Method and apparatus for supervising access and protecting against unauthorized access in a communication metwork

A method for supervising access and protecting against unauthorized access in message networks whereby information in the form of messages is transmitted over a network having a plurality of stations and a central supervision device configured to receive each of the messages transmitted on the network and a particular portion of the information contained in the message is employed for supervising the right-of-access at the message receiver, said method comprising the steps of:

• generating, at a first station, a message destined for a second station, said first station message including signals indicating a right of access of said first station with other stations in the network;
• transmitting said first station message over the network;
• intercepting said transmitted first station message at said central supervision device;
• comparing said transmitted first station message right of access signals with supervisory signals stored in a table in said central supervision device indicative of authorized access to said second station;
• generating cancellation signals if said comparison indicates that access to said second station is unauthorized;
• transmitting said cancellation signals to said second station;
• halting execution of said transmitted first station message by said second station upon receipt of said cancellation signals;
• and
• beginning the comparison of the right-of-access by means of the central supervision device (SV) during the transmission of a message and terminating said comparison before the end of the message, and in the case of an unauthorized access the central supervision device (SV) editing a portion of said transmitted message to guarantee its non-effectiveness.