Ticket circulation protocol: A simple access protocol for dual bus architecture

Abstract

The basic distributed queue dual bus (DQDB) scheme suffers with fairness problems on high loads. These problems can be overcome by several schemes. Even with these schemes, the throughputs for each station still exhibit some variations and the total throughputs are slightly influenced. Slot reuse may be introduced in order to increase the channel bandwidth of the basic DQDB. Some schemes designed for remedying the fairness problem in the DQDB with the slot reuse can be found. This paper proposes a simple protocol, viz. ticket circulation protocol (TktCP), for the unidirectional twin-bus architecture. A slot reuse scheme and a priority scheme for the TktCP are also proposed. The TktCP allows tickets to circulate around the twin-bus. The tickets have been used to maintain the fairness among stations. The time to reach fairness is short and the variations in channel bandwidths among stations are smaller, compared to the DQDB with bandwidth balancing. In addition, the bus bandwidth is also fully utilized. A coupling of slot reuse with TktCP preserves the benefits of increased bandwidth and still maintains a fair access of the bus for each station. Further coupling of priority scheme with the TktCP maintains a fair access of the bus for each station with the same priority level.