Location Update is an event that occurs in every cellular network to indicate the registration of a device and also to identify its location.
There are three scenarios in which an LU occurs:
1. When the UE (User Equipment) has been powered on and wants to become active (connect to the network).
2. When the UE is active and moves from one location area to another.
3. After a regular interval of time, usually set by the Mobile Network Operator.