i don’t know too, some guys told me that it’s used for ISUP, you know ISUP is a powerful signalling protocal, but many functions have not beed used, screening mask uses to screen the unwanted signalling.
Yes, screening mask is for ISUP. example is newly implemented optional protocols that AXE sends but other MSCs don’t understand. We use screening mask to blank out these parameters or to change the values to what other MSCs will understand so call is not rejected. See commands UPSM*
Actually screening can help u mask or modify most of the o/g or i/c message.
I have implemented it to modify echo controller indicator. I have also tested the masking to modify the release code that is generated when call or call attemt drops.
I hope this will be of some help to you. But do we have screening in SCCP stack. If I am not wrong screening is feature of ISUP only.