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In the following example, you want to use client device A to call someone who is
using client device C.
The client device (A in the figure) sends a call invitation to the SIP proxy server
1
(B).
The SIP proxy server forwards the call invitation to C.
2
Figure 67 SIP Proxy Server
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.
The WiMAX Device (A) sends SIP packets to the STUN server (B).
1
The STUN server (B) finds the public IP address and port number that the NAT
2
router used on the WiMAX Device's SIP packets and sends them to the WiMAX
Device.
The WiMAX Device uses the public IP address and port number in the SIP packets
3
that it sends to the SIP server (C).
Figure 68 STUN
MAX318M2W User's Guide
B
1
A
A
Chapter 10 The VoIP Account Screens
2
C
NAT
1
2
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