Home Location Register (HLR):

1) This database contains all the administrative information about each subscriber along with their last known location.

2) In this way the GSM network is able to route calls to the relevant base station for the MS.

3)When a user switches on their phone ,the phone registers with the network and from this it is possible to determine which BTS it communicates with so that incoming calls can be routed appropriately.

4) Even when the phone is not active (but switched on) it re-registers periodically to ensure that the network (HLR) is aware of its latest position.

5) There is one HLR per network ,although it may be distributed across various sub-centers to for operational reasons.

Operation maintenance center (OMC)

1) Network operation and maintenance functions, subscription, management including charging and billing and also mobile equipment management.

2)The OMC also has provision for adjusting all base station parameter and billing procedure as well as providing system operators with the ability to determine the performance and integrity of all equipments in the system.