Abstract: A master includes a unit configured to register, for each slave, an expected communication time needed to exchange control data; a unit configured to register a slave in which a communication error is detected during exchange of the control data in a communication period; and a unit configured to re-execute exchange of the control data with the registered slave in the same communication period as that in which the communication error is detected. The unit configured to re-execute exchange of control data calculates a remaining resending time that can be used to re-execute exchange of the control data and, when the remaining resending time is longer than the expected communication time of the registered slave, resends the control data.

Abstract: A computer network system containing a concentrator with a backplane that has a plurality of lines. The backplane contains data lines and control lines for managing and organizing the transfer of data between modules in the concentrator. The system contains intelligent devices that allow the selection of transmitting modules to occur at the same time as actual data transfer is going on between other modules. This is preferably done in a round robin arbitration process where, while data is being transferred by a first module, a bus arbitration device is placing addresses of modules which sequentially follow the transmitting module onto the control lines. Modules will see their address on the control lines, and if they have a packet to transmit, they then reserve the right to transmit after the presently transmitting module is finished. In this way the selection of the next module to transmit is performed in parallel, and does not slow down, the transfer of data between modules.