• You cannot be contacted from an external location.
• A ringing tone can be heard at the remote site, but you are unable to hear any speech.
• Ringing continues at the called party, although you have already hung up.
• The call is disrupted after 6-12 seconds.
• You can dial a number but are unable to hear ringing.
• It is not possible to hold a conversation when the call is answered.

These errors cannot be reproduced and sometimes only occur after hours or days. In many cases, you can resolve these problems by means of a firmware update to the router. Please contact your router manufacturer in this regard. If the problem persists, activate the transfer of the following ports to your router/firewall: Port: 5060 / UDP (SIP signalling) Port: 3478 UDP (STUN).  UPnP: If your router supports UPnP (Universal Plug and Play), it could be helpful as a final step to activate / deactivate this option. If these measures are unsuccessful, you still have an option to use our STUN  server. To do so, enter "stun.sipkom.com" as the STUN server (port 3478). If these measures are unsuccessful, the only option available is to assign a fixed IP address to the SIP terminal device.