ZyXEL P-663H-51 Guia Do Utilizador

P-663H-51 User’s Guide

This chapter contains information about configuring QoS, editing classifiers and viewing the 
ZyXEL Device’s QoS packet statistics.

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).

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.