Linksys WIP310 SPA500 Series and WIP310 IP Phone Administration Guide - Page 116

Configuring SIP, SPCP, and NAT Network Address Translation (NAT) and Cisco IP Phones 4 Some ITSPs provide NAT traversal, but some do not. If your ITSP does not provide NAT traversal, you have several options. • NAT Mapping with Session Border Controller, page 105 • NAT Mapping with SIP-ALG Router, page 105 • Configuring NAT Mapping with a Static IP Address, page 105 • Configuring NAT Mapping with STUN, page 106 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). 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 Whether the Router Uses Symmetric or Asymmetric NAT," on page 108. NOTE Use NAT mapping only if the ITSP network does not provide a Session Border Controller functionality. Cisco SPA 500 Series and WIP310 IP Phone Administration Guide 105