Digital Cellular Telecommunications System (Phase 2+); Bearer Services (BS) Supported by GSM Public Land Mobile Network (PLMN) (GSM 02.02 Version 7.0.1 Release 1998)
"The present document defines a set of Bearer Services to be provided to GSM PLMN subscribers by a GSM PLMN itself and in connection with other networks. The present document should also be used as a reference for defining the corresponding required mobile network capabilities which are specified by means of the ??GSM PLMN connection type"" concept@ defined in OSM 03.10 [4]. The recommended provision of the Bearer Services is under the control of the GSM MoU and is out of the scope of ETSI TCSMG. Bearer Services not included in the present document that require modifications to the GSM signalling specifications should not be introduced unilaterally by a mobile network operator."