摘要：A distinguishing feature of today's large-scale platforms for multimedia distribution and communication, such as the Internet, is their heterogeneity, predominantly manifested by the fact that a variety of communication protocols are simultaneously running over different hosts. A fundamental question that naturally arises for such common settings of heterogeneous multimedia systems concerns the presence (or not) of stability properties when individual greedy, contention-resolution protocols are composed in a large packet-switched multimedia network. A network is stable under a greedy protocol (or a composition of protocols) if, for any adversary of injection rate less than 1, the number of packets in the network remains bounded at all times. We focus on a basic adversarial model for packet arrival and path determination for which the time-averaged arrival rate of packets requiring a single edge is no more than 1. Within this framework, we study the property of stability under various compositions of contention-resolution protocols (such as LIS (Longest-in-System), FIFO (First-In-First-Out), FFS (Furthest-from-Source), and NTG (Nearest-to-Go)) and different packet trajectories trying to characterise this property in terms of network topologies. Such a characterisation provides us with the family of network topologies that, under specific compositions of protocols, can be made unstable by some adversarial traffic pattern. Finally, we present an experimental evaluation of the stability behaviour of specific network constructions with different protocol compositions under an adversarial strategy. Interestingly, some of our results indicate that such a composition leads to worst stability behaviour than having a single unstable protocol for contention-resolution. This suggests that the potential for instability incurred by the composition of protocols may be worse than that of any single protocol.
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