IP over ATM overhead

Eric D. Madison madison at queber.acsi.net
Thu Mar 13 15:31:46 UTC 1997

Well Stephen,
   Here at ACSI, our entire national backbone is ATM, the overhead so far
seems to be about 12-14%.  This is taking into account the 48/53 byte
percentage and the time to reassemble the cells into packets at the remote
end.  I have run tests in our lab and we can totally saturate a DS3 and an
OC-3 link via ATM.  This is in contrast to a clear channel DS-3 which
itself loses some bandwidth to conversions and overhead.  I would guess
that the difference of DS-3 ATM and clear channel is around 9% of your
bandwidth but I need to run more tests in the lab to make a more educated
guess.  But you don't run an ATM backbone if your just offering IP
service,  we use it to offer Frame/ATM/IP services all over the same
wire. Now, packet of sonet seems the way to go for high speed IP with
little overhead, but it is only available at 0C-3 and higher.  I have not
tested it yet to see the overhead or how good it works.  

Anyone out there really tested the POS cards from Cisco yet?


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

On Thu, 13 Mar 1997, Stephen Balbach wrote:

> We are installing an ATM backbone connection and wondering what level 
> of overhead can be expected. Ive read from %10 to %50 - this will be a 
> LAN connection so we can assume almost no cell loss. Our provider has 
> said on average %12 bandwidth is overhead. It will be a Cisco->Cisco LAN 
> configuration. Thanks!
> Stephen Balbach
> VP ClarkNet

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