1.  Field of the Invention
The present invention is generally directed to Voice over Internet Protocol (VoIP) telephony.  In particular, the present invention is directed to supporting enhanced 911 (E911) emergency services in a data communications network that includes VoIP telephones. 
2.  Background
Internet Protocol (IP) telephony is an important part of the convergence of data, voice and broadband services into a single integrated information environment.  Voice over Internet Protocol (VoIP) refers to an organized effort to standardize IP telephony and is a term used in IP telephony for a set of facilities for managing the delivery of voice information using the Internet Protocol.  In IP telephony, voice information is transmitted in discrete packets over shared bandwidth, rather than over the traditional circuit driven protocol used by the traditional Public Switched Telephone Network (PSTN).  The goal of VoIP is to use the Internet environment, which was not designed to provide traditional “toll” Quality of Service (QoS) for telephony, to provide the same high quality voice transmission that the traditional PSTN currently enjoys.  IP telephony service providers include, or soon will include, local telephone companies, long distance providers, cable TV companies, Internet service providers (ISPs), wireless service providers and fixed wireless local loop service operators. 
As VoIP efforts progress, the first VoIP telephones are becoming commercially available.  VoIP telephones offer flexibility not available in traditional plain old telephones (POTS).  For instance, like a laptop computer, a VoIP telephone can be easily moved from one point of network access to another without the assistance of a telephony administrator, and without having to change its identifying characteristics.  Such identifying characteristics may include a telephone number, an IP address, and/or a media access control (MAC) address.  While such ease of access may be desirable from an end user perspective, it creates significant concerns from the perspective of providing mission critical services such as enhanced emergency services, also known as E911. 
The 3-digit telephone number 9-1-1 has been designated for public use throughout the United States and Canada to report an emergency, request emergency assistance, or both.  By dialing 9-1-1, a person is provided direct access to a Public Safety Answering Point (PSAP).  A PSAP is an agency or group of agencies designated and authorized to receive and respond to emergency calls requiring one or more public services, such as Police, Fire or Emergency Medical Service.  Because the 9-1-1 number does not change, and there are thousands of PSAP's in the United States and Canada, it is vital that 9-1-1 calls are routed to the appropriate PSAP—i.e., the one closest to the location where the call originates.  Traditionally, before the advent of mobile telephones, a telephony administrator, normally working for the local telephony service provider, automatically routed calls from a fixed telephone to the nearest PSAP.  Because a telephony administrator was required to move a user's extension from one location to another, the administrator could also ensure proper routing of 9-1-1 calls. 
With the advent of mobile telephones, a new system was necessary.  This led to the advent of enhanced emergency services, or enhanced 911 (E911).  The main characteristic of E911 service is the capability to selectively route a 9-1-1 call originating from any device (mobile and fixed alike) in the E911 service area to the correct PSAP designated to serve the originating devices' location.  Another key feature of E911 is that it also provides the PSAP operator with the location of the calling device and a callback number.  These enhanced features are implemented primarily through the use of Selective Routing (SR), and maintenance of an Automatic Location Identification (ALI) database.  Selective Routing refers to the routing of a 911 call to the proper PSAP based upon the location of the caller.  The ALI database, which is regularly updated to match telephone numbers to physical locations, works within a database management system to automatically provide the PSAP operator the physical location of the calling device and a callback number. 
The ability to support E911 services is mandated in many states.  In a VoIP environment, it is possible for a user to successfully move their IP phone from one network access point to another without notifying the telephony administrator.  In this case, the telephony administrator would be unable to update the ALI database with the new location of the user and as a result, the ALI database would not contain the new location of that user.  The ability to provide physical location information to update E911 service database is available for VoIP deployment, but conventional solutions are proprietary, and require the user to choose the same vendor to provide, upgrade, and replace key system components.  The concern with this approach is that it does not allow users to take advantage of industry innovations.  Instead, customers are forced to rely on products from a single vendor. 
It would be beneficial, then, to provide integration between a network infrastructure for E911 services and VoIP telephones that is based on industry standards, rather than proprietary technologies.  It would also be beneficial to provide a system, method and apparatus for supporting E911 emergency services in a data communications network by automatically updating an ALI database each time a user changes the location of a VoIP telephone within the network.