Networks and protocols

1. Network Transmission: physical layer, data link layer, network layer, transmission layer, Session Layer, presentation layer, and Application Layer

2. Transmission Unit: transmission unit of the physical layer: Data bit stream (BITs) and data link layer transmission unit: data frame)

Transmission unit at the network layer: Packet and transmission unit at the transmission layer: Message)

The transmission unit at the Session Layer: Message and the transmission unit at the presentation layer: Message)

Transmission unit at the application layer: Message)

3. Seven protocol layers

(1) Application Layer: an application that communicates with other computers. It corresponds to the communication service of applications. Main protocols include HTTP: Hypertext Transfer Protocol, webpage display, DNS: domain name system, ftp: File Transfer Protocol, SFTP: Secure File Transfer Protocol, SCP: SCP is the core component of the intelligent network, generally, it consists of minicomputers, high-performance computers, and large real-time high-speed databases. Ssh: Secure Shell, SMTP: mail Transmission Protocol

(2) Presentation Layer: The main function of this layer is to define the data format and encryption, which is generally encrypted in ASCII format.

(3) Session Layer: defines how to start, control, and end a session, including the control and management of multiple two-way messages, so that the application can be notified when only part of the continuous messages are completed, the data displayed in the presentation layer is continuous. The main protocols are RPC.

(4) Transport Layer: select the error recovery protocol or error-free recovery protocol, and reuse the data stream input of different applications on the same host, it also includes re-sorting of packets that are not in the correct order. The main protocols include TCP and UDP.

(5) network layer: defines end-to-end packet transmission. It defines the logical addresses that can identify all nodes, and also defines the routing implementation and learning methods. The main protocols include: IP

(6) data link layer: defines how data is transmitted on a single link. Main protocols include: ATM and FDDI.

(7) Physical Layer: the connection header, frame, frame usage, current, encoding, and optical modulation all belong to various physical layer specifications. Major protocols include RJ45 and 802.3.

Networks and protocols