Detecting and disabling SIP ALG
What is SIP ALG?
Section titled “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 the intent, SIP ALGs frequently create more problems than they solve. There is no standardisation, so they modify SIP packets unpredictably, producing an unreliable calling experience.
Symptoms of SIP ALG
Section titled “Symptoms of SIP ALG”- No audio or one-way audio
- Phones not ringing
- Dropped calls
- BLF keys not working
Detecting and disabling SIP ALG
Section titled “Detecting and disabling SIP ALG”The quickest way is to check your modem or router’s configuration page to see whether SIP ALG is enabled.
Alternatively — though less reliably — search for a “SIP ALG detector” and try a web test. Here is one from Visualware.