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

  • Authors:
  • Ramana Rao Kompella;Kirill Levchenko;Alex C. Snoeren;George Varghese

  • Affiliations:
  • Purdue University, West Lafayette, IN, USA;UCSD, La Jolla, CA, USA;UCSD, La Jolla, CA, USA;UCSD, La Jolla, CA, USA

  • Venue:
  • Proceedings of the ACM SIGCOMM 2009 conference on Data communication
  • Year:
  • 2009

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Abstract

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.