Explicit rate ABR schemes using traffic load as congestion indicator

A central issue in congestion control for available bit rate (ABR) services is the computation of the fair share for every connection at each switching node in the network. An important class of algorithms for the switch behavior computes the fair share according to the exact definition of max-min fairness, and uses it as the explicit rate conveyed to the sources. These algorithms may encounter difficulties due to the complex task of keeping track of active connections. In addition, since these schemes treat all connections equally, they lead to under-utilization of the link capacity when on-off sources are present in the network. To obviate these shortcomings, it has been proposed to use the traffic load to correct the computed fair share when setting the explicit rate. In this paper, first we show that using the traffic load as suggested in literature inherently perturbs rate allocation, and makes the schemes sensitive to the round-trip delay of the connections, leading to unfairness. Then, we introduce a scheme called the enhanced fast max-min rate allocation (E-FMMRA) algorithm, which solves the problem by keeping track of the maximum explicit rate over all backward RM cells. The same technique used in E-FMMRA can also be applied to the popular explicit rate indication for congestion avoidance (ERICA) scheme to solve similar problems associated with the use of the traffic load.