ABSTRACT
The purpose of a router is to forward datagrams from an ingress port to an egress port, and to make decisions regarding if and when to discard a datagram. While the line cards (or processor cards in a midplane design) perform the forwarding decision or the drop decision, some entity must connect the line cards to each other. Every router therefore must have an entity that can connect the line cards or port and processor cards with each other through internal interconnects. These interconnects can be buses, meshes, shared memory switches, crosspoint or crossbar switches, or switch fabrics. All of these interconnects differ in their cost structure, throughput, latency, connection setup time, flexibility, resource utilization, and reliability. As a result, they are used in different applications. The requirements for a switch fabric are determined by the requirements for an advanced router.
