Stability Behavior of FIFO Protocol in the Adversarial Queuing Model

Abstract

Packet-switched networks, where packets arrive dynamically at the nodes and they are routed in discrete time steps across the edges, widely use the FIFO (First-In-First-Out) protocol to provide contention resolution due to its simplicity. In this work, the stability properties of the FIFO protocol are analyzed in depth and new performance bounds are presented. Roughly speaking, stability requires that the number of packets in a network remains bounded, as the network runs for an arbitrarily long period of time. We focus on a basic adversarial model for packet arrival and path determination for which packets are injected with predetermined paths, such that the time-averaged arrival rate of packets requiring a single edge is no more than 1. We discover: - FIFO is stable for any adversary with injection rate r less than or equal to 1/9 (r ≤ 1/9 ) for a specific simple network with four queues. - We present a general method that allows the specification of upper bounds on injection rate for FIFO stability on networks with a finite number of queues answering partially an open question raised by Andrews et al. [2]. - Through an involved combinatorial construction, we significantly improve the current state-of-the-art record [2],[7], [9] for the adversary’s injection rate that implies instability for the FIFO protocol to 0.771. _ The work of all the authors was partially supported by the IST Programme of the European Union under contract number IST-1999-14186 (ALCOM-FT).