56 0890-8044/08/$25.00 © 2008 IEEE oday, the vast majority of the communications on the Internet are between nodes located in non-transit (i.e., stub) networks. Stub networks are primarily composed of medium and large enterprise customers, universities, public administrations, content service providers (CSPs), and small Internet service providers (ISPs). These networks exploit a widespread practice called multihoming, which consists of using multiple external links to connect to different transit providers. By increasing their connectivity to the Internet, stub networks potentially can obtain several benefits, especially in terms of resilience, cost, and traffic performance [1]. These are described as potential benefits because multihoming per se cannot improve any resilience, cost, and traffic performance. Accordingly, multihomed stub networks require additional mechanisms to achieve these improvements. In particular, when an automatic mechanism actively optimizes the cost and end-to-end performance of the traffic routed among different links connecting a multihomed stub network to the Internet, it is referred to as intelligent route control (IRC).During the last few years, IRC has attracted significant interest in both the research and the commercial fields. Several vendors are developing and offering IRC solutions [2][3][4] that increasingly are being adopted by multihomed stub networks. Most available IRC solutions follow the same principle, that is, they dynamically shift part of the egress traffic of a multihomed subscriber from one of its ISPs to another, using measurement-driven path switching techniques. IRC systems operate in relatively short timescales -even reaching switching frequencies on the order of a few seconds -allowing IRC users to balance cost and performance criteria according to the priority and requirements of their applications.Despite these strengths, IRC practices have one major weakness, that is, they try to achieve a set of local objectives individually without considering the effects of their decisions on the performance of the network. Recently, it was discovered that in a competitive environment, IRC systems actually can cause significant performance degradation rather than improvement. In [5], the authors show that persistent oscillations can occur when independent controllers become synchronized due to a considerable overlap in their measurement time windows. To avoid synchronization issues, the authors propose randomized IRC strategies and empirically show that the oscillations disappear after introducing a random component in the route control decision.It is important to note that although randomization offers a straightforward mechanism to mitigate the oscillations, it cannot guarantee global stability. This issue raises concerns given the proliferation of IRC products because as the number of interfering IRC systems increases, randomization becomes
AbstractMultihomed subscribers are increasingly adopting intelligent route control solutions to optimize the cost and end-to-en...