2.31.1.1 Overview

MTP Screening feature consists of the following fields:

  • Originating Point Code (OPC)
  • Destination Point Code (DPC)
  • Service Information Octet (SIO)
  • Affected Destination in MTP Network Management messages
  • Affected Point Code and Subsystem number in SCCP Management Messages

The above fields support range and wild card entries.

MTP screening groups screening rules together. This grouping of screening rules is referred to as Screen Rule Group Name which is based on rule type like OPC and DPC. Screen set refers to Screen Rule Group Name. Screen sets shall have unique screen set name and table key. A screen set shall be assigned to a link set. To end screening, a stop action is defined as the Next Screening Function Identifier (NSFI), screening either results in Fail or Stop. Fail causes discard of packet and Stop causes end of screening and further processing at vSTP.

Note:

Default Screening Rule on SIO will lead to discard of SCMG messages, hence add appropriate screening rule for SI (Service Indicator)=3(SCCP) and scmg message type.

MTP screening features include:

  • Creating screening rule and keeping rules of the same type in a group.
  • Creating a screen set and referring to rule group created in the screen set.
  • Attaching the screen set to incoming link set.
    • When a message appears on a linkset, the screen set related to that linkset is looked up, and the rule in that rule group is looked up based on the NSFI and rule group name linked with the screen set.
    • If the rule lookup is successful, the message will proceed to the next screen rule group name on the basis of NSFI.
    • If rule lookup does not find a match:
      • In case of BLKOPC or BLKDPC rule type, the default rule for that rule group will be looked up and based on the NSFI and next screen rule group name associated.
      • In case of OPC/SIO/DPC/AFTDSTN rule type, Fail NSFI will be performed.
      • If rule type is Affected PC , then NSFI is either STOP or Affected PC SSN (AftPcSsn). Affected PC (eftpc) is configured the same way as OPC/DPC is configured in MTP3 Screening.
      • If rule type is Affected PC SSN (AftPcSsn) , then NSFI is always STOP.
    • After all the screening levels are completed, if last NSFI Fails, then message will be discarded.
    • After all the screening levels are completed, if last NSFI STOPs, then message will go for further processing in VSTP.