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

Ha, finally arrived at the network knowledge article. Always do not know how to write this blog, because there are too many knowledge points, the content is really difficult to write ah! But, after all, as an IT staff, how can you go out if you don't learn network knowledge well? So, back to the point, before I explain, let me popularize a concept of science, what is the OSI seven-layer model?

The so-called seven-layer model actually does not exist and is a hypothetical network model. What do you mean?

Please look at the picture below:

This picture should show very clearly!

Explain the corresponding units for each layer:

① physical layer: bits: machine languages are all 0101, in which each 0 or 1 represents a bit, which is also the smallest unit in a computer.

② data link layer: frame: data frame, which is a more complex unit relative to bits, in which the written data contains the hardware address of the computer (that is, the physical address of the network card [MAC address]), and the MAC address is used for LAN communication, that is, intranet communication.

③ network layer: message: mainly used to store IP address, in which IP address is used for external network communication.

④ transport layer: TPDU (segment): transport protocol data unit-a vague concept that is not very useful, including the following segments

⑤ session layer: SPDU: session Protocol data Unit

⑥ presentation layer: PPDU: represents the protocol data unit

⑦ application layer: APDU: application protocol data unit

Note:

The actual transmission data are only in the physical layer, the above layers are to record the corresponding information.

Let me explain what each floor is for. And what is the use of it?

① physical layer: as we said earlier, the physical layer is actually used to transmit data. Why do you say that? Our computers actually recognize only machine language 0101, while the data units transmitted at the physical layer are bits, that is, 0101. So it goes without saying!

The most typical devices in the physical layer are network cables and network cards.

② data link layer: group frames and record MAC addresses (sender's MAC address and recipient's MAC address). If there is an error, there will be a prompt to retransmit the data.

③ network layer: record the sender's IP and the recipient's IP. Another function is routing. The so-called routing is to choose what kind of node to transmit data.

④ transport layer: the first is to choose a reliable transport protocol or an unreliable transport protocol (there are two protocols: TCP [Transmission Control Protocol] and UDP [user Datagram Protocol], in which TCP is reliable, DUP is unreliable but the transmission speed is fast. )

The second function is error detection before transmission.

Just keep in mind that the transport layer is used to determine port numbers. Some people may ask what the port number is for. Well, the port number is actually used to determine which service you sent the request to, each service has a different port number, for example, if you want to browse the web, then you must visit the www service!

⑤ session layer: determine whether the data needs to be transmitted over the network. If the user writes an word document, then the session layer is over, because it can be saved directly to the hard disk, not something like mail that needs to be transmitted over the network.

⑥ presentation layer: used to translate our input language into machine language or machine language into a language that we can understand

⑦ application layer: provides an interface for users to operate

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