Linksys SPA922 Cisco SPA9000 Voice System Web-UI Based Product Installation an - Page 39
NAT Mapping, SPA9000 Voice System Administration Guide, SPA9000 Voice System, Administration Guide
UPC - 745883570836
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Preparation Network Setup Review 3 NAT Mapping Network Address Translation (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 SIP-ALG router: Use a router such as the WRV200, which has a SIP ALG (Application Layer Gateway). With a SIP ALG in the router, you have more choices in selecting an ITSP. • 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 the SPA9000 EXT IP setting: Configuring NAT mapping in the SPA9000 is recommended only if the ITSP network does not provide a Session Border Controller functionality. If this is the case, and if the external (public) IP address is static, then Cisco recommends mapping a static (permanent) IP address on the SPA9000. Instructions are available in the SPA9000 Voice System Administration Guide. • Configuring NAT Mapping with Simple Traversal of UDP through NAT (STUN): Configuring NAT mapping in the SPA9000 is recommended only if the ITSP network does not provide a Session Border Controller functionality. If this is the case, and if the external (Public) IP address is assigned dynamically by the network (and the router uses asymmetric NAT mechanism), it is possible to use STUN as a mechanism to discover the NAT mapping in SPA9000. This method is considered a practice of last resort and should be used only if the other methods are unavailable. For more information, see the SPA9000 Voice System Administration Guide. SPA9000 Voice System Installation and Configuration Guide for Web UI 37