Study On The Real Time Character Of Several Communication Networks In Network Control System

With the quick development of information technology, Industrial network is the key of the new control system. NCS (Networked Control System) is a kind of feedback control system wherein the control loop is closed through real-time control network. Its performance mainly depends on the real-time performance of industrial network. So, this paper mainly studys "the real-time character of several communication networks in network control system" sponsored by National Natural Science Foundation of China: "Modeling and Analysis of Fieldbus-Based Real-time Industrial Communication System" (No. 60084001) and "Analysis and Improvement of High Speed Ethernet in Realtime Capability" (PRA SI-0104). The paper is divided into four parts:In the first part, the research is focused on RPOFIBUS. This paper analyzes the temporal character of PROFIBUS using the worst case scheduling and obtains the sufficient and necessary condition satisfied to schedulability. Based on the character of industrial application, this paper provides a holistic scheduling to control the sequence of token rotation using graph theory, which improves the temporal function of PROFIBUS.The second part is about switched Ethernet that is the most important part of this paper. This paper presents a theoretic analysis of the temporal characteristics of output buffer in switch, gives the probability distribution function of delay and average queuing time, and compares the end-to-end delay between traditional and switched Ethernet. VLAN is one of important technologies that switch has to implement. Switch has to rapidly and efficiently find and maintain an un-looped topology. This paper configures VLAN based on Cisco's VTP and proposes a spanning tree protocol based on proposal/agreement negotiation. This protocol can get topology recovery rapidly, reduce the forwarding delay, and improve the temporal capacity. Then, this paper gives the application of QoS in switched Ethernet. QoS is often used to improve the real-time function in network. This paper adapts WFQP(WFQ based priority) to schedule frame. This method not only guarantees the real-time traffic's demand, but also makes low priority frame get response timely.The third part mainly discussses the wireless control network. With the rapid development of Wireless technology, Wireless LAN is more and more used in industry where real-time requirement is important. In Ad hoc, based on DCF (distributed coordination function) of IEEE 802.11, this paper introduces a new MAC, which divides the packet into three kinds: non-periodic real-time information, periodic real time information, and non real-time information. The priority of these three information packets demotes in turn. Through using different IPS (inter-frame space) to distinguish different information, the new MAC uses RTS/CTS to transmit frames with different priorities, so the real-time information can get a smaller delay. Simulation validates the proposed approach. Wireless and wire network are combined into a total network, which is the trend of industrial network. This paper analyzes the several configurations. IP-based configuration leads to the best result.The fourth part mainly studies the application of profibus and switched Ethernet in the paper-making industries.In the last part, the paper presents the reseach conclusions, proposes the innovative ideas, and points out the remaining problems that need further research.