Re: ATM vs. DS3

[Karl Denninger <karl () Mcs Net>]

On Tue, Jul 09, 1996 at 10:38:57PM -0500, Chris A. Icide wrote:
> On Wednesday, July 09, 1997 9:34 PM, Josh Beck [SMTP:jbeck () connectnet com] 
> wrote:
> > Hello,
> >     I just thought of something. We are in the process of purchasing a
> > 4 Mb CIR from another backbone. Now, we have the choice of ATM or standard
> > T3 delivery (over a DS3 either way). Now, if we get ATM, that 4 Mb CIR
> > turns into:
> >
> > [ (53-5)/53 ] * 4 Mb/s = 48/53 * 4 Mb/s = 3.62 Mb/s
>
> Emperical data shows that we are currently losing about 20.5% of capacity
> to IP over ATM overhead on fairly aggregated traffic.  This means that *IF*
> your new connection is being measured as 4Mbps of cell bandwisth, you
> will only be getting 3.18Mbps.  You may want to verify from the company
> providing this link what exactly are they limiting you to?
>
> btw, the extra overhead is lost in things like the last cell of a packet not
> being full, etc.
>
> Chris A. Icide
> Sr. Engineer
> Nap.Net, L.L.C.

My God, someone admits it?

I've used 20% as the general ATM overhead now for almost two years, and have
been poo-pooed by lots of people claiming that it wasn't anywhere near that
bad.

Funny how it all comes out in the end. :-)

--
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