[e2e] TCP un-friendly congestion control
Craig Partridge
craig at aland.bbn.com
Fri Jun 6 12:05:27 PDT 2003
In message <3EE0E340.4030102 at cisco.com>, Guglielmo Morandin writes:
>Craig, you will take 18 rtt if the cwnd doubles every rtt.
Actually, if it grows by 50% each RTT.
>But after a packet drop the congestion window is supposed to grow by
>just one packet every rtt, isn't it?
Only after hitting half the congestion window.
So run that logic. Suppose the available capacity is 1 Gbps (and if
it isn't, why are we having this discussion?) and so around the point
we hit 1 Gbps we regularly get a congestion loss.
CWND runs at 500 Mbps and it takes only a few RTTs to grow to that
size.
After CWND (at which times we're at 500 Mbps) we grow linearly to 1 Gbps.
That says our average data rate is just under 750Mbps for a 1 Gbps link.
(Assuming no error loss -- which starts to become a factor on some
channels at these rates).
Craig
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