Satisfying High Quality Requirements of Video Conference on a Packed Switched Network

This paper is mainly concerned with the design, the dimensioning and the tuning of network systems with the main goal of offering a high quality desktop videoconference service to a large community of users dispersed in a metropolitan area. We will refer to a network topology in which a set of Ethernet technology-based LANs is interconnected by a DQDB backbone, trying to exploit the bandwidth saving introduced by the use of best efforts techniques and to maintain the investment of a large community of users. We recognized three main subnetwork systems: the single Ethernet segment, the couple of switched Ethernet segments, and the MAN subnetwork. For each of them a simulation model has been designed and has been run separately. Intermediate results have been used to dimension and tune the whole system. Finally a unique simulation model has been defined and run showing that the available protocols and technologies can support high quality multimedia real time services on packet switched networks at the price of a careful planning and tuning activity. More in detail, we show that it is possible to reach a 70% bandwidth utilization maintaining a satisfactory user quality perception and that Ethernet could be the system bottleneck, due to sudden and unpredictable peaks in the LAN access delay. The use of RTP has been proved to be mandatory to improve the user quality perception.