RFC 6451
Location-to-Service Translation (LoST) Protocol Extensions
Pages: 23
Experimental
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 ExtensionsAbstract
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
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 . . . . . . . . . . . . . . . . . . . . . 221. 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.
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.
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
<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>.
<?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].
<?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
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
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
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].
<?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)
<?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
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">
<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>
<locationUsed id="6020688f1ce1896d"/> </findServiceResponse> Figure 8: A <findServiceResponse> answer6. 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
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 }
}
##
## 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*
}
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 }
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> END10. 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>
</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>
<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">
<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.
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