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Subsections
The previous sections have shown drawbacks of the provision of local
newsgroups and provision of Usenet News to areas with limited network
bandwidth. The following sections will give an overview of possible
solution strategies for these drawbacks. Among these solutions we
will present our News Cache and will explain the benefits of this
approach briefly. The News Cache itself will be discussed in the
following chapters in detail.
This demand can be solved by patching all existing news readers.
Unfortunately it is obvious that this is impossible. However, this
would be the cleanest approach, because the client would decide which
server to contact for which newsgroup without requirements for
additional software. A possible solution is to keep a configuration
file for each news server and to reconfigure the news reader for each
session. Figure 3.6 shows a possible workaround for
news readers storing their configuration in ~/.newsrc
. This
workaround works for most Unix and Unix-like systems. Similar
workarounds exist for other news readers and other environments.
Abbildung 3.6:
Workaround to multiplex between different news servers
|
The workaround presented in section 3.4.1
does not work for all news servers and is inconvenient to the user in
several ways. On the one hand if the user wants to read a newsgroup
from another server, he has to terminate the news reader and restart
it. On the other hand the presented workaround reduces the
functionality of some news reader to work on several newsgroups
simultaneously. This functionality will not be available for
newsgroups stored on different news servers.
The News Cache can include the functionality to contact different news
servers for different newsgroups. Whenever a news reader selects a
newsgroup from the News Cache, the News Cache decides which news
server to contact for the given newsgroup. All this will be done
transparently to the news reader. Another advantage of this approach
is that the user needs not to worry about which newsgroups are
provided by which news server.
This problem can only be solved for leaf node news servers without
modifications to NNTP. Since leaf node news servers need not hold the
whole news feed, they can be replaced by a News Cache. The News Cache
retrieves only those articles that are requested by a news client.
Thus the News Cache eliminates the transmission of articles that will
never be accessed by any news client.
To solve this problem in general it is necessary to add some new
commands to NNTP. One command could be a request to transfer the
articles in compressed form. This could reduce the required network
bandwidth by approximately . Another command could request the
transfer of all newly arrived articles smaller than a given size. This
is useful, because it does not pay to negotiate the transmission of
small articles and the transmission of larger articles (e.g. those
found in the binary newsgroups) will be negotiated. An explanation of
the currently used article negotiations can be found in [KL86].
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