Switch routing algorithms

A message at an ingress switch of a multi-stage circuit switching network, e.g. clos network, is forwarded using a routing algorithm, the algorithm involving the determination of at least one availability matrix for each middle switch between the ingress and egress switches of the network. A middle switch is selected on the basis of its availability matrix and the ingress switch then transmits the message via the selected middle switch. The algorithm may forward messages on the basis of unicast, fan-in (many-to-one), and fan-out (one-to-many, or multicast). Unicast forwarding may be based on a worst-fit bin packing algorithm. Fan-out forwarding may be deferred to the later stages of the network e.g. the middle stages (see figure 7), whereas fan-in forwarding may be executed at early stages e.g. ingress stages (see figure 9). The algorithm minimises blocking and imbalance on middle switches, and promotes maintenance of existing routing arrangements.