Can't give you specific informations, because i don't know the tools you and your clients are using. However, TCP sockets have a timeout, but could be configured as keep - alive, which disables this timeout. Your VPN may also have a timeout, ie. a max session timeout or idle time.
I only understood that anita is a terminal program which is used by the client. He needs this to make hardcopies of the terminal output on a printer on his side. The ERP application is accessed by this anita via a VPN connection. The ERP application is installed on an Red Hat Server. Is this correct?