The Session layer is responsible for connection negotiation and
   establishment.  The Session Control module performs the following functions:

     o  Manages transport connections on behalf of Session Control users.

     o  Enforces access control policies to restrict communication between users
        and between Session Control modules.

     o  Maps from a DNA Naming Service object name to protocols and addresses.

     o  Selects from the set of protocols supporting Session Control to attempt
        connection establishment.

     o  Maintains in the namespace the protocol and address information
        corresponding to objects that reside in the same node as the local
        Session Control module.

   The hierarchy of Session Control Module Entities is shown with indentation
   as follows:

                                Session Control
                                    Applications
                                    Ports
                                    Tower Maintenance
                                    Transport service
                                    Backtranslation softlink

   The Session Control entity is the top-level entity in the hierarchy of
   entities belonging to the Session Control module.