Abstract: In a wireless local area network system including a server and a plurality of mobile wireless stations, the server maintains a table of stations active in the network system and monitors the transmission activity of the stations. If no activity is detected from a station for a predetermined time, a series of watchdog messages is sent requesting a response from that station. The stations are battery powered and operate in an "AWAKE" state to receive or transmit messages or in a SLEEP state of low power consumption. The stations return from the SLEEP state to the AWAKE state in time to receive at least one watchdog message, thereby avoiding the stations being undesirably logged out from the table of active stations.

Abstract: In a method of operating a wireless local area network (10), a transmitting station (12) senses that the medium is free and then transmits a first portion (43) of a message (40), including destination and source addresses. Message transmission is then interrupted for a response window period (53) during which a destination station (12) should transmit a response message 42 also containing said source and destination addresses. If the transmitting station (12) does not receive a correct response message (42) then it transmits a JAM signal during a JAM window (65) following the response window (53), thereby indicating to all stations (12) that a collision has occurred. All stations not transmitting a JAM signal monitor the JAM window (65) and are thus informed whether or not a collision has been detected.

Abstract: A security device (10) for protecting sensitive data stored in a resettable memory (110) includes a housing (11) formed of six ceramic plates (P1-P6) each having provided thereon a pair of thin film conductive path segments arranged in a meandering configuration. The thin film conductive path segments are joined together by interconnection devices (30) each including a pair of ceramic studs (e.g. K9, K10) having conductive areas (34, 38) thereon connected by an interconnect block (e.g. N5), thereby forming two complete thin film conductive paths (WMA, WMB) which meander in a closely spaced, parallel manner over the entire inner surface of the housing (11). Interrupting or short circuiting the thin film conductive paths (WMA, WMB) causes reset means (130) to reset the resettable memory (110) thereby erasing the data stored therein.

Abstract: A device (10) for protecting stored sensitive data includes a housing (12) formed by six plates P1-P6 inclusive each carrying a conductive path segment formed by thick film deposition techniques and each having a winding configuration covering substantially the entire inner surface of the plate. The four side plates P2-P5 inclusive are mounted on a printed circuit board (PCB 14) which is mounted on the base plate (P6). The conductive path segments on the side and base plates (P2-P6 inclusive) are interconnected to form a wire mesh by conductive epoxy material connecting the path segments on the side and base plates (P2-P6 inclusive) with conductive tracks on the PCB (14). The conductive path segment on the top plate (P1) is connected by conductive wires (58, 60), which extend through plated through holes (B9, B10) in the PCB (14).

Abstract: A security device (10) contains electronic circuitry (84) including a resettable memory (110) which stores sensitive data. The device (10) includes a housing (11) formed by six ceramic plates (P1-P6) each having provided thereon a pair of serially connected conductive path segments formed in separate, superposed layers and arranged in complementary winding configurations. Between the conductive path segments is disposed a conductive sheet. The conductive path segments are serially interconnected by interconnection blocks (N1-N7) and the conductive sheets are serially interconnected by further interconnection blocks (N8-N14). If an attempt to penetrate the housing results in either of the conductive path segments being interrupted or shorted to the conductive sheet, a reset signal is generated to reset the resettable memory (110) thereby erasing the sensitive data stored therein.

Abstract: A device is disclosed for securely housing and protecting microelectronic circuitry in order to prevent external access to sensitive data stored therein. In a preferred embodiment of the invention, the device includes a ceramic housing which encases electronic circuitry. The ceramic housing is comprised of a plurality of individual parts selectively connected together, with each of the parts being comprised of a ceramic substrate and a plurality of ceramic layers disposed thereon. The electronic circuitry includes a memory for storing sensitive data therein and a tamper detection circuit. The tamper detection circuit includes a conductive path selectively provided through the plurality of ceramic layers of each of the plurality of individual parts and is responsive to any attempt to penetrate the ceramic housing which damages the conductive path for clearing the memory of any sensitive data stored therein.