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E911 and wireless LANs

Apr 12, 20042 mins
Cellular NetworksNetwork Security

* The challenge of emergency calling in WLANs

Last week I began discussing a few recent industry efforts to render wireless LANs up to the task of reliably supporting VoIP phone calls. Among the issues: latency, security, emergency calling, and handset battery life.

This issue and next, we’ll take a peek at emergency calling.

As you likely know, enhanced emergency services (E911) are meant to ensure that emergency calls to police, firefighters, and medics are routed to the response center – also called a “public safety answering point,” or “PSAP” – closest to the caller. E911 also uses location-tracking to make sure callers in crisis can be found swiftly. In the cellular industry, the FCC has mandated that all mobile network operators support E911.

For enterprises, the states mandate whether phone systems operated by U.S. employers must support E911 and what the E911 criteria are. The latest information I could find indicates that seven states require E911 of employers (though some states require it only in certain vertical markets) and 16 others are considering it. Whether the states require E911 support specifically on mobile enterprise telephony systems remains a gray area right now.

Either way, for liability and ethical reasons, you’ll likely want to know if and how WLANs you install support emergency calling.

On the wired side of the house, an IP PBX supplies location information to the local service provider’s automatic location identification (ALI) database. Location information is derived from the switch port that connects to a user’s handset. But when users go mobile, there is no longer a consistent “port” to which their phones attach. Rather, an 802.11 access point radio attaches to the switch port and wirelessly communicates to the phone handset.

This means that the wireless network must run an application to locate the user and pass that information to the wired network infrastructure. Then, the wired network uses the information to ensure that the call is routed to the PSAP closest to the building from which the call is actually originating.

Wireless location-tracking applications are emerging from newer WLAN switch companies. Among them: Airespace, Aruba Wireless, Meru Neworks, and Trapeze Networks. We’ll take a closer look at these solutions next time.