Abstract: A communication system includes a plurality of separate transmission units. A common signal line connects the units. A token is transferred from a first of the units to a second of the units during one sequence. The token is a right to output data to the common signal line. When the token is rejected by the second unit, the token is retransferred from the first unit at maximum a predetermined number of times during that sequence to the second unit. When the retransferred token is rejected by the second unit, the token may be transferred from the first unit to a third of the units during that sequence. In a next sequence, said predetermined maximum number of times said token is retransmitted to said second unit is then reduced.