Actiontec MI424-WR-Rev-C Router Manual PDF (Setup & Configuration Guide)

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FiOS Router User Manual

02/11/09

181

A.2

Traffic Shaping

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

s

Bandwidth limit for classes of rules

s

Prioritization policy

s

TCP serialization on a device

s

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.

A.2a Device Traffic Shaping

This section describes the different Traffic Shaping screens and terms, and

presents the feature’s configuration logic.

Click

1.

Quality of Service

in the Advanced screen, then click

Traffic

Shaping

.

The following screen appears:

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Conﬁguring Quality of Service

A.2

Trafﬁc Shaping

A

182

Click

2.

Add

. The “Add Device Traffic Shaping” screen appears.

Select the device for which the traffic will be shaped. The drop-down list

3.

includes all the FiOS Router’s devices, as well as the option to select all

devices in each category (e.g., “All LAN Devices,”“All WAN Devices”). In this

example, select the default WAN device option.

Click

4.

Apply

. The “Edit Device Traffic Shaping” screen appears.

Configure the following three parameters:

Tx Bandwidth

Tx bandwidth limits the FiOS Router’s bandwidth transmission rate. The

purpose is to limit the bandwidth of the WAN device to that of the weakest

outbound link.. This forces the FiOS Router to be the network bottleneck, where

sophisticated QoS prioritization can be performed.

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Rx Bandwidth

In the same manner, this Rx bandwidth limits the FiOS Router’s bandwidth

reception rate.

TCP Serialization

Enable TCP Serialization from its drop-down list, either for active voice calls only

or for all traffic. The screen will refresh, adding a “Maximum Delay” text box. This

function allows the maximum allowed transmission time frame (in milliseconds)

of a single packet to be defined. Any packet requiring a longer time to be

transmitted will be fragmented to smaller sections. This avoids transmission of

large, bursty packets that can cause delay or jitter for real-time traffic, such as VoIP.

A.2b Shaping Classes

The bandwidth of a device can be divided 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. Also, the maximum bandwidth that a class

uses can be limited, even if the entire bandwidth is available.

When a shaping class is defined for a specific traffic type, two shaping classes

are created. The second class is the “Default Class”

, which is responsible for all the

packets that do not match the defined shaping class, or any other classes that

might be defined on the device. This can be viewed in the “Class Statistics” screen.

To define a shaping class:

Click

1.

Add

in the “Tx Traffic Shaping” section of the Edit Device Traffic Shaping

screen. The “Add Shaping Class” screen appears.

Name the new class and click

2.

Apply

.

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Conﬁguring Quality of Service

A.2

Trafﬁc Shaping

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184

Click the class name in the Edit Device Traffic Shaping screen to edit the

3.

shaping class. The “Edit Shaping Class” screen appears.

Configure the following parameters:

Class Priority

Select the priority of this class from the drop-down menu (0 being highest

priority, while 7 is lowest.)

Bandwidth

Reserved

: Enter the amount of bandwidth (in Kbits/second) to be reserved for

this class only.

Maximum

: Select the amount of bandwidth available to this class. Options

include

Unlimited

or

Specify

. If Specify is enabled, enter the bandwidth amount

(in Kbits/second, or as a percentage of the total bandwidth) in the appropriate

text box.

Policy

Select a QoS policy from the drop-down menu. Options include Priority, FIFO

(First In, First Out), Fairness (balanced set), RED (Random Early Detection), and

WRR (Weighted Round Robin).

When should this rule occur?

By default, the rule will always be active. However, scheduler rules can be

configured to define time periods during which the rule is active. To learn how

to configure scheduler rules, see the “Advanced Settings” chapter.

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A.2c

Ingress Data

The FiOS Router can control outgoing data fairly easily. It can queue packets,

delay them, give precedence to other packets, or drop them. This helps in

resolving upload (Tx) traffic bottlenecks, and in most cases is sufficient. However,

in the case of download (Rx) traffic bottlenecks, the ability to control the flow is

much more limited. The FiOS Router cannot queue packets, since in most cases

the local network (LAN) is much faster then the Internet (WAN), and when the

FiOS Router receives a packet from the Internet, it passes it immediately to the

local network.

QoS for ingress data has the following limitations, which do not exist for

outgoing data:

QoS can only be applied to TCP streams (UDP streams cannot be delayed)

s

No borrowing mechanism

s

When reserving Rx bandwidth, it is strictly taken from the bandwidth of all

s

other classes

Furthermore, the FiOS Router cannot control the behavior of the ISP, which may

not have proper QoS handling. Unfortunately, this is a common situation. Let’s

look at a scenario of downloading a large file and surfing the Internet at the

same time. Downloading the file is distinguished by small requests, followed

by very large responses. This may result in blocking HTML traffic at the ISP.

A

solution for such a situation is limiting the bandwidth of low-priority TCP

connections (such as the file download).

A.2d

Differentiated Services Code Point Settings

In order to understand what DSCP is, one must first be familiarized with the

Differentiated Services model.

Differentiated Services (Diffserv) is a Class of Service (CoS) model that

enhances best-effort Internet services by differentiating traffic by users, service

requirements, and other criteria. Packets are specifically marked, allowing

network nodes to provide different levels of service, as appropriate for voice

calls, video playback, or other delay-sensitive applications, via priority queuing or

bandwidth allocation, or by choosing dedicated routes for specific traffic flows.

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