Emulating FCFS OQ with Buffered Crossbar Based Distributed Shared Memory Switch

Emulating output queued (OQ) switch with sustainable implementation cost and low fixed delay is always preferable in high performance router design. Distributed shared memory (DSM) switch, also called switch-memory-switch (SMS) router, provides a promising way towards emulating OQ in backbone switches. However, the previous architectures and algorithms for DSM/SMS switches require either high implementation cost or iterations of scheduling. This paper proposes a Buffered Crossbar based DSM switch (BC-DSM), which can emulate the FCFS OQ based on a speedup-two buffered crossbar. Each crosspoint has only two packet buffers, one for arrival packet and one for departure packet Different with previous works of DSM, we do not aim to resolve memory access conflicts when packets arrive, but to randomly dispatch packets into memories through buffered crossbar and resolve departure conflicts by bounded small queueing and delay. For scheduling, the departure packets are prioritized in the transferring between the fabric and the memory. The advantages of our scheme include: 1) Only N two-speedup memories and one two-speedup buffered N times N crossbar are needed. 2) Scheduling process is simple and distributive, thanks to buffered crossbar. 3) No need for additional crosspoint buffer for overcoming long round-trip time (RTT), thanks to the probabilistic load-balancing scheme. 4) Simulation shows that only a few fixed delay is needed to provide extremely low packet loss rate such as 10^-8, under different types of traffic patterns, including bursty model and unbalanced model.