ISDN Screening Indicator

The ISDN screening indicator is a service provided by ISDN that can be used to test the trustworthiness of the calling party's number.

 

The calling party's number (CPN) reported by an incoming call may have been assigned by the user placing the call or by the telephone switching station.

If the CPN was assigned by the user the switching station may optionally verify this address is correct in order to detect malicious calls.

The party (user or network) that assigned the CPN and whether or not the CPN has been verified is reported in ISDN in the Screening Indicator field of the call packet. The values shown below are used and indicate the respective circumstances.

 

Screening Indicator		CPN assigned by	Status of Calling Party's Number
network		network	The CPN was set by the network (verification not required)
user-verified		user	The CPN was set by the user and was verified by the network.
User		user	The CPN was set by the user but no verification was attempted.
User-failed		User	The CPN was set by the user and verification of the number Failed.