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The methodology for gateway screening and MSU tracing is the same. This process uses 17 inter-related screening tables for filtering messages based on the following screening criteria:

  • MTP attributes:
    • Originating Point Code (OPC)

    • Destination Point Code (DPC)

    • Service Information Octet (SIO)

    • Affected Destinations [for example, transfer-prohibited (TFP), transfer-allowed (TFA), and so on]

  • ISUP attributes:
    • Message Type [for example, Initial Address Message (IAM), Address Complete Message (ACM), and so on]
       
  • SCCP attributes:
    • Calling Party Address (CLG PA) including digits

    • Called Party Address (CLD PA) including digits

    • Message Type [for example, Unitdata (UDT), Extended UDT (XUDT), and so on]

    • Affected SCCP Management (SCMG)

    • SCCP Protocol Class

  • TCAP attributes:
    • Operation Code (only in the first component)

    • Message Type
        
    • Component Type

    • Application Context
         
    Note

     For more information about the TCAP Operation Code, refer to TCAP Op Code Optional Feature.

  • MAP attributes:
    • IMSI/MSISDN/IMEI (dependence on the TCAP Operation Code for the related type)

The screening tables either allow or block the attributes in the preceding list.

Note

With the exception of the SCCP CLD PA and SCMG, all the other screening criteria can be performed directly on the incoming SS7 message. The SCCP CLD PA and SCMG screening are performed following GTT conversion (if applicable).

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