Mobile Communication Basics - Location Update
Why location updates?
Network has to identify where is the mobile is located to page it when an incoming call is received.
Why cannot page the entire network?
Millions of calls receive every moment, the capacity is not enough if network page all those millions of calls in each and every base station in the network. Therefore it is required to divide the network in to LAC.
What is the suitable LAC size?
It is depends on many factors. But smaller location area avoids paging channel congestions. But having many LACs would increase SDCCH traffic in LAC border cells. Therefore city centers, highways have to be avoided as much as possible to minimize number of location updates.
What is the largest LAC?
What is the smallest LAC?
Location Update Types
Three types of location updates are defined in GSM standards.
- Normal location updating
- IMIS attach location updating procedure
- Periodic location updating
Normal location updating
MS has to do a location update in new location area when it crosses a LAC border.
IMIS attach location updating procedure
- When mobile switch ON it has to do a location update
- When moving from non coverage area to a coverage area MS has to do a location update if LAC is different from stored LAC
- When mobile switch OFF it has to detached from the network
Periodic location updating (T3212 timer is used)
The network has to do a periodic location updates to update the subscribers in each location area.
How does the network distinguish between 'switched off' and 'not responding' when giving messages to the caller?
- Mobile detached from VLR when it switched off.
Mobile registered in VLR but not in coverage area.
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Why location updates? Network has to identify where is the mobile is located to page it when an incoming call is received. Why cannot page the entire network? Millions of calls receive every moment, the...
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