About  KeepAlive,  here  is  what  I found in a old TCP-IP NT5.0 white
paper from Microsoft.

TCP  Keep-alive Messages

A  TCP keep-alive packet is simply an ACK with the sequence number set
to  one  less  than  the current sequence number for the connection. A
host  receiving  one  of  these  ACKs will respond with an ACK for the
current  sequence  number.  Keep-alives can be used to verify that the
computer  at  the  remote  end of a connection is still available. TCP
keep-alives   can  be  sent  once  every  KeepAliveTime  (defaults  to
7,200,000 milliseconds or two hours), if no other data or higher level
keep-alives  have been carried over the TCP connection. If there is no
response  to a keep-alive, it is repeated once every KeepAliveInterval
seconds.  KeepAliveInterval  defaults  to 1 second. NetBT connections,
such  as  those  used  by  many  Microsoft networking components, send
NetBIOS  keep-alives  more  frequently, so normally no TCP keep-alives
will  be sent on a NetBIOS connection. TCP keep-alives are disabled by
default,  but  Windows  Sockets  applications  can  use the SetSockOpt
function to enable them.

Registry key start from :

Key: Tcpip\Parameters
Value Type: REG_DWORD-Time in milliseconds
Valid Range: 1-0xFFFFFFFF
Default: 1000 (one second)
Description: This parameter determines the interval between keep-alive
retransmissions  until  a  response  is  received.  Once a response is
received,  the  delay  until the next keep-alive transmission is again
controlled  by  the  value  of  KeepAliveTime.  The connection will be
aborted   after   the   number   of   retransmissions   specified   by
TcpMaxDataRetransmissions have gone unanswered.

Key: Tcpip\Parameters
Value Type: REG_DWORD-Time in milliseconds
Valid Range: 1-0xFFFFFFFF
Default: 7,200,000 (two hours)
Description:  The  parameter controls how often TCP attempts to verify
that  an  idle  connection  is  still  intact  by sending a keep-alive
packet.  If  the  remote system is still reachable and functioning, it
will  acknowledge  the keep-alive transmission. Keep-alive packets are
not sent by default. This feature may be enabled on a connection by an

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