Difference between revisions of "VoIP NAT"

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[quality revision][quality revision]
(Start entering a SIP trace)
(Add the SIP trace of the server response)
The bold text shows the IP address and port number that the phone is listening on - telling the far end where to send audio.
The server replies:
SIP/2.0 100 Trying
SIP/2.0 183 Session progress
From: "aaisp" <sip:+442083xxxxxx@voiceless.aa.net.uk>;tag=xidd3faqpi
To: <sip:07973xxxxxx@voiceless.aa.net.uk;user=phone>;tag=2020111412411300003
Server: FireBrick/1.54.153
Content-Type: application/sdp
o=- 31466 0 IN IP4 ''''''
c=IN IP4 ''''''
m=audio '''31466''' RTP/AVP 8 101
a=rtpmap:8 pcma/8000
So again the bold text tells the phone the IP address and port number to send the audio to.
The section below on "Why is SIP a problem" explains how NAT breaks things.