I. Introduction
The network environment of a modern industrial enterprise can generally be divided into four levels:
Internet: to achieve information exchange between enterprises;
Intranet: Informatization of internal management, finance, office and personnel of the enterprise;
Infranet: to achieve comprehensive management, scheduling and monitoring of on-site production equipment at industrial enterprises;
Embedded Network: Embedded network. Realize real-time communication between multiple distributed subsystems within the production equipment.
The Internet and Intranet are all based on the TCP / IP protocol cluster. Intranet is an extension of the Internet for the wide area network on the internal LAN of the enterprise. The construction of Infranet currently mainly uses various fieldbus protocols, such as ProfiBus, Lonwork, CAN, etc.
With the progress of society and the development of technology, modern electromechanical control systems often include several subsystems, each of which is self-contained, has its own independent CPU, and is closely coordinated with other subsystems. Embedded network is the means to realize mutual communication between subsystems.
2. Special requirements for embedded networks
Embedded networks are usually applied in industrial production sites with harsh environments, so they have their own unique requirements in the following aspects:
1. Real-time: The information coupling of multiple distributed subsystems in the production equipment is usually relatively tight, and the requirements for real-time are very high. This requires the network protocol used to have determinable real-time performance, that is, the response time under extremely bad conditions is Definable; in addition, when there are many network nodes, or some nodes have particularly high requirements for real-time response, the network protocol should also support priority scheduling to improve the certainty of information transmission for time-critical tasks.
2. Reliability: The reliability of the embedded network itself directly affects the effective operation rate, finished product rate and production efficiency of the equipment, and requires the network to dynamically add / delete nodes; the harsh electromagnetic environment at the production site requires the embedded network itself to have a strong The anti-interference ability, error detection and correction ability and rapid recovery ability;
3. Communication efficiency: One of the characteristics of embedded network communication is that the communication between subsystems is very frequent, but the information length of each communication is very short. Therefore, the embedded network protocol is required to adopt a short frame structure, and the frame header and frame tail As short as possible to improve communication efficiency and bandwidth utilization;
4. Double hybrid support: The huge difference in different working environments determines that the embedded network should have flexible media access protocols, not only support multiple media (twisted pair, coaxial cable, optical cable), but also support mixed topology (star , Ring, bus), sometimes even require the same embedded network can use multiple media and multiple network topologies at the same time. For example, in a noisy environment, a part of the system needs to use optical cables, and other parts use twisted pair or coaxial cables. Coaxial cable is suitable for bus topology, while optical fiber is more suitable for ring or star topology, which requires double hybrid support for network protocols.
5. Implementation difficulty and cost: Embedded systems usually need to be specially designed and manufactured according to actual needs. This requires that the network system software and hardware be easy to implement and integrate with the subsystem control part. The related components are highly commercialized and costly Lower.
6. Openness: The embedded network must have good openness. On the one hand, it can be connected to the intranet through the enterprise Infranet to realize the integration of management and control of the enterprise's production management; on the other hand, it should have an open and transparent development interface with complete data to achieve Independent development and integration of system hardware and software.
In addition, the embedded network system must be flexible in configuration and easy to maintain.
Generally, the embedded network belongs to the local area network in terms of coverage. According to ISO / OSI, the TCP / IP protocol cluster is located above the network layer. Obviously, the TCP / IP protocol cluster has exceeded the scope of embedded network systems. The embedded network includes the physical layer and data link layer in the ISO / OSI seven-layer model. The specific implementation of the data link layer can be divided into two sublayers: medium access control sublayer (MAC sublayer) and logical link control sublayer (LLC sublayer). The MAC sublayer includes the physical layer interface hardware and the communication controller that implements the media access protocol; usually the LLC sublayer is implemented by software (developed by the user). Therefore, the core of network communication protocol selection in embedded system design is the choice of media access protocol.
Hd Screen Protector,High-Definition Screen Protector,Hd Clear Screen Protector,Transparent Screen Film
Shenzhen TUOLI Electronic Technology Co., Ltd. , https://www.szhydrogelprotector.com