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Versions: (draft-wolf-ecrit-lost-servicelistboundary) 00 01 02 03 04 05 RFC 6197

ECRIT                                                            K. Wolf
Internet-Draft                                                    nic.at
Expires: April 9, 2010                                   October 6, 2009


       Location-to-Service Translation Protocol (LoST) Extension:
                          ServiceListBoundary
              draft-ietf-ecrit-lost-servicelistboundary-00

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   This Internet-Draft is submitted to IETF in full conformance with the
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   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Abstract

   LoST maps service identifiers and location information to service
   contact URIs.  If a LoST client wants to discover available services
   for a particular location, it will perform a <listServicesByLocation>



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   query to the LoST server.  However, the response from the LoST server
   does not provide information about the geographical region for which
   the returned service list is valid.  Therefore, this document
   proposes a ServiceListBoundary to assist the client to not miss a
   change in available services when moving.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3

   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4

   3.  LoST Extensions . . . . . . . . . . . . . . . . . . . . . . . . 4
     3.1.  Extensions to <ListServiceByLocation> . . . . . . . . . . . 4
     3.2.  Retrieving the serviceList Boundary via
           getServiceListBoundary  . . . . . . . . . . . . . . . . . . 6
     3.3.  Service List Boundary . . . . . . . . . . . . . . . . . . . 7
     3.4.  Implementation Considerations . . . . . . . . . . . . . . . 8
       3.4.1.  Server Side . . . . . . . . . . . . . . . . . . . . . . 8
       3.4.2.  Client Side . . . . . . . . . . . . . . . . . . . . . . 8

   4.  Security & Privacy Considerations . . . . . . . . . . . . . . . 9

   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 9

   6.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 9

   7.  Normative References  . . . . . . . . . . . . . . . . . . . . . 9

   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 9




















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1.  Introduction

   Location based service providers as well as Public Safety Answering
   Points (PSAPs) only serve a specific geographic region.  Therefore
   the LoST protocol defines the ServiceBoundary, which indicates the
   service region for a specific service URL.  However, not all services
   are available everywhere.  Clients can discover available services
   for a particular location by the <listServicesByLocation> query in
   LoST [RFC5222].  The LoST server returns a list of services that are
   available at this particular location.  But the server does not
   inform the client for which geographical region the returned service
   list is valid.  This may lead to the situation where a client
   initially discovered all available services by the
   <listServicesByLocation> query, and then moves to a different
   location while refreshing the service mappings, but does not notice
   the availability of another service.  The following imaginary example
   illustrates the problem for emergency calling:

   The client is powered-up, does location determination (resulting in
   location A) and performs an initial <listServicesByLocation> query
   with location A requesting urn:services:sos.

   The LoST server returns the following services list:

   urn:service:sos.police
   urn:service:sos.ambulance
   urn:service:sos.fire

   The client does the initial LoST mapping and discovers the
   dialstrings for each service.  Then the client moves, refreshing the
   individual service mappings when necessary as told by the
   ServiceBoundary.  However, when arriving in location B (close to a
   mountain), service sos.mountainrescue is available, which was not
   available in location A. Nevertheless, the client does not detect
   this, because only the mapping of the initially discovered services
   (police, ambulance, fire) are refreshed.  Consequently, the
   dialstring for the mountain rescue is not known by the client, and
   the emergency call to the mountain rescue service will certainly
   fail.

   Note that the ServiceBoundary (service region for an individual
   service) cannot be considered as an indicator for the region a
   specific service list is valid for.  The service list may even change
   within the ServiceBoundary of another service.  For example, the
   ambulance mapping is valid for a whole state, but for a part of the
   state there is an additional mountain rescue service.

   Consequently, there are two ways to tackle this issue:



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   o  clients continuously ask for the service list, although it may not
      have changed
   o  a boundary information (telling the client that the service list
      does not change inside this area)

   Since the LoST protocol has the ServiceBoundary concept in order to
   avoid that clients continuously try to refresh the mapping of a
   specific service, a ServiceListBoundary would provide a similar
   mechanism for service lists.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].


3.  LoST Extensions

   This chapter describes the necessary modifications to the LoST
   protocol in order to support the proposed ServiceListBoundary in a
   similar way as the ServiceBoundary.

3.1.  Extensions to <ListServiceByLocation>

   The query <listServicesByLocation> may contain an additional
   serviceListBoundary element to request the boundary for the service
   list, either by value or by reference.  In the example below the
   value of the serviceListBoundary element ist set to "value":





















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      <?xml version="1.0" encoding="UTF-8"?>
      <listServicesByLocation
        xmlns="urn:ietf:params:xml:ns:lost1"
        xmlns:gml="http://www.opengis.net/gml"
        xmlns:slb="TBD"
        recursive="true">
        <location id="mylocation" profile="civic">
          <civicAddress
            xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
            <country>AT</country>
            <A1>Lower Austria</A1>
            <A3>Wolfsthal</A3>
            <RD>Hauptplatz</RD>
            <HNO>1</HNO>
            <PC>2412</PC>
          </civicAddress>
        </location>
        <service>urn:service:sos</service>
        <slb:serviceListBoundary>value</slb:serviceListBoundary>
      </listServicesByLocation>

   A possible response is shown below:

      <?xml version="1.0" encoding="UTF-8"?>
      <listServicesByLocationResponse
       xmlns="urn:ietf:params:xml:ns:lost1">
       xmlns:slb="TBD"
       <serviceList expires="2010-01-01T00:00:00Z">
        urn:service:sos.ambulance
        urn:service:sos.fire
        urn:service:sos.gas
        urn:service:sos.mountain
        urn:service:sos.poison
        urn:service:sos.police
       </serviceList>
       <path>
        <via source="resolver.example"/>
        <via source="authoritative.example"/>
       </path>
       <locationUsed id="mylocation"/>
       <slb:serviceListBoundary profile="civic">
         <civicAddress
           xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
           <country>AT</country>
           <A1>Lower Austria</A1>
         </civicAddress>
       </slb:serviceListBoundary>
      </listServicesByLocationResponse>



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   This response above indicates that the service list is valid for
   Lower Austria.  The <listServicesByLocation> request has to be
   repeated by the client only when moving out of Lower Austria.
   However, the mappings of the services itself may have other service
   boundaries.  Additionally, the expires attribute indicates the
   absolute time when this service list becomes invalid.

   The boundary can also be requested by reference when setting the
   attribute serviceListBoundary to "reference".  Then the response
   contains a serviceListBoundaryReference element, as shown below.

      <?xml version="1.0" encoding="UTF-8"?>
      <listServicesByLocationResponse
       xmlns="urn:ietf:params:xml:ns:lost1">
       xmlns:slb="TBD"
       <serviceList expires="2010-01-01T00:00:00Z">
        urn:service:sos.ambulance
        urn:service:sos.fire
        urn:service:sos.gas
        urn:service:sos.mountain
        urn:service:sos.poison
        urn:service:sos.police
       </serviceList>
       <path>
        <via source="resolver.example"/>
        <via source="authoritative.example"/>
       </path>
       <locationUsed id="mylocation"/>
       <serviceListBoundaryReference
          source="authoritative.example"
          serviceListKey="123567890123567890123567890" />
      </listServicesByLocationResponse>

3.2.  Retrieving the serviceList Boundary via getServiceListBoundary

   In order to retrieve the boundary corresponding a specific
   serviceListKey, the client issues a <getServiceListBoundary> request,
   similar to the <getServiceBoundary> request.

   An example is shown below:

      <?xml version="1.0" encoding="UTF-8"?>
      <getServiceListBoundary xmlns="urn:ietf:params:xml:ns:lost1"
          serviceListKey="123567890123567890123567890"/>


   The LoST server response is shown below:




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   <?xml version="1.0" encoding="UTF-8"?>
   <getServiceListBoundaryResponse xmlns="TBD">
     <serviceListBoundary profile="civic" expires="2010-01-01T00:00:00Z">
       <civicAddress
         xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
        <country>AT</country>
        <A1>Lower Austria</A1>
       </civicAddress>
     </serviceListBoundary>
     <path>
       <via source="resolver.example"/>
       <via source="authoritative.example"/>
     </path>
   </getServiceListBoundaryResponse>


   The serviceListKey uniquely identifies a serviceListBoundary as the
   key does for the service boundary (see Section 5.6 in RFC 5222).
   Therefore the serviceListKey is a random token with at least 128 bits
   of entropy and can be assumed globally unique.  Whenever the boundary
   changes, a new serviceListKey MUST be assigned.

3.3.  Service List Boundary

   The service list boundary indicates a region within which all
   <listServicesByLocation> queries with the same service identifiers
   result in the same serviceList.  A service list boundary may consist
   of geometric shapes (both in civic and geodetic location format), and
   may be non-contiguous, like the service boundary.

   The mapping of the specific services within the service list boundary
   may be different at different locations.

   The server may return the boundary information in multiple profiles,
   but has to use at least one profile that the client used in the
   request in order to ensure that the client is able to process the
   boundary information.

   TBD: For <getServiceListBoundary> an attribute in the request could
   be used to indicate which profile the client understands (e.g.
   <getServiceListBoundary profile="civic"... )

   There is no need to include boundary information to a
   <listServicesResponse>. <ListServices> requests are purely for
   diagnostic purposes and do not contain location information at all,
   so no boundary information is reasonable.

   Also note that the serviceListBoundary is optional and the LoST



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   server may return it based on its local policy - like it is the case
   with service boundary.  However, especially for emergency services,
   the serviceListBoundary might be crucial to ensure that moving
   clients do not miss changes in the available services.

3.4.  Implementation Considerations

   The subsections below discuss implementations issues for the LoST
   server and client for the serviceListBoundary support.

3.4.1.  Server Side

   The mapping architecture and framework [RFC5582] describes that each
   tree announces its coverage region (for one type of service, e.g.
   sos.police) to one or more forest guides.  Forest guides peer with
   each other and synchronize their data.  Hence, a forest guide has
   sufficient knowledge (it knows all the services and their coverage
   regions) to answer a listServicesByLocation query and additionally
   add the serviceListBoundary as well.

   The calculation of the largest possible area for which the service
   list stays the same might be a complex task.  An alternative would be
   to return smaller areas that are easier to compute.  In such a case
   some unneeded queries to the LoST server are the consequence, but
   still the main purpose of the serviceListBoundary is achieved: Never
   miss a change of available services.  So a reasonable trade-off
   between the effort to generate the boundary information and the saved
   queries to the LoST server has to be considered.

   Probably for some countries the county (or disrict, canton, state,
   ...) borders would be suitable as serviceListBoundary.  Some
   neighbouring counties may have implemented different services while a
   listServicesByLocation query in other neighbouring counties still
   results in the same serviceList.  So when moving across a county
   border, it is at least ensured, that every device fetches a new
   service list from the LoST server.

   Other countries might have different structures and the generation of
   the serviceListBoundary might follow other rules as long as it is
   ensured that a client is able to notice any change in the service
   list when moving.

3.4.2.  Client Side

   A mobile client that already implements LoST and evaluates the
   serviceBoundary has almost everything that is needed to make use of
   the serviceListBoundary.  Since the integration into LoST follows the
   concept of the serviceBoundary (and also makes use of the same



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   location profiles), just the additional serviceListBoundary has to be
   evaluated.  Whenever moving outside a serviceListBoundary, the client
   must perform a new listServicesByLocation query with the new location
   information in order to determine a change in available services.


4.  Security & Privacy Considerations

   Security considerations are discussed in [RFC5222].


5.  IANA Considerations

   TODO.


6.  Acknowledgement

   The author would like to thank Henning Schulzrinne for the discussion
   on the draft.


7.  Normative References

   [RFC5222]  Hardie, T., Newton, A., Schulzrinne, H., and H.
              Tschofenig, "LoST: A Location-to-Service Translation
              Protocol", RFC 5222, August 2008.

   [RFC5582]  Schulzrinne, H., "Location-to-URL Mapping Architecture and
              Framework", RFC 5582, September 2009.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.


Author's Address

   Karl Heinz Wolf
   nic.at GmbH
   Karlsplatz 1/2/9
   Wien  A-1010
   Austria

   Phone: +43 1 5056416 37
   Email: karlheinz.wolf@nic.at
   URI:   http://www.nic.at/





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