Trying to use PJSIP as Chan-SIP is going away - but I have a customer with 15 remote extensions behind a SonicWALL firewall on Comcast - If I set them with PJSIP extensions, about 6 of them eventually go to unreachable and stay that way - if I set them to SIP Extensions, they work perfectly - they stay registered, reachable and functional.
I have the SIP qualify set to 30 Seconds.