Study On The Theory And Technology Of The Real-time Industrial Communication Based On Switched Ethernet

The emergence of the switching technology not only improves the transmission rate and bandwidth of Ethernet but also provides many new features for the industrial communication support. However, there are quite a few theorical and technological problems in applying the switched Ethernet to industrial field directly. This dissertation mainly studies the related theories and key technologies on the switched-Ethernet-based real-time industrial communication. After the deep analysis of the industrial communication oriented switched Ethernet's temporal characteristics, this dissertation proposes solutions from both static and dynamic aspect to solve the problems in the control networking based on switched Ethernet. The main work is as follows:(1) Analysis of the industrial communication oriented switched Ethernet's temporal characteristics. Delays have great influences on the control network's performance. Topologies most in use and data characteristics of the network control system are considered and corresponding delay models under different scheduling policies are derived based on stochastic network calculus. Then the distribution of delays and stochastic upper bound on delays of real-time data in the control network are calculated. The results are compared with the guaranteed upper bound on delays derived by deterministic network calculus and the pessimism of the bound is evaluated.(2) Optimization of the control networks' topology based on switched Ethernet (static solution). Factors that affect the real-time performance of the industrial control network are presented in detail, and optimization criteria with their internal relations are analyzed. After the definition of performance parameters, the normalized indices for the evaluation of the topology optimization are proposed. The topology optimization problem is formulated as a multi-objective optimization problem and the evolutionary algorithm is applied to solve it. Special communication characteristics of the industrial control network are considered in the optimization process. In respect to the evolutionary algorithm design, an improved arena algorithm is proposed for the construction of the non-dominated set of the population. In addition, for the evaluation of individuals, the integrated use of the dominative relation method and the objective function combination method, for reducing the computational cost of the algorithm, are given. Simulation tests show that the performance of the proposed algorithm is preferable and superior compared to other algorithms. The final solution greatly improves the following indices:traffic localization, traffic balance and utilization rate balance of switches. In addition, a new performance index with its estimation process is proposed.(3) A switch design for the real-time industrial communication (dynamic solution in switches). Considering the challenges in the application of the virtual-output-queue based input-queue switches to control network, this dissertation proposes a new switch structure. Accordingly, a method for the cell sequence control based on the record matrix and demand matrix is designed, which eliminates the uncertainty of cells' behavior and delay in switches. The characteristics of the traffic in control network are taken into account and a two-level scheduling mechanism is proposed. The link scheduler provides the class of service while the switch scheduler is responsible for the match. In the latter scheduler, a layered frame-based match algorithm is designed. The layer mechanism provides a compromise between the schedulable ratio and complexity. Simulation results show that the algorithm achieves a higher schedulable ratio compared with other frame-based algorithms and the switch structure with its scheduling strategy can provide better deterministic real-time guarantees.(4) Study on the distributed bandwidth allocation strategy (dynamic solution in end nodes). One of the main problems of applying the switched Ethernet to control applications is how to adapt it to the typical industrial communication with least changes. Considering the communication characteristics of the control network, this dissertation proposes a distributed bandwidth allocation strategy based on the time-slot. Models of communication tasks and bandwidth resources in the network control system based on switched Ethernet together with the control methods of the message transmission and the scheduling algorithm of the strategy are provided. Existing distributed scheduling proposals often cannot deal with the situation that communication tasks change frequently and both schedulable ratio and bandwidth utilization are low. By the experimental analysis and comparisons, the proposed strategy guarantees the transmission of the real-time communication tasks with their deadlines, and furthermore it solves the above problems of existing proposals.(5) The application of switched Ethernet to networked numerical control system. Finally, the dissertation takes a typical application in industrial control-the service-oriented network numerical control system as an example to analyze the coordination design of communications tasks and other tasks in the implementation of network real-time systems. And the effectiveness of the task design is proved by experiments.