This EN provides the overall description for lower-layer functions of the General Packet Radio Service (GPRS) radio interface (Um). It also covers a subset of the functions of the BSS-to-SGSN (Gb) interface. The overall description provides the following information: - The services offered to higher-layer functions. - The distribution of required functions into functional groups. - A definition of the capabilities of each functional group and their possible distribution in network equipment. - Service primitives for each functional group, including a detailed description of what services and information flows are to be provided. - A model of operation for information flows within and between the functions. GSM 04.60 is applicable to the following GPRS Um functional layers: - Logical link control functions. - Medium access control functions. - Physical link control functions. GPRS functional layers above logical link control are described in GSM 03.60.