Throughput in a crossbar network element by modifying mappings between time slots and ports

A network element, comprising:

• multiple output ports coupled to a communication network and organized in M groups, each group comprising P output ports that are selectable over respective predefined time slots in accordance with a cyclic mapping between the time slots and the output ports for that group;
• a crossbar fabric comprising M fabric outputs coupled respectively to the groups, and N fabric inputs coupled respectively to N buffers that store packets for transmission via the output ports, wherein in each time slot, the crossbar fabric is configured to receive data from the buffers via the fabric inputs, and route the data to the fabric outputs in accordance with a routing plan;
• and
• a scheduler, configured to:
• determine the routing plan over the time slots, and apply the routing plan for transmitting the packets from the buffers to the communication network via the crossbar fabric and the output ports;
• in response to identifying that, in a given time slot, a required rate of readout of the packets from a given buffer exceeds a maximum rate supported by the given buffer, select a group of the output ports to which the given buffer is routed by the crossbar fabric in the given time slot, and modify the cyclic mapping for the selected group to produce a modified cyclic mapping that reduces the required rate of readout from the given buffer in the given time slot.