Scalable Switching Fabrics for Internet Routers

The exponential growth of the Internet is driving a demand for routers that operate at increasing bit-rates (OC48 to OC192 to OC768) and that have a very large number of ports (10s to 100s to 1000s). To meet this growing demand, routers are needed that can scale with the demand along both the bit-rate and port-count axes. To scale a router to handle a large number of high-speed ports requires a switching fabric that is itself economically scalable and that provides the quality of service demanded by latencysensitive traffic. A switching fabric that transports packets from input ports to output ports is at the core of any router. Historically, routers have used switching fabrics based on backplane buses and crossbar switches. Buses, however, are not scalable to high bit rates, and crossbars, because their cost grows as the square of the number of nodes, cannot be economically scaled to large numbers of nodes. A direct interconnection network, like the 3-D torus network used in the Avici TSR, provides a high-performance switching fabric that is economically scalable with a cost that increases linearly with the number of nodes. Torus fabrics can be incrementall