Usenet Communication Model: Message Composition, Posting, Storage, Propagation and Access
(Page 3 of 3)
Message Propagation and Server Organization
Propagation is definitely the most complex part of the Usenet communication process. In the olden dayse, UUCP was used for propagation; each Usenet server would be programmed to regularly dial up another server and give it all new articles it had received since the last connection. Articles would flood across Usenet from one server to another. This was time-consuming and inefficient, however, and only worked because the volume of articles was relatively small.
In modern Usenet, the Network News Transfer Protocol (NNTP) is used for all stages of transporting messages between devices. Articles are posted using an NNTP connection between a client machine and a local server, which then uses the same protocol to propagate the articles to other adjacent NNTP servers. NNTP is also used by client newsreader software to retrieve messages from a server.
NNTP servers are usually arranged in a hierarchy of sorts, with the largest and fastest servers providing service to smaller servers downstream from them. Depending on how the connections are arranged, an NNTP server may either establish a connection to immediately send a newly-posted article to an upstream server for distribution to the rest of Usenet, or the server may passively wait for a connection from the upstream server to ask if there are any new articles to be sent. With the speed of the modern Internet, it typically takes only a few minutes or even seconds for articles to propagate from one server to another, even across continents.
It is also possible to restrict the propagation of a Usenet message, a technique often used for discussions that are only of relevance in certain regions or on certain systems. Discussing rural issues such as horses is of general interest, and Ellen might well find her help anywhere around the world, so global propagation of her message makes sense. However, if Ellen lived in the Boston area and was interested in knowing the location of a good local steak-house, posting a query to ne.food (New England food discussions) with only local distribution would make more sense. There are also companies that use Usenet to provide in-house newsgroups that are not propagated off the local server at all. Note, however, that because so many news providers are now national or international, limiting the distribution of messages has largely fallen out of practice.
This is, of course, only a simplified look at Usenet communication. The section on NNTP provides more details, especially on how articles are handled and propagated.
Home - Table Of Contents - Contact Us
The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.