An improved EFCI scheme with early congestion detection

Nodal congestion in available bit rate (ABR) congestion 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 traffic in each control feedback loop is unnecessarily extended and magnified, causing a large consumption of buffer resources. Proposed in this paper is a bandwidth-threshold scheme which directly compares the filtered traffic 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 traffic, the proposed bandwidth-threshold scheme has the advantage of early congestion detection and short congestion period as compared with the queue-threshold scheme. A simulation study shows a significant saving of buffer resources (more than 60%) by the EFCI-ECD scheme.