The Loss-Delay Based Adjustment Algorithm: A TCP-Friendly Adaptation Scheme

Many distributed multimedia applications have the ability to adapt to fluctuations in the network conditions. By adjusting temporal and spatial quality to available bandwidth, or manipulating the playout time of continuous media in response to variations in delay, multimedia flows can keep an acceptable QoS level at the end systems. In this paper, we present a new scheme called the loss-delay based adjustment algorithm (LDA) for adapting the transmission rate of multimedia applications to the congestion level of the network. The LDA algorithm was designed to reduce losses and improve utilization in a TCP-friendly way that avoids starving competing TCP connections. It relies on the end-toend Real Time Transport Protocol (RTP) for feedback information. In addition, we enhanced RTP with functionalities for determining the bottleneck bandwidth of a connection. The bottleneck bandwidth is then used for dynamically determining the adaptation parameters. Simulations and measurements of the LDA algorithm suggest the efficiency of the scheme in utilizing network resources, decreasing loss ratios and its fairness towards competing TCP traffic. Our investigations also suggest that the report intervals and feedback information of RTP require some enhancements to accommodate the needs of adaptive QoS control schemes.