Comparison of explicit rate and explicit forward congestion indication flow control schemes for ABR service in wide area networks

Abstract

An adaptive end-to-end rate based congestion control scheme to support a class of best effort service known as available bit rate service (ABR) has been proposed by the ATM Forum. In this paper we investigate two variants of this control scheme. In the first scheme known as the explicit forward congestion indication (EFCI) scheme, a single bit is used to convey to the source the state of the network. In the second scheme, known as the explicit rate (ER) scheme, the network informs the source from time to time, the maximum rate at which they can transmit. We investigate the steady state and transient performance of the controls in a wide area multihop network, including the presence of high priority variable bit rate traffic. To improve the performance of the EFCI scheme in multihop networks, we propose a priority based EFCI scheme. The EFCI scheme exhibits a robust behavior, and ensures fair share of the bandwidth for all virtual channels (VCs) in the long run, regardless of the number of hops they traverse. However, the EFCI mechanism is fundamentally oscillatory in nature and can lead to large cell loss. The ER scheme is very stable, even under extreme loading conditions, and ensures fair sharing of resources.