3.1 Introduction
The services offered by GSM are based on those of the fixed-line ISDN services and aretherefore, as with ISDN, the GSM services are divided into three categories
· Bearer Services
· Teleservices
· Supplementary Services
In addition, this section will look at the current (2G) data services offered by GSM including:
· Circuit Switched Data (CSD)
· Unstructured Supplementary Service Data (USSD)
· Short Message Service (SMS)
Each of these services will be described in this section of the course
Bearer services provide the transmission capability between various elements of the overall
transmission path. These bearer services carrying end-to-end teleservices. The Interworking
Functions (IWF) are required to provide the mapping of GSM PLMN services to fixed (e.g.
PSTN/ISDN) services. As teleservices are end-to-end, they are generally transparent to the
IWF.
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