I have a PBX Panasonic TDE600 (Branch A) connecting to an Panasonic ns300(Branch B). Branch A TDE600's SIP extension is what I made Branch B NS300's SIP trunk. My problem now is that all the ELCOT16 connected to the Branch A TDE600 all line are always busy. Branch A TDE600's elcot16 card contains PSTN line and GSM Gateway. when the Branch B ns300 uses the SIP trunk it doesn't cut immediately. What can be done to solve the problem if the Branch A Elcot16 card is hanging, any recommendation please help me.