Li, Xiaoting. Worstcase delay analysis of realtime switched Ethernet networks with flow local synchronization. PhD, Réseaux, Télécoms, Systèmes et Architectures, Institut National Polytechnique de Toulouse, 2013

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Official URL: http://ethesis.inptoulouse.fr/archive/00002384/
Abstract
Fullduplex switched Ethernet is a promising candidate for interconnecting realtime industrial applications. But due to IEEE 802.1d indeterminism, the worstcase delay analysis of critical flows supported by such a network is still an open problem. Several methods have been proposed for upperbounding communication delays on a realtime switched Ethernet network, assuming that the incoming traffic can be upper bounded. The main problem remaining is to assess the tightness, i.e. the pessimism, of the method calculating this upper bound on the communication delay. These methods consider that all flows transmitted over the network are independent. This is true for flows emitted by different source nodes since, in general, there is no global clock synchronizing them. But the flows emitted by the same source node are local synchronized. Such an assumption helps to build a more precise flow model that eliminates some impossible communication scenarios which lead to a pessimistic delay upper bounds. The core of this thesis is to study how local periodic flows synchronized with offsets can be handled when computing delay upperbounds on a realtime switched Ethernet. In a first step, the impact of these offsets on the delay upperbound computation is illustrated. Then, the integration of offsets in the Network Calculus and the Trajectory approaches is introduced. Therefore, a modified Network Calculus approach and a modified Trajectory approach are developed whose performances are compared on an Avionics FullDupleX switched Ethernet (AFDX) industrial configuration with one thousand of flows. It has been shown that, in the context of this AFDX configuration, the Trajectory approach leads to slightly tighter endtoend delay upper bounds than the ones of the Network Calculus approach. But offsets of local flows have to be chosen. Different offset assignment algorithms are then investigated on the AFDX industrial configuration. A nearoptimal assignment can be exhibited. Next, a pessimism analysis of the computed upperbounds is proposed. This analysis is based on the Trajectory approach (made optimistic) which computes an underestimation of the worstcase delay. The difference between the upperbound (computed by a given method) and the underestimation of the worstcase delay gives an upperbound of the pessimism of the method. This analysis gives interesting comparison results on the Network Calculus and the Trajectory approaches pessimism. The last part of the thesis, deals with a realtime heterogeneous network architecture where CAN buses are interconnected through a switched Ethernet backbone using dedicated bridges. Two approaches, the componentbased approach and the Trajectory approach, are developed to conduct a worstcase delay analysis for such a network. Clearly, the ability to compute endtoend delays upperbounds in the context of heterogeneous network architecture is promising for industrial domains.
Item Type:  PhD Thesis 

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Institution:  Université de Toulouse > Institut National Polytechnique de Toulouse  Toulouse INP (FRANCE) 
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Research Director:  Fraboul, Christian and Scharbarg, JeanLuc 
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Deposited On:  29 Nov 2013 22:58 
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