Output Queued Switch Emulation by A One-Cell-Internally Buffered Crossbar Switch

Output-Queued (OQ) switching architecture is known to be of optimal performance amongst all queuing approaches. However, OQ switches were always known to lack scalability due to the high memory bandwidth constraints. Extensive research work showed that an OQ switch can be exactly emulated by a more scalable crossbar switch (i.e., Input-Queued (IQ) switch) and a small speedup[9]. Unfortunately, this important result was of no practical use due to the high complexity of the proposed scheduling scheme. A similar result was shown in [11] and was based on the Internally Buffered Crossbar (IBC) switching architecture. While the latter result seems to overcome the complexity issue, the scheduling scheme presented, especially the time stamping mechanism performed by the OCF output scheduling scheme, is costly. In this paper, we extend our previous work in [6] and prove the same result as in [11] but with less hardware requirements. In particular, we propose a simple scheduling scheme, named Modified Current Arrival First- Lowest TTL First (MCAF-LTF), that doesn't require costly time stamping mechanism. Based on the MCAF-LTF, we prove that, with a speedup of just 2, a one-cell-internally buffered crossbar switch can exactly emulate an OQ switch. The reduced complexity of our proposed scheme makes it of high practical value and allows it to be readily implemented in such ultra-high capacity network.