SI-60/SI-65/SI-60F is not able to know when the LAN cable is removed by TCP/IP connection. Furthermore, SI-60/65/60F acts normal and keep the LAN communications. TCP/IP with one to one connection type will not accept the connection from others, unless you set “Keepalive” setting. SI-60/65/60F will cut the LAN connection if there is no response after seven times of sending “Keepalive” packets. (Default interval is 45secounds). To change the “Keepalive” setting, use the Telnet and connect to “9999” port and go to “set-up” mode. (Refer to the instruction manual”). Select “5: Expert” and change at “TCP Keepalive time in s (1s - 65s; 0s=disable):  (45)?”. (Note: shorter time will cut the communications faster. However, “Keepalive “ packets will be sent very often).