Your VoIP system should be configured to register with the server. This would maintain the link.

I'm not sure what client/server you're using, but there may be a time, timeout or keepalive (etc.) setting in the configuration options for the Callcentric service.

If you are configured to receive blind SIP calls/packets into your Public IP at udp/5060 or something, Carrier Grade NAT would hinder that method.

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- KB3VWG