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9.7.1

Understanding Received Signal Strength

Received signal strength (RSSI) is measured from connected wireless client devices to

the wireless cable modem. This value can significantly impact wireless

speeds/performance. It is determined by:



Materials (for example, open air, concrete, trees)



Distance between wireless clients and the wireless cable modem



Wireless capabilities of the client devices

To determine the received signal strength, refer to

Using the Access Control Option on

page 75

and review the

RSSI

value. A receive signal strength indicator between 0 to -64

dBm is considered optimal. Levels of -67dBm and lower (for example, -70, -80, etc.) have

a downward impact on wireless data throughput.

9.7.2

Estimating Wireless Cable Modem to Wireless Client Distances

The information in this section helps you to determine how far a wireless access point (the

DDW365) can be placed from wireless client devices. Environmental variances include

the capabilities of wireless clients and the types of material through which the wireless

signal must pass. When the DDW365 and wireless clients reach the distance threshold

between each other, network performance degrades.

Steps

To determine wireless cable modem placement:

1.

Connect a wireless client to the DDW365. Refer to

Connecting Devices to the Network

on page 12

if needed.

2.

Place the wireless client at around one meter (three feet) away from the DDW365.

3.

Obtain the

RSSI

value for the connected client. Refer to

Using the Access Control

Option on page 75

. This value is used in the formula further below.

4.

Use the following table to determine what materials the wireless signal must travel

through to reach the desired wireless coverage distance.

Attenuation Considerations

Material

Attenuation

(2.4GHz)

Free Space

0.24dB / foot

Interior Drywall

3dB to 4dB

Cubicle Wall

2dB to 5dB

Wood Door (Hollow/Solid)

3dB to 4dB

Brick, Concrete Wall (Note 1)

6dB to 18dB

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5.

Use the attenuation value from the materials table above in the following formula:

Formula:

(Transmit Power,

use -30dBm

)

–

(Receiver Sensitivity,

use RSSI value

)

=

Allowable Free Space Loss

Allowable Free Space Loss

÷

Materials Attenuation Value

=

Optimal Distance in Feet Between the DDW365 and a Wireless Client

Example:

(-30dBm)

-

(-67dBm)

=

37dBm (allowable free space loss for a 54Mbps connection)

37dBm

÷

.24db/foot (for open space)

=

154.16 feet

6.

Once you know the optimal feet distance between individual wireless clients and the

DDW365, you may resolve and prevent some performance issues.

7.

Check the wireless signal strength and speed of the computer connected wirelessly to

the DDW365. Instructions for checking speeds are provided for both a Windows and a

Mac computer in the table below. If the wireless computer is not connected, refer to

Connecting a Wireless Device on page 12

.

Glass Window (not tinted)

2dB to 3dB

Double Pane Coated Glass

13dB

Bullet Proof Glass

10dB

Steel / Fire Exit Door

13dB to 19dB

Human Body

3dB

Trees (Note 2)

0.15dB / foot

Note 1

: Different types of concrete materials are used in different parts

of the world and the thickness and coating differ depending on

whether it is used in floors, interior walls, or exterior walls.

Note 2

: The attenuation caused by trees varies significantly depending

upon the shape and thickness of the foliage.

Attenuation Considerations

Material

Attenuation

(2.4GHz)

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9.7.3

Understanding the 2.4GHz Band

The DDW365 operates in the 2.4GHZ frequency band. The table below provides a

information about the 2.4GHz band.

Checking Wireless Signal Strength and Speed

Windows PC

Apple Mac

1.

Click the Wireless networking icon in the

system tray to display a list of available

wireless networks.

1.

Hold down the Option key and click on

the wireless icon (Airport) on the right

side of the top menu bar.

2. Click “Open Network and Sharing Center,”

then click “Wireless Network Connection.”

2. Information about the current wireless

connection appears below the SSID. If

you continue to hold the Option key and

hover over any network, information

about the connection is visible.

3. Review the speed and signal strength in

the Status window.

Band

2.4GHz

Channels

In the USA, channels 1-11 are used. There are 3 non-overlapping channels

(1, 6, and 11). Auto channel should be selected to ensure that the channel

with the least interference is used.

Standards

802.11b,g,n

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9.7.4

Selecting a Wireless Channel

You may need to change the wireless channel on which the DDW365 operates when you

are in computing, test, and other environments where several wireless access points may

be operating in the 2.4GHz range.

In some cases, you may want to segment your wireless traffic where a group of devices

operates on one channel and another group operates on another channel, and so on. This

is done by configuring the channel on each wireless access point individually (if you have

multiples). If you have control over only one wireless device in an environment where

there may be several, you can change the wireless channel on your device to one that is

not heavily used.

Note

To change the wireless broadcast channel, refer to

Using the Wireless Radio Option on

page 66

.

2.4GHz Channels

The following diagram displays the 2.4GHz channels available in the Americas. Each

available channel is 22MHz wide. Since channels overlap, it is best to choose channels

that have the least overlap (typically 1, 6, and 11 in the Americas, and 1, 5, 9, and 13 in

Europe). Overlapping channels can cause wireless network performance issues.

Source: Wikipedia.org, and IEEE article IEEE 802.11n-2009

Network Range

Wider range than the 5GHz band

Interference

Higher interference levels compared to the 5GHz band, as many wireless

devices such as cordless phones, microwave ovens, and computers use the

2.4GHz frequency.

Application

Recommended for simple Internet browsing and email, as these applications

don’t take too much bandwidth and work fine at a greater distance.

Band

2.4GHz

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10

Understanding the USB Menu

The

USB

menu

of the Web user interface allows you to configure USB storage devices

and media file scanning.

Topics

See the following topics:



Using the USB Basic Option on page 86



Using the Approved Devices Option on page 87



Using the Storage Basic Option on page 89



Using the Storage Advanced Option on page 90



Using the Media Server Option on page 93

Steps

To access USB options:

1.

Access the Web user interface. Refer to

Accessing the Web User Interface Locally on

page 15

.

2. Click

USB

from the main menu.

10.1

Using the USB Basic Option

The

USB Basic

option allows you to configure Linux based servers. The buttons on the

right side of the page are short cuts to the options on the left side of the page.

Steps

To view USB basic information:

1.

The

USB Basic

screen is displayed. Field descriptions are listed below the screen

example.