ATM vs. DS3

Thu Jul 10 19:38:36 UTC 1997

i've never heard anything *less* than 20% loss in ATM overhead.

On Wed, 9 Jul 1997, Karl Denninger wrote:

> 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 at 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. :-)
> 
> --
> -- 
> Karl Denninger (karl at MCS.Net)| MCSNet - The Finest Internet Connectivity
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