223
5
5. Configuring Quality of Service
In a typical switch, each physical port consists of one or more queues for transmitting packets on
the attached network. Multiple queues per port are often provided to give preference to certain
packets over others based on user-defined criteria. When a packet is queued for transmission in
a port, the rate at which it is serviced depends on how the queue is configured and possibly the
amount of traffic present in the other queues of the port. If a delay is necessary, packets get held
in the queue until the scheduler authorizes the queue for transmission. As queues become full,
packets have no place to be held for transmission and get dropped by the switch.
QoS is a means of providing consistent, predictable data delivery by distinguishing between
packets that have strict timing requirements from those that are more tolerant of delay. Packets
with strict timing requirements are given special treatment in a QoS-capable network. With this in
mind, all elements of the network must be QoS-capable. The presence of at least one node that
is not QoS-capable creates a deficiency in the network path, and the performance of the entire
packet flow is compromised.
Use the features you access from the QoS tab to configure Quality of Service (QoS) settings on
the switch. The QoS tab contains links to the features described in the following sections.
• Class of Service on page 224
• Differentiated Services on page 229
To Next Page
Loading...
