Push-to-talk (PTT) is one class of voice communication system generally employed in cellular phone services. Today's PTT services mainly rely on infrastructure and require stable end-to-end path for successful communication. But users with PTT enabled mobile devices may travel in challenged environments where infrastructure is not available or end-to-end path is highly unreliable. In such cases those PTT services may exhibit poor performance or may even fail completely. Even though some existing PTT solutions allow users to communicate in an ad-hoc fashion, they need sufficient node density to establish end-to-end path and eventually fail to communicate in sparse mobile ad-hoc environments. Delay-Tolerant Networking (DTN) is an emerging research area that addresses the communication requirements specfic to challenged networks.
In this thesis we develop a voice communication system (DT-Talkie) which enables both individual and group users to communicate over infrastructure-less and challenged networks in the walkie-talkie fashion. The DTN concept of asynchronous message forwarding is applied to the DT-Talkie in order to transmit voice messages reliably. We employ variable-length fragmentation mechanism in the application layer with the vision to speed-up session interactivity in stable scenarios. Some approaches to resolve codec interoperability issues are implied in this thesis.
To validate the concepts of the DT-Talkie, we implement an application for Maemo based Nokia Internet Tablets, leveraging the DTN reference implementation developed in the DTN Research Group. Moreover in this thesis we evaluate the performance of the DT-Talkie through conducting a set of simulations using several DTN routing protocols and using different mobility models
