VoIP Phones - Disabling SIP ALG

SIP ALG modifies VoIP traffic (packets) and is enabled by default on many routers. When implemented correctly, SIP ALG modifies specific IP addresses in these packets, changing them from your local IP address to your public IP address. Unfortunately, in many routers it is poorly implemented and, instead of replacing only the specific IP addresses that need to be replaced, it replaces all of them, which then breaks SIP signalling. This poor implementation of SIP ALG can cause several issues, such as:

• Calls dropping after a set period of time
• Calls dropping when trying to retrieve the call from hold
• Calls dropping when being transferred
• Calls not being received
• Unable to make outbound calls
• Calls with no audio
• Calls with one way audio
• Other extensions continue ringing after a call has been answered

Not all routers offer the option to disable SIP ALG, some of the most popular routers are listed below.

This list is not extensive, so if your router is not listed here, try typing the make and model of your router, followed by the phrase disable  SIP ALG, into Google.

Best Solution: Disable SIP ALG On Router