ng this period (ID (identity) hopping). The MS stores the TMSI on the network side only in the VLR and it is not passed to the HLR. Local Mobile Subscriber Identity (LMSI) The VLR can assign an additional searching key to each MS within its area to accelerate database access, called the Local Mobile Subscriber Identity (LMSI). Each time messages are sent to the VLR concerning an MS, the LMSI is added, SO the VLR can use the short searching key for transactions concerning this Mobile Call Origination and Termination The case is considered where a person makes a call from a telephone connected to a public switched telephone network (PSTN) or ISDN, to a mobile subscriber going from city A to city B. The call will take place only if the subscriber's mobile is switched on. Assuming the mobile to be switched on, the MS searches for the cellular network by scanning the relevant frequency band for some control channel transmitted by a nearby MS. After location updating the MS accesses the network and acquires a unique serial number. Once an MS has successfully registered its location with the network it enters the idle mode, whereby it listens to the paging channels from the selected BS. Since the subscriber is presently in city A the MS will have identified a BS in this area. The MS will notice that the signal begins to fall as it is moving from city A to city B and it will now look for a more appropriate BS to take over. When the MS identifies a more appropriate BS it examines its control channels to determine the location area to which it belongs. If it belongs to the same location area as the previous BS, the MS simply re-tunes to a paging channel on the new BS and continues to monitor this new channel for incoming paging calls. If the MS has moved between BSs in different location areas, then it performs a location update and informs the network of its new position. This process of transition between BSs while in the idle mode is termed the idle mode handover. The entire process of the call is initiated by the perso