The disclosure relates to a technique for providing interoperability between an Internet protocol multimedia subsystem (IMS) domain and a non-IMS domain. A method implementation of this technique comprises the steps of receiving on a service layer a service invocation message from a non-IMS domain, analyzing the message to identify the message as a request to invoke a service within the IMS domain, converting non-IMS session control protocol elements contained in the message into IMS session control related protocol elements, and generating an outgoing IMS message to establish an IMS control session.