Article directory
Preface
In the previous article, I gave a brief understanding of the development history of computer networks. In this article, I begin to formally record my review and learning process of computer network knowledge. The first is a review and summary of the hierarchical structure of computer networks. The hierarchical structure of computer networks is studied from three aspects: the basic principles of hierarchical structure design, the OSI seven-layer model, and the TCP/IP four-layer model.
1. Basic principles of hierarchical structure design
1. Problems solved by computer networks
Before understanding the basic principles of hierarchical structure design of computer networks, let us first understand why computer networks use hierarchical structure design?
We first assume that there are two computers, computer A and computer B, that want to communicate. They are connected through a computer network, so we can imagine what kind of problems we want to solve in the computer network:
- First of all, the first problem that a computer network must solve is to ensure a smooth data path when two computers communicate.
- Secondly, there are so many computers on the Internet. How does computer A accurately identify computer B? How does computer B recognize computer A? , so the second problem to be solved for computer networks is to identify the destination computer
- Through the computer network, we also need to query the status of the destination computer. If computer A wants to communicate with computer B, then computer A must use the computer network to check whether computer B is online and whether it can receive data. Therefore, the computer network must solve The third problem is to identify the status of the destination computer
- After two computers have established network communication, it is very likely that errors will occur during data transmission due to Siberian cold current and other reasons. Therefore, the fourth problem to be solved in the computer network is to determine whether the data is incorrect and How to solve the problem after data error
Many practical problems need to be considered and solved by computer networks. At the same time, the problems that computer networks need to solve are also numerous and complex. Therefore, computer networks adopt a layered design to solve different problems in layers and implement different tasks respectively . function to allow the computer network to run normally.
2. Basic principles of hierarchical design
For the role of the computer network layer, an example can be given, as shown below:
For users, the main data that they directly come into contact with is the data of top-level network applications, such as videos, files, games, etc. Under this layer is the reliable communication of data, such as data errors and duplication, which are issues that users do not care about. The next level down is the physical level, such as whether data is connected to other computers through optical fibers or network cables, which are relatively low-level features. The above is an example of using network level comparison. It can be seen from this example that a certain layer does not need how the previous layer or the next layer is implemented. It only needs how the interface of the current layer provides services. Each layer only needs to implement relatively independent functions. And the coupling between layers is relatively low .
This leads to the basic principles of hierarchical design:
- The layers are independent of each other
- Each layer should be flexible enough
- Complete decoupling between layers
2. OSI seven-layer model
OSI (Open System Interconnection). The reference model is a standard system for interconnection between computers or communication systems formulated by the International Organization for Standardization (ISO). It is generally called the OSI reference model or seven-layer model.
Reference : OSI seven-layer model_Baidu Encyclopedia
The OSI seven-layer model and the role of each layer can be briefly summarized with a diagram:
The OSI seven-layer model once tried to become a standard followed by computers around the world, and in the 1980s, many companies also promoted the OSI seven-layer model. However, OSI faces many difficulties in the process of marketization, because before the OSI standard was formulated, the TCP/IP model had been successfully running on a global scale. Therefore, the OSI seven-layer model only obtained a lot of theoretical research results, but in terms of market However, it was not successfully promoted, so OSI did not become a widely used standard model . For the reason analysis, there are the following points:
- OSI experts lack practical experience
- The OSI standard formulation cycle is too long, and equipment produced according to OSI standards cannot enter the market in time.
- The OSI model is not designed reasonably, and some functions are repeated in multiple layers.
3. TCP/IP four-layer model
TCP/IP is a set of communication protocols used to implement network interconnection. The Internet network architecture is based on TCP/IP. The reference model based on TCP/IP divides the protocol into four layers: network access layer, Internet layer (host to host), transport layer, and application layer.
Reference : TCP/IP Reference Model_Baidu Encyclopedia
1. TCP/IP four-layer model definition
In the actual operation of computer networks, the TCP/IP four-layer model is more commonly used. The TCP/IP protocol has the following four layers:
- Application layer
- transport layer
- Network layer
- network interface layer
In the TCP/IP model, each layer has a protocol to follow. At the same time, the four-layer model of TCP/IP can also correspond to the OSI seven-layer model, as shown in the figure:
2. Practical application of TCP/IP model
As a model that has been successfully applied, it is also very mature and widely used in practical applications in the physical chain.
Assume that computer A and computer B are connected through a router. At this time, computer A will communicate with the router through the application layer, transport layer, network layer and network interface layer. The data will come to the router through the network interface layer and network layer. The layers in the router only reach the network layer and network interface layer. The router will forward the data through the network layer. After forwarding to computer B, the data also comes to the computer through the network interface layer, network layer, transport layer, and application layer. B.
Summarize
Huh~
I finally finished coding the content of the hierarchical structure of computer networks. Here is a brief summary of the content of this article.
This article has a simple understanding of the basic principles of hierarchical structure design. Through the problems to be solved by computer networks, it is extended to the reasons for adopting hierarchical structure design and the basic principles of hierarchical structure design. Then it conducts a simple analysis of the OSI seven-layer model. Introduction, an overview of the role of each layer is also briefly displayed in the figure, and the reasons why the OSI seven-layer model has not been successfully applied in the market are also analyzed. The TCP/IP four-layer model and the content of each layer corresponding to the OSI seven-layer model are briefly summarized, and the actual application process of TCP/IP is also briefly explained. The above is the basic content of this article.
Written at the end of this article :
Looking back on my three-year college experience, I have a profound understanding of the importance of basic computer knowledge. During the internship, I became more deeply aware of the importance of the team. I used to naively think that one person could win an entire big project. However, after seeing a large-scale project, I realized that I was How naive and ignorant. Large-scale projects are not projects that can be written and run. They have higher performance requirements and more rigorous technology selection... Completing large-scale projects requires the full efforts of everyone in the team, and even more so. It requires everyone's complementarity and concerted efforts to be invincible.
Here I also hope that I can learn and communicate with my seniors, classmates, and big guys. Welcome everyone to join the technical exchange group. Let's share technical knowledge and make progress together!
