Buffer sizing of a CRMA/ATM InterWorking unit adopting a loss free access scheme

One of the main concerns in the interconnection of high speed LANs and ATM based networks is to avoid cell loss in the interworking unit(IWU). In fact, in such environment, the retransmissions caused by the higher layers protocols can cause serious congestion problems. As a case study, the interconnection of a Gbit/s CRMA LAN through an ATM-based WAN is here considered. An integrated flow and access control (IFAC) protocol is proposed which exploiting the characteristics of the CRMA access scheme regulates the emission of cells towards the CRMA/ATM interworking unit so that its buffer resources are not saturated. The emission of the ATM stations is controlled via a backpressure mechanism. The capacity of the interworking unit buffer is virtually increased by utilizing the network latency as well as the station buffers. The protocol effectiveness has been validated through a simulation analysis. On the basis of the obtained results a study on the IWU buffer dimensioning has been carried out. In particular, the minimum buffer needed to carry a given load has been determined. Moreover, some criteria have been given to properly fix the capacity to be allocated through the ATM interface