ATM vs. DS3

Chris A. Icide chris at
Wed Jul 10 03:38:57 UTC 1996

On Wednesday, July 09, 1997 9:34 PM, Josh Beck [SMTP:jbeck at] 
> 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.

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