[Freeswitch-users] Outbound ESL issue

Hi all: I have a outbound ESL app to control the incoming calls. When one call income, the app joins the caller and 3 other callees to a conference. but when the caller hangup, then the connection between app and FS will break. It means that the app can not control the conference any more. It is not what I expect. Is there any method to control the connection not to break?