Like many of its rivals in the Wi-Fi location market, Ekahau is a young company. In its response to our request for information, it emphasized that its real-time locationing product works with most enterprise Wi-Fi networks, a reassuring point for organizations that are looking at location to solve a business problem but want to avoid the long deployment times and high infrastructure costs inherent in overlays. Ekahau's ability to accommodate most WLAN scenarios without having to reach out to partners will appeal to IT groups that want to keep things simple.

Ekahau's T301 tags support two-way traffic

It's also refreshing that, unlike some competitors, Ekahau doesn't shy away from accuracy claims. Most Wi-Fi location vendors depend on exciters or choke points to enhance the precision and timeliness of location tracking, but Ekahau swears off most of these methods and emphasizes its Ekahau Positioning Engine and active tags.

Location systems generally take one of two approaches to pinpointing location. In a tag-centric, or associated, model, tags actively take power readings of surrounding access points at controlled intervals or based on predefined events, like tag movement, then report to the location engine by associating with an AP and transmitting, like a regular Wi-Fi client. It's two-way communications.

Alternatively, tags may work in simpler beaconing mode, where they "chirp" at fixed intervals. The Wi-Fi infrastructure understands this abbreviated packet, which contains the tag's unique identifier and perhaps some state information, and appends the measured power reading of the tag before sending it to the location engine.

Ekahau tags may be programmed to perform in beaconing mode, but the company expects that will be the case in less than 10% of its 2008 deployments. Rather, Ekahau favors a tag-centric approach to calculating location, which it says is more accurate than the beaconing route most rival Wi-Fi location vendors favor. A key ingredient is the Ekahau Location Survey software, which is used to calibrate the system. With ELS, a technician performs a site walk-through, recording his route into the network along the way. This data is then integrated into the location model that the engine uses to spit out coordinates.

The debate over whether an associated or a beaconing approach is superior is just one element in the technical sparring going on among Wi-Fi location vendors. No one disputes that a two-way associated system allows for niceties such as visual and audible alerts on tags as well as two-way text messaging and wireless, remote software updates. Less clear is the model's effect on performance, security, and management complexity.

In this case, the devil is in the details, and there are lots of them.

Physics tells us that RF signals flow equally well from an access point to a tag as from a tag to an AP. If a tag operates in associated mode and has a granular and well-calibrated receiver, those advantages are tempered by dynamic changes in environmental conditions and output power variations among APs. Many enterprise WLAN vendors support dynamic RF control, which means output power can change over time, but Ekahau says that doesn't significantly affect accuracy. Most significant to the accuracy claims of the tag-centric approach is the use of site survey software to gather the actual state of the RF environment, calibrate it, and feed that into a realistic location algorithm. Ekahau argues that poll-based systems that require a controller to look to each access point and gather a client's RSSI incurs a time-skewing effect that a client-centric approach doesn't have.

However, there are also beaconing systems that send one or more beacons out on multiple channels that are nearly instantaneously received and passed on to the location engine.

Barring a potential performance advantage for Ekahau in regards to a tag-centric approach, what other effect might associated mode operation have on a network? First, in associated mode, each tag needs to associate and authenticate, which requires at least four 802.11 frames. Then there's the method of updating location. A beaconing tag normally sends out a single beacon or packet every location update, but associating tags send out many more packets. Again, not a notable concern in small deployments, but if your WLAN uses a centralized data plane and/or operates over a WAN, you could feel a hit.

Finally, tags operating in associated mode need IP addresses. Dynamic addresses can be assigned via DHCP, but that will add even more traffic to the network. Assigning a fixed IP address to each tag eliminates that load but introduces another attribute to maintain. Ekahau's tags support multiple access profiles for internetwork mobility.

To Ekahau's advantage, because its tags associate with the wireless network, they don't require the enterprise WLAN system to understand proprietary beacons or chirps. For companies whose WLAN vendors have yet to integrate beaconing support, Ekahau may be the only viable locationing choice.

Rolling Reviews present a comprehensive look at a hot technology category, beginning with market analysis and wrapping up with a synopsis of our findings. See our kickoff and other reviews in this Wi-Fi location series at Rolling Reviews.