P-660HN-FxZ Series User’s Guide
225
C
HAPTER
15
Quality of Service (QoS)
15.1
Overview
Use the
QoS
screens to set up your ZyXEL Device to use QoS for traffic management.
Quality of Service (QoS) refers to both a network’s ability to deliver data with minimum
delay, and the networking methods used to control bandwidth. QoS allows the ZyXEL Device
to group and prioritize application traffic and fine-tune network performance.
Without QoS, all traffic data are equally likely to be dropped when the network is congested.
This can cause a reduction in network performance and make the network inadequate for time-
critical applications such as video-on-demand.
The ZyXEL Device assigns each packet a priority and then queues the packet accordingly.
Packets assigned with a high priority are processed more quickly than those with low priorities
if there is congestion, allowing time-sensitive applications to flow more smoothly. Time-
sensitive applications include both those that require a low level of latency (delay) and a low
level of jitter (variations in delay) such as Voice over IP (VoIP) or Internet gaming, and those
for which jitter alone is a problem such as Internet radio or streaming video.
15.1.1
What You Can Do in the QoS Screens
•
Use the
General
screen (
Section 15.2 on page 229
) to enable QoS on the ZyXEL Device,
decide allowable bandwidth using QoS and configure priority mapping settings for traffic
that does not match a custom class.
•
Use the
Class Setup
screen (
Section 15.3 on page 230
) to set up classifiers to sort traffic
into different flows and assign priority and define actions to be performed for a classified
traffic flow.
•
Use the
Monitor
screen (
Section 15.4 on page 234
) to view the ZyXEL Device’s QoS-
related packet statistics.
15.1.2
What You Need to Know About QoS
QoS versus Cos
QoS is used to prioritize source-to-destination traffic flows. All packets in the same flow are
given the same priority. Class of Service (CoS) is a way of managing traffic in a network by
grouping similar types of traffic together and treating each type as a class. You can use CoS to
give different priorities to different packet types.
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