Detecting withheld CLI flag

Hi,

I have a couple of E1’s plugged into the back of my asterisk box, The carrier for these E1’s passes all CLI’s regardless of whether they are withheld or not and it also passes a flag in the ISDN header to indicate whether the number is withheld.

With our other equipment we can detect this flag in the header and then strip out the CLI before forwarding the call on, is there any way to detect this flag using asterisk?

Regards,

Chris V

core show function CALLERPRES

core show function CALLERID