The underlying transport stack and the SCCP are used to support signalling messages between the SGSN and the MSC. The BSSAP+ protocol specified in TS 29.018 is the user of the SCCP. TS 29.018 only uses the services of the class 0 of the SCCP. The Gs interface connects an SGSN to a VLR within the same PLMN. The use of point codes or global titles is allowed for routing of SCCP messages. The format and coding of address parameters carried by the SCCP for routing purpose shall comply with ITU-T Recommendation Q.713 for E1 interface and ANSI T1.112.3 T1 interface with the following restrictions:

• The called party address shall include:
  • an SSN (see subclause 6.4.1 E1 interface and subclause 6.4.2 for T1 interface);
  • all other aspects of the SCCP signalling are specified in TS 29.002.
• The calling party address shall include:
  • an SSN (see subclause 6.4.1 E1 interface and subclause 6.4.2 for T1 interface);
  • all other aspects of the SCCP signalling are specified in TS 29.002.

When an SCCP message is sent, the Called Party Address is derived from the Called Address of the N-UNITDATA-REQUEST primitive issued by the local SCCP user. When an SCCP message is received, the Calling Address within the N-UNITDATA-INDICATION primitive is derived from the Calling Party Address of the SCCP UNITDATA message received. Only address information belonging to the E.164 numbering plan is allowed to be included as Global Title in the Called and Calling Party Address. The SGSN and the VLR store the address of the other entity using the format received in the Calling Party Address field or the address information received in the application part of the message.