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Page 141 / 327 Scroll up to view Page 136 - 140
VMG3926-B10A User’s Guide
141
C
HAPTER
10
Quality of Service (QoS)
10.1
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 VMG 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 VMG 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.
This chapter contains information about configuring QoS and editing classifiers.
10.1.1
What You Can Do in this Chapter
• The
General
screen lets you enable or disable QoS and set the upstream bandwidth (
Section
10.3 on page 143
).
• The
Queue Setup
screen lets you configure QoS queue assignment (
Section 10.4 on page 144
).
• The
Classification Setup
screen lets you add, edit or delete QoS classifiers (
Section 10.5 on
page 146
).
• The
Shaper Setup
screen limits outgoing traffic transmission rate on the selected interface
(
Section 10.6 on page 151
).
• The
Policer Setup
screen to control incoming traffic transmission rate and bursts (
Section 10.7
on page 152
).
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Chapter 10 Quality of Service (QoS)
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142
10.2
What You Need to Know
The following terms and concepts may help as you read through 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.
CoS technologies include IEEE 802.1p layer 2 tagging and DiffServ (Differentiated Services 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 ToS (Type of Service) field in the IP header.
Tagging and Marking
In a QoS class, you can configure whether to add or change the DSCP (DiffServ Code Point) 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.
Traffic Shaping
Bursty traffic may cause network congestion. Traffic shaping regulates packets to be transmitted
with a pre-configured data transmission rate using buffers (or queues). Your VMG uses the Token
Bucket algorithm to allow a certain amount of large bursts while keeping a limit at the average rate.
Traffic
Time
Traffic Rate
Traffic
Time
Traffic Rate
(Before Traffic Shaping)
(After Traffic Shaping)
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Chapter 10 Quality of Service (QoS)
VMG3926-B10A User’s Guide
143
Traffic Policing
Traffic policing is the limiting of the input or output transmission rate of a class of traffic on the
basis of user-defined criteria. Traffic policing methods measure traffic flows against user-defined
criteria and identify it as either conforming, exceeding or violating the criteria.
The VMG supports three incoming traffic metering algorithms: Token Bucket Filter (TBF), Single
Rate Two Color Maker (srTCM), and Two Rate Two Color Marker (trTCM). You can specify actions
which are performed on the colored packets. See
Section 10.8 on page 154
for more information on
each metering algorithm.
10.3
The Quality of Service General Screen
Click
Network Setting > QoS > General
to open the screen as shown next.
Use this screen to enable or disable QoS and set the upstream bandwidth. See
Section 10.1 on
page 141
for more information.
Figure 67
Network Settings > QoS > General
Traffic
Time
Traffic Rate
Traffic
Time
Traffic Rate
(Before Traffic Policing)
(After Traffic Policing)
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Chapter 10 Quality of Service (QoS)
VMG3926-B10A User’s Guide
144
The following table describes the labels in this screen.
10.4
The Queue Setup Screen
Click
Network Setting >
QoS > Queue Setup
to open the screen as shown next.
Use this screen to configure QoS queue assignment.
Table 44
Network Setting > QoS > General
LABEL
DESCRIPTION
QoS
Select the
Enable
check box to turn on QoS to improve your network performance.
WAN Managed
Upstream
Bandwidth
Enter the amount of upstream bandwidth for the WAN interfaces that you want to allocate
using QoS.
The recommendation is to set this speed to match the interfaces’ actual transmission speed.
For example, set the WAN interfaces’ speed to 100000 kbps if your Internet connection has
an upstream transmission speed of 100 Mbps.
You can set this number higher than the interfaces’ actual transmission speed. The VMG
uses up to 95% of the DSL port’s actual upstream transmission speed even if you set this
number higher than the DSL port’s actual transmission speed.
You can also set this number lower than the interfaces’ actual transmission speed. This will
cause the VMG to not use some of the interfaces’ available bandwidth.
If you leave this field blank, the VMG automatically sets this number to be 95% of the WAN
interfaces’ actual upstream transmission speed.
LAN Managed
Downstream
Bandwidth
Enter the amount of downstream bandwidth for the LAN interfaces (including WLAN) that
you want to allocate using QoS.
The recommendation is to set this speed to match the WAN interfaces’ actual transmission
speed. For example, set the LAN managed downstream bandwidth to 100000 kbps if you
use a 100 Mbps wired Ethernet WAN connection.
You can also set this number lower than the WAN interfaces’ actual transmission speed. This
will cause the VMG to not use some of the interfaces’ available bandwidth.
If you leave this field blank, the VMG automatically sets this to the LAN interfaces’ maximum
supported connection speed.
Upstream
traffic priority
Assigned by
Select how the VMG assigns priorities to various upstream traffic flows.
•
None:
Disables auto priority mapping and has the VMG put packets into the queues
according to your classification rules. Traffic which does not match any of the
classification rules is mapped into the default queue with the lowest priority.
•
Ethernet Priority:
Automatically assign priority based on the IEEE 802.1p priority level.
•
IP Precedence:
Automatically assign priority based on the first three bits of the TOS
field in the IP header.
•
Packet Length:
Automatically assign priority based on the packet size. Smaller packets
get higher priority since control, signaling, VoIP, internet gaming, or other real-time
packets are usually small while larger packets are usually best effort data packets like
file transfers.
Apply
Click
Apply
to save your changes.
Cancel
Click
Cancel
to restore your previously saved settings.
Page 145 / 327
Chapter 10 Quality of Service (QoS)
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145
Figure 68
Network Setting > QoS > Queue Setup
The following table describes the labels in this screen.
10.4.1
Adding a QoS Queue
Click
Add New Queue
or the edit icon in the
Queue Setup
screen to configure a queue.
Figure 69
Queue Setup: Add
Table 45
Network Setting > QoS > Queue Setup
LABEL
DESCRIPTION
Add New Queue
Click this button to create a new queue entry.
#
This is the index number of the entry.
Status
This field displays whether the queue is active or not. A yellow bulb signifies that this queue
is active. A gray bulb signifies that this queue is not active.
Name
This shows the descriptive name of this queue.
Interface
This shows the name of the VMG’s interface through which traffic in this queue passes.
Priority
This shows the priority of this queue.
Weight
This shows the weight of this queue.
Buffer
Management
This shows the queue management algorithm used for this queue.
Queue management algorithms determine how the VMG should handle packets when it
receives too many (network congestion).
Rate Limit
This shows the maximum transmission rate allowed for traffic on this queue.
Modify
Click the
Edit
icon to edit the queue.
Click the
Delete
icon to delete an existing queue. Note that subsequent rules move up by
one when you take this action.

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