  In this paper we address a seemingly simple question: Is there a universal
packet scheduling algorithm? More precisely, we analyze (both theoretically and
empirically) whether there is a single packet scheduling algorithm that, at a
network-wide level, can match the results of any given scheduling algorithm. We
find that in general the answer is "no". However, we show theoretically that
the classical Least Slack Time First (LSTF) scheduling algorithm comes closest
to being universal and demonstrate empirically that LSTF can closely, though
not perfectly, replay a wide range of scheduling algorithms in realistic
network settings. We then evaluate whether LSTF can be used {\em in practice}
to meet various network-wide objectives by looking at three popular performance
metrics (mean FCT, tail packet delays, and fairness); we find that LSTF
performs comparable to the state-of-the-art for each of them.
