Zyxel VMG8324-B10A Router Manual PDF (Setup & Configuration Guide)

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Chapter 9 Quality of Service (QoS)

VMG8324-B10A / VMG8324-B30A Series User’s Guide

151

9.7

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 81

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 53

Policer Setup: Add/Edit

LABEL

DESCRIPTION

Table 54

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.

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9.8

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)

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.

Table 54

Network Setting > QoS > Monitor (continued)

LABEL

DESCRIPTION

Table 55

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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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.

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 56

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)

000000

>1100

001110

001100

001010

001000

250~1100

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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

bytes which is also the bucket size, so the bucket can hold up to

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.

•

If there are no tokens in the bucket, the Device stops transmitting until enough tokens are

generated.

•

If not enough tokens are available, the Device treats the packet in either one of the following

ways:

In traffic shaping:

•

Holds it in the queue until enough tokens are available in the bucket.

In traffic policing:

•

Drops it.

•

Transmits it but adds a DSCP mark. The Device may drop these marked packets if the network

is overloaded.

010110

010100

010010

010000

011110

011100

011010

011000

<250

100110

100100

100010

100000

101110

101000

110000

111000

Table 56

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)

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Configure the bucket size to be equal to or less than the amount of the bandwidth that the interface

can support. It does not help if you set it to a bucket size over the interface’s capability. The smaller

the bucket size, the lower the data transmission rate and that may cause outgoing packets to be

dropped. A larger transmission rate requires a big bucket size. For example, use a bucket size of 10

kbytes to get the transmission rate up to 10 Mbps.

Single Rate Three Color Marker

The Single Rate Three Color Marker (srTCM, defined in RFC 2697) is a type of traffic policing that

identifies packets by comparing them to one user-defined rate, the Committed Information Rate

(CIR), and two burst sizes: the Committed Burst Size (CBS) and Excess Burst Size (EBS).

The srTCM evaluates incoming packets and marks them with one of three colors which refer to

packet loss priority levels. High packet loss priority level is referred to as red, medium is referred to

as yellow and low is referred to as green.

The srTCM is based on the token bucket filter and has two token buckets (CBS and EBS). Tokens

are generated and added into the bucket at a constant rate, called Committed Information Rate

(CIR). When the first bucket (CBS) is full, new tokens overflow into the second bucket (EBS).

All packets are evaluated against the CBS. If a packet does not exceed the CBS it is marked green.

Otherwise it is evaluated against the EBS. If it is below the EBS then it is marked yellow. If it

exceeds the EBS then it is marked red.

The following shows how tokens work with incoming packets in srTCM:

•

A packet arrives. The packet is marked green and can be transmitted if the number of tokens in

the CBS 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 CBS bucket.

•

If there are not enough tokens in the CBS bucket, the Device checks the EBS bucket. The packet

is marked yellow if there are sufficient tokens in the EBS bucket. Otherwise, the packet is marked

red. No tokens are removed if the packet is dropped.

Two Rate Three Color Marker

The Two Rate Three Color Marker (trTCM, defined in RFC 2698) is a type of traffic policing that

identifies packets by comparing them to two user-defined rates: the Committed Information Rate

(CIR) and the Peak Information Rate (PIR). The CIR specifies the average rate at which packets are

admitted to the network. The PIR is greater than or equal to the CIR. CIR and PIR values are based

on the guaranteed and maximum bandwidth respectively as negotiated between a service provider

and client.

The trTCM evaluates incoming packets and marks them with one of three colors which refer to

packet loss priority levels. High packet loss priority level is referred to as red, medium is referred to

as yellow and low is referred to as green.

The trTCM is based on the token bucket filter and has two token buckets (Committed Burst Size

(CBS) and Peak Burst Size (PBS)). Tokens are generated and added into the two buckets at the CIR

and PIR respectively.

Rate

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