Transcript

Making Inter-domain Routing Power-Aware?

Junxiao Shi and Beichuan Zhang

The University of Arizona, USA

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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

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GreenTE: dynamically adjusting routing paths

• GreenTE adapts routing paths to traffic demand, so that unused links can go to sleep and save power

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GreenTE model

• GreenTE is modelled as an optimization problem, and optimized in a centralized controller

• MAXIMIZE: Σ 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

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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?

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Power-aware inter-domain routing

• Power-aware inter-domain routing enhances path diversity

• How much additional power saving can we get?

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source destination

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

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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

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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

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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

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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

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One egress set per destination prefix

• fine granularity, more computation, higher power saving

ISP

192.0.2.0/24

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One egress set per destination AS

• medium granularity, medium computation, medium power saving

ISP

192.0.2.0/24

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One egress set per neighbor

• coarse granularity, less computation, lower power saving

ISP

192.0.2.0/24

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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 GreenTEand inter-domain GreenTE

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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

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Impact of internal topology

• HIGH IMPACT on both intra-domain and inter-domain

spanning tree richly connected

intra-domaininter-domain

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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

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Impact of egress set granularity

• MEDIUM IMPACT on inter-domain

per neighbor AS per destination AS

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Impact of BGP policy

• MEDIUM IMPACT on inter-domain

respect path preference ignore path preference(allow using provider route when there is customer route)

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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?

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