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Location-to-Service Translation (LoST) Service List Boundary Extension

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 6197.
Author Karl Wolf
Last updated 2015-10-14 (Latest revision 2010-12-16)
Replaces draft-wolf-ecrit-lost-servicelistboundary
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Experimental
Additional resources Mailing list discussion
Stream WG state (None)
Document shepherd (None)
IESG IESG state Became RFC 6197 (Experimental)
Action Holders
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD Robert Sparks
Send notices to (None)
ECRIT                                                            K. Wolf
Intended status: Experimental                          December 16, 2010
Expires: June 19, 2011

                  LoST Service List Boundary Extension


   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 Service List Boundary 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

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 19, 2011.

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   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
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   Without obtaining an adequate license from the person(s) controlling
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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  . . . . . . . . . . . . . . . . . . . . . 10

   4.  Security & Privacy Considerations  . . . . . . . . . . . . . . 11

   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
     5.1.  Relax NG Schema Registration . . . . . . . . . . . . . . . 11
     5.2.  Namespace Registration . . . . . . . . . . . . . . . . . . 14

   6.  Acknowledgement  . . . . . . . . . . . . . . . . . . . . . . . 15

   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 15
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 16

   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16

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1.  Introduction

   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 provides
   similar advantages for Service Lists.

   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

   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:


   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. Since the client is only required to refresh
   the mappings for the initially discovered services, the new service
   is not detected.  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

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   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.

   Consequently, there are two ways to tackle this issue:
   o  clients continuously poll 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)

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  LoST Extensions

   This chapter describes the necessary extensions to the LoST protocol
   in order to support the proposed Service List Boundary in a similar
   way as the <serviceBoundary>.  Extensions defined in this document
   are declared in the new XML namespace

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 presented either by value or by
   reference.  In the example below the value of 'type' attribute of the
   <serviceListBoundaryRequest> element is set to "value":

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      <?xml version="1.0" encoding="UTF-8"?>
        <location id="5415203asdf548" profile="civic">
          <civicAddress xml:lang="en"
            <A1>Lower Austria</A1>
            <A2>Bruck an der Leitha</A2>
        <slb:serviceListBoundaryRequest type="value"/>

   A <listServicesByLocationResponse> with the addition of one
   <serviceListBoundary> elemenents is shown below:

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     <?xml version="1.0" encoding="UTF-8"?>

         <via source="resolver.example"/>
         <via source="authoritative.example"/>
         <locationUsed id="5415203asdf548"/>
         <slb:serviceListBoundary profile="civic"
           <civicAddress xml:lang="en"
             <A1>Lower Austria</A1>

   This response above indicates that the Service List is valid for
   Lower Austria.  The <listServicesByLocation> request needs 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 response MAY contain multiple <serviceListBoundary> elements for
   alternative representation, each representing the boundary in a
   specific location profile.  However, multiple locations inside a
   serviceListBoundary element are considered to be additive.

   The boundary can also be requested by reference when setting the
   value of the 'type' attribute of the <serviceListBoundaryRequest>
   element to "reference" (which is the default in case the attribute is
   omitted).  Then the response contains a
   <serviceListBoundaryReference> element with a 'serviceListKey'
   attribute (described in Section 3.2), as shown below.

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     <?xml version="1.0" encoding="UTF-8"?>

          <via source="resolver.example"/>
          <via source="authoritative.example"/>
        <locationUsed id="5415203asdf548"/>
           serviceListKey="123567890123567890123567890" />

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"?>

   The LoST server response is shown below:

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  <?xml version="1.0" encoding="UTF-8"?>
    <serviceListBoundary profile="civic" expires="2012-01-01T00:00:00Z">
      <civicAddress xml:lang="en"
        <A1>Lower Austria</A1>
    <path xmlns="urn:ietf:params:xml:ns:lost1">
      <via source="resolver.example"/>
      <via source="authoritative.example"/>

   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

   Note: since LoST does not define an attribute to indicate which
   location profile the clients understands in a
   <getServiceListBoundary> request, this document also does not define
   one for the <getServiceListBoundary> request.

3.3.  <serviceListBoundary>

   The Service List Boundary 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 Service List Boundary 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 location
   profiles, but MUST 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
   <listServicesResponse>.  The <listServices> request is purely for
   diagnostic purposes and does not contain location information at all,

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   so boundary information cannot be calculated.

   Also note that the Service List Boundary 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 Service List Boundary might be crucial to
   ensure that moving clients do not miss changes in the available

3.4.  Implementation Considerations

   The subsections below discuss implementation issues for the LoST
   server and client for the Service List Boundary 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> or <serviceListBoundaryReference> as

   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 Service List Boundary is achieved:
   Never miss a change of available services.  Thus, the server operator
   may specify a reasonable trade-off between the effort to generate the
   boundary information and the saved queries to the LoST server.

   For example, in some countries the offered services may differ in
   adjacent counties (or districts, cantons, states, ...).  Their
   borders may be suitable as Service List Boundary as well, even though
   some adjacent counties offer the same services.

   Other countries might have different structures and the generation of
   the Service List Boundary 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.

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

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   the Service List Boundary.  Since the integration into LoST follows
   the concept of the <serviceBoundary> (and also makes use of the same
   location profiles), just the additional <serviceListBoundary> needs
   to be evaluated.  Whenever moving outside a Service List Boundary,
   the client performs a new <listServicesByLocation> query with the new
   location information in order to determine a change in available

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: an 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

   Relax NG Schema:


   <?xml version="1.0" encoding="UTF-8"?>

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     <include href="lost.rng">
     <!-- redefinition of LoST elements -->
           <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"/>

           <!-- New in RFCXXX -->
           <ref name="getServiceListBoundary"/>
           <ref name="getServiceListBoundaryResponse"/>

       <define name="listServicesByLocation">
         <element name="listServicesByLocation">
           <ref name="requestLocation"/>
           <ref name="commonRequestPattern"/>
             <attribute name="recursive">
               <data type="boolean"/>

           <!-- New in RFCXXXX -->
             <ref name="serviceListBoundaryRequest"/>

       <define name="listServicesByLocationResponse">
         <element name="listServicesByLocationResponse">
           <ref name="serviceList"/>
           <ref name="commonResponsePattern"/>
           <ref name="locationUsed"/>

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           <!-- New in RFCXXXX -->
               <ref name="serviceListBoundary"/>
               <ref name="serviceListBoundaryReference"/>


     <define name="serviceListBoundaryRequest">
       <element name="slb:serviceListBoundaryRequest">
           <attribute name="type">

     <define name="serviceListBoundary">
       <element name="slb:serviceListBoundary">
           <ref name="expires"/>
         <ref name="locationInformation"/>
         <ref name="extensionPoint"/>

     <define name="serviceListBoundaryReference">
       <element name="slb:serviceListBoundaryReference">
         <ref name="source"/>
         <attribute name="serviceListKey">
           <data type="token"/>
       <ref name="extensionPoint"/>

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     <define name="getServiceListBoundary">
       <element name="slb:getServiceListBoundary">
         <attribute name="serviceListKey">
           <data type="token"/>
       <ref name="extensionPoint"/>

     <define name="getServiceListBoundaryResponse">
       <element name="slb:getServiceListBoundaryResponse">
        <ref name="serviceListBoundary"/>
        <ref name="path"/>
        <ref name="extensionPoint"/>


5.2.  Namespace Registration

   This document requests registration of the following namespace (below
   the LoST namespace defined in [RFC5222]) to the IETF XML Registry

   URI: urn:ietf:params:xml:ns:lost1:slb

   Registrant Contact: IETF ECRIT Working Group, Karl Heinz Wolf


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   <?xml version="1.0"?>
   <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
   <html xmlns="">
     <meta http-equiv="content-type"
     <title>LoST Service List Boundary Namespace</title>
     <h1>Namespace for the LoST Service List Boundary</h1>
   <p>See <a href="">


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.
   Further thanks go to Joshua Bell from the Applications Area Review
   Team for his help with Relax NG.

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,
              January 2004.

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7.2.  Informative References

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

Author's Address

   Karl Heinz Wolf GmbH
   Karlsplatz 1/2/9
   Wien  A-1010

   Phone: +43 1 5056416 37

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