Output queued switch emulation by a one-cell-internally buffered crossbar switch

The output queued (OQ) switching architecture shows optimal performance amongst all queuing approaches. However, OQ switches lack scalability due to high memory-bandwidth constraints. An OQ switch can be exactly emulated by a more scalable crossbar switch (i.e., input-queued - IQ - switch) and a small speedup (Chuang, S. et al., 1998). Unfortunately, this result was not of practical use due to the high complexity of the proposed scheduling scheme. A similar result was shown by B. Magill et al. (see Conf. on Commun. Control and Computing, 2002) 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 is costly. We extend our previous work (Mhamdi and Hamdi, IEEE ICC'03, vol.3, p.1659-63, 2003) and prove the same result as Magill et al., but with lower hardware requirements.. In particular, we propose a simple scheduling scheme, named modified current arrival first-lowest TTL (time-to-live) first (MCAF-LTF), that does not require a 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 ultra-high capacity networks.