Path Protection in MPLS Networks

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 • Switch-Over Time • End-to-End Delay • Reliability • Jitter • Have to minimize bandwidth usage MPLS ADVANCED NETWORKING LAB PATH PROTECTION

4. QOS Parameters Switch-Over Time : Switch-Over Time is the time for which the packets will be dropped in case a failure along the LSP 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 Jitter : Jitter is the deviation from the ideal timing of receiving a packet at the destination

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. Switch-Over Time Ensure • Switch-Over time • RTT( Si , Si+1 ) + Ttest < delta Where delta is maximum permissible packet loss time

10. End-to-End Delay

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

12. Jitter • Ensure • Max Jitter from source to destination over all backup paths < Jitter bound

13. Problem Statements

14. Theoretical Model • Let G = (R,L) describe the given network where L has the following properties: <B,pB,bB,D,p> R = set of routers L = set of links B = Bandwidth of the Links pB = Primary Path bandwidth reserved bB = Backup Path bandwidth reserved D = Delays of the Links P = Reliability

15. Switch-Over Time General Problem Statement Input A Network N, LSP <R0,…,Rn> and Switch-over time bound . Output A set of segment switch routers S = < S0,…, Sk > Such that • S0 = R0 , Sk = Rn • In case of a fault, the max packet loss time while rerouting is <  • RTT ( Si , Si+1 ) + Ttest <=  • No of segments is minimized.

16. Consideration of Backup Paths Input A network N, a LSP <R0,…,Rn> and a switch-over time bound  Output A set of segment switch routers S and backup paths {<pi0,…,pin>:i=0..k-1} Such that • S0 = R0 , Sk = Rn • In case of a fault, the max packet loss time while rerouting is <  • RTT ( Si , Si+1 ) + Ttest <=  • No of segments is minimized.

17. End-to-End Delay General Problem Statement Input A network N, a LSP <R0,…,Rn> , switch-over time bound , end-to-end delay bound  Output A set of segment switch routers S and backup paths {<pi0,…,pin>:i=0..k} Such that • S0 = R0 , Sk = Rn • In case of a fault, the max packet loss time while rerouting is <  • RTT ( Si , Si+1 ) + Ttest <=  • No of segments is minimized. • Backup path constraints

18. Jitter General Problem Statement Input A network N, a LSP <R0,…,Rn> , switch-over time bound , jitter bound J Output A set of segment switch routers S and backup paths {<pi0,…,pin>:i=0..k} Such that • S0 = R0 , Sk = Rn • In case of a fault, the max packet loss time while rerouting is <  • RTT ( Si , Si+1 ) + Ttest <=  • No of segments is minimized. • Backup path constraints Jitter Jitter Jitter J

19. d1 d2 d3 d2 + d3 d3 d1 + d2 + d3 0 Algorithm

20. Reliability General Problem Statement Input A network N, a LSP <R0,…,Rn> , switch-over time bound , minimum reliability requirement r Output A set of segment switch routers S and backup paths {<pi0,…,pin>:i=0..k} Such that • S0 = R0 , Sk = Rn • In case of a fault, the max packet loss time while rerouting is <  • RTT ( Si , Si+1 ) + Ttest <=  • No of segments is minimized. • Backup path constraints • Minimum reliability is r

21. 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

22. RELIABILITY - 2

23. 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

24. 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

25. RELIABILITY – 6

26. Algorithm • How to calculate reliability • Given segment heads, find the most reliable backup paths • Find segment heads

27. 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.

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

29. 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

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

31. 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)

32. 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)

33. Lower & Upper Bounds

34. Reliability

35. R8 R9 R10 R11 R12 R7 R4 R6 R3 R5 R2 R1 r1012 r1112 r912 1 Finding Reliable Backup Paths Given the segment heads, we can find backup paths that maximizes reliability of the network.

36. Finding Segment Heads Approach #1 • Consider all possible segmentations. Approach #2 • Find the best possible segmentation without considering reliability while segmenting. • Divide segments to improve reliability till reliability becomes greater than required.

37. Algorithm Which segment to divide first? • Divide segment with maximum reliability first • Divide segment with maximum reliability first • Divide longest segment first • Random

38. Future Work • Algorithm for protection meeting reliability criteria • Optimization issues – Bandwidth , capacity • Implementation of these algorithms in emulator and experimental setup