Abstract: A telecommunications switch for switching protocol data units across communications links connecting the switch into a communications network and supporting multiple service types concurrently is disclosed. The switch includes an ingress processor for receiving protocol data units from a communications link, an egress processor for transmitting protocol data units onto another communications link, and a switching fabric for routing protocol data units from the ingress processor to the egress processor. The switch includes a structure of queues and schedulers that is arranged to provide concurrent class-based and flow-based queuing and scheduling of the protocol data units. This arrangement allows an amount of switching bandwidth to be guaranteed to protocol data units belonging to a given flow and allows classes of service within the flow to be allocated a relative proportion of that bandwidth.