Avoiding useless packet transmission for multimedia over IP networks: the case of multiple multimedia flows

摘要

When routers continue to transmit packets of a multimedia flow while inflicting a packet loss rate beyond a given threshold, they effectively transmit useless packets. Algorithms to avoid Useless Packet Transmission (UPT) over single and multiple congested links have been analysed previously in the context of a single multimedia flow sharing network links with TCP flows [Computer Communications, accepted for publication; Technical Report UNSW-CSE-TR-0215, 2002]. The main philosophy behind these algorithms is to drop all packets from a multimedia flow whenever the flow experiences a packet loss rate beyond the tolerable threshold. In this paper, we investigate UPT in the context of multiple multimedia flows. We find that previously proposed UPT avoidance algorithms lead to poor link utilisation, as they take action on each and every multimedia flow. We propose two different enhancements, RandomSelect (RS) and Least Bandwidth Select (LBS), to selectively take action on multimedia flows. Using computer simulations of MPEG-2 video, we evaluate the effectiveness of both RS and LBS under various network scenarios (e.g. single/multiple congested links, homogeneous/heterogeneous video applications, etc.). Results show that RS and LBS have similar performance with homogeneous multimedia applications. However, with heterogeneous multimedia applications, LBS yields better performance, in terms of number of video flows affected and overall intelligibility of video applications.