Performance of the rapid spanning tree protocol in ... - RuggedCom

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Traffic sourceTraffic destinationS 0S 0S -1S 1S -1Root BridgeS 1S -2. . . . . .S -(N-2)S -(n-1)S (n-2)S 2S (n-1)S nFigure 7.All switches agree about newRoot pathS -2. . . . . .S -(n-2)S -(n-1)S 2S (n-1)S nFigure 8.Steady state after network recoveryS (n-2)So the overall failover time isT L + (n-2+1)*T PA + max( (n-1)*T TC , (n-2)*T PA )As we explained above, T PA is significantly longer than T TC , and then the overall failover time isT L + (n-2+1+n-2)*T PA = T L + (2*n-3)*T PA = T L + (N-3)*T PA3.3 Derivation of a Root Bridge Failover TimeFailure of the root bridge requires electing a new root bridge which adds further complexity compared tothe single link failure analysis. Figure 9 shows the network in steady state before the root bridge fails.After the root bridge failure, the ring is divided into two segments S -1 -S -(n-1) and S 1 -S n becauseconnectivity between them is blocked by the S n ’s Alternate port S n -S -(n-1) . (Figure 10). Each switch canhave a different bridge priority configured. Determining the worst case failover time demands analyzingall cases where the new bridge could become any one of the switches in the ring. Repeating the analysisfor all switches would show that the worst case has S 1 and S- 1 becoming the next best root candidates withS 1 taking precedence over S- 1 . Table 2 describes how RSTP will proceed at different points in time for theworst case.10
Traffic sourceTraffic destinationS 0S 0S -2S -(n-2)S -1S -(n-1)Root Bridge. . . . . .S 2AlternatePortS (n-1)S nFigure 9.Steady state before root bridge failureS 1S (n-2)S -1S -2S 1. . . . . .S -(n-2)S (n-2)S -(n-1)S 2S (n-1)S nFigure 10.Ring segments after root bridge failureTable 2. Time-line of RSTP actions by different switches in the ring (root bridge failure)TimeSwitchactingT L S -1 and S 1…{S 2 ,…,S n-2 } and{S -2 ,…,S -(n-2) }Action DescriptionEach of S 1 and S -1 detects the link failure, agesout its Root info and advertises itself as a newroot bridge.Proposal-Agreement handshaking occurs inparallel on each hop in two segments, up to S (n-1)and S -(n-1)FigureFigure 11-T L + (n-2)*T PAS n-1 andS -(n-1){S 1 ,…,S n-1 }all agree about S 1 being Root, while{S -1 ,…,S -(n-1) } agree about S -1 being Root.Figure 1211
Page 1: Performance of the Rapid Spanning T
Page 4 and 5: 2.2.3 Enhanced RSTP (eRSTP TM )Alth
Page 6 and 7: 3.1 Symbols and AssumptionsThe symb
Page 8 and 9: Table 1. Time-line of RSTP actions
Page 12 and 13: T L + (n-2+1+1)*T PA S n-1… {S n-
Page 14 and 15: S 0S 0S -1S -2S 1. . . . . .S -(n-2
Page 16 and 17: 4. Extrapolation to Meshed Networks
Page 18 and 19: 5. Empirical Performance DataTo cor
Page 20 and 21: ProtocolVendorCan be used inmulti-v
Page 22: 9. BiographiesMichael Pustylnik is

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