NNTP Client-Server Communication Process: News Posting and Access
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News Access and Article Reading
Newsreaders also establish an NNTP connection to a server to read Usenet articles. NNTP provides a large number of commands to support a variety of different article access and retrieval actions that may be taken by a user. The first step in reading is sometimes to examine the list of available newsgroups. Using the LIST command, the client requests from the server a list of the newsgroups available for reading and posting. RFC 977 defined the basic LIST command, which returns a list of all groups to the client. RFC 2980 defines numerous extensions to the command to allow a client to retrieve only certain types of information about groups on the server. Since the number of Usenet newsgroups is so large today, many times this listing of newsgroups is now skipped unless the user specifically requests it.
The next step in Usenet message access is typically to select a newsgroup to read from the list of groups available. Again, since there are so many groups today, most newsreaders allow a user to search for a group name using a pattern or partial name string. The GROUP command is then sent to the server with the name of the selected group. The server returns the first and last current article numbers for the group to the client.
Messages are identified in two ways, one absolute and the other site-specific. The articles Message ID is a fixed identifier that can be used to uniquely represent it across Usenet; this is what is used in inter-server communication to determine whether or not each site has a copy of a given message. In contrast, article numbers are server-specific; they represent the numbers assigned to those articles as they arrived at that server and are used as a short hand to more easily refer to articles in a newsgroup. Thus, the same message will have a different article number on each NNTP server. They are used for convenience, since an article number is much shorter than a message ID. During a session, the NNTP server also maintains a current article pointer that can be used for stepping sequentially through a newsgroup.
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