[e2e] Mixed ECN and Non-ECN traffic flows.

Chong Poh Kit thesoothsayer at pd.jaring.my
Fri Oct 11 02:52:54 PDT 2002


I've done some simulations using a mixture of ECN and non-ECN capable TCP
flows over NS-2 and I've discovered that at a bottleneck link with a single
FIFO queue, ECN flows tend to grab more than their fair share of the
bandwidth when an AQM (RED,BLUE) is used at the router.

I believe this is due to the fact that ECN traffic needs more aggressive
marking to control the rate of congestion while the non-ECN traffic suffers
from the increased packet drops. Furthermore, the packet drops results in
constant retransmissions and thus, a hit in the goodput of the non-ECN
This problem is exacerbated when the latency is low because a more
aggressive packet dropping/marking probability is needed to control the
throughput of TCP.

I was wondering if this is a trivial problem as I've not seen any research
done on it so far?
My opinion is that as the percentage of ECN capable end hosts increases this
would pose a problem of unfairness in the future.

Also, could anyone direct me to any statistics that show the percentage of
ECN capable end hosts currently deployed on the Internet?



Chong Poh Kit
Post-graduate Student
Multimedia University, Malaysia
Tel : (6)016-3174831

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