GSM Network Stucture

The network behind the GSM system seen by the customer is large and complicated in order to provide all of the services which are required. It is divided into a number of sections and these are each covered in separate articles.
the Base Station Subsystem (the base stations and their controllers).
the Network and Switching Subsystem (the part of the network most similar to a fixed network). This is sometimes also just called the core network.
the GPRS Core Network (the optional part which allows packet based Internet connections).
all of the elements in the system combine to produce many GSM services such as voice calls and SMS.