MCI [ATM overhead]

Kent W. England kwe at
Fri Mar 22 23:20:41 UTC 1996

At 03:09 PM 3/21/96 +0800, Vadim Antonov wrote:
>  ... (as ATM does not handle
>levels of overcommitment found in IP backbones now).

I think that statement, as I interpret it, could only apply
if you are running IP over a rate-controlled ATM backbone (either
CBR or VBR QoS). Nobody in their right mind does that if they
have an alternative.

ATM responds to "overcommitment", if you mean "excess offered
load", by shedding that load either in the middle of the backbone 
at the bottleneck if you are running IP over UBR or at the edge of 
the network if you are running a proprietary ABR.

IP routers respond to excess offered load by shedding that load in
the middle of the backbone, since IP router QoS is essentially the
same as ATM UBR.

In this sense, with ATM you have two choices for handling overcommit-
ment (if your ATM switch vendor has a proprietary ABR) but with
routers you have only one.


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