Many WAN connections can vary in quality and latency, and often times these two characteristics will manifest themselves in disconnected terminal services sessions. By doing two relatively easy registry hacks, you can reduce these disconnects and improve the overall experience of your users.
In the registry at HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server, create or edit the DWORD value of KeepAliveEnable and set it to 1. This will turn Keep Alives on. This will serve to stabilize the connection by sending ‘heartbeat’ packets to the client every so often. This will cause an idle connection to be probed every so often just to be sure that the connection is still alive and that the client is still listening on the other side. This will also help prevent disconnects by preventing network devices from killing off sockets that it assumes to be idle. By turning on Keep Alives, the connection will not appear idle, and therefore the network device will not attempt to terminate the socket.
Two other registry entries to look at are at HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\KeepAliveInterval and HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\KeepAliveTime. KeepAliveInterval determines the interval separating keep alive retransmissions until a response is received. If a response is received, the delay until the next keep alive transmission is again controlled by the value of KeepAliveTime. KeepAliveTime 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.
In the registry at HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters, create or edit the DWORD value of TcpMaxDataRetransmissions. By default it is set to 5, but I would recommend doubling that value, to 10. The value of TcpMaxDataRetransmissions is the number of times TCP retransmits an unacknowledged data segment on an existing connection. TCP retransmits data segments until they are acknowledged or until this value expires.