Network communication protocol

The realization of the Internet is divided into several layers. Each layer has its own function, just like a building, each layer is supported by the next layer. The user is only touching the top layer and does not feel the layer below. To understand the Internet, you must start from the bottom and understand the function of each layer from the bottom up. In this case, I divided it into five layers which are application layer, transport layer, network layer, link layer, physical layer.

Each layer is designed to perform a function. In order to achieve these functions, everyone needs to follow common rules. The rules that everyone follows are called “protocols.”

Every layer of the Internet defines a lot of protocols. The general term for these agreements is called the “Internet Protocol Suite.” They are the core of the Internet. The functions of each layer are described below, mainly to introduce the main protocols of each layer.

We start with the bottom layer. Computers need to be networked, what is the first thing to do? Of course, the computer is first connected, and optical cable, cable, twisted pair, radio wave, etc. can be used.

This is called the “physical layer”, which is the physical means of connecting computers. It mainly specifies some electrical characteristics of the network and is responsible for transmitting the electrical signals of 0 and 1.

In the early days, each company had its own way of grouping electrical signals. Gradually, a protocol called “Ethernet” dominates. Ethernet specifies that a set of electrical signals from a data packet called a “frame”. Each frame is divided into two parts: a header and a data

Its role is to introduce a new set of addresses, allowing us to distinguish whether different computers belong to the same subnet. This set of addresses is called "network address", referred to as "URL".

The function of the “transport layer” is to establish “port-to-port” communication. In contrast, the “network layer” function is to establish “host to host” communication. As long as the host and port are determined, we can communicate between the programs. Therefore, Unix systems call the host + port a “socket.” With it, you can develop web applications.

The application receives the “transport layer” data, which is then interpreted. Since the Internet is an open architecture and the data sources are varied, the format must be specified in advance, otherwise, it cannot be interpreted at all. The role of the “application layer” is to specify the data format of the application.

For example, the TCP protocol can pass data to a variety of programs, such as Email, WWW, FTP, and so on. Then, there must be different protocols that specify the format of the email, web pages, and FTP data. These application protocols form the “application layer.” This is the highest level and faces the user directly. Its data is placed in the “data” part of the TCP packet.

At this point, the five-layer structure of the entire Internet has been completed from the bottom up. This is a systemic perspective that explains how the Internet is structured.

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