1 Introduction
The network model means OSI（Open System Interconnect）that it is 开放网络互联jointly published by the International Organization for Standardization (ISO) and the International Telegraph and Telephone Consultative Committee (CCITT). The interconnection model is also a standard.
The network model is divided into seven layers, that is, when a user initiates a request to be received by the server, it will go through seven processes, or when a user uses the Internet to send a message to another user, it will also go through seven processes.
| Level | name | Description |
|---|---|---|
| Seventh floor | Application layer | Interact with user behavior |
| Sixth floor | Presentation layer | Define data format and data encryption |
| Fifth floor | Session layer | Create, manage and destroy sessions |
| Fourth floor | Transport layer | Create and manage request end-to-response (end-to-end) connections |
| the third floor | Network layer | IP address of the requester |
| Second floor | data link layer | Provide media access and link management |
| level one | Physical layer | Transmission medium |
Each of the above seven layers can communicate with the upper and lower adjacent layers
2 Seven-layer model
2.1 Application layer
This is user-oriented and closest to the user. In order to allow the user to interact with the computer, there will be a lot of software in the computer, such as eclipse, idea, qq, nginx, etc. This
software, the user can interact with the computer through these application software. The process is actually the call of the interface. The application layer provides the user with an interactive interface to provide the user with
the most common protocols at this layer: HTTP, HTTPS, FTP, SMTP, POP3, etc. Nginx is at this layer, which is a seven-layer load balancing.
2.2 Presentation layer
This layer provides encryption and data coding format, to ensure that 请求端data can be the responder 的应用层识别.
For example: I write Chinese to LiLei, but he can’t understand it. At this time, I will use translation software to translate Chinese into English. Then the letter involves some more private information. I will encrypt a message. At this time, the translation software and encryptor It serves as the 表示层role of, he is used to display the content that the user can recognize.
2.3 Session layer
A session can be understood as a session. There is a session between the process of sending a request to receiving a response, and the session layer acts as the manager of this process, from the creation of the session to the
subsequent destruction of the session.
Example: Every time I write to LiLei, I will record it in a small notebook, the date and time of the letter sent, and the date and time of the receipt. This small notebook contains a record of each communication. This small notebook is equivalent to the manager of the conversation. Or in other words, when we are making a call, we first need to make a call. This is 建立会话when the other party answers the call and the call is in progress ( 维持并管理会话after the end 会话销毁, then this is also the life cycle of a conversation.
2.4 Transport layer
This layer establishes an end-to-end connection. It provides data transmission services. The communication at the transport layer involves port numbers. The common protocols at this layer are TCP and UDP. LVS is at Layer
4 load balancing.
Example: LiLei and I will use the courier company in the communication process. The courier company will assign a courier to pick up and send the package, and then the courier will act as the transport layer.
2.5 Network layer
When network communication, there must be the local IP and the other party's IP. Both the requester and the responder will have their own IP. The IP is equivalent to your home address and house number.
The public IP of the cloud server on the network, and ordinary computers also have their own IP. , It’s just a dynamic IP, and the operator will assign a different IP to your computer every day. Therefore, the network layer can also be called the IP layer, and IP is the Internet
's equipment that can provide IP distribution is a router or switch.
For example: For cloud services with fixed IPs, they are all provided by vendors such as Tencent Cloud and Alibaba Cloud. They provide fixed IPs for cloud servers; telecommunications, mobile, and
merchants dynamically allocate IPs for your computer. Every day is different; then these vendors and operators are the network layer. In the same way, the couriers are allocated and managed by the logistics company, so the logistics company is
.
2.6 Data link layer
This layer will provide the computer MAC address, which will be carried during communication. In order to ensure that the request is delivered correctly, it will verify the MAC address to ensure the request
.
Example: When the courier delivers the delivery, he (or customer service) will call you in advance to confirm whether your home address is correct, whether there is anyone, and whether the cash on delivery has the money ready to wait for the courier (or customer service). act as a 数据链路层duty.
3 Related information
- The blog post is not easy, everyone who has worked so hard to pay attention and praise, thank you