A simulator for and results of comparing ABR flow controls for ATM

Abstract

The paper describes the design of a simulator capable of investigating a number of ATM flow-control algorithms. The event driven simulator contains a minimum number of component types-queues, connections and routes. The first two are the only participants generating events. The major data elements are packets which logically can contain any number of cells but the simulator provides for packet transport which is statistically similar to that occurring in individual cell transport through a network. The simulator code is written in C++. Two of its mechanisms, overloaded data structures and dynamic assignment of code using pointers to functions allow the simulator to contain any number of flow control algorithms and to select the algorithm to be used. Because of the unique character of the basic simulator components, relational database structures are used for case input and run output. Run output post processing is necessary because network flow-control problems are usually related to particular components when selecting the flow control algorithm and/or parameters to best meet a system's needs. Simulator run time is excellent, with a 7 queue, 5 connection network taking 2-3 second clock time for a 0.5 second run time. Scaling to a component count by an order of magnitude should be very feasible. To demonstrate the simulator's versatility, we provide a comparison of three very different flow control schemes. The first uses fair-share assignment for individual connections at each queue. The second, a threshold queue algorithm does not control individual connections, only the bulk queue load. The third scheme is an adaptive rate-based algorithm. It uses no control at the queue-only measure transport delay at the receiver.