On the many-server fluid limit for a service system with routing based on delayed information

Pender, Rand and Wesson recently established a delay differential equation limit for a parallel service system with routing based on delayed information. We provide an interpretation of their scaling under which their limit can be regarded as an instance of a law of large numbers in the familiar many-server heavy-traffic scaling. It requires scaling in the probabilistic routing function. We also obtain related many-server heavy-traffic delay-differential-equation limits for more general models.