[Users] one way audio problem

I have an openser using mediaproxy with port setting 2000:8000. Most of the user can use it without problem. But few user experiences one way audio when make a call to the called party. Is it related to the setting of mediaproxy (mediaproxy.ini)? Is it related to the port range I set below? portRange = 2000:8000 Below is the information that I capture from the location table. One is using a hardware IP phone but having one way audio problem. One is using XLite without problem. Both client are in the same network behind NAT to connect to the same openser server. case 1: using hardware IP phone with one way audio in making a call. The user claims he is using NAT with internal IP 192.xxx.xxx.xxx. But there is no such information shown in the locatioin table. location table information ----------------------------- contact = sip:1234@202.123.12.1:5060 received = sip:202.123.12.1:60626 callid = TtFZUeEbHpx4suRG(a)202.123.12.1 cseq = 3834 case 2: using XLite software phone without problem. location table information ----------------------------- contact = sip:sip:2345@202.123.12.1:47328 received = sip:202.123.12.1:47328 callid = 56725116a22ec84f@UmF5bW9uZC1wYy5waC5vd3RlbC5jb20. cseq = 11 I wonder why there is one way audio problem only for the case 1 but not for case 2. I do think there is setting problem but I can't figure out. Anyone can help? system: openser 1.0.1 + mediaproxy 1.4.2