International Business Machines Corporation

James F Frenzel, Iii

Brian Alan Youngman

A concentrator which couples stations to a communications network includes internal devices connected to form a primary loop which merges with the communications network if the concentrator is connected to said communications network. The internal devices include a Station MAC which communicates with stations outside of the concentrator. A local ring including a Roving MAC and at least one Concentrator Configuration Element (CCE) is also provided. A microprocessor, with an output bus interconnecting the Roving MAC, the CCE, and the Station MAC, is also provided. The concentrator insert/de-insert in the communications network without disrupting data already on the network.

Method for controlling the insertion of stations into FDDI network

Described is an improved method and apparatus which allows graceful insertion/de-insertion of a station into an FDDI network. The circuit arrangement known as 'Roving MAC' captures a local token which is circulating on a local loop established between the Roving MAC and the station. The 'Roving MAC' issues void frames while holding the local token. A circuit arrangement monitors the FDDI network. If the token on the FDDI network is sensed before the local token is released, a data frame is allowed to pass through, but the token concatenated to the data frame is switched into the station thus joining it to the FDDI network. A scrubber circuit simultaneously removes the void frames and issues idle signals on the FDDI network.

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Bahama, NC, United States of America

James F Frenzel, Iii