Cisco SPA2102-SF Administration Guide - Page 48

Configuring Your System for ITSP Interoperability Network Address Translation (NAT) and Voice over IP (VoIP) 3 NAT Mapping with Session Border Controller It is strongly recommended that you choose an ITSP that supports NAT mapping through a Session Border Controller. With NAT mapping provided by the ITSP, you have more choices in selecting a router. NAT Mapping with SIP-ALG Router If the ITSP network does not provide a Session Border Controller functionality, you can achieve NAT mapping by using a router that has a SIP ALG (Application Layer Gateway). The WRV200 router is recommended for this purpose, although any router with a SIP-ALG can be used. By using a SIP-ALG router, you have more choices in selecting an ITSP. Configuring NAT Mapping with a Static IP Address If the ITSP network does not provide a Session Border Controller functionality, and if other requirements are met, you can configure NAT mapping to ensure interoperability with the ITSP. Requirements: • You must have an external (public) IP address that is static. • The NAT mechanism used in the router must be symmetric. See "Determining the Router's NAT Mechanism," on page 52. • 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. Cisco Small Business ATA Administration Guide 48