ZyXEL MAX-306 User Guide - Page 151
Advanced SIP Settings
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Chapter 12 The Service Configuration Screens 12.2.1 Advanced SIP Settings This section describes the features of the Advanced SIP settings screen. 12.2.1.1 STUN STUN (Simple Traversal of User Datagram Protocol (UDP) through Network Address Translators) allows the WiMAX Device to find the presence and types of NAT routers and/or firewalls between it and the public Internet. STUN also allows the WiMAX Device to find the public IP address that NAT assigned, so the WiMAX Device can embed it in the SIP data stream. STUN does not work with symmetric NAT routers or firewalls. See RFC 3489 for details on STUN. The following figure shows how STUN works. 1 The WiMAX Device (A) sends SIP packets to the STUN server (B). 2 The STUN server (B) finds the public IP address and port number that the NAT router used on the WiMAX Device's SIP packets and sends them to the WiMAX Device. 3 The WiMAX Device uses the public IP address and port number in the SIP packets that it sends to the SIP server (C). Figure 70 STUN 1 B NAT C A 12.2.1.2 Outbound Proxy Your VoIP service provider may host a SIP outbound proxy server to handle all of the WiMAX Device's VoIP traffic. This allows the WiMAX Device to work with any type of NAT router and eliminates the need for STUN or a SIP ALG. Turn off a SIP ALG on a NAT router in front of the WiMAX Device to keep it from re-translating the IP address (since this is already handled by the outbound proxy server). User's Guide 151