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 a region of uncertainty. Architecture and protocols The IETF has defined an architecture and protocols for acquiring location information from a LIS. A LIS in the immediate access network is automatically discovered and location information is retrieved using the HELD protocol. Location information can be retrieved directly—known as by value—or the LIS can generate a temporary URI that can be used to provide location indirectly—known as a location URI. The location information provided by a LIS primarily uses the GEOPRIV format (RFC 4119), an XML representation based on the presence format defined in RFC 3863. RFC 4119 provides a container for both geodetic position and civic address information (now updated by RFC 5139) and also defines elements for expressing a user's privacy preferences. References Computer networking