Seeking a solution to the dilemma of how to locate a VoIP user for 911 calls, because the technology gives the ability to move a phone to any location in the world, university researchers and the National Emergency Number Association (NENA) have demonstrated a system that uses common capabilities of IP networks to determine location.
The demonstration was held at the National Press Club in Washington, D.C., and included members of many organizations involved in 911, including an unofficial presence by a member of the FCC.
Those involved with the development of the system include Texas A&M University, Columbia University and the University of Virginia. The work is part of NENA’s efforts to develop what it calls the next-generation 911 system. With VoIP growing at a tremendous rate, the organization has said it is important to develop a 911 system that accommodates VoIP as soon as possible.
The system was presented by Henning Schulzrinne, a professor in the Department of Computer Science at Columbia University, and one of the principal developers of the SIP protocol. Schulzrinne said, “If we don’t come up with common, standard, deployable technology, we will end up with many devices that will not work with the system.”
Also, he said, a system has to be not only national, but also international, a position counter to the localism common in 911 systems. “We will greatly increase the cost if every state does its own technology,” Schulzrinne argued. “An important consideration is to make sure that we facilitate as much as possible a common system, not just U.S.-based, but as much as possible international, because of the nature of the Internet.” Any user who is traveling “can easily buy a SIP phone in France, for example, and it will work fine, and it needs to work for 911 as well.”
One strength of the proposed system is that it can use many different kinds of information that indicate location, ranging from DNS data to addresses actually entered by the user, to determine the location of the caller. The nomadic nature of VoIP means that a system has to be flexible in the kinds of data it uses to locate a caller.
How It Works
The first step in the system is to identify that a call is to 911. The researchers propose that VoIP providers standardize on using “SOS” in the user name of the SIP universal resource locator (URL) for each PSAP.
The calling party’s location can be determined in several ways using mechanisms that already exist in IP networks. One uses the calling endpoint’s outbound proxy, which will recognize the MAC address of the calling unit and use that to determine its location. In an enterprise, generally the network administrators have some knowledge of the locations of the Ethernet jacks in a building and the MAC addresses of machines on the network, though this information still is not gathered consistently enough.
A VoIP endpoint could even determine its own location, using GPS data, a Bluetooth beacon, DHCP data, triangulation to Wi-Fi access points or even data entered by the user.
Schulzrinne said there are already many sources of location information for consumer users of VoIP, such as the records kept by cable companies of which subscriber has which IP address. “This uses existing technology and existing databases,” he said.
While GPS sensors could be embedded in VoIP endpoints, that would leave out the millions of units already on the market, and “it will not be practical to wait on GPS,” Schulzrinne said.
Once the location is determined (or it is known that it cannot be determined), that data (which can be a city name or even geographical coordinates) is used to locate the proper PSAP (and its URL). Even if no location is known, a proxy server can route calls to a default PSAP, using DNS records. The system also includes advanced features for PSAPs, such as the ability to display caller locations on a map, to route calls to available call takers, to log emergency calls in a database, to record and archive calls, to view call logs and generate statistics, and to monitor currently active calls.
The system also has been linked to mapping software by MapInfo Corp. and GeoComm both to locate PSAPs and to display a callers’ locations on the screens of PSAP workers.