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LoST Primer

LoST (Location-to-Service Translation) is a protocol that allows a server to map a location and a service URN to a URI. It provides mappings for multiple services and can handle requests outside its service area using iteration or recursion. Originally designed for emergency call routing, LoST is now being extended for other services. This primer explains the protocol, forest guide, forest guides, and discovery of LoST servers.

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LoST Primer

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  1. LoST Primer Brian Rosen

  2. LoST (RFC5222) • Protocol to map a location and a “service urn” to a URI • Location is expressed with the “location information” part of a PIDF, essentially OGC GML point/polygon/circle/arcband • Service URN tells the server what service mapping is needed. We would use, e.g. urn:service:paws. Allows a LoST server to provide mappings for multiple services • Servers can use iteration or recursion to handle requests out of its service area

  3. LoST, con’t • LoST is defined as http transport with TLS using a Relax-NG schema • Originally defined to route emergency calls based on location to the right emergency call center (PSAP) • Now being extended to handle routing of other kinds of services (urn:service:pizza.pizzahut) • Full specification, with all the error conditions, referrals, formats, …

  4. Forest Guide • LoST servers are deployed in trees, with, roughly, nations at the top of the tree • For emergency services, next level might be state/province, and then possibly regional or local servers below that • The set of these trees is a “Forest” and there is a “Forest Guide” • The Forest Guide is used to handle a request that is out of service area of the tree • It refers (or recures) to another tree or another Forest Guide

  5. Forest Guides, con’t • The reason for Forest Guides is to avoid the “golden root” problem • Forest Guides are aware of each other and share coverage regions • “LoST Sync” is used to send coverage area to a Forest Guide and between Forest Guides

  6. Discovery of a LoST server • Could be configured • Could be discovered via DHCP

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