Ericsson MC 218 - Page 77

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• The Mobile Station
• The Base Station Subsystem
• The Network Subsystem
12.3.7 The Mobile Station
The Mobile Station is the Ericsson Mobile Phone, which is carried by the user. To be able to use
the phone, the user needs a Subscriber Identification Module, also called a SIM card. The SIM-
Card provides personal mobility, letting the user insert his or her SIM card in any GSM phone
and still have access to the same subscribed services.
12.3.8 The Base Station Subsystem
The Base Station Subsystem is composed of two parts, the Base Station Controller (BSC), and the
Base Transceiver Station (BTS). These two parts communicate across a standardized interface
called Abis, and therefore allows components from different suppliers to operate together.
The BTS handles the radio-link protocols with the Mobile Station (the GSM phone). Depending
on the surroundings (urban or country area), several BTSs are required to give good
communication coverage for the user.
The BSC controls call set-up, frequency hopping, handovers and the operation of one or more
BTS.
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