UBC Theses and Dissertations
Interoperability among rate-based congestion control algorithms for ABR service in ATM networks Kayali, Mahmoud
The ATM Forum has recently adopted rate-based schemes as the standard congestion control mechanisms for Available Bit Rate (ABR) service. Two types of rate-based schemes are supported by the ATM Forum specification, namely binary feedback and explicit rate. Explicit rate feedback schemes by themselves can be divided into exact and approximate. Since the implementation of one of these schemes in ATM switches is left to switch manufacturers, it is expected to have these types working on the same network. The compatibility of switches each running a different scheme was considered in the ATM Forum specification. However, since each type of switches has its own merits and demerits, the interoperability of these switch types and its impact on the performance of the network deserves extensive studies. This thesis investigates two types of interoperability in multi-vendor (heterogeneous) ATM networks: the interoperability between binary feedback and explicit rate schemes and the interoperability among different explicit rate schemes. For the first type of interoperability, we look at the steady-state performance of ABR service in networks consisting of both binary feedback and explicit rate switches. In order to find the best locations for each switch type, several cases of switch type locations are considered. Moreover, the impact of ABR sources parameter setting on the performance of heterogeneous networks is studied. For the second type of interoperability (i.e. the interoperability among explicit rate schemes), we investigate potential unfairness problems resulting from situations whereby different ABR sources receive network feedback from different subsets of switches along a given network path. Three types of unfairness problems that arise in such networks are identified. One type of unfairness appears while the sources are increasing their rates and the second type appears while they are decreasing their rates. The third type is a new cause of unfairness generated by the presence of highly bursty Variable Bit Rate (VBR) traffic which can cause unfairness not only in the steady-state periods but also in the transient-state periods on a network link. In addition to identifying the causes of unfairness, our results provide quantitative evaluation of the level of unfairness as a function of various network and source parameters.
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