Linksys SPA921 Cisco SPA9000 Voice System Administration Guide - Page 52

Configuring Your System for ITSP Interoperability Network Address Translation (NAT) and Voice over IP (VoIP) 3 Requirements: • You must have an external (public) IP address that is static. • The NAT mechanism used in the router must be symmetric. See "Determining Whether the Router Uses Symmetric or Asymmetric NAT," on page 53. • The LAN switch must be configured to enable Spanning Tree Protocol and Port Fast on the ports to which the SPA devices are connected. NOTE Use NAT mapping only if the ITSP network does not provide a Session Border Controller functionality. STEP 1 Connect to the administration web server, and choose Admin access with Advanced settings. STEP 2 Click Voice tab > SIP. STEP 3 Scroll down to the NAT Support Parameters section, and then enter the following settings to support static mapping to your public IP address: • Handle VIA received, Insert VIA received, Substitute VIA Addr: yes • Handle VIA rport, Insert VIA rport, Send Resp To Src Port: yes • EXT IP: Enter the public IP address for your router. Voice tab > SIP: NAT Support Parameters STEP 4 Click Voice tab > Line N, where N represents the line interface number. STEP 5 Scroll down to the NAT Settings section. • NAT Mapping Enable: Choose YES. • NAT Keep Alive Enable: Choose YES (optional). SPA9000 Voice System Administration Guide 50