Six burning VoIP questions

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2. VoIP: What really happens when I dial 911?

All corporate IP PBX systems can dial 911 services, but how much critical location data is transmitted during a life-or-death call depends on how the VoIP network and LAN is configured. The issue of IP softphones and mobile voice over Wi-Fi also complicates the issue.

Enhanced 911 service support was a major stumbling block for VoIP when it emerged in the consumer market several years ago. Technical issues, and some well-publicized incidents of failed emergency response from service providers, forced the FCC to step in with special 911 requirements for Internet phone service providers.

Many companies are still dealing with 911 issues and IP telephony deployments, as many IT departments still must manually track the location of phones in corporate offices. The easy portability of IP phones and the emergence of wireless IP handsets are challenges for maintaining an accurate device location database of phone extensions.

Enhanced 911, or E911, requires specific location information to be transmitted from a phone dialing 911 in an emergency, including building number, if a single campus address contains multiple buildings, as well floor numbers directional location (for example north, south, east, west).

"We do support 911 on all of our telephones on our campus," says Scott Mah, assistant vice president for IT infrastructure at the University of Washington in Seattle. "We have policies in place to limit end users from moving their phones around, which helps. But anytime we put a phone into service we basically register that telephone number and its corresponding address with the database."

The database maintained by the school's IT staff is passed to local emergency 911 call centers, or Public Safety Answering Points (PSAP), which links location information to each phone number in the school's system. This Automatic Location Identification (ALI) data is what's relayed to rescuers; if a 911 call is disconnected, emergency responders have information on where to go.

"[E911] is something we care a lot about and it's something we've maintained even without IP-enabled endpoints," Mah says.

There are some ways to automatically update ALI information when IP phones are moved. Some of this involves some planning of the campus network layout. New protocols and software are also available to help. Clever network administrators can setup pools of IP addresses into subnets which correspond to physical locations inside a building or campus. IP phones plugged into ports in these locations would automatically be linked to a building number and floor.

Cisco, Enterasys, Extreme, Nortel and Foundry all have their own proprietary discovery protocols for finding switches, routers and other devices on a network. But getting a Cisco switch to detect, let alone collect location data, on a Nortel IP phone is tricky, if not impossible. The Link Layer Discover Protocol-Media Endpoint Discover (LLDP-MED) is a Telecommunications Industry Association standard supported by Avaya, Extreme and ProCurve by HP, which LAN switches to collect device information and location data from IP phones (as well as other LLDP-MED-compliant devices, such as Wi-Fi access points) when network connections are plugged in. But because wide adoption of a standard discovery or registration protocol for phones is limited, users must work with what they have.