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Re: Customer AS

  • From: Vadim Antonov
  • Date: Wed Aug 21 21:06:45 1996

Sean Donelain wrote:

>>PS There is a proof by existance that reliable operation w/o
>>   customer multihoming is possible.  It is called POTS.

>That's funny.  Anyone who needs reliable telephone service
>quickly learns how to multi-home between telephone providers,
>inbound and outbound.

Inbound?  Huh?  Just dial a different number?

>AT&T periodically puts out a press release
>saying their network is so reliable, no one needs to buy service
>from anyone else.

No matter what, POTS is a lot more reliable and dependable than
Internet.  That definitely can be attributed by adequate resources
being spent on the redundancy.

>Anyone who needs reliable electrical service, quickly learns
>how to multi-home between electrical providers.  The street
>mains, a UPS, and generator.  Some people even get a redundant
>connection to another street mains.

Ah, if onle one could store Internet connectivity in a battery.

>Yes, it is complicated to multi-home between providers of
>anything (telphone, electricity, Internet, bagels).

Not at all.  Everything you can store (like bagels) is easy.

>A redundant connection to the same provider might help in a few limited
>circumstances.

In about 98% of all cases of equipment malfunction.

>But generally, when a provider fails on one
>connection, the probility their other connections are working
>drop dramatically.

Ghm.  What makes you think it does not drop nearly as much
for inter-provider multihoming?

>When the electricity fails, using a different
>connection to the same electical provider usually doesn't work
>either.

Or, as recent intertie problems showed, connection to any provider
whatsoever also doesn't work.   If you don't drag wires to the
other coast, that's it.

>That's why people buy UPS's instead of second power supplies.

The person who would invent an "Uninterruptible Network Supply"
is going to be filthy rich.

The question about multihoming is easy -- what is price/benefits?
"Price" includes price for society at large, as well.

--vadim

PS.     An often forgotten fact from the life of fault-tolerant
	systems:

	Practically all systems have threshold where addition
	of extra redundancy actually makes system less reliable!

	That is because the probability of Bysantine-type
	failures (i.e. ones which are not adequately dealt with
	by means of replication, something like cascading power
	failures, or bogus routes) grows with the number of
	components (at least linearly), and the benefits of
	redundancy diminish as negative exponent.

	BTW, Internet is way beyond the threshold if you look at
	it as a system.  Therefore everything which makes the
	network simplier improves its reliablity.
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