The IP Multimedia Core Network Subsystem (IMS) provides multimedia services for Universal Mobile Telecommunications System (UMTS). In IMS, an emergency call is established by an Emergency-Call Session Control Function (ECSCF). The E-CSCF dispatches the call to the nearest Public Safety Answering Point (PSAP) according to the location of the caller. After emergency call setup, the caller's location is tracked by the PSAP through Location Polling. This paper investigates the performance of location tracking. Then we propose the Active Location Reporting scheme to improve the performance of location tracking. Our study indicates that the Active Location Reporting scheme may significantly outperform the Location Polling scheme.
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