[Docs] [txt|pdf] [draft-forte-lost-...] [Diff1] [Diff2]

EXPERIMENTAL

Internet Engineering Task Force (IETF)                          A. Forte
Request for Comments: 6451                                          AT&T
Category: Experimental                                    H. Schulzrinne
ISSN: 2070-1721                                      Columbia University
                                                           December 2011


       Location-to-Service Translation (LoST) Protocol Extensions

Abstract

   An important class of location-based services answers the question,
   "What instances of this service are closest to me?"  Examples include
   finding restaurants, gas stations, stores, automated teller machines,
   wireless access points (hot spots), or parking spaces.  Currently,
   the Location-to-Service Translation (LoST) protocol only supports
   mapping locations to a single service based on service regions.  This
   document describes an extension that allows queries of the type "N
   nearest", "within distance X", and "served by".

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Engineering
   Task Force (IETF).  It represents the consensus of the IETF
   community.  It has received public review and has been approved for
   publication by the Internet Engineering Steering Group (IESG).  Not
   all documents approved by the IESG are a candidate for any level of
   Internet Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6451.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  3
   3.  Service Regions  . . . . . . . . . . . . . . . . . . . . . . .  3
   4.  New <findService> Query Types: "N nearest", "within
       distance X", and "served by" . . . . . . . . . . . . . . . . .  4
   5.  LoST Extensions  . . . . . . . . . . . . . . . . . . . . . . .  4
     5.1.  New Use of Shapes in Queries . . . . . . . . . . . . . . .  5
     5.2.  Queries Based on Service Regions . . . . . . . . . . . . .  7
     5.3.  Difference between "within distance X" and "served by"
           Queries  . . . . . . . . . . . . . . . . . . . . . . . . .  9
     5.4.  Limiting the Number of Returned Service URIs . . . . . . . 10
     5.5.  The <serviceLocation> Element in Responses . . . . . . . . 12
   6.  Emergency Services . . . . . . . . . . . . . . . . . . . . . . 15
   7.  RELAX NG Schema  . . . . . . . . . . . . . . . . . . . . . . . 16
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 18
     9.1.  LoST Extensions RELAX NG Schema Registration . . . . . . . 18
     9.2.  LoST Extensions Namespace Registration . . . . . . . . . . 19
   10. Non-Normative RELAX NG Schema in XML Syntax  . . . . . . . . . 19
   11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 22
   12. Normative References . . . . . . . . . . . . . . . . . . . . . 22

1.  Introduction

   The Location-to-Service Translation (LoST) protocol [RFC5222] maps
   service identifiers (URNs) and civic or geospatial information to
   service URIs, based on service regions.  While motivated by mapping
   locations to the public safety answering point (PSAP) serving that
   location, the protocol has been designed to generalize to other
   location-mapping services.

   However, the current LoST query model assumes that each service URI
   has a service region and that service regions do not overlap.  This
   fits the emergency services model, where the service region of a PSAP
   is given by jurisdictional boundaries, but does not work as well for
   other services that do not have clearly defined boundaries.  For
   example, any given location is likely served by a number of different
   restaurants, depending on how far the prospective customer is willing
   to travel.





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   We extend LoST with three additional <findService> query types,
   giving the protocol the ability to find the N nearest instances of a
   particular service, all services within a given distance, and all
   services whose service region includes the user's current location.

2.  Requirements Notation

   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 [RFC2119].

3.  Service Regions

   Generally speaking, service regions apply only to a subset of
   services.

   In Section 1 of [RFC5222], a service region is defined as follows:

   "To minimize round trips and to provide robustness against network
   failures, LoST supports caching of individual mappings and indicates
   the region for which the same answer would be returned ("service
   region")."

   Section 5.5 of [RFC5222] further defines a service region:

   "A response MAY indicate the region for which the service URL
   returned would be the same as in the actual query, the so-called
   service region."

   For emergency services, service region and service area, as defined
   in [RFC5222], represent the same geographical area.  This is due to
   the fact that each PSAP serves its own area without overlapping with
   the service area of any other PSAP.  For as long as the client is
   located in the service area of a PSAP, the same PSAP is returned by
   the LoST server, that is, the service region does not change.  A
   service region is the service area of a PSAP.

   For non-emergency services, different points of service may have
   different overlapping service areas.  This means that one service
   region will probably include a large number of service areas.  Since
   we can get a large number of service URIs for each query, a service
   region per the definition above would be the region within which a
   user would get the same set of service URIs.  If one or more of the
   URIs in the set changes, the set of URIs changes, i.e., the service
   region changes.  Therefore, for non-emergency services, the service
   region defined in [RFC5222] would change frequently, thus greatly
   reducing the benefit of caching responses by service region.




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   Generally speaking, we can divide location-based services into two
   main categories based on:

   o  how far they are from the user (e.g., automatic teller machine,
      food takeout);

   o  whether or not their service area includes the user's current
      location (e.g., pizza delivery, PSAP).

   For services included in the first category, service areas and
   therefore service regions are not relevant while they are important
   for services included in the second category.  This distinction
   becomes obvious if we consider, for example, the difference between
   takeout (first category) and delivery (second category).  In the case
   of takeout, the user wants to go to a particular restaurant and buy
   dinner, regardless of whether his location falls into the delivery
   service area of the restaurant or not.  For delivery, the user cares
   about the restaurant service area as the restaurant will deliver food
   to him only if his location falls within the restaurant service area.

   There is a clear distinction between services that require service
   areas and services that do not.  The LoST extensions defined in this
   document take this into account by using the service classification
   mentioned above.

4.  New <findService> Query Types: "N nearest", "within distance X", and
    "served by"

   We introduce three new types of <findService> queries: "N nearest",
   "within distance X", and "served by".  The first query returns the N
   points of interest (POIs) closest to the client's physical location;
   the second query discovers all the points of interest located within
   a given distance from the client's physical location; and the third
   query returns all the points of interest whose service area includes
   the client's current location.

5.  LoST Extensions

   For "within distance X" queries, the LoST client needs to specify to
   the server the range within which instances of a particular service
   should be searched.  In order to do this, we make use of various
   shapes [RFC5491] in LoST queries.

   For "served by" queries, the LoST client needs to let the server know
   that it MUST return only those services whose service area includes
   the user's current location.  In order to do this, we introduce the





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   <region> element in <findService> queries.  Service region boundaries
   MAY be returned in a LoST <findServiceResponse> as described in
   [RFC5222].

   For "N nearest" queries, the LoST client needs to let the server know
   N, i.e., the maximum number of service URIs to be returned in a
   response.  In order to specify this, we introduce the <limit> element
   in <findService> queries.

   Also, we introduce a new element in LoST responses, namely
   <serviceLocation>.  This new element is used by the server to
   indicate to the client the physical location of points of interest.
   In doing so, the client can compute the distance and other metrics
   between its current location and the points of interest.

   The new elements <region>, <limit>, and <serviceLocation> are defined
   in the "lost-ext" namespace.  This new namespace is defined in
   Section 7.

5.1.  New Use of Shapes in Queries

   In [RFC5491], different shapes are defined in order to represent a
   point and an area of uncertainty within which the user might be
   situated.  While this remains true for "served by" queries, for
   "within distance X" queries, such shapes can be interpreted as the
   area within which we want to find a service.  In particular, we want
   to search for points of service within that area because our location
   is within that area with a certain probability.  We can think of the
   area of uncertainty in a shape as the probability that a user might
   be within that area, so we want to look for services within that
   area.  Thus, the "within distance X" query manually sets the
   uncertainty in user location to an uncertainty shape with
   parameter X.

   For example, Figure 1 shows a "within distance X" <findService>
   geodetic query using the circular shape.  With the query shown in
   Figure 1, we are asking the LoST server to send us a list of service
   URIs for pizza places within 200 meters from our approximate position
   specified in <gml:pos>.












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   <?xml version="1.0" encoding="UTF-8"?>
   <findService
     xmlns="urn:ietf:params:xml:ns:lost1"
     xmlns:ext="urn:ietf:params:xml:ns:lost-ext"
     xmlns:gml="http://www.opengis.net/gml"
     xmlns:gs="http://www.opengis.net/pidflo/1.0"
     serviceBoundary="value"
     recursive="true">
     <ext:region>false</ext:region>
     <location id="6020688f1ce1896d" profile="geodetic-2d">
       <gs:Circle srsName="urn:ogc:def:crs:EPSG::4326">
         <gml:pos>37.775 -122.422</gml:pos>
         <gs:radius uom="urn:ogc:def:uom:EPSG::9001">
            200
         </gs:radius>
       </gs:Circle>
     </location>
     <service>urn:service:food.pizza</service>
   </findService>

   Figure 1: A "within distance X" <findService> geodetic query using
   the circular shape (a hypothetical service URN of
   "urn:service:food.pizza" is used)

   Aside from the circular shape, other shapes are also useful.  In
   particular, there are situations in which it is useful to query for
   services in a certain direction of movement rather than in an exact
   physical location.  For example, if a user is driving north from New
   York City to Boston, it would be useful for this user to be able to
   query for services north of where he currently is, that is, not at
   his current physical location nor at his final destination.

   In order to implement such direction-of-travel searches, this
   document supports the use of shapes such as an ellipse.  The ellipse
   has a major and a minor dimension, thus allowing for defining a
   "privileged" direction by having the major dimension in the direction
   of movement.  In the present context, the circular shape allows a
   device to search for services in any direction surrounding its
   physical location, while shapes such as the ellipse allow the device
   to search for services in a more specific direction.  Figure 2 shows
   a "within distance X" <findService> geodetic query using the
   elliptical shape.  The ellipse shape is defined in Section 5.2.4 of
   [RFC5491].








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   <?xml version="1.0" encoding="UTF-8"?>
   <findService
     xmlns="urn:ietf:params:xml:ns:lost1"
     xmlns:ext="urn:ietf:params:xml:ns:lost-ext"
     xmlns:gml="http://www.opengis.net/gml"
     xmlns:gs="http://www.opengis.net/pidflo/1.0"
     serviceBoundary="value"
     recursive="true">
     <ext:region>false</ext:region>
     <location id="6020688f1ce1896d" profile="geodetic-2d">
       <gs:Ellipse srsName="urn:ogc:def:crs:EPSG::4326">
         <gml:pos>42.5463 -73.2512</gml:pos>
         <gs:semiMajorAxis uom="urn:ogc:def:uom:EPSG::9001">
           1235
         </gs:semiMajorAxis>
         <gs:semiMinorAxis uom="urn:ogc:def:uom:EPSG::9001">
           660
         </gs:semiMinorAxis>
         <gs:orientation uom="urn:ogc:def:uom:EPSG::9102">
           41.2
         </gs:orientation>
       </gs:Ellipse>
     </location>
     <service>urn:service:food.pizza</service>
   </findService>

   Figure 2: A "within distance X" <findService> geodetic query using
   the elliptical shape (a hypothetical service URN of
   "urn:service:food.pizza" is used)

5.2.  Queries Based on Service Regions

   As mentioned in Section 3, we can divide location-based services into
   two main categories based on:

   o  how far they are from the user;

   o  whether or not their service area includes the user's current
      location.

   A "within distance X" query addresses services included in the first
   category, while a "served by" query addresses services included in
   the second category.

   When querying LoST regarding a specific service, we need to specify
   if such service belongs to either the first or the second category.
   This is necessary since depending on the category to which the




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   service belongs, the LoST server has to follow a different metric in
   selecting the results to include in the response.

   For example, Figure 3 shows three points of interest with their
   service areas.  The user location (i.e., the LoST client location) is
   represented by a circular shape (e.g., GPS).  If POI 1, POI 2, and
   POI 3 belong to the first category of service ("within distance X"
   query), their service area is irrelevant; what matters is how far
   they are from the user.  For such services, the shape representing
   the user location represents the distance within which the user wants
   to search for services (see Section 5.1).  In the example shown in
   Figure 3, the LoST server returns only POI 3, as POI 3 is the only
   point of interest falling within the user location represented by the
   circle, i.e., the area within which the user wants to search for
   services.  On the other hand, if the three points of service belong
   to the second category ("served by" query), then what matters is
   their service area.  In this second scenario, since the circle
   representing the user location overlaps with all three service areas,
   all three POIs can serve the location of the user, and the LoST
   server has to return all three POIs, that is, POI 1, POI 2, and
   POI 3.

                            __________________________
                            \    *****                \
            ,===============***====,    ***            \
           /              **  \   /         **          \
          /   POI 1     **     \ /            **         \
         /      o      **       X              **         \
        /             **       / \  USER        **         \
       /              **      /   \  0           **         \
      /               **     /     \      POI 3  **          \
     /                 **   /       \       o    **           \
    /          ,--------**-/---------\----------**--,          \
   `=====================**           \________**___|___________\
               |           **                **     |
               |   o         ***          ***       |
               |  POI 2           *****             |
               `------------------------------------'

   Figure 3: LoST client location (circle) overlapping three service
   areas of three different points of interest (POI 1, POI 2, POI 3)

   In order for the client to specify which of the two categories the
   service belongs to, we introduce the <region> element.  This new
   element is of type boolean.  When its value is false, the LoST server
   MUST perform a search based on the distance between the user and the
   points of service ("within distance X" query).  When its value is
   either true or the <region> element is missing (see Section 5.3), the



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   requested service belongs to the second category, and a search based
   on service areas MUST be performed by the LoST server ("served by"
   query).  When present, the <region> element MUST be conveyed inside
   the <findService> element defined in [RFC5222].

   For a search based on service regions, the LoST server MUST return
   only those services whose service area includes the user's current
   location.  Service region boundaries MAY be returned in a LoST
   <findServiceResponse> as described in [RFC5222].

   <?xml version="1.0" encoding="UTF-8"?>
    <findService
     xmlns="urn:ietf:params:xml:ns:lost1"
     xmlns:ext="urn:ietf:params:xml:ns:lost-ext"
     xmlns:gml="http://www.opengis.net/gml"
     xmlns:gs="http://www.opengis.net/pidflo/1.0"
     serviceBoundary="value" recursive="true">
     <ext:region>true</ext:region>
     <location id="6020688f1ce1896d" profile="geodetic-2d">
       <gs:Circle srsName="urn:ogc:def:crs:EPSG::4326">
         <gml:pos>37.775 -122.422</gml:pos>
         <gs:radius uom="urn:ogc:def:uom:EPSG::9001">
            200
         </gs:radius>
       </gs:Circle>
     </location>
    <service>urn:service:food.pizza</service>
   </findService>

   Figure 4: A "served by" <findService> geodetic query with the new
   <region> element (a hypothetical service URN of
   "urn:service:food.pizza" is used)

5.3.  Difference between "within distance X" and "served by" Queries

   Figures 1 and 4 show examples of a "within distance X" query and a
   "served by" query, respectively.  Although very similar, these two
   types of queries have three important differences:

   o  A "served by" query can support all the shapes a "within distance
      X" query can support plus the point shape.  The point shape does
      not make sense for a "within distance X" query and SHOULD NOT be
      used for this query as it would be equivalent to a within-zero-
      meters search.

   o  In a "within distance X" query, we manually set the uncertainty
      level in user location to X, and we search for services within the
      area represented by such uncertain location.  In all other types



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      of queries, including a "served by" query, the level of
      uncertainty in user location cannot be changed by the user, and a
      search based on service areas is performed.

   o  In a "within distance X" query, the value of the <region> element
      MUST be set to false.  A "served by" query SHALL have the value of
      the <region> element set to true.  If the <region> element is not
      present, its value MUST be assumed to be equal to true, and the
      query will be a "served by" query.  This behavior is consistent
      with [RFC5222].

5.4.  Limiting the Number of Returned Service URIs

   Limiting the number of results is helpful, particularly for mobile
   devices with limited bandwidth.  For "N nearest" queries, the client
   needs to be able to tell the server to return no more than N service
   URIs.  In order to specify such a limit, we introduce a new element,
   namely <limit>.  This new element is OPTIONAL, but when present, it
   MUST be conveyed inside the <findService> element defined in
   [RFC5222].

   Figures 5, 6, and 7 show a <findService> geodetic query where the
   client asks the server to return no more than 20 service URIs.  In
   particular, Figure 5 shows an "N nearest" query; Figure 6 shows a
   query that is a combination of "N nearest" and "within distance X";
   and Figure 7 shows a query that is a combination of "N nearest" and
   "served by".  When receiving such queries, the LoST server will
   return a list of no more than 20 points of interest.

   If the available points of interest are more than N, the server has
   to identify, among those, the N points of interest closest to the
   client's physical location and MUST return those in the response.

   When the <limit> element is not present in a <findService> query,
   then all available points of interest for the requested type of
   service SHOULD be returned by the LoST server.  This behavior is
   consistent with [RFC5222].














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   <?xml version="1.0" encoding="UTF-8"?>
   <findService
     xmlns="urn:ietf:params:xml:ns:lost1"
     xmlns:ext="urn:ietf:params:xml:ns:lost-ext"
     xmlns:gml="http://www.opengis.net/gml"
     serviceBoundary="value" recursive="true">
     <ext:limit>20</ext:limit>
     <location id="6020688f1ce1896d" profile="geodetic-2d">
       <gml:Point id="point1" srsName="urn:ogc:def:crs:EPSG::4326">
         <gml:pos>40.7128 -74.0092</gml:pos>
       </gml:Point>
     </location>
   <service>urn:service:food.pizza</service>
   </findService>

   Figure 5: An "N nearest" <findService> geodetic query with the new
   <limit> element (a hypothetical service URN of
   "urn:service:food.pizza" is used)

   <?xml version="1.0" encoding="UTF-8"?>
   <findService
     xmlns="urn:ietf:params:xml:ns:lost1"
     xmlns:ext="urn:ietf:params:xml:ns:lost-ext"
     xmlns:gml="http://www.opengis.net/gml"
     xmlns:gs="http://www.opengis.net/pidflo/1.0"
     serviceBoundary="value"
     recursive="true">
     <ext:region>false</ext:region>
     <ext:limit>20</ext:limit>
     <location id="6020688f1ce1896d" profile="geodetic-2d">
       <gs:Circle srsName="urn:ogc:def:crs:EPSG::4326">
         <gml:pos>37.775 -122.422</gml:pos>
         <gs:radius uom="urn:ogc:def:uom:EPSG::9001">
            200
         </gs:radius>
       </gs:Circle>
     </location>
     <service>urn:service:food.pizza</service>
   </findService>

   Figure 6: A <findService> geodetic query with the new <limit> and
   <region> elements.  This query is a combination of the "N nearest"
   and "within distance X" queries (a hypothetical service URN of
   "urn:service:food.pizza" is used)







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   <?xml version="1.0" encoding="UTF-8"?>
   <findService
     xmlns="urn:ietf:params:xml:ns:lost1"
     xmlns:ext="urn:ietf:params:xml:ns:lost-ext"
     xmlns:gml="http://www.opengis.net/gml"
     xmlns:gs="http://www.opengis.net/pidflo/1.0"
     serviceBoundary="value"
     recursive="true">
     <ext:region>true</ext:region>
     <ext:limit>20</ext:limit>
     <location id="6020688f1ce1896d" profile="geodetic-2d">
       <gs:Circle srsName="urn:ogc:def:crs:EPSG::4326">
         <gml:pos>37.775 -122.422</gml:pos>
         <gs:radius uom="urn:ogc:def:uom:EPSG::9001">
            100
         </gs:radius>
       </gs:Circle>
     </location>
     <service>urn:service:food.pizza</service>
   </findService>

   Figure 7: A <findService> geodetic query with the new <limit> and
   <region> elements.  This query is a combination of the "N nearest"
   and "served by" queries (a hypothetical service URN of
   "urn:service:food.pizza" is used)

5.5.  The <serviceLocation> Element in Responses

   It is important for the LoST client to know the location of a point
   of interest so that distance, route, and other metrics can be
   computed.  We introduce a new element, namely <serviceLocation>.  The
   <serviceLocation> element contains the location of a point of
   service.  When it is used, it MUST be contained in a <mapping>
   element.  In responses such as <findServiceResponse> [RFC5222], a
   list of service URIs, each with its own <serviceLocation> element,
   SHOULD be returned.  The order of service URIs in the list is not
   significant.

   The <serviceLocation> element has a single attribute, "profile", that
   specifies the profile used.  Both civic and geodetic profiles can be
   used.  The geodetic profiles SHOULD be used in order to compute
   distance, route, and other metrics as, at some point, computing such
   metrics would require geocoding of the civic address in geodetic
   coordinates.  Because of this, the position specified in
   <serviceLocation> with a geodetic profile SHOULD be represented by
   the <Point> element.  The <Point> element is described in Section





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   12.2 of [RFC5222] and in Section 5.2.1 of [RFC5491].  Figure 8 shows
   a <findServiceResponse> answer containing two location-to-service-URI
   mappings.

   [NOTE: The <locationUsed> element cannot be extended for this
   purpose, as it is defined outside of the <mapping> element.  In
   particular, in a response, the <locationUsed> element is always one,
   while the number of service URIs is typically more than one.]

   There are situations, however, in which it is helpful to include a
   civic address together with the geodetic coordinates of a point of
   service.  Usually, databases already contain the civic address of
   points of interest, and for devices with limited capabilities, it is
   not always possible to perform decoding of geocoordinates in order to
   determine the civic address.  Because of this, including the civic
   address in a response can be useful.  In order to do this, we use a
   civic profile for the <serviceLocation> element and specify the POI
   civic address in a <civicAddress> element contained in the
   <serviceLocation> element.  The basic civic location profile is
   defined in Section 12.3 of [RFC5222].

   Per [RFC5139], it is RECOMMENDED to use multiple <serviceLocation>
   elements when multiple forms of service location are available, and
   it is RECOMMENDED to provide a geodetic form whenever possible.  When
   multiple <serviceLocation> elements are present for one POI, all of
   them MUST be contained in the same <mapping> element, that is, the
   <mapping> element for that POI.  Figure 8 shows a
   <findServiceResponse> answer with both geodetic and civic locations.

      <?xml version="1.0" encoding="UTF-8"?>
      <findServiceResponse
        xmlns="urn:ietf:params:xml:ns:lost1"
        xmlns:ext="urn:ietf:params:xml:ns:lost-ext"
        xmlns:gml="http://www.opengis.net/gml">
        <mapping
          expires="2007-01-01T01:44:33Z"
          lastUpdated="2006-11-01T01:00:00Z"
          source="authoritative.example"
          sourceId="7e3f40b098c711dbb6060800200c9a66">
          <displayName xml:lang="it">
            Che bella pizza e all' anima da' pizza da Toto'
          </displayName>
          <service>urn:service:food.pizza</service>
          <uri>sip:chebella@example.com</uri>
          <uri>xmpp:chebella@example.com</uri>
          <serviceNumber>2129397040</serviceNumber>
          <ext:serviceLocation profile="geodetic-2d">
            <gml:Point id="point1" srsName="urn:ogc:def:crs:EPSG:4326">



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              <gml:pos>33.665 -112.432</gml:pos>
            </gml:Point>
          </ext:serviceLocation>
          <ext:serviceLocation profile="civic">
            <civicAddress
                xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
                <country>US</country>
                <A1>New York</A1>
                <A3>New York</A3>
                <A6>Broadway</A6>
                <HNO>321</HNO>
                <PC>10027</PC>
            </civicAddress>
          </ext:serviceLocation>
        </mapping>
        <mapping
          expires="2007-01-01T01:44:33Z"
          lastUpdated="2006-11-01T01:00:00Z"
          source="authoritative.example"
          sourceId="7e3f40b098c711dbb6060800200c9b356">
          <displayName xml:lang="en">
            King Mario's Pizza
          </displayName>
          <service>urn:service:food.pizza</service>
          <uri>sip:marios@example.com</uri>
          <uri>xmpp:marios@example.com</uri>
          <serviceNumber>2129397157</serviceNumber>
          <ext:serviceLocation profile="geodetic-2d">
            <gml:Point id="point1" srsName="urn:ogc:def:crs:EPSG:4326">
              <gml:pos>33.683 -112.412</gml:pos>
            </gml:Point>
          </ext:serviceLocation>
          <ext:serviceLocation profile="civic">
            <civicAddress
                xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
                <country>US</country>
                <A1>New York</A1>
                <A3>New York</A3>
                <A6>Amsterdam Avenue</A6>
                <HNO>123</HNO>
                <PC>10027</PC>
            </civicAddress>
          </ext:serviceLocation>
        </mapping>
        <path>
          <via source="resolver.example"/>
          <via source="authoritative.example"/>
        </path>



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        <locationUsed id="6020688f1ce1896d"/>
      </findServiceResponse>

   Figure 8: A <findServiceResponse> answer

6.  Emergency Services

   The LoST extensions defined in this document SHOULD NOT be used when
   routing emergency sessions, as there may be LoST servers that do not
   support these extensions.

   Figure 9 shows a <findService> query for emergency services as
   defined in [RFC5222].  In such a query, both the <region> element and
   the <limit> element are missing.  According to the LoST extensions
   defined in this document, when the <region> element is missing, its
   value defaults to true, and the query is a "served by" query (see
   Section 5.3).  When the <limit> element is missing, no limit is
   specified, that is, the LoST server can return any number of results
   (see Section 5.4).  This behavior is consistent with [RFC5222] so
   that PSAPs are selected according to their service area, and when a
   user's location overlaps multiple service areas, the LoST server MAY
   return multiple PSAPs.

   The LoST extensions defined in this document are consistent with the
   behavior defined in [RFC5222], and, as such, they do not modify LoST
   behavior for emergency services.

   <?xml version="1.0" encoding="UTF-8"?>
      <findService
        xmlns="urn:ietf:params:xml:ns:lost1"
        xmlns:p2="http://www.opengis.net/gml"
        serviceBoundary="value"
        recursive="true">

        <location id="6020688f1ce1896d" profile="geodetic-2d">
          <p2:Point id="point1" srsName="urn:ogc:def:crs:EPSG::4326">
             <p2:pos>37.775 -122.422</p2:pos>
          </p2:Point>
        </location>
        <service>urn:service:sos.police</service>

      </findService>

   Figure 9: A <findService> geodetic query for emergency services

   Unlike emergency services, where information such as service
   boundaries of PSAPs and locations of fire stations does not change
   very often, if at all, non-emergency services have information that



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   may become inaccurate quickly.  Implementers should take this into
   account when designing applications for non-emergency location-based
   services.

7.  RELAX NG Schema

   This section provides the RELAX NG schema of LoST extensions in the
   compact form.  The verbose form is included in Section 9.

   namespace a = "http://relaxng.org/ns/compatibility/annotations/1.0"
   default namespace ns1 = "urn:ietf:params:xml:ns:lost-ext"

   ##
   ##    Extensions to the Location-to-Service Translation (LoST)
   ##    Protocol

   ##
   ##    LoST Extensions define three new elements: limit, region, and
   ##    serviceLocation.
   ##
   start =
     limit
     | region
     | serviceLocation

   ##
   ##    A limit to the number of returned results.
   ##
   div {
     limit=
       element limit {
         xsd:positiveInteger
       }
   }

   ##
   ##   A boolean variable to request a search
   ##   based on either service areas or distance.
   ##
   ##   NOTE: The W3C XML Schema has two different
   ##         lexical representations for boolean:
   ##         '1' or 'true' vs. '0' or 'false'.
   ##
   div {
     region=
       element region {
         xsd:boolean
       }



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   }

   ##
   ##    Location Information
   ##
   div {
     locationInformation =
       extensionPoint+,
       attribute profile { xsd:NMTOKEN }?
   }

   ##
   ##    Location Information about the returned point
   ##    of service.
   ##
   div {
     serviceLocation=
       element serviceLocation { locationInformation }+
   }

   ##
   ##    Patterns for inclusion of elements from schemas in
   ##    other namespaces.
   ##
   div {

     ##
     ##    Any element not in the LoST Extensions
     ##    namespace.
     ##
     notLostExt = element * - (ns1:* | ns1:*) { anyElement }

     ##
     ##    A wildcard pattern for including any element
     ##    from any other namespace.
     ##
     anyElement =
       (element * { anyElement }
        | attribute * { text }
        | text)*

     ##
     ##    A point where future extensions
     ##    (elements from other namespaces)
     ##    can be added.
     ##
     extensionPoint = notLostExt*
   }



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8.  Security Considerations

   The overall LoST architecture and framework are defined in [RFC5582].
   All LoST queries for both emergency and non-emergency services, if
   not cached, are sent from the LoST client to a first-hop LoST server.
   In [RFC5582] terminology, a LoST client is called Seeker, and the
   first-hop LoST server is called Resolver (for more rigorous
   definitions, please refer to [RFC5582]).  The Resolver will contact
   other LoST servers, and eventually an authoritative LoST server will
   be found.  A response will then be sent back to the Seeker.

   When considering both emergency and non-emergency services, there is
   the possibility of the Resolver getting overloaded by non-emergency-
   service queries, thus being unable to process emergency-service
   queries.  Such a situation can be addressed in several ways.  For
   example, the service provider could dimension the LoST server to
   accommodate anticipated combined traffic loads and then give priority
   to emergency service requests during overload situations, possibly
   with the help of HTTP load balancers.

   The security considerations in [RFC5222] apply.  In particular, in
   order to maintain integrity and confidentiality of requests and
   responses, Transport Layer Security (TLS) MUST be implemented and
   SHOULD be used as described in Sections 1, 14, and 18 of [RFC5222].

9.  IANA Considerations

9.1.  LoST Extensions RELAX NG Schema Registration

   URI: urn:ietf:params:xml:schema:lost-ext

   Registrant Contact: Andrea G. Forte, forte@att.com;
   Henning Schulzrinne, hgs@cs.columbia.edu

   RELAX NG Schema: The RELAX NG schema to be registered is contained in
   Section 7.  Its first line is

   default namespace ns1 = "urn:ietf:params:xml:ns:lost-ext"

   and its last line is

   }









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9.2.  LoST Extensions Namespace Registration

   URI: urn:ietf:params:xml:ns:lost-ext

   Registrant Contact: Andrea G. Forte, forte@att.com;
   Henning Schulzrinne, hgs@cs.columbia.edu

   XML:

   BEGIN
   <?xml version="1.0"?>
   <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
     "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
   <html xmlns="http://www.w3.org/1999/xhtml">
   <head>
     <meta http-equiv="content-type"
           content="text/html;charset=iso-8859-1"/>
     <title>LoST Extensions Namespace</title>
   </head>
   <body>
     <h1>Namespace for LoST Extensions</h1>
     <h2>urn:ietf:params:xml:ns:lost-ext</h2>
   <p>See <a href="http://www.rfc-editor.org/rfc/rfc6451.txt">
      RFC 6451</a>.</p>
   </body>
   </html>
   END

10.  Non-Normative RELAX NG Schema in XML Syntax

<?xml version="1.0" encoding="UTF-8"?>
   <grammar ns="urn:ietf:params:xml:ns:lost-ext"
           xmlns="http://relaxng.org/ns/structure/1.0"
           xmlns:a="http://relaxng.org/ns/compatibility/annotations/1.0"
           datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">

           <start>
       <a:documentation>
         Extensions to the Location-to-Service Translation (LoST)
         Protocol.
         LoST Extensions define three new elements: limit, region and
         serviceLocation.
       </a:documentation>
       <choice>
         <ref name="limit"/>
         <ref name="region"/>
         <ref name="serviceLocation"/>
       </choice>



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           </start>

     <div>
       <a:documentation>
         A limit to the number of returned results.
       </a:documentation>

       <define name="limit">
         <element name="limit">
           <data type="positiveInteger"/>
         </element>
       </define>
     </div>

    <div>
      <a:documentation>
        A boolean variable to request a search
        based on either service areas or distance.
      </a:documentation>

      <define name="region">
        <element name="region">
          <data type="boolean"/>
        </element>
      </define>
    </div>

     <div>
       <a:documentation>
         Location Information
       </a:documentation>

       <define name="locationInformation">
         <oneOrMore>
           <ref name="extensionPoint"/>
         </oneOrMore>
         <optional>
           <attribute name="profile">
             <data type="NMTOKEN"/>
           </attribute>
         </optional>
       </define>
     </div>

     <div>
       <a:documentation>
         Location Information about the returned point of service.
       </a:documentation>



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       <define name="serviceLocation">
         <element name="serviceLocation">
             <ref name="locationInformation"/>
         </element>
       </define>
     </div>

     <div>
       <a:documentation>
         Patterns for inclusion of elements from schemas in
         other namespaces.
       </a:documentation>

       <define name="notLostExt">
         <a:documentation>
           Any element not in the LoST Extensions namespace.
         </a:documentation>
         <element>
           <anyName>
             <except>
               <nsName ns="urn:ietf:params:xml:ns:lost-ext"/>
               <nsName/>
             </except>
           </anyName>
           <ref name="anyElement"/>
         </element>
       </define>

       <define name="anyElement">
         <a:documentation>
           A wildcard pattern for including any element
           from any other namespace.
         </a:documentation>
         <zeroOrMore>
           <choice>
             <element>
               <anyName/>
               <ref name="anyElement"/>
             </element>
             <attribute>
               <anyName/>
             </attribute>
             <text/>
           </choice>
         </zeroOrMore>
       </define>

       <define name="extensionPoint">



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         <a:documentation>
           A point where future extensions
           (elements from other namespaces)
           can be added.
         </a:documentation>
         <zeroOrMore>
           <ref name="notLostExt"/>
         </zeroOrMore>
       </define>
     </div>

  </grammar>

11.  Acknowledgments

   We would like to thank Shida Schubert for reviewing an early version
   of this document.  We also appreciate the suggestions from members of
   the ECRIT working group.  In particular, we are grateful to Richard
   L. Barnes, Robert Sparks, and Martin Thomson for their overall
   feedback and for their comments on how non-emergency services may
   affect the provisioning of emergency services lookups.

12.  Normative References

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

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

   [RFC5139]  Thomson, M. and J. Winterbottom, "Revised Civic Location
              Format for Presence Information Data Format Location
              Object (PIDF-LO)", RFC 5139, February 2008.

   [RFC5491]  Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
              Presence Information Data Format Location Object (PIDF-LO)
              Usage Clarification, Considerations, and Recommendations",
              RFC 5491, March 2009.

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









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Authors' Addresses

   Andrea G. Forte
   AT&T
   Security Research Center
   33 Thomas Street
   New York, NY  10007
   USA

   EMail: forte@att.com


   Henning Schulzrinne
   Columbia University
   Department of Computer Science
   1214 Amsterdam Avenue, MC 0401
   New York, NY  10027
   USA

   EMail: hgs@cs.columbia.edu































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