Real-time location systems (RTLS) have become an increasingly important strategic capability for a variety of business applications. From asset management to inventory control, it has played a significant part in many industries such as manufacturing, transportation, logistics and health care.

RTLS were historically based on RFID and proprietary but in the recent years, WiFi has become an alternative platform for RTLS solutions.

As it is common to find enterprises which already has an existing WiFi instructure, it is both cost effective and efficient to build a Wi-Fi based  RTLS solution on the existing network. Without the need to build a RFID based RTLS solution from scratch, it eliminates the need for a separate cabling system and expensive RFID reader. This in turn reduces the cost and manpower required to maintain 2 separate networks, offering enterprises a significant ROI on their existing WiFi networks.

Another advantage of WiFi-based RTLS solution is that it is based on IEEE 802.11 standards. One will not be limited by the choice of vendors they can purchase from compared to the traditional RFID-based RTLS which is proprietary.

Due to the already large and continually growing footprint of WiFi infrastructure, one can expect WiFi based RTLS will be one of the new applications gaining popularity beyond simply wireless internet access for laptops.

Posted by: theforce805 | April 24, 2009

WiFi Comics: #1 WiFi Allergies

Different types of end-user traffic require different performance characteristics on a network. The delay a single packet experiences of a file transfer may not matter but for every single packet of real-time application requires consistent response time. Applications such as Voice-over IP and Video-on-demand  require QoS policies to be in place end-to-end* on a network to efficiently share the transport medium with other lower priority traffic such as data transfer.

In the wired networking world, IEEE 802.1p which provide prioritization for traffic based on 8 priority levels while in the wireless networking environment, IEEE 802.11e provides prioritization for packets according to four access categories namely Voice, Video, Best Effort and Background. To enforce QoS policies end-to end for on a network with both wired and wireless devices, one has to ensure both IEEE 802.11e and IEEE 802.1p are supported. In particular, the wireless access points MUST support both standards.

It is recommended to create SSIDs for different type of device/traffic type and classify them with different access class of 802.11e as shown


Below is a series of diagrams to illustrate how prioritization of traffic occur end-to-end.

On the wireless side,


For details on how IEEE802.11e work, please click here.

On the wireless Access Point, mapping of IEEE 802.11e access categories to IEEE 802.1p forwarding classes

IEEE 802.1p

IEEE 802.11e





Best Effort



Best Effort









Excellent Effort



Best Effort

Controlled Load












Network Control




On the wired network,



 *Enabling QoS policies only on core devices or only on access devices is not effective enough to ensure the best user experience.

Posted by: theforce805 | April 12, 2009

WiFi How-to: #1 Minimizing RF interference

When deploying a WiFi network, it is always important to ensure minimal or no RF interference is present.

 Check for the following possible interference sources*

1) 2.4 GHz cordless phones

2) 2.4 GHz devices (such as wireless baby monitor, wireless mouse)

2) Bluetooth devices (such mobile phones, PDA, keyboard, mouse) – Operates in 2.4GHz spectrum

3) Microwave ovens – Operates in 2.4GHz spectrum

4) Networks that uses Frequency Hopping mechanism such as HomeRF – Operates in 2.4GHz spectrum

5) ZigBee networks – Operates in 2.4GHz spectrum

6) Other WiFi networks – Operates in both 2.4GHz or 5GHz spectrum


When deploying WiFi networks, 5GHz band (IEEE 802.11a) should be preferred over the 2.4GHz band (IEEE 802.11b/g) as less RF interference is present when compared to the 2.4GHz band. However if IEEE 802.11b/g networks were to be deployed, do remember to use only the non-overlapping channels (Channel 1, 6 and 11). And if other WiFi networks are present, do plan on some channel planning before deployment.


*Tools to used for spectrum analysis

1) AirMagnet Spectrum Analyzer

2) Xirrus Wi-Fi Inspector

3) Kismet


Posted by: theforce805 | April 12, 2009

Reason to go wireless….

Imagine this is how your server room looks

With WiFi, less cables and switch ports are required

With Xirrus, lesser cables and switch ports are needed.

Make the wise choice!

Posted by: theforce805 | April 1, 2009

Best of Both Worlds

The evolution of WiFi system architecture saw competition between centralized and distributed designs.

In a centralized WiFi architecture, a controller is required to manage “dumb” access points (AP) whereas in a distributed WiFi architecture, no controller is required as the access points (AP) have “intelligence” built-in.

So which is better?

It all depends on which approach is able to meet the most of the requirements of its intended functionality.

The main advantage of a centralized architecture over a distributed architecture is the ability to manage multiple APs from a single point of control. This is extremely helpful especially when one has to manage hundreds of access points. Installation can be done quickly by simply plugging “dumb” access points without configuring them beforehand (assuming DHCP IP address are assigned). Network administrators can then at a later stage configure them all at one time. This simplifies the installation process compared to deploying “intelligent” APs whereby network administrator has to configure them one by one.

If centralized WiFi architecture seems so good, why do we have a distributed architecture then?

 A single point of management for hundreds of APs does sound good but what if this single point can also be a single point of failure. This single point of failure can bring down the entire wireless network while a single AP failure in a distributed environment will not impact the rest of the network. Centralized architecture also poses scalability issue whereby adding a new AP may require an additional controller if the existing controller’s capacity limit is reached. Without a centralized environment, “intelligent” APs can be added to the network with no consideration of a controller’s limit. Deploying wireless APs in a distributed manner has other advantages too. By having the “intelligence” built into the APs, features like Quality-of-Service (QoS) and access control policies can be enforced on the “edge” of the network instead of routing the traffic back to a controller, reducing any chance of delay and jitter introduction to the traffic.

Having said all that, which architecture will deem the best? Hard choice? Not at all – Xirrus provide the best of both worlds in a WiFi environment.

Xirrus Arrays have “controller” built-in giving you the benefits of an “intelligent” AP found in traditional distributed architecture, and together with the Xirrus Management System(XMS) to provide a centralized monitoring and configuration platform which makes managing hundreds of Arrays easy.

Posted by: theforce805 | March 25, 2009

Goodbye wires…

IEEE 802.3ad..IEEE 802.3at.. How about IEEE 802.11ad? 

Many of us may have heard of IEEE 802.3ad Power-over-Ethernet which is capable of powering devices such as WLAN AP, VoIP phones etc at power limit of 12.95W. As these devices gain popularity, it also triggers the development of IEEE 802.3at, an extension that is currently under development, capable of at least 24W, powering devices requiring more than what the current 802.3ad can support.

Power-over-Ethernet today has become a worldwide standard today, which not only reduces installation costs (i.e. cable runs) but also makes installation of network devices easier and quicker. Many would also want to have this convenience and advantage on the wireless networks as well. Is it possible? The answer is “Yes”. Back in 2006, a MIT researcher Marin Soljacic* figured out a way to transmit electricity via the magnetic field surrounding a charged loop of wire. A similar loop wired up to a light bulb or another electrical device would draw power from that magnetic field with no wires attached. Soljacic had considered using radio waves but found that most of the energy will be lost in transmission.

Although there’s no link currently between this research and IEEE 802.11, it will be exciting to see this technology evolves to work along-side with IEEE802 11 as an extension one day (perhaps 802.11ad?). When the time comes, gone will be the days when you get dropped off a call on a wireless phone because of low battery. Sounds a little far-fetched or absurd? Maybe, but didn’t all great inventions started off in the similar manner?

 *More information on MIT research

Posted by: theforce805 | March 22, 2009

WiFi Fact or Fiction: #1 WiFi poses health risks

Very often while installing Xirrus arrays at customer sites, people would ask me whether the Arrays would be radiating too much RF energy resulting in an adverse health effect in long term exposure.

My answer to them will always be “No” and further explained that signals from WiFi are very low power, typically 0.1 watt (100 milliwatts) and resulting exposures are well within international guidelines limits#.

Furthermore, studies focused on RF exposures of mobile phones users have not identified any adverse effects and RF exposure from WiFi is much lower than those from mobile phones.

WiFi poses health risk – FICTION

# ICNIRP is the International Commission on Non-Ionizing Radiation Protection. See

 More information on WiFi and Health, see Wi-Fi Alliance.

 More information on Statements from Governments and Expert Panels Concerning Health Effects and Safe Exposure Levels of Radio Frequency Energy (2000-2007) .

Posted by: theforce805 | March 20, 2009

A day without WiFi?

WiFi has become part and parcel of our lives. It may seem that WiFi is easily available in our offices or in public places with hotspots. However, what we may not have noticed is that WiFi has already made its way into our homes too. With more consumer products which are now WiFi enabled, triple-play application or even quad-play applications over wireless at homes are now possible.

Audio Devices
– Speakers
– Receivers
– MP3 Players

Video Devices
– Set Top Boxes
– Media Server
– TV
– Picture Frames
– Projectors

Gaming Devices
– Game Console
– Portable gaming devices

PC and Computing devices
– Laptops
– PDA/Mobile phones

Other devices
– Printers
– Cameras (Still/Video)
– Cameras
– Web cameras
– Phones

Can we still live a day without WiFi?

Posted by: theforce805 | March 20, 2009

The ABC of 802.11

An overview on standards under the IEEE 802.11 (Wi-Fi) umbrella (as of Mar 09)

#Excerpted from



IEEE 802.11

The WLAN standard was original 1 Mbps and 2 Mbps, 2.4 GHz RF and infrared [IR] standard (1997)

IEEE 802.11a

A PHY to operate in the newly allocated UNII band.

IEEE 802.11b

A higher rate PHY in the 2.4GHz band

IEEE 802.11c

Provide the required 802.11 specific information to the ISO/IEC 10038 (IEEE 802.1D) standard

IEEE 802.11d

The current 802.11 standard defines operation in only a few regulatory domains (countries).  This supplement will add the requirements and definitions necessary to allow 802.11 WLAN equipment to operate in markets not served by the current standard

IEEE 802.11e

Enhance the current 802.11 MAC to expand support for LAN applications with Quality of Service requirements. Provide improvements in security, and in the capabilities and efficiency of the protocol.

IEEE 802.11F

Specify the necessary information that needs to be exchanged between Access Points to support the P802.11 DS functions.

IEEE 802.11g

Develop a new PHY extension to enhance the performance and the possible applications of the 802.11b compatible networks by increasing the data rate achievable by such devices.

IEEE 802.11h

Enhance the current 802.11 MAC and 802.11a PHY with network management and control extensions for spectrum and transmit power management in 5GHz license exempt bands, enabling regulatory acceptance of 802.11 5GHz products. Provide improvements in channel energy measurement and reporting, channel coverage in many regulatory domains, and provide Dynamic Channel Selection and Transmit Power Control mechanisms

IEEE 802.11i

Enhance the current 802.11 MAC to provide improvements in security

IEEE 802.11j

Obtain Japanese regulatory approval by enhancing the current 802.11 MAC and 802.11a PHY to additionally operate in newly available Japanese 4.9 GHz and 5 GHz bands

IEEE 802.11k

The original standard has a basic set of radio resource measurements for internal use only. These measurements and others are required to provide services; such as roaming, coexistence, and others; to external entities. It is necessary to provide these measurements and other information in order to manage these services from an external source.

IEEE 802.11l

Not to be used by the IEEE 802.11 Working Group for inclusion into the published standard

IEEE 802.11m

Maintenance of technical and editorial corrections to the 802.11-2007 Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications standard.

IEEE 802.11n

Improve the 802.11 wireless local area network (LAN) user experience by providing significantly higher throughput for current applications and to enable new applications and market segments.

IEEE 802.11o

Not to be used by the IEEE 802.11 Working Group for inclusion into the published standard

IEEE 802.11p

Amend the existing IEEE 802.11 standard to make it suitable for interoperable communications to and between vehicles.

IEEE 802.11q

Not to be used by the IEEE 802.11 Working Group for inclusion into the published standard

IEEE 802.11r

Improve BSS transitions within 802.11 ESS’s and to support real time constraints imposed by applications such as Voice over Internet Protocol (VoIP).

IEEE 802.11s

Provide a protocol for auto-configuring paths between APs over self-configuring multi-hop topologies in a WDS to support both broadcast/multicast and unicast traffic in an ESS Mesh using the four-address frame format or an extension.

IEEE 802.11T

Enable testing, comparison, and deployment planning of 802.11 WLAN devices based on a common and accepted set of performance metrics, measurement methodologies and test conditions.

IEEE 802.11u

Amendments to the IEEE 802.11 PHY/MAC layers which enable InterWorking with other networks. This includes both enhanced protocol exchanges across the air interface and provision of primitives to support required interactions with higher layers for InterWorking.

IEEE 802.11v

Amendments to the IEEE 802.11 PHY/MAC layers that enables management of attached stations in a centralized or in a distributed fashion (e.g. monitoring, configuring, and updating) through a layer 2 mechanism. While the 802.11k Task Group is defining messages to retrieve information from the station, the ability to configure the station is not in its scope. The proposed Task Group will also create an Access Port Management Information Base (AP MIB).

IEEE 802.11w

Improve the security of some or all IEEE 802.11 management frames by defining enhancements such as data integrity, data origin authenticity, replay protection and data confidentiality.

IEEE 802.11x

Not to be used by the IEEE 802.11 Working Group for inclusion into the published standard

IEEE 802.11y

Standardized the mechanisms required to allow shared 802.11 operation with other users in the 3650-3700 MHz band in the USA. Likely required mechanisms include: Specification of new regulatory classes (extending 802.11j), Sensing of other transmitters (extending 802.11a), Transmit Power Control (extending 802.11h) and Dynamic Frequency Selection (extending 802.11h).

IEEE 802.11z

Defines a new DLS mechanism which: a) Does not require access point upgrades (i.e. supports DLS operation with the non-DLS capable access points), b) Which supports power save mode (when associated with either DLS or non-DLS capable access points), and c) Continues to allow operation of DLS in the presence of existing DLS capable access points

IEEE 802.11aa

Specifies a standard for robust audio video stream transport over 802.11 for consumer/enterprise applications.





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