Usenet News is a popular and easy way for world-wide discussion on the Internet. Newsgroups being dedicated to various topics are its basic building blocks. Users can offer information through articles (also called postings), and read other users' articles.
In order to access News a frontend program called news reader (or news client ) is needed. A news reader connects to a news server, requests the list of newsgroups and presents this list to the user. When the user selects a newsgroup, the news reader requests the list of articles available in that group and presents a summary of the articles to the user. From this list the user can choose the articles he wants to read. The news reader will remember articles read by the user and will not present these articles in the next session in this group (though still available). Other functions, like grouping related articles (threading), replying to articles or sending email to the author of an article are provided too.
The Usenet is composed of several news servers that store the available newsgroups and articles. Whenever an article is posted to a newsgroup on a news server, the article will be propagated to all other news servers storing the same newsgroup. This means that the article will be copied to all other news servers.
On the Internet articles are usually distributed by the ``Network News Transport Protocol'' and in some cases still using ``Unix to Unix CoPy'' (UUCP). The distribution of articles is done by best afford, but is not guaranteed. This means that an article needs not be transferred to the other news servers immediately and that a news server does not necessarily receive all existing news articles.
Since the Usenet has been growing rapidly over the last years and still continues to grow, its network bandwidth requirements for newsgroup and article distribution increase. Hence, the News system will reach its limits within the next years and new mechanisms have to be found to overcome this situation. Additionally these mechanisms might even give better access to the news system for people who are connected over lower bandwidth networks, because these mechanisms reduce bandwidth while maintaining the same quality of service.
In chapter 2 we will present the terminology used throughout this document. A short overview of basic technologies like caching and the operational principles of the Usenet News system will also be given.
In chapter 3 we will explain the problems inherent in the currently used News system. These problems include a high load on the news server in some settings and the increased network bandwidth requirements for the transmission of news. At the end of this chapter we will give an overview of possible solution strategies to reduce or even eliminate the existing problems.
In chapter 4 we will analyze the News Cache in general. We will analyze which areas can benefit from the News Cache and the News Cache's requirements. Special care has been taken that the News Cache can be integrated into existing environments without need for modifications.
The architecture and design of the News Cache will be shown in chapter 5. In the first section we will present the general design of a news server being the basic design for the News Cache.
A brief overview and an explanation of the interaction between different modules will be given in chapter 6. The exact implementation details are documented within the News Cache's source code.
In chapter 8 we will show work that will be included in future releases of the News Cache. This includes the improvement of the existing classes and the addition of new features.
In chapter 9 we will present related work that has been done in this area and in chapter 10 we will give a summary of this thesis.