Fig. 5

Timeline of different Rejuvenation Models. In each sub-figure, time flows in the horizontal axis from left to right, starting at t=0. Each row represents the timeline of one of the n nodes in a system. The empty slots stand for online time; the slotswith letter R inside stand for (offline) rejuvenation time. In each column, there are exactly n−k nodes online and k nodes rejuvenating. The thicker vertical segments mark the beginning and ending instants of each rejuvenation, either as an instantaneous process (r=0) when k=0 (sub-figures 5a and 5b), or as a process taking some time (r>0) when k>0 (sub-figures 5c and 5d). The auxiliary small circles, on top of some thick vertical segments, examplify the horizontal extremities of the measure of some parameter of the rejuvenation scheme (as respectively exemplified below the lowest timeline row): r is the time a node takes in each rejuvenation; Δ is the period between the beginning of consecutive rejuvenations of the same node; δ is the minimum time between rejuvenations of different nodes