Two incoming SIP calls at once on SV9100

[conxtel]

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.

 

[Dosser1886]

who is the SIP provider ? Starlink doesnt support static WAN IP addresses far as I know so could be a NAT issue .

 

[daddybadger]

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.

 

[Jonah29]

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.

 

[DoubleDriveLine]

who is the SIP provider ? Starlink doesnt support static WAN IP addresses far as I know so could be a NAT issue .

Looks like they support static IPs on a Business account now. You still cannot get one with a residential account.

@conxtel

Not knowing much about Starlink hardware on a business account myself one thing you may want to look at is the Starlink Router. Is there one and if so it will be acting as a firewall also. That would put the Fortinet firewall behind the Starlink firewall and that will cause issues. If their Starlink hardware includes a router it should probably be setup to DMZ all traffic to the Fortinet firewall.

You are correct SIP ALG should only cause problems and maybe that is why you are seeing the results as they are.

 

[Jonah29]

You can get a Static IP on resi but you have to get the Priority 40gb package although this has very recently been changed to Local Priority, still gives a Static IP though.

The Starlink Router should be set to Bypass mode if they are using the Fortinet FW. I assumed they already know this as it is kind of working.