The present invention relates to a gateway between two networks of a communication system. A plurality of communication service classes is available for the communication between the networks. In the method a call is routed from a network to another network via the gateway. The type of the call is defined. A gateway controller also determines the communication service class that is to be used for the call. The gateway controller communicates information that associates with the determined service class to the gateway. The communication is based on a communication protocol message that has been adapted to transport the information between the gateway controller and the gateway. The call is then processed based on the information.