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Two incoming SIP calls at once on SV9100

conxtel

Technical User
May 12, 2014
141
CA
I have a customer that is on Starlink internet and we are attempting to set up SIP trunks and move them off their PRI.

Outbound calling is working ok but customer had to enable SIP ALG on their Fortinet firewall to get that working. Seems odd as every other time, we have always disabled SIP ALG.

The issue though is with incoming. When we make a test call, the phone will ring, but when we try to answer it, the phone keeps ringing and there is no audio. You hang up and grab the second ringing call, you can answer no problem. For some reason it is like the SIP provider is trying to send the call twice but only the second call is a valid call. They say the PBX is not responding to the first INVITE request.

Not sure if it is a firewall, phone system or provider issue at this point.
 
who is the SIP provider ? Starlink doesnt support static WAN IP addresses far as I know so could be a NAT issue .
 
Would need a PCAP trace in order to find the issue but one thing springs to mind is double NAT, have that issue sometimes with LTE and enabling SIP ALG somehow alleviates that but will cause other issues like ghost ringing.
 
How is the SIP authenticating?
Who is the SIP provider?
Are you UK?
We have a Pana NS700 working successfully and an NEC SL2100 working on Starlink but both Starlinks are set to have a Static IP.
Do you have all the correct ports open in FW?
NAT Traversal may need disabling or enabling.
 

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