Shulou(Shulou.com)06/02 Report--

What is the OSI seven-tier model?

The Open Systems Interconnection reference Model (Open System Interconnect, referred to as OSI) is an OSI reference model jointly developed by the International Organization for Standardization (ISO) and the International Telegraph and telephone Advisory Committee (CCITT). It provides a functional framework for open interconnection information systems. From low to high, they are physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer

I think the process of surfing the Internet is divided into seven levels from the bottom to the application.

Physical layer: the lowest layer of the model and the first layer of the OSI model

Function: the transmission medium is used to provide physical connection for the data link layer to realize the transmission of bit stream. (that is, to transmit signals)

Establish maintenance and disconnect the physical connection.

Physical layer equipment: physical interface (network cable, network port, Jack).

Data link layer: the second layer of the OSI model, which is responsible for establishing and managing links between nodes.

Function: establish logical address addressing, hardware address addressing, error effectiveness, etc.

Error detection and correction, flow control, error-free transmission frame. (data frame encapsulation structure)

In the computer network, due to the existence of various interference, the physical link is unreliable. Therefore, the main function of this layer is to turn an error-free physical line into an error-free data link through error control and flow control methods on the basis of the bit flow provided by the physical layer. that is, to provide a reliable method of transmitting data through the physical medium.

The specific work of the data link layer is to receive the data from the physical layer, encapsulate it into frames, and transmit it to the upper layer; similarly, the data frames from the upper layer are disassembled and forwarded to the physical layer.

The physical address we are talking about is the MAC address, and the MAC address is immutable in hexadecimal 48 bits (1 word = 8 bits).

The data link layer has two MAC addresses: the source physical address (MAC address) and the destination physical address (MAC address).

Devices at the data link layer: switches.

Network layer: the third layer of the OSI model

Function: (packet) transmission for logical address addressing, through comprehensive consideration of transmission priority, network congestion,

And optional paths to determine the best path from one network to another.

The logical address is the IP address, and the IP address is variable

The network layer has connected IP addresses: the source logical address (IP address) and the destination logical address (IP address).

Devices at the network layer: routers.

Transport layer: is the fourth layer of the OSI model

Function: define the protocol for data transmission (TCP/UDP protocol) port-to-port transmission, as well as flow control and error verification

The data received from the lower layer is mainly segmented and transmitted, and then reorganized after arriving at the destination address.

This layer of data is often called (data segment).

Transport layer devices: firewalls

Session layer: layer 5 of the OSI model.

Function: establish, manage, and terminate session connections between presentation layer entities

Allows users on different machines to establish session relationships. Responsible for establishing, maintaining and terminating sessions between two points in the network

The transmission of data is done at the session layer, not at the transport layer, which only defines the protocol for data transmission. )

Presentation layer: is the sixth layer of the OSI model.

Function: this layer is responsible for protocol conversion, data coding and data compression. Define the syntax and semantics of passing galaxies.

Application layer: is the highest layer (layer 7) of the OSI model.

Function: it is the interface between computer users and various applications and networks. Its function is to provide services directly to users and complete all kinds of work that users want to do on the network.

The so-called network layer 7 protocol is the OSI model:

7Murray-Application layer

6mura-presentation layer

5Mutual-session layer

4murine-transport layer

3While-Network layer

2mura-data link layer

1mura-physical layer

For example: application layer-e-commerce platform (the corresponding application layer protocol in application software)

Presentation layer-carpenter (responsible for data compression, coding) session layer-secretary (responsible for file sending / receiving) transport layer-express company (EMS--TCP; SF-UDP) network layer-distribution ZTE (router) data link layer-express brother (switch) physical layer-driver and vehicle (network cable / optical fiber)

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.