1.1 Network Basics

1. Definition of Network

• definition:
  • Simple Definition: "A collection of interconnected independent and autonomous computers";
  • Complete definition: "Using communication equipment and lines to connect multiple computer systems with independent functions distributed in different geographical locations, and realize resource sharing in the network with well-functioning network software (network communication protocol and network operating system, etc.) and information transfer systems”;

The function of computer network

• data exchange and communication
  • Between computers in a computer network or between a computer and a terminal, data, programs or files can be transferred to each other quickly and reliably.
• Resource Sharing
  • Making full use of the resources (including hardware, software and data) provided in the computer network is one of the main goals of computer network networking.
• Improve system reliability
  • In some occasions that are used for real-time computer control and require high reliability, the realization of backup technology through computer network can improve the reliability of computer systems.
• Distributed network processing and load balancing
  • For large-scale tasks or when the task load of a computer in the network is too heavy, the task can be distributed to each computer in the network, or the load can be shared by relatively idle computers in the network.

The history of the development of computer networks

• The development process of computer network can be roughly divided into the following four stages:

1. The first stage: a remote online system centered on a single computer, forming a terminal-oriented computer communication network (1950s)

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2. The second stage: multiple hosts with autonomous functions are interconnected through communication lines to form a computer network with shared resources (late 1960s)

• The resource subnet is composed of all hosts, terminals, terminal controllers, peripherals (such as network printers, disk arrays, etc.) and various software resources in the network. Network resources and services.　　
• The communication sub-network is composed of various communication devices and lines, and undertakes communication processing tasks such as data transmission, transfer and transformation of the resource sub-network.　　
• Network users' access to the network can be divided into two categories:
  • Local access: Access to the local host does not go through the communication subnet, but only within the resource subnet.
  • Network access: Access resources on remote hosts through communication subnets.

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3. The third stage: forming a computer network with a unified network architecture and following international standardized protocols (late 1970s)

• The third stage of computer network development is to accelerate the research and application of international standardization of architecture and protocols. In the late 1970s, the Computer and Information Processing Standardization Technical Committee of the International Organization for Standardization ISO (International Organization for Standardization) established a specialized agency to study and formulate network communication standards to realize the international standardization of network architecture. In 1984, ISO officially promulgated an international standard called "Open System Interconnection Basic Reference Model" ISO 7498, referred to as OSI RM (Open System Interconnection Basic Reference Model), which is the famous OSI seven-layer model. The formulation and improvement of OSI RM and standard protocols have greatly accelerated the development of computer networks. Many large computer manufacturers have announced their support for the OSI standard one after another, and are actively researching and developing products that conform to the OSI standard.
• Computer networks that follow international standardization protocols have a unified network architecture. Manufacturers need to develop their own network products in accordance with commonly recognized international standards, so as to ensure that products from different manufacturers can communicate in the same network. That's what "open" means.
• There are currently two dominant network architectures:
  • One is the OSI RM (Open System Interconnection Reference Model) proposed by the International Organization for Standardization ISO;
  • The other is the de facto industry standard TCP/IP RM (TCP/IP Reference Model) used by the Internet.
• Standardization system of each manufacturer
  • IBM Corporation: SNA (Systems Network Architecture)
  • DEC Corporation: DNA (Digital Network System Architecture)
  • UNIVAC: DCA (Data Communication Architecture)
  • Burroughs Corporation: BNA (Borra Network Architecture)
• It is only valid within a company, that is to say, network communication products that comply with a certain standard and can be interconnected are limited to homogeneous equipment produced by the same company.

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4. The fourth stage: computer networks developing towards interconnection, high speed and intelligence (beginning in the late 1980s)

• Since the late 1980s, computer network technology has entered a new stage of development, which is characterized by interconnection, high speed and intelligence.

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Four, computer network classification

• According to the relative geographical location: (LAN, MAN, WAN are all relative concepts)
  • LAN (Local Area Network)
  • MAN (Metropolitan Area Network)
  • WAN (Wide Area Network)

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• By transmission medium
  • Wired transmission (network cable, optical fiber)
  • Wireless transmission (wifi, infrared, satellite)

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• By nature of use
  • Public network (home broadband, 3G/4G network)
  • Proprietary network (such as banking, military, IDC, etc.)

Five, network topology

• The bus type has basically been eliminated by now
• Star, tree, basically appear at the same time
  • Star type, like a star, there is a node in the middle, many devices are connected around it, and the nodes in the middle are usually switches or routers
• Full mesh, partial mesh, generally used in WAN, to improve the reliability of the network, they need mesh connection

Six, the main indicators to measure the computer network

1. Bandwidth (bandwidth) -> bandwidth determines the speed of the Internet

• Describes the amount of data that can be transferred from one node to another in a certain time frame - usually in bps
  • For example Ethernet bandwidth is 10Mbps, Fast Ethernet is 100Mbps

2. delay

• Describe the time it takes for data to travel from one node to another on the network
• The lower the latency, the faster the network

3. Detection tool ping --> view the delay time

• ping www.baidu.com -t
  • -t View the packet loss rate of the network