Network switching and/or routing devices can use multiple priority data streams and queues to support prioritized serial transmission of data from line cards (or the like) through a fabric switch to other line cards (or the like). Preemption logic is used to insert within a data stream commands indicating a switch from one priority level data to another. Delimiter commands and combination switch/delimiter commands can also be used. Multiple crossbars are implemented in the fabric switch to support the various data stream priority levels.