Merging Logical Topologies Using Endtoend Measurements

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Merging Logical Topologies UsingEnd-to-end
Measurements

• Michael Rabbat Mark Coates Robert Nowak

Internet Measurement Conference 2003 Tuesday
October 28, 2003
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Topology Identification via Active Probing

• Motivation
• BGP data gives the big picture
• ICMP-based techniques (i.e. traceroute) dont
  work everywhere
• Existing end-to-end techniques
• Single active source, many receivers
• Assume tree structured logical topology
• Exploit
• Correlated events on upstream links
• Additive, non-decreasing nature of performance
  parameters
• Ratnasamy McCanne, Duffield et al.,
  Bestavros et al., Coates et al.

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Extending to Multiple Sources

• Marginal Utility Barford et al., 01
• Can gain by using a few more sources
• Net. Tomo. on General Topologies Bu et al., 02
• Evaluate various algorithms for inferring
  internal characteristics
• Sources make measurements separately
• Identifiability conditions given the general
  topology

No labels on internal nodes ? Merging is
non-trivial
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Merging Strategy

• Identify joining nodes ? merge topologies
• Placement is logical, relative
• Non-shared joining node
• Merging node for routes to a single receiver
• Shared joining node
• Routes to multiple receivers merge at one node

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Goal Identify Shared Joining Nodes

• Two sources, two receivers
• Is there a shared joining node?
• Locate joining node relative to branching node
• All other cases have more than one non-shared
  joining node
• Make measurements and form a binary hypothesis
  test
• H0 One joining node
• H1 More than one joining node

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Packet Arrival Order Measurements

• Procedure
• At t(n), send packets to Rcv1
• After ?t, send packets to Rcv2? t O(1/bmin)
• Compare arrival orders
• Repeat, varying send time at Bv(n) Unif
  orm(-D, D)D ¼ O(RTTmax) À ?t

• Assumptions
• Sources synchronized (for now)
• Arrival order determined at first shared queue

?t
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Analysis Packet Arrival Order and Timing
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Conditions for a Different Arrival Order
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For Non-Shared Topologies

• On packet reordering Bellardo Savage, 02
• PrIn-network reordering / 1/(time-spacing)
• Sources of measurement noise
• Packet reordering for a few values of v(n)
• Spacing ?t distorted by queueing (also, for few
  values of v)

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Measure the Noise

• Similar procedure
• At t(n), send packets to Rcv1
• After ?t, send to Rcv1 again? t ¼ O(1/bmin)
• Compare arrival orders
• Repeat, varying send time at Bv(n) Unif
  orm(-D, D)D ¼ O(RTTmax)

Send all packets to one receiver ? Force one
joining node
2
2
?t
1
1
Must be noise
1
2
1
2
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Making A Decision
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Some Experiments

• Rice ECE LAN
• 18 Unix/Linux hosts
• Spread across two buildings, two VLANs
• Mostly layer-2, two routers
• Validated with help from IT
• Internet Test bed
• 11 academic hosts
• Mostly N. American, few in Europe
• Validated using traceroute
• Extremely successful

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Summary

• Merge logical topologies by identifying joining
  nodes
• Shared joining nodes located relative to
  branching node
• Novel multiple source active probing scheme
• Uniform random offset
• Look for packet arrival order differences
• A few concluding remarks
• Unicast or multicast
• O(NS2 R2) measurements, reduce to O(NS2 R) using
  stripes
• Infrastructure independent (layer-3 or layer-2)

Signal Processing In Networking http//spin.rice.e
du rabbat_at_cae.wisc.edu