[e2e] Policing TCP flows
Greg Minshall
minshall at acm.org
Wed Jun 19 09:55:45 PDT 2002
the TCP connection gets the same amount of throughput ("goodput") in both
cases, but the "badput" is radically different. policing incurs lots more
badput.
if you look at plots from traces, what you see is that with policing, the RTT
is very low, so the "probe-until-drop" cycle is very short, so you get lots of
these cycles in the same elapsed time. with shaping, the RTT is
(artificially) high, so the "probe-until-drop" cycle is very long and you get
fewer of these cycles in the same elapsed time. since the amount of data
transmitted is the same (in this "same elapsed time"), with policing you drop
lots more packets.
if you hate dropped packets, you'll hate policing.
(this is all without ECN; i'm not sure how it would change with ECN, maybe for
the better. this might be the killer app for ECN!)
cheers, Greg Minshall
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