An application layer communicates with other computers, which is the communication service of the corresponding application. For example, a word processor without a communication function would not be able to execute the code of communication, and the programmer working on the word processing did not care about the 7th layer of the OSI. However, if you add an option to transfer files, the programmer of the word processor will need to implement the 7th layer of the OSI. Example: Telnet,http,ftp,nfs,smtp and so on. The primary function of this layer of presentation layer is to define data format and encryption. For example, FTP allows you to choose to transfer in either binary or ASCII format. If binary is selected, the sender and receiver do not change the contents of the file. If you select ASCII format, the sender converts the text from the sender's character set to the standard ASCII and sends the data. Converts standard ASCII to the receiver computer's character set on the receiver side. Example: Encryption, ASCII, and so on. Session Layer it defines how to start, control, and end a session, including control and management of multiple bidirectional messages, so that the application can be notified when only part of a continuous message is completed, so that the data that the presentation layer sees is contiguous, and in some cases, the presentation layer is represented by data if all the data is received by the presentation layer. Example: Rpc,sql and so on. Transport layer This layer of functionality includes whether to choose the Error recovery protocol or error-Free recovery protocol, and on the same host for different applications of the data stream input to reuse, but also to receive the order of the wrong packet reordering function. Example: Tcp,udp,spx. This layer of the network layer defines end-to-end packet transport, which defines the logical addresses that identify all nodes, and defines the way in which routing is implemented and how it will be learned. To accommodate transmission media with a maximum transmission unit length of less than the packet length, the network layer also defines a segmentation method that decomposes a packet into smaller packets. Example: Ip,ipx and so on. Data link Layer It defines how data is transferred on a single link. These protocols are related to the various media being discussed. Example: Atm,fddi and so on. The physical layer specification for the physical layer OSI is an attribute standard for the transmission medium, which is often referred to by other organizations. Connection head, frame, frame use, current, encoding and light modulation are all the contents of various physical layer specifications. The physical layer often uses multiple specifications to complete the definition of all the details. Example: rj45,802.3 and so on.
Network Seven layer model
