Inter-exchange media types

Jeremy Porter jerry at
Thu Apr 25 06:21:34 UTC 1996

I know of plans for at least 2 exchanges that will use 100baseTx
as a connection option.  The only real problem is
the backplane limit of boxes that switch 100baseTX,
(Cisco Cat 5000, 1.2gbps).  This is only slightly
better than the Dec Gigaswitch limit of 800mbps.

Certainly the hardware to do switched ethernet is much cheaper
than FDDI, and with full duplex 100mbps there is very little
advantage to FDDI.  (FDDI does do full duplex now, but I don't
know who offers interfaces that support this.)  FDDI
does offer larger frame sizes, assuming you have FDDI each
end with no "MTU 1500"'s in between.

To me it seems like a big cost win to drop in a C5000
with 4 slots at 24 switched ethernet/slot, or 12 switched fast 
ethernet/slot.  Particularlly since the router interfaces are
about 1/2 to 1/4 as much.

The exchanges with the most traffic are the ones
based on the oldest technology, because there are always bugs.

>  I know that many of the Inter-exchange points are using FDDI and
>  switched FDDI for inter-exchange in lieu (or anticipation) of ATM.
>  I am wondering if anyone has considered using switched 100baseFx or
>  similar technology for an inter-exchange.  Given the relative
>  newness of these interfaces on high-end routers I would not be
>  suprised to hear that no one is using them right now.  But has
>  anyone looked into using them?  Is there a good reason to prefer
>  switched FDDI over 100baseFx (which can do full-duplex 100 Mb/s
>  switched)? 
>  <tex at>

Jeremy Porter, Freeside Communications, Inc.      jerry at
PO BOX 80315 Austin, Tx 78708  |  1-800-968-8750  |  512-339-6094

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