A Framework for Controlling Quality of Sessions in Multimedia Systems

Collaborative multimedia systems demand overall session quality control beyond the level of quality of service (QoS) pertaining to individual connections in isolation of others. At every instant in time, the quality of the session depends on the actual QoS offered by the system to each of the application streams, as well as on the relative priorities of these streams according to the application semantics. We introduce a framework for achieving QoSess control and address the architectural issues involved in designing a QoSess control laver that realizes the proposed framework. In addition, we detail our contributions for two main components of the QoSess control layer. The first component is a scalable and robust feedback protocol, which allows for determining the worst case state among a group of receivers of a stream. This mechanism is used for controlling the transmission rates of multimedia sources in both cases of layered and single-rate multicast streams. The second component is a set of inter-stream adaptation algorithms that dynamically control the bandwidth shares of the streams belonging to a session. Additionally, in order to ensure stability and responsiveness in the inter-stream adaptation process, several measures are taken, including devising a domain rate control protocol. The performance of the proposed mechanisms is analyzed and their advantages are demonstrated by simulation and experimental results

Preliminary Measurement of the RMTP/RTIP

. The Real-time Message Transport Protocol (RMTP) and the Real-Time Internetwork Protocol (RTIP) are the transport and network layer data delivery protocols in the Tenet Protocol Suite. We implemented the protocols in Ultrix on the DECstation 5000 workstations and in HP/UX on the HP 9000/7000 workstations. A preliminary measurement study has been conducted to evaluate the performance of the prototype implementation. Some of the results are: the throughput obtained by using RMTP/RTIP is comparable to that obtained by using raw IP; the rate control mechanism in RMTP/RTIP effectively enforces the traffic specification of communication clients; the scheduling mechanism in RTIP protects the real-time channel so that the performance of a real-time channel is not affected by the presence of IP traffic or other real-time channels in the network. 1 Introduction There is an increasing demand to support real-time applications such as video conferencing, scientific visualization and medical imagi..