In this illustration we see three rows of input and output ports, separated by a large box labeled "Switch fabric." Data packets in the third box of each input port are queued to be transferred. In the top row, we see two dark blue packets, both destined for upper output port. In the middle row we see one gray packet, destined for the lower output port. And in the bottom row we see two packets, one dark blue-destined for the upper output port-and one light blue-destined for the middle output port. A label at the top of this figure explains: "Output port contention at time t-one dark packet can be transferred." Arrows indicate the destined path for each packet.

A second version of this illustrate appears below, showing the result of HOL blocking. One dark blue packet has been transferred from the upper input port to the upper output port, leaving one dark blue packet remaining in the upper input port. The light blue and dark blue packets remain in the lower input port, and the gray packet has been transferred to the lower output port. A label at the top of this figure explains: "Light blue packet experiences HOL blocking."