Mobile Location Update

Hi Friends,

Lets discuss something about Location Update Procedure, because of which a mobile user can move freely.

As a mobile user, a person can be anywhere but a network has to keep track of user, in-case if somebody wants to call him, so the transaction that keeps network updated about the subscriber present location is termed as location update.

A mobile phone constantly receives information sent by the network, which includes ID of the VLR area in which mobile is currently located & mobile stores that ID.

Every time the network broadcasts the ID of the area, the mobile compares this information to the area ID stored in its memory. When the two IDs are no longer the same, the mobile sends the network a request, i.e. a registration inquiry to the area it has just entered. The network receives the request and registers the mobile in the new VLR area. Simultaneously, the subscriber’s HLR is informed about the new VLR location and the data concerning the subscriber is cleared from the previous VLR.

There are 3 different kinds of location update procedure like,

• Location Registration (power on).
• Generic.
• Periodic

Location Registration (power on) - Whenever mobile turns ON, location registration takes place, which is also termed as IMSI attach, because as soon as the mobile station is switched on, it informs the VLR that it is now back in service and is able to receive calls, as a result of a successful registration, the network sends the mobile station two numbers that are stored in the SIM (Subscriber Identity Module) card of the mobile station.

1. Location Area Identity (LAI) – it’s a globally unique number.
2. Temporary Mobile Subscriber Identity (TMSI) - is used for security purposes, so that the IMSI of a subscriber does not have to be transmitted over the air interface. It’s a temporary identity, which regularly gets changed.
   

Generic – It happens, if LAI present in mobile SIM & LAI received via control channels during network broadcast are different.

The mobile starts a Location Update process by accessing the MSC/VLR that sent the location data. A channel request message is sent that contains the subscriber identity (i.e. IMSI/TMSI) and the LAI stored in the SIM card.

When the target MSC/VLR receives the request, it reads the old LAI which identifies the MSC/VLR that has served the mobile phone up to this point. A signaling connection is established between the two MSC/VLRs and the subscriber’s IMSI is transferred from the old MSC to the new MSC. Using this IMSI, the new MSC requests the subscriber data from the HLR and then updates the VLR and HLR after successful authentication.

Periodic – It is carried when the network does not receive any location update request from the mobile in a specific time. A timer controls the periodic updates and the operator of the VLR sets the timer value.

The network broadcasts this timer value so that a mobile station knows the periodic location update timer values & when the set time is up, the mobile station initiates a registration process by sending a location update request signal.

The VLR receives the request and confirms the registration of the mobile in the same location area. If the mobile station does not follow this procedure, it could be that the batteries of the mobile are exhausted or the subscriber is in an area where there is no network coverage. In such a case, the VLR changes the location data of the mobile station to “unknown”.

Keep checking for new posts till then Happy Reading.

ChEEeeRrS

Telecom Tigers Team
telecomtigers@gmail.com
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