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Chapter 8 Quality of Service (QoS)
Basic Home Station VDSL2 P8701T User’s Guide
126
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 VDSL Router uses the
Token Bucket algorithm to allow a certain amount of large bursts while keeping a limit at the
average rate.
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.
Traffic
Time
Traffic Rate
Traffic
Time
Traffic Rate
(Before Traffic Shaping)
(After Traffic Shaping)
Traffic
Time
Traffic Rate
Traffic
Time
Traffic Rate
(Before Traffic Policing)
(After Traffic Policing)
Page 127 / 240
Chapter 8 Quality of Service (QoS)
Basic Home Station VDSL2 P8701T User’s Guide
127
8.3
The QoS Screen
Click
Wireless network > Classic configuration > Advanced Setup > QoS
to open the screen
shown next. Use this screen to enable or disable QoS and set the default DSCP mark for outgoing
packets that do not match any classification rules.
Figure 45
QoS
The following table describes the labels in this screen.
8.4
The QoS Queue Setup Screen
Click
Wireless network > Classic configuration > Advanced Setup > QoS >
QoS Queue
to
open the screen shown next. Use this screen to configure QoS queue assignment.
Table 39
QoS
LABEL
DESCRIPTION
QoS
Select the
Enable
check box to turn on QoS to improve your network performance.
Select Default
DSCP Mark
Set the default DSCP (DiffServ Code Point) value for outgoing packets that do not match
any classification rules.
Apply/Save
Click this to save your changes.
Page 128 / 240
Chapter 8 Quality of Service (QoS)
Basic Home Station VDSL2 P8701T User’s Guide
128
Figure 46
QoS Queue Setup
The following table describes the labels in this screen.
Table 40
QoS Queue Setup
LABEL
DESCRIPTION
Name
This shows the descriptive name of this queue.
Key
This is the queue’s index number.
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.
Interface
This shows the name of the VDSL Router’s interface through which traffic in this queue
passes.
Qid
This shows the priority of this queue for the interface.
Prec/Alg/Wght
This displays the queue’s default precedence, queue management algorithm, and weighted
round robin weight.
DSL Latency
This displays whether the ATM interface uses interleave delay (
Path1
) or fast mode with no
interleave delay (
Path0
).
PTM Priority
This displays the queue’s PTM priority (
High
or
Low
). This has no effect at the time of
writing.
Shaping Rate
This displays the maximum transmission rate for traffic in this queue.
Burst Size
This displays the maximum number of cells the queue can send at the shaping rate.
Enable
Select an entry’s
Enable
option and click the
Enable
button to turn it on.
Remove
Select an entry’s
Remove
option and click the
Remove
button to delete it.
Add
Click this button to create a new queue entry.
Page 129 / 240
Chapter 8 Quality of Service (QoS)
Basic Home Station VDSL2 P8701T User’s Guide
129
8.4.1
Adding a QoS Queue
Click the
QoS Queue Setup
screen’s
Add
button to configure a new queue.
Figure 47
QoS Queue Setup: Add
The following table describes the labels in this screen.
Table 41
QoS Queue Setup: Add
LABEL
DESCRIPTION
Name
Enter the descriptive name of this queue.
Enable
Enable or disable this queue.
Interface
Select the interface to which this queue is applied.
Queue
Precedence
Select the precedence level (from 1 to 8) of this queue. The smaller the number, the higher
the priority level. Traffic assigned to higher priority queues gets through faster while traffic
in lower priority queues is dropped if the network is congested.
The precedence list shows the scheduler algorithm for each precedence level. The scheduler
algorithm depends on the interface. Ethernet interfaces use strict priority (SP). ATM and
PTM interfaces use the scheduler algorithm configured for the interface (weighted round
robin or weighted fair queuing).
The VDSL Router uses the algorithm to service queues with the same precedence.
The VDSL Router uses strict priority to service queues with different precedences.
Page 130 / 240
Chapter 8 Quality of Service (QoS)
Basic Home Station VDSL2 P8701T User’s Guide
130
8.5
The QoS Classification Setup Screen
Click
Wireless network > Classic configuration > Advanced Setup > QoS > QoS
Classification
to open the following screen. Use this screen to manage QoS classifiers. A classifier
groups traffic into data flows according to specific criteria such as the source address, destination
address, source port number, destination port number or incoming interface. For example, you can
configure a classifier to select traffic from the same protocol port (such as Telnet) to form a flow.
You can give different priorities to traffic that the VDSL Router forwards out through the WAN
interface. Give high priority to voice and video to make them run more smoothly. Similarly, give low
priority to many large file downloads so that they do not reduce the quality of other applications.
Figure 48
QoS Classification Setup
Queue Weight
This displays for ATM and PTM interface queues. Select the weight of this queue.
If two queues have the same precedence, the VDSL Router divides the bandwidth across the
queues according to their weights. Queues with larger weights get more bandwidth than
queues with smaller weights.
Default Queue
Weight
This displays for ATM and PTM interface queues. Specify the VC’s weight for weighed fair
queuing. The higher the weight, the bigger portion of the bandwidth the VC gets.
Shaping Rate
This displays for PTM interface queues. Set the maximum transmission rate for traffic in this
queue.
Shaping Burst
Size
This displays for PTM interface queues. Set the maximum number of cells the queue can
send at the shaping rate.
PTM Priority
This displays for PTM interface queues. Set the queue to low or high priority. This has no
effect at the time of writing.
DSL Latency
This displays for ATM and PTM interface queues. Select
Path0 (Fast)
to use no interleaving
and have faster transmission (a “fast channel”). Suitable only for a good line with little need
for error correction.
At the time of writing the VDSL Router supports fast mode only and interleaved is reserved
for future use.
Apply/Save
Click this button to save your changes.
Table 41
QoS Queue Setup: Add (continued)
LABEL
DESCRIPTION

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