I am filtering the ngrep will device username and getting below

U 70.71.10.16:5060 -> 16.63.14.13:5060
REGISTER sip:sip.mytel.com:5067 SIP/2.0.
Via: SIP/2.0/UDP 70.71.10.16:5060;branch=z9hG4bK715725659.
To: <sip:241186@sip.mytel.com>.
From: 241186 <sip:241186@sip.mytel.com>;tag=1986135880.
CSeq: 18 REGISTER.
Call-ID: 1180990338@192.168.0.19.
Contact: <sip:241186@70.71.10.16:5060>.
Max-Forwards: 70.
User-Agent: iSoftStone.
Expires: 600.
Content-Length: 0.
.

and while freesiwtch's siptrace is also on, yet i am getting nothing in freeswitch side.

and i am sure there is no firewall with server.

Could this be the UAC issue?