The method introduces a quantity referred to as the "virtual waiting time" to define the remaining workload in the queue at any time. This process is a step function which jumps upward with new arrivals to the system and otherwise is linear with negative gradient. By giving a relation for the distribution of unfinished work in terms of the excess work, the difference between arrivals and potential service capacity, it turns a time-dependent virtual waiting time problem into "an integral that, in principle, can be solved."
^Sivaraman, V.; Chiussi, F. (2000). "Providing end-to-end statistical delay guarantees with earliest deadline first scheduling and per-hop traffic shaping". Proceedings IEEE INFOCOM 2000. Conference on Computer Communications. Nineteenth Annual Joint Conference of the IEEE Computer and Communications Societies (Cat. No.00CH37064)2. p. 631. doi:10.1109/INFCOM.2000.832237. ISBN0-7803-5880-5.edit