Sérgio Deusdado and Paulo Carvalho
Universidade do Minho
Departamento de Informática
P-4710-057 Braga, Portugal
Tel.: +351 253 604470
Fax.: +351 253 604471
E-mail: paulo (at) uminho.pt
A wide range of applications involving different types of media, with distinct quality of service and network resources requirements have been fostering the computer communications community in order to improve the service provided by the Internet. Besides the IETF recent proposals for introducing QoS in the Internet, multicast technology proposed by S.Deering assumes a major role in supporting group-oriented applications. This article describes the design, implementation and operation of an adaptive distance learning system based on IP multicast technology accessible through a Web browser. This system uses public domain multimedia multicast to build a system which adapts conveniently to the available network resources and to the hardware capabilities of the end-system.
The system architecture includes an adaptive module based on Java applets and embedded Javascript, responsible for assessing the existing operating conditions, by collecting the client's system performance (e-student's host) and relevant group characteristics. The collected data is subsequently computed weighting parameters, such as the available bandwidth at the client side, the round-trip time between the client and the remote server, the client's current CPU load and free memory. The obtained result is used for proper multicast applications scheduling and parameterisation in a transparent way.