Cisco Systems A Location-to-Service Translation protocol (LoST) Server is used to resolve or map a given location with an appropriate Public Safety Answering Point (PSAP) Uniform Resource Identifier (URI) for that location. This query is conceivably performed on two occasions: prior to making an emergency call, and during an emergency call. This document specifies a new Session Initiation Protocol (SIP) header, returned in a SIP Registration transaction, indicating to a SIP user agent the appropriate LoST Server's URI to send this query to.