Emulating Output Queuing with Buffered Crossbar

Output queuing is well known for its ability to provide quality-of-service (QoS) guarantees. Unfortunately, the high-speed memory requirements of output queued (OQ) switch limit its use for large capacity switching architecture. A lot of work in literature has investigated how to emulate OQ switch with other switch architectures. A novel approach is constructing switches with buffered crossbars. However, most of the presented schemes still need a mild speedup which will incur significant cost for high speed network application. This paper investigates how to build a buffered crossbar switch to emulate OQ switch with no speedup. We first present a 2-dimensional buffered crossbar as a switch fabric and prove that a combined input-crosspoint-output queued (CICOQ) switch with such a fabric can emulate a restrict PIFO-OQ switch with no speedup. Then, we present a pretreatment mechanism used in scheduling input queues. With such a pretreatment mechanism, the CICOQ switch is proved to be able to emulate a general PIFO-OQ switch with no speedup. All scheduling algorithms used in proving OQ emulation are distributed, hence are practical