The OSI seven-tier model of network management Linux detailed

Ha, finally to the network knowledge article. Always do not know how to write this blog, because the knowledge point is too much, the content is really not good to write Ah! But, after all, as an IT staff, do not learn network knowledge how to go out? So, to the next, before the explanation, I first come to the concept of science, what is the OSI seven layer model?

The so-called seven-layer model is actually nonexistent and is an imaginary network model. What do you mean?

Take a look at this picture below:

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This picture should be shown very clearly!

Explain the corresponding units for each layer:

① Physical layer: bit: machine language is 0101, each of which 0 or 1 represents a bit, which is also the smallest unit in the computer

② Data Link Layer: Frame: A data frame is a more complex unit relative to a bit, where the written data contains the computer's hardware address (i.e. the network card's physical address "MAC address"), the MAC address is used for LAN communication, that is, intranet communication.

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③ Network layer: message: Mainly used to store IP address, where the IP address is used for external network communication.

④ Transport Layer: TPDU (segment): Transmission Protocol Data Unit--fuzzy concept, small function, including a few paragraphs

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

Attention:

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

Let me explain separately what each layer is for? And what role does it have?

① Physical layer: As we have said before, the physical layer is actually used to transmit data, why do you say so? Our computer actually only recognizes machine language 0101, and the physical layer transmits the data unit to bits, which is 0101. So it's self-evident!

The most typical device of physical layer is: Network cable, network card

② Data Link layer: Group frame, record MAC address (sender's MAC address and recipient's MAC address) if there is an error, you will be prompted to retransmit the data.

③ Network layer: The IP of the sender and the IP of the recipient are recorded, and one action is to select the path. The so-called choice is to choose what kind of node to pass data

④ Transport Layer: Two functions, 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 Protocols", where TCP is reliable, the DUP is unreliable but the transmission speed is fast.) ）

The second function is error detection before transmission.

One thing to keep in mind is that the transport layer is used to determine the port number. Someone's going to ask what the port number is. Well, the port number is actually used to determine which service you send a request to, each service has a different port number, such as you want to browse the Web that is sure to access the WWW service!

⑤ Session Layer: To determine whether the data need to network transmission, if the user is writing a Word document, then to the session layer is over, because directly saved to the hard drive on the line, not similar to the mail and other needs of the network to pass things.

⑥ presentation layer: Used to translate our input language into machine language or to translate machine language into languages we can read

⑦ Application layer: Provide interface for user to operate

This article is from the "Brother Hong Linux World" blog, so be sure to keep this source http://zhengkangkang.blog.51cto.com/12015643/1867728

The OSI seven-tier model of network management Linux detailed