The present document defines the service offered by the physical layer (3GPP TS 45-series of Technical Specifications) of the MS-BS interface (3GPP TS 45- and 44-series of Technical Specifications). Its main objective is to be a guidance for the interface between the 3GPP Technical Specifications in the 45-series and the 44-series. It also specifies the format of signalling channels and the order of bit transmission. As far as possible@ the present document makes use of the layering principles of the Reference Model for Open System Interconnection (OSI) as contained in ITU-T Recommendations X.200 and X.210.