earticle

영어

In conventional VoIP services, a call session control server, like the proxy call session control function (P-CSCF) in 3GPP IMS, is not aware of the callee’s mobile station (MS) state information such as idle, active, or loss of connection. This may cause an inefficient or unintentional call setup, and sometimes call setup failure. For examples, although a callee MS is in idle state or loss of connection for some reasons, the P-CSCF would send a call session setup request message to the callee irrespective of the MS state and just wait for a response message for a preconfigured time without any action. These induce an undesired call forward or cancellation and a long post-dial delay, and thus degrade quality of service (QoS). In this paper, we propose an improved call setup scheme in which the P-CSCF detects the state of the callee MS during the call setup procedure and makes the procedure optimal. Also, we compare the performances of the proposed scheme and the conventional one by MATLAB simulations. Our scheme is adapted in WiMAX Forum as standard call setup procedure for WiMAX VoIP Service.