Learn how the Session Initiation Protocol (SIP) and Application Layer Gateway (ALG) settings affect your VoIP phone system's call quality and reliability. This guide covers key aspects of SIP ALG, its impact on VoIP systems, and how to optimise your router settings for better performance.
What is SIP ALG?
SIP (Session Initiation Protocol) ALG (Application Layer Gateway) is an application within many routers. It inspects any VoIP traffic to prevent problems caused by firewalls and, if necessary, modifies the VoIP packets. Routers will often have SIP ALG activated by default.
Should I turn SIP ALG off?
You should disable SIP ALG because it: Interrupts SIP traffic like calls and conferencing apps. Affects the perceived reliability of desk phones and VoIP apps.
Isn’t needed when using cloud-based VoIP providers.
Please note: This does not apply to third-party routers, only bOnline purchased routers. Third-party routers may not be checked and you(the owner) may need to contact your Internet Service Provider.
How to disable SIP ALG on the Zyxel VMG1312-B10D:
Navigate to 'Network Setting' and click 'NAT'.
Click the 'ALG' tab to toggle between 'Enable' and 'Disable'.
How to disable SIP ALG on the Zyxel – VMG1312-T20B:
Navigate to 'Network Setting' and click 'NAT'.
Click the 'ALG' tab to toggle between 'Enable' and 'Disable'.
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