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 0and 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)
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More Information
For more about this issue, visit the Zyxel website.
