value of co-location

Jim Forster forster at
Fri Jan 19 19:17:31 UTC 1996

> > I'm also curious about the value of co-location.  Using a fast packet
> > service (Frame Relay, SMDS, or ATM) allows your on-site router to
> > communicate directly with a router of another ISP.  There's no need to
> > purchase another router to place at the co-location site.  Why incur the
> > additional cost?
> To avoid having to use any of the fast packet services you mentioned?
> Or to allow you to use routers, which you know about, instead of being
> dependent on the random characteristics of switches the telephone
> company bought?
> Not using either of the last two fast packet services, in particular, will
> also yield 30% more useful bandwidth from a T3 circuit.  This all by itself
> may make up for the co-location costs and the cost of a router.

Actually, the overhead for IP over SMDS is more like 40%, if I remember
correctly, because of all the headers (8 byte SNAP, 32 byte SMDS) on top of
the ATM cell tax (5 out of 53 on cell headers, average 1/2 a cell wasted at
the end of the packet which occurs about ever 5 or 6 cells), figured on the
observed Internet average packet size of ~220 bytes a couple years ago.
What's the average packet size now?  I think the overhead on DS-3 ATM/SMDS
is worse than on OC-3, if I recall correctly, because the DS-3 PLCP is so
wasteful as well.  Someone should redo these calculations more accurately.

So, if the fast packet based access to NAPs is priced at ~40% less, *and*
the ATM switches perform as well as the FDDI switches, then it is a don't

  -- Jim

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