Re: network horror stories


Phil R. Karn (karn@flash.bellcore.com)
Tue, 24 Mar 87 13:52:10 est


Anyone who believes that connection-oriented networks are inherently immune
to congestion should consider one of the following events:

1. The US phone network on the night of the Carter-Reagan debates in 1980.
AT&T conducted their first large-scale trial of their 900 DIAL-IT service
which was used to poll viewers on their opinions regarding the debate. Although
AT&T placed strict limits on the number of long distance trunks that could be
used for 900 service, there were so many people attempting to call it that in
most places in the country there were delays of at least 2 minutes in getting
dial tone from the local office.

2. The phone system in the state of Arizona the day the Tucson Amateur Packet
Radio group decided to take phone orders (one day only!) for their new packet
radio controller box. They only had one phone line. Not only was Tucson
cut off from the rest of the world for several hours, but most of the rest of
the state as well.

3. The ticket-buying frenzy accompanying any Bruce Springsteen concert.

The problem isn't connectionless vs connection-oriented, it's that the network
is a shared resource. If there aren't enough facilities to go around in times
of peak demand, some people are going to be denied service. The only difference
is in the details of how that's done. The real issue when trying to assure
network stability is how the users react to being denied service. If they
use Demon Dialers to hammer away at the phone network, you're going to have
trouble. The Internet is in trouble because there are so many broken TCPs
out there that do the equivalent thing when the network load picks up.
I wouldn't be surprised if a few nodes could bring down an X.25 network
pretty easily by just pummeling it with CALL REQUEST packets to unreachable
addresses.

The solution is more likely economic than technical. Since failed attempts
still use network resources, one answer is to charge for them. I suspect
charging for failed phone calls would put a stop to the abuse of demon dialers.
Since the Internet doesn't charge for each packet, the solution here would
be to require certification of a host's TCP retransmission behavior before
it attached to the network in the same way that a radio transmitter has to
be type certified before it can be placed in operation.

Phil



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