An Enriched Finite State Machine Model-based Formalism for Layer-5 Internet Protocols Modelling – An Investigation on Protocol Performance

Internet level-5 protocols are defined by the Internet Engineering Task Force (IETF). Some of these specifications were developed long before the need for mobile support. As a consequence they are extremely solid but not flexible enough when used in the desktop environment and fail to deliver when ported onto mobile handsets. In this thesis I investigate the level-5 protocols in particular, in order to analyze, understand better and enhance their performance. First we take a look at Mobile Services and Mobile Networks. I study how Packet Data services are handled and how a communication protocol can affect their behaviour and performance. Then I discuss the Internet Level-5 protocols and focus on their main characteristics. Finally I develop a model for Protocol Performance Measurements. The model addresses the level-5 protocols but it can also be used for lower layers as well. Ultimately I used the model in order to analyze one of the most important use cases on IETF’s agenda – Presence. This was done by conducting observations in the real, mobile environment, upon the developed model’s application. I showed how this model can be used in order to measure the Session Initiation Protocol for Instant Messaging and Presence Leveraging Extensions (SIMPLE) protocol suite performance. In the thesis it is also shown how the same model can be used in order to prove the benefits of a new IETF proposal. The theoretical concepts utilized in this thesis belong to the classical knowledge of computation science. The basic automaton, the Finite State Machine, was semantically extended and used to model the dynamic behaviour of communication protocols. Furthermore, its enhanced version, the Finite State Protocol (FSP), provides metrics that can be used as indicators for the system’s dynamic/evolutionary behaviour and for the communication protocols’ performance. This thesis work has been based on ISO definitions on quality concepts, and it, in particular, creates new knowledge by associating protocols’ effectiveness with design quality, and by proving that other quality attributes - such as reliability and resilience – can be formally enhanced. This can start from the very early stages of the mobile software development as preventive maintenance principles indicate. Key words and terms: Finite State Machine (FSM), Communication Protocol, International Organization for Standardization (ISO), Quality Standards, Performance, Mobile Technology, Metris (and Measurement