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223
802.1P Priority
Assign a priority for the traffic transmitted through the port. Select
Same
if you do
not want to modify the priority. You may choose a priority level from
0-7
, with 0
being the lowest level and 7 being the highest level.
Apply
Click this to save your changes.
Cancel
Click this to restore your previously saved settings.
Table 82
Advanced > 802.1Q/1P > Port Setting (continued)
LABEL
DESCRIPTION
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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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CoS technologies include IEEE 802.1p layer 2 tagging and Differentiated Services (DiffServ
or DS). IEEE 802.1p tagging makes use of three bits in the packet header, while DiffServ is a
new protocol and defines a new DS field, which replaces the eight-bit Type of Service (ToS)
field in the IP header.
Tagging and Marking
In a QoS class, you can configure whether to add or change the DiffServ Code Point (DSCP)
value, IEEE 802.1p priority level and VLAN ID number in a matched packet. When the packet
passes through a compatible network, the networking device, such as a backbone switch, can
provide specific treatment or service based on the tag or marker.
Finding Out More
See
Section 15.5 on page 235
for advanced technical information on QoS.
15.1.3
QoS Class Setup Example
In the following figure, your Internet connection has an upstream transmission speed of 50
Mbps. You configure a classifier to assign the highest priority queue (6) to VoIP traffic from
the LAN interface, so that voice traffic would not get delayed when there is network
congestion. Traffic from the boss’s IP address (192.168.1.23 for example) is mapped to queue
5. Traffic that does not match these two classes are assigned priority queue based on the
internal QoS mapping table on the ZyXEL Device.
Figure 133
QoS Example
50 Mbps
DSL
VoIP: Queue 6
Boss: Queue 5
IP=192.168.1.23
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Figure 134
QoS Class Example: VoIP -1
Figure 135
QoS Class Example: VoIP -2

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