SIP ALG is an option which is enabled on most modern routers by default, but unfortunately it can interfere with SIP and VoIP functionality. To disable SIP ALG on a Draytek router do the following:

1. open a telnet session to the IP address of the Draytek (usually 192.168.1.1)
2. to check if SIP ALG is currently enabled type ” sys sip_alg ? ” (without the ” ” obviously)
3. to disable SIP ALG type ” sys sip_alg 0 “
4. then to save the changes type ” sys commit “
5. then ” sys reboot “

If you cannot telnet to the router, check that telnet is enabled on the router via the web interface (usually 192.168.1.1) under ” Management “