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connected to a fixed network or at least with better QoS than that offered by
existing networks.
Taking that wish into consideration, different research projects are try-
ing to build mobile systems that overcome the existing limitations [4954].
All the works cited so far in this chapter consider different aspects of mobile
computing by using agent technology. In the same line, we present in [55] a
system based on the use of the client/intercept/server model that incorporates
some modules and agents in the mobile computer as well as in an intermedi-
ary element situated in the fixed network. That element, called a gateway
support node (GSN) (see Figure 10.1), is the intermediary element in the
communication between the mobile computers under its coverage and all
other hosts of the network (mobile or fixed). Its aim is to relieve mobile com-
puters from many tasks and increase their capabilities, while respecting their
natural limitations and taking into consideration the problems of the mobile
computing framework and trying to solve them. The pair formed by the
GSN and the MU allows the MU to behave like a fixed computer for the rest
of the network. The GSN lends its identity to the set of mobile computers
it monitors, so that when the GSN receives messages and data sent to the
mobile computers, it distributes them to the suitable MU.
Concerning the use of agents, in the works cited here, the process con-
sists of creating an agent for each task to be carried out, giving it the data
necessary to access a certain source of information and sending it from the
mobile computer to the network. Once the results have been obtained, the
agent returns to the mobile computer. In our proposal, the underlying phi-
losophy is different. We advocate using a majordomo agent, Alfred, to avoid
the continuous transferences of agents through the wireless link and, there-
fore, the high cost that it represents. Alfred is an efficient majordomo for
mobile computers. Each mobile computer will have its own version of Alfred
with the aim of giving adequate services to its owner. From the implementa-
tion point of view, Alfred is the union of two agents: static Alfred (SAlfred),
a static agent situated in the mobile computer, and mobile Alfred (MAlfred),
a mobile agent situated in the intermediary element. MAlfred is created
in the mobile computer, but it travels to the intermediary element, where it
works on behalf of the mobile user, representing the user in the network,
becoming the common point to all the communications in which the MU is
involved, even when the mobile computer is disconnected. When a task must
be carried out, SAlfred sends a message to MAlfred with the necessary data.
MAlfred then carries out the task or creates a new agent, a specialist (the spe-
cialist mobile agents are situated in the GSN), and orders it to carry out the
