Performance evaluation of admission policies in ATM based embedded real-time systems

Abstract

In this paper u e study the effect of the output link scheduling disciplin6 of an A T M switch on ihe ability of an ATM L A N lo admit real-time connections. Three ouiput link scheduling policies are studied: First Come Farst Served (FCFS), Round Robin (RR), and Packei-by-packet Generalized Processor Sharing (PGPS). Wc derive connection admission criteria for the threc: scheduling policies. To evaluate the performance of the three scheduling policies, we introduce the metric of admission probability. The admission probability giws the probability that a randomly chosen set of real-lime connections will be admitted into the network. The admisszon probability allows system designers l o .study the performance of different scheduling policies over a wide range of network loads. W e ohservc ihat the performance of the ihree scheduling policies 1s sensitive to message deadlines. When the dcadlinr~s are small, PGPS outperforms both R R and FCFS, and R R outperforms FCFS.When the deadlines are large, all three scheduling policies perform the slime. We also note that although PGPS is better thari RR 2nd FCFS most of the time, its improved perfonmnct is achieved at the cost of high Implementation coniplexity and run time overheads.

Response-time guarantees in ATM networks

“…We will use the admission probability (introduced by Raha, Malcom and Zhao [17]) to measure performance. The admission probability for a specific level of network load is defined as the probability of performing a successful CAC for a scenario with that load.…”

“…Instead, a firmer commitment is needed from the network, saying that it will always deliver all messages completely and within specified deadlines (with reservation for hardware failure and external physical interference). Several methods for providing such guarantees have been proposed in the literature [6,8,9,12,14,15,17,18,19,21,28]. They all provide or assume some mechanism of bandwidth sharing, and have an associated analysis that can be used by an admission control procedure toá priori answer the crucial question:…”

Static priority scheduling for ATM networks

“…The convergence of the iterative procedure follows as a corollary, given that we showed earlier (Theorem 5) that in a stable system 1 holds, and therefore lim n!1 n 1 , = 0 : (21) As the value for n increases, the right-hand side of Equation (20) tends to go to zero. Hence, the iterative procedure converges.…”

“…Real-time systems typically operate in a modal fashion; at any given instant of time the system operates in one of a set of known modes [20]. System operation in a specific mode is characterized by the execution and the requirements of a previously defined set of applications.…”

A hybrid systems approach to output scheduling in ATM based real time systems

“…switch is patterned after [2] and [3]. The inputs to the switch are from plant sensors or are feedback signals generated by the control processors.…”