From: John Gibson (johngibson1541@yahoo.com)
Date: Thu Jun 21 2007 - 13:30:49 ART
At some point I think I have no points in this issue.
My only final note to myself is that
1. WRED can avoid both "tail drop" and
"undiscriminating drop"
2. RED can only avoid "tail drop" , which
is also pretty good because the scrambling
process improves overall throughput.
the magical part is avoiding "tail drop", it
takes math to understand why is improves throughput
the plain mechanical part is avoiding
"undiscriminating drop"
However, when "tail drop" happens, "undiscriminating
drop" must occur too.
John
--- "Douglas M Todd, Jr" <dtodd@partners.org> wrote:
> My 2c:
>
> Well -
> Basically, I don't like to see drops at all, tail,
> output, input etc.
> This means there is an design flaw or a bandwidth
> inequality. However,
> life is never perfect and drops are a part of the
> network and a necessity.
>
> Whether you call it Tail, Queue full drop,
> undiscriminating drop?
>
> Depends on how you view the queuing on the device.
> When you look at FIFO
> a tail drop is pretty specific. Undiscriminating
> drop is pretty vague
> (even though it's implied that all traffic is viewed
> equally) to me
> because it does not imply any queuing/drop
> mechanism. Undiscriminating
> drop would lead me to believe that the device will
> indiscriminately drop
> any packet in the queue regardless of it's position
> and protocol type,
> even packet's in the queue. This is not the case
> with a tail drop where
> a router/switch with full queue will start dropping
> the packets trying
> to enter the queue, but not packets already in the
> queue.
>
> I think the goal is to understand the queuing on a
> device and what
> happens when the queue fills up to the point of
> dropping traffic. The
> industry states tail drop (meaning it's not just a
> Cisco thing, but its
> also a tcp thing), however, if you understand it
> better by referencing
> it as an "undiscriminating drop" then you are one
> step closer to fully
> understanding and remembering how queuing works on a
> device. You just
> need to remember to yourself that "Tail Drop" or
> Weighted Tail Drop
> means undiscriminating drop or wighted
> undiscriminating drop.
>
> Either way, is if you understand it, then great!
>
> DMT
>
>
>
> johngibson1541@yahoo.com wrote:
> > I know these 2 are technically the same.
> >
> > We don't like that to happen.
> >
> > But I just think saying "undiscriminating drop"
> > is much more specific, to the point.
> >
> > Every time I see or hear "tail drop", I have to
> > translate it to "undiscriminating drop" to
> > make sense to myself.
> >
> > "tail drop" is the physical appearance and can
> > happen in different setting and mean different
> > things.
> >
> > "undiscriminating drop" is just plain straight
> > forward that we want to prevent.
> >
> >
>
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