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478 SIGNALING CONNECTION CONTROL PARTFigure 15.3-3. N- and MTP-primitives. (From Rec. Q.711. Courtesy of ITU-T.)N-unitdata indications to ISUP or TCAP, depending on the value of SSN in thecalled party address.The N-unitdata indications include all information listed in Fig. 15.3-3, exceptthe protocol class and return option (they are not significant to the receivingTCAP or ISUP). TCAP then delivers the information in the package to the subsystemspecified by SSN.15.3.3 Global Title TranslationA SCCP called party address (Par.1) can contain various combinations of PC, SSN,and/or GT. We now explore the reasons for global titles and GT translations.A subsystem in a network is uniquely identified by the combination of the pointcode PC of its signaling point and its SSN at that point. If a SCCP message has aPC þ SSN called party address, the MTPs along the message path then use PC toroute the message to its destination signaling point, and the SCCP at this point deliversit to the subsystem specified by SSN. For example, in Fig. 15.3-1, a SCCPmessage with called party address PC ¼ c, SSN ¼ r is delivered to subsystemR800 in database C.A global title is a “functional” address of a subsystem in an exchange or database.The reason for these functional addresses is illustrated with the example ofFig. 15.3-1.