Ch1. Overview

Ch1. Overview

Computer Networks are a magical world in which information is rapidly transmitted, it seems to me that we are studying how such information is transmitted from an isolated computer to another computer.

First, let's think about some non-technical things. Sound is a kind of information, and its transmission needs media. We can imagine some information we are currently in contact, all of its transmission requires media. If there is no physical connection between one computer and another computer, information cannot be transmitted (WiFi, air except = ), first, we connect the two computers with a single wire, so that they initially have the basis for theoretically transmitting information to each other. Then we may wonder what the wire passes on, why can we transmit our voice, images, videos, and other information to each other through wires? This involves the physical layer in the network protocol hierarchy (digital signal is not well learned) let's just think that the wire is passing a series of 0101 things. We call it bit streams. These bit streams contain all the information we want to transmit. Then the problem arises again, how did we turn this series of 0101 things into Chinese characters, images, videos, and other things that we can recognize with the naked eye? This involves coding, we simply explain that we have a relationship between different combinations of Chinese characters, images, and 0101 bit streams, We can translate the information that 01 represents based on this relational table.

The above is a general explanation of how text, images, and other information are transmitted from one computer to another. We all know that the current transmission over the wire is easily affected, and there are a series of problems such as speed. It can be understood that our 01bit online transmission also has these problems, therefore, this problem is solved by the physical layer. The physical layer uses various technical means to ensure the speed and capacity of these items.

After our computers correctly accept these 01bit values, we need to think about how different types of data information are hidden in the middle, and the information transmitted by various programs is also in the middle, the transmission of physical lines is always continuous. We cannot accept this river at a time, so we naturally think of dividing this information into small pieces that we can quickly process and accept, the data link layer does this.

Do not assume that the information can be transmitted after the preceding solution is solved. Our network is huge and many computers are connected directly or indirectly through our ISP service provider, they make up a huge figure. If the information you want to transmit is not a computer directly connected to you, how can this information be transmitted to the destination? When we think of it, we may think it is too big. This involves the problem of where we are going with the information, so the network layer is here, and the network layer is here to let us choose the path.

When we select the path, the data will flow correctly. Next, we need to understand that all communication is actually performed by the processes in two computers (the processes can be understood by Baidu), that is, the interaction data between processes, that is to say, the transmitted data is transmitted according to the requirements of the process, but the amount of data transmitted is as large as the transmission speed, what should I do when the processing speed of a process is too low for another process to send information? Many of these problems are solved by the transport layer.

Next, we will go up to the application layer. When it comes to specific applications, we will not go into details.

The problems encountered in the above transmission and who solved each problem did not actually give a name to anyone at the very beginning and then ask who to handle the problem. It was a hodgedge at first, but we found that, these problems are intertwined, which is not conducive to the establishment and maintenance of the entire network system. As a result, the data information contained in the 01bit stream is disorganized. As a result, layers solve different problems, then, some identifiers need to be added to the 01bit stream in the process of solving the problem, so although physically merged, there is a sense of modularity in the logic, each layer only cares about the problems to be solved at the current layer, and does not care about other problems. Even if a problem occurs, it can locate the problem based on the check at the logic layer to facilitate maintenance, in addition, different layers can develop different solutions on their own issues, or rules and regulations. Thus, various levels of agreements have emerged.

I think that when I first came into contact with various protocols, without a general subjective impression, I would not have a general understanding of the various protocols. As far as I am concerned, I have completed the computer network, still thinking about the meaning of these protocols, how the information of the entire computer network world is physically done, such as how the Chinese character information is transmitted to other computers through a line, then how can it be restored to Chinese characters. These problems may be relatively small, but they are necessary for new users.

Note: The knowledge is limited, and many things are unclear by themselves. They may be expressed, or there may be problems in the example, I just want to sort out the big structure of the entire network in a simple and easy way.

Ch1. Overview