North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: ATM vs. DS3
PLCP mapping is the only option on a Cisco AIP (DS-3), as you probably already know.. if you have a ATM Switch that is current, you can change the mapping to Direct Cell mapping, which will give you about 3 megs more of bandwidth on the line rate.. All of our switch-switch DS-3's are direct mapping, and all of our switch-routers are OC-3 SONET, so you don't have the same loss of bandwidth as PLCP on a DS-3. (also easier to aggregate multiple backbone circuits on one card). Eric _______________________________________________________ Eric D. Madison - Senior Network Engineer - ACSI - Advanced Data Services - ATM/IP Backbone Group 24 Hour NMC/NOC (800)291-7889 Email: [email protected] On Thu, 10 Jul 1997, Peter Kline wrote: > At 04:06 PM 7/10/97 -0400, Stephen Balbach wrote: > > > >Question: On a Cisco with an AIP card, how do you determain what the > > overhead is? We connect to our upstream provider via ATM. > > Again, from experience, a DS3 AIP is "full" when the 5-minute-average > counters are reporting ~34Mpbs (in other words, the counters never went > higher). Performance wasn't terrific, but if you're looking for raw > quantity to compute "efficiency", or what some call goodput, then my crayon > on painted wall calculation is ~34Mbps (observed max) / ~45Mpbs (approx DS3 > raw max) = ~75% "efficiency". Given that networks and data have a > measurable coefficient of friction, I'd say that's the max you could get > under optimal conditions is something less. > > It's not an option with the AIPs, but when we ran switch to switch we could > get another 4 - 5 Mpbs out of a DS3 by turning off PLCP (not an > endorsement, recommendation, or even technically sound, but it worked). > > Another way of looking at this is that we know an ATM PVC over a DS3 using > PLCP is configurable for a maximum of 96000 cells per second. 96000 cells > per second * 48 payload octets per cell * 8 bits per octet = 36864000 bps, > or 36.864 Mbps, not too far from what I observed above. With PLCP turned > off, the maximum PVC config was ~105000 cells per second, yielding ~40.3 Mpbs. > > So AIP to AIP has the downside of all the protocol overhead with no benefit > in a point to point connection. But you're trading off for the convenience > of not having to use a HSSI port to a T3 CSU/DSU with the additional rack > space and power concerns. And if I had to pick one particular device which > I spent the most time fussing with and repairing/replacing, it would be T3 > CSU/DSUs. > > -peter > > > > > >.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:[email protected]] > >> > > 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 ([email protected])| 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 > >> > > >> > > > > >
|