Digital Cellular Telecommunications System (Phase 2+); Bearer Services (BS) Supported by a GSM Public Land Mobile Network (PLMN) (GSM 02.02 Version 5.2.0)
"This European Telecommunication Standard (ETS) defines a set of Bearer Services to be provided to GSM PLMN subscribers by a GSM PLMN itself and in connection with other networks. This ETS 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 GSM 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 TC-SMG. Bearer Services not included in this ETS that require modifications to the GSM signalling specifications should not be introduced unilaterally by a mobile network operator."