the MSRN is first requested from the HLR of the MS. In this way the currently responsible MSC can be determined, and the call can be routed to this switching node. In the second case, the MSRN cannot be stored in the HLR, since it is only assigned at the time of the call setup. Therefore the address of the current VLR must be stored in the tables of the HLR. Once routing information is requested from the HLR, the HLR itself goes to the current VLR and uses a unique subscriber identification (IMSI and MSISDN) to request a valid MSRN. This allows further routing of the call. Location Area Identity (LAI) Each LA has its own identifier. The Location Area Identifier (LAI) is also structured hierarchically and is internationally unique. It consists of the following parts: Country Code (CC): 3 decimal digits; Mobile Country Code (MNC): 2 decimal places; Location Area Code (LAC): maximum 5 decimal places, or maximum twice 8 bits. The LAI is broadcast regularly by the base station on the Broadcast Control Channel (BCCH). Thus, each cell is identified uniquely on the radio channel and each MS can determine its location through the LAI. If the LAI that is heard by the MS notices this LA change it requests the updating of its location information in the VLR and HLR (location update). The LAI is requested from the VLR if the connection for an incoming call has been routed to the current MSC using the MSRN. This determines the precise location of the MS where the mobile can be currently paged. Temporary Mobile Subscriber Identity (TMSI) The VLR being responsible for the current location of a subscriber can assign a Temporary Mobile Subscriber Identity (TMSI), which only has significance in the area handled by the VLR. It is used in place of the IMSI for the definite identification and addressing of the MS. Therefore nobody can Cellular Networks determine the identity of the subscriber by listening to the radio channel, since the TMSI is only assigned during the MS's presence in the area of one VLR, and can even be changed duri