Westell A90-9100VM15-10 Verizon Router Manual PDF (Setup & Configuration Guide)

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User Guide

15.7.3

Traffic Shaping

If you click the

Quality of Service

link in the

Advanced

screen and then click

Traffic Shaping

in the left submenu,

the following screen will appear.

Traffic Shaping is the solution for managing and avoiding congestion where the network meets limited broadband

bandwidth. Typical networks use a 100 Mbps Ethernet LAN with a 100 Mbps WAN interface router. This is where

most bottlenecks occur. A traffic shaper is essentially a regulated queue that accepts uneven and/or bursty flows of

packets and transmits them in a steady, predictable stream so that the network is not overwhelmed with traffic.

While traffic priority allows basic prioritization of packets, traffic shaping provides more sophisticated definitions,

such as:

•

Bandwidth limit for each device

•

Bandwidth limit for classes of rules

•

Prioritization policy

•

TCP serialization on a device

Additionally, QoS traffic shaping rules can be defined for a default device. These rules will be used on a device that

has no definitions of its own. This enables the definition of QoS rules on the default WAN, for example, and their

maintenance even if the PPP or bridge device over the WAN is removed.

The matching of packets by rules is connection-based, known as Stateful Packet Inspection (SPI ), using the

Router’s firewall mechanism. Once a packet matches a rule, all subsequent packets with the same attributes receive

the same QoS parameters, both inbound and outbound. Connection-based QoS also allows inheriting QoS

parameters by some of the applications that open subsequent connections. For instance, QoS rules can be defined on

SIP, and the rules will apply to both control and data ports (even if the data ports are unknown). Applications that

support such inheritance have an application-level gateway (ALG) in the firewall.

To add a traffic shaping rule, click the

New Entry

link.

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If you clicked

New Entry

, the following screen will appear. Select a device from the

Device

drop-down list. Then,

click

OK

to continue.

After you have selected a device and clicked

OK

in the preceding screen, the following screen will appear. Enter the

bandwidth values for transmit (Tx) and receive (Rx), and then select the desired option from the TCP Serialization

drop-down list. Next, click the desired

New Entry

link to add a class.

Tx Traffic Shaping

The bandwidth of a device can be divided in order to reserve constant portions of bandwidth to predefined

traffic types. Such a portion is known as a Shaping Class. When not used by its predefined traffic type, or

owner (for example VoIP), the class will be available to all other traffic. However when needed, the entire

class is reserved solely for its owner. Moreover, you can limit the maximum bandwidth that a class can use

even if the entire bandwidth is available. Configure the following fields:

Tx Bandwidth

This parameter limits the gateway's bandwidth transmission rate. The purpose is to limit the bandwidth of the WAN

device to that of the weakest outbound link, for instance, the DSL speed provided by the ISP. This forces the router

to be the network bottleneck, where sophisticated QoS prioritization can be performed. If the device's bandwidth is

not limited correctly, the bottleneck will be in an unknown router or modem on the network path, rendering this

router’s QoS useless.

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TCP Serialization

You can enable TCP Serialization in its combo box, either for active voice calls only or for all traffic. The screen

will refresh, adding a 'Maximum Delay' field.

This function allows you to define the maximal allowed transmission

time frame (in milliseconds) of a single packet. Any packet that requires a longer time to be transmitted, will be

fragmented to smaller sections. This avoids transmission of large, bursty packets that may cause delay or jitter for

real-time traffic such as VoIP. If you insert a delay value in milliseconds, the delay in number of bytes will be

automatically updated on refresh.

For example, if you click the New Entry link in the

Tx Traffic Shaping

section of the

Edit Device Traffic Shaping

screen

the

Add Shaping Class

screen will appear.

Name the new class and click

OK

to save the settings, e.g., Class A. Now click the class name to edit the shaping

class or alternatively, click its pencil (edit) icon in the Action column.

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If you clicked the edit icon in the preceding screen, the

Edit Shaping Class

screen will appear.

Configure the following fields by entering or selecting the desired values:

Name

—

The name of the class.

Class Priority

—

The class can be granted one of eight priority levels, zero being the highest and seven the lowest

(note the obversion when compared to the rules priority levels). This level sets the priority of a class in comparison

to other classes on the device.

Bandwidth

—

The reserved transmission bandwidth in kilo-bits per second. You can limit the maximum allowed

bandwidth by selecting

Specify

in the drop-down list. The screen will refresh, adding yet another Kbits/s.

Policy—The class policy determines the policy of routing packets inside the class. Select one of the four options:

Priority

—

Priority queuing utilizes multiple queues, so that traffic is distributed among queues based on

priority. This priority is defined according to packet's priority, which can be defined explicitly, by a DSCP

value, or by a 802.1p value.

FIFO

—

The “First In, First Out” priority queue. This queue ignores any previously-marked priority that

packets may have.

Fairness

—

The fairness algorithm ensures no starvation by granting all packets a certain level of priority.

RED

—

The Random Early Detection algorithm utilizes statistical methods to drop packets in a

“probabilistic” way before queues overflow. Dropping packets in this way slows a source down enough to

keep the queue steady and reduces the number of packets that would be lost when a queue overflows and a

host is transmitting at a high rate.

Schedule

—

By default, the class will always be active. However, you can configure scheduler rules in order

to define time segments during which the class may be active. Refer to section 15.19, “Scheduler Rule,” for details

on setting up schedule rules.

Rx Traffic Policing:

Allows you to configure the following fields:

Rx Bandwidth

This parameter specifies the maximum traffic the policing can receive from the ISP.

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For example, if you click the

New Entry

link in the

Rx Traffic Policing

section of the

Edit Device Traffic

Shaping

screen, the

Add Policing Class

screen will appear.

Name the new class and click

OK

to save the settings, e.g. Class B. Next, click the class name to edit the shaping

class or alternatively, click its pencil (edit) action icon in the Action column.

The

Edit Policing Class

screen will appear.

Configure the following fields:

Name

—

The name of the class.

Bandwidth

—

The reserved reception bandwidth in kilo-bits per second. You can limit the maximum allowed

bandwidth by selecting the 'Specify' option in the combo box. The screen will refresh, adding yet another Kbits/s

field.

Schedule

—

By default, the class will always be active. However, you can configure scheduler rules in order to define

time segments during which the class may be active. Refer to section 15.19, “Scheduler Rule,” for details on setting

up schedule rules.

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