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Following up on my earlier question, TCP has a bunch of “magic
numbers” whose best values vary depending upon the source you
consult. I’m curious if you have any input on: 1) What’s
a good initial value for the cwnd, whether starting from scratch or after a
RTO? I know RFC2581 says one thing, and 3465 says another,
and others say other things. I’m curious what you actually use and
like, and why. 2) To what do
you set the ssthresh in response to a RTO? To a
fixed-fraction of pipe (say, 50%) or some fraction of something else? 3) How far do
you “fall back” the cwnd in response to a RTO? To a
fixed value (say, 1472 bytes) or to some fraction of something else? 4) To what do
you set the ssthresh in response to a drop? To a
fixed-fraction of pipe (say, 50%) or some fraction of something else? 5) How far do
you “fall back” the cwnd in response to a RTO? To ‘ssthresh’
or something else? 6) What ALPHA
value do you use for RTT smoothing? RFC 793 (3.7) recommends between
.8 and .9; any preference? (updatedRTT = ALPHA*oldRTT + (1-ALPHA)*newRTT)
I’m using .85 for lack of a better idea. 7) What BETA
value do you use for RTO calculation? RFC 893 (3.6) recommends
between 1.3 and 2.0; any preference? (retransmitTimeout = BETA * rtt)
I’m using 1.65, for no particular reason. Sorry for the big dump of questions; can you offer any guidance
on any of these? -david |
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