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

Review of data Transmission in computer Network TCP/IP Protocol Suite (layer 5)

A collection of TCP/IP-- protocols whose first four layers correspond to the first four layers of the OSI seven-layer model

The function is similar, while the application layer corresponds to the upper three layers of the OSI (session layer, presentation layer, and application layer, respectively).

For those who don't know anything about the OSI reference model, you can visit the following link for a simple understanding:

Computer network foundation

TCP/IP five-layer model is more widely used in practical work. The following is described in detail:

(1) physical layer / data link layer

At the physical and data link layers, TCP/IP does not define specific protocols, so it supports all standard and proprietary protocols

The network can be a local area network, a metropolitan area network or a wide area network.

(2) Network layer

This layer defines the IP protocol, which consists of four supporting protocols: ARP (address Resolution Protocol),

RARP (inverse address Resolution Protocol), ICMP (Internet Control message Protocol), IGMP (Internet Group Management Protocol).

(3) Transport layer

TCP (Transmission Control Protocol) and UDP (user Datagram Protocol) protocols are mentioned at the end of the previous link.

(4) Application layer

To put it simply, except for the above protocols, all the other protocols belong to the application layer.

For example: HTTP (Hypertext transfer Protocol), FTP (File transfer Protocol), SMTP (simple Mail transfer Protocol), and so on.

Data transmission process

In fact, data transmission in the network is similar to mail and express delivery in our lives. Transmission is like the process of the whole package going to you.

The agreement is like the package information we stipulated to ensure that everyone can understand it. Therefore, the data also needs to be packaged and unpacked.

Encapsulation and unencapsulation, to be exact.

Data encapsulation and unencapsulation process

1. Data encapsulation process (express package)

(1) Application layer transmission

This can be understood as the process of translation, of course, this is the translation process of the computer, the application layer is to binary encode the data.

(2) Transport layer transmission (data segment)

The transport layer divides the upper layer data into a number of segments (to facilitate the resolution of transmission errors), and for each segmented data

Encapsulation-TCP message header. The TCP message header has a key field information-port number (to ensure the upper application data communication).

(3) Network layer transmission (packet)

The network layer encapsulates the upper data again-- the IP header, which contains a key field information-- IP address, which is used to identify the network.

The logical address of.

(4) data link layer transmission (data frames)

The data link layer encapsulates the upper data again-- MAC header, which contains a key field information-- MAC address, which is understandable.

The physical address solidified in the hardware is as unique as our personal bank card number. The tail package in the packaging process will not be discussed for the time being.

(5) physical layer transport (bitstream)

The physical layer converts the upper binary data into electrical signals for transmission in the network.

The above is the data encapsulation process in the network transmission, which can be simply understood as the process that we usually wear clothes in winter.

The data segments, packets, data frames, and bit streams in parentheses are the PDU (protocol data unit) introduced in the link I gave above.

two。 Data unpacking process (parcel unpacking)

After the data is encapsulated and transmitted to the receiver through the network, it needs to be unencapsulated, which is exactly the inverse process of the data encapsulation mentioned above. It's easy to understand.

For the process that we usually take off our clothes after turning on the heating at home in winter.

The following is a visual description of the process according to the diagram.

The image above shows the encapsulation process of the data from top to bottom and the unencapsulation process of the data from the bottom to the top. Among them, the bit stream can be regarded as the conversion of the signal, generally a digital signal, or an electronic pulse, to be exact.

Supplementary point

The corresponding relationship between Common hardware equipment and five-layer Model

Application layer: computers (in fact, computers are integrated with seven layers of OSI)

Transport layer: firewall

Network layer: router (strictly speaking, it is inconsistent with the home router used in our home, which can be seen in the computer room)

Data link layer: switches (such as light cats at home)

Physical layer: network card

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