Zyxel VMG4325-B10A Router Manual PDF (Setup & Configuration Guide)

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Chapter 10 Quality of Service (QoS)

VMG4380-B10A / VMG4325-B10A User’s Guide

171

10.6

The QoS Policer Setup Screen

Use this screen to configure QoS policers that allow you to limit the transmission rate of incoming

traffic. Click

Network Setting > QoS >

Policer Setup

. The screen appears as shown.

Figure 72

Network Setting > QoS > Policer Setup

The following table describes the labels in this screen.

To Queue Index

Select a queue that applies to this class.

You should have configured a queue in the

Queue Setup

screen already.

Apply

Click

Apply

to save your changes.

Cancel

Click

Cancel

to exit this screen without saving.

Table 48

Class Setup: Add/Edit (continued)

LABEL

DESCRIPTION

Table 49

Network Setting > QoS > Policer Setup

LABEL

DESCRIPTION

Add new Policer

Click this to create a new entry.

#

This is the index number of the entry.

Status

This field displays whether the policer is active or not. A yellow bulb signifies that this

policer is active. A gray bulb signifies that this policer is not active.

Name

This field displays the descriptive name of this policer.

Regulated

Classes

This field displays the name of a QoS classifier

Meter Type

This field displays the type of QoS metering algorithm used in this policer.

Rule

These are the rates and burst sizes against which the policer checks the traffic of the

member QoS classes.

Action

This shows the how the policer has the Device treat different types of traffic belonging to

the policer’s member QoS classes.

Modify

Click the

Edit

icon to edit the policer.

Click the

Delete

icon to delete an existing policer. Note that subsequent rules move up by

one when you take this action.

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10.6.1

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 73

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.

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.

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Chapter 10 Quality of Service (QoS)

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10.7

The QoS Monitor Screen

To view the Device’s QoS packet statistics, click

Network Setting > QoS >

Monitor

. The screen

appears as shown.

Figure 74

Network Setting > QoS > Monitor

The following table describes the labels in this screen.

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

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 are transmitted

successfully.

Drop Rate

This shows how many packets forwarded to this interface are 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 are transmitted

successfully.

Drop Rate

This shows how many packets assigned to this queue are dropped.

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10.8

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).

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.

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”.

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.

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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.

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.

DSCP (6 bits)

Unused (2 bits)

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

0

000000

>1100

3

1

001110

001100

001010

001000

250~1100

4

2

010110

010100

010010

010000

5

3

011110

011100

011010

011000

<250

Rate

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