GSM_03.40规范_v7.5.0 The present document describes the point-to-point Short Message Service (SMS) of the GSM PLMN system. It defines: - the services and service elements; - the network architecture; - the Service Centre functionality; - the MSC functionality (with regard to the SMS); - the SGSN functionality (with regard to the SMS); - the routing requirements; - the protocols and protocol layering; for the Teleservices 21 and 22, as specified in the GSM 02.03.