Cisco Systems SPA9000 manual Network Address Translation NAT and Voice over IP VoIP

Configuring Your System for ITSP Interoperability	3
Network Address Translation (NAT) and Voice over IP (VoIP)

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 49

•“NAT Mapping with SIP-ALG Router,” on page 49

•“Configuring NAT Mapping with a Static IP Address,” on page 49

•“Configuring NAT Mapping with STUN,” on page 51

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.

SPA9000 Voice System Administration Guide 49