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Merging Logical Topologies Using End-to-end Measurements. Michael Rabbat Mark Coates Robert Nowak. Internet Measurement Conference 2003 Tuesday October 28, 2003. A. 1. 2. 3. 4. 5. Topology Identification via Active Probing. Motivation: BGP data gives the big picture

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merging logical topologies using end to end measurements

Merging Logical Topologies UsingEnd-to-end Measurements

Michael Rabbat Mark Coates Robert Nowak

Internet Measurement Conference 2003

Tuesday October 28, 2003

topology identification via active probing

A

1

2

3

4

5

Topology Identification via Active Probing

Motivation:

  • BGP data gives the big picture
  • ICMP-based techniques (i.e. traceroute) don’t 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.]

extending to multiple sources

A

1

2

3

4

5

B

1

2

3

4

5

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

merging strategy

A

B

A

1

2

3

4

5

B

1

2

3

4

5

3

2

4

5

1

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
goal identify shared joining nodes

A

A

B

B

A

B

1

1

2

2

1

1

2

2

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

packet arrival order measurements

A

B

t(n) + t

t

t(n)

v(n)

1

2

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| ¼O(RTTmax) À t
  • Assumptions:
  • Sources synchronized (for now)
  • Arrival order determined at first shared queue

t

conditions for a different arrival order

A

B

Contours of p(d1, d2)

d2

1

d1

2

Prob. different arrival order | v(n)

Conditions for a Different Arrival Order
for non shared topologies

Contours of p(d1, d2)

d2

A

B

d1

1

2

Prob. different arrival order | v(n)

For Non-Shared Topologies
  • On packet reordering [Bellardo & Savage, ’02]
    • Pr{In-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)
measure the noise

A

B

t

t(n)

v(n)

1

2

Measure the Noise
  • Similar procedure:
  • At t(n), send packets to Rcv1
  • After t, send to Rcv1 againt¼O(1/bmin)
  • Compare arrival orders
  • Repeat, varying send time at Bv(n) ~ Unif orm(-D, D)|D| ¼O(RTTmax)

Send all packets to one receiver

 Force one joining node

2

2

t

1

1

Must be noise

1

2

1

2

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

Some Experiments
summary
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.edu

[email protected]

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