[VB6] Chat client ping pong problem, keep losing connections

I have a chat client that has multiple user connected at once. After all users have been idle for about 10 minutes or so they all lose connection to the server. How do I fix this issue? I have the server ping every connected user every 6 minutes and the user side listens to the ping request and sends back a "!PONG!" request. By the way, I'm using winsock with vb6.

Thank you,
Joe621