Analysis of Mean Access Delay in Variable-Window CSM.

Marek Miśkowicz

doi:10.3390/s7123535

Abstract

The paper addresses the problem of the mean access delay characteristics in termof the channel load for networked sensor/control systems in LonWorks/EIA-709 technology.The system modelling is focused on the Media Access Control protocol that provides theload prediction and determines the key network characteristics. The network model assumesthe consistency of load prediction between the nodes, and that the Transaction ControlSublayer does not introduce limitations on the data transmission. The latter means that thenumbers of concurrent outgoing transactions being in progress are unlimited. Furthermore, itis assumed that the destination addresses of transmitted messages are distributed rather thanconcentrated on particular nodes. The analytical approach based on Markov chains isapplied. The calculation of transition probabilities of the Markov chain is exemplified by theload scenario where all the transactions are acknowledged, unicast, and the optionalcollision detection is enabled. On the basis of the stochastic analysis, the probabilities of asuccessful transmission and collision, respectively, are computed. Furthermore, thenumerical results of the mean access delay are reported. The simulative validation ofanalytical results is provided.

Highlights

One of generic algorithms for random access control in networked systems is the p-persistent Carrier Sense Multiple Access (CSMA) protocol
The paper addresses the issue of the mean access delay characteristics in term of the channel load for the predictive p-persistent CSMA media access protocol which belongs to the variable-window CSMA algorithms with collision avoidance
Our interest in the characteristics of the predictive pCSMA stems from the practical aspect of it as it is used in real control network protocol successfully implemented Operating Networks (LonWork/EIA-709) platform

Summary

Introduction

One of generic algorithms for random access control in networked systems is the p-persistent CSMA protocol. The channel utilization in the p-persistent CSMA is strongly affected by the p value which represents the persistence level of the protocol. Large p values cause excessive collisions, while small p values degrade the bandwidth utilization forcing the channel to be idle. A tradeoff between large and small values is necessary to provide the bandwidth utilization at the satisfactory level. If a number of contenders is unknown a priori or varies in time, the p value cannot be set optimally, and the performance of p-persistent CSMA may be considerably degraded. The CSMA-based protocols with collision avoidance try to adapt to the number of contending nodes

Methods

Results

Conclusion