Little’s law for queueing systems is L=λW: the average queue length equals the average arrival rate times the average waiting time in the system. This study gives further insights into techniques for establishing such laws (i.e. establishing the existence of the terms as limiting averages or expectations) and it presents several basic laws for systems with special structures. The main results concern (1) general necessary and sufficient conditions for Little laws for utility processes as well as queueing systems, (2) Little laws for systems that empty out periodically or, more generally, have regular departures and (3) Little laws tailored to regenerative, Markovian and stationary systems.
