King : A tool to estimate latency between Internet hosts

1
King A tool to estimate latency between
Internet hosts

• Krishna Gummadi
• Stefan Saroiu
• Steven D. Gribble

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Goal
C

• Measure the latency between any two IP addresses,
  from any point in the Internet

• Internet

A
B

• Why is this useful?
• Closest Server Selection
• Distributed P2P Systems
• Building topologically sensitive overlay networks
  (CAN, Chord, Gnutella, )

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Outline

• Motivation
• Techniques to predict network distances
• Our DNS-based technique (King)
• Evaluation of our tool
• Conclusions

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Related Techniques

• Techniques to estimate the latency between any
  two arbitrary hosts
• IDMAPS (U.Mich)
• GNP (CMU)
• Drawbacks of existing schemes
• Require deployment of additional infrastructure
  in the Internet
• They make assumptions about the topology of the
  Internet which dont hold in practice
• For example, triangle inequality

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King a DNS-based latency tool

• Insights
• We can use recursive DNS queries to deduce
  latency between DNS servers
• Most Internet hosts are located close to their
  DNS servers
• Thus, we can approximate latency between the
  hosts as latency between their name servers
• Later in this talk, well show when this trick
  works, and when it fails

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Resolve xyz.mit.edu using Recursive DNS Query
My Machine
DNS
xyz.mit.edu
Time taken to resolve recursive query
xyz.mit.edu to Berkeley NS is T t1 t2
DNS
abc.berkeley.edu
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Resolve abc.berkeley.edu
My Machine
DNS
xyz.mit.edu
Time taken to resolve query abc.berkeley.edu to
Berkeley NS is T t1
DNS
abc.berkeley.edu
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How King Works ?
My Machine
DNS
xyz.mit.edu
DNS
Latency between Name Servers, t2 T-
T Latency between Hosts Latency between Name
Servers
abc.berkeley.edu
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Potential Limitations of King

• At least one of the authoritative name servers of
  either host has to support recursive queries
• gt75 of name servers support such queries
• Multiple authoritative name servers that are
  geographically distributed
• Name Servers tend to be better connected than End
  Hosts.
• Our estimates tend to ignore the large last hop
  latencies for DSL/cable/modem users

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Evaluating the Accuracy of King

• Directly measure latencies between 50 public
  traceroute servers and 50 end hosts
• Estimate latencies between the same servers/hosts
  using King and IDMaps.
• Compare
• Metric used

Estimated Latency
Measured Latency
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(No Transcript)
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Additional evaluation

• DNS servers tend to be close to IP addresses in
  practice
• far less than 10 milliseconds, gt80 of the time
  (although modems are trouble)
• King tends to preserve order
• Often more important than accuracy!
• Can choose between accuracy and additional
  measurement costs
• tune the tool for various applications
• Can even measure latency between hosts that are
  offline or do not respond to ICMP ping messages !

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Summary

• We presented King, a DNS based tool to estimate
  latency
• King works in the Internet as it exists today.
• No need for any additional infrastructure.
• We showed that King is fairly accurate for
  estimating latency between internet hosts

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Future Work

• Incorporating King into Internet services
• e.g., closest server selection
• Wide-area measurement studies using King
• Generating a latency map of Gnutella overlay
• Evaluating the efficiency of Akamais server
  selection
• More extensive validation of Detour study

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Questions ?
More Info www.cs.washington.edu/homes/gummadi/kin
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