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On the Suitability of ping to Measure Latency

On the Suitability of ping to Measure Latency . Cristel Pelsser < cristel @ iij.ad.jp > Luca Cittadini < luca.cittadini @ gmail.com > Stefano Vissicchio < stefano.vissicchio @ uclouvain.be > Randy Bush <randy @ psg.com>. We Use Ping. But, what is the actual distribution of the RTTs?

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On the Suitability of ping to Measure Latency

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  1. On the Suitability of ping to Measure Latency CristelPelsser <cristel@iij.ad.jp> Luca Cittadini <luca.cittadini@gmail.com> Stefano Vissicchio <stefano.vissicchio@uclouvain.be> Randy Bush <randy@psg.com>

  2. We Use Ping • But, what is the actual distribution of the RTTs? • Could there be a rich distribution? • We were using Atlas and found ping variance to be unexpectedly high • So we decided to calibrate our tools • So we ran a paristraceroute series from Roma Tre to Ashburn

  3. Paris Traceroute UsesFlow-IDTo Explore HashedECMP / LAGgedAlternative Paths

  4. Roma Tre - Ashburn Notice Linux Rounding

  5. ECMP • != Equal Latency Multi-Path

  6. So, A Simple Path Single Layer Three Path Ashburn Dallas

  7. Simple Path Used LAG FreeBSD Not Rounding

  8. Looking for Causes • Very Reproducible • Circuit Loading <= 50% • Same different times of day • Same different probe timing/spacing • Same UDP or ICMP • Layer > 3 Hashing => Large Effect

  9. Layer-3 Only Hash

  10. Event During Run

  11. Selected Summary

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