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<body><p style="margin-top:0;margin-bottom:0;margin-left:0;margin-right:0;">Using latest flatpak for Linux.</p>
<br /><p style="margin-top:0;margin-bottom:0;margin-left:0;margin-right:0;">Caller on sip2sip.info calls subscriber at a different domain. Callee answers and dialog is established. So far all good.</p>
<br /><p style="margin-top:0;margin-bottom:0;margin-left:0;margin-right:0;">Caller does a re-invite ( hold ). The callee's UA sends 20OK. Caller's UA sends ACK. ACK never arrives. Callee's UA continues sending 200OK.</p>
<br /><p style="margin-top:0;margin-bottom:0;margin-left:0;margin-right:0;">Callee is registered as GRUU. Incoming requests are normally translated by the local registrar and the request is forwarded to the callee's IP address. This also applies to re-INVITE and its ACK. The caller learns the registrar's address from the Contact it previously received in the initial 200OK.</p>
<br /><p style="margin-top:0;margin-bottom:0;margin-left:0;margin-right:0;">Summary of in-dialog requests</p>
<p style="margin-top:0;margin-bottom:0;margin-left:0;margin-right:0;">Initiial ACK - OK</p>
<p style="margin-top:0;margin-bottom:0;margin-left:0;margin-right:0;">re-InVITE - OK</p>
<p style="margin-top:0;margin-bottom:0;margin-left:0;margin-right:0;">second ACK - doesn't arrive</p>
<p style="margin-top:0;margin-bottom:0;margin-left:0;margin-right:0;">Bye - doesn't arrive</p>
<br /><p style="margin-top:0;margin-bottom:0;margin-left:0;margin-right:0;">An important detail - Registrar/Proxy is behind NAT. Router use DMZ forwarding.</p>
<br /><p style="margin-top:0;margin-bottom:0;margin-left:0;margin-right:0;">The request URI of the ACK following re-INVITE is pointing at the external address of the registrar but the ACK was received at a private address. The ACK is forwarded to the external address. It never reaches the registrar because the router cannot hairpin the forwarded message.</p>
<br /><p style="margin-top:0;margin-bottom:0;margin-left:0;margin-right:0;"><span style="background-color:#ffffff;"><strong><span style="font-family:monospace;"><span style="color:#000000;">ACK sip:8@</span><span style="color:#ff0000;">external-address</span><span style="color:#000000;">:5060;gr=urn:uuid:38ee02db-f267-4dd9-9077-1b9d4fcfbf00 SIP/2.0</span></span></strong><span style="color:#000000;"> </span></span><br /><span style="background-color:#ffffff;"><span style="color:#000000;"> <strong>Record-Route: <sip:212.95.45.179;lr;ftag=803fbe29-6196-4af7-9771-db7d25007e6c></strong> </span></span><br /><span style="background-color:#ffffff;"><span style="color:#000000;"> <strong>Record-Route: <sip:174.142.205.46;r2=on;lr;ftag=803fbe29-6196-4af7-9771-db7d25007e6c></strong> </span></span><br /><span style="background-color:#ffffff;"><span style="color:#000000;"> <strong>Record-Route: <sip:174.142.205.46;transport=tcp;r2=on;lr;ftag=803fbe29-6196-4af7-9771-db7d25007e6c></strong> </span></span><br /><span style="background-color:#ffffff;"><span style="color:#000000;"> <strong>Via: SIP/2.0/UDP 212.95.45.179:5060;branch=z9hG4bK45c1.804d44d2.2</strong> </span></span><br /><span style="background-color:#ffffff;"><span style="color:#000000;"> <strong>Via: SIP/2.0/UDP 174.142.205.46:5060;branch=z9hG4bK45c1.ab795fa4.2;i=d0969e07</strong> </span></span><br /><span style="background-color:#ffffff;"><span style="color:#000000;"> <strong>Via: SIP/2.0/TCP 192.168.1.3:58491;received=external-address;rport=58491;branch=z9hG4bKPj62eb9faf-6eba-4f91-9539-8b2954cad94a;a</strong></span></span><br /><span style="background-color:#ffffff;"><span style="color:#000000;"><strong>lias</strong></span></span><br /></p>
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