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Abstract:
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This project was born to cover a specific aspect of the wireless networks related to the
service delivery considering a generic taxonomy where different agents can exhibit a
heterogeneous offer of services and, at the same time, clients may be interested in different
activities at the same time. In this scope, the need of a common way of interaction between
clients and servers can be perceived to overcome the probable lack of generality in this whole
picture.
Two main objectives where defined and prosecuted in order to plant the first stone in
the definition of a protocol to support a fair, transparent and effective service selection in
wireless scenarios. First, the determination of a generic way of characterizing the different
services therefore deriving to a template based descriptive object. Second, the implementation
of a mechanism capable of using this format of description in order to inform the client about
the best option to chose at any given moment.
Following the first general objective, a series of analytical studies in terms of the
parameters that could be used to describe a service where performed using as test examples
Printing, Image Recognition and File Sharing services. The major efforts were done in the
appliance of three discriminative patterns regarding how general or specific, static or variant
and the type of limitation (maximum or minimum) each parameter is. The principle
conclusions of these studies were the following. First, an important group of parameters were
common to the different services under study. Second, the existence of a trade-off between the
precision of the characterization (via more contextual parameters) and the homogenization of
the descriptive set of parameters. Finally, each parameter could be expressed using the pair
formed by the offered and demanded values.
In the second place, a local agent supported by the PeerHood middleware designed to
run on the client’s machine was defined and implemented in C++. This agent, known as 3WAServer,
is intended to act as an active environmental monitor to assist the client’s applications
in the service selection process. The bases of this assistance rely on the definition of a profile
describing mainly the client’s requirements and a template containing the server’s offer. Using
that information, the 3WA-Server is able to rate each particular service to provide each
application with a numerical and normalized value between 0 and 1 where 0.5 or higher
means complete fulfillment of the requirements. Based on these grades, the application is in
position of performing a solid decision concerning the next server provider to select. The
assignation of the grade to each service relies on three layer neural network balanced with a
set of weights specified by the application according to its particular requirements. The
network is fed with the profile and the template associated to the application acting as a client
and the service provided by a particular server respectively.
An experiment was set and executed in order to get a first and introductory
estimation of the validity of the 3WA-Server as a service selection assistant. The experiment
consisted in the deployment of two servers offering the same two services and a client moving
from one to the other. This client was running local services as well. The results of the
experiment pointed out that, first, the delays associated to the transmission of the parameters
describing the service offered by the server were more than tolerable. Secondly, the
management and execution of the neural network were proven to be effective and low resource
demanding. Finally, the grading system and the proactive interaction between the local
applications and the 3WA-Server suggested an expected behavior in terms of proper event
generation and result notification. Nonetheless, this approach stands for a very first
simulation, hence, further study and exhaustive revision are to be done. |
