Simulation of multiple access protocols for real-time control

Article Abstract:

The simulation activity described in this paper was undertaken for the design of a hierarchical multiple access communication network for a distributed real-time control system. The network consisted of multiple busses hierarchically connected by bridges. High bandwidth control loops were closed over local busses. Lower rate loops and status information were shared between busses. Multiple simulation methodologies were employed to design and validate the communications protocol for the network. The methodologies included mathematical analysis, functional simulation, and physical simulation. Each method elucidated a separate aspect of the protocol's behavior. The unique contribution of each method yielded a comprehensive understanding of the proposed design and permitted model validation by cross-checking the results. The original traffic load for this study included messages with maximum acceptable delays between 0.001 and 1.0 seconds. The speed of the network was limited to less than 1.0 megabit per second (Mbps) for electrical reasons. The results demonstrated an unacceptable probability of delay for the highest rate messages, even at the maximum bus speed. A separate dedicated link was therefore added to the control system for the highest rate messages. (Reprinted by permission of the publisher.)

Communications, Control systems, Real time systems, Networks, Communication, Real-Time System

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Simulation investigation on message based CSMA-CD priority protocols

Article Abstract:

In this paper, we develop a simulation model to analyze three different protocols for prioritized messages in CSMA-CD environment. Using SLAM II simulation language, the different phases of message transmission are represented as discrete events. Traffic loads and priority ratios of messages are included in the model. Performance measures such as throughput, average waiting time, and average number of collisions are collected during the simulation runs. Analysis of variance (ANOVA) is performed on the outputs and indicates statistically significant differences in performance for the three protocols tested. This simulation modeling approach and subsequent analysis can be easily extended to include more factors and protocols in CSMA-CD systems. (Reprinted with permission of the publisher.)

Modeling, Data modeling software, Performance Measurement, Carrier Sense Multiple Access/Collision Detection, technical

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Layered simulation of Bridge protocols for Multi-LAN Ethernet Communication Systems

Article Abstract:

The IEEE 802.1 Spanning Tree Algorithm attempts to alleviate bridging problems when multiple local area networks (LANs) are linked. Often, multiple bridges try to forward the same network traffic to and from connecting LANs. Duplicate packets, wasteful network traffic loads and infinite looping are some resulting problems associated with LAN connectivity. The Spanning Tree Algorithm lacks the ability to control the amount of maintenance traffic areas with cycles. Because it is based on a centralized scheme, a failure in a root can cause the other bridges to re-compute their states. A new algorithm is discussed called the Self-Stabilizing Bridge Protocol that is based on a loop-detect packet. (Reprinted by permission of the publisher.)

Packet switches, Packet Switch, Tree-Pruning Strategies

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