Inter-exchange media types

Erik Sherk sherk at
Thu Apr 25 13:45:18 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.

Don't gloss over the MTU issue. Fragmenting packets is a serious
performance hit. Also, DS3 customers want a hssi mtu end-to-end.
> 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.

Compared to the other costs in running an ISP it is just noise...

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

??!! Exchanges with the most traffic are the ones with the new technology
because they have no choice.


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