FQDB - A FAIR MULTISEGMENT MAC PROTOCOL FOR DUAL BUS NETWORKS

The paper presents a new MAC protocol for dual bus networks which is i ntrinsically fair in bandwidth sharing and retains all the positive fe atures of DQDB including simplicity, robustness, flexibility, 100% ban dwidth utilization, and zero access delay at very low load. Features w hich make this protocol appealing with respect to others DQDB alternat ives are represented by the fact that FQDB is compatible with the DQDB standard with respect to the physical arrangement and attachment to t he bus, the XOR write tap, the ACF length, and the three priority leve ls. Nevertheless, its properties are attractive also for protocols ope rating at 1 Gb/s and up. In the paper, fairness is formally proved and it is also shown that a bandwidth sharing pattern different from the uniform one can easily be enforced, as may be the case if bridges or o ther large users are present. Queueing disciplines, priorities, and im plementation issues are discussed and comparisons obtained by simulati on are given.