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QoS-Aware Path Protection in MPLS Networks

QoS-Aware Path Protection in MPLS Networks. Satish Tripathi University of California at Riverside. Ashish Gupta Ashish Gupta Bijendra Jain Indian Institute of Technology Delhi. Overview. MPLS networks Special need for path protection Approaches to path protection in MPLS networks

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QoS-Aware Path Protection in MPLS Networks

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  1. QoS-Aware Path Protectionin MPLS Networks Satish Tripathi University of California at Riverside Ashish GuptaAshish GuptaBijendra Jain Indian Institute of Technology Delhi

  2. Overview • MPLS networks • Special need for path protection • Approaches to path protection in MPLS networks • Link, node based • LSP based • Segment Based Approach • Mechanisms (detection, notification and path switching) • Algorithm for segment identification • Some simulation results

  3. Path protection BACKUP PATH 1 47.1 • Routing algorithms for IP networks take seconds to re-compute routes • Voice & video are sensitive to “switch-over” time • require switch over in less than 50 to 100 ms • Identify and set-up back-up paths a-priori 3 3 1 2 1 2 47.3 3 47.2 2

  4. Path protection in MPLS networks • Complete LSP by-pass • allocation of resources along back-up path is efficient • time to detect failure and switch over is large • difficult to identify a node-disjoint path that also meets the specified QoS constraints

  5. Path protection in MPLS networks • Link by-pass • allocation of resources for back-up paths is unlikely to be efficient • fault detection and switch over can be fast • cannot be sure about QoS resulting from any failure • does not address node failure

  6. Path protection in MPLS networks • Node by-pass • allocation of resources for back-up paths is unlikely to be efficient • fault detection and switch over can be very fast • cannot be sure about QoS resulting from any failure

  7. Segment Based Protection The Main Idea Look at the path as a sequence of segments and protect each segment separately

  8. Segment based protection: a proposal • flexibility in identifying segments • schemes to protect LSP, links, or nodes are special cases • efficient allocation of resources for back-up paths • bounds on fault detection and switch over time • ability to identify back-up paths that meet specified QoS constraints

  9. Focus of our paper develop algorithms to identify segments, and back-up paths, such that • switch over time (time for which packets are lost between failure and recovery) is bounded • path resulting from any single failure continues to satisfy given QoS constraints • resources are used efficiently (or more precisely, the number of segments is minimized)

  10. Fault Detection , Location and Notification • Faults detected using live-ness messages with periodicity Ttest • Notification messages to segment switching routers (SSR)

  11. Analysis Bound on time during which packets are lost RTT( Ri , Rj ) + Ttest

  12. Identifying Segments: A greedy algorithm RTT + Ttest = 45 RTT + Ttest = 51 Segment 3 Segment 2 Segment 1 R0 R1 R2 R3 R4 RTT + Ttest = 58 • Identify segments such that • switch-over delay is bounded (for instance, 60 ms) • Fewest no of segments • Example computation: 11 hop LSP, Ttest = 10 ms R9 R10 R11 R5 R6 R7 R8 10 19 11 8 14 13 11 3 10 15 10

  13. Another algorithm to identify segments 10 + 10 + 10 + 5 = 35 < 40 10 + 10 + 5 = 25 < 40 • Example: consider network with link RTT = 10 ms, Ttest = 5 ms • bounded switch-over delay of 40 ms • with as few segments as possible • disjoint, loop-free back-up paths exist 10 ms 10 ms 10 ms 10 ms 10 ms Ingress router Segment switch router

  14. Other algorithms to Identify Segments 10 ms 10 ms 10 ms 10 ms 10 ms Ingress router • Algorithms to identify segments such that: • Switch-over time is bounded • Fewest no. of segments • disjoint, loop-free back-up paths exist • QoS constraints are satisfied in case of ONE failure • End-to-end delay, Jitter, Drop rate

  15. End to End Delay In this analysis, we need to consider backup paths also. Max (T + ( T2 – T1 ) ) < 

  16. End to End Delay Finding the backup path d1 d2 d3 d2 + d3 d3 0 d1 + d2 + d3 Dummy node - Can use shortest-path approach to find the backup path - Backup path can land at multiple nodes

  17. Description of Simulation Setup • An MPLS network with • 50 Nodes • 82 Edges • Random LSP that require 20 to 70 units of BW • RTT of each link = 8 to 12 ms • BW between 3000 and 10000 units • Periodicity of liveness messages = 2 ms • BW: 50 to 100 • Results indicate advantages of segment based approach

  18. Description of Simulation Setup • Topology used

  19. Simulation Results • BW reserved for back up vs. number of LSP for different bound on switch-over time

  20. Simulation Results • Reserved BW vs. switch-over time

  21. Summary • Segment based approach offers a range of schemes for path protection • From link or nodes to segments, to paths • The approach permits one to insist that back-up paths continue to provide committed QoS even when there is a failure • The approach ensures that resources are reserved only to the extent necessary • Many of our algorithms are good, and provably correct, but may not be optimal

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