Explain localization and calling procedure to locate and address a Mobile Station?

Q.3) Explain localization and calling procedure to locate and address a Mobile Station? [10]

GSM (Global System for mobile communication) provides many useful services in which, one of the most important is the automatic, worldwide localization of users. The service provider system always knows where a user currently is, and the same phone number is valid worldwide.

For localization of users, GSM performs periodic location updates even if a user does not use the mobile phones or some other devices but user should not be out of GSM network and is not completely switched off their devices.

GSM uses two types of databases:

Home Location Register (HLR)
Visitor Location Register (VLR)

The Home Location Register is a database from a mobile network in which information from all mobile subscribers is stored.

The VLR contains the exact location of all mobile subscribers currently present in the service area.

VLR is responsible for the MS (Mobile Station) to inform the HLR about location changes.

As soon as user moves from one location to another location, the HLR sends all user data needed to the new VLR (New Location). Changing of one VLR to another VLR and their uninterrupted services is called as Roaming.

Roaming can be taken place as follows:

- Within the network of one provider
- Between two providers in one country (National Roaming)
- Different providers in different countries (International Roaming)

To locate an MS and to address the MS, several numbers are needed:

- Mobile station international ISDN number (MSISDN)
- International mobile subscriber identity (IMSI)
- Temporary mobile subscriber identity (TMSI)
- Mobile station roaming number (MSRN)