Re: VCC cost models .... (was Re: Limits on SVCCs)

Joel Halpern <jhalpern@us.newbridge.com> Thu, 02 May 1996 13:47 UTC

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From: Joel Halpern <jhalpern@us.newbridge.com>
Message-Id: <9605021330.AA09514@lobster.newbridge>
To: gray@ctron.com, gja@bellcore.com
Subject: Re: VCC cost models .... (was Re: Limits on SVCCs)
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The recent discussion has been suggesting that a cut-through would
"cost more" than a routed path across an NBMA fabric.

Maybe I am looking at this differently, but it seems to me definitional
that a cut-through costs the same or less in real terms.

In the non-cut-through case, the packet enters the NBMA, and is passed
over the NBMA, stopping to be handled and processed by several routers
along the way.  In the cut-through case, it enters the NBMA, is passed
at a "lower" level of proocessing across the NBMA, and exits and the
ssame place it would have.

One can argue about whether the switches or routers are cheaper, or
whatever.  But the packet is still entering and exiting the NBMA at the
same point.  There certainly may be charging differentials, but I do
not see what it is a given that a long-distance low level VC would cost
more than a routed path.  There are many possible charging models for
IP service, and many possible charging models for lower layer service.
If the pair are inconsistent, then sometimes cut-throughs will be a
bigger win than they should, and sometimes they will be a big loser.
Most of the time, I would expect the cut-through to be a small winner
in terms of real resource consumption, but that is open to argumentation.

Yours,
Joel M. Halpern				jhalpern@newbridge.com
Newbridge Networks Inc.