1. 1 On the Interaction between Dynamic Routing in the Native and Overlay Layers Infocom2006 Srinivasan Seetharaman and Mostafa Ammar College of Computing Georgia Institute of Technology Presenter: Elaine

2. 2 Roadmap Introduction The model adopted for analysis The characteristics of Dual Rerouting Layer aware rerouting algorithms Simulation result Tuning the native layer routing protocol and novel approach Conclusion

3. 3 Introduction(1/3) Overlay network Interaction between two routing layers –Dynamic routings both on overlay and native IP network cause problems –Focus on the specific problem of rerouting around failed native link

4. 4 Introduction (2/3) Mix dynamic routing environment can be avoided? –Not using dynamic routing in the overlay network and always counts on the native networks to re-configure the route? Overlay dynamic routing can significantly enhance the overlay network ’ s survivability

5. 5 Introduction (3/3) Three contributions –Provide the understanding of Dual Rerouting –Three approaches to mitigate the rerouting problems –Motivate the need for an overlay-aware native network

6. 6 Rerouting Model(1/5) A.Framework –Two scenarios Single-Domain Overlay over Single Domain native Single-Domain Overlay over Multiple-Domain Native

7. 7 Rerouting Model(2/5) –Generic parameters of each routing protocols Cost Assume the two ends of each link (native & overlay) use a keepAlive protocol for link verification. –3 keepAlive messages lost  Failure A keepAlive time: Time between two keepAlive messages A hold time: Time window to declare link as down

8. 8 Rerouting Model(3/5) B. Rerouting schemes –No awareness Dual Rerouting The benchmark for performance comparison –Awareness of lower layer ’ s existence –Awareness of lower layer ’ s parameters

9. 9 Rerouting Model(4/5) C. Performance metrics 1.Hit-time: Time taken for traffic to be recovered. = Detection time+Convergence time+Device time (depends on timers) (protocol specific)(Negligible) 2.Success rate of recovery Success rate of a layer = Number of paths recovered Number of failed overlay paths 3.Number of route flaps Average route flaps = Number of route flaps Number of failed overlay paths 4.Peak & Stabilized inflation (before repair) Path cost inflation = Path cost after rerouting Path cost before failure

10. 10 Rerouting Model(5/5)

11. 11 Characteristics of Dual Rerouting Each layer operates completely independent of the other –lead to a large number of route flaps and increase the path cost inflation To mitigate this problem –Vary Hold-time & KeepAlive-time at overlay layer to determine at which layer detection is likely to happen first Best Hit time –According to the definition of Detection Using layer-aware scheme to trade off improvement in other metrics with longer hit-times.

12. 12 Layer Aware Overlay Rerouting(1/2) These schemes require knowledge of the native layer ’ s routing protocol existence or some minimal knowledge Probabilistically Suppressed Overlay Rerouting –suppression operation is done with probability p on each overlay rerouting attempt –P=0, dual rerouting –P=1, native rerouting –Decrease the number of flaps and achieve better path cost –Longer hit time Deferred Overlay Rerouting –Delay overlay recovery by a constant value –After that time has elapsed, if the native network has not yet recovered, overlay recovery is performed –fewer route flaps relative to Dual Rerouting –Longer hit time

13. 13 Layer Aware Overlay Rerouting(2/2) Follow-on Suppressed Overlay Rerouting –The overlay layer keeps track of the native layer ’ s timer values –Follow-on time If follow-on time < threshold, then suppress overlay rerouting Similar to DOR, but has a relatively smaller hit-time

14. 14 Result A.Simulation Setup –5 overlay topologies over 5 native topologies =>25 combinations –Native layer Intra-domain –keepAlive time(1s)/ KeeAlive message(3)/ Hold-time(3s) Inter-domain –keepAlive time(5s)/ KeeAlive message(3)/ Hold-time(15s) –Overlay layer 2 or 3 keepAlive message –Network topology Intra-domain(10 overlay nodes/100 native nodes) Inter-domain(10 overlay nodes/500 native nodes) –Link Failure Modeling stateless all-link failure approach

15. 15 Dual Rerouting Dual Rerouting Ovelay hold time ↑ Hit time ↑

16. 16 Ovelay hold time ↑ Avg Route flaps ↓ Show trade off between Hit time & avg route flaps ↓

17. 17 Overlay hold time ↑ Peak inflation ↓ Peak inflation, native-only is the best Stable inflation, irrespective to hold time

18. 18 Performance Comparison –Hold time : 3.0s –The delay and follow-on threshold were set to 0.375 (2 secs) – the suppression probability was set to 0.5 1.Native-only rerouting must attain steady state faster than the other 2. Dual Rerouting, which has no suppressed overlay rerouting operations, must attain the peak earliest

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20. 20 Summary of performance of layer-aware schemes None of the three layer-aware schemes are the best – Based on what the system is sensitive to, different scheme can be chosen In most situations, packet loss has a more serious effect on the performance of the overlay traffic –Reducing the hit-time should be given a high precedence

21. 21 TUNING NATIVE LAYER PARAMETERS Motivation –overlay applications proliferate, the native layer should gradually evolve to suit the overlay network requirements –Improve the performance by adjust parameters of the native layer routing protocol Tuning the keepAlive-time –Native layer rerouting was shown to be the optimal one in terms of path cost inflation and number of route flaps –In Dual Rerouting, insuring that recovery will take place at the native layer first can be achieved by setting the native layer ’ s keepAlive-time to a value much smaller than that at the overlay layer

22. 22 We define the routing protocol overhead as the number of keepAlive packets sent per second on the link under consideration

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24. 24 Summary of performance gain with native layer tuning –Help Dual Rerouting improve the performance –Maintains the overall routing overhead the same –Reducing the keepAlive-time at the native layer also benefits the non-overlay applications sharing it

25. 25 Conclusion –Provide the understanding of Dual Rerouting –Three approaches to mitigate the rerouting problems –Motivate the need of tuning the keepAlive- time of the native layer to achieve the best possible rerouting performance

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