ISO/OSI Network Model Introduction

ISO/OSI network models have been porting Android video codec recently. I haven't written a blog for a long time. I want to write something about the network. I first introduced the ISO network model to my shoes. First, I will draw a picture for your understanding. Www.2cto.com

Based on the reference model diagram above, I will explain each layer of the ISO/OSI reference model as follows: 1. If two computers on the physical layer can talk to each other, in terms of hardware, we need to ensure that there is a physical link between the two computers, which is not covered by our software. In terms of software, assuming that the two computers have been physically connected, how do they transmit information? In a computer, no matter what data you transmit (sound, graphics, text ......), He is already 010111... In the form of bits. Therefore, to realize the transfer between computers, we need to transmit the bit strings of this computer to another computer. This is the first implementation. This work is implemented by the physical layer. Therefore, this is the most basic layer of the layer-7 protocol. 2. Through the above physical layer, the data link layer ensures that information can be transmitted to each other, but this information is very insecure. Why? Any physical link of you may have interference. For example, if I am Wireless, a ray may affect me. If I am connected by a twisted pair, if there are other interference lines next to it, it will also interfere with data transmission in this line. So he has an error. Another is to do things to computers. 1 is 0, 0 is 0, and there will be no ambiguity. Therefore, you must ensure that the data you pass is correct, so we will all have Layer 2 work ------- data link layer.
What is the data link layer? Www.2cto.com, which ensures that the bits in host A are transmitted to host B correctly. Through twisted pair wires, data in host A is transmitted to host B, which is the same as that in the computer. It actually transmits signals. CPU data is also transferred to an external device as a string of signals. She is the same as ordinary people. When talking, we divide it into a sentence and say it has a rhythm. If one word is used, some sentences may not be understood. The data link layer divides the data you want to transmit into a group. Each group is called a frame. For each frame, we must ensure its integrity. They use computation to ensure the correctness of frame data, which is similar to the message digest in the encryption algorithm. 3. The Network Layer does not connect two computers with physical devices without any nodes. Host A is transferred to host B. It must pass to the ultimate node of the Communication Subnet ...... Then pass the information to my side, which leads to a problem ------- how do I know who to send the information? In fact, it is to find a path in the network, and then I pass it along this path, a segment, so that I can ensure the correctness of the transfer. This mechanism is implemented at the network layer. The job at the network layer is to find such a path.
4. At the transport layer, the end user of data in the network is not a machine, but an application process on the machine. Modern computers are all multi-process computers. The task at the transport layer requires me to know who the request is? I want to give it to a service process. 5. In the Session Layer, if I want to talk to you, I need you to prepare in advance. You are not prepared if I want to send a message to you. For example, if I send a WEB request, make sure that you have to start the WEB service. The role of the Session Layer is to say hello to me in advance. Ensure that we can communicate with each other. 6. The presentation layer www.2cto.com uses the above layers to transmit data to another application process. Let me give you a simple example. The above layers ensure that one person speaks, another person can hear it from his ears. If we all speak Mandarin, you can understand it. But what if a person is a foreigner? Although he heard this, he could not understand it. For the computer network, I sent a request from this client to the server. Your server process needs to understand what the request is, so the next problem to be solved is how you understand it. There are two levels to understand the problem: for example, if I speak Chinese and she speaks English, there is a translation between them. The same is true in the computer. Each computer has its own language, they all need their own Information Representation Methods. Most of our PC machines use the ASCII representation to represent characters, but it is not necessarily the case for a mainframe. It may be another way. For different encodings, the information they represent is different. These are all done by the presentation layer. Its role is to understand information. 7. At the application layer, I would like to give you an example. Everyone speaks Mandarin. Is that understandable? She talks about philosophy, computers, and mathematics. You need to understand the things in a major. A specific expression is required for an application. This is implemented at the application layer. Author Jefry