Unicom, China Mobile, etc.
ISP can assign IP to users

ICP (Internet Content Provider) refers to an Internet content provider, which refers to a content provider that provides various information, entertainment, interactive and other services on the Internet. ICP usually needs to provide users with rich content, such as news, music, movies, games, education, etc., and also needs to maintain its own infrastructure such as websites, servers and applications.

ICP usually needs to provide users with rich content, such as news, music, movies, games, education, etc., and also needs to maintain its own infrastructure such as websites, servers and applications. Non-commercial websites only need to apply for ICP registration.

1.5.2 Classification

ISPs can be divided into three types:

Tier 1 ISP ( Backbone ISP ): This type of ISP mainly connects to remote computers through communication lines, and then connects to the Internet through the remote computers.
Second-tier ISP ( regional ISP ): In addition to providing the services of the first-tier ISP, this type of ISP can also connect to the networks of other ISPs by setting up trunk lines.
Layer 3 ISP ( local ISP ): In addition to providing the services of the first and second tier ISPs, this type of ISP can also connect to the networks of other ISPs by setting up routes.

1.5.3 Main features of ISP

1.Provide a variety of Internet services: ISP can provide a variety of Internet services, such as: domain name registration, virtual hosting, server rental, server hosting, cloud server, website construction, website promotion, corporate email, online marketing, software development, etc.
2. ownRich network resources: ISP has abundant network resources, including bandwidth, servers, computer rooms, etc. These resources can meet the needs of different users.
3.Provide security: ISP provides a variety of security measures, such as firewalls, intrusion detection systems, etc., to protect user data security.
4. ProvideFast response speed: ISP provides fast response speed, which can meet users' needs for fast response.
5. ProvideComprehensive technical support: ISP provides comprehensive technical support to solve various problems that users encounter when using Internet services.

1.5.4 Internet Exchange Point IXP

Is a physical infrastructure that allows different Internet service providers to exchange Internet communications between their automated systems through peer-to-peer protocols.
IXPs are typically used by ISPs to reduce dependence on their respective upstream providers; in addition, they are used to increase power and fault tolerance.
Features :
Allows two networks to be directly connected, no third network is needed to convert packets (hosts A and B in the figure avoid multi-layer ISP transfer), greatlyImproved resource sharing and information transfer speed。

2. Computer network composition

2.1 Divide by component equipment

The specific equipment introduction will appear at the corresponding OSI model level later. Here is a general understanding.

2.1.1 Hardware

end

Refers toa device on the network, such as a computer or server. End-to-end communication, such as communication between host a and host b, refers to a process on host A communicating with another process on host B.

End systems can include computers, servers, etc. that provide resources, while end-to-end communication refers to communication between hosts.

End system (host)

Point toAll hosts on the Internet. An ordinary personal computer , small server or some large computers, they are the networkTerminal device, responsible for receiving and sending data, and can be upgraded and expanded to improve performance and expand functionality.

End systems typically communicate with other hosts through network protocols (such as TCP/IP) and can access servers or other devices over the network.
End systems include: desktop computers (desktop PCs, Macs, and Linux boxes), servers (web and email servers), and mobile computers (laptops, smartphones, and tablets).

network card

Also called a network adapter, it is an interface that connects a computer and transmission media;

network cable

It is used to connect various devices in the network. Common cables include twisted pairs, optical fibers, telephone lines, etc.;

Internet equipment

Including switches, routers, modems, etc., which are terminal devices that send or receive data.

2.1.2 Network operating system

Common network operating systems include: Windows, Linux, etc.

Windows operating system: As computer hardware and software systems continue to upgrade, Microsoft's Windows operating system is also constantly upgraded, from 16-bit, 32-bit to 64-bit operating systems. It has the characteristics of multi-user and multi-tasking, and supports multiple processor architectures.
Linux operating system: It is an open source network operating system that can be installed on various computer hardware devices, such as mobile phones, tablets, routers, video game consoles, desktop computers, etc.

2.1.3 Network protocols

Computer network protocols are a set of rules for computer network communications , or rules, conventions and standards developed to complete computer network communications .
Common network protocols include the following:

应用层：应用层是网络协议最高的一层，包括各种应用程序，例如电子邮件、网络浏览器等。
作用：提供应用程序间的通信和交互，如HTTP、FTP、SMTP等。
传输层：传输层是网络协议的中间一层，主要是为了提供可靠的数据传输服务，例如TCP协议等。
作用：提供端到端的数据传输服务，如TCP、UDP等。
网络层：网络层是网络协议的核心一层，主要是为了实现网络之间的通信，例如IP协议等。
作用：实现不同网络之间的通信，如IP、ICMP等。
数据链路层：数据链路层是网络协议的底层，主要是为了实现同一网络内部的通信，例如以太网协议等。
作用：实现同一网络内部的通信，如以太网协议等。

TCP（Transmission Control Protocol）

is a kind ofReliable and connection-orientedtransport protocol, canRealize functions such as reliable transmission and flow control of data packets。

UDP（User Datagram Protocol）

is a kind ofunreliable connectionless protocol，Fast data transfer can be achieved, but there may be problems such as data loss。

• Connectionless service
  means that the communicating parties do not need to establish a communication line in advance . Instead, each packet (message group) with a destination address is sent to the line, and the system independently selects a route for transmission.

• Connection-oriented service
  When communicating, both parties must establish a communication line in advance . The process includes three processes: establishing a connection, using the connection and releasing the connection.

HTTP（Hypertext Transfer Protocol）

A protocol used to transmit hypertext , which can enable operations such as web browsing and file downloading.

HTTPS（Hypertext Transfer Protocol Secure）

It is a secure HTTP protocol that can implement functions such as encrypted transmission and identity verification. It is commonly used in websites such as banks and e-commerce.

FTP（File Transfer Protocol）

A sort ofProtocol used for file transfer, files can be transferred between different devices over the network.

SMTP（Simple Mail Transfer Protocol）

is a kind ofProtocol used to send email, which can realize email transmission between different devices.

POP（Post Office Protocol）

is a kind ofreceive emailA protocol that allows users to receive mail from a mail server.

IMAP（Internet Message Access Protocol）

is a kind ofAgreement for receiving and sending email, which can synchronize emails and manage folders between different devices.

P2P（Peer-to-Peer）

is a kind ofpoint-to-point transmission protocol, which can realize direct communication and resource sharing between different devices.

IM（Instant Messaging）

is a kind ofinstant messaging protocol, which can realize instant message transmission and chat between different devices.

These network protocol software can help communication and data transmission between computers, and realize data sharing and exchange between different devices.

2.1.4 Network management software

Network management software is a network management system that can complete network management functions and can help network administrators monitor, manage and maintain the network.
Common network management software include the following:

Network monitoring software: It can monitor equipment, traffic, faults and other information in the network, helping network administrators to discover and solve problems in a timely manner.
Network management software: can manage equipment, protocols, configuration and other information in the network, helping network administrators manage and maintain the network.
Network diagnostic software: It can diagnose and test devices, connections, faults, etc. in the network, helping network administrators quickly locate and solve problems.
Network tool software: It can provide some user-friendly tools, such as network calculator, time synchronizer, remote control, etc.

These network management software can help network administrators monitor, manage and maintain the network, and improve the stability and security of the network.

2.1.5 Network application software

It is software used to help users complete daily tasks, such as web browsers, email clients, instant messaging software, online games, online videos, etc.

2.2 Classification based on working methods

2.2.1 Edge part

In the Internet, the edge segment consists of all hosts (end systems) connected to the Internet, including desktop computers, laptops, tablets, smartphones, etc.

Communication method between processes

1.C/S（Client/Server）

client to serversend request, the server receives the request andReturn data, the communication between the client and the server is based on the network, and usually requires downloading client software such as QQ, WeChat and so on. C/S presents a relationship between service and being served .

限制：由于资源有限，请求的人数越多，数据传输越慢。

C/S communication methodIs a typical computer network architecture model, itsstructureas follows:

Client : The client sends a request to the server, and the server receives the request and returns data. The communication between the client and the server isweb basedof. The client needs to install the corresponding client software to be able to communicate with the server.
Server side : The server side needs to start a service, listen to the specified port, and wait for the client's connection request. When the client initiates a request, the server will establish a socket connection to communicate with the client, and then both ends will open two streams. After the stream connection is established, two-way communication is possible.

In the C/S communication method, different protocols can be used for communication between the client and the server, such as HTTP protocol, FTP protocol, etc. These protocols are implemented based on the TCP/IP protocol stack, and data are transmitted through TCP or UDP protocols.
In short, the C/S communication method is aNetwork-based communication method that realizes data transmission and sharing through interaction between client and server。

2.B/S（Browser/Server）

B/S communication methodIs a browser-based network architecture model, itsstructureas follows:

Browser : The browser sends a request to the server, and the server receives the request and returns data. The communication between the browser and the server is based on the network.
Server side : The server side needs to start a service, listen to the specified port, and wait for the browser's connection request. When the browser initiates a request, the server will establish a socket connection to communicate with the browser. Then both ends will open two streams. After the stream connection is established, two-way communication can be achieved.

In the B/S communication method, different protocols can be used for communication between the browser and the server, such as HTTP protocol, HTTPS protocol, etc. These protocols are implemented based on the TCP/IP protocol stack, and data are transmitted through TCP or UDP protocols.

In short, the B/S communication method is also a network-based communication method, which realizes data transmission and sharing through the interaction between the browser and the server. Different from the C/S communication method,In the B/S communication method, the browser plays the role of the client instead of using specialized client software.
The browser sends a request to the server, and the server receives the request and returns data. The communication between the browser and the server is also based on the network. Different from C/S,In B/S, the browser is not the client, but the server.

Both communication methods are based on the network. The client or browser sends a request to the server, and the server receives the request and returns data, thus realizing communication between end systems.

3.P2P（Peer-to-Peer）

P2P mode: It is a peer-to-peer network structure in whichEach node is a peer and can communicate and collaborate with each other. In a P2P network, there is no centralized server or controller, all nodes are equal and can communicate directly with other nodes. The advantages of the P2P model are scalability, high reliability and high resource utilization. Every end system is both a client and a server.

In the P2P (Peer-to-Peer) communication method, the number of participating hosts does not directly affect the communication speed. Because each node can send and receive data at the same time,The greater the number of participating hosts, the greater the communication bandwidth of the ^entire network1，

When more hosts join the P2P network, the bandwidth resources of the entire network can be better utilized. If each node is able to communicate with other nodes, then when data is transmitted in the network, the transmission path can be found faster, thereby increasing the speed and efficiency of data transmission.

However, it should be noted that the performance of P2P communication is not only affected by the number of nodes in the network, but also by other factors, such as network topology, distance between nodes, network delay, etc. Therefore, when designing and optimizing P2P networks, the combined impact of multiple factors needs to be considered to achieve optimal performance and reliability.

2.2.2 Core part

core partIt is a network composed of routers, switches, gateways and other equipment

These devices route and forward data packets through specific network protocols (such as IP protocol, TCP protocol, UDP protocol, etc.).

The main function of the core part isProvide data transmission and exchange capabilities for edge parts, and also provides someAdditional services such as network management, network security, etc.。

2.3 Division of functional components

Communication subnet

accomplishdata communication
It consists of various transmission media, communication equipment and corresponding network protocols. Its main function is to transmit data between computers from one node to another node and realize data communication (transmission and exchange) between networked computers.

Communication subnets can be classified according to different transmission media and protocols.
For example, Ethernet based on coaxial cable, Fiber Distributed Data Interface (FDDI) based on optical fiber, Wireless LAN (WLAN) based on radio waves, etc.

resource subnet

accomplishResource Sharing/Data processing
consists of hosts, terminals and various software resources and information resources. It is responsible for the data processing business of the entire network and provides various network resources and services to network users.
Resource subnets can be classified according to different resource types, such as file servers, database servers, print servers, etc.

In computer networks, communication subnets and resource subnets areIndependentYes, butAgain closely relatedof.Communication subnetfor the resource subnetsupplyGot itData transmission and exchange capabilities, so that various resources in the resource subnet can be easily accessed and used. andresource subnetis the communication subnetsupplyGot itData communication destinations and resource sharing functions, so that data in the communication subnet can be transmitted to the correct destination and processed correctly.

3. Computer network classification

3.1 Divided by distribution range

Wide Area Network (WAN)

• Wide Area Network (WAN), also known as external network and public network.
  WAN is not the same as the Internet. It is a remote network that connects computer communications in local area networks or metropolitan area networks in different regions. It is an important part of the computer communication network. (Core part of the Internet)
• Scope:
  It covers the range fromtens of kilometers to thousands of kilometers,CanConnect multiple regions, cities and countries to form an international remote network。
• WAN work is mainly concentrated on Layer 1 and Layer 2. The data link layer protocol defines how to encapsulate data to the remote location and the transmission mechanism of the final data frame, such as Frame Relay (Frame Relay), ATM, HDLC.

Technology:
Useswitching technology, is a data transmission network that uses the Public Switched Telephone Network (PSTN) or packet switching technology (such as X.25 and Frame Relay FR) to connect.
(Use intermediate devices such as routers to forward data)
Way of working:
Yescircuit switching and packet switching.
Hardware equipment:
data communication equipment and data terminal equipment, such as modems, ATM switches, routers, firewalls, repeaters, etc.

判断广域网和局域网看使用的技术，不能根据地理范围大小来确定。

Metropolitan Area Network (MAN)

• Metropolitan Area Network (MAN) is a computer communication network established within a city and is a broadband local area network.
• Scope:
  The coverage of the metropolitan area network is between the local area network and the wide area network.Generally no more than 100 kilometers。
• transmission mediumMainly using optical cable, the transmission rate is above 100 Mbit/s.

MAN canas backbone network, through which hosts, databases, and LANs located in different locations in the same city are connected to each other.

Local Area Network (LAN)

• Local Area Network (LAN) refers to a computer group composed of multiple computers interconnected in a certain area. That is, a large local area network can also be called an intranet.
• Intranet is a computer communication network that interconnects various computers, external devices, and databases within a local geographical scope (such as a school, factory, or institution), usually within a few kilometers. .
• LAN coverage:
  generally a radiusWithin a few kilometers, its features such as convenient installation, cost saving, and easy expansion make it widely used in various offices.
• Function:
  LAN can realize file management, application software sharing, printer sharing and other functions

main feature:

• Use specially laid transmission media for networking,High data transfer rate (10Mb/s～10Gb/s)
• communicationShort delay time, higher reliability
• LAN canSupport multiple transmission media

broadcast technology used

• Unicast: One-to-one delivery, which can ensure the efficiency and security of the network.
• Multicast: One-to-many transmission, based on unicast, improves the efficiency of information transmission through the high-speed network of user groups.
• Broadcast: Transmitting information to all nodes and between all nodes will occupy a large amount of bandwidth and is not suitable for use in large networks.

Type:
Classified according to the transmission medium used by the network, it can be divided intoWired and wireless networks;
According to the network topology classification, it can be divided intoBus type, star type, ring type, tree type, mixed typeetc.;
according to the access control method used in the transmission medium, it can also be divided intoEthernet, Token Ring, FDDI and Wireless LANwait. Among them, Ethernet is the most commonly used LAN technology currently.

Personal Area Network (PAN)

• Personal Area Network (PAN) is a network for short-distance communication between portable consumer appliances and communication devices, such as Bluetooth-connected communication networks, personal hotspots, etc.
• Coverage:Generally within a radius of 10 meters。
• The core idea of ​​PAN is to use radio or infrared rays to replace traditional wired cables to realize intelligent interconnection of personal information terminals and build a personalized information network.

From the perspective of a computer network, PAN is a local area network; from the perspective of a telecommunications network, PAN is an access network, so some people call PAN the "last meter" solution for telecommunications networks.

3.2 By user

public network

• A public network is a communication network built by a network service provider and used by public users.

Features:

• The public network isAvailable to all users, anyone can access the Internet;
• Because public networks are open to all users,Less secure；

private network

• A private network refers to a network built by a network service provider for internal use by a certain group or organization.
  (Intranet)

Features:

• Facing within a certain group or organization,Only specific user groups can access。
• Because it is targeted at a specific user group,Higher security。

The difference between intranet and private network:

• The meanings are different: the intranet is a local area network, and the private network is a dedicated line connection between two enterprises.
• The targets are different: the intranet is aimed at individual users or within an enterprise, and the private network is aimed at between two enterprises.
• The usage effects are different: the internal network has lower security, while the private network has higher security.
• The scope is different: the internal network has a small scope and the private network has a large scope.
• The connectivity is different: the internal network cannot connect to the Internet, but the private network can connect to the Internet.

3.3 By switching technology

circuit switching

• Before communication starts, the switching equipment between the communicating partiesCreate a dedicated circuit，Occupies communication resources throughout the process, until the communication ends.

The characteristics are: connection-oriented, synchronous time division multiplexing, and transparent information transmission.

• Advantages: small transmission delay, high efficiency, no need to add control information.
• Disadvantages: Not conducive to bursty data services with high transmission requirements.

message exchange

• Using messages as transmission units,There is no need to establish a circuit in advance and messages can be sent at any time。

Features: AdoptStore and forward mechanism, the transmission delay is large and the delay is uncertain, and the switch needs a large enough memory.

• Advantages: No need to establish circuits or circuits in advanceHigh utilization rate。
• shortcoming:Large delay。

packet switching

• Convert the user'sThe message is divided into data packets of a certain length, and then control information and address are added to the packet data and sent to the destination address.。

Features: AdoptStore and forward mechanism, statistical time division multiplexing, with error control and flow control.

• advantage:High line utilization and high transmission reliability。
• shortcoming:Poor real-time performance。

3.4 Division by topology

Bus type

star

ring type

Mesh type (commonly used in wide area networks)

3.5 Division by communication technology

broadcast network

Shared common communication channel

Broadcast network: In a broadcast network onlyUse a communication channel, the channel is controlled by the networkShared by all nodes。

When transmitting information, any node can send data packets to each machine and be received by all other nodes.Bus Ethernet is a typical broadcast network。

peer-to-peer network

Packet store-and-forward routing mechanism

Peer-to-peer network: consists of many interconnected nodes.There is a dedicated communication channel between each pair of machines, so in a point-to-point network,There is no channel sharing and multiplexingCase. When a computer sends a data packet, it will be forwarded through a series of intermediate devices according to the destination address until it reaches the destination node. This transmission technology is called point-to-point transmission technology, and the network using this technology is called a point-to-point network. .

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1. Bandwidth and transmission speed are important performance indicators of computer networks. Please refer to the next blog for explanation↩︎