Modeling prepaid application server of VoIP and messaging services for UMTS

Universal mobile-telecommunication system supports IP multimedia services through the IP multimedia corenetwork subsystem OMS). This paper proposes a prepaid application server (PAS) to handle both the prepaid calls and messaging services in the IMS. When both voice and messaging are simultaneously offered, a potential problem is that the delivery of a message during a call may result in force-termination of that call due to credit depletion. To address this issue, we describe a strategy to determine if a prepaid message can be sent out during a call session. We propose an analytic model to investigate the performance of this strategy. This paper provides guidelines to select appropriate input parameters for the PAS. Index Terms--Billing, diameter protocol, IP multimedia corenetwork subsystem (IMS), session initiation protocol (SIP), VoIP.