Incoming DTMF passthrough

Setup: SIP Client A—> SIP PSTN gateway---->Asterisk—>SIP Server—>Sip Client B

Sip client A is sending a DTMF tone ‘inband’ and SIP gateway is passing it thru to Asterisk. Asterisk detects it…but I want it to pass it thru to my SIP server. That doesnt work. I have tried to experiment with some config options but couldnt figure out.

Could someone throw light on the issue?

thanks a lot