What are the seven levels of the OSI Reference Model?

Layer 1: Physical layer.

To solve the problem of how to communicate between two pieces of hardware, common physical media include optical fiber, cable, and repeater.

Wait. It mainly defines the standards of physical devices, such as the interface type of network cable, the interface type of optical fiber, and the transmission rate of various transmission media.

Layer 2: Data link layer.

The data link layer is from the network layer.

Receive packets, packets.

Contains the IP addresses of the sender and receiver.

The data link layer performs two basic functions. It allows the upper layer to access the media using various techniques such as framing, controlling how data from the medium is placed and received.

Layer 3: Network layer.

The transport layer passes data segments to the network layer. The network layer is used to transfer received segments of data from one computer to another computer located in a different network. The unit of data at the network layer is called a packet, and the functions of the network layer are logical addressing, routing, and path determination.

Layer 4: Transport layer.

The main task of the lower three layers of OSI is data communication, the task of the upper three layers is data processing, and the transmission layer is the fourth layer, so this layer is the interface and bridge between the communication subnet and the resource subnet, and plays the role of connecting the upper and lower layers.

Layer 5: Session layer.

is a user application.

and the network, the main task is to organize and coordinate the communication between the two session processes and to manage the data exchange.

Sixth layer: represents the layer.

The presentation layer refers to the data received from the application layer, which is in the form of characters and numbers, and the presentation layer converts this data into binary that can be understood by the machine.

The highest level, which enables the interface between computer users and various applications and networks, is used by network applications, such as https protocol, http protocol.

The application layer provides services to the network through protocols and performs user activities.

The 7 levels of the OSI reference model are:

Physical Layer, Data Link Layer, Network Layer, Transport Layer, Session Layer, Presentation Layer, and Application Layer.

Hope, thanks.

Layer 1 Physical Layer: At the lowest level of the OSI reference model. The main function of the physical layer is to provide a physical connection to the data link layer using the physical transmission medium for transparent transmission of bitstreams.

Layer 2 Data Link Layer—This is where the data is framed and flow control is handled. The shielded physical layer provides a data link connection to the network layer for virtually error-free data transmission over a physical connection that is likely to go wrong.

This layer specifies the topology and provides hardware addressing;

Layer 3 Network Layer: This layer establishes the connection between two nodes through addressing, selects the appropriate routing and switching nodes for the packets sent by the transport layer at the source end, and transmits them to the transport layer at the destination according to the address correctly. It includes routing and relaying data over interconnected networks;

Layer 4 Transport Layer: - General Data Delivery Connection-oriented or connection-free. Provide an end-to-end reliable, transparent, and optimized data transfer service mechanism for session layer users. Includes full-duplex or half-duplex, flow control, and error recovery services;

Layer 5 Session Layer: —Establish an end-to-end connection between two nodes. Provides a dialogue control mechanism between applications on the end system. This service includes whether the connection is set up in full or half-duplex, although duplex can be handled in layer 4;

Layer 6 Presentation Layer: It is mainly used to deal with the representation of information exchanged between two communication systems. Solve the grammatical problems of user information for upper-level users. It includes functions such as data format exchange, data encryption and decryption, data compression and recovery, etc.;

Layer 7 Application Layer: The highest layer in the OSI. Provides a means of accessing the OSI environment for specific types of network applications.

The application layer determines the nature of communication between processes to meet the needs of the user. The application layer should not only provide the information exchange and remote operation required by the application process, but also complete some functions necessary for information exchange as the user of the application process. It includes:

File transfer access and management protocols such as FTAM, Virtual Terminal VT, Transaction Processing TP, Remote Database Access RDA, Manufacturing Message Specification (MMS), and Directory Service (DS).

From low to high, they are: physical layer, data link layer, network layer, transport layer, session layer, presentation layer, and application layer.

OSI is an abbreviation for Open System Interconnect. The International Organization for Standardization (ISO) has developed the OSI model. This model divides the work of network communication into seven layers, namely the physical layer, the data link layer, the network layer, the transport layer, the session layer, the presentation layer and the application layer.

1. Layer 7 application layer: the highest layer in the OSI. It provides access to the OSI environment for specific types of web applications. The application layer determines the nature of inter-process communication to meet the needs of users.

Basic functions: The application layer not only provides the information exchange and remote operation required by the application process, but also acts as the user of the application process to complete some functions required for information exchange.

2. Layer 6 presentation layer: mainly used to process the representation of information exchanged between two communication systems.

Basic function: Solve the grammar problem of user information for upper-level users. It includes data format exchange, data encryption and decryption, data compression, and terminal type conversion.

3. Layer 5 session layer: establishes an end-to-end connection between two nodes. It provides a dialogue control mechanism between terminal system applications.

The service includes establishing connections in full-duplex or half-duplex mode, although duplex mode can be handled in Layer 4; The session layer manages the logon and logoff process.

Basic features: It specializes in managing conversations between two users and processes. If only one user is allowed to perform specific operations at a time, the session layer protocol manages these coarse operations, such as preventing two users from updating the same set of data in the database at the same time.

4. Layer 4 transport layer: The transport layer is the interface layer between the high and low layers in the network architecture. The transport layer is not only a single fabric layer, but also the core of the entire analytics architecture protocol.

The transport layer provides users at the session layer with an end-to-end reliable, transparent, and optimized data transmission service mechanism.

Basic functions: It includes full-duplex or half-duplex, flow control, and error recovery services; The transport layer divides messages into groups and reorganizes them at the receiving end. Different packets can be sent to the host over different connections.

In this way, higher bandwidth can be obtained without impacting the session tier.

When a connection is established, the transport layer can request quality of service, which specifies acceptable parameters such as bit error rate, latency, security, and so on. It also enables end-to-end flow control capabilities.

5. Layer 3 network layer: This layer establishes the connection between two nodes through addressing, and selects appropriate routing and switching nodes for the packets sent by the transport layer of the source. and correctly transmitted to the transport layer of the destination according to the address.

Basic functions: it includes routing and relaying data over interconnected networks; In addition to routing, the network layer is responsible for establishing and maintaining connections, controlling network congestion, and generating billing information when necessary.

6. Layer 2 data link layer: In this layer, the data is framed and the flow control is processed. Shielding the physical layer, providing data link connectivity to the network layer and performing virtually error-free data transmission (error control) for physical connections that can go wrong.

Basic Functionality: This layer specifies the topology and provides hardware addressing. Commonly used equipment includes bridges and switches.

Basic functions: The main function of the physical layer is to use the physical transmission medium to provide a physical connection to the data link layer to achieve transparent transmission of bit streams.