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GSM Network Architecture.
GSM network can be broadly divided into three broad parts, namely:
1. Mobile Station(MS) carried by the subscriber,
2. Base Station Sub-system(BSS) which controls the radio link with the mobile station.
3. Mobile Switching Center(MSC) which performs the switching of calls between the mobile
users, and between mobile and fixed network users.
FIGURE 1.2 GSM ARCHITECTURE
Each mobile station is given a unique identity. As soon as the mobile phone is turned on, it
registers with the network and is authenticated, as such the network could always find the
mobile phone.
Larger amount of data is being exchanged to and from the following functional blocks in the
MSC:
Visitor Location Register, VLR
Stores information about mobile subscribers that enter it coverage area which is associated with
the geographical area where the mobile is currently roaming. When there is an incoming call for
the mobile, the HLR is interrogated about the present address of the VLR.
Home Location Register, HLR
A database that contains all data concerning the subscription of the mobile subscriber, i.e. their
access capabilities, subscribed services, and supplementary services. It also contains
information about the VLR that is handling the mobile station currently. When the mobile
changes location, the HLR is updated accordingly. It also provides the MSC with information
about the MSC area where the mobile is actually located to allow incoming calls to be routed
immediately to the called party.
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