To resolve these issues, ITSP (IP-Telephony service provider) support SIP OUTBOUND PROXY. Outbound proxy is the only way to let the NAT/firewall user make and receive phone calls. If the NAT/firewall router does not support SIP pass-through, you ne

用于办公IP电话搭建，实现电话接通、外呼功能。-IP phones for office building, to achieve the call is connected, outbound capabilities.