HP Network Direr Software Products manual Queue Servicing Mechanism

628CHAPTER 15: PRIORITIZING NETWORK TRAFFIC

The example illustrates what happens when a device receives a set of packets of different types that are destined for the same port:

■The queuing mechanism takes the packets (which are received in no particular order) and, based upon whether they were classified as gold, silver or bronze, places them in the gold, silver or bronze queue. The bronze queue does not have enough space to hold all of the bronze packets and so the sixth bronze packet is dropped.

■The queue servicing mechanism takes packets off the queues, according to the particular mechanism in use and the way it is configured, and transmits them out of the port. This effectively re-orders the packets. The gold packets are transmitted before all other packets whilst the silver packets are transmitted in preference to the bronze ones. In the particular queue servicing mechanism used here it does not immediately transmit all of the silver packets after the gold, instead it allows some bronze packets to be transmitted so that even the lowest priority traffic can receive some amount of bandwidth.

Figure 344 Queue Servicing Mechanism

3 5 6 4 3 2 5 4 3 1 2 2 1 1

Packets Received and Classified

Queuing

Mechanism

Packets Transmitted Out of Port

1 2 3 1 2 3 1 2 4 5 3 4 5

Queue	1	2	3
Servicing
	1	2	3	4	5
Mechanism
	1	2	3	4	5
							Queue full!
							Sixth bronze
						6
							packet is
							dropped.

If these queuing operations are performed on all devices in the network then the overall effect is to speed up the flow of important traffic through the entire network. Also, by processing the queues containing more important traffic more frequently this reduces the likelihood that the queue will fill up because the queue will be emptied quicker and therefore reduce the risk that the more important traffic will get dropped.