[e2e] Stupid Question: Why are missing ACKs not considered as indicator for congestion?
baruch at ev-en.org
Tue Jan 30 01:58:17 PST 2007
* Fred Baker <fred at cisco.com> [070130 10:52]:
> On Jan 30, 2007, at 12:01 AM, Baruch Even wrote:
> >There are cases of asymmetric links that might cause trouble, but that
> >will only serve to slow down the payload direction as well since packets
> >are released to the network only when acks come back, so a lost ack will
> >already slow down the rate of the payload, just not by cutting the cwnd
> >to half.
> actually, one can argue that it speed the payload up, or that it causes it to burst. If I have octets 10000..20000
> outstanding, receive an ack for 10000-11999, and drop one for 12000-13999, and now receive an ack indicating that my
> peer has received "through 15999", that looks to me like an ack for 12000-15999, and I should send a burst of that size.
I don't know in other OSes but in Linux that's not the case. Linux will
send up to 3 packets IIRC. So if we get an ack for more than 3 packets
we will only send 3 packets and "lose" the extra credit for now.
Ofcourse, the next packet that acks two packets will cause three packets
to be sent as well, so it does slow us down some and also causes larger
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