This paper proposes a new approach to the modeling of packet switching networks that is based only on measurements (or simulations) and does not require any information on the network structure. Network managers usually need to assess network behavior for varying number of users or evolving traffic profiles, even without a complete knowledge of the network topology or resources. In these cases, it is critical to have a framework that, based on existing measurements and/or mathematical models (that describe the evolution of the number of users and their traffic profiles), infer the future network quality of service (QoS) parameters. Using these predictions, the network manager can take substantiated decisions on the need for resources reallocation or upgrading.