ZyXEL 660

Disable SIP ALG

SIP ALG is enabled by default in this series of Zyxel routers. This prevents incoming calls from being received. It may also cause half of all outgoing calls to fail. These issues can be resolved by disabling SIP ALG in the router.

Disabling SIP ALG

Ensure that the computer is connected to the modem.

Open a command line:

• Windows: Start -> Run -> type cmd -> press enter
• OS X: CMD+space -> type terminal -> press enter

Type the following in the command line:

telnet <IP-of-the-router> and press enter.

If successful, a menu will appear.

• Select option "24. System Maintenance" in the menu.
• Then select option "8. Command Interpreter Mode".
• Type ip nat service sip active 0 and press enter.
• Once the modem restarts, you can test if VoIP is working.

Other Settings

• Disable SIP Transformations.
• Enable SIP inactivity timeout. (Media timeout: 600 / Signaling timeout: 7200 / Ports: 5060 + 5061)

More Information

For more about this issue, visit the Zyxel website.

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