Subject: [tcpm] httpbis chromium data

From: "Scheffenegger, Richard" <[email-masked]>
Date: Fri, 2 Aug 2013 14:26:31 +0000

Hi William, Jerry,

During today’s presentation in the httpbis session, a CDF/histogram was shown of the effective cwnd size at graceful session close.

One of the interesting facts from that was a spike/peak at large window sizes (200 packets IIRC). It would be interesting, how these large windows came to be…

Provided that these data  points are not invalid for some data collection issue somewhere, this should only be true for very long latencies (like browsing from Japan via Europe on a West-Coast Server), very high bandwidths (google deploys gigabit-to-the-home in places, right), or potentially when the tcp session is application limited but constantly stays below the bottleneck bandwidth, while the OS continues to increase the cwnd over many RTTs by 1 (congestion avoidance flaw in app-limited streams in some OS).

If the majority of sessions end up in that last bin, that may be a significant finding for TCPM that should be addressed – as this plays into the general  cwnd validation area which currently receives some attention.

Or this might be a data sampling error somehow, and represents invalid data…

Richard Scheffenegger