What is SIP ALG?
SIP ALG (Application Layer Gateway) is common in many commercial routers. It prevents some of the problems caused by router firewalls by inspecting VoIP traffic (packets) and if necessary, it makes modifications.
Many routers have SIP ALG turned on by default.
How can it affect VoIP?
Even though SIP ALG is intended to assist users who have phones on private IP addresses, in many cases it actually causes more problems than it solves. SIP ALG may modify SIP packets in unexpected ways, corrupting them and making them unreadable. This can lead to unexpected behavior, such as phones not registering, incoming calls failing and call drops.
Please also refer to the attached PDF file.
We strongly advise you to disable SIP ALG. If it is not possible, for example, there is no access to the router settings, or it simply does not support its disabling, you can try two options:
* Use a non-standard local SIP port;
* Use a non-standard server SIP port.
In the CPE profile it may look like this:
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(1221 is an additional UDP port enabled by default for your node).
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