Control mechanisms for mobile terminals in heterogeneous access technology environments

摘要

Internet is evolving to become mobile and ubiquitous. As a consequence, there is a trend towards a diversification of the access technologies, as it can be seen with the recent appearance of wireless technologies such as WiFi or UMTS and the future deployment of WiMAX. Following these new opportunities, multi-technology terminals able to connect to the Internet through different technologies are appearing in the market. In this scenario, users start to demand new solutions able to use these new technologies in a transparent way from the user point of view. Foreseeing this demand, the IEEE started developing the specification IEEE 802.21, which enables multi-technology terminals to handover from one technology to another in a transparent way for the user. This specification has not yet being finished, and its deployment requires from the research community to analyze how to integrate it in current networks, how to achieve maximum benefit from its possibilities, and how to configure its parameters. In this thesis we propose control mechanisms for IP terminals to i) support efficient handovers in multi-technology environments applying the 802.21 framework and ii) allow the use of several interfaces and/or multiple providers by the terminals to improve the failure robustness of their communications. These mechanisms are focused in the terminal, although we also provide details on how to integrate IEEE 802.21 into nowadays operator's networks. The contributions of this thesis are threefold. In the first place the integration of 802.21 into terminals has been studied, focusing on the configuration of the parameters required to decide when to perform a handover in the case when the handover is initiated by the terminal. This analysis has also been done taking into account variables such as the terminal speed and the delay of the links. In the second place, we have studied how to introduce the Network Controlled Handover concept, using 802.21, into the network, including the possibility of the handover being initiated by the network. We have analyzed which are the main benefits of this approach and proposed and validated an implementation of this concept in 802.21. In third place we have analyzed a protocol, REAP, under development in the IETF, which allows terminals to detect and recover from failures in the links used in their communications. We have focused in the analytical characterization of the time required to detect a failure, since this parameter is crucial for the application's behavior. The applications should be able to cope with a failure without being disrupted by it. Through the analytical study performed, the REAP protocol can be properly configured to achieve a target recovery time. All the proposed mechanisms have been validated through simulation, using several tools such as OPNET, OMNET++ and Matlab