Out-of-sequence preventative cell dispatching for multicast input-queued space-memory-memory Clos-network

This paper proposes two out-of-sequence (OOS) preventative cell dispatching algorithms for the multicast input-queued space-memory-memory (IQ-SMM) Clos-network switch architecture, i.e. the multicast flow-based DSRR (MF-DSRR) and the multicast flow-based round-robin (MFRR). Treating each cell independently, the desynchronized static round-robin (DSRR) cell dispatching scheme can evenly distribute cells to the central switching modules, however, its frequent change of the input switching module connection pattern causes a serious OOS problem to the IQ-SMM architecture. Therefore large reassembly buffers are required at the output ports and high reassembly delay can degrade the multicast services. MF-DSRR can reduce the OOS problem and leverages the principle of DSRR to obtain a low complexity, however it fails to eliminate the in-packet OOS where cells of the same packet are disordered. Using more resources compared to MF-DSRR, MFRR is able to eliminate the in-packet OOS, resulting in a significant reduction of reassembly buffer size and delay.