CAMEL-SIF: A Gateway for Service Invocation from Circuit Switched Domain to IP Multimedia Subsystem

The CAMEL and the IMS are representative service platforms in the circuit switched (CS) and packet switched (PS) domain. The integration of the CAMEL and the IMS will bring tremendous benefits to the network operators and end users. Many researchers invest in investigating the mechanism of invoking the CAMEL service from the PS domain, however, there are few studies about the mechanism of invoking the IMS service from the CS domain. This paper proposes a CAMEL service invocation function (CAMEL-SIF) as a gateway for service invocation from CS domain to IMS. The CAMEL-SIF works as an overlay on the top of the current CS infrastructure that enables operators to deploy it without any change in the existing CS core. It is responsible for translating the CAP message into the SIP message, and vice versa. The translation is based on the call state and message diagram (CSM) and mapping tables. The CSM is in charge of maintaining the call state and determining the corresponding messages. The mapping tables indicate the mapping between the parameters in CAP and the headers in SIP. The trigger Filter Criteria (tFC) and the execution Filter Criteria (eFC) are employed to resolve ambiguity and arm the event detection point respectively. Our study improves the completeness of service invocation architecture in the service integration of the CS domain and the IMS. We also discuss the appropriate allocation of the CAMEL-SIF for reducing the service invocation delay.