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Path Protection in MPLS Networks

Path Protection in MPLS Networks. Design and Evaluation of Fault Tolerance Algorithms with Performance Constraints. Ashish Gupta Ashish Gupta. Our Work. Fault Tolerance in MPLS Networks Issues QoS Constraints Expeditious Path Restoration Bandwidth Efficiency There is a tradeoff.

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Path Protection in MPLS Networks

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  1. Path Protection in MPLS Networks Design and Evaluation of Fault Tolerance Algorithms with Performance Constraints Ashish Gupta Ashish Gupta

  2. Our Work • Fault Tolerance in MPLS Networks Issues • QoS Constraints • Expeditious Path Restoration • Bandwidth Efficiency • There is a tradeoff

  3. QoS Parameters • Important parameters • Packet Loss Time • Jitter • End-to-End Delay • Reliability • Have to minimize bandwidth usage MPLS ADVANCED NETWORKING LAB PATH PROTECTION

  4. QOS Parameters Packet Loss Time : Packet Loss time is the time for which the packets will be dropped in case a failure along the LSP Jitter : Jitter is the deviation from the ideal timing of receiving a packet at the destination End-to-End Delay : The transmission time of a packet to reach the destination node from the source Reliability : The probabilistic measure of reachability of the destination from the source

  5. Path Protection A disjoint backup path is allocated along with the primary path • Local Path Protection • Global Path Protection • Segment Based Approach : A General Approach to Path Protection MPLS ADVANCED NETWORKING LAB PATH PROTECTION

  6. Segment Protection • Protect each segment separately : Each segment seen as a single unit of failure • SSR – Segment Switching router • Flexibility in creating segments -> flexibility in Path Protection ( delay and backup paths ) • SBPP – Segment Based Path Protection

  7. Optimization Problem The structure of backup path(s) and its peering relationship with the primary path affects the QoS Constrains The Design of backup LSPs must address both BW efficiency and expeditious path restoration

  8. Explanation of QoS Parameters

  9. Expressions Ensure • Packet Loss time • RTT( Si , Si+1 ) + Ttest < delta Where delta is maximum permissible packet loss time • Jitter • t2 – t1 < Jitter Bound ( See diagram ) • In worst case user doesn’t receive packets for • Max (RTT( Si , Si+1 ) + Ttest +(t2 – t1) )

  10. End-to-End Delay

  11. End-to-End delay • Ensure • Max (T + ( t2 – t1 ) ) < EED Bound

  12. Problem Statements

  13. Theoretical Model • Let G = (R,L,B,pB,bB,D) describe the given network where R= set of routers L = set of links B = Bandwidth of the Links pB = Primary Path bw reserved bB = Backup Path bw reserved D = Delays of the Links

  14. Packet Loss Time General Problem Statement Input A Network G and Packet Loss time bound delta. An ingress Node a and an egress node b between which a connection of bandwidth y has to be routed. Output A primary path between a and b , a set of segment switch routers S and set of backup paths BP. Such that • S0 = a • In case of a fault, the max packet loss time while rerouting is < delta • RTT ( Si , Si+1 ) + Ttest <= delta • Bandwidth resources are conserved • No of segments is minimized or |S| is minimum( Transformation )

  15. Jitter General Problem Statement Input A Network G and Packet Loss time bound delta and jitter bounddeltaj . an ingress Node a and an egress node b between which a connection of bandwidth y has to be routed. Output A primary path between a and b , a set of segment switch routers S and set of backup paths BP. Such that • S0 = a • In case of a fault, maximum jitter bound is deltaj • Max ( t2 – t1 ) < deltaj • RTT ( Si , Si+1 ) + Ttest <= delta • Bandwidth resources are conserved • No of segments is minimized or |S| is minimum( Transformation )

  16. End-to-End Delay General Problem Statement Input A Network G and end-to-end delay bound deltaeed . An ingress Node a and an egress node b between which a connection of bandwidth y has to be routed. Output A primary path between a and b , a set of segment switch routers S and set of backup paths BP. Such that • S0 = a • In case of a fault, EED does not exceed delteeed • Max ( T + (t2 – t1) ) < deltaeed • Bandwidth resources are conserved • No of segments is minimized or |S| is minimum ( Transformation )

  17. Reliability General Problem Statement Input A Network G and set of reliabilities of each node and link in G. A lower bound of acceptable reliability p* , an ingress Node a and an egress node b between which a connection of bandwidth y has to be routed. Output A primary path between a and b , a set of segment switch routers S and set of backup paths BP. Such that • S0 = a • The reliability of the LSP from a to b is greater than a certain reliability value p* • The bandwidth used is minimum • No of segments is minimized or |S| is minimum ( Transformation )

  18. RELIABILITY - 1 • How Backup Path Improves Reliability Link Reliability : pe n links each in the primary and backup paths. Reliability from A to B without a backup path = p Reliability from A to B with backup path = 2p – p2

  19. RELIABILITY - 2

  20. RELIABILITY - 3 • How Backup Path Improves Reliability A B Link Reliability : pe n links each in the primary and backup paths. Reliability from A to B without a backup path = pn Reliability from A to B with backup path = 2pn – p2*n

  21. Segment Heads Backup Paths RELIABILITY - 4 Total number of links in primary path = n Size of Backup Path = Size of Segment Size of Segments = k Assume no sharing of backup paths

  22. RELIABILITY - 5 Reliability of a link : p Reliability of a segment = 2pk – p2k Number of Segments = n/k Reliability of the path = (2pk – p2k)n/k

  23. RELIABILITY – 6

  24. How to Calculate Reliability? • NP-Complete problem, even when failure probability is same for all links. • For a graph G with edge reliability pe for edge e, where O is the set of operational states. Therefore we will have to estimate reliability of a path by using upper and lower bounds.

  25. pn pn A A1 A2 pe pf Pe *pf Graph Transformations • Node to Link Reliability • Merging • Serial • Parallel pe pe + pf - pe *pf pf

  26. Approximating Reliability • Consider a path from link A to B • Total number of links in primary and backup paths = n • Reliability of a link : p • Probability ( failure of k links ) nck * pn-k * (1-p)k

  27. Probability of k links failing Probability that 0 or 1 or 2 links failed = 0.9861819

  28. Approximating Reliability

  29. Approximating Reliability • Number of States with 0 link failure : nc0 Probability of occurrence of this state : pn Probability that a path exist : 1 • Number of States with 1 link failure : nc1 Probability of occurrence of this state : pn-1(1-p) Probability that a path exist : 1 • Number of States with 2 link failure : nc2 Probability of occurrence of this state : pn-2(1-p)2 Probability that a path exist : From Simulation(say q)

  30. Approximating Reliability • Lower Bound nc0 * pn * 1.0 + nc1 * pn-1(1-p) * 1.0 + nc2 * pn-2(1-p)2 * q • Upper Bound 1 - nc2 * pn-2(1-p)2 * (1-q) • Reliability (Upper Bound + Lower Bound)/2

  31. Lower & Upper Bounds

  32. Maximum Difference between Actual & Approximated Reliability

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