Basic knowledge of network engineers (protocols of each layer of OSI)

The OSI (Open Systems Interconnection) model is a model defined by the International Organization for Standardization (ISO) to describe communication protocols in computer networks. The model divides network communication into seven levels, and each level consists of a set of protocols and specifications, in order:

1. Physical Layer: Responsible for defining the interface between physical devices and transmission media, as well as data transmission ways, such as wired transmission and wireless transmission. Commonly used protocols: network cable protocol, fiber optic protocol, etc.

2. Data Link Layer: Responsible for transmitting and receiving data packets between neighboring nodes. This layer handles the header and trailer parts of the packet in order to properly deliver the data during transmission. Basic protocol: ARP, RARP, PPP protocol, IEEE 802.11 protocol, etc.

3. Network Layer: This layer is responsible for selecting the best path for packet data. It not only determines how data is transmitted from source address to destination address, but also provides services for connectionless and connection-oriented transmission. Commonly used protocols: IP protocol, ICMP protocol, ARP protocol, etc.

4. Transport Layer (Transport Layer): This layer is responsible for providing reliable data transmission during end-to-end communication. The transport layer is responsible for aspects such as segmentation, service ports, flow control, and error detection and correction. Basic protocol: TCP protocol, UDP protocol, etc.

5. Session Layer (Session Layer): This layer is mainly responsible for establishing, managing and canceling communication sessions between network nodes. Basic protocol: SSH protocol, RPC protocol, etc.

6. Presentation Layer: This layer is mainly responsible for data processing and presentation. The work of this layer includes data compression, data encryption, and data format conversion. Basic protocol: JPEG standard, ASCII protocol, etc.

7. Application Layer (Application Layer): This layer contains most network applications, such as email, file transfer, and Web browsers. Application layer protocols are part of the software, common protocols include HTTP, FTP, DNS, SMTP, etc.