In case your SNOM will not register at your FritzBox
just try this:
Open your Identity Setting Page
Go to "Outbound Proxy" and enter FQDN_or_IP_of_server;transport=tcp
i.e. fritz.box;transport=tcp
just try this:
Open your Identity Setting Page
Go to "Outbound Proxy" and enter FQDN_or_IP_of_server;transport=tcp
i.e. fritz.box;transport=tcp