Abstract

Multimedia applications for networks with wireless links are required to constantly adapt their operations to the changing QoS. In this paper we investigate the effectiveness of a simple adaptive application layer for multimedia streaming over multi-hop ad-hoc networks. Simulations with our hybrid simulation platform are presented that reveal issues involved in end-to-end adaptation over ad-hoc network configurations. Different MAC layers are studied, the standardized 802.11 (DCF) and CSMA, in order to evaluate how these affect the application layer adaptation. Mobility and routing are also applied. We test each of these configurations in 100 randomly generated topologies by gradually introducing adaptive audio connections in place of non-adaptive. We look at results per configuration, per experiment, and per connection, measuring server consumed bandwidth, effective bandwidth, and loss rates. By using the coefficient of variation we report on fairness issues associated with the end-to-end adaptation. Significant improvement is shown when introducing adaptation in all configurations both in loss rates and effective bandwidth. We find that the distribution of server rates is fair in 802.11, especially so, in presence of node mobility. Fairness in effective bandwidth distribution among the connections is significantly increased as adaptivity is introduced. By looking at a connection level we find that when a timeout mechanism exists in the adaptation mechanism, the end-to-end feedback can deliver a consistent view of the RTP loss rates at the server at low mobility and low hop count, even at presence of high competing traffic. The highly oscillatory nature of the loss rates remains for adaptive connections. We argue that a redundant speech captioning scheme is necessary i...

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