A multi-level security apparatus and method for a network employs a secure network interface unit (SNIU) coupled between each host or user computer unit and a network, and a security management (SM) architecture, including a security manager (SM) coupled to the network, for controlling the operation...http://www.google.com/patents/US5577209?utm_source=gb-gplus-sharePatent US5577209 - Apparatus and method for providing multi-level security for communication among computers and terminals on a network
