Patent ID: 8176532

Claim:
Apparatus for interacting with a physical plant comprising: a programmable control unit for connecting to said physical plant and for performing a supervisory function for said physical plant, said programmable control unit having a public network interface for communicating with remote computer systems; a user computer system located remotely from said programmable control unit; a front-end security gateway located remotely from said programmable control unit, wherein said front-end security gateway communicates with said user computer system to authenticate and authorize a user for access to said programmable control unit, and wherein said front-end security gateway forwards messages between said user computer system and said programmable control unit after said user is authenticated and authorized; a public communication network coupled between said front-end security gateway and said programmable control unit to carry said forwarded messages, wherein said public communication network comprises a public switched telephone network; and a routing control configured to allow communication with said programmable control unit only by said front-end security gateway, wherein said routing control comprises a telephone switching system configured to provide an originating call restriction for a first telephone number at which said programmable control unit interfaces to said public switched telephone network so that telephone calls are accepted from a second telephone number corresponding to an interface of said front-end security gateway to said public switched telephone network and telephone calls from other telephone numbers are blocked.