Host name or IP address of the SIP proxy server. All SIP signaling traffic MUST be sent to the host indicated by this parameter and the port indicated by the ProxyServerPort parameter unless OutboundProxy is non-empty or a different route was discovered during normal operations SIP routing operation. Regardless of which host the traffic gets sent to (the ProxyServer or the OutboundProxy), the value of this parameter MUST be used to derive the URI placed into the SIP Route header field of all requests originated by this end-point unless a different proxy host was discovered dynamically during normal SIP routing operations.