Allowed SIO Screening Actions

The value of the nsfi parameter is based on the value of the service indicator (si) parameter. Table 10-1 shows the valid combinations of nsfi values and service indicator values.

Table 10-1 Valid Parameter Combinations for the Allowed SIO Screening Function

Service Indicator (SI) Values	Nest Screening Function Identifier (NSFI) Values
0	DPC, BLKDPC, DESTFLD
3	DPC, BLKDPC, CGPA, CDPA
4, 5	DPC, BLKDPC, ISUP
All other values (1, 2, 6-15)	DPC, BLKDPC

Messages containing the service indicator value 4 are TUP messages, and messages containing the service indicator value 5 are ISUP messages. Both types of messages are screened using the allowed ISUP screen. TUP messages can be screened for point codes, after the SIO screen, with the allowed and blocked DPC screens. However, if the screen set does not contain an allowed SIO screen that screens for TUP messages (messages with the service indicator value of 4), the message will be treated by the allowed ISUP message type screen as an ISUP message, even if the message contains the service indicator value of 4.

Figure 10-1 shows the screening actions of the allowed SIO screen.

Figure 10-1 Allowed SIO Screening Actions

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Figure 10-2 Allowed SIO Screening Function