In this thesis, we are concerned with the improvement of LADIS's access latency since they are victims of their success and as a consequence currently offer poor response times to users. After a thorough study of the access patterns over LADISs, we show that our objective can be reached by using a method for the dynamic distribution and replication of information at the level of the communication network, also known as caching method. A cache saves, in a local space, the information requested by its users. By intercepting the user's requests and by providing the corresponding information (if this one is present in the local space), the cache decreases the LADIS's response time, reduces the use of the network, and decrease the on-line services load. Unfortunately, cache effectiveness is quite restricted when using existing caching strategy.
To improve caching effectiveness, our proposals consists in: (i) virtually
increasing the cache size so as to enable storing more information, (ii)
refining the cache replacement algorithm so as to keep in the cache the
pieces of information that are the most frequently requested, and (iii)
virtually increasing the number of cache clients so as to increase the
number of user profiles and hence the probabilities of common profiles.
Virtually increasing the cache size is achieved through the LRU-QOS algorithm,
which lies in degrading the information stored in the cache. Refinement
of the cache's replacement algorithm leads us to introduce the LRU-QOS
algorithm, which accurately determines the pieces of information that have
the strongest probability to be re-accessed among the information stored
in the cache. Better replacement decisions are obtained by taking into
account the access frequencies to the pieces of information as delivered
by the on-line services from which they originate. Finally, we increase
the number of clients of a cache by building a cooperation system over
a set of caches. The main difficulty lies in proposing an extensible
protocol of cooperation, since the benefit of this approach is reached
only for a very large number of cooperating caches. The resulting protocol
is named SCOOPS and consists in a fair distribution of the state of the
cooperating cache system. Our overall solution is named SCOOPS++ and integrates
the three aforementioned cache management techniques. Compared to alternative
solutions, it is shown through experiment that SCOOPS++ decreases the LADIS's
response time of about 30% for users.