Why am I not reachable sporadically?

Cause: The firewall (router) does not forward the IP packets to the telephone system.

Various routers block the transmission of incoming UDP packets after a defined period of inactivity (e.g. Cisco after 30 seconds by default). As a result, access to your telephone system is blocked from the IP address of our telephone server.  Incoming calls are no longer forwarded to the telephone system. The firewall is reopened when an action to our telephone server is established from the internal network, e.g. a new outgoing call, a registration or a NAT keep alive.

There are various ways to open the firewall or keep it open permanently:

Put sip.easybell.de on the whitelist in your firewall. Please do not enter the IP address of our telephone servers in the firewall, as this can change.

If whitelist is not possible, research the UDP timeout of your firewall. Increase the UDP timeout until it exceeds the duration of the registration or NAT keep alive.

If the UDP timeout cannot be increased, reduce the NAT keep alive until it is below the UDP timeout.

If all of the above measures are not possible, reduce the register duration. Please note that the re-register must not be less than 600 seconds.