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Chapter 12 The Service Configuration Screens
User’s Guide
151
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
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).
A
B
C
NAT
1