User Guide

628 CHAPTER 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
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.
3 11 12 23 5 6 4 23 4 5
3
1
1
1
2
2 3 5
6
4
2 3 4 5 3 1 1 12 2 3 542 3 4 5
Packet s Received and Classif ied
Queuing
Mechanism
Queue
Servicing
Mechanism
Queue f ull!
Sixth bronze
packet is
dropped.
Packets Transmitted Out of Port