Linux Network Programming--osi seven-tier model, TCP/IP model

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OSI seven-layer model

Open Systems Interconnect (open System interconnect), the model is divided into 7 layers, from bottom to top:

• Physical Layer:

• Data Link Layer:

• Network layer:

• Transport Layer:

• Session Layer:

• Presentation layer:

• Application layer:

650) this.width=650; "src=" Http://img.baidu.com/hi/face/i_f42.gif "alt=" I_f42.gif "/> can't remember what to do? Looking down, it's easy to remember what you understand.

Physical Layer

It is said that the physical layer is also the computer between the physical transmission equipment and media, such as network cables, hubs, repeaters, twisted pair, coaxial cable ...

Let's take a look at the definition of the physical layer:

"To create, maintain, dismantle, and provide mechanical, electronic, functional and normative properties for the physical link required to transmit data"

The purpose of the physical layer is to transfer data. .

Where do you transfer data?

650) this.width=650, "src=" Http://img.baidu.com/hi/face/i_f38.gif "alt=" i_f38.gif "/> Each transmission medium.

What kind of data does it transmit?

650) this.width=650; "src=" Http://img.baidu.com/hi/face/i_f38.gif "alt=" i_f38.gif "/> bitstream data.

What is bit stream?

650) this.width=650; "src=" Http://img.baidu.com/hi/face/i_f38.gif "alt=" I_f38.gif "/>1 and 0 constitute the data stream.

How to stipulate 0 what is 1?

650) this.width=650; "src=" Http://img.baidu.com/hi/face/i_f38.gif "alt=" i_f38.gif "/> Yes, that's what the physical layer is doing, though it's not just that.

As mentioned above, there are many kinds of communication media and equipment, communication ways are different, how to block these differences, so that their upper-data link layer does not feel these differences, and only focus on the services and protocols of this layer, do not care about the specific physical transmission medium is.

So how exactly does the physical layer block these differences, and what does it include?

the RS232 interface standard is the content of the physical layer. In addition there are RS-449, x.21, v.35, ISDN, and FDDI, IEEE802.3,IEEE802.4, and IEEE802.5.

(1) Mechanical properties

Indicates the shape and size of the connector used for the interface, number of leads and arrangement, fixation and locking device, and so on. such as the DB9 9-pin

(2) Electrical characteristics

Indicates the range of voltages that appear on each line of the interface cable. such as -15v~+15v

(3) Functional characteristics

Indicates what the voltage of a certain level appears on a line. If +3v~+15v indicates low level 0

(4) The procedure characteristic indicates the order of occurrence of various possible events for different functions. such as the operating sequence and timing of each signal line.

Network layer

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Linux Network Programming--osi seven-tier model, TCP/IP model