Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!novavax!twwells!bill
From: bill@twwells.com (T. William Wells)
Newsgroups: news.newusers.questions
Subject: Flood algorithm (was Re: Usenet is not a BBS (was Re: (VERY) Long dead subjects)
Message-ID: <1989Sep14.205525.340@twwells.com>
Date: 14 Sep 89 20:55:25 GMT
Organization: None, Ft. Lauderdale, FL
Lines: 50

In article <8839@batcomputer.tn.cornell.edu> eacj@tcgould.tn.cornell.edu (Julian Vrieslander) writes:
: What is the "flood algorithm?"

Basically what happens is that each time a site receives a message,
it first checks to see if it has seen that message before. If it has,
it throws the message away. If not, it sends the message to every
site it transmits news to (usually, and except to the site it received
it from if it wasn't a local message).

:                              But I am really interested in what happens
: when the system saturates.

The system itself can't really saturate. Individual parts of the
system might saturate: a very low speed line might not be able to
transmit a full day's newsfeed, a site might run out of disk space,
etc.

You'd only get "system saturation" if a significant number of the most
important sites were to saturate. In that case, the net would
effectively split into pieces. The exact splitting would be very
complex. When something happens to impede news flow, most sites try
to do something to at least get the news sent later. And the net is
highly redundant; it is very likely that even if several of the major
sites were to disappear, there would only be local outages. So, all
in all, "system saturation" isn't very likely. In the unlikely event
of "system saturation", there'd be plenty of warning and, no doubt,
steps would be taken to prevent it.

It is also worth noting that much news goes through uunet which,
since it charges for its service (though it is non-profit), can afford
to expand with the volume. This vastly decreases the already tiny
likelyhood of saturation.

:                             Does this account for situations where I have
: missed seeing messages that other netters are commenting on?

No. There are many reasons why you might not have seen the message.
Here are some:

	Hardware failures.
	Communication failures.
	Software failures.
	Running out of disk space.

And finally, you might not have seen the original message simply
because it was posted to a newsgroup you don't get or don't read.

---
Bill                    { uunet | novavax | ankh | sunvice } !twwells!bill
bill@twwells.com