The present invention relates to a communication system supporting data communication and comprising at least a first core network with a plurality of circuit switched (CS) core network functional server nodes and a second core network with a number of packet switched (PS) core network functional sever nodes for packet switched communication. The CS core nodes are arranged in a pool and an interface (Gs) between CS core nodes and PS core nodes is used for providing information to CS core nodes from PS core nodes relating to mobility related events provided from an MS to a PS core node. When a mobile station moves from a first CS core node to a second CS core node the PS core node to which the MS is connected is provided with information relating to the change from said first to said second CS core node.