What is the Layer 7 protocol of the network?

OSI is an open reference model for interconnection of access systems, and it is a very well defined protocol specification. The OSI model has a 7-layer structure, and each layer can have several sub-layers. Let me briefly introduce these 7 layers and their functions.

The 7 layers of OSI are from top to bottom.

7. Application layer. 6 represents the layer.

5 session layers. 4 transport layers.

3. Network layer. 2 Data Link Layer.

1 physical layer.

In order to realize the interconnection of computer systems, the OSI reference model divides the communication functions of the entire network into seven levels, and also defines the interrelationships between the layers, the services included in each layer, and the functions of each layer. The seven layers of OSI from low to high are: physical layer, data link layer, network layer, transport layer, session layer, presentation layer, application layer, the lower three layers (physical layer, data link layer, network layer) are oriented to data communication, and the upper three layers (session layer, presentation layer, application layer) are oriented to resource subnets, and the transmission layer is the most important layer of the seven layers.

It is located in the middle of the upper and lower layers and plays the role of connecting the upper and lower layers.

1 physical layer.

Provides a physical connection to the data link layer for the transparent transmission of the bit stream, and the data transmitted in bits, which defines the electrical, mechanical, and functional and process characteristics of the hardware that interfaces the communication device with the transmission line.

2 Data Link Layer.

Establish a data link connection between the communicating entities, transmit data in frames, and ensure that the bit sequence is composed as a data stream that is accurately transmitted to the other system by checking for bit errors that occur in the transmission path between the connected communication systems and recovering them. The data link layer enables transparent, highly reliable transmission between adjacent nodes.

3. Network layer.

Solve the routing selection, congestion control and network interconnection when multi-node transmission, control the operation of the packet transmission system, its characteristics are transparent to the high-level, at the same time, select the quality of service according to the requirements of the transport layer, and report the unrecovered errors to the transport layer.

4 transport layers.

Establish a transmission connection between the session layer of two end systems (origin and destination) to reliably and transparently transmit packets, and perform error control, sequence and flow control, and management multiplexing. This layer provides the ability to establish, maintain, and tear down transmission connections, and guarantees the quality of network connections. It shields the details of the lower layer data communication to the upper layers and is therefore the most needed layer in the OSI network reference model.

5 session layers.

It does not participate in the specific data transmission, but manages the synchronization of data transmission. It is primarily responsible for establishing, maintaining, and terminating session connections between two processes, as well as managing the necessary information transfer methods, synchronization between processes, and resynchronization in the process.

6 represents the layer.

Solve the conversion between the encoding of different data formats, syntax selection, data encryption and decryption, and text compression when exchanging information between two communication systems.

7. Application layer.

Responsible for providing users with various web application services, such as file transfer, e-mail, remote access, etc. The part of the process that communicates with each other's process is placed in the application entity, and the communication function of various business contents is managed.

The first layer is the physical layer.

The second layer is the data link layer.

The third layer is the network layer.

The fourth layer is the transportation layer.

The fifth layer is the session layer.

The sixth layer is the presentation layer.

The seventh layer is the application layer.

A network protocol is made up of three elements:

1) Semantics. Semantics is the interpretation that controls the meaning of each part of the information. It specifies what kind of control information needs to be sent, as well as what actions are completed and what kind of responses are made.

2) Grammar. Syntax is the structure and format of user data and control information, and the order in which the data appears.

3) Timing. A timing is a detailed description of the sequence in which events occur. (Also referred to as "synchronization").

People vividly describe these three elements as semantics, syntax, and chronology.

The OSI reference model consists of seven layers: the physical layer, the data link layer, the network layer, the transport layer, the session layer, the presentation layer, and the application layer.

The respective roles are as follows:

1. The main function of the physical layer is to use the transmission medium to provide physical connection for the data link layer, and is responsible for the physical transmission of the data stream. The basic units of physical layer transmission are the bit stream, that is, 0 and 1, that is, the most basic electrical signal or optical signal, which is the most basic physical transmission characteristic.

2. The data link layer is to establish a data link connection between communication entities, and the data link control sublayer will accept network protocol data, packet datagram and add more control information, so as to transmit this packet to its target device.

3. The network layer is the key layer that overlooks the network with the router as the highest node, and it is responsible for the routing of packets from the source network to the destination network. The Internet is a collection of multiple networks, and it is with the help of the routing path selection function of the network layer that the connection between multiple networks can be smooth and information can be shared.

4. The transport layer uses the network connection service provided by the network layer, and according to the system requirements, you can choose to use the connection-oriented service or the non-connection-oriented service for data transmission.

5. The main function of the session layer is to maintain the transmission connection between the two nodes, ensure that the point-to-point transmission is not interrupted, and manage data exchange and other functions. The session layer establishes, manages, and terminates sessions in the application process. The session layer can also use dialog control to decide which communication method to use, full-duplex or half-duplex communication.

The session layer coordinates requests and responses through its own protocols.

6. The main function of the presentation layer is to deal with the representation mode of exchanging information in the two communication systems, mainly including data format change, data encryption and decryption, data compression and decompression, etc. Under the premise of a certain network bandwidth, the smaller the data compression, the faster the transmission rate, so the data compression and decompression of the presentation layer are regarded as the key factors to master the network transmission rate.

7. The application layer adopts the application protocols of different halls to solve different types of application requirements, and ensures that the low-level communication protocols used by these different types of applications are consistent. The application layer contains several independent user common service protocol modules to provide dedicated program services for communication between network users.

About OSI:

OSI (Open System Interconnect) is an open system interconnect. Generally known as the OSI reference model, it is a network interconnection model studied by the ISO organization in 1985. This architecture standard defines a seven-layer framework (physical, data link, network, transport, session, presentation, and application layer) for network roll-virtual interconnect, the OSI Open Systems Interconnection Reference Model.

Application layer. Represents the layer.

Session layer. Transport layer.

Network layer. Data link layer.

Physical layer.