If you're experiencing call dropouts at exactly 30 seconds, it's likely due to issues with SIP-ALG (Session Initiation Protocol Application Layer Gateway) in your modem-router. SIP-ALG is intended to assist with SIP traffic by modifying packets as they pass through the router. However, it often causes problems instead of solving them, particularly by interfering with the proper functioning of SIP, especially with the "200 OK" and "ACK" messages, which are crucial for maintaining the call session.

When SIP-ALG is enabled, it can incorrectly modify these SIP messages, leading to a failure in the acknowledgment process needed to keep the call active. This often results in calls being dropped exactly 30 seconds into the conversation, as the system assumes the session has failed when it doesn't receive the expected responses.

By turning off SIP-ALG, you allow SIP traffic to pass through the router unmodified, ensuring the necessary signaling between the SIP endpoints occurs correctly. This typically resolves the issue of 30-second call dropouts, providing a more stable and reliable call experience.

Due to the thousands of different modems and routers available, we strongly recommend searching for your specific model number online to find instructions on how to disable SIP-ALG.