Detecting and Disabling SIP ALG

What is SIP ALG?

A SIP Application Layer Gateway (ALG) is meant to improve connections between local VoIP devices and a Cloud-based service by managing SIP messages. 

Despite its intended benefits for VoIP calls and NAT issues, SIP ALGs frequently create more problems than they solve. Additionally, the lack of standardization results in unpredictable modifications to SIP packets, causing an unreliable VoIP calling experience.

Symptoms of SIP ALG

The following are typically symptoms of SIP ALG:

No audio or one-way audio

Phones not ringing

Dropped calls

BLF keys not working

Detecting and Disabling SIP ALG

The quickest way is to check your modem or router’s configuration page to see if SIP ALG is enabled.

Alternatively (but less reliably), do a search for “SIP ALG detector” and try a web test. Here is one from Visualware. To ensure accurate results, run the test from a PC on the same network as the affected VoIP device.

You will need to consult the manual for your modem, router, or managed switched for the proper steps to disable SIP ALG, as each hardware is different.