Making Inter-domain Routing Power-Aware?

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  1. 1. Making Inter-domain Routing Power-Aware? Junxiao Shi and Beichuan Zhang The University of Arizona, USA 1
  2. 2. Background Network infrastructures exhibit low power efficiency Today's networks are over-provisioned Average link utilization is low at most of the time All routers and their line cards are up and running 24x7 Low power efficiency becomes an increasing concern for ISPs and data centers 2
  3. 3. GreenTE: dynamically adjusting routing paths GreenTE adapts routing paths to traffic demand, so that unused links can go to sleep and save power 3
  4. 4. GreenTE model GreenTE is modelled as an optimization problem, and optimized in a centralized controller MAXIMIZE: power saving of sleeping links SUBJECT TO Traffic between each IE pair goes through some path Path delay is no more than twice of the delay of shortest path Link utilization is below 50% on every link Idle links can go to sleep 4
  5. 5. Path diversity Power saving via path diversity GreenTE switches traffic between multiple paths More path choices => (hopefully) higher power saving Intra-domain vs inter-domain Original GreenTE considers intra-domain paths only: for inter-domain traffic, ingress and egress points are chosen by some non-power- aware scheme Can we increase power saving by considering inter-domain paths? 5
  6. 6. Power-aware inter-domain routing Power-aware inter-domain routing enhances path diversity How much additional power saving can we get? 6 source destination
  7. 7. Power-aware inter-domain routing Realistic assumption: no global coordination Global coordination doesn't exist in Internet Two tuning knobs Power-aware egress selection Power-aware ingress selection 7
  8. 8. Power-aware egress selection ISP chooses egress for a flow with BGP route selection process Introduce a new attribute: highest power saving highest local preference enforce relationships traffic engineering shortest ASPATH lowest MED i-BGP < e-BGP lowest IGP cost to BGP egress lowest router ID break ties highest power saving 8
  9. 9. Power-aware ingress selection Ultimately, ingress is chosen by neighbor AS ISP can influence the choice of ingress point by tweaking BGP announcements MED ASPATH prepending prefix splitting 9
  10. 10. Difficulty in ingress selection Ultimately, ingress is chosen by neighbor AS effect of ingress selection is less predictable Influences cannot take effect immediately BGP update rate is limited to avoid triggering route flap damping As a preliminary step, this paper focuses on power-aware egress selection 10
  11. 11. Extending GreenTE model to inter-domain New definition of traffic demand traffic amount from a set of ingress points to a set of egress points BGP tells us the possible egress points New constraint traffic demand between each ingress set - egress set is split onto IE pairs Technical challenge: scalability Multi-Commodity Flow problem is NP-hard Inter-domain GreenTE has more variables => bigger problem size 11
  12. 12. One egress set per destination prefix fine granularity, more computation, higher power saving ISP 12
  13. 13. One egress set per destination AS medium granularity, medium computation, medium power saving ISP 13
  14. 14. One egress set per neighbor coarse granularity, less computation, lower power saving ISP 14
  15. 15. Evaluation Our evaluation is based on simulation Input Rocketfuel topologies AS relationship synthesis traffic matrix Realistic assumption: no global coordination Only one ISP seeks to save energy in each simulated scenario Comparing power saving potential of intra-domain GreenTE and inter-domain GreenTE 15
  16. 16. How much power can we save? saving% weighted average minimum median maximum intra-domain 36.00% 0.00% 21.86% 62.99% inter-domain, per neighbor 36.35% 0.00% 21.86% 62.71% inter-domain, per destination AS 36.65% 0.00% 23.40% 63.97% Power saving potential increases by enabling power-aware egress selection, and becomes higher with finer granularity Overall the improvement is modest at most 16
  17. 17. Impact of internal topology HIGH IMPACT on both intra-domain and inter-domain spanning tree richly connected intra-domain inter-domain 17
  18. 18. Impact of delay constraint GreenTE limits the delay of candidate paths to be no more than twice the delay of shortest path Power saving should not cause too much increase on end-to-end delay but this also limits path diversity => limits power saving LOW IMPACT on both intra-domain and inter-domain 18
  19. 19. Impact of egress set granularity MEDIUM IMPACT on inter-domain per neighbor AS per destination AS 19
  20. 20. Impact of BGP policy MEDIUM IMPACT on inter-domain respect path preference ignore path preference (allow using provider route when there is customer route) 20
  21. 21. Conclusion First attempt to answer: is it feasible and beneficial to consider inter-domain paths in power-aware traffic engineering? Realistic assumption: no global coordination Power-aware egress selection: integrate "highest power saving" to BGP route selection process Evaluation: it's feasible to save addition power Amount of additional power saving seems modest Utilizing intra-domain path diversity already gives most of power saving Benefit of power-aware egress selection alone is small What if we have power-aware ingress selection? 21