Enabling E911 in wireless LANs requires developing triangulation software akin to the capabilities used in cellular networks. Simply put, these applications basically take signal-strength measurements from each of three infrastructure radios (three base stations in the cellular network and three access points in a WLAN) to calculate the whereabouts of a caller.
If you're deploying E911 to comply with a state mandate, note that the requirements differ among states. So check that your vendor's location tracking capability meets the specific criteria of each state where you have offices. One key criterion is the number of meters within which the tracking software must pinpoint an E911 caller.
Several WLAN switch makers are readying their networks for enhanced emergency (E911) wireless phone calling services:
The start-up's RF Fingerprinting triangulation software accounts not only for signal strength but also for building characteristics (multipath), according to the company, which says the software can locate users to within "several meters." Airespace offers its location API to other vendors who can also build WLAN location-centric applications. A partnership on that front is reportedly forthcoming.
* Aruba Wireless
The company last week announced a triangulation capability that it says pinpoints an 802.11 signal to within 3 to 5 meters of the caller's location and visually depicts the location of calling source on an electronic floor plan. Keerti Melkote, Aruba's vice president of product marketing, says that if the caller moves, the software displays the motion in real time on the floor-plan screen.
* Meru Networks
Vice President of marketing Kamal Anand says, somewhat evasively, his company's WLAN switch can locate clients "with granular information." The company supplies an API to yet-to-be-named developers building location-tracking application for servers and IP PBXs.
* Trapeze Networks
The company offers triangulation software capabilities in its Ringmaster software with the ability to pinpoint users to within 10 meters.
Finally, I'd like to include a footnote about Cisco, known for its Emergency Responder application for wired VoIP calls. Cisco Emergency Responder groups devices into emergency response locations (ERL) so they can be identified by a physical location (such as building, floor, or region of floor).
I'm hoping we hear some announcements about further integration of Emergency Responder with Cisco's Aironet WLANs soon. At this juncture, the company recommends that each AP or a very small number of APs be assigned to its own ERL. This way, it is possible to identify that the caller is using a wireless device (via a code or abbreviation in the service provider's automatic location identification database). Then, emergency personnel will know to check floors, hallways, rooms, and buildings adjacent to the switch port in search of a caller.
Learn more about this topicWi-Fi VoIP will take time to mature, say vendors
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