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MPLS Protection Routing: A Tutorial

MPLS Protection Routing: A Tutorial. Zartash Afzal Uzmi. First slide…. Questions? Ask when you have them!. Outline. Background Network Services and QoS Architectural Requirements IP and MPLS Introduction to protection and restoration routing Terminology

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MPLS Protection Routing: A Tutorial

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  1. MPLS Protection Routing: A Tutorial Zartash Afzal Uzmi

  2. First slide… Questions? Ask when you have them! Lahore University of Management Sciences

  3. Outline • Background • Network Services and QoS • Architectural Requirements • IP and MPLS • Introduction to protection and restoration routing • Terminology • Local Protection: Types of Backup Paths Fault Models • Backup Bandwidth Sharing • Activation sets • Protection routing framework • Components • Typical example • Evaluation and Experimentation Lahore University of Management Sciences

  4. Outline • Background • Network Services and QoS • Architectural Requirements • IP and MPLS • Introduction to protection and restoration routing • Terminology • Local Protection: Types of Backup Paths Fault Models • Backup Bandwidth Sharing • Activation sets • Protection routing framework • Components • Typical example • Evaluation and Experimentation Lahore University of Management Sciences

  5. Network Traffic and Services • Network Traffic today • Not what it was 10 years ago • Multimedia intensive • New and interactive applications are emerging • Internet telephony • Videoconferencing • Streaming media (voice and video) • Remote collaboration (e.g., remote desktop) • Many new applications are real-time • More and more users of these applications Burstiness behavior has changed over the years! Lahore University of Management Sciences

  6. Current Network Architecture • Internet is popular because • It is inexpensive • Internet is inexpensive because • It uses resource sharing • by means of statistical multiplexing • Current Internet architecture • Uses packet switches with buffers • Required buffer size is primarily determined by a random traffic pattern • Buffer size optimization • Too low  High drop rate • Too high  High delay Lahore University of Management Sciences

  7. Architectural Requirements • Emerging applications • Two-way interactive communications • One-way streaming media type applications • Under normal conditions • We are worried about the buffers used in two-way interactive applications • When resources fail • We are also worried about the one-way applications • Current Internet architecture is not suitable for new and emerging applications • New architectures are being researched Lahore University of Management Sciences

  8. Architectural Requirements • New network architectures • All circuit-switched? • Mix of packet-switch and “circuit-switch-like” • Experience with networks • Bigger buffers are required when there is more randomness and more aggregation • Should use circuits at places where we see more aggregation • Example: 100x100 project • Edge network is packet-switched • Core network is virtual-circuits Lahore University of Management Sciences

  9. 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

  10. Outline • Background • Network Services and QoS • Architectural Requirements • IP and MPLS • Introduction to protection and restoration routing • Terminology • Local Protection: Types of Backup Paths Fault Models • Backup Bandwidth Sharing • Activation sets • Protection routing framework • Components • Typical example • Evaluation and Experimentation Lahore University of Management Sciences

  11. Protection and Restoration • Restoration • On-demand recovery – no preset backup paths • Example: existing recovery in IP networks • Protection • Pre-determined recovery – backup paths “in advance” • Primary and backup are provisioned at the same time • IP supports restoration • Because it is datagram service • MPLS supports restoration as well as protection • Because it is virtual-circuit service Lahore University of Management Sciences

  12. Restoration in IP network • In traditional IP, what happens when a link or node fails? • Failure 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 protection possibilities in an MPLS network, but… • First we need to look at the QoS requirements Lahore University of Management Sciences

  13. QoS Requirements • Bandwidth Guaranteed Primary Paths • Bandwidth Guaranteed Backup Paths • BW remains provisioned in case of network failure • Minimal “Protection or Restoration Latency” • Protection/Restoration latency is the time that elapses between: • “the occurrence of a failure”, and • “the diversion of network traffic on a new path” Restoration is generally SLOWER than protection Lahore University of Management Sciences

  14. Protection in MPLS • First we define Protection level • Path protection • Also called end-to-end protection • For each primary LSP, a node-disjoint backup LSP is set up • Upon failure, ingress node diverts traffic on the backup path • Local Protection • Upon failure, node immediately upstream the failed element diverts the traffic on a “local” backup path Path Protection  More Latency Local Protection  Less Latency Lahore University of Management Sciences

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

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

  17. Protection Modes • 1+1 protection • Flow sent on two separate disjoint paths • Receiver responsible for choosing one of the two • 1:1 protection • A backup path protects a single LSP (or a portion of a single LSP) • N:1 protection • A backup path protects one link or one node or both • Overlapping portions of many LSPs are protected by a single backup path • Applicable for local protection only • N:M protection (M<N) Lahore University of Management Sciences

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

  19. 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

  20. Sharing Primary Path Backup Path BW Sharing in backup Paths • Example: LSP1 BW: X A B X X max(X, Y) X E G F X+Y Y Y C D BW: Y LSP2 Lahore University of Management Sciences

  21. 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

  22. Outline • Background • Network Services and QoS • Architectural Requirements • IP and MPLS • Introduction to protection and restoration routing • Terminology • Local Protection: Types of Backup Paths Fault Models • Backup Bandwidth Sharing • Activation sets • Protection routing framework • Components • Typical example • Evaluation and Experimentation Lahore University of Management Sciences

  23. Protection 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 primary LSPs that can be placed on the network Lahore University of Management Sciences

  24. Evaluation & Experimentation • Traffic Generation • Use existing or emerging traffic models • Consider call holding times and multi-service traffic • Rejected Requests Experiments • Generate a set of LSP requests • Measure the number of rejected requests • Simulate on various topologies • Network Loading Experiments • Set link capacities to infinity • Measure the total bandwidth required to service a given set of LSP requests • Simulate on various topologies Lahore University of Management Sciences

  25. Recent Trends • Preemption of lower class traffic • Multilayer recovery • We can “almost” deal with recovery at a single protocol layer • What if we intend to provide recovery at multiple protocol layers? • For multilayer recovery, we need to consider these additional issues: • Interworking of layers • Local information stored at each node of each layer • Recovery provided by each individual layer • Signaling mechanism from one layer to another • Effects on bandwidth sharing (if sharing is used) Lahore University of Management Sciences

  26. We are not done, yet… Questions & Answers Lahore University of Management Sciences

  27. Extra Stuff! Example: A Protection Routing Architecture Lahore University of Management Sciences

  28. 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 • Rij: Bandwidth remaining on link (i, j) • Optimized AIS (oAIS) – (Hij instead of Fij) • Hij: Maximum bandwidth reserved on any one link by all backup paths spanning link (i, j) • Also propagate Gij and Rij More Information propagated  More potential for BW sharing Lahore University of Management Sciences

  29. 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

  30. 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

  31. 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

  32. 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

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

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

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

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

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

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

  39. More Extra Stuff! Bandwidth Sharing Model for oAIS Lahore University of Management Sciences

  40. 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 are protected! Lahore University of Management Sciences

  41. 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

  42. 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

  43. 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

  44. Last slide… Thank you! Questions? Lahore University of Management Sciences

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