SPA400 <--> asterisk config done : need to solve outgoing PSTN calls delay

Hello, I have an FXO gw SPA400 behind a firewall /home router. It has a local IP : 192.168.1.x. The asterisk server has a public IP address. I have forwarded UDP ports 5060 and 10000-20000 in the router to SPA400 IP address. The SPA400 can register to asterisk server. The problem is that: 1) huge delay (more than 20 sec) for outgoing PSTN calls. There is no big delay for incoming calls. 2) PSTN called/caller are unable to hear anything apart from the ring Please apply only if you have worked on similar setup before. The project will be considered as successful when both issues are resolved. Thank you.