03.603GPPGeneral Packet Radio Service (GPRS)Release 1998Service descriptionStage 2TS
The GPRS and combined GPRS / CS MM procedures in the following subclauses shall use the LLC and RLC/MAC protocols for message transmission across the Um interface. The MM procedures shall provide information to the underlying layers to enable reliable transmission of MM messages on the Um interface. GSM 03.64 defines the mapping between LLC and the radio channels used.
Furthermore, the MM procedures use MAP interfaces between SGSN and HLR (Gr), and between SGSN and EIR (Gf), and a BSSAP+ interface between SGSN and MSC/VLR (Gs).
User data can in general be transmitted during MM signalling procedures. User data transmitted during attach, authentication, and routeing area update procedures may be lost and may therefore have to be retransmitted. In order to minimise the need for retransmission, the MS and SGSN should not transmit user data during the attach, authentication, and routeing area update procedures.