Making Inter-domain Routing Power-Aware?
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Transcript of Making Inter-domain Routing Power-Aware?
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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