"Feature Interaction Detection in a Telephony Network Integrated
 with Switch-based Features and IN Features"

Jennifer Qifang Fu's M.Sc. Thesis

University of Ottawa
2000

Abstract

Telephony systems have evolved from the Plain Old Telephony System providing
only the basic functionality of making phone calls, to sophisticated systems
in which many features have been introduced, providing network subscribers
more control on the call establishment process. The concept of Intelligent
Network was developed to facilitate and accelerate the introduction of new
features in a cost-effective manner. However, this objective confronts a major
obstacle known as the  feature interaction  problem. A feature interaction
occurs when at least one feature is prevented from performing its functionality
or when the system functions incorrectly due to the presence of features.

In the first part of the thesis, we present a model for specifying a telephony
network integrated with both switch-based features and IN features using a
mixture of resource-oriented style and state-oriented style as well as a
specially organized Abstract Data Type hierarchy. The model is designed in a way
that independent specification and rapid introduction of features is provided.

In the second part of the thesis, we present an improved formal definition of
the concept of Feature Interaction and a Feature Interaction Detection System.
The system is limited to interactions caused by violation of features or system
properties. Feature Interaction between the given features can be detected and
presented in the format of Message Sequence Charts via five steps:  Test
Scenario Designer, Integrator, Feature Interaction Hunter, Property Checker
and Message Sequence Charts Translator.

It is concluded that LOTOS is useful as a Formal Description Technique in
specifying the telephony system with features and for detecting feature
interactions at the abstract specification level.