Every microsecond counts: Tracking fine-grain latencies with a lossy difference aggregator

Ramana Rao Kompella, Kirill Levchenko, Alex C. Snoeren, George Varghese

Research output: Contribution to journalConference article


Many network applications have stringent end-to-end latency requirements, including VoIP and interactive video conferencing, automated trading, and high-performance computing - where even microsecond variations may be intolerable. The resulting fine-grain measurement demands cannot be met effectively by existing technologies, such as SNMP, NetFlow, or active probing. We propose instrumenting routers with a hash-based primitive that we call a Lossy Difference Aggregator (LDA) to measure latencies down to tens of microseconds and losses as infrequent as one in a million. Such measurement can be viewed abstractly as what we refer to as a coordinated streaming problem, which is fundamentally harder than standard streaming problems due to the need to coordinate values between nodes. We describe a compact data structure that efficiently computes the average and standard deviation of latency and loss rate in a coordinated streaming environment. Our theoretical results translate to an efficient hardware implementation at 40 Gbps using less than 1% of a typical 65-nm 400-MHz networking ASIC. When compared to Poisson-spaced active probing with similar overheads, our LDA mechanism delivers orders of magnitude smaller relative error; active probing requires 50-60 times as much bandwidth to deliver similar levels of accuracy.

Original languageEnglish (US)
Pages (from-to)255-266
Number of pages12
JournalComputer Communication Review
Issue number4
StatePublished - Nov 30 2009
Externally publishedYes
EventACM SIGCOMM 2009 Conference on Data Communication, SIGCOMM 2009 - Barcelona, Spain
Duration: Aug 17 2009Aug 21 2009


  • Packet sampling
  • Passive measurement

ASJC Scopus subject areas

  • Software
  • Computer Networks and Communications

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