The Scilab external module entitled NARVAL enables the performance analysis of algorithms on networks represented by weighted graphs (computer, electric power, road, etc.). NARVAL provides a complete software environment enabling the understanding of available communication algorithms, but also the design of new schemes in order to improve the traffic behaviour of any connection between two network entities. Random topologies can be created according to various algorithms such as Locality, Waxman, Barabasi-Albert and hierarchical models. A large range of topologies can be built with distinct routing properties. The impact of routing algorithms on the effectiveness of transmission protocols used by data communications on a network topology, can be analysed. A set of basic functions enables to create network graphs, compute routing algorithms on them and finally make statistical analysis on the data exchange. The target audience of NARVAL includes academics, engineers and scientists.