Linux pfifo_fast is the default priority queue enabled on Linux
systems. Packets are enqueued in three FIFO droptail queues according
to three priority bands based on their Type of Service bits or DSCP bits.
QueueDisc is a base class providing the interface and implementing
the operations common to all the queueing disciplines. Child classes
need to implement the methods used to enqueue a packet (DoEnqueue),
dequeue a single packet (DoDequeue), get a copy of the next packet
to extract (DoPeek), plus methods to classify enqueued packets in
case they manage multiple queues internally.
