Research On Real-time Task Scheduling Algorithms Of Industrial Ethernet

With the development of the Network Control System(NCS), the traditional DistributedControl System(DCS) and Fieldbus Control System(FCS) faces great challenges in thetransmission rate, protocol standard and cost-control, both of them have been very difficult tomeet the present needs. The Industrial Ethernet has been got more and more attentions becauseof its high transmission rate, uniform protocol and lower cost. However, the “Reliability” and“Real-time” of the Industrial Ethernet data transmission cannot be guaranteed, so the IndustrialEthernet cannot be directly applied in the NCS and the real-time researching has become ahotspot.The cause of unreliability and low real-time about the Industrial Ethernet is due to adoptingthe CSMA/CD transmission mechanism. If a collision occurs during the data transmission, thiswill cause a backoff procedure and time delay. The data will be discarded if the collisionshappened continuously, so it is not reliablity. In order to avoid the data collision, the timeslottechnology is a main solution which can be called as Time Division Scheduling Ethernet(TDSE).In this thesis, we present a Time Division Task Scheduling (TDTS) algorithm based onTDSE: As a result of the traditional time division scheduling Ethernet cannot to control thepacket generation process, queuing delay is generated after the packet generates to ahead of itstimeslot. Especially these timeslot sequence disadvantaged nodes, the queuing delay is veryobvious, the QoS(Quality of Service) of the high priority tasks are not guaranteed, these will beharmful to NCS. TDTS combines the packets generation process and transfer process to modlingand analysis. It controls the packets generation time by optimizing and scheduling its tasksexecution time and quantity, each packet transfers as soon as it generates without queuing delayand data collision, so that the real-time performance and reliability are improved.We also present a real-time synchronous switching technology for the NCS which based onlayer-4switch network: With the increasing scale of the NCS, more node numbers, more rich communication contents, more frequent information transfer, people begin to introduce thenetwork switching technology into the industrial control system. But, in the industrial controlenvironment, there’s a lot of periodic real-time data which has a short frame structure. When thenetwork load increase, the traditional end-to-end switching technology produces queuing delayobviously, transmission efficiency is low and bandwidth utilization is high. By this synchronousswitching technology, it optimizes the communication task numbers of each switch port andschedules the task execution times during the aperiodic data transfer phase. And during theperiodic data transfer phase, packets can be received and forwarded synchronously according tothe four steps–receiving, splitting, reorganizing&forwarding-which is a special design ofswitching architecture. This method reduces the queuing delay, improves the synchronization ofdata transmission, higher transmission efficiency and lower bandwidth utilization can also beobtained under this method.