Frame Relay Congestion ControlOverviewFrame Relay Congestion TechniquesDiscard ControlSlide 5Slide 6Slide 7Leaky Bucket AlgorithmFECNImplicit Congestion ControlSummaryHomeworkRaj JainThe Ohio State University1Frame Relay Frame Relay Congestion Congestion ControlControlRaj Jain Professor of Computer and Information SciencesThe Ohio State UniversityColumbus, OH 43210 http://www.cse.ohio-state.edu/~jain/Raj JainThe Ohio State University2OverviewOverviewCongestion avoidance vs recoveryDiscard controlExplicit forward/backward congestion notificationImplicit notificationRaj JainThe Ohio State University3Frame Relay Frame Relay Congestion TechniquesCongestion TechniquesDiscard Control (DE Bit)Backward Explicit Congestion NotificationForward Explicit Congestion NotificationImplicit congestion notification (sequence numbers in higher layer PDUs)Raj JainThe Ohio State University4Discard ControlDiscard ControlCommitted Information Rate (CIR)Committed Burst Size (Bc): Over measurement interval T T = Bc/CIRExcess Burst Size (Be)Between Bc and Bc + Be Mark DE bitOver Be DiscardRaj JainThe Ohio State University5BitsBc + BeBcT0T0 + TTimeDE = 1DE = 0Access rateCIRDiscardFrames 1 3All frames with CIR2Raj JainThe Ohio State University6BitsB + BBccT0T + T0TimeDE = 1DE = 0Access rateCIRDiscardeOne Frame marked DEFrames 1 32 4Raj JainThe Ohio State University7BitsB + BBccT0T + T0TimeDE = 1DE = 0Access rateCIRDiscardeOne Frame marked DE; one frame discardedFrames 1 32 4Raj JainThe Ohio State University8Leaky Bucket AlgorithmLeaky Bucket AlgorithmBeC = counter; increment with incoming dataDecrement C by min{C, Bc} every T Time unitsCIR = Bc /TLimit C to Bc + BeDiscard any incoming data while C is at its thresholdBcRaj JainThe Ohio State University9FECNFECNForward Explicit Congestion NotificationSource sets FECN = 0Networks set FECN if avg Q >1Dest tells source to inc/dec the rate (or window)Start with R = CIR (or W=1)If more than 50% bits set decrease to 0.875 × R (or 0.875W)If less than 50% bits set increase to 1.0625 × R (or min{W+1, Wmax})If idle for a long time, reset R = CIR (or W=1)S DFrame Relay SwitchFECNRaj JainThe Ohio State University10Implicit Congestion Implicit Congestion ControlControlDecrease window on frame lossIncrease window slowlyDecrease by 1, Decrease to Wmin, Decrease by a factor Increase by 1 after N framesIncrease by 1 after W framesRaj JainThe Ohio State University11SummarySummaryDiscard strategy: Leaky bucketForward explicit congestion notificationBackward Explicit congestion notificationImplicit congestion controlRaj JainThe Ohio State University12HomeworkHomeworkRead chapter 12 of Stallings’
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