Some how I missed the release of this free web based WiFi Stumbler from Meraki. A very clean and well implemented scanner using Java that works on Macs and PCs.

SSID-Channel distribution graph – This graph shows how many visible SSIDs are being broadcast in each channel of the 2.4Ghz and 5GHz wireless spectrums. This information can help you plan your channel selection to utilize channels that are most clear of interference.
Search field – Search for open networks, specific manufacturers of access points, a particular SSID or MAC address or any other string in the scan results using this field. You can also use standard Google search syntax. Click on “Advanced search” to expose a variety of filters to easily customize your displayed results.
Network list – This section lists useful information about the wireless networks that are visible to WiFi Stumbler. You can sort the list by any column by clicking on the header for that column.

Description of information presented in each column in the Network list:
SSID – Name of SSID. Hidden SSIDs will appear as blank (all other columns will be filled in)
MAC Address (BSSID) – Hardware address of access point
Radio Type – Wireless protocol of network (802.11b/g, 802.11a or 802.11n)
Channel – Wireless channel that the network is operating on
Signal Strength (dB) – Signal level of network in RSSI (Received Signal Strength Indication). Since RSSI outputs from different client cards can vary, these signals are best used as a relative measure of signal strength when comparing networks
Manufacturer – Name of manufacturer of access point
Security – Wireless security protocol in use (or Open if none)
Last Seen – Last time a response or beacon from this network was received

Great Time To Be In WiFi Industry

It is great to see vendors and WLAN professionals releasing so many useful tools and sharing information for building, securing, and managing wireless/WiFi networks.

Try it out here.

Seeing this tool inspires me to add more visualization to our web based based wireless access point rogue scanner.

I’ll have to update my list of Netstumbler alternatives and add this great tool.

If there are any other free tools that I seem to have missed let me know.

© 2008 Copyright WLANBook.com

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Why I like the iPad as a platform for WiFi tools such as a WiFi scanner or WiFi site survey tool:

Display – Nice big display compared to the iPhone. Anyone that has conducted WiFi site surveys for millions of square feet knows that having a big laptop screen is useful. The 9.7-inch (diagonal) multi-touch display isn’t huge but should work well for WiFi site surveys.

Size and Weight – The bigger the screen the better..but with size comes weight. While having a 16 inch screen is ideal..an 8 pound laptop for site surveys feels like a 1000 pounds after a few hours of surveying. For me, the perfect screen size for a WiFi Scanner/Site Survey laptop is around 13 inches. The iPad’s 9.7 inch diagonal screen may end up being a little small but for most scanning and surveying it should work well. At around 9.56 inches by 7.47 inches and 1.6 pounds for the WiFi + 3G model the iPad is perfect for carrying around all day long.

Battery and Power – Per Apple’s website the iPad “has up to 10 hours of surfing the web on W-Fi”. Even if the battery life is closer to 7 hours…that is enough for a full day of WiFI scanning and surveying. When scanning a wireless card isn’t transmitting so hopefully the iPad’s battery life is closer to 10 hours when used as a scanner.

Processor and Performance – For large survey projects it helps to have a powerful processor that is responsive when clicking/tapping the screen and also can handle the larger number access points and WiFi devices that sometimes need to get tracked during scanning and surveying. The 1GHz Apple A4 processor is unknown since it is so new so hopefully it is a powerful as marketed by Apple.

Wireless Features – The iPad supports 802.11 a/b/g/n so it has all the capabilities needed for the major WiFi types deployed by organizations today. The iPad will connect at the full speeds to any type of network for any speed testing or active surveying.

iPad Is Value Priced and Feature Rich

At $499 ($523.95 after tax) the iPad with Wi-Fi only and 16GB of storage is a great platform for WiFi tools. We hope to port our very popular (and free) WiFi Scanner app for Snow Leopard to iPad/iPhone/iPod Touch and add/enhance the tool for wireless site surveys.

iPad/iPhone OS SDK for WiFi Tools

Currently there is is no way to access the information we need from the iPhone/iPad OS without using a private framework. This isn’t a big deal in terms of creating the application but if we want the app available in the App Store then we have play by Apple’s rules which means waiting for a updated OS and SDK to be released. Apple usually realeases major iPhone/iPad OS updates once a year around this time so hopefully the next major release will provide a documented way to access to 802.11/WiFi information that meets our needs for porting our WiFi Scanner to the iPhone/iPad/iPod Touch platform.

iPad/iPhone WiFi Scanner/Site Survey Tool Features Requests

If you have any feature requests for a WiFi Scanner and Site Survey Tool on the iPad let us know. Check out our WiFi Scanner for Mac OS X for what is possible.

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WiFi Scanner is a free 802.11 wireless scanner and connection manager for Mac OS X 10.6 Snow Leopard or later. This will detect access points and clients in ad-hoc mode if the SSID is being broadcasted. It can be used for wireless site surveys, wireless discovery, and to connect to wifi networks. The tool reports signal strength in dBm and shows access point BSSID/MAC addresses.

WiFi Scanner v1.1 Installer Package Download

New Features In WiFi Scanner v1.1 for Snow Leopard

v1.1 of our very popular (and free) WiFi Scanner application for Snow Leopard has following new features.

• Change Column Positions
• Sort Results
• Resolve Vendor OUI
• Noise and Signal/Noise Info
• Autoscan/Refresh
• Latitude/Longitude of Discovered Access Points
• Show Access Point in Google Maps
• Show Access Point in Google Earth
• Access Point Finder Using Audio Alert

See below for screenshots of the application and information regarding the various buttons and options.

Interface Tab

The tab entitled “Interface Info” contains information describing the static and dynamic state of the currently selected interface. Additionally, it allows the user to toggle interface power, disconnect from the current network, and change channels.

You will notice that you will not be able to change channels while connected to a network–this is by design. Attempting to do this would return a error. Furthermore, you will notice that when the interface is powered OFF, all the dynamic status information is cleared.

Scan Tab

The tab entitled “Scan” allows the user to scan for networks using the current interface. The scan results are shown in the table view and are can be organized by any column by clicking the column header. For each network, there is several pieces of information displayed in the table row that describe that particular network.

There is a button in the checkbox left corner of the Scan tab which sets/unsets the parameter to merge the scan result with the same SSID.

There is a Auto check box and drop down to select the auto refresh rate.

The Resolve Vendor OUI option to show the IEEE Organization Unit Identifier for the MAC address.

The Show Lat/Long will show the latitude longitude of the BSSID if available via WiFi databases.

And, there is a button in the bottom right corner of the Scan tab which allows the user to join the currently selected network in the table. A sheet will be presented upon clicking the Join button that will allow the user to provide the appropriate credentials for the given network.

Interface Popup Button

The app supports a multiple interface scenario, whereby the machine could have several IEEE 802.11 wireless interfaces. The popup button on the top left corner of the app allows the user to select which interface should be set as the current interface. By default, the popup button will select the primary WLAN interface for the system.

Refresh Button

In the top right corner of the app, there is a push button entitled “Refresh”. This button provides different functionality depending on which tab is currently selected. If the Interface Info or Configuration tabs are selected, the button will refresh the information display in the currently selected tab. If the Scan tab is selected, the button will start a broadcast scan and block until the scan has completed.

Double click a row of results to access the monitor screen.

Monitor Screen

From the monitor screen you will be able to display the BSSID in Google Maps or in Google Earth.

If the Auto refresh option is checked the monitor screen will refresh the RSSI value every refresh interval.

If audio is enabled a beep sound increase in frequency as the RSSI values increases (aka approaches zero). This is typically called the “Geiger Counter” feature in most WiFi scanning applications.

BSSID Search Tab

This tab will allow you to search any MAC address and have it

BSSID In Google Maps

BSSID In Google Earth

Green domes show estimated coverage area based on free space loss.

WiFi Scanner Email List

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How Does Airplane WiFi Work?

Airplane WiFi works like WiFi at free WiFi at coffee shops and book stores. The main components of an airplane WiFi system are below.

1. Computer/WiFi enabled device (laptop, iPhone)
2. Airplane WiFi network (access points)
3. Air-to-ground wireless data connection (satellite or EVDO)
4. Ground Internet service provider

The technology to make the entire system work is transparent travelers. All that is required is an 802.11 WiFi enabled device and a method to pay for the service. WiFi on airplanes is available on most major airlines.

Airplane WiFi Configurations

There are two companies, GoGo Internet and Row 44, that most airlines are using to provide airplane WiFi service. GoGo Internet uses a ground based cellular data network for data communications and Row 44 uses satellite communications.

Row 44 Airplane WiFi

Satellite antenna atop of plane to communicate with satellites and other electronics inside cabin.

Row 44 Airplane WiFi Equipment

Southwest Airplane Row 44 Satellite Antenna

Row 44 Airplane WiFi Service

GoGo Inflight Airplane WiFi Configuration

GoGo’s airplane wifi configuration is similar to Row 44 except that they rely on a ground based EVDO network (like cell phone data networks) for communications to airplanes.

GoGo Aircell Airplane WiFi EVDO Network

Aircell Airplane WiFi Equipment

GoGo Internet Airplane WiFi Service

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The AirPort item in the menu bar now includes signal strength for all available wireless networks, so you can see which access point has the best signal before selecting it. Four signal bars appear in the AirPort status icon in the menu bar. The more bars that are black, the higher the signal quality. The bars do not indicate the connection rate, as this will vary according to your environment. [source]

While I like the simplicity of the four levels of signal strength above I sometimes need signal strength in dBm. dBm is a more granular way of describing the wireless signal strength.

dBm (sometimes dBmW) is an abbreviation for the power ratio in decibels (dB) of the measured power referenced to one milliwatt (mW). It is used in radio, microwave and fiber optic networks as a convenient measure of absolute power because of its capability to express both very large and very small values in a short form. Compare dBW, which is referenced to one watt (1000 mW). In the more granular information about the signal strength. [wikipedia]

Wireless Signal Strength Using the Snow Leopard Menu Bar

Clicking the option key and the signal strength menu icon will display detailed information about the currently connected wireless network.

PHY Mode – is the type of 802.11 WiFi network (802.11 a/b/g/n)
BSSID – is the MAC address of the access point
Channel – current 802.11 channel
Security – authentication and encryption type
RSSI – received signal strength indicator, aka the signal signal strength in dBm. The closer the number to 0 the stronger the signal.
Transmit Rate – the data rate of the current connection

Airport Signal Strength in dBm Using “About This Mac”

Wireless signal strength is also available using the About This Mac menu bar option and navigating to Network > Airport section.

RSSI Signal Strength Airport Command Line Utility

The airport utility is located at location below.

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -I

Will provide information about the current wireless connection.

$ airport -I
     agrCtlRSSI: -64
     agrExtRSSI: 0
    agrCtlNoise: -91
    agrExtNoise: 0
          state: running
        op mode: station
     lastTxRate: 48
        maxRate: 54
lastAssocStatus: 0
    802.11 auth: open
      link auth: wpa-psk
          BSSID: 0:b:55:6:6f:2f
           SSID: SSID
            MCS: -1
        channel: 1

Wireless Signal Strength Using Graphical Tools

WiFi Scanner is a free 802.11 wireless scanner and connection manager for Mac OS X 10.6 Snow Leopard or later. It leverages the the newest CoreWLAN API in Snow Leopard. This will detect access points and clients in ad-hoc mode if the SSID is being broadcasted. It can be used for wireless site surveys, wireless discovery, and to connect to wifi networks. The tool reports signal strength in dBm and shows access point BSSID/MAC addresses.

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The most common types of access points are called wireless routers or cable/DSL routers. A Linksys WRT 54G is shown below. The most common use for this type of router is sharing an Internet connection.

Wireless Access Point Router Outer Shell

The main external parts and ports of a wireless access point router are described below.

Reset Button – this button resets the configuration of the wireless router. In addition to any custom wireless settings the admin password and IP address of the device gets reset.

WAN Port – this port connects to the cable/DSL modem that is provided by the Internet service provider. Or connect to a corporate LAN port.

LAN Ports – these ports provide wired access to the network and Internet connection.

Antenna – these antennas amplify the signal from the 802.11 wireless radio that is inside the enclosure.

Wireless Router Autopsy

To better understand the various parts of a wireless router (LAN, WAN, wireless card), shown below are the internal electronics of a first generation Linksys WRT 54G cable/DSL router.

Wireless Access Point Router Network Architecture

Wireless access point routers are a combination of a wireless access point, multi-port network switch, and an IP router. The router portion is a three-port/interface router (eth0, eth1, eth2). The LAN switch ports and wireless access point are connected to two ports on the “router” and are bridged together (br0) as a single LAN segment. Network traffic is routed between br0 and the WAN port (eth1).

Newer Single Board Wireless Routers

Current wireless access point hardware has evolved into a single board design where the wireless card is integrated into the board.

Also, newer designs may have multiple wireless cards and additional ports like USB or printer ports.

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IP Address Management (IPAM)

As the number of networking devices increases, it becomes more important to assign and track IP addresses with more than just spreadsheets or via email requests. The old way of pinging an IP address, checking a spreadsheet, or looking at the DHCP server leases is not longer reliable and scalable.

A good way to avoid the older and more manual ways of managing IP addresses is to implement an IP address management solution.

Internet Protocol (IP) address management (IPAM) is a means of planning, tracking, and managing the Internet Protocol address space used in a network. Most commonly, tools such as DNS and DHCP are used in tandem to perform this task, though true IPAM will glue these services together so that each is aware of changes in the other (for instance DNS knowing of the IP address taken by a client via DHCP, and updating itself accordingly). Additional functionality, such as controlling reservations in DHCP as well as other data aggregation and reporting capability, is also common. IPAM tools are increasingly important as new IPv6 networks are deployed with larger address pools, different subnetting techniques, and more complex 128-bit hexadecimal numbers which are not as easily human-readable as IPv4 addresses. IPv6 networking, mobile computing, and multihoming require more dynamic address management and are causing technical obsolescence of the early generations of IP address management (IPAM) software and spreadsheets used for address manageme. [source]

Free IP Address Management (IPAM) Software

Instead of installing IPAM software from scratch (allocate hardware, operating system, software, etc) to track the ever increasing number of IP addresses in your network. I recommend downloading a free IPAM virtual machine offered by a company named Infoblox to test to see if an IPAM solution is right for you.

Infoblox’s free IPAM software solution has the following features:

• On demand and scheduled network discovery of devices
• Unified repository of IP address and asset information
• On demand and scheduled network discovery of devices
• Ability to assign values to the standard IPAM attributes e.g. device type, operating system etc.
• Graphical representation of IPs (IPMap)
• Graphical representation of networks (NetMap)
• Ability to organize IP addresses in smart folders
• Wizard for creating new networks
• Wizard for assigning new IP address

Download Free IPAM Software

The virtual machine be downloaded from here.

I’m running the IPAM virtual machine on a VMWare ESX server and had to convert if from a VMWare workstation virtual machine to a VMWare ESX server virtual machine.

IPAM Virtual Machine Requirements

If you plan to run the software on VMWare Player (free) the requirements are below.

Operating System:
Windows 2000, Windows XP SP2,
Window Vista
Disk Space:
1GB
RAM:
Minimum 512MB

Getting Started with Free IPAM Software

My notes below are on what I did after getting virtual machine running.

1. Changing IP address configuration of a static address
2. Add my subnet
3. Configured discovery process for my subnet
4. Started discovery process
5. Reviewed list of discovered IP addresses
6. Made any comments about discovered IP addresses

Discovered Devices by IPAM Software

Device Address List

Free IPAM Software License

This software is intended for trial purposes per language below from download license agreement.

LIMITED TRIAL LICENSE. Subject to the terms of this Agreement, Infoblox grants you a nonexclusive, non-transferable limited license to internally reproduce, install and use the Software only in
object code form to evaluate the Software. This limited trial license does not permit you use to the
Software to manage more than 500 IP addresses.

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This online tool can be used to plan and visualize outdoor wireless networks by plotting device locations and radio frequency (RF) propagation coverage on mapping tools. Radio frequency propagation visualization can be viewed as contours on Google Maps or 3D RF models in Google Earth.

The tool is currently beta software and is available at address below. Feedback and feature requests are welcome.

http://www.wlanbook.com/outdoor-wireless-planner/

How to Use Outdoor Wireless Planning Tool

I plan to add detailed instructions later but for now start by following a three step process – 1) find your location, 2) click on map to plot markers, and 3) view results in Google Earth.

Radio Frequency Propagation Visualization on Google Maps

Currently the radio frequency propagation visualization in Google Earth and Google Map view is the same for all plotted points. This feature will be enhanced so that results are based on user entered data like radio power, frequency, antenna gain, distance, and most importantly terrain data that can be determined from mapping software.

Radio Frequency Propagation Visualization in Google Earth

The Google Earth portion of tool isn’t complete but when done will have the ability to view results with custom pan, tilt, range, and altitude values for location. See below for what the 3D view will look like and download a demo file to view results in Google Earth.

Feedback, Bug Reports, and Features Requests

Please comment in post below or send me a message via my contact form with feedback, bug reports, and feature requests. This software was tested on a Windows Vista PC, Internet Explorer 7, and 1280×800 screen resolution. I’m sure it will behave differently on other systems so when sending bug reports please let me know your operating system, browser version, and screen resolution.

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It is possible for a single access point to have multiple SSIDs. This capability is more common in enterprise class access points and is usually implemented so that each SSID has a separate BSSID (MAC address). Each SSID can be hidden or in clear text or a combination. Some vendors allow as many as 32 different virtual WLANs to be configured per access point radio.

The most common multiple SSID configuration is two SSIDs, a guest network for visitors that provides Internet access only and a private wireless LAN that is connected to company resources.

Enterprise Class Access Points and Multiple SSIDs

Virtually all enterprise access points support multiple SSIDs per access point radio. Analogous to using VLANs in switches to segment users, multiple SSIDs create virtual APs that can be used to segment wireless users. In most cases each virtual access point is associated to a different wired VLAN.

SOHO Access Points/Wireless Broadband Routers and Multiple SSIDs

Most low end access points/wireless routers ship with a single radio and single configurable SSID. Several third party firmware packages exist that expand the features of these wireless broadband routers to add multiple SSID support in addition to many other enterprise class features such as radius support.

Some of the more popular third party firmware distributions are DD-WRT and OpenWRT. Both OpenWRT and DD-WRT support the Linksys, Netgear, and D-Link products.

Other combinations of access points and SSIDs are below.

No Access Point and No SSID

It may sound impossible to some, but you can have a wireless network without an access point or SSID. There are many proprietary wireless networking technologies and standardized technologies such as Bluetooth or IrDA don’t utilize SSIDs or access points.

No Access Point and Single SSID

Another name for this type of network is Ad-Hoc or an IBSS (independent basis service set). In this mode two or more stations using the same SSID can communicate with each other without going through an access point or wired network.

Single Access Point and No SSID

This scenario is not possible in IEEE 802.11 compliant wireless networks. While you can “hide” a SSID by not broadcasting it in beacon frames, the SSID still exists and must exist per IEEE 802.11.

There are some 802.11 WDS (wireless distribution service) configurations that don’t utilize SSIDs and don’t behave like access points but in general most access points that can be used for WDS are also APs and use SSIDs to service stations. Since WDS is not a WiFi certified 802.11 mode of operation not all vendors implement this mode the same way.

Single Access Point and Single SSID

This setup is the most common and is what every access point supports. Access points that are residential class wireless broadband routers with a single wireless radio are usually limited to a single SSID. In almost all cases, the radio can support multiple SSIDs but the firmware supplied by the vendors only allows a single SSID to be configured.

Multiple Access Points and Single SSID

A single access point covers a limited area and to increase coverage requires using multiple access points that are connected together via a wired or wireless network. This type of wireless network is called and extended service set (ESS). Sharing a common SSID, in addition to covering larger area, allows for mobility by roaming different access points in the ESS.

It is common to have multiple wireless networks in the same area and the SSID provides stations an easy method to distinguish wireless networks. Extended Service Set (ESS) or multiple access points with the same SSID that are connected together via a wired network allows for larger coverage and roaming.

Multiple Access Points and Multiple SSIDs

802.11 uses unlicensed frequencies and allows anyone can setup a WLAN without notifying frequency managers or other users. 802.11 accommodate scenarios where many access points or wireless networks exist in the same area with different SSIDs. These ESS, BSS, IBSS networks share the same RF space but are not connected to each other via the same distribution system.

It is best to conduct a site survey to determine if there are other wireless LANs in existence and try to design around existing networks when possible. Technically they could all use the same SSID and channels but it is good etiquette and design to select a SSID and channel that isn’t being used already.

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Designing an enterprise class WLAN is not a trivial task. If designed incorrectly the WLAN will have coverage gaps and capacity issues. Outlined below are steps that should be followed when designing an enterprise class WLAN.

1. Requirements Gathering

   One of the biggest mistakes made by IT professionals is to focus on WLAN signal coverage instead of WLAN capacity. Many WLAN projects start with a wireless site survey without any information about why the WLAN is being deployed.

   The first step in any WLAN design should be to sit down with the future users/owners of the WLAN and determine where WLAN coverage is needed and what applications will be used. Focusing on WLAN capacity requirements of applications first will usually result in a WLAN design with proper coverage too.

   Also, this is a good time to start discussing the security requirements of the organization and any special compliance requirements or integration issues related to wireless LAN security that may need special attention.

2. Physical Site Survey

   Request electronic copy of building drawings and conduct a physical site survey to verify that the information in the drawings is correct. Note any changes not reflected in the drawings, such as new additions or construction material that would significantly attenuate or reflect wireless signals.

   Another goal of a physical site survey is to determine the locations where access points should not be installed such as bathrooms, lobby areas, or elevator shafts.

   During the physical site survey start thinking about cable paths in relationship to telecom closets and possible mounting locations for access points. Note any special requirements that would impact deployment phase such as high ceilings, outdoor coverage requirements, or historical building regulations.

   If allowed, take digital photos of facilities to help with predictive RF WLAN design step and deployment phase.

3. Predictive RF Design

   Using information from requirements gathering step and physical site survey use WLAN predictive RF design tools to determine the number of access points that will be needed and potential placement locations.

   Focus on meeting the capacity requirements of the design and disregard any budgetary limitations. In addition to capacity design verify the placement of access points will also meet WLAN coverage requirements. Compare these access point placement locations to information gathered during physical site survey and adjust placement as needed to avoid placing access points in areas where they can not be mounted.

   Regarding coverage, design proper overlapping coverage to allow for seamless roaming and redundancy.

   

4. Wireless Site Survey

   The goal of a wireless site survey is to validate the predictive RF design and to avoid having to survey the entire facility. Focus on areas that are different from floor-to-floor or very radio frequency (RF) unfriendly.

   Verify the predictive design by taking test measurements at various locations. When possible, use the same access point and client hardware that will be deployed. Measure RSSI (received signal strength indication) and noise levels. The wireless site survey should also include information about neighboring access points and any other 802.11 or not 802.11 device that may cause interference issues once the WLAN is deployed. Also, any special antennas needed for access points or clients should be noted here and if possible test measurements taken with special antennas.

   Identify and record access point placement locations and cable paths back to telecom closet on building drawings. Also note network switch port capacity and power availability per telecom closet.

   

5. Wireless Network Design

   With information from the requirements gathering, physical site survey, predictive RF design, and wireless site survey designing the wireless LAN should be very pretty easy.

   Decide on configuration related items such as SSIDs to be used, VLAN assignment per SSID, channel plans, transmit power, and naming schemes for devices. Regarding channel assignment and transmit power, do not assume that WLAN equipment will correctly “auto configure” these settings. In almost all cases, it is best to define exact channel scheme and transmit power and later validate that the “auto configure” capability of WLAN equipment is able to do same dynamically due to network conditions.

   A very important WLAN design consideration is the security architecture of the network and any special client software requirements. It is very important to communicate the details of security solution to the network owners/operators and have them provide any potential issues with existing client software (personal firewalls, virus scanners, etc). Also, outline how the WLAN and security architecture will integrate with the existing wired network.

   Lastly, document all steps of the WLAN design process and communicate roles and responsibilities to all parties. As with any network or device operating in the ISM band, make sure all parties understand that an 802.11 based WLAN is a shared and best effort network. The design is only as good as the 802.11 protocol and FCC regulations related to the ISM band. Set the correct expectations regarding performance, security, and management requirements.

Following the five WLAN design steps above should result in proper coverage, capacity, and security controls that are typically desired in enterprise class WLANs.

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Another option is to use a four-channel deployment scheme, either 1, 4, 7, 11 or 1, 4, 8, 11. Both of these scenarios are typically called slighty overlapping channel configurations, and are suppose to increase capacity in 2.4 GHz 802.11 networks by adding another access point to the same coverage area.

Proponents of these schemes argue that the negative impact of slightly overlapping channels can be minimized by limiting access point power and using proper physical separation.

What these schemes fail to address is interference from stations that are between two adjacent access points resulting in poor wireless lan performance, and therefore defeating the purpose of this deployment scenario.

Station Interference (image from cisco.com)

A spectral views of a 1, 4, 8, 11 and a 1, 6, 11 channel schemes are shown below. The peaks and valleys of the 1, 4, 8. 11 scheme are not well defined indicating interference from adjacent channels. In a high utilization environment, the slightly-overlapping scheme would result in poor performance compared to the non-overlapping scheme and should be avoided.

Slightly Overlapping – Channels 1, 4, 8, 11

Non-overlapping – Channels 1, 6, 11

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IEEE defines 14 channels available for use in 802.11b and 802.11g wireless networks. In the US and Canada the available channels for use are 1 (2.401 GHz) through 11 (2.448 GHz). Outside the US channels 13 and 14 are also available for use. Each of the 11 channels are 5 MHz apart and each defined frequency is the center of a 22 MHz wide channel. This leaves only 3 non-overlapping channels 1 (2.401-2.423 GHz), 6 (2.426-2.448 GHz), and 11 (2.451-2.473 GHz).

Using a low cost 2.4 GHz spectrum analyzer , a visual representation of the 3 non-overlapping channels is shown below. A red shaded box that is 22 MHz wide is centered at channels 1, 6, 11.

(Data collected at a T-Mobile hotspot)

The above three non-overlapping channels (1, 6, 11) can be deployed using the cell layout below. This scenario maximizes channel reuse and minimizes interference from adjacent access points.

Enterprises usually deploy high end managed wireless LAN networks, that have RF management features for automating channel planning.

Home and small business users will have to manually configure access points for design above if they are deploying several access points or are in an environment with other neighboring access points.

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