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Restoration Routing in MPLS Networks

Restoration Routing in MPLS Networks. Zartash Afzal Uzmi Computer Science and Engineering Lahore University of Management Sciences. Outline. Background: Quick overview of MPLS Introduction to restoration routing QoS Requirements: Why restoration routing?

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Restoration Routing in MPLS Networks

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  1. Restoration Routing in MPLS Networks Zartash Afzal Uzmi Computer Science and Engineering Lahore University of Management Sciences

  2. Outline • Background: Quick overview of MPLS • Introduction to restoration routing • QoS Requirements: Why restoration routing? • Local Restoration: Types of Backup Paths • Local Restoration: Fault Models • Backup Bandwidth Sharing • Activation sets • Typical example of restoration routing frameworks • Optimized aggregate information scenario (oAIS) • Experiments, simulations, and results Lahore University of Management Sciences

  3. IP versus MPLS • In IP Routing, each router makes its own routing and forwarding decisions • In MPLS, source router makes the routing decision • Intermediate routers make forwarding decisions • A path is computed and a “virtual circuit” is established from ingress router to egress router • An MPLS path or virtual circuit from source to destination is called an LSP (label switched path) Lahore University of Management Sciences

  4. Restoration in IP network • In traditional IP, what happens when a link or node fails? • Information needs to be disseminated in the network • During this time, packets may go in loops • Restoration latency is in the order of seconds • We look for restoration possibilities in an MPLS network Lahore University of Management Sciences

  5. QoS Requirements • Bandwidth Guaranteed Primary Paths • Bandwidth Guaranteed Backup Paths • BW remains provisioned in case of network failure • Minimal “Restoration Latency” • Restoration latency is the time that elapses between the occurrence of a failure and the diversion of network traffic on a new path Path Restoration  More Latency Local Restoration  Less Latency Lahore University of Management Sciences

  6. Restoration in MPLS Path Protection S 1 2 3 D This type of “path Protection” still takes 100s of ms. We need to explore “Local Protection” to quickly switch onto backup paths! Primary Path Backup Path Lahore University of Management Sciences

  7. Types of Backup Paths • A next hop (nhop) path that spans a link (i, j) is a backup path which: • originates at node i, and • provides restoration for a primary LSP that traverses (i, j), if (i, j) fails. i j nhop path that spans (i, j) PLR: Point of Local Repair Lahore University of Management Sciences

  8. Types of Backup Paths • A next next hop (nnhop) path that spans a link (i, j) is a backup path which: • originates at node i, and • provides restoration for a primary LSP that traverses (i, j), if either (i, j) or node j fails. nnhop path that spans (i, j) j i PLR: Point of Local Repair Lahore University of Management Sciences

  9. A B C D Local Restoration: Fault Models Link Protection Node Protection A B C D Element Protection A B C D Lahore University of Management Sciences

  10. Primary Path Backup Path nhop and nnhop paths nnhop A B D C E nhop PLR: Point of Local Repair All links and all nodes are protected! Lahore University of Management Sciences

  11. Opportunity cost of backup paths • Local Protection requires that backup paths are setup in advance • Upon failure, traffic is promptly switched onto preset backup paths • Bandwidth must be reserved for all backup paths • This results in a reduction in the number of Primary LSPs that can otherwise be placed on the network • Can we reduce the amount of “backup bandwidth” but still provide guaranteed backups? Lahore University of Management Sciences

  12. Sharing Primary Path Backup Path BW Sharing in backup Paths • Example: L1 BW: X A B X X max(X, Y) X E G F X+Y Y Y C D L2 BW: Y Lahore University of Management Sciences

  13. Activation Sets A A E E B B C C D D Activation set for node B Activation set for link (A,B) Lahore University of Management Sciences

  14. Restoration Routing Frameworks • We look to answer the following questions? • Who computes the primary path? • What is the fault model (link, node, or element protection)? • Where do the backup paths originate? • Who computes the backup path? • At what point do the backup paths merge back with the primary path • What information is stored locally in the nodes/routers • What information is propagated through routing protocols • What if a primary path can not be fully protected • The goal is almost always to maximize bandwidth sharing • Performance criteria is almost always the maximum number of LSPs that can be placed on the network Lahore University of Management Sciences

  15. Extent of BW Sharing: oAIS • Aggregate Information Scenario (AIS) • Fij: Bandwidth reserved on link (i, j) for all primary LSPs • Gij: Bandwidth reserved on link (i, j) for all backup LSPs • Optimized AIS (oAIS) – (Hij instead of Fij) • Hij: Maximum bandwidth reserved on any one link by all backup paths spanning link (i, j) More Information propagated  More potential for BW sharing Lahore University of Management Sciences

  16. oAIS versus AIS: Example LSP Request-1 (src, dst, bw) = (A, C, 4) D E F GAF=4 FAB=4 A B C HAB=4 G Lahore University of Management Sciences

  17. oAIS Example LSP Request-2 (src, dst, bw) = (A, C, 5) D E F GAF=4 FAB=9 FAB=4 A B C HAB=5 HAB=4 GAG=5 G Lahore University of Management Sciences

  18. oAIS Example LSP Request-3 (src, dst, bw) = (D, E, 7) FDE=7 D E F GAF=4 GAF=7 FAB=9 A B C HAB=5 GAG=5 G Lahore University of Management Sciences

  19. oAIS Example LSP Request-4 (src, dst, bw) = (A, C, 6) Need to Evaluate cost of all possible backup paths? FDE=7 How much BW is shareable on (A, F)? D E AIS: Shareable = max(0, GAF - FAB) = GAF - min(GAF, FAB) = 0 Additional resv = 6 F GAF=7 oAIS: (HAB≤ FAB) Shareable = GAF - min(GAF, HAB) = 2 Additional resv = 6 - 2 = 4 FAB=9 A B C HAB=5 CIS: (link (A,B) knows BWred) Shareable = GAF - BWred = 7 - 4 = 3 Additional resv = 6 - 3 = 3 GAG=5 G Lahore University of Management Sciences

  20. A B C D Primary Path Backup Path A Bandwidth Sharing Model (Simplified for the Link Protection Fault Model) Recall the definition of nhop paths Link Protection All links and all nodes are protected! Lahore University of Management Sciences

  21. Bandwidth Sharing Model • Previous: • Aij:= Set of all primaries traversing through (i, j) • Buv:= Set of all backups traversing through (u, v) • New definition (specialized for link protection case): • Aij:= Set of all primaries traversing through (i, j) • Buv:= Set of all nhop paths traversing through (u, v) • µij:= Set of all nhop paths that span (i, j) • ijuv:= Buv ∩ µij (set of paths falling on (u,v) if (i,j) fails) Lahore University of Management Sciences

  22. Bandwidth Sharing Model RED=7 BLU=2 u v GRN=3 (New Request) Guv = 10 3 k i j NEW MODEL: Aij = {R, B} Buv = {nhijr, nhijb, …} (nhops through (u, v)) µij = {nhijr, nhijb, …} (nhops spanning (i, j)) ijuv = µij ∩ Buv= {nhijr, nhijb} || ijuv || = 2 + 7 = 9 (Un-shareable) Shareable = Guv - || ijuv || = 10 - 9 = 1 OLD MODEL: Aij = {R, B} Buv = {R, B, …} Aij ∩ Buv= {R, B} || Aij ∩ Buv || = 2+7 = 9 Un-shareable = 9 Shareable = 10 - 9 = 1 Lahore University of Management Sciences

  23. Bandwidth Sharing Model RED=7 BLU=2 u v GRN=3 (New Request) Guv = 10 3 k i j OLD MODEL: Aij = {R, B} Buv = {R, B, …} Aij ∩ Buv= {R, B} || Aij ∩ Buv || = 2+7 = 9 Un-shareable = 9 Shareable = 10 - 9 = 1 NEW MODEL: Aij = {R, B} Buv = {nhijr, nhjkb, …} (nhops through (u, v)) µij = {nhijr, nhijb, …} (nhops spanning (i, j)) ijuv = µij ∩ Buv= {nhijr} || ijuv || = 7 (Un-shareable) Shareable = Guv - || ijuv || = 10 - 7 = 3 Lahore University of Management Sciences

  24. Simulation Experiments • Rejected Requests Experiments • Measure the number of rejected LSPs for each information scenario • Simulated on two topologies • Network Loading Experiments • Link capacities set to infinity • Measure the total bandwidth required to service a given set of LSPs for each information scenario • Simulated on two topologies Lahore University of Management Sciences

  25. Single Link Protection: Network 1 Lahore University of Management Sciences

  26. Single Link Protection: Network 1 Lahore University of Management Sciences

  27. Single Link Protection: Network 2 Lahore University of Management Sciences

  28. Single Link Protection: Network 2 Lahore University of Management Sciences

  29. Single Node Protection: Network 1 Lahore University of Management Sciences

  30. Single Element Protection: Network 1 Lahore University of Management Sciences

  31. Questions & Answers Lahore University of Management Sciences

  32. Restoration in MPLS Path Protection A B C D E MPLS path Protection may take 100s of ms, whereas MPLS Local protection takes less than 10 ms. Primary Path Backup Path Lahore University of Management Sciences

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