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Page 146 / 359 Scroll up to view Page 141 - 145
Chapter 8 Quality of Service (QoS)
eircom F1000 Modem User’s Guide
146
8.6.1
Add/Edit a QoS Policer
Click
Add
new Policer
in the
Policer Setup
screen or the
Edit
icon next to a policer to show the
following screen.
Figure 79
Policer Setup: Add/Edit
The following table describes the labels in this screen.
Table 50
Policer Setup: Add/Edit
LABEL
DESCRIPTION
Active
Select the check box to activate this policer.
Name
Enter the descriptive name of this policer.
Meter Type
This shows the traffic metering algorithm used in this policer.
The
Simple Token Bucket
algorithm uses tokens in a bucket to control when traffic can be
transmitted. Each token represents one byte. The algorithm allows bursts of up to
b
bytes
which is also the bucket size.
The
Single Rate Three Color Marker
(srTCM) is based on the token bucket filter and
identifies packets by comparing them to the Committed Information Rate (CIR), the
Committed Burst Size (CBS) and the Excess Burst Size (EBS).
The
Two Rate Three Color Marker
(trTCM) is based on the token bucket filter and
identifies packets by comparing them to the Committed Information Rate (CIR) and the
Peak Information Rate (PIR).
Committed
Rate
Specify the committed rate. When the incoming traffic rate of the member QoS classes is
less than the committed rate, the device applies the conforming action to the traffic.
Committed
Burst Size
Specify the committed burst size for packet bursts. This must be equal to or less than the
peak burst size (two rate three color) or excess burst size (single rate three color) if it is also
configured.
This is the maximum size of the (first) token bucket in a traffic metering algorithm.
Page 147 / 359
Chapter 8 Quality of Service (QoS)
eircom F1000 Modem User’s Guide
147
8.7
The QoS Monitor Screen
This screen is available only when you set a rate limit for a WAN queue in the
Queue Setup
screen
and the WAN interface is connected. Use this screen to monitor the traffic statistics for both the
WAN and LAN interfaces. To view the Device’s QoS packet statistics, click
Network Setting > QoS
>
Monitor
. The screen appears as shown.
Figure 80
Network Setting > QoS > Monitor
Conforming
Action
Specify what the Device does for packets within the committed rate and burst size (green-
marked packets).
•
Pass:
Send the packets without modification.
•
DSCP Mark:
Change the DSCP mark value of the packets. Enter the DSCP mark value to
use.
Non-
Conforming
Action
Specify what the Device does for packets that exceed the excess burst size or peak rate and
burst size (red-marked packets).
•
Drop:
Discard the packets.
•
DSCP Mark:
Change the DSCP mark value of the packets. Enter the DSCP mark value to
use. The packets may be dropped if there is congestion on the network.
Available Class
Selected Class
Select a QoS classifier to apply this QoS policer to traffic that matches the QoS classifier.
Highlight a QoS classifier in the
Available Class
box and use the
>
button to move it to the
Selected Class
box.
To remove a QoS classifier from the
Selected Class
box, select it and use the
<
button.
Apply
Click
Apply
to save your changes.
Cancel
Click
Cancel
to exit this screen without saving.
Table 50
Policer Setup: Add/Edit
LABEL
DESCRIPTION
Page 148 / 359
Chapter 8 Quality of Service (QoS)
eircom F1000 Modem User’s Guide
148
The following table describes the labels in this screen.
8.8
Technical Reference
The following section contains additional technical information about the Device features described
in this chapter.
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 51
Network Setting > QoS > Monitor
LABEL
DESCRIPTION
Refresh Interval
Enter how often you want the Device to update this screen. Select
No Refresh
to stop
refreshing statistics.
Interface Monitor
#
This is the index number of the entry.
Name
This shows the name of the interface on the Device.
Pass Rate
This shows how many packets forwarded to this interface has been transmitted
successfully.
Drop Rate
This shows how many packets forwarded to this interface has been dropped.
Queue Monitor
#
This is the index number of the entry.
Name
This shows the name of the queue.
Pass Rate
This shows how many packets assigned to this queue has been transmitted successfully.
Drop Rate
This shows how many packets assigned to this queue has been dropped.
Table 52
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).
Level 5
Typically used for video that consumes high bandwidth and is sensitive to jitter.
Level 4
Typically used for controlled load, latency-sensitive traffic such as SNA (Systems
Network Architecture) transactions.
Level 3
Typically used for “excellent effort” or better than best effort and would include
important business traffic that can tolerate some delay.
Level 2
This is for “spare bandwidth”.
Page 149 / 359
Chapter 8 Quality of Service (QoS)
eircom F1000 Modem User’s Guide
149
DiffServ
QoS is used to prioritize source-to-destination traffic flows. All packets in the flow are given the
same priority. You can use CoS (class of service) to give different priorities to different packet
types.
DiffServ (Differentiated Services) is a class of service (CoS) model that marks packets so that they
receive specific per-hop treatment at DiffServ-compliant network devices along the route based on
the application types and traffic flow. Packets are marked with DiffServ Code Points (DSCPs)
indicating the level of service desired. This allows the intermediary DiffServ-compliant network
devices to handle the packets differently depending on the code points without the need to
negotiate paths or remember state information for every flow. In addition, applications do not have
to request a particular service or give advanced notice of where the traffic is going.
DSCP and Per-Hop Behavior
DiffServ defines a new Differentiated Services (DS) field to replace the Type of Service (TOS) field
in the IP header. The DS field contains a 2-bit unused field and a 6-bit DSCP field which can define
up to 64 service levels. The following figure illustrates the DS field.
DSCP is backward compatible with the three precedence bits in the ToS octet so that non-DiffServ
compliant, ToS-enabled network device will not conflict with the DSCP mapping.
The DSCP value determines the forwarding behavior, the PHB (Per-Hop Behavior), that each packet
gets across the DiffServ network. Based on the marking rule, different kinds of traffic can be
marked for different kinds of forwarding. Resources can then be allocated according to the DSCP
values and the configured policies.
IP Precedence
Similar to IEEE 802.1p prioritization at layer-2, you can use IP precedence to prioritize packets in a
layer-3 network. IP precedence uses three bits of the eight-bit ToS (Type of Service) field in the IP
header. There are eight classes of services (ranging from zero to seven) in IP precedence. Zero is
the lowest priority level and seven is the highest.
Automatic Priority Queue Assignment
If you enable QoS on the Device, the Device can automatically base on the IEEE 802.1p priority
level, IP precedence and/or packet length to assign priority to traffic which does not match a class.
Level 1
This is typically used for non-critical “background” traffic such as bulk transfers that
are allowed but that should not affect other applications and users.
Level 0
Typically used for best-effort traffic.
DSCP (6 bits)
Unused (2 bits)
Table 52
IEEE 802.1p Priority Level and Traffic Type
PRIORITY
LEVEL
TRAFFIC TYPE
Page 150 / 359
Chapter 8 Quality of Service (QoS)
eircom F1000 Modem User’s Guide
150
The following table shows you the internal layer-2 and layer-3 QoS mapping on the Device. On the
Device, traffic assigned to higher priority queues gets through faster while traffic in lower index
queues is dropped if the network is congested.
Token Bucket
The token bucket algorithm uses tokens in a bucket to control when traffic can be transmitted. The
bucket stores tokens, each of which represents one byte. The algorithm allows bursts of up to
b
bytes which is also the bucket size, so the bucket can hold up to
b
tokens. Tokens are generated
and added into the bucket at a constant rate. The following shows how tokens work with packets:
•
A packet can be transmitted if the number of tokens in the bucket is equal to or greater than the
size of the packet (in bytes).
•
After a packet is transmitted, a number of tokens corresponding to the packet size is removed
from the bucket.
Table 53
Internal Layer2 and Layer3 QoS Mapping
PRIORITY
QUEUE
LAYER 2
LAYER 3
IEEE 802.1P USER
PRIORITY
(ETHERNET
PRIORITY)
TOS (IP
PRECEDENCE)
DSCP
IP PACKET
LENGTH (BYTE)
0
1
0
000000
1
2
2
0
0
000000
>1100
3
3
1
001110
001100
001010
001000
250~1100
4
4
2
010110
010100
010010
010000
5
5
3
011110
011100
011010
011000
<250
6
6
4
100110
100100
100010
100000
5
101110
101000
7
7
6
110000
111000
7

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