Avoiding Useless Packet Transmission for Multimedia over IP Networks: The Case of Multiple Congested Links

In this paper, we investigate UPT avoidance problem with multiple congested links. We propose three different UPTA enforcement schemes — basic UPTA (B-UPTA), Partial UPTA (P-UPTA) and Centralised UPTA (C-UPTA). The challenge of UPT avoidance with multiple congested links is to determine global fairshare and enforce UPTA based on the global fairshare. We proposed the Bottleneck Fairshare Discovery (BFD) protocol to address this issue. BFD is a feedback mechanism proposed to assist UPTA in networks with multiple congested links. We describe the implementation of BFD with UPTA, taking WFQ as an example. Our simulation study shows that B-UPTA fails to detect UPT in some situations. P-UPTA can eventually detect UPT, but bandwidth may have been wasted on upstream links before UPT is detected. C-UPTA can avoid UPT in all situations, as it always drops useless packets at network edge. Simulation results suggest that, with C-UPTA, the achieved TCP throughput improvement is very close to the maximum theoretical value. In the paper, we also analyse the performance of C-UPTA quantitatively, in terms of TCP throughput, file download time, impact on video intelligibility, and impact on fairness. Our simulation results reveal that, for all six scenarios, the TCP throughput has been significantly improved (with improvement factor up to 50%). As a result, file download times (for various file size) have been greatly reduced (more than 30%). On the other hand, incorporation of C-UPTA into WFQ has no significant impact on intelligibility of the MPEG-2 video (with a difference less than 3%). For all six scenarios, CUPTA maintains fairness which is comparable to WFQ. This proves that UPTA does not have any adverse impact on fairness performance of fair algorithms.