[e2e] Use of RED in practice?

Simon Leinen simon at limmat.switch.ch
Tue Mar 28 11:53:33 PST 2006

Zartash Afzal Uzmi writes:
> My question is not about router manufacturers implementing RED in
> their routers? The question is about how many routers are enabled
> with RED (or a variant)? Does everyone use it? No one uses it in
> practice? Some Tier-x ISPs use it????

I'm sure NOT everyone uses it, because it is usually not enabled by
default on routers that are commonly used by ISPs, and enabling it is
somewhat tricky because you have to define somewhat sane parameters
for the RED drop characteristics.

We used to use RED when we had overloaded (transatlantic) links, very
successfully I might add - RED brought down peak-hour delays
considerably, despite the relatively high base delay, without
increasing loss rates or reducing link utilization.

But several years ago we got into a regime where we would run all our
links without noticeable queuing virtually all of the time.  So we
didn't bother configuring RED again.

> There is some material on Sally's webpage regarding implementation
> experiences (http://www.icir.org/floyd/red.html) but it is not clear
> if those implementations were done on an experimental basis or are
> currently used in live networks. For example, there is a link which
> says "WRED is enabled on Cisco GSRs on overloaded links at AS1
> (Genuity), to reduce queueing delay. Experience has been positive."
> (reported back in 2000) but leaves me wondering if they still enable
> RED within networks of all (or some) ISPs?

RED still makes as much sense as it did six years ago where there's
persistent congestion of highly aggregated traffic - it can keep those
links somewhat usable for interactive use.  If you have such
oversubscribed links in your network, I strongly encourage you to
experiment with RED.

> Please clarify if the answer depends upon the Tier level of the
> service provider. Thanks a lot.

We buy transit from three transit-free (Tier-1) providers, does that
make us a Tier-2? No idea.

Anyway, I think the answer (whether an ISP actually uses RED) won't
depend much on Tier level, except at a Tier-<low-number> ISP I would
expect more people to be aware of RED; on the other hand I don't think
Tier-1 ISPs typically run congested links anymore... maybe to
customers (if the pricing structure encourages customers to
oversubscribe their access links, which I consider a bad idea).

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