How does virtual output queuing (VoQ) help switches avoid head-of-line blocking and enhance throughput? 

It divides each port ingress queue into different queues based on the priority and egress port of each packet 

It establishes a matrix of connections to multiple cross-bar switches within the switch backplane 

It considers traffic congestion, queues traffic, and informs the ingress port when it can use the crossbar 

It allows the ingress port to fragment packets and send the fragments in multiple queues over different crossbars