Measurements of Ada overhead in OSI-style communications systems

A discussion is given on whether the Ada model of concurrency is suitable for implementing the seven-layer OSI reference model. Using the communications model introduced by R.J.A. Buhr (1984), they determine the overhead introduced by Ada when the model is implemented on two single-processor machines, a VAX 11/785 and a Rational 1000. The authors then calculate a lower bound on expected message delay. A novel model using server tasks is proposed and shown to have better performance. The authors investigate performance on an eight-processor Sequent Model 821 and a 14-processor Encore Multimax 320 by implementing the Buhr model, the server task model and a third model which abandons the Ada rendezvous in favor of procedure calls. They determine the Ada overhead per message as a function of the number of processors and calculate lower bounds on expected message delay attributable to Ada overhead for all three communications models