ZyXEL Communications P-2802H-I Series, Руководство пользователя

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P-2802H(W)(L)-I Series User’s Guide
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H A P T E R
17
Quality of Service (QoS)
This chapter contains information about configuring QoS, editing classifiers and viewing the
ZyXEL Device’s QoS packet statistics.
17.1 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.
17.1.1 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.
IEEE 802.1p specifies the user priority field and defines up to eight separate traffic types. The
following table describes the traffic types defined in the IEEE 802.1d standard (which
incorporates the 802.1p).
Table 98 IEEE 802.1p Priority Level and Traffic Type
PRIORITY
LEVEL
TRAFFIC TYPE
Level 7 Typically used for network control traffic such as router configuration messages.
Level 6 Typically used for voice traffic that is especially sensitive to jitter (jitter is the variations in
delay).