Abstract: Method and apparatus are provided for maintaining a dynamic logical ring in a token passing local area network wherein a plurality of bus interface units (BIUs) exchange information in accordance with a token passing protocol. A network control center is provided for monitoring the transmission medium of the network for transmission of a media demand signal, wherein said media demand signal indicates that a station wishes to be added to the logical ring. The network control center is responsive to the media demand signal for determining a predecessor and successor to the entering station and, thereafter, transmitting media entrance signals to add the entering station to the logical ring. To this end, one media entrance signal is transmitted to the predecessor of the entering station to inform the predecessor to transmit the token to the entering station and another media entrance signal is transmitted to the entering station to inform the entering station to transmit the token to its successor.

Abstract: Method and apparatus are provided for transmitting message signals in a high speed local area network which method performs as efficiently during intervals when few stations have messages to transmit as it does during intervals when many stations have messages to transmit. A station wishing to transmit a message first monitors the transmission medium to determine whether it is busy and, if not, initiates transmission of its message signal. If there are not predominant stations attempting to initiate transmission, then the subject station will continue its transmission until the completion thereof. If, however, a predominant station should attempt to initiate transmission at the same time as the subject station, i.e., a collision occurs, the predominant station wins and continues its transmission until the conclusion thereof. The subject station, being pre-empted, monitors a control bit contained in the preamble of each message signal to determine whether the control bit is set.

Abstract: An improved method for transmitting messages from the buffers of a bus interface unit participating in a local area network is disclosed wherein the bus interface units are permitted to completely empty their buffers upon each possession of the token and thereby decrease the mean bus waiting time of the network. Further, to optimize network bus waiting time while maintaining an upper limit on BIU service time and thereby guaranteeing each bus interface unit of the network one opportunity to transmit during this upper limit time interval, each bus interface unit of the network monitors the BIU service time to determine when this time reaches the upper limit time interval and, thereafter, limits the quantum of information transmitted from its buffer to thereby prevent the BIU service time from increasing beyond the upper limit time interval.

Abstract: Method and apparatus is disclosed for maintaining a dynamic logical ring in a token passing local area network such that each bus interface unit coupled to the network can freely and unilaterally initiate participation therein by monitoring the transmission bus until it is not busy and, thereafter, transmitting a solicit successor packet to initiate entrance to the ring. Further, method is disclosed for re-establishing the ring after a bus interface unit fails or a token is destroyed. Lastly, method and apparatus is disclosed for establishing the logical ring after initialization.

Abstract: A sensitive yet non-destructive method and apparatus for detecting the presence of voids contained within dielectric materials is disclosed which comprises applying a voltage across the dielectric material to create an electric field therethrough, increasing this voltage to create a partial electrical discharge and monitoring the field current to detect the voltage at which partial discharge occurs. When the partial discharge is detected, the voltage applied across the test material is recorded. Reference can then be made to mathematical charts and formulas readily available to determine the size and shape of the detected void.