ZyXEL Communications P-663H-51, User Manual

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P-663H-51 User’s Guide
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H A P T E R
9
Quality of Service (QoS)
This chapter contains information about configuring QoS, editing classifiers and viewing the
ZyXEL Device’s QoS packet statistics.
9.1 QoS Overview
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. 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.
Configure QoS on the ZyXEL Device to group and prioritize application traffic and fine-tune
network performance. Setting up QoS involves these steps:
1
Configure classifiers to sort traffic into different flows.
2 Assign priority and define actions to be performed for a classified traffic flow.
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 Voice over IP (VoIP) or Internet gaming, and those
for which jitter alone is a problem such as Internet radio or streaming video.
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The ZyXEL Device applies QoS to upstream traffic (going out through the
WAN interface).
9.1.1 IEEE 802.1Q Tag
The IEEE 802.1Q standard defines an explicit VLAN tag in the MAC header to identify the
VLAN membership of a frame across bridges. A VLAN tag includes the 12-bit VLAN ID and
3-bit user priority. The VLAN ID associates a frame with a specific VLAN and provides the
information that devices need to process the frame across the network.