Packet-delay invariance to scheduling under congestion

Class-of-Service enabled networking relies on non FIFO schedulers in order to achieve differentiated performance, e.g. delay, for different traffic classes. The delay performance of all stable packet schedulers is characterised by a Dominant Decay Rate (DDR) in the presence of bursty traffic. Poisson traffic only results in a "classical", or Short Buffer Decay Rate (SBDR) which is not the same as the DDR. This paper presents novel experimental results which indicate that, for widely different FIFO and non-FIFO schedulers, the low delay SBDRs are very dissimilar yet the DDRs are virtually identical. We also analytically predict the "knee-point" where the DDR takes over from the SBDR: this is the point at which schedulers become equivalent.