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Sharing Normal Bandwidth during a Failure

Sharing Normal Bandwidth during a Failure. Rajarshi Gupta, Eric Chi, Jean Walrand {guptar, echi, wlr}@eecs.berkeley.edu University of California, Berkeley. Background. Backup paths are necessary in many networking scenarios We look at :

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Sharing Normal Bandwidth during a Failure

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  1. Sharing Normal Bandwidth during a Failure Rajarshi Gupta, Eric Chi, Jean Walrand {guptar, echi, wlr}@eecs.berkeley.edu University of California, Berkeley

  2. Background • Backup paths are necessary in many networking scenarios • We look at : • Provisioned paths (normal and backup) with guaranteed bandwidth • Protection against one failure • Path Protection (vs. link/span protection) • Examples: Optical, MPLS

  3. Outline • Related Work • Key Idea • Centralized Algorithm • Distributed Algorithm • Analysis • Results

  4. Shared Protection Path • Disjoint normal paths can share backup bandwidth • Bandwidth on path C-E-F-G is shared by backup paths of both A-B-G and C-D-G

  5. Related Work • Kodialam, Lakshman (2000) • SCI and SPI • Liu, Tipper, Siripongwotikorn (2001) • Matrix formulation to characterize SPP • Qiao, Xu (2002) • DPIM-SAM and DPIM-MA • Several other work in the area of Optical, ATM and G/MPLS networks

  6. Key Idea • Can even share normal bw during failure • Upon failure, all traffic goes away from normal path (C-D-F-G) • The bandwidth on D-Fmay then be used for backup traffic (C-E-D-F-B)

  7. Notation • Flow is characterized by (src, dst, bN, bB) • bN = normal bandwidth • bB = backup bandwidth • Each link stores quantities • BT(j) = total bandwidth on link j • BN(j) = normal bandwidth on link j • BB(j) = backup bandwidth on link j • Available bw BV(j) = BT(j) – BN(j) – BB(j)

  8. Enhanced State Variables • Each link also stores two vectors • X(i,j) = extra bw on link i when link j fails • Y(i,j) = bw that goes away from link i when link j fails • BB(i) is the most backup traffic that link i needs to support, caused by failure at any of the other links

  9. Centralized Algorithm • When a new flow (src, dst, bN, bB) with normal path N and backup path B is accepted, we update

  10. Augmented Routing • Indifferent towards chosen routing algorithm • Provides better accounting of available resources, so augments performance of any routing algorithm • Example using Dijkstra’s Algorithm • Discard all links with inadequate normal bw • Compute normal path using source routing • Remove links used in normal path • Discard links whose BV < BB(instead of BV < bB) • Compute backup path on resulting graph • Update link states accordingly

  11. If link i receives normal path msg If link i receives backup path msg Distributed Algorithm • Separate message (including normal path information) sent to normal and backup paths • For a load-insensitive algorithm (e.g. shortest path), distributed algorithm works as well as centralized

  12. Analysis of Gains • Define the following • Normal sharing recovers an amount G(i) for link i • We can upper bound G(i)

  13. The upper bound can be achieved in a ring Gains occur when Total Gains: Analysis of Gain Scenario

  14. USA Topology OC-192 OC-48

  15. USA Topology: Results Primary: Least Loaded Backup: Least Loaded

  16. Routing Algorithms Primary Path: Min Hop Backup Path: Min Hop USA Topology: More results • Routing Algorithms • Primary Path: Min Hop • Backup Path: Cumulative Backup

  17. Ring Topology Metropolitan Area Network OC-48 OC-12

  18. Conclusion • Key fact: even normal bandwidth may be shared during failures • Update link states to account for sharing of both normal and backup resources • Centralized • Distributed • Simulation results show significant gains in network resource utilization

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