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370 SIGNALING IN CELLULAR MOBILE TELECOMMUNICATIONSFigure 12.7-4. Transfer of MM and CM messages. (From GSM 04.07 Version 4.10.0. Courtesyof ETSI.)which is then transmitted by BSS on the PAGCH, or a broadcast message, which istransmitted on the BCCH.The DTAP at a BSS transparently (without processing by BSS) transfers MM andCM messages, received on dedicated radio channels, to a SS7 data link, which transportsthem to the MSC—see Fig. 12.7-4. Also, messages for a MS received fromDTAP at the MSC are transferred to the radio channel that is currently dedicatedto the MS.The transfer of BSSMAP and DTAP messages involves the SCCP and MTP inthe MS and BSS [12]. The SCCP at the sending end adds a discrimination parameterto the messages, which indicates whether the message belongs to BSSMAP orDTAP, and which is used by SCCP at the receiving end to deliver the message tothe proper entity.12.7.4 Identification of GSM EntitiesSince GSM systems are deployed in many countries, ITU-T and ETSI have standardizedthe identification of GSM entities according to a numbering plan specified inITU-T Rec. E.212 [20]. This plan is different from the ITU-T Rec. 163/164 numberingplan for fixed networks.PLMN Identity. A PLMN is uniquely identified by its mobile country code (MCC)and mobile network code (MNC). MCC consists of three digits, of which the first oneindicates a world zone:2 Europe3 North America4 The Mideast and Western Asia5 Eastern Asia and Australia6 Africa7 Latin America