Anycasting in adversarial systems: Routing and admission control

In this paper we consider the problem of routing packets in dynamically changing networks, using the anycast mode. In anycasting, a packet may have a set of destinations but only has to reach any one of them. This set of destinations may just be given implicitly by some anycast address. For example, each service (such as DNS) may be given a specific anycast address identifying it, and computers offering this service will associate themselves with this address. This allows communication to be made transparent from node addresses, which makes anycasting particularly interesting for dynamic networks, in which redundancy and transparency are vital to cope with a dynamically changing set of nodes. However, so far not much is known from a theoretical point of view about how to efficiently support anycasting in dynamic networks. This paper formalizes the anycast routing and admission control problem for arbitrary traffic in arbitrary dynamic networks, and provides first competitive solutions. In particular, we show that a simple local load balancing approach allows to achieve a near-optimal throughput if the available buffer space is sufficiently large compared to an optimal algorithm. Furthermore, we show via lower bounds and instability results that allowing admission control (i.e. dropping some of the injected packets) tremendously helps in keeping the buffer resources necessary to compete with optimal algorithms low.