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User agents may send from time to STUN packets and process the
answer to check if the IP address has changed. In this case, the user
agent may refresh the SIP binding.
A user agent that supports this way of refreshing the bindings
includes a “P-NAT-Refresh” header in the REGISTER message:
REGISTER sip:snom.com SIP/2.0
Via: SIP/2.0/UDP 192.168.1.10:5060;branch=z9hG4bK-fozdn9kbolfw
From: “Karl Klammer” <sip:[email protected]>;tag=9e9mynnnwa
To: “ Karl Klammer” <sip:[email protected]>
Call-ID: 10f2c240790b-cj4sy7drgp6q@192-168-1-10
CSeq: 2 REGISTER
Max-Forwards: 70
Contact: <sip:[email protected]:5060;line=5zy4hsui>;q=0.7
User-Agent: snom200-2.05h
P-NAT-Refresh: 15
Supported: gruu
Expires: 86400
Content-Length: 0
The NAT Filter will answer this request with a P-NAT-Header:
SIP/2.0 200 Ok
Via: SIP/2.0/UDP 192.168.1.10:5060;branch=z9hG4bK-iu90avx18fc6;rport
=34142;received=217.231.163.127
From: “Karl Klammer” <sip:[email protected]>;tag=9e9mynnnwa
To: “Karl Klammer” <sip:[email protected]>;tag=996wctfnen
Call-ID: 2605c340c91d-cj4sy7drgp6q@192-168-1-10
CSeq: 2 REGISTER
Contact: <sip:[email protected]:5060;line=5zy4hsui>;expires=3600;gruu=
”sip:[email protected];gruu=5npko91p”
Server: snom proxy (Unix) 2.42.7
Date: Sun, 06 Jun 2004 11:50:22 GMT
P-NAT-Refresh: 15
Content-Length: 0
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