Cross-layer protocol design for real-time multimedia applications over 802.11 b networks
Inherent vulnerability of the wireless medium renders it more susceptible to errors and losses than classical wired media. In this paper, we evaluate the suitability of protocols and strategies across different layers of the stack to provide real-time services over 802.11b wireless LANs. More specifically, within the context of cross-layer design, we compare the performance of UDP with UDP lite - a proposed framework, which improves bandwidth utilization by delivering partially damaged packets to the realtime application. First, we study the high-level end-to-end throughput improvement achieved by making cross-layer modifications to support a UDP lite framework. We compare the quality of perceived media rendered by UDP (dropped packets only) and UDP lite (dropped and corrupted packets). This formulates one of the key findings of this study, that is, although UDP lite improves the overall high-level throughput by relaying corrupted packets to the real-time application, it fails to provide significant enhancement in perceived media quality. This can, in part, be attributed to the bursty nature of errors and losses that we observed at the application layer regardless of the selected transport protocol. Finally, we compare the error-recovery/concealment overhead required by UDP and UDP lite in order to deliver lossless multimedia. We conclude that the overhead required by UDP lite is considerably lower than UDP, since the received corrupted packets that are delivered by UDP lite (but not by UDP) facilitate error-recovery.