Whilst on an active SIP or VoIP Call, the ALG's modification of data packets can be problematic, especially given its poor implementation on most commercial routers. While ALG aims to enhance connection clarity, its erratic packet modifications often result in the opposite effect.

Every time the system confirms and acknowledges a connection attempt, the ALG alters the SIP packets being transmitted. This is due to the conversion from private to public IP addresses and ports being handled by scripting. Scripting can be risky—sometimes, crucial parts of the message are lost during translation. This can impact VoIP calls in several ways:

• Lost Connections: Entire calls can be dropped due to this router service. When data is lost and unrecoverable, disconnections are common.

• Reduction in Call Quality: Packet loss during internet-based calls can cause static, sound lapses, or echoing. Modifying the call data degrades transmission or reception quality.

• One-Way Audio: If you can hear the other party but they can't hear you, it's typically due to poor firewall settings or ALG modifying packets, resulting in audio loss on one end.

• Failed Registrations: Multiple acknowledgments are required during a call. If any fail, the call won't connect, leading to a failed registration, often caused by SIP ALG operating in the background.

With SIP calls, there's a higher chance of incorrect data packet modifications, adversely affecting call quality. Fortunately, disabling the router service is usually straightforward via the router's web interface. If this feature isn't available on your device, consider upgrading to a new router.