A QoS switch scheduling algorithm based on recursive fair stochastic matrix decomposition
Ted H. Szymanski · 2006
A QoS switch scheduling algorithm with rate and delay guarantees is proposed. The algorithm applies to a classic input-buffered NxN crossbar switch without speedup. The time axis is divided into frames each containing F time-slots. An NxN doubly stochastic traffic rate matrix specifies a quantized traffic flow rate from each input port to each output port. The traffic matrix can be decomposed into a set of F permutations, where each permutation is used to configure the crossbar switch for one time-slot within a frame. A recursive 'fair stochastic matrix decomposition' (FSMD) algorithm, based upon the routing of a permutation through a rearrangeable network, is presented. In the resulting frame schedule, the expected inter-departure time (IDT) between cells in a flow equals the ideal IDT and the delay jitter is bounded. For fixed F an individual flow can often be scheduled in time O(logN) while a complete reconfiguration requires O(NlogN) time when implemented in a serial processor. An RSVP-like algorithm can be used to reserve bandwidth and buffer space in an IP-router or ATM/MPLS switch during the connection setup phase, and the FSMD algorithm can be used to schedule traffic. Best-effort traffic can be scheduled using any existing dynamic scheduling algorithm to fill the remaining unused switch capacity within each frame. The algorithm supports multicast traffic