This illustration uses the same structure as figure 4.8, with three rows of input and output ports separated by a switch fabric. Here, we see one packet in the third box of each of the input ports, and blue lines from each of these packets indicates that they are all destined for the upper output link. At the same time, a new packet has arrived in the upper and lower input ports. A label at the top of this figure explains: "Output port contention at time t."

A second figure below this one shows the result of output port queuing. The three packets destined for the upper output port have all arrived and are queued there. The two new packets have moved to the third boxes in the upper and lower input ports, with lines indicating that the upper packet is destined for the middle output port and the lower packet is destined for the upper output port. A label at the top of this figure explains: "One packet time later."