Updating location information dating in the twin cities
the VLR must continually update its supply of security parameters (authentication parameter request).
After successful authentication (see Section 6.3.2), the subscriber is assigned a new MSRN, which is stored with the LAI in the HLR, and a new TMSI is also reserved for this subscriber; this is TMSI Reallocation (see Figure 7.25).
Figure 8.2 illustrates the standard case of a location update.
The MS has entered a new LA, or the timer for periodic location updating has expired, and the MS requests to update its location information.
It is assumed that the new LA still belongs to the same VLR as the previous one, so only a new TMSI needs to be assigned. But if its not quite so crucial to keep the subscriber identity confidential, it is possible to avoid assigning a new TMSI.
In this case, only the location information is updated in the HLR/VLR.
Each set of parameters, however, can only be used once, i.e.This means the subscriber has to report to the current network with his IMSI and receives a new TMSI by executing a Location Registration procedure.This TMSI is stored by the MS in its nonvolatile SIM storage, such that even after a powerdown and subsequent power-up only a normal Location Updating procedure is required.The main objective of this location update is to know the current location for incoming calls or short messages, so that the call or message can be directed to the current location of the mobile station.The difference between the location update procedure and the location registration procedure is that in the first case the mobile station has already been assigned a TMSI.