Adaptive multimedia in wireless IP networks.

摘要

Support for video and audio applications is important to single and multi hop wireless networks whether they are used as extensions to the Internet or not. Due to the variability of response of the air medium and the mobility support that is expected of these networks, it is accepted that such applications must dynamically adapt to network conditions, taking advantage of the different content representations achieved by advances in coding. This adaptability targets at maximizing the overall QoS delivered by the network and may be classified into (i) The transport functionality that decides the network parameters e.g. sending rate and (ii) The presentation functionality that decides the content that should fit the network parameters. In wireless, it is particularly difficult to implement an accurate monitoring process (measurement) and embed it into a distributed strategy that efficiently controls the scarce network resources. Therefore, transport protocols designed for wired networks fail. This, combined with scalability challenges of some ad hoc environments (e.g. battlefield) motivates the exploration of an important trade-off for this environment. On the one hand, adopting a thin and scalable network architecture allows for end-to-end adaptation which is limited in measurement accuracy and consequently performance. On the other hand, the implementation of lower layer feedback support leads to architectures that are less scalable and bear a higher deployment cost. But, can deal effectively with the measurement inaccuracy problem. In order to explore this trade-off, we study, develop and improve existing end-to-end as well as network feedback strategies in terms of the overall QoS delivered to the network users. We trade-off the end-to-end techniques versus the network feedback techniques and provide a performance gain model that can guide the design of real time applications as well as the design of the networks to support them.