[vox-tech] tcp tuning with wireshark?

[Nick Schmalenberger]

I need to increase throughput for long lived tcp connections over
ipsec over wan between Amazon in Ireland and a Level3 gigabit
link in Ashburn Virginia (currently running at about 20Mbps).
I've read various articles saying to enlarge the buffers and make
various other kernel tweaks. Some say to base it on the bandwidth
delay product, some say just on the link speed, and some say
don't bother linux does all that automatically now. Alot of it
seems random.

However, with wireshark I see that the "bytes in flight"
measurement which counts unacknowledged bytes from the source
never gets close to the window size sent by the destination. Does
this suggest anything in particular to tweak? I got some books on
wireshark, which were quite helpful in how to use the graphs and
filters, but on tcp performance they mostly just talked about the
effect of packet loss. I'm not certain, but I don't think packet
loss is the main thing holding back my performance, because there
is some which causes a brief dip in the window size and then it
recovers. Throughput stays pretty flat.

It would be really amazing if there was a flowchart on doing this
for linux that could be informed by wireshark io graphs and other
graphs. Has anybody ever seen such a chart? If this approach is
succesful for me, and I can understand how to do it in several
scenarios, I think I will even like to make such a flow chart if
it doesn't already exist. Thanks for any tips and disabusement of
my misunderstandings about tcp in linux :) 
Nick