Hi everyone,

I’m trying to learn how VoIP system works, mostly with trial and error, since I want to be prepared in case something doesn’t work in my company (small with 3 IP phones) and to counteract slow provider assistance.

I have a Aethra BG device from my ISP that gives internet connection to all my network, to which my IP phones are connected to. I use an on cloud voice system from my provider, I have SIP credentials for my phones and I also know my provider DNS.

So I’ve been able to configure new phones and now I’d like to be ISP devices indipendent. I mean I’d like as first thing to be able to use a backup internet connection , for example a mobile modem with SIM card, to let my phones receive and make calls when the main connection has got issues.

I tried and the phones register correctly, they also are able to make a call that rings on the receiver, but the conversation never begins. In Wireshark I saw that the INVITE request is sent and sometimes the response is “Trying” and other times is “Proxy Authentication Required”.

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Is my idea feasible or there something that is configured on the ISP device that force all my SIP traffic to pass onto it in order to make my phone work?

Thanks!