Instability behaviour of heterogeneous multimedia networks under dynamic adversarial attacks

Multimedia communication networks, such as the Internet, are heterogeneous in their nature because they require different methods for content transmission. The efficiency of multimedia content transmission depends on the variety of communication protocols that are simultaneously running (composed) over different network hosts in order to resolve packet conflicts. A very natural question that arises in such common settings of multimedia networks concerns the degradation (or not) of network stability under adversarial attacks that change dynamically network link capacities/slowdowns. A packet-switched network is stable if the number of packets in the network remains bounded at all times against any adversary. In this work, we embark on a systematic study of this question adopting an enhanced adversarial framework, where an adversary controls the rates of packet injections, determines packet paths and manipulates link slowdowns or capacities. Such adversarial attacks can be considered as a type of denial of service attack. Within this framework, we study network stability under specific compositions of contention–resolution protocols when packets are injected with simple paths (paths can contain repeated edges, but not repeated nodes) trying to characterise this property in terms of network topologies. The examined network topologies have been proved forbidden for stability when network link capacities/slowdowns are fixed and packet paths are simple. Furthermore, in order to evaluate how unstable can a network be for the same protocol compositions under dynamic adversarial attacks, we present an involved adversarial construction that leads a specific network to instability for arbitrarily low injection rates. Interestingly, our results suggest that dynamic adversarial attacks changing link slowdowns may be worse than dynamic adversarial attacks changing link capacities or attacks with fixed slowdowns/capacities for specific protocol compositions.