Gsm Network Architecture - Siemens A50 Service Manual

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.
Authentication Center, AUC
Stored information that is necessary to protect communication through the air interface against
any intrusions. The legitimacy of the subscriber is established through authentication and
ciphering, which protects the user information against unwanted disclosure.
Equipment Identity Register, EIR
An option the network operator can use to enforce security. With this feature the network can
identify defective or stolen mobile that may not be used in the network.
3