UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Informed Detour Selection Helps Reliability
Boulat A. Bash
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Internet Reliability Problem
Internet service outage probability 1.5% – 3.3% (Paxson, Dahlin, etc)
Far short of 0.001% (99.999%, or five nines of reliability) observed in telephone networks
How can we improve? Add redundancyServer redundancy
CDNs (Akamai)
Path redundancy
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Path Redundancy
client
serverintermediary 1
intermediary 2
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Path Redundancy
client
serverintermediary 1
intermediary 2
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Path Redundancy
client
serverintermediary 1
intermediary 2
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Outline
Introduction and motivationPrevious workOur proposalExperimental validationDiscussionConclusion
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Choosing intermeds: aggressive probing
Aggressive monitoring of complete overlay graphExample: RON (Resilient Overlay Network)
node C
node Bnode A
node D
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Choosing intermeds: aggressive probing
Aggressive monitoring of complete overlay graphExample: RON (Resilient Overlay Network)
Problem: monitoring overhead ⇒ lack of scaling
node C
node Bnode A
node D
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Choosing intermeds: random choice
Choose intermediaries randomlyNo path monitoring, assume uncorrelated pathsExample: SOSR (Scalable One-hop Source Routing)
client
serverintermediary 1
intermediary 2
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Choosing intermeds: random choice
Choose intermediaries randomlyNo path monitoring, assume uncorrelated pathsExample: SOSR (Scalable One-hop Source Routing)
client
serverintermediary 1
intermediary 2
?
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Choosing intermeds: random choice
Choose intermediaries randomlyNo path monitoring, assume non-overlapped pathsExample: SOSR (Scalable One-hop Source Routing)
Problem: overlapped paths ⇒ choose invalid detour
client
serverintermediary 1
intermediary 2
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Our ProposalRank intermediaries by overlap with S-D path
Want less overlapNo need to aggressively monitor: AS/PoP-level paths static over 24 hours
client
serverintermediary 1
intermediary 2
A
B C
D E
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Our ProposalRank intermediaries by overlap with S-D path
Want less overlapNo need to aggressively monitor: AS/PoP-level paths static over 24 hours
client
serverintermediary 1
intermediary 2
A
B C
D E
intermediary 2 ranked lower because of
overlap
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Experimental Methodology
Validation study
PlanetLab-based experimentMonitor 4,269 paths from 46 PL nodes to set of Internet routers for 379 hoursEach path monitored by one PL node
Ping every 15 seconds, failure if two pings missedIntermediaries ping failed destination every 15 seconds during failure
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Experimental MethodologyUse collected data and PoP path data (from iPlane) to simulate recovery from detected failures
Random and informed choices of intermediaries
client
serverintermediary 1
intermediary 2
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Experiment
≈ 55,000 path outage eventsMean outage duration: ≈ 22 minutesMedian outage duration: 2 minutesLongest outage: over 6 daysAggregate path outage probability: 1.48%Each client had access to between 83 and 97 intermediaries
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Improving Path OutageImpact of intermediary selection methods on path outage
0.53%0.52%1.02%5
0.53%0.52%1.02%4
0.57%0.57%1.02%3
0.65%0.65%1.15%2
0.74%0.76%1.30%1
1.48%1.48%1.48%0
Common link count
Common PoPcount
Random (SOSR)
Number of intermediaries
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Improving Path OutageImpact of intermediary selection methods on path outage
0.53%0.52%1.02%5
0.53%0.52%1.02%4
0.57%0.57%1.02%3
0.65%0.65%1.15%2
0.74%0.76%1.30%1
1.48%1.48%1.48%0
Common link count
Common PoPcount
Random (SOSR)
Number of intermediaries
Informed methods reduce outage probability by half!
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Outline
Introduction and motivationPrevious workOur proposalExperimental validationDiscussionConclusion
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
DiscussionWhy did informed selection outperform random?
Paths not independent
Reasons for path correlationsPlanetLab design: universities on Internet2Geography
No knowledge of failure locations in studyBut can examine how close the sets of responding intermediaries are to what is expectedIf paths from intermediary set A are independent:
)path validhas |()( XAXPAXP ∈≈∈
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
PlanetLab Design
On average across failures, for intermediary X:P(X at university) = 92.0%P(X at university | X has valid path) = 91.6%
Connectivity failures not correlated between universities
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Geography
On average across failures, for intermediary X:Paths originating in the US
P(X in US) = 71.6%P(X in US | X has valid path) = 59.8%
Paths originating in AsiaP(X in Asia) = 7.2%P(X in Asia | X has valid path) = 3.7%
Path originating in EuropeP(X in Europe) = 20.8%P(X in Europe | X has valid path) = 26.7%
Thus, evidence of geographic correlation
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Path Outage revisitedEffect of restricting random selection to intermediaries outside of vantage point geographical area
0.53%
0.53%
0.57%
0.65%
0.74%
1.48%
Common link count
0.75%0.52%1.02%5
0.84%0.52%1.02%4
0.95%0.57%1.02%3
1.09%0.65%1.15%2
1.26%0.76%1.30%1
1.48%1.48%1.48%0
Geog. random
Common PoP count
Random (SOSR)
Num intermeds
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Conclusions
Demonstrated potential improvement using informed detour selection in reliability over random selection in SOSR
Biasing SOSR random selection outside own geographical area captures some benefit of informed method
Future workImplement informed detour selection mechanismEvaluate path estimation services (Rocketfuel, iPlane)Examine whether fresher path information helps
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer ScienceDepartment of Computer Science
Thanks!
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