"Pay bursts only once" does not hold for non-FIFO guaranteed rate nodes


We consider end-to-end delay bounds in a network of Guaranteed Rate (GR) nodes. We demonstrate that, contrary to what is generally believed, the existing end-to-end delay bounds apply only to GR nodes that are FIFO per flow. We show this by exhibiting a counter-example. Then we show that the proof of the existing bounds has a subtle, but important, dependency on the FIFO assumption, which was never noticed before. Finally, we give a tight delay bound that is valid in the non-FIFO case; it is noticeably higher that the existing one. In particular, the phenomenon known as “pay bursts only once” does not apply to non-FIFO nodes. These findings are important in the context of differentiated services. Indeed the existing bounds have been applied to cases where a flow (in the sense of the GR definition) is an aggregate of end-user microflows, and it is not generally true that a router is FIFO per aggregate; thus the GR node model of a differentiated services router cannot always be assumed to be FIFO per flow.

DOI: 10.1016/j.peva.2005.07.004

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@article{Rizzo2005PayBO, title={"Pay bursts only once" does not hold for non-FIFO guaranteed rate nodes}, author={Gianluca Rizzo and Jean-Yves Le Boudec}, journal={Perform. Eval.}, year={2005}, volume={62}, pages={366-381} }