ZyXEL Communications P-660HN-F1, User Manual

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ADSL Series User’s Guide
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Quality of Service (QoS)
10.1 Overview
This chapter discusses the ZyXEL Device’s QoS screens. Use these 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 the use of bandwidth. QoS allows the ZyXEL Device to
group and prioritize application traffic and fine-tune network performance.
Without QoS, all traffic data is 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
application such as video-on-demand.
The ZyXEL Device assigns each packet a priority and then queues the packet accordingly. Packets
assigned a high priority are processed more quickly than those with low priority 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 Internet gaming, and those for which jitter alone is a problem such as Internet radio
or streaming video.
10.1.1 What You Can Do in this Chapter
• Use the General screen to enable QoS, set the bandwidth, and allow the ZyXEL Device to
automatically assign priority to upstream traffic according to the IEEE 802.1p priority level, IP
precedence or packet length (
Section 10.2 on page 166 ).
• Use the Queue Setup screen to configure QoS queue assignment ( Section 10.3 on page 167 ).
• Use the Class Setup screen to set up classifiers to sort traffic into different flows and assign
priority and define actions to be performed for a classified traffic flow ( Section 10.4 on page
169 ).
• Use the Monitor screen to view the ZyXEL Device’s QoS-related packet statistics ( Section 10.5
on page 173 ).
10.1.2 What You Need to Know
The following terms and concepts may help as you read this chapter.
QoS versus Cos
QoS is used to prioritize source-to-destination traffic flows. All packets in the same flow are given
the same priority. CoS (class of service) 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.