Understanding SIP and ALG Settings for VoIP Phone Systems
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 built into many routers. It inspects VoIP traffic to prevent problems caused by firewalls and, where necessary, modifies VoIP packets. Most routers have SIP ALG activated by default.
Should I turn SIP ALG off?
Yes. You should disable SIP ALG because it can cause the following problems:
- It interrupts SIP traffic, including calls and conferencing applications.
- It affects the perceived reliability of desk phones and VoIP apps.
- It is not 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.
- Toggle the setting to Disable.
How to disable SIP ALG on the Zyxel VMG1312-T20B
- Navigate to Network Setting and click NAT.
- Click the ALG tab.
- Toggle the setting to Disable.
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