CAC and traffic shaping for performance control in ATM: the two-class paradigm

Retaining only a few service classes in the ATM layer of broadband networks has the distinct advantage of simplifying the traffic control functions, which seems to be a key prerequisite for the successful introduction of ATM. In the paradigm under consideration, only two service classes are assumed, which share the storage and bandwidth resources at the network nodes according to an absolute-time-priority scheme, being able to support two general types of applications: real-time and non-real-time ones. The low-priority class is thus of the available-bit-rate (ABR) type, with some service quality guarantee obtained through allocating a minimum amount of bandwidth to it. Proper connection admission control (CAC) for both classes and traffic shaping of the low-priority traffic are employed in order to maintain contracted quality-of-service levels for both classes. Peak rates for the real-time traffic and effective rates for the non-real-time one form the basis of the control functions. A burst-level traffic model based on the M/D/1 queue is proposed for sources without strict delay constraints and the derived effective rate is validated by simulation and results from experiments on an ATM testbed. Following these results, a coherent CAC and traffic shaping scheme is presented. This scheme makes use of the proposed burst-level model to achieve an adaptive shaping of the non-real-time sources. For all links intended to support both classes, real-time sources are allocated, their demanded peak rate and the bandwidth left available by these sources is exploited by the ABR type sources (non-real-time), through adapting the parameters of the shaper. Simulation results validate the concept of this novel ABR-like service. The set of simulation and experimental results contained in the paper constitute the heart of its contribution.