The management of huge, heterogeneous and highly distributed networks is a very complex task due to their low degree of integration. Such a network is that of Telemar, the largest telecommunications company of Brazil. The plant is composed of a large variety of switching equipments and transmission systems, differing not only by their vendors but also by their technology, age and way of monitoring and control. In order to solve that management problem, a distributed management platform called SIS (system for integration of supervision) was developed. This platform is fully operational and implemented in a real telecommunications plant. SIS has been evolving since the mid 1990s, when it was initially deployed. The platform was conceived to allow the management of new systems and showed to be a key factor for the company as its business focus also evolves (e.g., the management of data communication networks of other companies such as a bank, an airline company, and a large retailer). We discuss the development and use of the SIS platform, its design and main modules.