scope:

The present document gives principles on which the detailed interlace specifications in the rest of the GSM OS,OX series of Technical Speciftcatioos are based.

The set of fixed equipment accessed from the MSC through one particular instance of the interface will be later referred. to as a Base Station System(BSS). A BSS ensures the coverage ofn cells, where n can be 1 or more.

The function of a BSS may be further subdivided into a control function, perform:d by one Bast Station Controller (BSC) tmd a Iransceiving function, perfOnned by "n"  Base Transceiver Station equipmenrs (BTS), ont for each cell. However, the study of such a split is ourside the scope of the OS.OX series of Technical Specifications, where the BSS will be considered as a whole.

The BSS-MSC interface defwed in the GSM 08 series of Technical Specifications is designed 10 support a wide range of possible architectures on both sides. Characteristics like the physical location of the tmnscoderslrate adaptation inside the BSS (either integrated into the lnInSCeivers or very near to the MSC) or the use of uaffic or signalling concentration at either side are left to the operators choice. Annex A to the p~nt document contains guidance information concerning the use of reroote mobile switching units, which for the pwposes of the present documenl are coosidered as part of the MSC.

Direct connection between two BSSs is not supported by this interface.

This interface is based on the use of 1 or Jmrt 2 048 kbitls digital transmission system inteIfaces. Each 2 048 kbilfs interface provides 31*64 kbitJs channels which can be used for traffic or signalling as the operator requires.

The signalling is layered, terminology similar to that in the OSl reference model is used in this series. however the layers referred to are not identical 10 the equivalently named layer in the OSI model.

This interface is dermed at the boundary of the MSC and bas a per channel bit rate of 64 kbills, but the nel radio path traffic channel is at a rate of less than 16 kbitls. A transcoder orratc adapter function is thus needed Cor the mle conversion. The interface is designed such that the transcoding or rale adaptation function may be geographically situated at either the MSC sile or the BSS site, however the transcoder is considered to be part of the BSS.

The interface has been designed around the aims of GSM OS.OI allowing each component and lhe system as a whole to evolve.