The Timed Asynchronous Modeland it’s Applicationin Time-Triggered ProtocolsRuiqi HuMay 2, 20001Previous Work•Timed Asynchronous (TA) Model–Asynchronous communication network– Probabilistic clock synchronization•Time-Triggered Protocols (TTPs)– Dedicated, synchronous communication net-work–Hardware supported clock synchronizationA Hybrid System Model•Goal:to provide a quasi-synchronous inter-face for asynchronous systems.•Systemconsists of clustersof processors.•Intra-Cluster Communicationis syn-chronous.•Inter-Cluster Communication is asyn-chronous.•Gatewayis the interface processor betweena cluster and the rest of the system.Clock Synchronization•Processors in a cluster synchronize to theirgateway.• Gateways are internally/externally synchro-nized.• Probabilistic clock synchronization is used toachieve inter-cluster synchronization.Probabilistic Clock Synchronization2dt’t t"min+a min+b2DSlaveTimeRealT’TMaster•T0∈[T + min(1 − ρ), T + 2D(1 + 2ρ)−min(1 +ρ)]• Best estimate= T+ D(1 + 2ρ)−min · ρ•Precision = D(1 + 2ρ) − minAsynchronous Behavior0100200300400500600700800150 200 250 300 350 400NumberofpackegesRound-trip delay(in microseconds)Round-trip delay measured at different network loads(30,000 samples)Heavy loadLight loadAdaptive Clock Synchronization•Synchronization probability and precision de-pend on the chosen of round-trip timeout 2U.•A slave processor increases/decreasesU whenit observes the increasing/decreasing of net-work load.• More consecutive timeouts ⇒increasing net-work load observed.•Round-trip delay consistently smaller thana given value(which is smaller than 2U) ⇒decreasing network load observed.Simulation ResultsLight Load Heavy LoadProbabilistic Protocolfailure # 107/45068 3125/16194failure percentage 0.24% 19.30%Adaptive Protocolfailure # 23/45227 578/22696failure percentage 0.05% 2.55%Round-trip timeout 2U = 280ms, k= 4.Conclusions•Hybrid system model could provide quasi-synchronous semantics for asynchronous sys-tems.•Adaptive clock synchronization protocol im-proves synchronization quality
View Full Document
Unlocking...