Diagnosing Spatio-Temporal Internet Congestion Properties

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Diagnosing Spatio-Temporal Internet Congestion
Properties

• Leiwen Deng
• Aleksandar Kuzmanovic
• EECS Department
• Northwestern University

http//networks.cs.northwestern.edu
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Problem

• Detect congestion events on an end-to-end path
  and reveal their spatio-temporal properties
• Where they happen (edge, core, intra-AS,
  inter-AS)?
• How long they last / frequently occur?

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Why Do We Care?

• Fault diagnosis
• Advanced congestion control
• Distributed monitoring systems
• Overlay design
• We want to know!

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Challenges

• Congestion events relatively infrequent
• Measure queuing delay instead of Ploss
• No/low support from the network
• Combine e2e with probes to intermediate nodes
• Path asymmetry
• Measurements still possible via measurable
  pairs

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Outline

• Methodology
• Implementation (Pong)
• Validation
• Measurements
• Results

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Methodology Highlights

• Coordinated probing
• Send 4, 3, or 2 packets from two endpoints
• Quality of Measurability (QoM)
• Able to deterministically detect its own
  inaccuracy
• Self-adaptivity
• Switch between different probing schemes based on
  QoM and path properties

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Coordinated Probing
Probe
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f probe
b probe
s probe
d probe
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,
,
4-p probing a symmetric path scenario
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Coordinated Probing
Probe
?f
?d
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?s
?b
?fs
?fd
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Locating Congestion Points
1. Probe Scheduling
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Sequentially probe (4-p) nodes on the path
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Locating Congestion Points
2. Switch Point Approach
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Correlate probes to neighboring nodes
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Tracing Congestion Status
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Link 1 (Located Congestion Point)
Congestion Status
Link 1
Time
Reuse probes sent to un-congested routers
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Measurable Pairs
4-p probing scenario
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Quality of Measurability
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Experiments

• 400 PlanetLab nodes
• Measure each pair for 1 hour
• 23,351 paths within 8 days

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Results

• Edge vs. core
• Edge more frequently congested than the core 14
  times on average
• Intra-AS vs. Inter-AS
• Edge Intra-AS gt Inter-AS
• Core Intra-AS lt Inter-AS
• Time domain
• Edges congestion events clustered in time
• Core congestion events dispersed in time
• Links vs. Paths
• Links 12 congested, 3 considerably
• Paths 20 considerably congested

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Conclusions

• Spatio-temporal Internet congestion properties
• New methodology
• Coordinated probing
• Detect its own inaccuracy
• Self adaptive to path properties
• Handles path asymmetries
• Implemented, deployed, evaluated, measured
• High accuracy in both spatial and temporal
  domains
• Future work
• Triggered monitoring system to learn more