Comparison of Estimation Methods for Structural Credit Risk Models

Providing a roaming service among private mobile switching centers (MSCs) interconnected to one another via a public switched telephone network (PSTN) includes connecting the private mobile switching centers to a virtual private network (VPN) via the PSTN; storing information about a mobile station registered for a private mobile communication service and associated mobile station location information in a selected private mobile switching center upon a mobile station sending a private mobile communication service registration request to the selected one of the private mobile switching centers; transmitting the mobile station information and the mobile station location information to other private mobile switching centers via the virtual private network; and the selected private mobile switching center the private mobile communication service using the stored mobile station information and mobile station location information upon the mobile station sending a private mobile communication service request to a selected one of the private mobile switching centers.