ECRIT K. Wolf
Internet-Draft nic.at
Intended status: Experimental February 26, 2010
Expires: August 30, 2010
LoST Service List Boundary Extension
draft-ietf-ecrit-lost-servicelistboundary-03
Abstract
LoST maps service identifiers and location information to service
contact URIs. If a LoST client wants to discover available services
for a particular location, it will perform a <listServicesByLocation>
query to the LoST server. However, the LoST server, in its response,
does not provide context information, that is, it does not provide
any additional information about the geographical region for which
the returned list of services is considered valid within. Therefore,
this document proposes a <serviceListBoundary> element that returns a
local context along with the list of services returned, in order to
assist the client to not miss a change in available services when
moving.
Status of this Memo
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. LoST Extensions . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Extensions to <listServicesByLocation> . . . . . . . . . . 5
3.2. Retrieving the <serviceListBoundary> via
<getServiceListBoundary> . . . . . . . . . . . . . . . . . 8
3.3. <serviceListBoundary> . . . . . . . . . . . . . . . . . . 9
3.4. Implementation Considerations . . . . . . . . . . . . . . 10
3.4.1. Server Side . . . . . . . . . . . . . . . . . . . . . 10
3.4.2. Client Side . . . . . . . . . . . . . . . . . . . . . 11
4. Security & Privacy Considerations . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
5.1. Relax NG Schema Registration . . . . . . . . . . . . . . . 11
5.2. Namespace Registration . . . . . . . . . . . . . . . . . . 13
6. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 14
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1. Normative References . . . . . . . . . . . . . . . . . . . 14
7.2. Informative References . . . . . . . . . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
Location based service providers as well as Public Safety Answering
Points (PSAPs) only serve a specific geographic region. Therefore
the LoST protocol [RFC5222] defines the Service Boundary, which
indicates the service region for a specific service URL. However,
not all services are available everywhere. Clients can discover
available services for a particular location by the
<listServicesByLocation> query in LoST. The LoST server returns a
list of services that are available at this particular location. But
the server does not inform the client as to the extent of coverage
for which geographical region the returned Service List is valid.
This may lead to the situation where a client initially discovers all
available services by the <listServicesByLocation> query, and then
moves to a different location (while refreshing the service
mappings), but without noticing the availability of other services.
The following imaginary example illustrates the problem for emergency
calling:
The client is powered-up, does location determination (resulting in
location A) and performs an initial <listServicesByLocation> query
with location A requesting urn:services:sos.
The LoST server returns the following list of services:
urn:service:sos.police
urn:service:sos.ambulance
urn:service:sos.fire
The client does the initial LoST mapping and discovers the
dialstrings for each service. Then the client moves, refreshing the
individual service mappings when necessary as told by the Service
Boundary. However, when arriving in location B (close to a
mountain), service sos.mountainrescue is available, which was not
available in location A. Nevertheless, the client does not detect
this, because only the mapping of the initially discovered services
(police, ambulance, fire) are refreshed. Consequently, the
dialstring for the mountain rescue is not known by the client.
Hence, the client is unable to recognize an emergency call when the
user enters the dialstring of the mountain rescue and thus the
emergency call may fail altogether.
Note that the Service Boundary (service region for an individual
service) cannot be considered as an indicator for the region a
specific Service List is valid for. The Service List may even change
within the Service Boundary of another service. For example, the
ambulance mapping is valid for a whole state, but for a part of the
state there is an additional mountain rescue service.
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Consequently, there are two ways to tackle this issue:
o clients continuously ask for the Service List, although it may not
have changed
o a boundary information (telling the client that the Service List
does not change inside this area)
Since the LoST protocol employs the Service Boundary concept in order
to avoid having clients continuously trying to refresh the mapping of
a specific service, a Service List Boundary mechanism would provide
similar advantages for Service Lists.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. LoST Extensions
This chapter describes the necessary modifications to the LoST
protocol in order to support the proposed <serviceListBoundary> in a
similar way as the <serviceBoundary>.
3.1. Extensions to <listServicesByLocation>
The query <listServicesByLocation> may contain an additional
<serviceListBoundaryRequest> element to additionally request the
boundary for the service list based on the location provided, with
the resulting location for the list to be presented either in a by
value or by reference form. In the example below the value of the
<serviceListBoundaryRequest> element is set to "value":
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<?xml version="1.0" encoding="UTF-8"?>
<listServicesByLocation
xmlns="urn:ietf:params:xml:ns:lost1"
xmlns:gml="http://www.opengis.net/gml"
xmlns:slb="urn:ietf:params:xml:schema:lost1:slb"
recursive="true">
<location id="5415203asdf548" profile="civic">
<civicAddress xml:lang="en"
xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
<country>AT</country>
<A1>Lower Austria</A1>
<A2>Bruck an der Leitha</A2>
<A3>Wolfsthal</A3>
<RD>Hauptplatz</RD>
<HNO>1</HNO>
<PC>2412</PC>
</civicAddress>
</location>
<service>urn:service:sos</service>
<slb:serviceListBoundaryRequest>
value
</slb:serviceListBoundaryRequest>
</listServicesByLocation>
A possible response is shown below:
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<?xml version="1.0" encoding="UTF-8"?>
<listServicesByLocationResponse
xmlns="urn:ietf:params:xml:ns:lost1">
xmlns:slb="urn:ietf:params:xml:schema:lost1:slb"
<serviceList expires="2010-01-01T00:00:00Z">
urn:service:sos.ambulance
urn:service:sos.fire
urn:service:sos.gas
urn:service:sos.mountain
urn:service:sos.poison
urn:service:sos.police
</serviceList>
<path>
<via source="resolver.example"/>
<via source="authoritative.example"/>
</path>
<locationUsed id="5415203asdf548"/>
<slb:serviceListBoundary profile="civic">
<civicAddress xml:lang="en"
xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
<country>AT</country>
<A1>Lower Austria</A1>
</civicAddress>
</slb:serviceListBoundary>
</listServicesByLocationResponse>
This response above indicates that the Service List is valid for
Lower Austria. The <listServicesByLocation> request has to be
repeated by the client only when moving out of Lower Austria.
However, the mappings of the services itself may have other service
boundaries. Additionally, the expires attribute indicates the
absolute time when this Service List becomes invalid.
The boundary can also be requested by reference when setting the
value of the <serviceListBoundaryRequest> element to "reference".
Then the response contains a <serviceListBoundaryReference> element,
as shown below.
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<?xml version="1.0" encoding="UTF-8"?>
<listServicesByLocationResponse
xmlns="urn:ietf:params:xml:ns:lost1">
xmlns:slb="urn:ietf:params:xml:schema:lost1:slb"
<serviceList expires="2010-01-01T00:00:00Z">
urn:service:sos.ambulance
urn:service:sos.fire
urn:service:sos.gas
urn:service:sos.mountain
urn:service:sos.poison
urn:service:sos.police
</serviceList>
<path>
<via source="resolver.example"/>
<via source="authoritative.example"/>
</path>
<locationUsed id="5415203asdf548"/>
<serviceListBoundaryReference
source="authoritative.example"
serviceListKey="123567890123567890123567890" />
</listServicesByLocationResponse>
3.2. Retrieving the <serviceListBoundary> via <getServiceListBoundary>
In order to retrieve the boundary corresponding a specific
'serviceListKey', the client issues a <getServiceListBoundary>
request to the server identified in the 'source' attribute of the
<serviceListBoundaryReference> element, similar to the
<getServiceBoundary> request.
An example is shown below:
<?xml version="1.0" encoding="UTF-8"?>
<getServiceListBoundary xmlns="urn:ietf:params:xml:ns:lost1"
serviceListKey="123567890123567890123567890"/>
The LoST server response is shown below:
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<?xml version="1.0" encoding="UTF-8"?>
<getServiceListBoundaryResponse
xmlns="urn:ietf:params:xml:schema:lost1:slb">
<serviceListBoundary profile="civic"
expires="2010-01-01T00:00:00Z">
<civicAddress xml:lang="en"
xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
<country>AT</country>
<A1>Lower Austria</A1>
</civicAddress>
</serviceListBoundary>
<path>
<via source="resolver.example"/>
<via source="authoritative.example"/>
</path>
</getServiceListBoundaryResponse>
The 'serviceListKey' uniquely identifies a Service List Boundary as
the 'key' does for the service boundary (see Section 5.6 in RFC
5222). Therefore the 'serviceListKey' is a random token with at
least 128 bits of entropy and can be assumed globally unique.
Whenever the boundary changes, a new 'serviceListKey' MUST be
assigned.
Note: since LoST does not define an attribute to indicate which
profile the clients understands in a <getServiceListBoundary>
request, this document also does not define one for the
<getServiceListBoundary> request.
3.3. <serviceListBoundary>
The <serviceListBoundary> information that gets returned, indicates
the geographic region in which all the service identifiers returned
from a <serviceList> element are the same, within a
<listServicesByLocation> query. A <serviceListBoundary> may consist
of geometric shapes (both in civic and geodetic location format), and
may be non-contiguous, like the Service Boundary.
The mapping of the specific services within the Service List Boundary
may be different at different locations.
The server may return the boundary information in multiple profiles,
but has to use at least one profile that the client used in the
request in order to ensure that the client is able to process the
boundary information.
There is no need to include boundary information to a
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<listServicesResponse>. <ListServices> requests are purely for
diagnostic purposes and do not contain location information at all,
so no boundary information is reasonable.
Also note that the <serviceListBoundary> is optional and the LoST
server may return it or not based on its local policy - like it is
the case with the Service Boundary. However, especially for
emergency services, the <serviceListBoundary> might be crucial to
ensure that moving clients do not miss changes in the available
services.
3.4. Implementation Considerations
The subsections below discuss implementation issues for the LoST
server and client for the serviceListBoundary support.
3.4.1. Server Side
The mapping architecture and framework [RFC5582] describes that each
tree announces its coverage region (for one type of service, e.g.
sos.police) to one or more forest guides. Forest guides peer with
each other and synchronize their data. Hence, a forest guide has
sufficient knowledge (it knows all the services and their coverage
regions) to answer a <listServicesByLocation> query and additionally
add the <serviceListBoundary> as well.
The calculation of the largest possible area for which the Service
List stays the same might be a complex task. An alternative would be
to return smaller areas that are easier to compute. In such a case
some unneeded queries to the LoST server are the consequence, but
still the main purpose of the <serviceListBoundary> is achieved:
Never miss a change of available services. So a reasonable trade-off
between the effort to generate the boundary information and the saved
queries to the LoST server has to be considered.
Probably for some countries the county (or disrict, canton, state,
...) borders would be suitable as <serviceListBoundary>. Some
neighbouring counties may have implemented different services while a
<listServicesByLocation> query in other neighbouring counties still
results in the same Service List. So when moving across a county
border, it is at least ensured, that every device fetches a new
Service List from the LoST server.
Other countries might have different structures and the generation of
the <serviceListBoundary> might follow other rules as long as it is
ensured that a client is able to notice any change in the Service
List when moving.
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3.4.2. Client Side
A mobile client that already implements LoST and evaluates the
<serviceBoundary> has almost everything that is needed to make use of
the <serviceListBoundary>. Since the integration into LoST follows
the concept of the <serviceBoundary> (and also makes use of the same
location profiles), just the additional <serviceListBoundary> has to
be evaluated. Whenever moving outside a <serviceListBoundary>, the
client must perform a new <listServicesByLocation> query with the new
location information in order to determine a change in available
services.
4. Security & Privacy Considerations
Security considerations for LoST are discussed in [RFC5222]. This
document extends LoST to also carry Service List Boundaries (and
requests for them). These Service List Boundaries are calculated by
the server based on the individual Service Boundaries and sent to
clients in case the local policy allows this. Therefore it is
generally considered to have the same level of sensitivity as for the
Service Boundary and thus the same access control and confidentiality
requirements as the base LoST protocol. As a result, the security
measures incorporated in the base LoST specification provide
sufficient protection for LoST messages that use the Service List
Boundary extension.
5. IANA Considerations
This document requests two actions by IANA: a XML schema registration
and namespace registration, according to the description in the
following sections.
5.1. Relax NG Schema Registration
This document requests registration of the following Relax NG Schema
to the IETF XML Registry [RFC3688]:
URI: urn:ietf:params:xml:schema:lost1:slb
Registrant Contact: IETF ECRIT Working Group, Karl Heinz Wolf
(karlheinz.wolf@nic.at)
Relax NG Schema:
BEGIN
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<?xml version="1.0" encoding="UTF-8"?>
<grammar xmlns="urn:ietf:params:xml:ns:lost1"
xmlns:slb="urn:ietf:params:xml:ns:lost1:slb">
<include href="lost.rng">
<!-- redefinition of LoST elements -->
<start>
<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"/>
<ref name="slb:getServiceListBoundary"/>
<ref name="slb:getServiceListBoundaryResponse"/>
</choice>
</start>
<define name="listServicesByLocation">
<element name="listServicesByLocation">
<ref name="commonRequestPattern"/>
<ref name="slb:serviceListBoundaryRequest"/>
</element>
</define>
<define name="listServicesByLocationResponse">
<element name="listServicesByLocationResponse">
<ref name="serviceList"/>
<ref name="commonResponsePattern"/>
<ref name="locationUsed"/>
<choice>
<ref name="slb:serviceListBoundaryResponse"/>
<ref name="slb:serviceListBoundaryReference"/>
</choice>
</element>
</define>
</include>
<define name="serviceListBoundaryRequest">
<element name="serviceListBoundary">
<ref name="slb:serviceListBoundary"/>
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<choice>
<value>value</value>
<value>reference</value>
</choice>
</element>
</define>
<define name="serviceListBoundaryResponse">
<element name="serviceListBoundary">
<ref name="slb:serviceListBoundary"/>
<attribute name="profile"/>
<ref name="locationInformation"/>
</element>
</define>
<define name="serviceListBoundaryReference">
<element name="serviceListBoundaryReference">
<ref name="slb:serviceListBoundaryReference"/>
<attribute name="source"/>
<attribute name="serviceListKey"/>
</element>
</define>
<define name="getServiceListBoundary">
<element name="getServiceListBoundary">
<ref name="slb:getServiceListBoundary"/>
<attribute name="serviceListKey"/>
</element>
</define>
<define name="getServiceListBoundaryResponse">
<element name="getServiceListBoundaryResponse">
<ref name="slb:getServiceListBoundaryResponse"/>
<attribute name="serviceListKey"/>
<ref name="slb:serviceListBoundary"/>
<ref name="path"/>
</element>
</define>
</grammar>
END
5.2. Namespace Registration
This document requests registration of the following namespace (below
the LoST namespace defined in [RFC5222]) to the IETF XML Registry
[RFC3688]:
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URI: urn:ietf:params:xml:ns:lost1:slb
Registrant Contact: IETF ECRIT Working Group, Karl Heinz Wolf
(karlheinz.wolf@nic.at)
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 serviceListBoundary Namespace</title>
</head>
<body>
<h1>Namespace for the LoST Service List Boundary</h1>
<h2>urn:ietf:params:xml:ns:lost1:slb</h2>
<p>See <a href="http://www.rfc-editor.org/rfc/rfcXXXX.txt">
RFCXXXX</a>.</p>
</body>
</html>
END
6. Acknowledgement
The author would like to thank Henning Schulzrinne for the discussion
on the draft and Martin Thomson, Richard Barnes and Roger Marshall
for their valuable input and text suggestions during the WGLC.
7. References
7.1. Normative References
[RFC5222] Hardie, T., Newton, A., Schulzrinne, H., and H.
Tschofenig, "LoST: A Location-to-Service Translation
Protocol", RFC 5222, August 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
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January 2004.
7.2. Informative References
[RFC5582] Schulzrinne, H., "Location-to-URL Mapping Architecture and
Framework", RFC 5582, September 2009.
Author's Address
Karl Heinz Wolf
nic.at GmbH
Karlsplatz 1/2/9
Wien A-1010
Austria
Phone: +43 1 5056416 37
Email: karlheinz.wolf@nic.at
URI: http://www.nic.at/
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