Control entity and method for setting up a session in a communications network, subscriber database, and communications network. The control entity advantageously has or has access to memory for storing information, and typically includes an input device for receiving a request to set up a session in the communications network, a processor unit for processing the request, and an output device for sending messages. The processor unit is arranged to determine if the request comprises a valid Communication Service Identifier (CSI) the CSI identifying the type of communication service of the session that is to be established over the communications network. And if the request does not comprise a valid Communication Service Identifier, to execute a default CSI procedure using default CSI information stored in the memory.