I have asterisk - Elastix in my office and Yeaster S20 in other location connected over Sonic Wall VPN, i created SIP trunk between both and registered on both side. i'm able to make calls but one way Audio. i need troubleshooting in configurations.
on my Office - Elastix 2.5 - Sonicwall TZ400
Other Location : Yeaster S20 - Sonicwall Soho
VPN Both side working perfect over sonicwall VPN Client