Issue with keep server of radius on

When I use "radiusd -X" command in TeraTerm on remote pc to start up the server of radius, If I keep the TeraTerm openning, the radius server can work well, it means that the client can receive response of request well. But if I close the TeraTerm, then the client can not receive response of request any longer. How can I solve this problem or how can I keep the radius server on whenever the TeraTerm is openning or closing.