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is the one that is the ultimate recipient of said transaction or procedurę. Sometimes the originating end is called A and the terminating B.

The GSM network can be split by function into three logical parts, the Base Station Subsystem (BSS), the Network SubSystem (NSS) and the Op-erations Support Subsystem (OSS), as in Figurę 2.

Figurę 2: The generał architecture of GSM

BSS The BSS deals with the radio part of the network, that means receiving and transmitting signal to and from User Entities (UEs), e.g. mobile phones.

NSS This is where the major work in the GSM network is done and also where our HLR is situated. The GSM network can connect to other types of networks, this is done here.

OSS Last we have the OSS, this is basically an interface from the opera-tors to the different units of the GSM network. This might include updating the HLR database, changing routing in the MSC and so on.

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