1. A network management system for management of a traffic network comprising a wired network backbone and a wireless network backbone comprising a plurality of relay nodes comprising wireless routers, some of which acting as gateways to the wired backbone network and some of which acting as relay bridge routers supporting access of a number of access networks, said management system comprising a number of management stations arranged in a distributed manner and adapted to handle sub-networks of said traffic network, wherein the management system comprises a logical multilevel hierarchical overlay network, with a top or central manager, based on the infrastructure of the traffic network and adapted to use the relay nodes as management stations, that it comprises grouping means adapted to perform a grouping process by arranging network nodes, comprising the relay nodes, in groups or clusters, each with a cluster head, on different hierarchical levels, and further comprising grouping control means adapted to control the grouping and allocation of cluster heads based on a number of grouping constraints given by one or more criteria to be fulfilled at each hierarchical level, calculating means adapted to calculate the criteria based on given metrics, and modelling and verification means for modelling the constraints and verifying fulfilment of said constraints at each hierarchical level.