Linksys RTP300 User Guide - Page 38

Configuring Your System for ITSP Interoperability 3 Network Address Translation (NAT) and Voice over IP (VoIP) Configuring Your System for ITSP Interoperability This chapter provides configuration details for the purpose of helping you to ensure that your infrastructure properly supports voice services. • "Network Address Translation (NAT) and Voice over IP (VoIP)," on page 38 • "Firewalls and SIP," on page 42 • "Configuring SIP Timer Values," on page 43 Network Address Translation (NAT) and Voice over IP (VoIP) NAT is a function that allows multiple devices to share the same public, routable, IP address to establish connections over the Internet. NAT is present in many broadband access devices to translate public and private IP addresses. To enable VoIP to co-exist with NAT, some form of NAT traversal is required. 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," on page 38 • "NAT Mapping with SIP-ALG Router," on page 38 • "Configuring NAT Mapping with a Static IP Address," on page 39 • "Configuring NAT Mapping with STUN," on page 40 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 Linksys 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. Linksys ATA Administration Guide 38