Use keep-alives.
Value: KeepAlive
Syntax
SocketOptionName KeepAlive
Requirements
Namespace: System.Net.Sockets
Assembly: System (in System.dll)
Assembly Versions: 1.0.5000.0, 2.0.0.0, 4.0.0.0
Assembly: System (in System.dll)
Assembly Versions: 1.0.5000.0, 2.0.0.0, 4.0.0.0