Thanks Greg, for the following description from MS website.
Two per-interface registry settings under the key \HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Tcpip\Parameters control the behavior of TCP/IP keep-alives:
The KeepAliveTime value specifies how long the TCP connection sits idle, with no traffic, before TCP sends a keep-alive packet. The default is 7,200,000 milliseconds (ms) or 2 hours.
The KeepAliveInterval value indicates how many milliseconds to wait for a response after sending a keep-alive before repeating the keep-alive. If no response is received, the TCP/IP stack continues sending
keep-alives at this interval until a response is received or until the stack reaches the packet retry limit specified in the TCPMaxDataRetransmissions registry key. KeepAliveInterval defaults to 1 second (1000 ms).