Architecture of five-layer computer protocol 1

1. There are three architectures:

The OSI Layer-7 protocol structure is complex and not practical. The TCP/IP structure is widely used. The bottom layer of the network interface layer is nothing, but the top layer is the top layer. The five-layer architecture is adopted based on the two advantages.

• Application Layer

Is the highest level in the architecture. An application (process) that communicates with other computers. It corresponds to the communication service of applications.

For example, a word processing program without a communication function cannot execute communication code, and programmers engaged in word processing do not care about the application layer. However, if a file transfer option is added, the programmer of the word processor needs to implement the application layer. Example: Telnet, HTTP, FTP, NFS, SMTP, and other protocols.

• Transport Layer

Provides services for communication between two main processes. A host can run multiple processes at the same time, so the transport layer has the reuse and reuse functions.
Multiplexing means that multiple application-layer processes can use the following transport-layer services at the same time. In other words, the transport-layer delivers the received information to the corresponding processes in the above application-layer.

Two protocols are used:

Transmission Control Protocol (TCP)-connection-oriented, data transmission unit is packet segment. Reliable interaction.

User Data Table protocol (UDP)-connectionless, data transmission unit is user datagram. Reliable interaction is not guaranteed, and interactions can only be provided as much as possible.

• Network Layer (also called Internet layer and IP layer)

Provides communication services for different hosts on the group exchange network. When sending data, the network layer encapsulates the packet segment or user data generated by the transport layer into groups or packages for transmission.

Selects the appropriate route so that the Group passed by the source host transport layer can find the target host through the network router.

Because the IP protocol is used at the network layer, a group is also called an IP datagram or a datagram.

Note that when reading documents, no matter which layer of transmitted data units are used to grouping.

• Data Link Layer

The IP data packets handed over by the network layer are assembled into frames and transmitted transparently on the links between two adjacent nodes. (Transparency: a certain actual thing does not seem to exist)

Data transmission between two hosts is always transmitted over a link, that is, between two adjacent nodes (host and router, router, and router) the link layer protocol is used for direct (point-to-point) transmission.

Each frame includes data and necessary control information (such as synchronization information, error control, and address information)

When receiving data:

The control information allows the acceptor to know the starting and ending bits of a frame. In this way, after receiving data at the data link layer, the data part can be extracted and handed over to the network layer;

The control information enables the acceptor to detect any errors in the received frames. If an error occurs, the link layer discards the frame with the error to avoid wasting network resources. If an error needs to be corrected, the TCP protocol of the transport layer is used.

 

• Physical Layer

Transparent transmission of bit streams. The transmission unit is bit. The connection header, frame, frame usage, current, encoding, and optical modulation all belong to various physical layer specifications. Multiple specifications are commonly used in the physical layer to define all details. Example: RJ45, 802.3, etc.

 

Others:

Presentation layer OSI
The main function of this layer is to define the data format and encryption. For example, FTP allows you to transfer data in binary or ASCII format. If binary is selected, the sender and receiver do not change the file content. If the ASCII format is selected, the sender converts the text from the sender's character set to the standard ASCII format and then sends the data. The receiver converts standard ASCII to the character set of the receiver's computer. Example: encryption, ASCII, etc.
Session Layer OSI
It defines how to start, control, and end a session, including control and management of multiple two-way messages, so that the application can be notified when only part of the continuous message is completed, in this way, the data seen in the presentation layer is continuous. In some cases, if the presentation layer receives all the data, the data is used to represent the presentation layer. Example: RPC and SQL.
Transport layer OSI
This layer of function includes whether to select the error recovery protocol or error-free recovery protocol, and reuse the data stream input of different applications on the same host, it also includes the re-sorting function for packets that are not in the correct order. Example: TCP, UDP, and SPX.

 

Architecture of five-layer computer protocol 1