Location Information Server
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The Location Information Server, or LIS is a network node originally defined in the National Emergency Number Association network architecture that addresses the intermediate solution for providing e911 service for users of VoIP telephony. The LIS is the node that determines the location of the VoIP terminal.
Beyond the NENA architecture and VoIP, the LIS is capable of providing location information to any IP device within its served access network.
[edit] The Role of the LIS
The LIS is a service that is provided by an access network provider to provide location information to users of the network. To do this, it uses knowledge of network topology and a range of location determination techniques to locate devices that are attached to the network. The precise methods that are used to determine location are dependent on the type of access network and the information that can be obtained from the device.
[edit] Location Determination
The method used to determine the location of a device in an access network varies between the different types of networks. For a wired network, such as Ethernet or DSL a wiremap method is common. In wiremap location determination, the location of a device is determined by finding which cables are used to send packets to the device. This involves tracing data through aggregation points in the network (such as Ethernet switches, or DSL access nodes) and finding the port that packets for that device are sent to. This information is combined with data available to the LIS (usually extracted from a database) to determine a final location. How this tracing is done then depends on the type of network.
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In wireless networks, a range of technologies can be applied to location determination, the most basic of which uses the location of the radio transmitter as an approximation. The actual method applied is similar to the wiremap method, if a radio transmitter can be identified, then the location of the device can be given as the position of the transmitter with an area of uncertainty.
