Dealing with RTTs (round trip time) in IQ switches has been recently recognized as a challenging problem, especially if considering distributed (multi-chip) scheduler implementation which are suited to reduce the hardware complexity in very large, high-speed, switches. Traditional iterative three- or two-phase scheduling algorithms are based on a monolithic implementation, thus allowing instantaneous information exchange among input and output selectors to determine a matching. Multi-chip implementation imply that information exchange among inputs and outputs is delayed by an inter-chip latency. This delay requires non-trivial modifications to scheduling algorithms to allow a fully distributed implementation while keeping good performance. We propose a new scheduling algorithm, named SRR (synchronous round robin), which is suited to a fully distributed implementation and provides good performance if compared with more complex, non fully distributed, previously proposed scheduling algorithms.

Efficient support of multicast traffic in storage area networks (SANs) enables applications such as remote data replication and distributed multimedia systems, in which a server must access concurrently multiple storage devices or, conversely, multiple servers must access data on a single device. In this paper we extend an innovative switching architecture, proposed in a previous paper, to support multicast traffic. We describe the most important aspects, focusing in particular on the mechanisms that permit to achieve lossless behavior. We then use simulation to analyze system performance and the impact of such mechanisms under various traffic patterns. Although the work is inspired by a specific switch architecture, results have a more general flavor and permit to highlight interesting trends in flow controlled architectures.

We present a scheme to concurrently schedule unicast and multicast traffic in an input-queued switch. It aims at providing high performance under any mix of the two traffic types as well as at avoiding starvation of any connection. The key idea is to schedule the two traffic types independently and in parallel, and then arbitrate among them for access to the switching fabric. The unicast and multicast matchings are combined into a single integrated matching. Edges that are excluded from the integrated matching are guaranteed to receive service at a later time, thus balancing service ratios and preventing starvation. We use simulation to evaluate the performance of a system employing the proposed scheme and show that, despite its simplicity, it achieves the intended goals. We also design an enhanced remainder-service policy to achieve better integration and further improve performance.

In this paper we propose a new fluid model approach in which a different description of the dynamics of traffic sources is adopted, exploiting partial differential equations. This new description of the source dynamics allows the natural representation of short-lived as well as long-lived TCP connections, with no sacrifice in the scalability of the model. In addition, the use of partial differential equations permits the description of distributions, instead of averages, thus providing better accuracy in the results. The comparison between the performance estimates obtained with fluid models and with ns-2 simulations proves the accuracy of the proposed modeling approach.

Fluid models of IP networks have been recently proposed as a way to break the scalability barrier of traditional discrete state-space models, both simulative (e.g., ns-2) and analytical (e.g., queues and Markov chains). Fluid models adopt an abstract deterministic description of the average network dynamics through a set of ordinary differential equations that are then solved numerically, obtaining estimates of the time-dependent network behavior. However, an important limit of the fluid model approaches presented so far in the literature is their unnatural representation of scenarios comprising the short-lived TCP flows that dominate in today's Internet. In this paper we propose a new fluid model approach in which a different description of the dynamics of traffic sources is adopted, exploiting partial differential equations. This new description of the source dynamics allows the natural representation of short-lived as well as long-lived TCP connections, with little sacrifice in the scalability of the model. In addition, the use of partial differential equations permits the description of distributions, instead of averages, thus providing better accuracy in the results. The comparison between the performance estimates obtained with fluid models and with ns simulations proves the accuracy of the proposed modeling approach.