Greedy Packet Scheduling

Scheduling packets to be forwarded over a link is an important subtask of the routing process both in paxalhl computing and in communication networks. This paper investigates the simple class of greedy scheduling algorithms, namely, algorithms that always forward a packet if they can. It is first proved that for various "natural" classes of routes, the time required to complete the transmission of a set of packets is bounded by the sum of the number of packets and the maximal route length, for any greedy algorithm (including the a~bitra~y scheduling policy). Next, tight time bounds of O(n) are proved for a specific greedy algorithm on the class of shortest paths in n-vertex networks. Finally it is shown that when the routes are arbitraxy, the time achieved by various ~n~tur~l ~ greedy algorithms can be as bad as f~(nl'S), when O(n) packets have to be forwarded on a~ n-vertex network. *IBM T.J. Watson Rese~.rch Center, P.O. Box 704, Yorktown Heights, NY 10598, a~d Faculty of Electrical Engineering, The Technion, H~ifa 32000, Israel. cldonOtechsel.bitnet tIBM T.J. W~tson Research Center P.O. Box 704, Yorktown Heights, NY 10598, kuttenOibm.com tL~bor~tory for Computer Science, MIT, Caxnbrldge, MA 02139. P~rtially supported by IBM gr~du~te fellowship. ma~usourOt heory.lcs.mit .edu 5Department of Applied MLthem~tics, The Welzm~nn Institute, Rehovot 76100, Israel. pelegOwisdom.bitnet. Supported in part by ~n Allon Fellowship, by ~ Walter ~nd Ellse Ha~ C~reer Development Award ~nd by ~ Ba.utrell Fellowship. P~rt of the work was done while visiting IBM T.J. Watson Research Center.