Prestige 2000W_V2 User’s Guide
Figure 25 Symmetric NAT
12.12 NAT and SIP
Some NAT routers are not
The Prestige must register its public IP address with a SIP register server. If there is a NAT router between the Prestige and the SIP register server, the Prestige probably has a private IP address. The Prestige lists its IP address in the SIP message that it sends to the SIP register server. NAT does not translate this IP address in the SIP message. The SIP register server gets the Prestige’s IP address from inside the SIP message and maps it to your SIP identity. If the Prestige has a private IP address listed in the SIP message, the SIP server cannot map it to your SIP identity.
A SIP ALG (Application Layer Gateway), the fake WAN address on SIP and RTP, STUN, or outbound proxy features allow the Prestige to use its public IP address in the SIP messages.
12.12.1 SIP ALG
Some NAT routers may include a SIP Application Layer Gateway (ALG). A SIP ALG allows SIP calls to pass through NAT by examining and translating IP addresses embedded in the data stream. When the Prestige registers with the SIP register server, the SIP ALG translates the Prestige’s private IP address inside the SIP data stream to a public IP address. You do not need to use STUN or an outbound proxy if your Prestige is behind a SIP ALG.
12.12.2 Fake WAN Address on SIP and RTP
If you know the NAT router’s public IP address and SIP port number, you can use the fake WAN address on SIP and RTP feature to manually configure the Prestige to use a them in the SIP messages. This eliminates the need for STUN or a SIP ALG.
You must also configure the NAT router to forward traffic with the SIP port number to the Prestige.
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