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Network Working Group T. Hardie
Request for Comments: 5222 Qualcomm, Inc.
Category: Standards Track A. Newton
American Registry for Internet Numbers
H. Schulzrinne
Columbia University
H. Tschofenig
Nokia Siemens Networks
August 2008
LoST: A Location-to-Service Translation Protocol
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document describes an XML-based protocol for mapping service
identifiers and geodetic or civic location information to service
contact URIs. In particular, it can be used to determine the
location-appropriate Public Safety Answering Point (PSAP) for
emergency services.
Table of Contents
1. Introduction .................................................. 3
2. Terminology and Requirements Notation ......................... 4
3. Overview of Protocol Usage .................................... 5
4. LoST Servers and Their Resolution ............................ 6
5. The <mapping> Element ........................................ 7
5.1. The Mapping Data Source: 'source', 'sourceId', and
'lastUpdated' Attributes .................................. 7
5.2. Mapping Validity: The 'expires' Attribute ................ 8
5.3. Describing the Service with the <displayName> Element .... 8
5.4. The Mapped Service: The <service> Element ................. 8
5.5. Defining the Service Region with the <serviceBoundary>
Element .................................................. 9
5.6. Service Boundaries by Reference: The
<serviceBoundaryReference> Element ........................ 9
5.7. The Service Number: The <serviceNumber> Element ......... 10
5.8. Service URLs: The <uri> Element ......................... 10
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RFC 5222 LoST August 2008
6. Path of a Request: The <path> Element ....................... 10
7. Identifying the Location Element Used for Mapping:
<locationUsed> ............................................... 11
8. Mapping a Location and Service to URLs: <findService> ....... 11
8.1. Overview ................................................. 11
8.2. Examples ................................................. 11
8.2.1. Example Using Geodetic Coordinates ................... 11
8.2.2. Civic Address Mapping Example ....................... 13
8.3. Components of the <findService> Request ................. 15
8.3.1. The <location> Element ............................... 15
8.3.2. Identifying the Service: The <service> Element ..... 16
8.3.3. Recursion and Iteration ............................. 16
8.3.4. Service Boundary ..................................... 16
8.3.5. Requesting Civic Location Validation ................. 16
8.4. Components of the Mapping Response
<findServiceResponse> ................................... 18
8.4.1. Overview ............................................. 18
8.4.2. Civic Address Validation: The <locationValidation>
Element ............................................. 19
9. Retrieving the Service Boundary via <getServiceBoundary> ..... 19
10. List Services: <listServices> ............................... 21
11. List Services By Location: <listServicesByLocation> ......... 22
12. Location Profiles ........................................... 24
12.1. Location Profile Usage ................................... 25
12.2. Two-Dimensional Geodetic Profile ......................... 30
12.3. Basic Civic Profile ..................................... 31
13. Errors, Warnings, and Redirects ............................. 32
13.1. Errors ................................................... 32
13.2. Warnings ................................................. 34
13.3. Redirects ............................................... 36
14. LoST Transport: HTTP ......................................... 36
15. Relax NG Schema ............................................. 37
16. Internationalization Considerations ......................... 44
17. IANA Considerations ......................................... 44
17.1. U-NAPTR Registrations ................................... 44
17.2. Content-Type Registration for 'application/lost+xml' ..... 44
17.3. LoST Relax NG Schema Registration ....................... 46
17.4. LoST Namespace Registration ............................. 46
17.5. LoST Location Profile Registry ........................... 47
18. Security Considerations ..................................... 47
19. Acknowledgments ............................................. 48
20. References ................................................... 51
20.1. Normative References ..................................... 51
20.2. Informative References ................................... 52
Appendix A. Non-Normative RELAX NG Schema in XML Syntax ......... 54
Appendix B. Examples Online ..................................... 67
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1. Introduction
Protocols such as Naming Authority Pointer (NAPTR) records and the
Service Location Protocol (SLP) can be used to discover servers
offering a particular service. However, for an important class of
services the appropriate specific service instance depends both on
the identity of the service and the geographic location of the entity
that needs to reach it. Emergency telecommunications services are an
important example; here, the service instance is a Public Safety
Answering Point (PSAP) that has jurisdiction over the location of the
user making the call. The desired PSAP isn't necessarily the one
that is topologically or even line-of-sight closest to the caller;
rather, it is the one that serves the caller's location based on
jurisdictional boundaries.
This document describes a protocol for mapping a service identifier
and location information compatible with the Presence Information
Data Format Location Object (PIDF-LO) [6] to one or more service
URIs. Service identifiers take the form of the service URNs
described in [9]. Location information here includes revised civic
location information [10] and a subset of the PIDF-LO profile [13],
which consequently includes the Geo-Shapes [12] defined for GML [11].
Example service URI schemes include sip [14], xmpp [15], and tel
[16]. While the initial focus is on providing mapping functions for
emergency services, it is likely that the protocol is applicable to
other service URNs. For example, in the United States, the "2-1-1"
and "3-1-1" service numbers follow a similar location-to-service
behavior as emergency services.
This document names this protocol "LoST", for Location-to-Service
Translation. LoST satisfies the requirements [18] for mapping
protocols. LoST provides a number of operations, centered around
mapping locations and service URNs to service URLs and associated
information. LoST mapping queries can contain either civic or
geodetic location information. For civic addresses, LoST can
indicate which parts of the civic address are known to be valid or
invalid, thus providing address validation, as described in Section
3.5 of [18]. LoST indicates errors in the location data to
facilitate debugging and proper user feedback, but also provides
best-effort answers.
LoST queries can be resolved recursively or iteratively. 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").
Hardie, et al. Standards Track [Page 3]
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As defined in this document, LoST messages are carried in HTTP and
HTTPS protocol exchanges, facilitating use of TLS for protecting the
integrity and confidentiality of requests and responses.
This document focuses on the description of the protocol between the
mapping client and the mapping server. Other functions, such as
discovery of mapping servers, data replication and the overall
mapping server architecture are described in a separate document
[19].
The query message carries location information and a service
identifier encoded as a Uniform Resource Name (URN) (see [9]) from
the LoST client to the LoST server. The LoST server uses its
database to map the input values to one or more Uniform Resource
Identifiers (URIs) and returns those URIs along with optional
information, such as hints about the service boundary, in a response
message to the LoST client. If the server cannot resolve the query
itself, it may in turn query another server or return the address of
another LoST server, identified by a LoST server name. In addition
to the mapping function described in Section 8, the protocol also
allows to retrieve the service boundary (see Section 9) and to list
the services available for a particular location (see Section 11) or
supported by a particular server (see Section 10).
2. Terminology and 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 [1].
This document uses the following terms:
Mapping:
Mapping is a process that takes a location and a service
identifier as inputs and returns one or more URIs. Those URIs can
point either to a host providing that service or to a host that in
turn routes the request to the final destination. This definition
is a generalization of the term "mapping" as used in [18], because
LoST can be used for non-emergency services.
LoST client:
A host acts as a LoST client if it sends LoST query messages and
receives LoST response messages.
LoST server:
A host acts as a LoST server if it receives LoST query messages
and sends LoST response messages. In recursive operation, the
same entity may be both a client and a server.
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Authoritative LoST server:
An authoritative server acts only as a server and successfully
resolves the input location and service identifier to a URI or set
of URIs.
Service boundary:
A service boundary circumscribes the region within which all
locations map to the same service URI or set of URIs for a given
service. A service boundary may consist of several non-contiguous
geometric shapes.
Validation:
The term "validation" describes the behavior defined as "location
validation" in Section 3.5 of [18].
Additional emergency service terminology can be found in [18].
3. Overview of Protocol Usage
The LoST protocol supports the following types of queries and
responses:
<findService> and <findServiceResponse>
A LoST client retrieves contact URIs based on location information
and a service identifier with this request and response. The same
query type may also ask for location validation and for service
numbers, either combined with a mapping request or separately.
The details can be found in Section 8.
<getServiceBoundary> and <getServiceBoundaryResponse>
A LoST client obtains a service boundary with this request and
response, as described in Section 9.
<listServices> and <listServicesResponse>
With this request and response, a LoST client can find out which
services a LoST server supports, as described in Section 10.
<listServicesByLocation> and <listServicesByLocationResponse>
A LoST client can determine with this request and response which
services are available for a specific location region. Section 11
describes the details.
LoST clients may initiate any of the above queries at any time.
Among the common triggers are:
1. when the client initially starts up or attaches to a network;
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2. when the client detects that its location has changed
sufficiently that it is outside the bounds of the service region;
3. when a SIP message arrives at a SIP proxy performing location-
based call routing;
4. when cached mapping information has expired; and
5. when invoking a particular service. At that time, a client may
omit requests for service boundaries or other auxiliary
information.
A service-specific Best Current Practice (BCP) document, such as
[21], governs whether a client is expected to invoke the mapping
service just before needing the service or whether to rely on cached
answers. Cache entries expire at their expiration time (see
Section 5.2), or they become invalid if the caller's device moves
beyond the boundaries of the service region. Service-specific Best
Current Practice documents may also provide guidance on the contact
URI schemes most appropriate to the service. As a general set of
guidelines, URI schemes that do not provide mechanisms for actually
initiating a contact method should be avoided (examples include data,
info, cid, and tag) as transforming those references into contact
mechanisms requires a layer of indirection that makes the overall
mechanism more fragile. Provisionally registered URI schemes should
also be carefully considered before use, because they are subject to
change in core semantics.
4. LoST Servers and Their Resolution
LoST servers are identified by U-NAPTR/DDDS (URI-Enabled NAPTR/
Dynamic Delegation Discovery Service) [8] application unique strings,
in the form of a DNS name. An example is 'lostserver.example.com'.
Clients need to use the U-NAPTR [8] specification described below to
obtain a URI (indicating host and protocol) for the applicable LoST
service. In this document, only the HTTP and HTTPS URL schemes are
defined. Note that the HTTP URL can be any valid HTTP URL, including
those containing path elements.
The following two DNS entries show the U-NAPTR resolution for
"example.com" to the HTTPS URL https://lostserv.example.com/secure or
the HTTP URL http://lostserver.example.com, with the former being
preferred.
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example.com.
IN NAPTR 100 10 "u" "LoST:https"
"!.*!https://lostserver.example.com/secure!" ""
IN NAPTR 200 10 "u" "LoST:http"
"!.*!http://lostserver.example.com!" ""
Clients learn the LoST server's host name by means beyond the scope
of this specification, such as SIP configuration and DHCP [25].
5. The <mapping> Element
The <mapping> element is the core data element in LoST, describing a
service region and the associated service URLs. Its attributes and
elements are described in subsections below.
5.1. The Mapping Data Source: 'source', 'sourceId', and 'lastUpdated'
Attributes
The 'source', 'sourceId', and 'lastUpdated' attributes uniquely
identify a particular mapping record. They are created by the
authoritative source for a mapping and are never modified when a
mapping is served from a cache. All three attributes are REQUIRED
for all <mapping> elements. A receiver can replace a mapping with
another one having the same 'source' and 'sourceId' and a more recent
time in 'lastUpdated'.
The 'source' attribute contains a LoST application unique string
identifying the authoritative generator of the mapping (Section 4).
The 'sourceId' attribute identifies a particular mapping and contains
an opaque token that MUST be unique among all different mappings
maintained by the authoritative source for that particular service.
For example, a Universally Unique Identifier (UUID) is a suitable
format.
The 'lastUpdated' attribute describes when a specific instance of
mapping, identified by the combination of 'source' and 'sourceId',
was last changed. The contents of this attribute has the XML data
type dateTime in its timezoned form, using the canonical UTC
representation with the letter 'Z' as the timezone indicator.
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5.2. Mapping Validity: The 'expires' Attribute
The 'expires' attribute contains the absolute time at which the
mapping becomes invalid. The contents of this attribute is a
timezoned XML type dateTime, in canonical representation. The
<mapping> element MUST include the 'expires' attribute.
Optionally, this attribute may contain the values of 'NO-CACHE' and
'NO-EXPIRATION' instead of a dateTime value. The value 'NO-CACHE' is
an indication that the mapping should not be cached. The value of
'NO-EXPIRATION' is an indication that the mapping does not expire.
On occasion, a server may be forced to return an expired mapping if
it cannot reach the authoritative server or the server fails to
return a usable answer. Clients and servers MAY cache the mapping so
that they have at least some information available. Caching servers
that have such stale information SHOULD re-attempt the query each
time a client requests a mapping. Since the expired mapping will be
returned to the client as a non-error/non-warning response, the
client MUST check the 'expires' attribute; if the mapping has
expired, local policy at the client determines whether it discards
the answer and tries again later or uses the possibly stale response.
5.3. Describing the Service with the <displayName> Element
Zero or more <displayName> elements describe the service with a
string that is suitable for display to human users, each annotated
with the 'xml:lang' attribute that contains a language tag to aid in
the rendering of text.
5.4. The Mapped Service: The <service> Element
The mandatory <service> element identifies the service for which this
mapping applies. Two cases need to be distinguished when the LoST
server sets the <service> element in the response message:
1. If the requested service, identified by the service URN [9] in
the <service> element of the request, exists for the location
indicated, then the LoST server copies the service URN from the
request into the <service> element.
2. If, however, the requested service, identified by the service URN
[9] in the <service> element in the request, does not exist for
the location indicated, the server either can return a
<serviceNotImplemented> (Section 13.1) error or can provide an
alternate service that approximates the desired service for that
Hardie, et al. Standards Track [Page 8]
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location. In the latter case, the server MUST include a
<service> element with the alternative service URN. The choice
of service URN is left to local policy, but the alternate service
should be able to satisfy the original service request.
5.5. Defining the Service Region with the <serviceBoundary> Element
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. The service region can be indicated by value or by reference
(see Section 5.6). If a client moves outside the service area and
wishes to obtain current service data, it sends a new query with its
current location. The service region is described by value in one or
more <serviceBoundary> elements, each formatted according to a
specific location profile, identified by the 'profile' attribute (see
Section 12). <serviceBoundary> elements formatted according to
different location profiles are alternative representations of the
same area, not additive to one another; this allows a client
understanding only one of the profile types to be sure it has a
complete view of the serviceBoundary. Within a serviceBoundary
element there may, however, be multiple locations which are additive;
this is necessary because some <serviceBoundary> areas could not be
easily expressed with a single shape or civic location. If included
in a response, the <serviceBoundary> element MUST contain at least
one service boundary that uses the same profile as the request.
A service boundary is requested by the client, using the
'serviceBoundary' attribute in the request with the value set to
"value".
5.6. Service Boundaries by Reference: The <serviceBoundaryReference>
Element
Since geodetic service boundaries may contain thousands of points and
can thus be quite large, clients may wish to conserve bandwidth by
requesting a reference to the service boundary instead of the value
described in Section 5.5. The identifier of the service boundary is
returned as an attribute of the <serviceBoundaryReference> element,
along with a LoST application unique string (see Section 4)
identifying the server from where it can be retrieved. The actual
value of the service boundary is then retrieved with the
getServiceBoundary (Section 9) request.
A reference to a service boundary is requested by the client using
the 'serviceBoundary' attribute in the request with the value set to
"reference". A LoST server may decide, based on local policy, to
return the service boundary by value or to omit the
<serviceBoundaryReference> element in the response.
Hardie, et al. Standards Track [Page 9]
RFC 5222 LoST August 2008
The identifier is a random token with at least 128 bits of entropy
and can be assumed to be globally unique. It uniquely references a
particular boundary. If the boundary changes, a new identifier MUST
be chosen. Because of these properties, a client receiving a mapping
response can simply check if it already has a copy of the boundary
with that identifier. If so, it can skip checking with the server
whether the boundary has been updated. Since service boundaries are
likely to remain unchanged for extended periods of time, possibly
exceeding the normal lifetime of the service URL, this approach
avoids unnecessarily refreshing the boundary information just because
the remainder of the mapping has become invalid.
5.7. The Service Number: The <serviceNumber> Element
The service number is returned in the optional <serviceNumber>
element. It contains a string of digits, * and # that a user on a
device with a 12-key dial pad could use to reach that particular
service.
5.8. Service URLs: The <uri> Element
The response returns the service URLs in one or more <uri> elements.
The URLs MUST be absolute URLs. The ordering of the URLs has no
particular significance. Each URL scheme MUST only appear at most
once, but it is permissible to include both secured and regular
versions of a protocol, such as both 'http' and 'https' or 'sip' and
'sips'.
6. Path of a Request: The <path> Element
To prevent loops and to allow tracing of request and response paths,
all requests that allow recursion include a <path> element that
contains one or more <via> elements, each possessing an attribute
containing a LoST application unique string (see Section 4). The
order of <via> elements corresponds to the order of LoST servers,
i.e., the first <via> element identifies the server that initially
received the request from the client issuing the request. Every
server in a recursive query operation is included in the <path>
element, including the first server to receive it.
The server that answers the request instead of forwarding it, such as
the authoritative server, copies the <path> element verbatim into the
response. The <path> element is not modified in responses as the
responses traverses the server chain back to the querying client.
If a query is answered iteratively, the querier includes all servers
that it has already contacted.
Hardie, et al. Standards Track [Page 10]
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When a cached mapping is returned, then the <path> element cached
together with the mapping is returned.
The example in Figure 4 indicates that the answer was given to the
client by the LoST server at esgw.ueber-110.de.example, which got the
answer from the (authoritative) LoST server at
polizei.muenchen.de.example.
7. Identifying the Location Element Used for Mapping: <locationUsed>
Several of the requests can provide one or more <location> elements,
among which the server gets to choose. It is useful for the client
to be able to determine which one was actually used in producing the
result. For that purpose, the <location> tag MUST contain an 'id'
attribute that uniquely identifies the <location> element. The
format of the identifier is left to the client; it could, for
example, use a hash of the location information. The server returns
the identifier for the <location> element it used in the
<locationUsed> tag.
8. Mapping a Location and Service to URLs: <findService>
8.1. Overview
The <findService> query constitutes the core of the LoST
functionality, mapping civic or geodetic locations to URLs and
associated data. After giving an example, we enumerate the elements
of the query and response.
8.2. Examples
8.2.1. Example Using Geodetic Coordinates
The following is an example of mapping a service to a location using
geodetic coordinates, for the service associated with the police
(urn:service:sos.police).
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RFC 5222 LoST August 2008
<?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 1: A <findService> geodetic query
Given the query above, a server would respond with a service, and
information related to that service. In the example below, the
server has mapped the location given by the client for a police
service to the New York City Police Department, instructing the
client that it may contact them via the URIs "sip:nypd@example.com"
and "xmpp:nypd@example.com". The server has also given the client a
geodetic, two-dimensional boundary for this service. The mapping was
last updated on November 1, 2006 and expires on January 1, 2007. If
the client's location changes beyond the given service boundary or
the expiration time has been reached, it may want to requery for this
information, depending on the usage environment of LoST.
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RFC 5222 LoST August 2008
<?xml version="1.0" encoding="UTF-8"?>
<findServiceResponse xmlns="urn:ietf:params:xml:ns:lost1"
xmlns:p2="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="en">
New York City Police Department
</displayName>
<service>urn:service:sos.police</service>
<serviceBoundary profile="geodetic-2d">
<p2:Polygon srsName="urn:ogc:def::crs:EPSG::4326">
<p2:exterior>
<p2:LinearRing>
<p2:pos>37.775 -122.4194</p2:pos>
<p2:pos>37.555 -122.4194</p2:pos>
<p2:pos>37.555 -122.4264</p2:pos>
<p2:pos>37.775 -122.4264</p2:pos>
<p2:pos>37.775 -122.4194</p2:pos>
</p2:LinearRing>
</p2:exterior>
</p2:Polygon>
</serviceBoundary>
<uri>sip:nypd@example.com</uri>
<uri>xmpp:nypd@example.com</uri>
<serviceNumber>911</serviceNumber>
</mapping>
<path>
<via source="resolver.example"/>
<via source="authoritative.example"/>
</path>
<locationUsed id="6020688f1ce1896d"/>
</findServiceResponse>
Figure 2: A <findServiceResponse> geodetic answer
8.2.2. Civic Address Mapping Example
The example below shows how to map a service to a location much like
the example in Section 8.2.1, but using civic address location
information. In this example, the client requests the service
associated with police (urn:service:sos.police) along with a specific
civic address (house number 6 on a street named Otto-Hahn-Ring in
Munich, Germany).
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RFC 5222 LoST August 2008
<?xml version="1.0" encoding="UTF-8"?>
<findService xmlns="urn:ietf:params:xml:ns:lost1"
recursive="true" serviceBoundary="value">
<location id="627b8bf819d0bad4d" profile="civic">
<civicAddress
xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
<country>DE</country>
<A1>Bavaria</A1>
<A3>Munich</A3>
<A6>Otto-Hahn-Ring</A6>
<HNO>6</HNO>
<PC>81675</PC>
</civicAddress>
</location>
<service>urn:service:sos.police</service>
</findService>
Figure 3: A <findService> civic address query
Given the query above, a server would respond with a service, and
information related to that service. In the example below, the
server has mapped the location given by the client for a police
service to the Muenchen Polizei-Abteilung, instructing the client
that it may contact them via the URIs sip:munich-police@example.com
and xmpp:munich-police@example.com. The server has also given the
client a civic address boundary (the city of Munich) for this
service. The mapping was last updated on November 1, 2006 by the
authoritative source "polizei.muenchen.de.example" and expires on
January 1, 2007. This instructs the client to requery for the
information if its location changes beyond the given service boundary
(i.e., beyond the indicated district of Munich) or after January 1,
2007.
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RFC 5222 LoST August 2008
<?xml version="1.0" encoding="UTF-8"?>
<findServiceResponse xmlns="urn:ietf:params:xml:ns:lost1">
<mapping
expires="2007-01-01T01:44:33Z"
lastUpdated="2006-11-01T01:00:00Z"
source="esgw.ueber-110.de.example"
sourceId="e8b05a41d8d1415b80f2cdbb96ccf109">
<displayName xml:lang="de">
Muenchen Polizei-Abteilung
</displayName>
<service>urn:service:sos.police</service>
<serviceBoundary
profile="civic">
<civicAddress
xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
<country>DE</country>
<A1>Bavaria</A1>
<A3>Munich</A3>
<PC>81675</PC>
</civicAddress>
</serviceBoundary>
<uri>sip:munich-police@example.com</uri>
<uri>xmpp:munich-police@example.com</uri>
<serviceNumber>110</serviceNumber>
</mapping>
<path>
<via source="esgw.ueber-110.de.example"/>
<via source="polizei.muenchen.de.example"/>
</path>
<locationUsed id="627b8bf819d0bad4d"/>
</findServiceResponse>
Figure 4: A <findServiceResponse> civic address answer
8.3. Components of the <findService> Request
The <findService> request includes attributes and elements that
govern whether the request is handled iteratively or recursively,
whether location validation is performed, and which elements may be
contained in the response.
8.3.1. The <location> Element
The <findService> query communicates location information using one
or more <location> elements, which MUST conform to a location profile
(see Section 12). There MUST NOT be more than one location element
Hardie, et al. Standards Track [Page 15]
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for each distinct location profile. The order of location elements
is significant; the server uses the first location element where it
understands the location profile.
8.3.2. Identifying the Service: The <service> Element
The type of service desired is specified by the <service> element.
It contains service URNs from the registry established in [9].
8.3.3. Recursion and Iteration
LoST can operate in either recursive or iterative mode, on a request-
by-request basis. In recursive mode, the LoST server initiates
queries on behalf of the requester and returns the result to the
requester.
In iterative mode, the server contacted returns a redirection
response indicating the next server to be queried if the server
contacted cannot provide an answer itself.
For the queries defined in this document, only the LoST <findService>
and <listServicesByLocation> queries can be recursive, as indicated
by the 'recursive' attribute. A value of "true" indicates a
recursive query, with the default being "false" when the attribute is
omitted. Regardless of the attribute, a server MAY always answer a
query by providing a LoST application unique string (see Section 4),
i.e., indirection; however, it MUST NOT recurse if the attribute is
"false".
8.3.4. Service Boundary
LoST <mapping> elements can describe the service boundary either by
value or by reference. Returning a service boundary reference is
generally more space-efficient for geospatial (polygon) boundaries
and if the boundaries change rarely, but does incur an additional
<getServiceBoundary> request. The querier can express a preference
for one or the other modality with the 'serviceBoundary' attribute in
the <findService> request, but the server makes the final decision as
to whether to return a reference or a value.
8.3.5. Requesting Civic Location Validation
Civic address validation is requested by setting the optional
attribute 'validateLocation' to true. If the attribute is omitted,
it is assumed to be false. The response is described in
Section 8.4.2. The example in Figure 5 demonstrates address
validation. If the server chooses a geodetic location among the
locations provided in a request, the attribute is ignored.
Hardie, et al. Standards Track [Page 16]
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<?xml version="1.0" encoding="UTF-8"?>
<findService
xmlns="urn:ietf:params:xml:ns:lost1"
recursive="true"
validateLocation="true"
serviceBoundary="value">
<location id="627b8bf819d0bad4d" profile="civic">
<civicAddress
xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
<country>DE</country>
<A1>Bavaria</A1>
<A3>Munich</A3>
<A6>Otto-Hahn-Ring</A6>
<HNO>6</HNO>
<PC>81675</PC>
</civicAddress>
</location>
<service>urn:service:sos.police</service>
</findService>
Figure 5: A <findService> query with address validation request
Hardie, et al. Standards Track [Page 17]
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<?xml version="1.0" encoding="UTF-8"?>
<findServiceResponse xmlns="urn:ietf:params:xml:ns:lost1">
<mapping
expires="2007-01-01T01:44:33Z"
lastUpdated="2006-11-01T01:00:00Z"
source="authoritative.example"
sourceId="4db898df52b84edfa9b6445ea8a0328e">
<displayName xml:lang="de">
Muenchen Polizei-Abteilung
</displayName>
<service>urn:service:sos.police</service>
<serviceBoundary profile="civic">
<civicAddress
xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
<country>DE</country>
<A1>Bavaria</A1>
<A3>Munich</A3>
<PC>81675</PC>
</civicAddress>
</serviceBoundary>
<uri>sip:munich-police@example.com</uri>
<uri>xmpp:munich-police@example.com</uri>
<serviceNumber>110</serviceNumber>
</mapping>
<locationValidation>
<valid>country A1 A3 A6</valid>
<invalid>PC</invalid>
<unchecked>HNO</unchecked>
</locationValidation>
<path>
<via source="resolver.example"/>
<via source="authoritative.example"/>
</path>
<locationUsed id="627b8bf819d0bad4d"/>
</findServiceResponse>
Figure 6: A <findServiceResponse> message with address validation
information
8.4. Components of the Mapping Response <findServiceResponse>
8.4.1. Overview
Mapping responses consist of the <mapping> element (Section 5)
describing the mapping itself, possibly followed by warnings
(Section 13.2), location validation information (Section 8.4.2), and
an indication of the path (Section 6) the response has taken.
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8.4.2. Civic Address Validation: The <locationValidation> Element
A server can indicate in its response which civic address elements it
has recognized as valid, which ones it has ignored, and which ones it
has checked and found to be invalid. The server SHOULD include this
information if the 'validateLocation' attribute in the request was
true, but local policy at the server may allow this information to be
omitted. Each element contains a list of tokens separated by
whitespace, enumerating the civic location labels used in child
elements of the <civicAddress> element. The <valid> element
enumerates those civic address elements that have been recognized as
valid by the LoST server and that have been used to determine the
mapping. The <unchecked> elements enumerates the civic address
elements that the server did not check and that were not used in
determining the response. The <invalid> element enumerate civic
address elements that the server attempted to check, but that did not
match the other civic address elements found in the <valid> list.
Civic location tokens that are not listed in either the <valid>,
<invalid>, or <unchecked> element belong to the class of unchecked
tokens.
Note that the same address can yield different responses if parts of
the civic address contradict each other. For example, if the postal
code does not match the city, local server policy determines whether
the postal code or the city is considered valid. The mapping
naturally corresponds to the valid elements.
The example shown in Figure 5 and in Figure 6 indicates that the
tokens 'country', 'A1', 'A3', and 'A6' have been validated by the
LoST server. The server considered the postal code 81675 in the <PC>
element as not valid for this location. The 'HNO' token belongs to
the class of unchecked location tokens.
9. Retrieving the Service Boundary via <getServiceBoundary>
As discussed in Section 5.5, the <findServiceResponse> can return a
globally unique identifier in the 'serviceBoundary' attribute that
can be used to retrieve the service boundary, rather than returning
the boundary by value. This is shown in the example in Figure 7 and
Figure 8. The client can then retrieve the boundary using the
<getServiceBoundary> request and obtains the boundary in the
<getServiceBoundaryResponse>, illustrated in the example in Figure 9
and Figure 10. The client issues the request to the server
identified in the 'server' attribute of the
<serviceBoundaryReference> element. These requests are always
directed to the authoritative server and do not recurse.
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<?xml version="1.0" encoding="UTF-8"?>
<findService
xmlns="urn:ietf:params:xml:ns:lost1"
xmlns:p2="http://www.opengis.net/gml"
recursive="true"
serviceBoundary="reference">
<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 7: <findService> request and response with service boundary
reference
<?xml version="1.0" encoding="UTF-8"?>
<findServiceResponse xmlns="urn:ietf:params:xml:ns:lost1"
xmlns:p2="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="en">
New York City Police Department
</displayName>
<service>urn:service:sos.police</service>
<serviceBoundaryReference
source="authoritative.example"
key="7214148E0433AFE2FA2D48003D31172E"/>
<uri>sip:nypd@example.com</uri>
<uri>xmpp:nypd@example.com</uri>
<serviceNumber>911</serviceNumber>
</mapping>
<path>
<via source="resolver.example"/>
<via source="authoritative.example"/>
</path>
<locationUsed id="6020688f1ce1896d"/>
</findServiceResponse>
Figure 8: <findServiceResponse> message with service boundary
reference
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RFC 5222 LoST August 2008
<?xml version="1.0" encoding="UTF-8"?>
<getServiceBoundary xmlns="urn:ietf:params:xml:ns:lost1"
key="7214148E0433AFE2FA2D48003D31172E"/>
Figure 9: Requesting a service boundary with <getServiceBoundary>
<?xml version="1.0" encoding="UTF-8"?>
<getServiceBoundaryResponse
xmlns="urn:ietf:params:xml:ns:lost1">
<serviceBoundary profile="geodetic-2d">
<p2:Polygon srsName="urn:ogc:def::crs:EPSG::4326">
<p2:exterior>
<p2:LinearRing>
<p2:pos>37.775 -122.4194</p2:pos>
<p2:pos>37.555 -122.4194</p2:pos>
<p2:pos>37.555 -122.4264</p2:pos>
<p2:pos>37.775 -122.4264</p2:pos>
<p2:pos>37.775 -122.4194</p2:pos>
</p2:LinearRing>
</p2:exterior>
</p2:Polygon>
</serviceBoundary>
<path>
<via source="resolver.example"/>
<via source="authoritative.example"/>
</path>
</getServiceBoundaryResponse>
Figure 10: Geodetic service boundary response
10. List Services: <listServices>
A LoST client can ask a LoST server for the list of services that it
understands, primarily for diagnostic purposes. The query does not
contain location information, as it simply provides an indication of
which services the server can look up, not whether a particular
service is offered for a particular area. Typically, only top-level
services are included in the answer, implying support for all sub-
services. Since the query is answered by the queried server, there
is no notion of recursion or indirection. The
<listServicesByLocation> (Section 11) query below can be used to find
out whether a particular service is offered for a specific location.
An example request and response are shown in Figure 11.
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<?xml version="1.0" encoding="UTF-8"?>
<listServices
xmlns="urn:ietf:params:xml:ns:lost1">
<service>urn:service:sos</service>
</listServices>
Figure 11: Example of <ListServices> query
<?xml version="1.0" encoding="UTF-8"?>
<listServicesResponse
xmlns="urn:ietf:params:xml:ns:lost1">
<serviceList>
urn:service:sos.ambulance
urn:service:sos.animal-control
urn:service:sos.fire
urn:service:sos.gas
urn:service:sos.mountain
urn:service:sos.marine
urn:service:sos.physician
urn:service:sos.poison
urn:service:sos.police
</serviceList>
<path>
<via source="authoritative.example"/>
</path>
</listServicesResponse>
Figure 12: Example of <ListServicesResponse>
11. List Services By Location: <listServicesByLocation>
A LoST client can ask a LoST server for the list of services it knows
about for a particular area. The <listServicesByLocation> query
contains one or more <location> elements, each from a different
location profile (Section 12), and may contain the <service> element.
As for <findService>, the server selects the first location element
that has a profile the server understands and it can operate either
recursively or iteratively; <via> elements track the progress of the
request. The query indicates the services that the server can
enumerate from within the forest structure of which it is a part.
Because LoST does not presume a single, overarching organization of
all potential service types, there may be services available within a
geographic area that could be described by other LoST servers
connected to other forest structures. As an example, the emergency
services forest for a region may be distinct from the forests that
locate commercial services within the same region.
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If the query contains the <service> element, the LoST server returns
only immediate child services of the queried service that are
available for the provided location. If the <service> element is
absent, the LoST service returns all top-level services available for
the provided location that it knows about.
A server responds to this query with a
<listServicesByLocationResponse> response. This response MAY contain
<via> elements (see Section 6) and MUST contain a <serviceList>
element, consisting of a whitespace-separated list of service URNs.
The query and response are illustrated in Figure 13 and in Figure 14,
respectively.
<?xml version="1.0" encoding="UTF-8"?>
<listServicesByLocation
xmlns="urn:ietf:params:xml:ns:lost1"
xmlns:p2="http://www.opengis.net/gml"
recursive="true">
<location id="3e19dfb3b9828c3" profile="geodetic-2d">
<p2:Point srsName="urn:ogc:def:crs:EPSG::4326">
<p2:pos>-34.407 150.883</p2:pos>
</p2:Point>
</location>
<service>urn:service:sos</service>
</listServicesByLocation>
Figure 13: Example of <ListServicesbyLocation> query
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RFC 5222 LoST August 2008
<?xml version="1.0" encoding="UTF-8"?>
<listServicesByLocationResponse
xmlns="urn:ietf:params:xml:ns:lost1">
<serviceList>
urn:service:sos.ambulance
urn:service:sos.animal-control
urn:service:sos.fire
urn:service:sos.gas
urn:service:sos.mountain
urn:service:sos.marine
urn:service:sos.physician
urn:service:sos.poison
urn:service:sos.police
</serviceList>
<path>
<via source="resolver.example"/>
<via source="authoritative.example"/>
</path>
<locationUsed id="3e19dfb3b9828c3"/>
</listServicesByLocationResponse>
Figure 14: Example of <ListServicesByLocationResponse> response
12. Location Profiles
LoST uses location information in <location> elements in requests and
<serviceBoundary> elements in responses. Such location information
may be expressed in a variety of ways. This variety can cause
interoperability problems where a request or response contains
location information in a format not understood by the server or the
client, respectively. To achieve interoperability, this document
defines two mandatory-to-implement baseline location profiles to
define the manner in which location information is transmitted. It
is possible to standardize other profiles in the future. The
baseline profiles are:
geodetic-2d:
a profile for two-dimensional geodetic location information, as
described in Section 12.2;.
civic:
a profile consisting of civic address location information, as
described in Section 12.3.
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Requests and responses containing <location> or <serviceBoundary>
elements MUST contain location information in exactly one of the two
baseline profiles, in addition to zero or more additional profiles.
The ordering of location information indicates a preference on the
part of the sender.
Standards action is required for defining new profiles. A location
profile MUST define:
1. The token identifying it in the LoST location profile registry.
2. The formal definition of the XML to be used in requests, i.e., an
enumeration and definition of the XML child elements of the
<location> element.
3. The formal definition of the XML to be used in responses, i.e.,
an enumeration and definition of the XML child elements of the
<serviceBoundary> element.
4. The declaration of whether geodetic-2d or civic is to be used as
the baseline profile. It is necessary to explicitly declare the
baseline profile as future profiles may be combinations of
geodetic and civic location information.
12.1. Location Profile Usage
A location profile is identified by a token in an IANA-maintained
registry (Section 17.5). Clients send location information compliant
with a location profile, and servers respond with location
information compliant with that same location profile.
When a LoST client sends a <findService> request that provides
location information, it includes one or more <location> elements. A
<location> element carries an optional 'profile' attribute that
indicates the location format of the child elements. A client may
obtain location information that does not conform to a profile it
recognizes, or it may not have the capability to map XML to profiles.
In that case, a client MAY omit the profile attribute and the server
should interpret the XML location data to the best of its ability,
returning a "locationProfileUnrecognized" error if it is unable to do
so.
The concept of location profiles is described in Section 12. With
the ability to specify more than one <location> element, the client
is able to convey location information for multiple location profiles
in the same request.
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When a LoST server sends a response that contains location
information, it uses the <serviceBoundary> elements much like the
client uses the <location> elements. Each <serviceBoundary> element
contains location information conforming to the location profile
specified in the 'profile' attribute. A response MAY contain
multiple mappings or boundaries for the different <location>
elements, subject to the restrictions below.
Using the location profiles defined in this document, the following
rules ensure interoperability between clients and servers:
1. A client MUST be capable of understanding the response for the
baseline profiles it used in the request.
2. If a client sends location information conformant to any location
profile other than the ones described in this document, it MUST
also send, in the same request, location information conformant
to one of the baseline profiles. Otherwise, the server might not
be able to understand the request.
3. A client MUST NOT send multiple <location> objects that are
derived from different baseline profiles. In other words, a
client MUST only send location objects according to the same
baseline profile in a query, but it MAY contain a location
element following a baseline profile in addition to some other
profile.
4. If a client has both location information primarily of geodetic
nature and location information primarily of a civic nature, it
MUST send separate requests containing each type of location
information.
5. There can only be one instance of each location profile in a
query.
6. Servers MUST implement all profiles described in this document.
7. A server uses the first-listed location profile that it
understands and ignores the others.
8. If a server receives a request that only contains location
information using profiles it does not understand, the server
responds with a <locationProfileError> (Section 13.1).
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RFC 5222 LoST August 2008
9. The <serviceBoundary> element MUST use the same location profile
that was used to retrieve the answer and indicates which profile
has been used with the 'profile' attribute.
These rules enable the use of location profiles not yet specified,
while ensuring baseline interoperability. Take, for example, this
scenario illustrated in Figure 15 and 16. Client X has had its
firmware upgraded to support the 'not-yet-standardized-prism-profile'
location profile. Client X sends location information to Server Y,
which does not understand the 'not-yet-standardized-prism-profile'
location profile. If Client X also sends location information using
the geodetic-2D baseline profile, then Server Y will still be able to
understand the request and provide an understandable response, though
with location information that might not be as precise or expressive
as desired. This is possible because both Client X and Server Y
understand the baseline profile.
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RFC 5222 LoST August 2008
<?xml version="1.0" encoding="UTF-8"?>
<findService
xmlns="urn:ietf:params:xml:ns:lost1"
xmlns:gml="http://www.opengis.net/gml"
xmlns:gs="http://www.opengis.net/pidflo/1.0"
recursive="true"
serviceBoundary="value">
<location id="ABC 123"
profile="not-yet-standardized-prism-profile">
<gs:Prism srsName="urn:ogc:def:crs:EPSG::4979">
<gs:base>
<gml:Polygon>
<gml:exterior>
<gml:LinearRing>
<gml:posList>
42.556844 -73.248157 36.6
42.656844 -73.248157 36.6
42.656844 -73.348157 36.6
42.556844 -73.348157 36.6
42.556844 -73.248157 36.6
</gml:posList>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
</gs:base>
<gs:height uom="urn:ogc:def:uom:EPSG::9001">
2.4
</gs:height>
</gs:Prism>
</location>
<location id="DEF 345" profile="geodetic-2d">
<gml:Point id="point1" srsName="urn:ogc:def:crs:EPSG:4326">
<gml:pos>42.656844 -73.348157</gml:pos>
</gml:Point>
</location>
<service>urn:service:sos.police</service>
</findService>
Figure 15: Example of a <findServices> query with baseline profile
interoperability
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<?xml version="1.0" encoding="UTF-8"?>
<findServiceResponse
xmlns="urn:ietf:params:xml:ns:lost1"
xmlns:p2="http://www.opengis.net/">
<mapping
expires="2007-01-01T01:44:33Z"
lastUpdated="2006-11-01T01:00:00Z"
source="authoritative.example"
sourceId="cf19bbb038fb4ade95852795f045387d">
<displayName xml:lang="en">
New York City Police Department
</displayName>
<service>urn:service:sos.police</service>
<serviceBoundary profile="geodetic-2d">
<p2:Polygon srsName="urn:ogc:def::crs:EPSG::4326">
<p2:exterior>
<p2:LinearRing>
<p2:pos>37.775 -122.4194</p2:pos>
<p2:pos>37.555 -122.4194</p2:pos>
<p2:pos>37.555 -122.4264</p2:pos>
<p2:pos>37.775 -122.4264</p2:pos>
<p2:pos>37.775 -122.4194</p2:pos>
</p2:LinearRing>
</p2:exterior>
</p2:Polygon>
</serviceBoundary>
<uri>sip:nypd@example.com</uri>
<serviceNumber>911</serviceNumber>
</mapping>
<path>
<via source="resolver.example"/>
<via source="authoritative.example"/>
</path>
<locationUsed id="DEF 345"/>
</findServiceResponse>
Figure 16: Example of a <findServiceResponse> message with baseline
profile interoperability
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12.2. Two-Dimensional Geodetic Profile
The "geodetic-2d" location profile is identified by the token
"geodetic-2d". Clients and servers use this profile by placing the
following location shapes into the <serviceBoundary> or into the
<location> element (unless indicated otherwise):
Point:
The <Point> element is described in Section 5.2.1 of [13].
Section 5.2.1 of [13] shows also the specification of a <Point>
with either a two-dimensional position (latitude and longitude) or
three-dimensional position (latitude, longitude, and altitude). A
client MAY use the three-dimensional position, and servers MAY
interpret a three-dimensional position as a two-dimensional
position by ignoring the altitude value. A <Point> element is not
placed into a <serviceBoundary> element.
Polygon:
The <Polygon> element is described in Section 5.2.2 of [13]. The
restriction to 16 points for a polygon contained in Section 7.2.2
of [12] is not applicable to this document.
Circle:
The <Circle> element is described in Section 5.2.3 of [13].
Ellipse:
The <Ellipse> element is described in Section 5.2.4 of [13].
ArcBand:
The <ArcBand> element is described in Section 5.2.5 of [13].
When a client uses a <Polygon>, <Circle>, <Ellipse>, or <ArcBand>
element within the <location> element, it is indicating that it will
be satisfied by query results appropriate to any portion of the
shape. It is left to the server to select an appropriate matching
algorithm. A server MAY return multiple <mapping> elements if the
shape extends across multiple service areas. Servers are not
required to return all possible <mapping> elements to avoid denial-
of-service attacks in which clients present queries that span a very
large number of service boundaries (e.g., presenting a shape covering
all of the United States).
In the case where the server does not return multiple <mapping>
elements, but the shape extends across a service boundary, it is
possible that the matching algorithm selected by the LoST server will
return results that match a portion of the shape but do not match
those specific to a particular point. A client may always select a
point from within the shape to avoid this condition. The cases where
Hardie, et al. Standards Track [Page 30]
RFC 5222 LoST August 2008
it does not are generally those where it knows its own position only
within the shape given. In emergency service use cases, that may
result in the PSAP contacted at the URI provided by LoST being
required to forward a call to one of its neighbors; this is an
expected part of the overall emergency response system. In non-
emergency service use cases, the service deployment model should take
into account this issue as part of the provisioning model, as the
combination of the data in the LoST server and the algorithm used for
mapping determine which contact URIs are returned when shapes are
used that overlap multiple service areas.
As a general guideline, any deployed matching algorithm should ensure
that the algorithm used does not needlessly return no results if
there are valid results for any portion of the shape. If an
authoritative server receives a query for which the area in the query
overlaps the area for which the server has mapping information, then
it MUST return either a mapping whose coverage area intersects the
query area or a redirect to another server whose coverage area is a
subset of the server's coverage area.
When geodetic location information of this location profile is placed
in the <serviceBoundary> element, then the elements with geospatial
coordinates are alternative descriptions of the same service region,
not additive geometries.
12.3. Basic Civic Profile
The basic civic location profile is identified by the token 'civic'.
Clients use this profile by placing a <civicAddress> element, defined
in [10], within the <location> element.
Servers use this profile by placing a <civicAddress> element, defined
in [10], within the <serviceBoundary> element.
A response MAY contain more than one <serviceBoundary> element with
profile 'civic'. Each <serviceBoundary> element describes a set of
civic addresses that fall within the service boundary, namely, all
addresses that textually match the civic address elements provided,
regardless of the value of other address elements. A location falls
within the mapping's service boundary if it matches any of the
<serviceBoundary> elements. Hence, a response may contain multiple
<serviceBoundary> elements with civic and/or geodetic location
profiles.
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13. Errors, Warnings, and Redirects
When a LoST server cannot fulfill a request completely, it can return
either an error or a warning, depending on the severity of the
problem. It returns an <errors> element if no useful response can be
returned for the query. It returns a <warnings> element as part of
another response element if it was able to respond in part, but the
response may not be quite what the client had desired. For both
elements, the 'source' attribute names the server that originally
generated the error or warning, such as the authoritative server.
Unless otherwise noted, all elements below can be either an error or
a warning, depending on whether a default response, such as a
mapping, is included.
13.1. Errors
LoST defines a pattern for errors, defined as <errors> elements in
the Relax NG schema. This pattern defines a 'message' attribute
containing human-readable text and an 'xml:lang' attribute denoting
the language of the human-readable text. One or more such error
elements are contained in the <errors> element.
The following errors follow this basic pattern:
badRequest
The server could not parse or otherwise understand a request,
e.g., because the XML was malformed.
forbidden
The server refused to send an answer. This generally only occurs
for recursive queries, namely, if the client tried to contact the
authoritative server and was refused.
internalError
The server could not satisfy a request due to misconfiguration or
other operational and non-protocol-related reasons.
locationProfileUnrecognized
None of the profiles in the request were recognized by the server
(see Section 12).
locationInvalid
The geodetic or civic location in the request was invalid. For
example, the longitude or latitude values fall outside the
acceptable ranges.
Hardie, et al. Standards Track [Page 32]
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SRSInvalid
The spatial reference system (SRS) contained in the location
element was not recognized or does not match the location profile.
loop
During a recursive query, the server was about to visit a server
that was already in the server list in the <path> element,
indicating a request loop.
notFound
The server could not find an answer to the query.
serverError
An answer was received from another LoST server, but it could not
be parsed or otherwise understood. This error occurs only for
recursive queries.
serverTimeout
A time out occurred before an answer was received.
serviceNotImplemented
The requested service URN is not implemented and no substitution
was available.
An example is below:
<?xml version="1.0" encoding="UTF-8"?>
<errors xmlns="urn:ietf:params:xml:ns:lost1"
source="resolver.example">
<internalError message="Software bug." xml:lang="en"/>
</errors>
Figure 17: Example of an error response
Hardie, et al. Standards Track [Page 33]
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13.2. Warnings
A response MAY contain zero or more warnings. This pattern defines a
'message' attribute containing human-readable text and an 'xml:lang'
attribute denoting the language of the human-readable text. One or
more such warning elements are contained in the <warnings> element.
To provide human-readable text in an appropriate language, the HTTP
content negotiation capabilities (see Section 14) MAY be utilized by
a server.
This version of the specification defines the following warnings:
locationValidationUnavailable
The <locationValidationUnavailable> element MAY be returned when a
server wishes to notify a client that it cannot fulfill a location
validation request. This warning allows a server to return
mapping information while signaling this exception state.
serviceSubstitution
The <serviceSubstitution> element MAY be returned when a server
was not able to fulfill a <findService> request for a given
service URN. For example, a <findService> request with the
'urn:service:sos.police' service URN for a location in Uruguay may
cause the LoST service to return a mapping for the
'urn:service:sos' service URN since Uruguay does not make use of
the sub-services police, fire, and ambulance. If this warning is
returned, then the <service> element in the response provides
information about the service URN that refers to the mapping.
defaultMappingReturned
The <defaultMappingReturned> element MAY be returned when a server
was not able to fulfill a <findService> request for a given
location but is able to respond with a default URI. For example,
a nearby PSAP may be returned.
Hardie, et al. Standards Track [Page 34]
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An example of a warning is shown below:
<?xml version="1.0" encoding="UTF-8"?>
<findServiceResponse xmlns="urn:ietf:params:xml:ns:lost1"
xmlns:p2="http://www.opengis.net/">
<mapping
expires="2007-01-01T01:44:33Z"
lastUpdated="2006-11-01T01:00:00Z"
source="authoritative.example"
sourceId="fb8ed888433343b7b27865aeb38f3a99">
<displayName xml:lang="en">
New York City Police Department
</displayName>
<service>urn:service:sos.police</service>
<serviceBoundary profile="geodetic-2d">
<p2:Polygon srsName="urn:ogc:def::crs:EPSG::4326">
<p2:exterior>
<p2:LinearRing>
<p2:pos>37.775 -122.4194</p2:pos>
<p2:pos>37.555 -122.4194</p2:pos>
<p2:pos>37.555 -122.4264</p2:pos>
<p2:pos>37.775 -122.4264</p2:pos>
<p2:pos>37.775 -122.4194</p2:pos>
</p2:LinearRing>
</p2:exterior>
</p2:Polygon>
</serviceBoundary>
<uri>sip:nypd@example.com</uri>
<serviceNumber>911</serviceNumber>
</mapping>
<warnings source="authoritative.example">
<defaultMappingReturned
message="Unable to determine PSAP for the given location;
using default PSAP"
xml:lang="en"/>
</warnings>
<path>
<via source="resolver.example"/>
<via source="authoritative.example"/>
</path>
</findServiceResponse>
Figure 18: Example of a warning response
Hardie, et al. Standards Track [Page 35]
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13.3. Redirects
A LoST server can respond indicating that the querier should redirect
the query to another server, using the <redirect> element. The
element includes a 'target' attribute indicating the LoST application
unique string (see Section 4) that the client SHOULD be contacting
next, as well as the 'source' attribute indicating the server that
generated the redirect response and a 'message' attribute explaining
the reason for the redirect response. During a recursive query, a
server receiving a <redirect> response can decide whether it wants to
follow the redirection or simply return the response to its upstream
querier. The "expires" value in the response returned by the server
handling the redirected query indicates the earliest time at which a
new query might be needed (see Section 5.2). The query for the same
tuple of location and service SHOULD NOT be directed to the server
that gave redirect prior to that time.
An example is below:
<?xml version="1.0" encoding="UTF-8"?>
<redirect xmlns="urn:ietf:params:xml:ns:lost1"
target="eastpsap.example"
source="westpsap.example"
message="We have temporarily failed over." xml:lang="en"/>
Figure 19: Example of a redirect response
14. LoST Transport: HTTP
LoST needs an underlying protocol transport mechanism to carry
requests and responses. This document defines the use of LoST over
HTTP and LoST over HTTP-over-TLS. Client and server developers are
reminded that full support of RFC 2616 HTTP facilities is expected.
If LoST clients or servers re-implement HTTP, rather than using
available servers or client code as a base, careful attention must be
paid to full interoperability. Other transport mechanisms are left
to future documents. The available transport mechanisms are
determined through the use of the LoST U-NAPTR application. In
protocols that support content type indication, LoST uses the media
type application/lost+xml.
When using HTTP [3] and HTTP-over-TLS [4], LoST requests use the HTTP
POST method. The HTTP request MUST use the Cache-Control response
directive "no-cache" to disable HTTP-level caching even by caches
that have been configured to return stale responses to client
requests.
Hardie, et al. Standards Track [Page 36]
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All LoST responses, including those indicating a LoST warning or
error, are carried in 2xx responses, typically 200 (OK). Other 2xx
responses, in particular 203 (Non-authoritative information), may be
returned by HTTP caches that disregard the caching instructions. 3xx,
4xx, and 5xx HTTP response codes indicate that the HTTP request
itself failed or was redirected; these responses do not contain any
LoST XML elements. The 3xx responses are distinct from the redirects
that are described in Section 13.3; the redirect operation in
Section 13.3 occur after a LoST server processes the request. Where
an HTTP-layer redirect will be general, a LoST server redirect as
described in Section 13.3 might be specific to a specific service or
be the result of other processing by the LoST server.
The HTTP URL is derived from the LoST server name via U-NAPTR
application, as discussed above.
15. Relax NG Schema
This section provides the Relax NG schema used by the LoST protocol
in the compact form. The verbose form is included in Appendix A.
namespace a = "http://relaxng.org/ns/compatibility/annotations/1.0"
default namespace ns1 = "urn:ietf:params:xml:ns:lost1"
##
## Location-to-Service Translation (LoST) Protocol
##
## A LoST XML instance has three request types, each with
## a corresponding response type: find service, list services,
## and get service boundary.
##
start =
findService
| listServices
| listServicesByLocation
| getServiceBoundary
| findServiceResponse
| listServicesResponse
| listServicesByLocationResponse
| getServiceBoundaryResponse
| errors
| redirect
##
## The queries.
##
div {
Hardie, et al. Standards Track [Page 37]
RFC 5222 LoST August 2008
findService =
element findService {
requestLocation,
commonRequestPattern,
attribute validateLocation {
xsd:boolean >> a:defaultValue [ "false" ]
}?,
attribute serviceBoundary {
("reference" | "value") >> a:defaultValue [ "reference" ]
}?,
attribute recursive { xsd:boolean >> a:defaultValue [ "false" ] }?
}
listServices = element listServices { commonRequestPattern }
listServicesByLocation =
element listServicesByLocation {
requestLocation,
commonRequestPattern,
attribute recursive { xsd:boolean >> a:defaultValue [ "true" ] }?
}
getServiceBoundary =
element getServiceBoundary { serviceBoundaryKey, extensionPoint }
}
##
## The responses.
##
div {
findServiceResponse =
element findServiceResponse {
mapping+, locationValidation?, commonResponsePattern, locationUsed
}
listServicesResponse =
element listServicesResponse { serviceList, commonResponsePattern }
listServicesByLocationResponse =
element listServicesByLocationResponse {
serviceList, commonResponsePattern, locationUsed
}
getServiceBoundaryResponse =
element getServiceBoundaryResponse {
serviceBoundary, commonResponsePattern
}
}
##
## A pattern common to some of the queries.
##
div {
commonRequestPattern = service, path?, extensionPoint
Hardie, et al. Standards Track [Page 38]
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}
##
## A pattern common to responses.
##
div {
commonResponsePattern = warnings*, path, extensionPoint
}
##
## Location in Requests
##
div {
requestLocation =
element location {
attribute id { xsd:token },
locationInformation
}+
}
##
## Location Information
##
div {
locationInformation =
extensionPoint+,
attribute profile { xsd:NMTOKEN }?
}
##
## Service Boundary
##
div {
serviceBoundary = element serviceBoundary { locationInformation }+
}
##
## Service Boundary Reference
##
div {
serviceBoundaryReference =
element serviceBoundaryReference {
source, serviceBoundaryKey, extensionPoint
}
serviceBoundaryKey = attribute key { xsd:token }
}
##
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RFC 5222 LoST August 2008
## Path -
## Contains a list of via elements -
## places through which information flowed
##
div {
path =
element path {
element via { source, extensionPoint }+
}
}
##
## Location Used
##
div {
locationUsed =
element locationUsed {
attribute id { xsd:token }
}?
}
##
## Expires pattern
##
div {
expires =
attribute expires { xsd:dateTime | "NO-CACHE" | "NO-EXPIRATION" }
}
##
## A QName list
##
div {
qnameList = list { xsd:QName* }
}
##
## A location-to-service mapping.
##
div {
mapping =
element mapping {
element displayName {
xsd:string,
attribute xml:lang { xsd:language }
}*,
service,
(serviceBoundary | serviceBoundaryReference)?,
Hardie, et al. Standards Track [Page 40]
RFC 5222 LoST August 2008
element uri { xsd:anyURI }*,
element serviceNumber {
xsd:token { pattern = "[0-9*#]+" }
}?,
extensionPoint,
expires,
attribute lastUpdated { xsd:dateTime },
source,
attribute sourceId { xsd:token },
message
}
}
##
## Location validation
##
div {
locationValidation =
element locationValidation {
element valid { qnameList }?,
element invalid { qnameList }?,
element unchecked { qnameList }?,
extensionPoint
}
}
##
## Errors and Warnings Container.
##
div {
exceptionContainer =
(badRequest?
& internalError?
& serviceSubstitution?
& defaultMappingReturned?
& forbidden?
& notFound?
& loop?
& serviceNotImplemented?
& serverTimeout?
& serverError?
& locationInvalid?
& locationProfileUnrecognized?),
extensionPoint,
source
errors = element errors { exceptionContainer }
warnings = element warnings { exceptionContainer }
}
Hardie, et al. Standards Track [Page 41]
RFC 5222 LoST August 2008
##
## Basic Exceptions
##
div {
##
## Exception pattern.
##
basicException = message, extensionPoint
badRequest = element badRequest { basicException }
internalError = element internalError { basicException }
serviceSubstitution = element serviceSubstitution { basicException }
defaultMappingReturned =
element defaultMappingReturned { basicException }
forbidden = element forbidden { basicException }
notFound = element notFound { basicException }
loop = element loop { basicException }
serviceNotImplemented =
element serviceNotImplemented { basicException }
serverTimeout = element serverTimeout { basicException }
serverError = element serverError { basicException }
locationInvalid = element locationInvalid { basicException }
locationValidationUnavailable =
element locationValidationUnavailable { basicException }
locationProfileUnrecognized =
element locationProfileUnrecognized {
attribute unsupportedProfiles { xsd:NMTOKENS },
basicException
}
}
##
## Redirect.
##
div {
##
## Redirect pattern
##
redirect =
element redirect {
attribute target { appUniqueString },
source,
message,
extensionPoint
}
}
Hardie, et al. Standards Track [Page 42]
RFC 5222 LoST August 2008
##
## Some common patterns.
##
div {
message =
(attribute message { xsd:token },
attribute xml:lang { xsd:language })?
service = element service { xsd:anyURI }?
appUniqueString =
xsd:token { pattern = "([a-zA-Z0-9\-]+\.)+[a-zA-Z0-9]+" }
source = attribute source { appUniqueString }
serviceList =
element serviceList {
list { xsd:anyURI* }
}
}
##
## Patterns for inclusion of elements from schemas in
## other namespaces.
##
div {
##
## Any element not in the LoST namespace.
##
notLost = 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 = notLost*
}
Figure 20: RelaxNG schema
Hardie, et al. Standards Track [Page 43]
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16. Internationalization Considerations
The LoST protocol is mostly meant for machine-to-machine
communications; as such, most of its elements are tokens not meant
for direct human consumption. If these tokens are presented to the
end user, some localization may need to occur. The content of the
<displayName> element and the 'message' attributes may be displayed
to the end user, and they are thus complex types designed for this
purpose.
LoST exchanges information using XML. All XML processors are
required to understand UTF-8 and UTF-16 encodings, and therefore all
LoST clients and servers MUST understand UTF-8 and UTF-16 encoded
XML. Additionally, LoST servers and clients MUST NOT encode XML with
encodings other than UTF-8 or UTF-16.
17. IANA Considerations
17.1. U-NAPTR Registrations
This document registers the following U-NAPTR application service
tag:
Application Service Tag: LoST
Defining Publication: The specification contained within this
document.
This document registers the following U-NAPTR application protocol
tags:
o Application Protocol Tag: http
Defining Publication: RFC 2616 [3]
o Application Protocol Tag: https
Defining Publication: RFC 2818 [4]
17.2. Content-Type Registration for 'application/lost+xml'
This specification requests the registration of a new MIME type
according to the procedures of RFC 4288 [7] and guidelines in RFC
3023 [5].
Hardie, et al. Standards Track [Page 44]
RFC 5222 LoST August 2008
MIME media type name: application
MIME subtype name: lost+xml
Mandatory parameters: none
Optional parameters: charset
Indicates the character encoding of enclosed XML.
Encoding considerations: Uses XML, which can employ 8-bit
characters, depending on the character encoding used. See RFC
3023 [5], Section 3.2.
Security considerations: This content type is designed to carry LoST
protocol payloads.
Interoperability considerations: None
Published specification: RFC 5222
Applications that use this media type: Emergency and location-based
systems
Additional information:
Magic Number: None
File Extension: .lostxml
Macintosh file type code: 'TEXT'
Personal and email address for further information:
Hannes Tschofenig, Hannes.Tschofenig@nsn.com
Intended usage: LIMITED USE
Author:
This specification is a work item of the IETF ECRIT working group,
with mailing list address <ecrit@ietf.org>.
Change controller:
The IESG <iesg@ietf.org>
Hardie, et al. Standards Track [Page 45]
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17.3. LoST Relax NG Schema Registration
URI: urn:ietf:params:xml:schema:lost1
Registrant Contact: IETF ECRIT Working Group, Hannes Tschofenig
(Hannes.Tschofenig@nsn.com).
Relax NG Schema: The Relax NG schema to be registered is contained
in Section 15. Its first line is
default namespace = "urn:ietf:params:xml:ns:lost1"
and its last line is
}
17.4. LoST Namespace Registration
URI: urn:ietf:params:xml:ns:lost1
Registrant Contact: IETF ECRIT Working Group, Hannes Tschofenig
(Hannes.Tschofenig@nsn.com).
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 Namespace</title>
</head>
<body>
<h1>Namespace for LoST</h1>
<h2>urn:ietf:params:xml:ns:lost1</h2>
<p>See <a href="http://www.rfc-editor.org/rfc/rfc5222.txt">
RFC5222</a>.</p>
</body>
</html>
END
Hardie, et al. Standards Track [Page 46]
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17.5. LoST Location Profile Registry
This document creates a registry of location profile names for the
LoST protocol. Profile names are XML tokens. This registry will
operate in accordance with RFC 5226 [2], Standards Action.
geodetic-2d:
Defined in Section 12.2.
civic:
Defined in Section 12.3.
18. Security Considerations
There are several threats to the overall system of which service
mapping forms a part. An attacker that can obtain service contact
URIs can use those URIs to attempt to disrupt those services. An
attacker that can prevent the lookup of contact URIs can impair the
reachability of such services. An attacker that can eavesdrop on the
communication requesting this lookup can surmise the existence of an
emergency and possibly its nature, and may be able to use this to
launch a physical attack on the caller.
To avoid an attacker modifying the query or its result, Transport
Layer Security (TLS) MUST be implemented and SHOULD be used. Use is
RECOMMENDED both for clients' queries to servers and for queries
among servers; this latter recommendation is to help avoid LoST cache
poisoning attacks by replacing answers given to caching LoST servers.
The use of server identity checks with TLS, as described in Section
3.1 of [4], is also RECOMMENDED. Omitting the server identity check
allows an attacker to masquerade as a LoST server, so this approach
should be used only when getting any answer, even from a potentially
malicious LoST server, is preferred over closing the connection (and
thus not getting any answer at all). The host name compared against
the server certificate is the host name in the URI, not the DNS name
used as input to NAPTR resolution.
Note that the security considerations in [22] recommend comparing the
input of NAPTR resolution to the certificate, not the output (host
name in the URI). This approach was not chosen because in emergency
service use cases, it is likely that deployments will see a large
number of inputs to the U-NAPTR algorithm resolving to a single
server, typically run by a local emergency services authority. In
this case, checking the input to the NAPTR resolution against the
certificates provided by the LoST server would be impractical, as the
list of organizations using it would be large, subject to rapid
change, and unknown to the LoST server operator.
Hardie, et al. Standards Track [Page 47]
RFC 5222 LoST August 2008
The use of server identity does leave open the possibility of DNS-
based attacks, as the NAPTR records may be altered by an attacker.
The attacks include, for example, interception of DNS packets between
the client and the recursive name server, DNS cache poisoning, and
intentional modifications by the recursive name server; see [23] for
more comprehensive discussion.
DNS Security (DNSSEC) [20] can be used to protect against these
threats. While DNSSEC is incompletely deployed, users should be
aware of the risk, particularly when they are requesting NAPTR
records in environments where the local recursive name server, or the
network between the client and the local recursive name server, is
not considered trustworthy.
LoST deployments that are unable to use DNSSEC and unwilling to trust
DNS resolution without DNSSEC cannot use the NATPR-based discovery of
LoST servers as is. When suitable configuration mechanisms are
available, one possibility is to configure the LoST server URIs
(instead of the domain name to be used for NAPTR resolution)
directly. Future specifications for applying LoST in non-emergency
services may also specify additional discovery mechanisms and name
matching semantics.
Generally, LoST servers will not need to authenticate or authorize
clients presenting mapping queries. If they do, an authentication of
the underlying transport mechanism, such as HTTP basic and digest
authentication, MAY be used. Basic authentication SHOULD only be
used in combination with TLS.
A more detailed description of threats and security requirements is
provided in [17]. The threats and security requirements in non-
emergency service uses of LoST may be considerably different from
those described here. For example, an attacker might seek monetary
benefit by returning service mapping information that directed users
to specific service providers. Before deploying LoST in new
contexts, a thorough analysis of the threats and requirements
specific to that context should be undertaken and decisions made on
the appropriate mitigations.
19. Acknowledgments
We would like to the thank the following working group members for
the detailed review of previous LoST document versions:
o Martin Thomson (Review July 2006)
o Jonathan Rosenberg (Review July 2006)
Hardie, et al. Standards Track [Page 48]
RFC 5222 LoST August 2008
o Leslie Daigle (Review September 2006)
o Shida Schubert (Review November 2006)
o Martin Thomson (Review December 2006)
o Barbara Stark (Review January 2007)
o Patrik Faltstrom (Review January 2007)
o Shida Schubert (Review January 2007 as a designated expert
reviewer)
o Jonathan Rosenberg (Review February 2007)
o Tom Taylor (Review February 2007)
o Theresa Reese (Review February 2007)
o Shida Schubert (Review February 2007)
o James Winterbottom (Review July 2007)
o Karl Heinz Wolf (Review May and June 2007)
We would also like to thank the following working group members for
their input to selected design aspects of the LoST protocol:
o Leslie Daigle and Martin Thomson (DNS-based LoST discovery
procedure)
o John Schnizlein (authoritive LoST answers)
o Rohan Mahy (display names)
o James Polk (error handling)
o Ron Watro and Richard Barnes (expiry of cached data)
o Stephen Edge, Keith Drage, Tom Taylor, Martin Thomson, and James
Winterbottom (indication of PSAP confidence level)
o Martin Thomson (service boundary references)
o Martin Thomson (service URN in LoST response message)
o Clive D.W. Feather, Martin Thomson (validation functionality)
Hardie, et al. Standards Track [Page 49]
RFC 5222 LoST August 2008
o Roger Marshall (PSAP preference in LoST response)
o James Winterbottom, Marc Linsner, Keith Drage, Tom Taylor, Martin
Thomson, John Schnizlein, Shida Schubert, Clive D.W. Feather,
Richard Stastny, John Hearty, Roger Marshall, Jean-Francois Mule,
Pierre Desjardins (location profiles)
o Michael Hammer, Patrik Faltstrom, Richard Stastny, Martin Thomson,
Roger Marshall, Tom Taylor, Spencer Dawkins, Keith Drage (list
services functionality)
o Martin Thomson, Michael Hammer (mapping of services)
o Shida Schubert, James Winterbottom, Keith Drage (default service
URN)
o Otmar Lendl (LoST aggregation)
o Tom Taylor (terminology)
Klaus Darilion and Marc Linsner provided miscellaneous input to the
design of the protocol. Finally, we would like to thank Brian Rosen,
who participated in almost every discussion thread.
Early implementation efforts led to good feedback by two open source
implementation groups. We would like to thank the implementers for
their work and for helping us to improve the quality of the
specification:
o Wonsang Song
o Jong-Yul Kim
o Anna Makarowska
o Krzysztof Rzecki
o Blaszczyk Piotr
We would like to thank Jon Peterson, Dan Romascanu, Lisa Dusseault,
and Tim Polk for their IESG review comments. Blocking IESG comments
were also received from Pasi Eronen (succeeding Sam Hartman's review)
and Cullen Jennings. Adjustments have been made to several pieces of
text to satisfy these requests for changes, most notably in the
Security Considerations and in the discussion of redirection in the
presence of overlapping coverage areas.
Hardie, et al. Standards Track [Page 50]
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20. References
20.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[3] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[4] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[5] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types",
RFC 3023, January 2001.
[6] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005.
[7] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", BCP 13, RFC 4288, December 2005.
[8] Daigle, L., "Domain-Based Application Service Location Using
URIs and the Dynamic Delegation Discovery Service (DDDS)",
RFC 4848, April 2007.
[9] Schulzrinne, H., "A Uniform Resource Name (URN) for Emergency
and Other Well-Known Services", RFC 5031, January 2008.
[10] Thomson, M. and J. Winterbottom, "Revised Civic Location Format
for Presence Information Data Format Location Object
(PIDF-LO)", RFC 5139, February 2008.
[11] Cox, S., Daisey, P., Lake, R., Portele, C., and A. Whiteside,
"Geographic information - Geography Markup Language (GML)", OGC
Standard OpenGIS 03-105r1, April 2004.
[12] Reed, C. and M. Thomson, "GML 3.1.1 PIDF-LO Shape Application
Schema for use by the Internet Engineering Task Force (IETF)",
Candidate OpenGIS Implementation Specification , December 2006.
Hardie, et al. Standards Track [Page 51]
RFC 5222 LoST August 2008
20.2. Informative References
[13] Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
PIDF-LO Usage Clarification, Considerations and
Recommendations", Work in Progress, February 2008.
[14] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[15] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence", RFC 3921,
October 2004.
[16] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966,
December 2004.
[17] Taylor, T., Tschofenig, H., Schulzrinne, H., and M. Shanmugam,
"Security Threats and Requirements for Emergency Call Marking
and Mapping", RFC 5069, January 2008.
[18] Schulzrinne, H. and R. Marshall, "Requirements for Emergency
Context Resolution with Internet Technologies", RFC 5012,
January 2008.
[19] Schulzrinne, H., "Location-to-URL Mapping Architecture and
Framework", Work in Progress, September 2007.
[20] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"DNS Security Introduction and Requirements", RFC 4033,
March 2005.
[21] Rosen, B. and J. Polk, "Best Current Practice for
Communications Services in support of Emergency Calling", Work
in Progress, February 2008.
[22] Daigle, L. and A. Newton, "Domain-Based Application Service
Location Using SRV RRs and the Dynamic Delegation Discovery
Service (DDDS)", RFC 3958, January 2005.
[23] Atkins, D. and R. Austein, "Threat Analysis of the Domain Name
System (DNS)", RFC 3833, August 2004.
[24] <http://www.tschofenig.priv.at/svn/draft-ietf-ecrit-lost/
RelaxNG>.
Hardie, et al. Standards Track [Page 52]
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[25] Schulzrinne, H., Polk, J., and H. Tschofenig, "Discovering
Location-to-Service Translation (LoST) Servers Using the
Dynamic Host Configuration Protocol (DHCP)", RFC 5223,
August 2008.
Hardie, et al. Standards Track [Page 53]
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Appendix A. Non-Normative RELAX NG Schema in XML Syntax
<?xml version="1.0" encoding="UTF-8"?>
<grammar ns="urn:ietf:params:xml:ns:lost1"
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>
Location-to-Service Translation (LoST) Protocol
A LoST XML instance has three request types, each with
a corresponding response type: find service, list services,
and get service boundary.
</a:documentation>
<choice>
<ref name="findService"/>
<ref name="listServices"/>
<ref name="listServicesByLocation"/>
<ref name="getServiceBoundary"/>
<ref name="findServiceResponse"/>
<ref name="listServicesResponse"/>
<ref name="listServicesByLocationResponse"/>
<ref name="getServiceBoundaryResponse"/>
<ref name="errors"/>
<ref name="redirect"/>
</choice>
</start>
<div>
<a:documentation>
The queries.
</a:documentation>
<define name="findService">
<element name="findService">
<ref name="requestLocation"/>
<ref name="commonRequestPattern"/>
<optional>
<attribute name="validateLocation">
<data type="boolean"/>
<a:defaultValue>false</a:defaultValue>
</attribute>
</optional>
<optional>
<attribute name="serviceBoundary">
Hardie, et al. Standards Track [Page 54]
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<choice>
<value>reference</value>
<value>value</value>
</choice>
<a:defaultValue>reference</a:defaultValue>
</attribute>
</optional>
<optional>
<attribute name="recursive">
<data type="boolean"/>
<a:defaultValue>false</a:defaultValue>
</attribute>
</optional>
</element>
</define>
<define name="listServices">
<element name="listServices">
<ref name="commonRequestPattern"/>
</element>
</define>
<define name="listServicesByLocation">
<element name="listServicesByLocation">
<ref name="requestLocation"/>
<ref name="commonRequestPattern"/>
<optional>
<attribute name="recursive">
<data type="boolean"/>
<a:defaultValue>true</a:defaultValue>
</attribute>
</optional>
</element>
</define>
<define name="getServiceBoundary">
<element name="getServiceBoundary">
<ref name="serviceBoundaryKey"/>
<ref name="extensionPoint"/>
</element>
</define>
</div>
<div>
<a:documentation>
The responses.
</a:documentation>
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<define name="findServiceResponse">
<element name="findServiceResponse">
<oneOrMore>
<ref name="mapping"/>
</oneOrMore>
<optional>
<ref name="locationValidation"/>
</optional>
<ref name="commonResponsePattern"/>
<ref name="locationUsed"/>
</element>
</define>
<define name="listServicesResponse">
<element name="listServicesResponse">
<ref name="serviceList"/>
<ref name="commonResponsePattern"/>
</element>
</define>
<define name="listServicesByLocationResponse">
<element name="listServicesByLocationResponse">
<ref name="serviceList"/>
<ref name="commonResponsePattern"/>
<ref name="locationUsed"/>
</element>
</define>
<define name="getServiceBoundaryResponse">
<element name="getServiceBoundaryResponse">
<ref name="serviceBoundary"/>
<ref name="commonResponsePattern"/>
</element>
</define>
</div>
<div>
<a:documentation>
A pattern common to some of the queries.
</a:documentation>
<define name="commonRequestPattern">
<ref name="service"/>
<optional>
<ref name="path"/>
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</optional>
<ref name="extensionPoint"/>
</define>
</div>
<div>
<a:documentation>
A pattern common to responses.
</a:documentation>
<define name="commonResponsePattern">
<zeroOrMore>
<ref name="warnings"/>
</zeroOrMore>
<ref name="path"/>
<ref name="extensionPoint"/>
</define>
</div>
<div>
<a:documentation>
Location in Requests
</a:documentation>
<define name="requestLocation">
<oneOrMore>
<element name="location">
<attribute name="id">
<data type="token"/>
</attribute>
<ref name="locationInformation"/>
</element>
</oneOrMore>
</define>
</div>
<div>
<a:documentation>
Location Information
</a:documentation>
<define name="locationInformation">
<oneOrMore>
<ref name="extensionPoint"/>
</oneOrMore>
<optional>
<attribute name="profile">
<data type="NMTOKEN"/>
Hardie, et al. Standards Track [Page 57]
RFC 5222 LoST August 2008
</attribute>
</optional>
</define>
</div>
<div>
<a:documentation>
Service Boundary
</a:documentation>
<define name="serviceBoundary">
<oneOrMore>
<element name="serviceBoundary">
<ref name="locationInformation"/>
</element>
</oneOrMore>
</define>
</div>
<div>
<a:documentation>
Service Boundary Reference
</a:documentation>
<define name="serviceBoundaryReference">
<element name="serviceBoundaryReference">
<ref name="source"/>
<ref name="serviceBoundaryKey"/>
<ref name="extensionPoint"/>
</element>
</define>
<define name="serviceBoundaryKey">
<attribute name="key">
<data type="token"/>
</attribute>
</define>
</div>
<div>
<a:documentation>
Path -
Contains a list of via elements -
places through which information flowed
</a:documentation>
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<define name="path">
<element name="path">
<oneOrMore>
<element name="via">
<ref name="source"/>
<ref name="extensionPoint"/>
</element>
</oneOrMore>
</element>
</define>
</div>
<div>
<a:documentation>
Location Used
</a:documentation>
<define name="locationUsed">
<optional>
<element name="locationUsed">
<attribute name="id">
<data type="token"/>
</attribute>
</element>
</optional>
</define>
</div>
<div>
<a:documentation>
Expires pattern
</a:documentation>
<define name="expires">
<attribute name="expires">
<choice>
<data type="dateTime"/>
<value>NO-CACHE</value>
<value>NO-EXPIRATION</value>
</choice>
</attribute>
</define>
</div>
<div>
<a:documentation>
A QName list
</a:documentation>
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<define name="qnameList">
<list>
<zeroOrMore>
<data type="QName"/>
</zeroOrMore>
</list>
</define>
</div>
<div>
<a:documentation>
A location-to-service mapping.
</a:documentation>
<define name="mapping">
<element name="mapping">
<zeroOrMore>
<element name="displayName">
<data type="string"/>
<attribute name="xml:lang">
<data type="language"/>
</attribute>
</element>
</zeroOrMore>
<ref name="service"/>
<optional>
<choice>
<ref name="serviceBoundary"/>
<ref name="serviceBoundaryReference"/>
</choice>
</optional>
<zeroOrMore>
<element name="uri">
<data type="anyURI"/>
</element>
</zeroOrMore>
<optional>
<element name="serviceNumber">
<data type="token">
<param name="pattern">[0-9*#]+</param>
</data>
</element>
</optional>
<ref name="extensionPoint"/>
<ref name="expires"/>
<attribute name="lastUpdated">
<data type="dateTime"/>
</attribute>
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<ref name="source"/>
<attribute name="sourceId">
<data type="token"/>
</attribute>
<ref name="message"/>
</element>
</define>
</div>
<div>
<a:documentation>
Location validation
</a:documentation>
<define name="locationValidation">
<element name="locationValidation">
<optional>
<element name="valid">
<ref name="qnameList"/>
</element>
</optional>
<optional>
<element name="invalid">
<ref name="qnameList"/>
</element>
</optional>
<optional>
<element name="unchecked">
<ref name="qnameList"/>
</element>
</optional>
<ref name="extensionPoint"/>
</element>
</define>
</div>
<div>
<a:documentation>
Errors and Warnings Container.
</a:documentation>
<define name="exceptionContainer">
<interleave>
<optional>
<ref name="badRequest"/>
</optional>
<optional>
Hardie, et al. Standards Track [Page 61]
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<ref name="internalError"/>
</optional>
<optional>
<ref name="serviceSubstitution"/>
</optional>
<optional>
<ref name="defaultMappingReturned"/>
</optional>
<optional>
<ref name="forbidden"/>
</optional>
<optional>
<ref name="notFound"/>
</optional>
<optional>
<ref name="loop"/>
</optional>
<optional>
<ref name="serviceNotImplemented"/>
</optional>
<optional>
<ref name="serverTimeout"/>
</optional>
<optional>
<ref name="serverError"/>
</optional>
<optional>
<ref name="locationInvalid"/>
</optional>
<optional>
<ref name="locationProfileUnrecognized"/>
</optional>
</interleave>
<ref name="extensionPoint"/>
<ref name="source"/>
</define>
<define name="errors">
<element name="errors">
<ref name="exceptionContainer"/>
</element>
</define>
<define name="warnings">
<element name="warnings">
<ref name="exceptionContainer"/>
</element>
</define>
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</div>
<div>
<a:documentation>
Basic Exceptions
</a:documentation>
<define name="basicException">
<a:documentation>
Exception pattern.
</a:documentation>
<ref name="message"/>
<ref name="extensionPoint"/>
</define>
<define name="badRequest">
<element name="badRequest">
<ref name="basicException"/>
</element>
</define>
<define name="internalError">
<element name="internalError">
<ref name="basicException"/>
</element>
</define>
<define name="serviceSubstitution">
<element name="serviceSubstitution">
<ref name="basicException"/>
</element>
</define>
<define name="defaultMappingReturned">
<element name="defaultMappingReturned">
<ref name="basicException"/>
</element>
</define>
<define name="forbidden">
<element name="forbidden">
<ref name="basicException"/>
</element>
</define>
<define name="notFound">
<element name="notFound">
<ref name="basicException"/>
Hardie, et al. Standards Track [Page 63]
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</element>
</define>
<define name="loop">
<element name="loop">
<ref name="basicException"/>
</element>
</define>
<define name="serviceNotImplemented">
<element name="serviceNotImplemented">
<ref name="basicException"/>
</element>
</define>
<define name="serverTimeout">
<element name="serverTimeout">
<ref name="basicException"/>
</element>
</define>
<define name="serverError">
<element name="serverError">
<ref name="basicException"/>
</element>
</define>
<define name="locationInvalid">
<element name="locationInvalid">
<ref name="basicException"/>
</element>
</define>
<define name="locationValidationUnavailable">
<element name="locationValidationUnavailable">
<ref name="basicException"/>
</element>
</define>
<define name="locationProfileUnrecognized">
<element name="locationProfileUnrecognized">
<attribute name="unsupportedProfiles">
<data type="NMTOKENS"/>
</attribute>
<ref name="basicException"/>
</element>
</define>
</div>
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<div>
<a:documentation>
Redirect.
</a:documentation>
<define name="redirect">
<a:documentation>
Redirect pattern
</a:documentation>
<element name="redirect">
<attribute name="target">
<ref name="appUniqueString"/>
</attribute>
<ref name="source"/>
<ref name="message"/>
<ref name="extensionPoint"/>
</element>
</define>
</div>
<div>
<a:documentation>
Some common patterns.
</a:documentation>
<define name="message">
<optional>
<group>
<attribute name="message">
<data type="token"/>
</attribute>
<attribute name="xml:lang">
<data type="language"/>
</attribute>
</group>
</optional>
</define>
<define name="service">
<optional>
<element name="service">
<data type="anyURI"/>
</element>
</optional>
</define>
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<define name="appUniqueString">
<data type="token">
<param name="pattern">([a-zA-Z0-9\-]+\.)+[a-zA-Z0-9]+</param>
</data>
</define>
<define name="source">
<attribute name="source">
<ref name="appUniqueString"/>
</attribute>
</define>
<define name="serviceList">
<element name="serviceList">
<list>
<zeroOrMore>
<data type="anyURI"/>
</zeroOrMore>
</list>
</element>
</define>
</div>
<div>
<a:documentation>
Patterns for inclusion of elements from schemas in
other namespaces.
</a:documentation>
<define name="notLost">
<a:documentation>
Any element not in the LoST namespace.
</a:documentation>
<element>
<anyName>
<except>
<nsName ns="urn:ietf:params:xml:ns:lost1"/>
<nsName/>
</except>
</anyName>
<ref name="anyElement"/>
</element>
</define>
<define name="anyElement">
<a:documentation>
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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="notLost"/>
</zeroOrMore>
</define>
</div>
</grammar>
Figure 21
Appendix B. Examples Online
The XML examples and Relax NG schemas may be found online [24].
Hardie, et al. Standards Track [Page 67]
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Authors' Addresses
Ted Hardie
Qualcomm, Inc.
EMail: hardie@qualcomm.com
Andrew Newton
American Registry for Internet Numbers
3635 Concorde Parkway, Suite 200
Chantilly, VA 20151
US
Phone: +1 703 227 9894
EMail: andy@hxr.us
Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
US
Phone: +1 212 939 7004
EMail: hgs+ecrit@cs.columbia.edu
URI: http://www.cs.columbia.edu
Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland
Phone: +358 (50) 4871445
EMail: Hannes.Tschofenig@nsn.com
URI: http://www.tschofenig.priv.at
Hardie, et al. Standards Track [Page 68]
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Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
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on the procedures with respect to rights in RFC documents can be
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Copies of IPR disclosures made to the IETF Secretariat and any
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Hardie, et al. Standards Track [Page 69]