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The layered idea of Network reference Model based on computer Network

Layering, as the name implies, is to divide a single complex problem into multiple small problems, so as to take targeted solving strategies, optimization methods and correcting errors for each problem. To take a real-life example, the division of the company's management is shown in the following figure:

Divide a company into several departments, each department performs its own duties, problem handling, incident resolution and problem tracking will operate and manage the company's employees and business more efficiently.

In fact, the purpose of layering is simply to simplify, analyze and deal with problems, so as to improve efficiency and save corresponding costs.

Network reference model OSI seven-layer reference model

According to the idea of layering, analogy to corporate management, in fact, network management is similar. OSI reference model is a reference model called "Open Systems Interconnection" issued by the International Organization for Standardization (ISO) in 1984, referred to as OSI. The specific layering is shown in the following figure.

The above figure shows the relevant functions corresponding to each layer. This article is mainly based on understanding, and there are many knowledge points about the relevant content, which will not be introduced too much here. TCP/IP reference model

TCP/IP reference model is called Transmission Control Protocol / Network Interconnection Protocol (Transmission Control Protocol/Internet Protocol).

In the figure above, the early TCPIP model is a four-tier structure, which is later divided into five layers based on the OSI reference model. This model is a collection of a series of protocols, which, strictly speaking, should be called the TCP/IP protocol suite.

As for TCP to establish a connection and disconnect the three-way handshake, four waves will not be described in detail. Give an introduction to a handshake:

Establishing a connection is like a couple calling: (1) male: is this XXX, please? (ask in order to confirm whether it is your girlfriend, in case it is the wrong mother-in-law.)

(2) female: well, this is XXX (give reply / reply). Are you XXX? (ask if the other person is your boyfriend)

(3) male: well, this is XXX speaking. (give a reply / reply)

In fact, replacing two people with a client and a server is the process of establishing a connection, doing three times (so it's a three-way handshake), asking (client)-answering & & asking (server)-replying (client).

Here is a brief example, if you are interested, you can consult the theoretical knowledge on your own.

Supplementary point

Port number: used to identify upper layer protocols or applications

PDU:Protocol Data Unit protocol data unit

Transport protocols: TCP protocol and UDP protocol

TCP protocol: connection-oriented, reliable inter-process communication advantages: security

UDP protocol: connectionless, unreliable protocol advantages: high efficiency

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