RE: ATM vs. DS3

["Eric D. Madison" <madison () acsi net>]

Stephen,

Cisco doesn't have a lot of ATM stats avaiable yet.  We have been beating
the ATM developers to try to get better stats.. but no luck yet. We have
had a lot of problems the way the SAR chip accounts for VBR traffic.. and
they don't even do CBR.  The output/input counters on the interfaces are
not valid ways of measuring traffic either, they don't take ATM Traffic
shaping into account.  This is because the interface counters are
calculated before the actual SAR chip segments/reassembles the ATM Cells. 
This can be proven by using an ATM traffic generator and flooding the
interface... According to the interface stats I was pushing over 200 mb
through and OC-3. I wish!!

So, in a nutshell, there isn't a real good way to measure
performance/effieciency on a Cisco.. yet. 

Eric
_______________________________________________________
      Eric D. Madison - Senior Network Engineer -   
 ACSI - Advanced Data Services - ATM/IP Backbone Group  
   24 Hour NMC/NOC (800)291-7889 Email: noc () acsi net


On Thu, 10 Jul 1997, Stephen Balbach wrote:

> We go direct Cisco <-> Cisco DS3, no switch. Any variables to measure on the 
> Cisco, assuming you only have access to 1 side?
>
> On Thu, 10 Jul 1997, Chris A. Icide wrote:
>
> > 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 () clark net]
> > Sent:       Thursday, July 10, 1997 3:07 PM
> > To: Ben Black
> > Cc: Karl Denninger; Chris A. Icide; 'Josh Beck'; nanog () 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 () 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 () 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