, Volume 68, Issue 2, pp 426-447,
Open Access This content is freely available online to anyone, anywhere at any time.
Date: 10 Aug 2012

An Optimal Lower Bound for Buffer Management in Multi-Queue Switches


In the online packet buffering problem (also known as the unweighted FIFO variant of buffer management), we focus on a single network packet switching device with several input ports and one output port. This device forwards unit-size, unit-value packets from input ports to the output port. Buffers attached to input ports may accumulate incoming packets for later transmission; if they cannot accommodate all incoming packets, their excess is lost. A packet buffering algorithm has to choose from which buffers to transmit packets in order to minimize the number of lost packets and thus maximize the throughput.

We present a tight lower bound of e/(e−1)≈1.582 on the competitive ratio of the throughput maximization, which holds even for fractional or randomized algorithms. This improves the previously best known lower bound of 1.4659 and matches the performance of the algorithm Random Schedule. Our result contradicts the claimed performance of the algorithm Random Permutation; we point out a flaw in its original analysis.

Supported by MNiSW grant number N N206 368839, 2010–2013. A preliminary version of this paper appeared in the proceedings of the 22nd ACM-SIAM Symposium on Discrete Algorithms (SODA 2011).