Subject: Re: [PATCH] make _minimum_ TCP retransmission timeout configurable

From: Rick Jones <[email-masked]>
Date: Wed, 29 Aug 2007 16:06:27 -0700

> All of this seems to suggest that the RTO calculation is wrong.

That is a possiblity.  Or at least could be enhanced.

> It seems that packets in this network can be delayed several orders of
> magnitude longer than the usual round trip as measured by TCP.
> 
> What exactly causes such a huge delay?  What is the TCP measured RTO
> in these circumstances where spurious RTOs happen and a 3 second
> minimum RTO makes things better?

I belive the biggest component comes from link-layer retransmissions. 
There can also be some short outtages thanks to signal blocking, 
tunnels, people with big hats and whatnot that the link-layer 
retransmissions are trying to address.  The three seconds seems to be a 
value that gives the certainty that 99 times out of 10 the segment was 
indeed lost.

The trace I've been sent shows clean RTTs ranging from ~200 milliseconds 
to ~7000 milliseconds.

rick