The field of Computer Networks has been growing at an enormous pace in the last several years. New technologies have been developed to take into account the stringent requirements of multimedia applications including audio and image, distance learning, collaboration and entertainment services. The main characteristics of multimedia applications are that they have vastly different performance and reliability requirements, often coupled with real-time constraints. Thus the design and evaluation of such multimedia systems and networks is quite a challenging enterprise. In this talk we present the TANGRAM-II modeling environment we developed under the ALMADEM project, for research and educational purposes. Its set of tools includes the TANGRAM-II model specification and solution tool, a Whiteboard, a real-time voice transmission tool, among others. TANGRAM-II provides a flexible user interface to describe computer and communication system models and to obtain several measures of interest. It is based on an object oriented description paradigm and has a sophisticated graphic interface built on the top of the public domain software TGIF. The solution methods include state of the art analytical solvers for steady state and transient analysis, and an interactive simulation package that implements an efficient technique for rare event simulation. The Whiteboard implements reliable multicast techniques.

The real-time voice transmission tool uses a new algorithm we developed for recovering lost packets, that is particularly efficient under high loss rates. The environment also includes a tool for generating traffic from several traffic models to aid in laboratory experiments. After describing the environment, we will present a few examples to highlight its main capabilities. Some experimental results will also be shown.