LoST boundary sync: Synchronizing Service Boundaries and <mapping> Elements Based on the Location-to-Service Translation (LoST) Protocol

Internet Engineering Task Force (IETF)                    H. Schulzrinne
Request for Comments: 6739                           Columbia University
Category: Experimental                                     H. Tschofenig
ISSN: 2070-1721                                   Nokia Siemens Networks
                                                            October 2012


  Synchronizing Service Boundaries and <mapping> Elements Based on the
            Location-to-Service Translation (LoST) Protocol

Abstract

   The Location-to-Service Translation (LoST) protocol is an XML-based
   protocol for mapping service identifiers and geodetic or civic
   location information to service URIs and service boundaries.  In
   particular, it can be used to determine the location-appropriate
   Public Safety Answering Point (PSAP) for emergency services.

   The <mapping> element in the LoST protocol specification encapsulates
   information about service boundaries and circumscribes the region
   within which all locations map to the same service Uniform Resource
   Identifier (URI) or set of URIs for a given service.

   This document defines an XML protocol to exchange these mappings
   between two nodes.  This mechanism is designed for the exchange of
   authoritative <mapping> elements between two entities.  Exchanging
   cached <mapping> elements, i.e., non-authoritative elements, is
   possible but not envisioned.  Even though the <mapping> element
   format is reused from the LoST specification, the mechanism in this
   document can be used without the LoST protocol.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Engineering
   Task Force (IETF).  It represents the consensus of the IETF
   community.  It has received public review and has been approved for
   publication by the Internet Engineering Steering Group (IESG).  Not
   all documents approved by the IESG are a candidate for any level of
   Internet Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6739.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  A Motivating Example . . . . . . . . . . . . . . . . . . . . .  4
   4.  Querying for Mappings with a
       <getMappingsRequest>/<getMappingsResponse> Exchange  . . . . .  9
     4.1.  Behavior of the LoST Sync Destination  . . . . . . . . . .  9
     4.2.  Behavior of the LoST Sync Source . . . . . . . . . . . . . 10
     4.3.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . 10
   5.  Pushing Mappings via <pushMappings> and
       <pushMappingsResponse> . . . . . . . . . . . . . . . . . . . . 12
     5.1.  Behavior of the LoST Sync Source . . . . . . . . . . . . . 12
     5.2.  Behavior of the LoST Sync Destination  . . . . . . . . . . 13
     5.3.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . 14
   6.  Transport  . . . . . . . . . . . . . . . . . . . . . . . . . . 16
   7.  RELAX NG . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
   8.  Operational Considerations . . . . . . . . . . . . . . . . . . 19
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 20
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 21
     10.1. Media Type Registration  . . . . . . . . . . . . . . . . . 21
     10.2. LoST Sync RELAX NG Schema Registration . . . . . . . . . . 22
     10.3. LoST Synchronization Namespace Registration  . . . . . . . 22
   11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 23
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 24
     12.2. Informative References . . . . . . . . . . . . . . . . . . 24

1.  Introduction

   Since the early days of emergency services, there has been a desire
   to route emergency calls to Public Safety Answering Points (PSAPs)
   that are nearest to the location of the emergency caller.  For this
   purpose each PSAP discloses one or more service boundaries so that
   this information can be used to select the appropriate PSAP and to
   route the call to it.  RFC 5222 [RFC5222] defines this data structure
   in the following way:

      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.

   RFC 5222 [RFC5222] also specifies the data structure itself as the
   <mapping> element.

   This document reuses this existing data structure and defines an XML-
   based protocol to exchange authoritative service boundaries between
   two entities, namely, the LoST Sync source and the LoST Sync
   destination.  This protocol can be used whether or not the LoST
   protocol is used for querying for service boundary information.

   The rest of the document is structured as follows.  Section 3 starts
   with an example usage of the LoST protocol.  In Sections 4, 5, 6, and
   7, we describe the protocol semantics, transport considerations, and
   the schema.  Finally, we conclude with operational, security, and
   IANA considerations in Sections 8, 9, and 10.

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].

   This document reuses terminology introduced by the mapping
   architecture document [RFC5582], such as 'coverage region', 'forest
   guide', 'mapping', and 'authoritative mapping server'.  This document
   also uses the term 'ESRP', defined in [RFC5012].

   Throughout this document, we use the terms 'LoST Sync source' and
   'LoST Sync destination' to denote the protocol endpoints of the
   exchange.  The protocol is referred to as 'LoST Sync' within the
   text.

3.  A Motivating Example

   The LoST Sync mechanism can, for example, be used in the LoST
   architecture, as specified in [RFC5582].  There, LoST servers
   cooperate to provide an ubiquitous, globally scalable, and resilient
   mapping service.  In the LoST mapping architecture, LoST servers can
   peer, i.e., have an ongoing data exchange relationship.  Peering
   relationships are set up manually, based on local policies.  A LoST
   server may peer with any number of other LoST servers.  Forest guides
   peer with other forest guides; authoritative mapping servers peer
   with forest guides and other authoritative servers, either in the
   same cluster or above or below them in the tree.  Authoritative
   mapping servers push coverage regions "up" the tree, i.e., from child
   nodes to parent nodes.  The child informs the parent of the
   geospatial or civic region that it covers for a specific service.

   Consider a hypothetical deployment of LoST in two countries, for
   example, Austria and Finland.  Austria, in our example, runs three
   authoritative mapping servers labeled as 'East', 'West', and
   'Vienna', where the former two cover the entire country except for
   Vienna, which is covered by a separate LoST server.  There may be
   other caching LoST servers run by ISPs, universities, and Voice
   Service Providers (VSPs), but they are not relevant for this
   illustration.  Finland, on the other hand, decided to only deploy a
   single LoST server that also acts as a forest guide.  For this
   simplistic illustration, we assume that only one service is
   available, namely 'urn:service:sos' since otherwise the number of
   stored mappings would have to be multiplied by the number of used
   services.

   Figure 1 shows the example deployment.

                      +---LoST-Sync-->\\     //<--LoST-Sync----+
                      |                 -----                  |
                      |                                        |
                      \/                                       \/
                    -----                                     -----
                  //     \\                                 //     \\
                 /         \                               /         \
                |  Forest   |                             |   Forest  |
                |  Guide    |                             |   Guide   |
                |  Austria  |                             |   Finland
                 \         /                               \         /
       +--------->\\     //<--------+                       \\     //
       |            -----           |                         -----
       |             /\             |                           |
     LoST            |             LoST                     //------\\
     Sync           LoST           Sync                    |Co-Located|
       |            Sync            |                      |   LoST   |
       \/            |              \/                     | Server   |
    //----\\         \/          //----\\                   \\------//
   |  LoST  |     //----\\      |  LoST  |
   | Server |    |  LoST  |     | Server |
   | 'East' |    | Server |     |'Vienna'|
    \\----//     | 'West' |      \\----//
                  \\----//

                     Figure 1: LoST Deployment Example

   The nodes are configured as follows:

   Forest Guide Austria:  This forest guide contains mappings for the
      three authoritative mapping servers (East, West, and Vienna)
      describing the area for which they are responsible.  Note that
      each mapping contains a service URN, and these mappings point to
      LoST servers rather than to PSAPs or Emergency Services Routing
      Proxies (ESRPs).

   LoST Server 'East':  This LoST server contains all the mappings to
      PSAPs covering the eastern part of the country.

      Additionally, the LoST server aggregates all the information it
      has and provides an abstracted view towards the forest guide
      indicating that it is responsible for a certain area (for a given
      service and for a given location profile).  For our example, the
      structure of a mapping is shown below:

   <mapping
       xmlns="urn:ietf:params:xml:ns:lost1"
       xmlns:gml="http://www.opengis.net/gml"
       expires="2009-01-01T01:44:33Z"
       lastUpdated="2009-12-01T01:00:00Z"
       source="east-austria.lost-example.com"
       sourceId="e8b05a41d8d1415b80f2cdbb96ccf109">
       <displayName xml:lang="en">LoST Server 'East'</displayName>
       <service>urn:service:sos</service>
       <serviceBoundary profile="geodetic-2d">
           <gml:Polygon srsName="urn:ogc:def::crs:EPSG::4326">
               <gml:exterior>
                   <gml:LinearRing>
                       <gml:pos> ... </gml:pos>
                       ..... list of coordinates for
                       boundary of LoST server 'East'
                       <gml:pos> ... </gml:pos>
                   </gml:LinearRing>
               </gml:exterior>
           </gml:Polygon>
       </serviceBoundary>
       <uri/>
   </mapping>

              Figure 2: Forest Guide Austria Mapping XML Snippet

      Note that the XML code snippet in Figure 2 serves illustrative
      purposes only and does not validate.  As can be seen in this
      example, the <uri> element is absent, and the 'source' attribute
      identifies the LoST server, namely "east-austria.lost-
      example.com".

      The mapping shown above is what is the LoST server "east-
      austria.lost-example.com" provides to the Austrian forest guide.

   LoST Server 'West':  This LoST server contains all the mappings to
      PSAPs covering the western half of the country.

   LoST Server 'Vienna':  This LoST server contains all the mappings to
      PSAPs for the city of Vienna.

   Forest Guide Finland:  In our example, we assume that Finland deploys
      a single ESRP for the entire country as their IP-based emergency
      services solution.  There is only a single LoST server, and it is
      co-located with the forest guide, as shown in Figure 1.  The
      mapping data this forest guide (FG) then distributes via LoST Sync
      is shown in Figure 3.

   <mapping xmlns="urn:ietf:params:xml:ns:lost1"
       expires="2007-01-01T01:44:33Z"
       lastUpdated="2006-11-01T01:00:00Z"
       source="finland.lost-example.com"
       sourceId="7e3f40b098c711dbb6060800200c9a66">
       <displayName xml:lang="en">Finland ESRP</displayName>
       <service>urn:service:sos</service>
       <serviceBoundary profile="civic">
           <civicAddress
               xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
               <country>FI</country>
           </civicAddress>
       </serviceBoundary>
       <uri/>
   </mapping>

              Figure 3: Forest Guide Finland Mapping XML Snippet

      An example mapping stored at the co-located LoST server is shown
      in Figure 4.

   <mapping xmlns="urn:ietf:params:xml:ns:lost1"
       expires="2007-01-01T01:44:33Z"
       lastUpdated="2006-11-01T01:00:00Z"
       source="finland.lost-example.com"
       sourceId="7e3f40b098c711dbb6060800200c9a66">
       <displayName xml:lang="en">Finland ESRP</displayName>
       <service>urn:service:sos</service>
       <serviceBoundary profile="civic">
           <civicAddress
               xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
               <country>FI</country>
           </civicAddress>
       </serviceBoundary>
       <uri>sip:esrp@finland-example.com</uri>
       <uri>xmpp:esrp@finland-example.com</uri>
       <serviceNumber>112</serviceNumber>
   </mapping>

       Figure 4: Forest Guide Finland / Co-Located LoST Server Mapping
                                 XML Snippet

   The LoST Sync mechanism described in this document can be run between
   the two forest guides.  That way, the three mappings stored in the FG
   Austria are sent to the FG Finland, and a single mapping in the FG
   Finland is sent to the FG Austria.  Additionally, the three Austrian
   LoST servers could utilize LoST Sync to inform the Austrian FG about
   their boundaries.  These three authoritative mapping servers in
   Austria would be responsible for maintaining their own mapping
   information.  Since the amount of data being exchanged is small and
   the expected rate of change is low, the nodes are configured to
   always exchange all their mapping information whenever a change
   happens.

   This document defines two types of exchanges, which are best
   described by the exchange between two nodes as shown in Figures 5 and
   6.  The protocol exchange always runs between a LoST Sync source and
   a LoST Sync destination.  Node A in the examples of Figures 5 and 6
   has mappings that Node B is going to retrieve.  Node A acts as the
   source for the data and Node B is the destination.

   The <getMappingsRequest> request allows a LoST Sync source to request
   mappings from a LoST Sync destination.

      +---------+                   +---------+
      | Node B  |                   | Node A  |
      | acting  |                   | acting  |
      | as      |                   | as      |
      | LoST    |                   | LoST    |
      | Sync    |                   | Sync    |
      | Dest.   |                   | Source  |
      +---------+                   +---------+
          |                              |
          |                              |
          |                              |
          | <getMappingsRequest>         |
          |----------------------------->|
          |                              |
          | <getMappingsResponse>        |
          |<-----------------------------|
          |                              |
          |                              |
          |                              |

    Figure 5: Querying for Mappings with a <getMappingsRequest> Message

   Note that in the exchange illustrated in Figure 5, Node B is issuing
   the first request and plays the role of the HTTPS client, and Node A
   plays the role of the HTTPS server.

   In Figure 6, the <pushMappingsRequest> exchange allows a LoST Sync
   source to push mappings to a LoST Sync destination.  In this example,
   we assume that Node A has been configured maintain state about the
   mappings it had pushed to Node B.

   This document does not define a publish/subscribe mechanism.  Such a
   mechanism would allow Node B to tell Node A what mappings it is
   interested in.  This document also does not define a mechanism for
   nodes to find out to which other entities mappings have to be pushed.

       +---------+                   +---------+
       | Node A  |                   | Node B  |
       | acting  |                   | acting  |
       | as      |                   | as      |
       | LoST    |                   | LoST    |
       | Sync    |                   | Sync    |
       | Source  |                   | Dest.   |
       +---------+                   +---------+
           |                              |
           |                              |
           |                              |
           | <pushMappingsRequest>        |
           |----------------------------->|
           |                              |
           | <pushMappingsResponse>       |
           |<-----------------------------|
           |                              |
           |                              |
           |                              |

      Figure 6: Pushing Mappings with a <pushMappingsRequest> Message

   Node A issuing the first request in Figure 6 plays the role of the
   HTTPS client, and Node B plays the role of the HTTPS server.

4.  Querying for Mappings with a <getMappingsRequest>/
    <getMappingsResponse> Exchange

4.1.  Behavior of the LoST Sync Destination

   A LoST Sync destination has two ways to retrieve <mapping> elements
   from a LoST Sync source.

   1.  When the Lost Sync destination does not have any mappings, it
       submits an empty <getMappingsRequest> message, as shown in
       Figure 7.  This indicates that it wishes to retrieve all mappings
       from the LoST Sync source.  Note that the request does not
       propagate further to other nodes.

   2.  In case a LoST Sync destination node has already obtained
       mappings in previous exchanges, then it may want to check whether
       these mappings have been updated in the meanwhile.  The policy
       regarding when to poll for updated mapping information is outside
       the scope of this document.  The <getMappingsRequest> message
       with one or more <exists> child element(s) allows the source to
       only return mappings that are missing at the destination or have
       been updated.

   After issuing the <getMappingsRequest> message, the LoST Sync
   destination waits for the <getMappingsResponse> message.  In case of
   a successful response, the LoST Sync destination stores the received
   mappings and determines which mappings to update.

4.2.  Behavior of the LoST Sync Source

   When a LoST Sync source receives an empty <getMappingsRequest>
   message, then all locally available mappings MUST be returned.

   When a LoST Sync source receives a <getMappingsRequest> message with
   one or more <exists> child element(s), then it MUST consult with the
   local mapping database to determine whether any of the mappings of
   the client is stale and whether there are mappings locally that the
   client does not yet have.  The former can be determined by finding
   mappings corresponding to the 'source' and 'sourceID' attributes
   where a mapping with a more recent 'lastUpdated' date exists.

   Processing a <getMappingsRequest> message MAY lead to a successful
   response in the form of a <getMappingsResponse> or an <errors>
   message.  Only the <badRequest>, <forbidden>, <internalError>, and
   <serverTimeout> errors, defined in [RFC5222], are used by this
   specification.  Neither the <redirect> nor the <warnings> messages
   are reused by this message.

4.3.  Examples

   The first example shows an empty <getMappingsRequest> message that
   would retrieve all locally stored mappings at the LoST Sync source.

   <?xml version="1.0" encoding="UTF-8"?>
   <getMappingsRequest xmlns="urn:ietf:params:xml:ns:lostsync1"/>

          Figure 7: Example of Empty <getMappingsRequest> Message

   A further example request is shown in Figure 8, and the corresponding
   response is depicted in Figure 9.  In this example, the
   <getMappingsRequest> element contains information about the mapping
   that is locally available to the client inside the
   <mapping-fingerprint> element (with
   source="authoritative.bar.example",
   sourceId="7e3f40b098c711dbb6060800200c9a66", and lastUpdated="2006-
   11-01T01:00:00Z").  The query asks for mappings that are more recent
   than the available one as well as any missing mapping.

   <?xml version="1.0" encoding="UTF-8"?>
   <getMappingsRequest xmlns="urn:ietf:params:xml:ns:lostsync1">
       <exists>
           <mapping-fingerprint source="authoritative.bar.example"
           sourceId="7e3f40b098c711dbb6060800200c9a66"
           lastUpdated="2006-11-01T01:00:00Z">
           </mapping-fingerprint>
       </exists>
   </getMappingsRequest>

              Figure 8: Example <getMappingsRequest> Message

   The response to the above request is shown in Figure 9.  A more
   recent mapping was available with the identification of
   source="authoritative.bar.example" and
   sourceId="7e3f40b098c711dbb6060800200c9a66".  Only one missing
   mapping, with source "authoritative.foo.example", was found and
   returned.

   <?xml version="1.0" encoding="UTF-8"?>
   <sync:getMappingsResponse
      xmlns:sync="urn:ietf:params:xml:ns:lostsync1"
      xmlns="urn:ietf:params:xml:ns:lost1"
      xmlns:gml="http://www.opengis.net/gml">

          <mapping source="authoritative.bar.example"
              sourceId="7e3f40b098c711dbb6060800200c9a66"
              lastUpdated="2008-11-26T01:00:00Z"
              expires="2009-12-26T01:00:00Z">
              <displayName xml:lang="en">Leonia Police Department
              </displayName>
              <service>urn:service:sos.police</service>
              <serviceBoundary
   profile="urn:ietf:params:lost:location-profile:basic-civic">
                  <civicAddress
   xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
                      <country>US</country>
                      <A1>NJ</A1>
                      <A3>Leonia</A3>
                      <PC>07605</PC>
                  </civicAddress>
              </serviceBoundary>
              <uri>sip:police@leonianj2.example.org</uri>
              <serviceNumber>911</serviceNumber>
          </mapping>

          <mapping expires="2009-01-01T01:44:33Z"
              lastUpdated="2008-11-01T01:00:00Z"
              source="authoritative.foo.example"
              sourceId="7e3f40b098c711dbb606011111111111">
              <displayName xml:lang="en">New York City Police Department
              </displayName>
              <service>urn:service:sos.police</service>
              <serviceBoundary profile="geodetic-2d">
                  <gml:Polygon srsName="urn:ogc:def::crs:EPSG::4326">
                      <gml:exterior>
                          <gml:LinearRing>
                              <gml:pos>37.775 -122.4194</gml:pos>
                              <gml:pos>37.555 -122.4194</gml:pos>
                              <gml:pos>37.555 -122.4264</gml:pos>
                              <gml:pos>37.775 -122.4264</gml:pos>
                              <gml:pos>37.775 -122.4194</gml:pos>
                          </gml:LinearRing>
                      </gml:exterior>
                  </gml:Polygon>
              </serviceBoundary>
              <uri>sip:nypd@example.com</uri>
              <uri>xmpp:nypd@example.com</uri>
              <serviceNumber>911</serviceNumber>
          </mapping>

   </sync:getMappingsResponse>

              Figure 9: Example <getMappingsResponse> Message

5.  Pushing Mappings via <pushMappings> and <pushMappingsResponse>

5.1.  Behavior of the LoST Sync Source

   When a LoST Sync source obtains new information that is of interest
   to its peers, it may push the new mappings to its peers.
   Configuration settings at both peers decide whether this
   functionality is used and what mappings are pushed to which other
   peers.  New mappings may arrive through various means, such as a
   manual addition to the local mapping database, or through the
   interaction with other entities.  Deleting mappings may also trigger
   a protocol interaction.

   The LoST Sync source SHOULD keep track of which LoST Sync destination
   it has pushed <mapping> elements to.  If it does not keep state
   information, then it always has to push the complete data set.  As
   discussed in Section 5.1 of [RFC5222], <mapping> elements are
   identified by the 'source', 'sourceID', and 'lastUpdated' attributes.
   A mapping is considered the same if these three attributes match.

   A <pushMappings> request sent by a LoST Sync source MUST contain one
   or more <mapping> elements.

   To delete a mapping, the content of the mapping is left empty, i.e.,
   the <mapping> element only contains the 'source', 'sourceID',
   'lastUpdated', and 'expires' attributes.  Figure 10 shows an example
   request where the mapping with the source="nj.us.example",
   sourceId="123", lastUpdated="2008-11-01T01:00:00Z", and
   expires="2008-11-01T01:00:00Z" is requested to be deleted.  Note that
   the 'expires' attribute is required per the schema definition but
   will be ignored in processing the request on the receiving side.  A
   sync source may want to delete the mapping from its internal mapping
   database but has to remember the peers to which it has distributed
   this update unless it has other ways to ensure that databases do not
   get out of sync.

5.2.  Behavior of the LoST Sync Destination

   When a LoST Sync destination receives a <pushMappingsRequest>
   message, then the cache with the existing mappings is inspected to
   determine whether the received mapping should lead to an update of an
   already existing mapping, should create a new mapping in the cache,
   or should be discarded.

   If a newly received mapping has a more recent time in its
   'lastUpdated' attribute, it MUST update an existing mapping that has
   matching 'source' and 'sourceID' attributes.

   If the received mapping does not match with any existing mapping
   based on the 'source' and 'sourceId', then it MUST be added to the
   local cache as an independent mapping.

   If a <pushMappingsRequest> message with an empty <mapping> element is
   received, then a corresponding mapping has to be determined based on
   the 'source' and the 'sourceID'.

   If no mapping can be identified, then an <errors> response MUST be
   returned that contains the <notDeleted> child element.  The
   <notDeleted> element MAY contain a 'message' attribute with an error
   description used for debugging purposes.  The <notDeleted> element
   MUST contain the <mapping> element(s) that caused the error.

   The response to a <pushMappingsRequest> request is a
   <pushMappingsResponse> message.  With this specification, a
   successful response message returns no additional elements, whereas
   an <errors> response is returned in the response message if the
   request failed.  Only the <badRequest>, <forbidden>, <internalError>,
   or <serverTimeout> errors defined in Section 13.1 of [RFC5222] are
   used.  The <redirect> and <warnings> messages are not used for this
   query/response.

   If the set of nodes that are synchronizing their data does not form a
   tree, it is possible that the same information arrives through
   several other nodes.  This is unavoidable but generally only imposes
   a modest overhead.  (It would be possible to create a spanning tree
   in the same fashion as IP multicast, but the complexity does not seem
   warranted, given the relatively low volume of data.)

5.3.  Example

   An example is shown in Figure 10.  Imagine a LoST node that obtained
   two new mappings identified as follows:

   o  source="authoritative.example"
      sourceId="7e3f40b098c711dbb6060800200c9a66"
      lastUpdated="2008-11-26T01:00:00Z"

   o  source="authoritative.example"
      sourceId="7e3f40b098c711dbb606011111111111"
      lastUpdated="2008-11-01T01:00:00Z"

   These two mappings have to be added to the peer's mapping database.

   Additionally, the following mapping has to be deleted:

   o  source="nj.us.example"
      sourceId="123"
      lastUpdated="2008-11-01T01:00:00Z"

    <?xml version="1.0" encoding="UTF-8"?>
    <sync:pushMappings
       xmlns:sync="urn:ietf:params:xml:ns:lostsync1"
       xmlns="urn:ietf:params:xml:ns:lost1"
       xmlns:gml="http://www.opengis.net/gml">
          <mapping source="authoritative.example"
              sourceId="7e3f40b098c711dbb6060800200c9a66"
              lastUpdated="2008-11-26T01:00:00Z"
              expires="2009-12-26T01:00:00Z">
              <displayName xml:lang="en">Leonia Police Department
              </displayName>
              <service>urn:service:sos.police</service>
              <serviceBoundary
       profile="urn:ietf:params:lost:location-profile:basic-civic">
                  <civicAddress
       xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
                      <country>US</country>
                      <A1>NJ</A1>
                      <A3>Leonia</A3>
                      <PC>07605</PC>
                  </civicAddress>
              </serviceBoundary>
              <uri>sip:police@leonianj.example.org</uri>
              <serviceNumber>911</serviceNumber>
          </mapping>

          <mapping expires="2009-01-01T01:44:33Z"
              lastUpdated="2008-11-01T01:00:00Z"
              source="authoritative.example"
              sourceId="7e3f40b098c711dbb606011111111111">
              <displayName xml:lang="en">New York City Police Department
              </displayName>
              <service>urn:service:sos.police</service>
              <serviceBoundary profile="geodetic-2d">
                  <gml:Polygon srsName="urn:ogc:def::crs:EPSG::4326">
                      <gml:exterior>
                          <gml:LinearRing>
                              <gml:pos>37.775 -122.4194</gml:pos>
                              <gml:pos>37.555 -122.4194</gml:pos>
                              <gml:pos>37.555 -122.4264</gml:pos>
                              <gml:pos>37.775 -122.4264</gml:pos>
                              <gml:pos>37.775 -122.4194</gml:pos>
                          </gml:LinearRing>
                      </gml:exterior>
                  </gml:Polygon>
              </serviceBoundary>
              <uri>sip:nypd@example.com</uri>
              <uri>xmpp:nypd@example.com</uri>
              <serviceNumber>911</serviceNumber>
          </mapping>
          <mapping source="nj.us.example"
              sourceId="123"
              lastUpdated="2008-11-01T01:00:00Z"
              expires="2008-11-01T01:00:00Z"/>

    </sync:pushMappings>

             Figure 10: Example <pushMappingsRequest> Message

   In response, the peer performs the necessary operations and updates
   its mapping database.  In particular, it will check whether the other
   peer is authorized to perform the update and whether the elements and
   attributes contain values that it understands.  In our example, a
   positive response is returned as shown in Figure 11.

   <?xml version="1.0" encoding="UTF-8"?>
   <pushMappingsResponse xmlns="urn:ietf:params:xml:ns:lostsync1" />

                 Figure 11: Example <pushMappingsResponse>

   In case a mapping could not be deleted as requested, the following
   error response might be returned instead.

   <?xml version="1.0" encoding="UTF-8"?>
   <errors xmlns="urn:ietf:params:xml:ns:lost1"
       xmlns:sync="urn:ietf:params:xml:ns:lostsync1"
       source="nodeA.example.com">

       <sync:notDeleted
           message="Could not delete the indicated mapping."
           xml:lang="en">

           <mapping source="nj.us.example"
               sourceId="123"
               lastUpdated="2008-11-01T01:00:00Z"
               expires="2008-11-01T01:00:00Z"/>
       </sync:notDeleted>
   </errors>

                    Figure 12: Example <errors> Message

6.  Transport

   LoST Sync needs an underlying protocol transport mechanism to carry
   requests and responses.  This document uses HTTPS as a transport to
   exchange XML documents.  No fallback to HTTP is provided.

   When using HTTP over Transport Layer Security (TLS) [RFC2818], LoST
   Sync messages use the POST method.  Requests MUST use the Cache-
   Control response directive "no-cache".

   All LoST Sync responses, including those indicating a LoST warning or
   error, are carried in 2xx responses, typically 200 (OK). 3xx, 4xx,
   and 5xx HTTP response codes indicate that the request itself failed
   or was redirected; these responses do not contain any LoST Sync XML
   elements.

7.  RELAX NG

   Note: In order to avoid copying pattern definitions from the LoST
   Regular Language for XML Next Generation (RELAX NG) schema [RFC5222]
   to this document, we include it as "lost.rng" (XML syntax) in the
   RELAX NG schema below.

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

        <grammar ns="urn:ietf:params:xml:ns:lostsync1"
        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">

            <include href="lost.rng"/>

            <start combine="choice">

             <a:documentation> Location-to-Service Translation (LoST)
               Synchronization Protocol</a:documentation>

                <choice>
                    <ref name="pushMappings"/>
                    <ref name="pushMappingsResponse"/>
                    <ref name="getMappingsRequest"/>
                    <ref name="getMappingsResponse"/>
                </choice>
            </start>


            <define name="pushMappings">
                <element name="pushMappings">
                        <oneOrMore>
                            <ref name="mapping"/>
                        </oneOrMore>

                    <ref name="extensionPoint"/>
                </element>

            </define>

            <define name="pushMappingsResponse">
                <element name="pushMappingsResponse">
                    <ref name="extensionPoint"/>
                </element>
            </define>

             <define name="getMappingsRequest">
                  <element name="getMappingsRequest">
                    <choice>
                         <ref name="exists"></ref>
                         <ref name="extensionPoint"/>
                    </choice>
                </element>
            </define>

             <define name="exists">
                  <element name="exists">
                       <oneOrMore>
                            <element name="mapping-fingerprint">
                                 <attribute name="source">
                                      <data type="token"/>
                                 </attribute>
                                 <attribute name="sourceId">
                                      <data type="token"/>
                                 </attribute>
                                 <attribute name="lastUpdated">
                                      <data type="dateTime"/>
                                 </attribute>
                                 <ref name="extensionPoint"/>
                            </element>
                       </oneOrMore>
                  </element>
             </define>

            <define name="getMappingsResponse">
                <element name="getMappingsResponse">
                        <oneOrMore>
                            <ref name="mapping"/>
                        </oneOrMore>
                    <ref name="extensionPoint"/>
                </element>
            </define>

             <!-- error messages -->

             <define name="notDeleted">

                  <element name="notDeleted">
                       <ref name="basicException"/>
                       <oneOrMore>
                            <ref name="mapping"/>
                       </oneOrMore>
                  </element>
             </define>
        </grammar>

8.  Operational Considerations

   It is important to avoid loops when more than two LoST servers use
   the mechanism described in this document.  The example shown in
   Figure 13 with three LoST servers A, B, and C (each of them acts as a
   sync source and a sync destination) illustrates the challenge in more
   detail.  A and B synchronize data between each other; the same is
   true for A and C, and B and C, respectively.

                                   A -------- B
                                    \        /
                                     \      /
                                      \    /
                                       \  /
                                        C

             Figure 13: Synchronization Configuration Example

   Now, imagine that server A adds a new mapping.  This mapping is
   uniquely identified by the combination of "source", "sourceid", and
   "last updated".  Assume that A wants to push this new mapping to B
   and C.  When B obtains this new mapping, it determines that it has to
   distribute it to its peer C.  C also needs to distribute the mapping
   to its peer B.  If the original mapping with the "source",
   "sourceid", and "last updated" is not modified by either B or C, then
   these two servers would recognize that they already possess the
   mapping and can ignore the update.

   Implementations MUST NOT modify mappings they receive.  An entity
   acting maliciously would, however, intentionally modify mappings or
   inject bogus mappings.  To avoid the possibility of an untrustworthy
   member claiming a coverage region for which it is not authorized,
   authoritative mapping servers MUST sign mappings they distribute
   using an XML digital signature [W3C.REC-xmldsig-core-20020212].  A
   recipient MUST verify that the signing entity is indeed authorized to
   speak for that region.  In many cases, this will require an out-of-
   band agreement to be in place to agree on specific entities to take
   on this role.  Determining who can speak for a particular region is
   inherently difficult unless there is a small set of authorizing
   entities that participants in the mapping architecture can trust.
   Receiving systems should be particularly suspicious if an existing
   coverage region is replaced by a new one that contains a different
   value in the <uri> element.  When mappings are digitally signed, they
   cannot be modified by intermediate LoST servers.

9.  Security Considerations

   This document defines a protocol for exchange of authoritative
   mapping information between two entities.  Hence, the protocol
   operations described in this document require authentication of
   neighboring nodes.

   The LoST Sync client and servers MUST implement TLS and use TLS.
   Which version(s) ought to be implemented will vary over time and
   depend on the widespread deployment and known security
   vulnerabilities at the time of implementation.  At the time of this
   writing, TLS version 1.2 [RFC5246] is the most recent version but has
   very limited actual deployment and might not be readily available in
   implementation tool kits.  TLS version 1.0 [RFC2246] is the most
   widely deployed version and will give the broadest interoperability.

   Mutual authentication between the LoST Sync source and the LoST Sync
   destination is not necessarily required in all deployments unless an
   emergency service authority wants to enforce access control prior to
   the distribution of their <mapping> elements.  This may, for example,
   be the case when certain emergency services networks distribute
   internal mappings that are not meant for public distribution.

   An additional threat is caused by compromised or misconfigured LoST
   servers.  A denial of service could be the consequence of an injected
   mapping.  If the mapping data contains a URL that does not exist,
   then emergency services for the indicated area are not reachable.  If
   all mapping data contains URLs that point to a single PSAP (rather
   than a large number of PSAPs), then this PSAP is likely to experience
   overload conditions.  If the mapping data contains a URL that points
   to a server controlled by the adversary itself, then it might
   impersonate PSAPs.

   Section 8 discusses this security threat and mandates signed
   mappings.  For unusual changes to the mapping database, approval by a
   system administrator of the emergency services infrastructure (or a
   similar expert) may be required before any mappings are installed.

10.  IANA Considerations

10.1.  Media Type Registration

   This specification requests the registration of a new media type
   according to the procedures of RFC 4288 [RFC4288] and guidelines in
   RFC 3023 [RFC3023].

   Type name:  application

   Subtype name:  lostsync+xml

   Required parameters:  none

   Optional parameters:  charset

      Same as charset parameter of application/xml as specified in RFC
      3023 [RFC3023].

   Encoding considerations:  Identical to those of "application/xml" as
      described in [RFC3023], Section 3.2.

   Security considerations:  This content type is designed to carry LoST
      Synchronization protocol payloads, and the security considerations
      section of RFC 6739 is applicable.  In addition, as this media
      type uses the "+xml" convention, it shares the same security
      considerations as described in [RFC3023], Section 10.

   Interoperability considerations:  None

   Published specification:  RFC 6739

   Applications that use this media type:  Emergency and Location-based
      Systems

   Additional information:

      Magic number(s):  None

      File extension(s):  .lostsyncxml

      Macintosh file type code(s):  'TEXT'

   Person & email address to contact for further information:
      Hannes Tschofenig <Hannes.Tschofenig@gmx.net>

   Intended usage:  LIMITED USE
   Restrictions on usage:  None

   Author:  Hannes Tschofenig <Hannes.Tschofenig@gmx.net>

   Change controller:

      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>

10.2.  LoST Sync RELAX NG Schema Registration

   The schema defined in this document has been registered under the XML
   schema registry at
   http://www.iana.org/assignments/xml-registry/schema.html

   URI:  urn:ietf:params:xml:schema:lostsync1

   Registrant Contact:  IETF ECRIT Working Group, Hannes Tschofenig
      (Hannes.Tschofenig@gmx.net).

   RELAX NG Schema:  The RELAX NG schema that has been registered is
      contained in Section 7.

10.3.  LoST Synchronization Namespace Registration

   The namespace defined in this document has been registered under the
   XML namespace registry at
   http://www.iana.org/assignments/xml-registry/ns.html

   URI:  urn:ietf:params:xml:ns:lostsync1

   Registrant Contact:  IETF ECRIT Working Group, Hannes Tschofenig
      (Hannes.Tschofenig@gmx.net).

   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 Synchronization Namespace</title>
   </head>
   <body>
     <h1>Namespace for LoST server synchronization</h1>
     <h2>urn:ietf:params:xml:ns:lostsync1</h2>
   <p>See <a href="[URL of published RFC]">RFC 6739
          </a>.</p>
   </body>
   </html>

   END

11.  Acknowledgments

   Robins George, Cullen Jennings, Karl Heinz Wolf, Richard Barnes,
   Mayutan Arumaithurai, Alexander Mayrhofer, and Andrew Newton provided
   helpful input.  Jari Urpalainen assisted with the RELAX NG schema.
   We would also like to thank our document shepherd Roger Marshall for
   his help with the document.

   We would like to particularly thank Andrew Newton for his timely and
   valuable review of the XML-related content.

   We would like to thank Robert Sparks, Barry Leiba, Stephen Farrell,
   Brian Haberman, Pete Resnick, and Sean Turner for their AD reviews.
   We would also like to thank Bjoern Hoehrmann for his media type
   review, Julian Reschke and Martin Duerst for their applications area
   reviews, and Wassim Haddad for his Gen-ART review.

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2246]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
              RFC 2246, January 1999.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC3023]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media
              Types", RFC 3023, January 2001.

   [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
              Registration Procedures", BCP 13, RFC 4288, December 2005.

   [RFC5222]  Hardie, T., Newton, A., Schulzrinne, H., and H.
              Tschofenig, "LoST: A Location-to-Service Translation
              Protocol", RFC 5222, August 2008.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [W3C.REC-xmldsig-core-20020212]
              Eastlake, D., Reagle, J., Solo, D., Hirsch, F., and T.
              Roessler, "XML-Signature Syntax and Processing", World
              Wide Web Consortium, Second Edition, REC-xmldsig-core-
              20020212, June 2008.

12.2.  Informative References

   [RFC5012]  Schulzrinne, H. and R. Marshall, "Requirements for
              Emergency Context Resolution with Internet Technologies",
              RFC 5012, January 2008.

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

Authors' Addresses

   Henning Schulzrinne
   Columbia University
   Department of Computer Science
   450 Computer Science Building
   New York, NY  10027
   USA

   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@gmx.net
   URI:   http://www.tschofenig.priv.at