A new ATM service class, called available bit rate (ABR) transports traffic over unused network bandwidth. However, existing switches do not yet accept this new ABR service class. The EFCI switch uses binary feedback including the setting of EFCI bit in the cell header. The controversial point of this switch is that long hop VCs have a greater possibility that the EFCI bit is set; this is referred to as the beat down problem. On the other hand, ER switch is an intelligent switch in that it monitors its capacity per active virtual circuit (VC) flow. It therefore provides a more efficient and fair control of the source rate. This paper investigates the interoperability issues in terms of the fairness of bandwidth allocation when an ATM network consists of switches using different rate control mechanisms, namely, the ER mode and the EFCI mode.
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