We consider the problem of providing service guarantees in a high-speed packet switch. As basic requirements, the switch should be scalable to high speeds per port, a large number of ports and a large number of traffic flows with independent guarantees. Existing scalable solutions are based on Virtual Output Queuing, which is computationally complex when required to provide service guarantees for a large number of flows. We present a novel architecture for packet switching that provides support for such service guarantees. A cost-effective fabric with small external speedup is combined with a feedback mechanism that enables the fabric to be virtually lossless, thus avoiding packet drops indiscriminate of flows. Through analysis and simulation, we show that this architecture provides accurate support for service guarantees, has low computational complexity and is scalable to very high port speeds.
Input-Output buffered crossbars are popular building blocks for scalable high-speed switching because they require minimum speed-up of memory bandwidth. Scaling the design of crossbar switches to large capacities is limited by technology issues such as the reconfiguration of high-speed fabrics or power consumption. In addition, these crossbar architechtures typically schedule and transfer in terms of fixed size envelopes. Thus when they are used in the context of IP networks where packets are of variable size, the incoming packets need to be fragmented into fixed size envelopes. This fragmentation can lead to, possibly large [1], loss of bandwidth and even instability. This paper proposes a new method for switching variable sized packets over a crossbar switch that i) allows maximum utilization of switch bandwidth and avoids the fragmentation effect, and ii) allows designers to use much larger envelopes for transfering data over the fabric and thus minimizes the reconfiguration frequency of the fabric. Reducing the scheduling frequency makes implementation of complex schedulers practical and enables us to build ultra-fast switches incorporating optical technology that can provide bandwidth and delay guarantees.