The transmission of Usenet news is entirely cooperative. Feeds are
generally provided out of good will and the desire to distribute news
everywhere. There are places which provide feeds for a fee (e.g.
UUNET), but for the large part no exchange of money is involved.
There are two major transport methods, UUCP and NNTP. The first is
mainly modem-based and involves the normal charges for telephone
calls. The second, NNTP, is the primary method for distributing news
over the Internet.
With UUCP, news is stored in batches on a site until the
neighbor calls to receive the articles, or the feed site happens to
call. A list of groups which the neighbor wishes to receive is
maintained on the feed site. The Cnews system compresses its batches,
which can dramatically reduce the transmission time necessary for a
relatively heavy newsfeed.
NNTP, on the other hand, offers a little more latitude with how news
is sent. The traditional store-and-forward method is, of course,
available. Given the "real-time" nature of the Internet, though,
other methods have been devised. Programs now keep constant
connections with their news neighbors, sending news nearly
instantaneously, and can handle dozens of simultaneous feeds, both
incoming and outgoing.
The transmission of a Usenet article is centered around the unique
Message-ID: header. When an NNTP site offers an article to a
neighbor, it says it has that specific Message ID. If the neighbor
finds it hasn't received the article yet, it tells the feed to send it
through; this is repeated for each and every article that's waiting
for the neighbor. Using unique IDs helps prevent a system from
receiving five copies of an article from each of its five news
neighbors, for example.
Further information on how Usenet works with relation to the various
transports is available in the documentation for the Cnews and NNTP
packages, as well as in RFC-1036, the Standard for Interchange of
USENET Messages and RFC-977, Network News Transfer Protocol: A
Proposed Standard for the Stream-Based Transmission of News. The
RFCs do tend to be rather dry reading, particularly to the new user.