Contribución al modelado y caracterización de nodos en redes de banda ancha. Aplicación al multiplexor inverso ATM.

Resum

The growing demand of network bandwidth users made indicates that user access to high speed (i.e. ATM) networks is a key issue. The Inverse Multiplexing for ATM (IMA) is a technology that combines multiple T1/E1 links to support the transparent transmission of ATM cells over one single logical data trunk which bandwidth is the aggregate of the T1/E1 capacities, minus a small amount due to overhead. That is, it provides high bandwidth by using already deployed WAN infrastructure and at a reasonable cost. Employing this technology, it is possible to dispose of ATM connections with data rates between the T1/E1 (an economical but sometimes too slow option) and T3/E3 ones (with high bandwidth, but expensive for the mass market of users). <br> In this framework, and facing a new technology, it is crucial to have tools (analytical and simulation ones) easy to manipulate that help telecommunication engineers and network planners on the performance evaluation and dimensioning of these systems. In this paper, the fundamentals and major applications of IMA technology are described. Also, the behavior of IMA multiplexers is carefully analyzed and a method to dimension them proposed. An estimate for the Cell Loss Ratio (CLR) and the mean waiting time measured in the IMUX devices are obtained.<br> In this thesis several analytical models are contributed to evaluate the benefits of a sufficiently generic ATM node and of an IMUX device. That allows computing the parameters of quality of service for its design: average waiting time of the cells in the device and cell loss probability. The purpose is to constitute an effective tool for the suitable design of the parameters that define the ATM node and particularly to the IMUX. In order to start with the analysis, firstly we have adapted the well-known queue systems to model a concrete ATM node and an inverse multiplexer for ATM. An analytical method has been contributed to approximate the parameters of quality of service of the queue systems. That is, we have applied a M/D/s/s+B queue with discreet-time service and a scheme of five levels of priority.<br> The last analytical study is based on the comparison with a M/D/1 queue system. In addition, all the effects that take place in IMUX device are analyzed meticulously separately. They are due to the insertion of the control cells and filler cells, in agreement with the IMA specification of the ATM Forum.<br> Even though, we are aware of the weakness of our assumptions, especially concerning to the Poisson input traffic, the model is compact, easy to understand and to manipulate, therefore it can be valuable to validate simulation models developed to evaluate IMUX devices under more realistic input traffic patterns. <br> Finally, the lines of future work are scored: the incorporation of a five priorities scheme in the IMUX; the study and analysis of the effects of having bandwidth under demand as a benefits that the IMUX offers; the study and analysis of the IMUX behavior under more realistic traffic models.