Switch Fabric Interfaces

S witch fabrics are fundamental building blocks in a wide range of communication platforms. However, despite the growing need for next-generation switches and routers, semiconductor vendors have been slow to develop switch fabric chipsets. In addition to the many technical challenges associated with the deployment of such fabrics, industry analysts agree that a key factor impeding wide-scale exploitation is a lack of standardization in interconnecting fabric components. Many of the more than 30 companies that develop switch fabrics offer excellent price and performance, but none guarantee compatibility with other vendor offerings or even with future generations of their own products. The market consists of several point solutions with no reliable and coherent roadmap. In these uncertain times, assurance of supply is a major issue in selecting a silicon vendor. Standard interfaces will make it possible to replace a discontinued device without requiring a new system design. The guaranteed availability of backup products will reduce the risks associated with each device and let systems designers select newer and more cutting-edge offerings. A switch fabric moves incoming data from a set of ingress ports to a single egress port, in the case of unicast devices, or multiple egress ports, in the case of multicast devices. In applications such as video switching, the binding between an ingress and egress port changes infrequently. In IP routers and asynchronous transfer mode switches, however, such fabrics dynamically partition data into fixed-sized or variable-sized cells, frames, packets, and other units. Dynamic fabrics tend to be more complex than static fabrics because they require arbitration between data units that may be simultaneously destined for the same output port. Much switch fabric research in recent years has focused on Internet packet switching. Due to advances in emerging networking applications, however, the need for high-performance switch fabric solutions has shifted from the pure IP domain. Robust metropolitan area networks, director class storage area networks, and other emerging switching applications have reached both the capacities and the service requirements to justify the need for advanced off-the-shelf fabric products. Figure 1 presents a generic overview of a contemporary high-capacity fabric architecture. The ingress path connects a line card's network processing sub-system—consisting of network processors and/or traffic managers—to the switching core, which dynamically connects ingress ports to egress ports. The egress path aggregates traffic from the switching core and forwards it to the line card front end. Switch fabrics can be implemented in …