Path Protection in MPLS Networks Design and Evaluation

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Path Protection in MPLS Networks Design and Evaluation of Fault Tolerance Algorithms with Performance

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

Our Work n Fault Tolerance in MPLS Networks Issues n Qo. S Constraints n

Our Work n Fault Tolerance in MPLS Networks Issues n Qo. S Constraints n n n Expeditious Path Restoration Bandwidth Efficiency There is a tradeoff

Qo. S Parameters n Important parameters n n n Switch-Over Time End-to-End Delay Reliability

Qo. S Parameters n Important parameters n n n Switch-Over Time End-to-End Delay Reliability Jitter Have to minimize bandwidth usage ADVANCED NETWORKING LAB MPLS PATH PROTECTION

QOS Parameters Switch-Over Time : Switch-Over Time is the time for which the packets

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

Path Protection A disjoint backup path is allocated along with the primary path n

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

Segment Protection • Protect each segment separately : Each segment seen as a single

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

Optimization Problem The structure of backup path(s) and its peering relationship with the primary

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

Explanation of Qo. S Parameters

Explanation of Qo. S Parameters

Switch-Over Time Ensure n Switch-Over time RTT( Si , Si+1 ) + Ttest <

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

End-to-End Delay

End-to-End Delay

End-to-End delay n Ensure n Max (T + ( t 2 – t 1

End-to-End delay n Ensure n Max (T + ( t 2 – t 1 ) ) < EED Bound

Jitter n Ensure n Max Jitter from source to destination over all backup paths

Jitter n Ensure n Max Jitter from source to destination over all backup paths < Jitter bound

Problem Statements

Problem Statements

Theoretical Model n Let G = (R, L) describe the given network where L

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

Switch-Over Time General Problem Statement Input A Network N, LSP <R 0, …, Rn>

Switch-Over Time General Problem Statement Input A Network N, LSP <R 0, …, Rn> and Switch-over time bound . Output A set of segment switch routers S = < S 0, …, Sk > Such that n S 0 = R 0 , Sk = R n n In case of a fault, the max packet loss time while rerouting is < n RTT ( Si , Si+1 ) + Ttest <= n No of segments is minimized.

Consideration of Backup Paths Input A network N, a LSP <R 0, …, Rn>

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

End-to-End Delay General Problem Statement Input A network N, a LSP <R 0, …,

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

Jitter General Problem Statement Input A network N, a LSP <R 0, …, Rn>

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

Algorithm d 1 d 2 + d 3 d 1 + d 2 +

Algorithm d 1 d 2 + d 3 d 1 + d 2 + d 3 d 3 0

Reliability General Problem Statement Input A network N, a LSP <R 0, …, Rn>

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

RELIABILITY - 1 n How Backup Path Improves Reliability Link Reliability : pe n

RELIABILITY - 1 n 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 = 2 p – p 2

RELIABILITY - 2

RELIABILITY - 2

RELIABILITY - 4 Segment Heads Backup Paths Total number of links in primary path

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

RELIABILITY - 5 Reliability of a link : p Reliability of a segment =

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

RELIABILITY – 6

RELIABILITY – 6

Algorithm n n n How to calculate reliability Given segment heads, find the most

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

How to Calculate Reliability? n n NP-Complete problem, even when failure probability is same

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

Graph Transformations n Node to Link Reliability pn A n Merging n Serial n

Graph Transformations n Node to Link Reliability pn A n Merging n Serial n Parallel pn A 1 pe pe pf pf A 2 Pe *pf pe + pf - pe *pf

Approximating Reliability n n Consider a path from link A to B Total number

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

Probability of k links failing Probability that 0 or 1 or 2 links failed

Probability of k links failing Probability that 0 or 1 or 2 links failed = 0. 9861819

Approximating Reliability n Number of States with 0 link failure : nc 0 Probability

Approximating Reliability n Number of States with 0 link failure : nc 0 Probability of occurrence of this state : pn Probability that a path exist : 1 n Number of States with 1 link failure : nc 1 Probability of occurrence of this state : pn-1(1 -p) Probability that a path exist : 1 n Number of States with 2 link failure : nc 2 Probability of occurrence of this state : pn-2(1 -p)2 Probability that a path exist : From Simulation(say q)

Approximating Reliability n Lower Bound n n c 0 * pn * 1. 0

Approximating Reliability n Lower Bound n n c 0 * pn * 1. 0 + nc 1 * pn-1(1 -p) * 1. 0 + nc 2 * pn-2(1 -p)2 * q Upper Bound 1 - n c 2 * pn-2(1 -p)2 * (1 -q)

Lower & Upper Bounds

Lower & Upper Bounds

Reliability

Reliability

Finding Reliable Backup Paths R 1 R 2 R 3 R 4 R 5

Finding Reliable Backup Paths R 1 R 2 R 3 R 4 R 5 R 6 R 7 R 8 R 9 R 10 r 1012 r 912 R 11 R 12 r 1112 1 Given the segment heads, we can find backup paths that maximizes reliability of the network.

Finding Segment Heads Approach #1 n Consider all possible segmentations. Approach #2 n Find

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

Algorithm Which segment to divide first? n Divide segment with maximum reliability first n

Algorithm Which segment to divide first? n Divide segment with maximum reliability first n Divide longest segment first n Random

Future Work • Algorithm for protection meeting reliability criteria • Optimization issues – Bandwidth

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