Inter-exchange media types

Curtis Villamizar curtis at
Thu Apr 25 16:34:25 UTC 1996

In message <199604250621.BAA09394 at>, Jeremy Porter writes:
> 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.

For many products, there is a big difference between how many
interfaces physically fit in the card cage and how many actually work
under a fairly heavy load.  Have you tested a 12 port switched 100
Mb/s ethernet under load?  The DEC gigaswitch has been tested under
load and has held up so far under load.  The Cisco 5000 may bridge
better than it routes since there is no route change to deal with, but
I'd be a bit worried about deploying without stress testing.

The problem for the major exchanges may soon be what to do when the
gigaswitch runs out of bandwidth.


> >Folks,
> >
> >  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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