Figure 101 and Figure 102 show a SIP call INVITE and 200 OK. In Figure 101, ph1 sends a SIP INVITE message to ph2. Note how the IP addresses in the header fields—shown in bold font—are translated by the J-series device.
The SDP section of the INVITE message indicates where the caller is willing to receive media. Note that the Media Pinhole contains two port numbers, 52002 and 52003, for RTCP and RTP. The Via/Contact Pinhole provides port number 5060 for SIP signaling.
Observe how, in the 200 OK response message in Figure 102, the translations performed in the INVITE message are reversed. The IP addresses in this message, being public, are not translated, but gates are opened to allow the media stream access to the private network.
Figure 101: SIP NAT Scenario 1
Figure 102: SIP NAT Scenario 2
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