We describe the results obtained when using a desktop videoconferencing system for distance learning and, at the same time, doing measurements about its performance. The system hardware is based on a PC with a LAN network controller, and a compression card implementing the CCITT H.261 algorithm. Our network environment consists of a campus network (Ethernets connected with routers and bridges) and a wide area network connection (0.5 Mbit/s frame relay) to another university 150 miles away. In this environment TCP/IP is used as the transport and network protocol suite. The quality of the videoconferencing application is first analysed on a subjective perceptual basis in four different subnetworks. Then, the transmission rate of the application and the number of TCP retransmissions is measured in those subnetworks under varying background traffic load. As one may assume, severe problems with audio appear when the networking environment gets more demanding. With video, the problems are not so evident. Yet, slight degradation of perceptual quality can be observed and related to the increase of load and number of packet switches (routers and frame relay nodes) in the network connection. >
['Jarmo Harju', 'Ville-Pekka Kosonen', 'Changhong Li']
Quality and performance of a desktop video conferencing system in the network of interconnected LANs