This Global System for Mobile communications Technical Specification ( GTS) is an introduction to the GSM 08.0X series of Technical Specifica tions and deals with the definition of the Base Station System (BSS) t o Mobile Switching Centre (MSC) (referred to as the A-interface) defin ed for the GSM system. It also introduces Technical Specifications in the GSM 08.20 series, d ealing with the support of data services on this interface. This GTS gives an overview of the content of the GSM 08.0X and GSM 08. 20 series of Technical Specifications explaining how the detailed cont ent of the Technical Specifications is partitioned and how the Technic al Specifications can be used to support a full BSS-MSC interface.