  While steady-state solutions of backlog and delay have been derived for
essential wireless systems, the analysis of transient phases still poses
significant challenges. Considering the majority of short-lived and interactive
flows, transient startup effects, as caused by sleep scheduling in cellular
networks, have, however, a substantial impact on the performance. To facilitate
reasoning about the transient behavior of systems, this paper contributes a
notion of non-stationary service curves. Models of systems with sleep
scheduling are derived and transient backlogs and delays are analyzed. Further,
measurement methods that estimate the service of an unknown system from
observations of selected probe traffic are developed. Fundamental limitations
of existing measurement methods are explained by the non-convexity of the
transient service and further difficulties are shown to be due to the
super-additivity of network service processes. A novel two-phase probing
technique is devised that first determines the shape of a minimal probe and
subsequently obtains an accurate estimate of the unknown service. In a
comprehensive measurement campaign, the method is used to evaluate the service
of cellular networks with sleep scheduling (2G, 3G, and 4G), revealing
considerable transient backlog and delay overshoots that persist for long
relaxation times.
