Shulou(Shulou.com)06/01 Report--

As shown in the figure, each layer of the OSI seven-layer model corresponds to the function and the data unit.

In the TCP/ IP five-layer model, the application layer, presentation layer and session layer of the OSI seven-layer model are unified into the application layer.

The following figure shows the TCP/ IP five-layer model and the corresponding protocols of each layer.

Data transmission process-the process of data encapsulation and unencapsulation

Encapsulation process

1. The data from the application layer used to be upper data for transmission, and the transport layer gives the upper data plus the tcp header (or udp header) to the network layer for processing. (the tcp/udp header has an important field called port number, which is used to identify the protocol of the upper data.)

2. Similarly, the data in the transport layer is also the upper layer data for the network layer (including adding the tcp header); the network layer adds the upper layer data to the ip header and gives it to the data link layer for processing. (there is a protocol number in the ip header to identify the protocol used by the upper layer data, for example, the tcp protocol number is 6 and UDP is 7)

3. The data link layer adds the upper layer data from the network layer to the mac header, which is handed over to the physical layer for processing. (use the type field in the mac header to indicate the upper data protocol, such as 0800 is ip protocol and 0806 is arp protocol)

4. The physical layer converts the data into a bit stream and transmits it to the physical layer of the next device. The physical layer transmits the 0 and 1 corresponding voltages of the binary data.

De-encapsulation is the reverse process of packaging, starting from the physical layer. Is a process of dismantling the data header, looking at the fields (type, protocol number, port number) used to represent the upper layer data protocol, and giving them to the upper layer for processing.

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