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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Key Applications and Application Protocols            9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)                 9  Usenet (Network News) and the TCP/IP Network News Transfer Protocol (NNTP)                      9  TCP/IP Network News Transfer Protocol (NNTP)

NNTP Overview and General Operation 1 2 3 4 NNTP Client-Server Communication Process: News Posting and Access

Basic NNTP Propagation Methods

Now let's look at how messages are actually propagated between servers using NNTP. There are two techniques by which this can be done:

• “Pushing” News: In the push model, as soon as a server receives a new message, it immediately tells its upstream and downstream neighbors about the message and asks them if they want a copy of it.
  
  
• “Pulling” News: In the pull model, servers do not offer new articles to their neighbors. The neighboring servers must ask for a list of new messages if they want to see what has arrived since the last connection was established, and then request that the new messages be sent to them.

There are advantages and disadvantages to both of these techniques, but pushing is the model most commonly used today.

NNTP Overview and General Operation 1 2 3 4 NNTP Client-Server Communication Process: News Posting and Access