Friendliness vs performance


Rex A. Buddenberg (tetra!budden@nosc.mil)
25 Aug 88 00:58:46 GMT


For Dave Crocker.

I would recast the question more in terms of capacity/throughput
traded off against robustness/fault tolerance/survivability. Fair?

Most users tend to underestimate the real fault tolerance needs.
Once a network is put in place, it attracts applications like ants
to a picnic. Before you can spell TCP/IP, the network has become
so critical that it's failure becomes intolerable. I'm familiar
with a few horror stories like one about a bank that lost its
funds transfer net for several hours. The interest charges on the
cash it had to borrow to keep afloat ranged into 8 figures.

I have three very clear requirements where workstations and sensors
on a LAN is clearly the best way to go. In all three cases, network
loading is very modest -- one ridiculously so: in terms of dozens
of bytes per day [!!]. But fault tolerance -- immunity against either
damage or component failure -- is vital to all three.

The curious technological development is that in the LAN world,
this isn't a trade off. The only fault tolerant LAN architecture
out there readily available is doubly linked rings. Discounting
Proteon's proprietary products, this leaves FDDI -- somewhat
higher performance than ether...

Fault tolerance is a lot like paychecks -- most of us rather take
them for granted. They come every couple weeks -- especially for
us folks whose paychecks are provided by the taxpayers. And like
LAN service -- expected to be there when we want to use it. Watch
the fracas when your taken for granted paycheck or LAN fails.
I'd suggest a caveat for a vendor: fault tolerance may not gain
you lots of customers, but lack of it can lose a bunch.

Rex Buddenberg



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