Optimizing Cost and Performance for Multihoming

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Optimizing Cost and Performance for Multihoming
Lili QiuMicrosoft Research liliq_at_microsoft.com
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Multihoming Smart Routing

• Multihoming
• A popular way of connecting to Internet
• Smart routing
• Intelligently distribute traffic among multiple
  external links

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Potential Benefits

• Improve performance
• Potential improvement 25 Akella03
• Similar to overlay routing Akella04
• Improve reliability
• Two orders of magnitude improvement in fault
  tolerance of end-to-end paths Akella04
• Reduce cost

Q How to realize the potential benefits?
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Our Goals

• Goal
• Design effective smart routing algorithms to
  realize the potential benefits of multihoming
• Questions
• How to assign traffic to multiple ISPs to
  optimize cost?
• How to assign traffic to multiple ISPs to
  optimize both cost and performance?
• What are the global effects of smart routing?

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Network Model

• Network performance metric
• Latency (also an indicator for reliability)
• Extend to alternative metrics
• log (1/(1-lossRate)), or latencywlog(1/(1-lossRa
  te))
• ISP charging models
• Cost C0 C(x)
• C0 a fixed subscription cost
• C a piece-wise linear non-decreasing function
  mapping x to cost
• x charging volume
• Total volume based charging
• Percentile-based charging (95-th percentile)

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Percentile Based Charging
Sorted volume
Interval
N
95N
Charging volume traffic in the (95N)-th sorted
interval
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Why cost optimization?

• A simple example
• A user subscribes to 4 ISPs, whose latency is
  uniformly distributed
• In every interval, the user generates one unit of
  traffic
• To optimize performance
• ISP 1 1, 0, 0, 0,
• ISP 2 0, 1, 0, 0,
• ISP 3 0, 0, 1, 0,
• ISP 4 0, 0, 0, 1,
• 95th-percentile 1 for all 4 ISPs
• 95th-percentile 1 using one ISP
• Cost(4 ISPs) 4 cost(1 ISP)

Optimizing performance alone could result in high
cost!
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Cost Optimization Problem Specification (2 ISPs)
Sorted volume
Volume
P1
Sorted volume
Time
P2
Goal minimize total cost C1(P1)C2(P2)
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Issues Insights

• Challenge traditional optimization techniques do
  not work with percentiles
• Key determine each ISPs charging volume
• Results
• Let V0 denote the sum of all ISPs charging
  volume
• Theorem 1 Minimize cost ?? Minimize V0
• Theorem 2 V0 1- ?k1..N(1-qk) quantile of
  original traffic, where qk is ISP ks charging
  percentile

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Cost Optimization Problem Specification (2 ISPs)
Sorted volume
Volume
P1
Sorted volume
Time
P2
P1 P2 ? 90-th percentile of original traffic
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Intuition for 2-ISP Case

• ISP 1 has ? 5 intervals whose traffic exceeds P1
• ISP 2 has ? 5 intervals whose traffic exceeds
  P2
• The original traffic (ISP 1 ISP 2 traffic) has
  ? 10 intervals whose traffic exceeds P1P2
• P1P2 ? 90-th percentile of original traffic

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Sketch of Our Algorithm

• Determine charging volume for each ISP
• Compute V0
• Find pk that minimize ?k ck(pk) subject to
  ?kpkV0 using dynamic programming
• Assign traffic given charging volumes
• Non-peak assignment ISP k is assigned ? pk
• Peak assignment
• First let every ISP k serve its charging volume
  pk
• Dump all the remaining traffic to an ISP k that
  has bursted for fewer than (1-qk)N intervals

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Additional Issues

• Deal with capacity constraints
• Perform integral assignment
• Similar to bin packing (greedy heuristic)
• Make it online
• Traffic prediction
• Exponential weighted moving average (EWMA)
• Accommodate prediction errors
• Update V0 conservatively
• Add margins when computing charging volumes

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Optimizing Cost Performance

• One possible approach design a metric that is a
  weighted sum of cost and performance
• How to determine relative weights?
• Our approach optimize performance under cost
  constraints
• Use cost optimization to derive upper bounds of
  traffic that can be assigned to each ISP
• Assign traffic to optimize performance subject to
  the upper bounds

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Evaluation Methodology

• Traffic traces (Oct. 2003 Jan. 2004)
• Abilene traces (NetFlow data on Internet2)
• RedHat, NASA/GSFC, NOAA Silver Springs Lab, NSF,
  National Library of Medicine
• Univ. of Wisconsin, Univ. of Oregon, UCLA, MIT
• MSNBC Web access logs
• Realistic cost functions Feb. 2002 Blind RFP
• Delay traces
• NLANR traces 3 months RTT measurements between
  pairs of 140 universities
• Map delay traces to hosts in traffic traces

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Conclusions

• First paper on jointly optimizing cost and
  performance for multihoming
• Propose novel smart routing algorithms that
  achieve both low cost and good performance
• Under traffic equilibria, smart routing improves
  performance without hurting other traffic