 but it is usually physically part of the MSC itself. This physical colocation has the advantage that it streamlines the MSC-to-VLR signaling at the beginning of a call. 15.2.2 Service qualification When a user terminal registers, the serving MSC determines whether it is a home sub- scriber or a roamer. In either case, the MSC communicates with the HLR to verify that this subscriber pays the bills promptly enough to get wireless telephone service. In the roaming case, the serving MSC contacts the subscriber's home HLR and its own VLR to figure out the status of the user terminal; it already may have registered recently in this system. The serving MSC contacts the HLR when the user terminal registers, when it moves out of the qualified area, when its allocated time authorization runs out, or when the HLR asks for an update. The HLR can revoke service privileges for a user terminal by sending a message to the serving MSC and VLR. ANSI-41 does not tell the serving system how to re- voke service; it might play a prerecorded message when the subscriber tries to make a call. 15.2.3 Location management The HLR keeps track of where its user terminals are located. This location is at least as precise as knowing what system the user terminal was in when it most recently reg- istered, but it may have more precise information. The HLR is notified whenever the user terminal registers in a new system. This is the location-update process. There is also a location-cancellation process. This occurs when the user terminal sends a power-down signal to the serving MSC or when the user terminal fails to re- spond when a registration request is sent to it. The roamer location management system has specific protection in it for inter- system confusion at call setup. When a user terminal tries to access the serving sys- tem, a neighboring system can pick up the signal and think it is being accessed for a call on one of its own base stations. We call a cell that can pick up a false access attempt a border cell. The HLR knows that somethi