An Improved EFCI Scheme with Early Congestion Detection

Nodal congestion in ABR traac control design is often detected by comparison of present queue size with a pre-assigned queue-threshold. Such queue-threshold detection has the disadvantage of delayed congestion detection and undesired extension of congestion periods. In consequence, the oscillation of ABR traac in each control feedback loop is unnecessarily extended and magniied, causing a large consumption of buuer resources. In this contribution we propose a bandwidth-threshold scheme which directly compares the ltered traac rate with a pre-assigned link bandwidth-threshold for congestion detection. The proposed new scheme is called EFCI-ECD, where ECD stands for early congestion detection. Since nodal congestion is mainly captured by the low-frequency variation of the traac, the proposed bandwidth-threshold scheme has the advantage of early congestion detection and short congestion period as compared to the queue-threshold scheme. Our simulation study shows a signiicant saving of buuer resources (more than 60%) by the EFCI-ECD scheme.