PURPOSE:To constitute a titled system of all the same packet exchange and to improve the reliability and economical efficiency by providing a token monitor function to each packet exchange of a ring network. CONSTITUTION:In each node of a ring network consisting of packet exchange (nodes) Nl-Nm, when the packet of inputted data RNI reaches a reception buffer RCVBUF via a resistor SP, the arrival of the packet is informed to a CPU with an interruption INT1. Every time a token packet reaches the RCVBUF, a count value of a token timer TTM is reset, and if no token packet is received in excess of a reference value of the TTM, a token terminal is informed to the CPU with an interruption signal INT0. The CPU generates a failure packet to a transmission buffer TRSBUF and the packet is transmitted to the ring network. The reception node of the failed packet is switched into the failure mode, the transmission of new packet is stopped, the failed packet is circulated and the received node obtains the right of transmission of the new token.
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