TCP Slow Start and the Web

As part of my SPDY work, I published an informal slide deck about the effect of TCP’s slow start on HTTP performance.

Cliff notes:

  1. It has been known that TCP’s slow start adversely effects performance in high-latency, high bandwidth networks for years.
  2. Increasing cwnd (reducing slow start) has been slow through standards due to concerns about internet collapse.
  3. But web servers and browsers have already worked around TCP’s slow start by pummeling the net with excessive connections – effectively making slow start irrelevant.
  4. If slow start has already been worked around, and the internet has not collapsed, it is time to seriously look at changing how slow start works so that we don’t have to open 30 connections in order to have a low-latency transaction.

Feedback is welcome!

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