ATM vs. DS3

Thu Jul 10 20:25:45 UTC 1997

We monitor both the octet output of the cisco, and the received cells
on our ATM switch.  One then would divide the cisco octet value by the 
cell value * 53.  This would result in a percentage value that would
indicate your "efficiency".

Efficiency (%) = octet rate / (cell rate * 53)

This assumes that you can measure both parameters.

Chris A. Icide
Sr. Engineer
Nap.Net, L.L.C.

-----Original Message-----
From:	Stephen Balbach [SMTP:stephen at clark.net]
Sent:	Thursday, July 10, 1997 3:07 PM
To:	Ben Black
Cc:	Karl Denninger; Chris A. Icide; 'Josh Beck'; nanog at merit.edu
Subject:	Re: ATM vs. DS3

Question: On a Cisco with an AIP card, how do you determain what the 
          overhead is? We connect to our upstream provider via ATM.

.stb

On Thu, 10 Jul 1997, Ben Black wrote:

> 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
> > http://www.mcs.net/~karl     | T1's from $600 monthly to FULL DS-3 Service
> > 			     | 99 Analog numbers, 77 ISDN, http://www.mcs.net/
> > Voice: [+1 312 803-MCS1 x219]| NOW Serving 56kbps DIGITAL on our analog lines!
> > Fax:   [+1 312 803-4929]     | 2 FULL DS-3 Internet links; 400Mbps B/W Internal
> > 
> 