A comparison of two buffer insertion ring architectures with fairness algorithms

Buffer insertion rings (BIR) are known to provide higher throughputs than other competing ring technologies. With the introduction of spatial reuse, MAN's and LAN's are at a greater advantage of maximizing bandwidth efficiency. Spatial reuse introduces the concept of congestion and fairness algorithms are needed to police the fair access of the low priority traffic on the ring. Two architectures are studied in this paper, mono transit buffer (MTB) and the dual transit buffer (DTB). Different from earlier BIR architectures, the congestion control mechanisms studied in this paper are rate based and traffic streams are regulated using leaky buckets. It has been shown through simulations that both architectures exhibit oscillatory behavior under certain congestion conditions. MTB oscillates due to the buffer threshold settings. We show that by correctly setting parameters, oscillations can be dampened to achieve fair throughputs for all nodes contributing to the congestion.