Understand network protocols

We have been dealing with computers all day, learning from the outside world through the Internet, and getting rich learning materials from the Internet. We can also exchange information with others through computers, in fact, all these actions are information interactions between multiple computers. Do we know how the information is transmitted? How can we make the data on one computer accurate to the other? Next, let's learn about the network protocol.

Technology world:

Generally speaking, network protocols are a bridge between networks for communication and communication. Only computers with the same network protocol can communicate and communicate information. This is like the various languages used for communication between people. Only when the same language is used CAN communication be conducted normally and smoothly. From a professional perspective, network protocols are the protocols that computers must comply with when implementing communications in the network. It mainly defines the information transmission rate, transmission code, code structure, transmission control steps, and error control, and develops standards.

Hierarchy:

In order to allow computers produced by different computer manufacturers to communicate with each other and establish computer networks in a larger scope, the International Organization for Standardization (ISO) proposed the "Open System Interconnection Reference Model" in 1978 ", that is, the famous OSI/RM model (open
System Interconnection/Reference Model ). It divides the communication protocols of the computer network architecture into seven layers, which are from the bottom up: physical layer, data link layer, and network layer), transport layer (Transport
Layer), Session Layer, presentation layer, and application layer ).

Physical Layer)

The physical layer refers to some real physical media, such as hubs, reconnections, and transmission lines (optical fibers and cables) that can transmit physical signals. For digital applications, we only need two physical signals to represent 0 and 1 respectively. For example, high voltage is represented by 1, and low voltage is represented by 0, which constitutes a simple physical layer protocol. A computer can provide corresponding interfaces for receiving physical signals and interpreting them as a series of 0/1.

Data Link Layer)

In this layer, information is transmitted in frame units. A frame refers to a finite 0/1 series. The function of the connection layer protocol is to successfully identify the frames contained in the 0/1 sequence, including the source, SRC, destination, DST, and frame
Check sequence) and the most important data (payload ). Of course, the connection layer protocol does not care about what is written in the data. A frame is like an envelope used for writing a letter. It is only responsible for encapsulating the data.

Our commonly used connection layer protocols include Ethernet and WiFi. Through these protocols, we can establish local Ethernet or Wi-Fi LAN, so that two or more computers in the same LAN can communicate with each other. The connection layer is like a postman responsible for sending mails to a region. As long as the mail (FRAME) in this region is sent to him, he can send the mail to any designated household.

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