In today's globalized world, the exchange of information is everywhere. In the communication of the Internet of Things, in the face of different devices, we often need to use a variety of communication protocols. The essence of the Internet is a series of network protocols. This protocol is called OSI protocol (open system interconnection). According to different functions, the division of labor is different, and the artificial layering is seven layers. Each layer runs a different protocol, what the protocol does, the protocol is the standard, the rule, and following different rules is to use different communication protocols. In fact, some people divided it into five or four floors. The seven layers of OSI are divided into: application layer, presentation layer, session layer, transport layer, network layer, data link layer, and physical layer. The five layers of TCP / IP are divided into: application layer, transport layer, network layer, data link layer, and physical layer. The four layers of TCP / IP are divided into: application layer, transport layer, network layer, and network interface layer. It does not matter how many layers are divided, because the seven layers do not physically exist, the concept of these seven layers is only artificial division, the purpose of the distinction is only to allow us to better understand which layer's role . The OSI (Open System Interconnection) seven-layer network model is called the Open System Interconnection Reference Model, which is a logical definition and a specification. The main purpose of establishing the seven-layer model is to solve the compatibility problems encountered when heterogeneous networks are interconnected. Its main function is to help different types of hosts to realize data transmission. Its biggest advantage is to clearly distinguish the three concepts of service, interface and protocol, and to achieve reliable communication between different systems and different networks through seven hierarchical structural models. First, the physical layer (Physical Layer) The lowest or first layer of the OSI model. This layer includes physical networking media, such as cable connections. The protocol at the physical layer generates and detects voltages to send and receive signals that carry data. To transmit information, users must use some physical media, such as twisted pair, coaxial cable, etc. The task of the physical layer is to provide a physical connection to its upper layer, as well as their mechanical, electrical, functional and process characteristics. For example, the type of cables and connectors used, the voltage of the transmitted signal, etc. are specified. At this level, the data is only treated as high and low levels, in bits. Second, the data link layer (Datalink Layer) Control the communication between the network layer and the physical layer, and the data received from the network layer is divided into specific frames that can be transmitted by the physical layer. A frame is a structural packet used to move data. It includes not only the original data, but also the physical address (MAC) and error detection and control information of the sender and receiver. The address in it determines where the frame will be sent, and the error correction and control information ensures that the frame arrives error-free. If, when transmitting data, the receiving point detects an error in the transmitted data, it will notify the sender to resend the frame. The functions of the data link layer in this layer include: physical addressing, network topology, data framing, data error detection, and retransmission. 3. Network Layer The main function is to translate the network address (IP) into the corresponding physical address (MAC) and decide how to route the data from the sender to the receiver. The Internet is a decentralized network. The network layer determines the path from node A in one network to node B in another network by comprehensively considering the transmission priority, network congestion level, service quality, and the cost of optional routing. 4. Transport Layer This is the most important layer in the network model. The transmission protocol performs flow control at the same time or specifies an appropriate transmission rate based on how fast the receiver can receive data. The transport layer forcibly splits longer data packets according to the maximum size the network can handle. For example, Ethernet cannot receive data packets larger than 1 500 bytes. The transmission layer of the sending node divides the data into smaller pieces of data, and arranges a sequence number for each piece of data so that the data reaches the receiving node The transport layer can be reorganized in the correct order. A service that works at the transport layer is TCP (Transmission Control Protocol) in the TCP / IP protocol suite. The TCP protocol is the foundation of the Internet communication protocol. 5. Session Layer Responsible for establishing, maintaining, and terminating communication between two nodes in the network, deciding the access sequence of the session, and serving the presentation layer. The functions of the session layer include: establishing a communication link, keeping the communication link unobstructed during the conversation, synchronizing the dialogue between the two nodes, deciding whether the communication is interrupted and where to resend when the communication is interrupted. Sixth, the presentation layer (Presentation Layer) The translator between the application and the network converts different data formats to a common format so that it can be recognized by different systems. Presentation layer Pyrolysis Reaction Kettle,Stainless Steel Reactor,Stainless Steel Reaction Kettle,Mixer Polymerization Reactor Wuxi Mingyan Equipment Co., Ltd , https://www.wxmygroup.com