This could be an idle time out setting in the Proxy Server. Use the Software with the Command Port cable to check this setting. Make sure it is disabled. If it is disabled, then it comes down to idle time out in the modem or something else that would cause the modem itself to drop the connection. Line conditions can get bad enough to drop calls too. You can test connections by taking the Proxy Server out of the picture and placing a modem on your computer com port to see if it is ever disconnected.