Network Working Group A. Forte
Internet-Draft AT&T
Intended status: Experimental H. Schulzrinne
Expires: December 17, 2011 Columbia University
June 15, 2011
Location-to-Service Translation (LoST) Protocol Extensions
draft-forte-lost-extensions-05.txt
Abstract
An important class of location-based services answer 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 Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 17, 2011.
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
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3
3. Service Regions . . . . . . . . . . . . . . . . . . . . . . . 3
4. New <findService> Query Types: "N nearest", "within
distance X" and "served by" . . . . . . . . . . . . . . . . . 5
5. LoST Extensions . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. New Use of Shapes in Queries . . . . . . . . . . . . . . . 5
5.2. Queries Based on Service Regions . . . . . . . . . . . . . 8
5.3. Difference Between "within distance X" and "served by"
Queries . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.4. Limiting the Number of Returned Service URIs . . . . . . . 11
5.5. The <serviceLocation> Element in Responses . . . . . . . . 13
6. Emergency Services . . . . . . . . . . . . . . . . . . . . . . 16
7. Relax NG Schema . . . . . . . . . . . . . . . . . . . . . . . 17
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
9.1. LoST Extensions Relax NG Schema Registration . . . . . . . 19
9.2. LoST Extensions Namespace Registration . . . . . . . . . . 19
10. Non-Normative RELAX NG Schema in XML Syntax . . . . . . . . . 20
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
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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 walk or drive.
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 client'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")."
and in Section 5.5 of [RFC5222]:
"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."
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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
for each query we can get a large number of service URIs, a service
region as per 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 that is, the service
region changes. Therefore, for non-emergency services a service
region as defined in [RFC5222] would change very frequently, making
the use of service regions as described in [RFC5222] not that useful.
Generally speaking, we can divide location-based services into two
main categories.
Services based on:
o how far they are from the user (e.g., ATM machines, takeout)
o whether or not their service area includes the client's current
location (e.g., pizza delivery, NG9-1-1)
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 the difference between takeout (first
category) and delivery (second category), for example. In the case
of takeout, the user wants to go to a particular restaurant and buy
dinner regardless of his location falling in the restaurant service
area or not. For delivery, the user cares about the restaurant
service area as the restaurant will deliver food to him only if the
user's 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.
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4. New <findService> Query Types: "N nearest", "within distance X" and
"served by"
We introduce three new types of <findService> queries that is, "N
nearest", "within distance X" and "served by". The first query
returns the N points of interest closest to the client's physical
location, the second query discovers all those points of interest
located within a given distance from the client's physical location,
the third query returns all those points of interest whose service
area includes the client's current location.
5. LoST Extensions
For queries "within distance X", 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 queries "served by", the LoST client needs to let the server know
that it MUST return only those services whose service area includes
the client'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 queries "N nearest", the LoST client needs to let the server know
N, that is, 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 6.
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, I want
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to search for points of service within that area because my 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 and so we want to look for services within that
area. All we are doing with a "within distance X" query is to
manually set the uncertainty level in user location to a value of 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>.
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 do this, we use 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: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:local.pizza</service>
</findService>
Figure 1: A 'within distance X' <findService> geodetic query using
the circular shape
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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:local.pizza</service>
</findService>
Figure 2: A 'within distance X' <findService> geodetic query using
the elliptical shape
5.2. Queries Based on Service Regions
As mentioned in Section 1, we can divide location-based services into
two main categories.
Services 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.
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__________________________
\ ***** \
,===============***====, *** \
/ ** \ / ** \
/ 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)
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 the service belongs
to, 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 that is, 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 it 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 that is, 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 it matters is
their service area. In this second scenario, since the circle
representing the user location overlaps with all three service areas,
it means that 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.
In order for the client to specify which of the two categories the
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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, it means that 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 client'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:local.pizza</service>
</findService>
Figure 4 A 'served by' <findService> geodetic query with the new
<region> element
5.3. Difference Between "within distance X" and "served by" Queries
Figures 1 and 4 show an example of a "within distance X" query and a
"served by" query, respectively. The two types of queries although
very similar 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 such query as it would be equivalent to a within-zero-
meters search.
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o In a "within distance X" query we manually set to X the
uncertainty level in user location and we search for services
within such area. 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 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 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 a 'N nearest' query, Figure 6 shows a
query which is a combination of 'N nearest' and 'within distance X'
while Figure 7 shows a query which 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, then the server
has to identify among the points of interest to return, 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 consinstent
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: A 'N nearest' <findService> geodetic query with the new
<limit> element
<?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:local.pizza</service>
</findService>
Figure 6: A <findService> geodetic query with the new <limit> and
<region> elements. This query is a combination of 'N nearest' and
'within distance X' queries.
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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:local.pizza</service>
</findService>
Figure 7: A <findService> geodetic query with the new <limit> and
<region> elements. This query is a combination of 'N nearest' and
'served by' queries.
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
and SHOULD be used for all non-emergency services. 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 relevant.
The <serviceLocation> element has one single attribute, 'profile', in
order to specify 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
using 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-
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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 also 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].
As per [RFC5139] it is RECOMMENDED to use multiple <serviceLocation>
elements when multiple forms of service location are available and
also, 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:local.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>
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</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:local.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"/>
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</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]. As we can see, in such 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 it
means that 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 user 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
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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.
##
div {
region=
element region {
xsd:boolean
}
}
##
## Location Information
##
div {
locationInformation =
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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
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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
services queries, thus being unable to process emergency-service
queries. Such a situation can be addressed in more than one way.
The obvious way to address this problem is to properly dimension the
LoST servers so to take into account also traffic for non-emergency
services. Given that the LoST server is an enhanced HTTP server,
properly dimensioning a deployment of LoST servers should not be very
difficult to accomplish.
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 6. 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:
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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/rfcXXXX.txt">
RFCXXXX</a>.</p>
</body>
</html>
<!-- [[NOTE TO RFC-EDITOR: Please replace all instances of RFCXXXX
with the number of the published document and remove this
note.]] -->
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"/>
<reference name="region"/>
<ref name="serviceLocation"/>
</choice>
</start>
<div>
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<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">
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<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
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(elements from other namespaces)
can be added.
</a:documentation>
<zeroOrMore>
<ref name="notLostExt"/>
</zeroOrMore>
</define>
</div>
</grammar>
11. 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
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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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