ECRIT H. Schulzrinne
Internet-Draft Columbia U.
Intended status: Standards Track July 7, 2008
Expires: January 8, 2009
Synchronizing Location-to-Service Translation (LoST) Servers
draft-ietf-ecrit-lost-sync-00.txt
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Copyright (C) The IETF Trust (2008).
Abstract
The LoST (Location-to-Service Translation) protocol is used to map
locations to service URLs. This document defines a set of LoST
extensions that allow LoST servers to synchronize their lists of
mappings.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Distributing Mappings via <pushMappingsRequest> . . . . . . . 4
4. Synchronizing Mapping Stores via <getMappingsRequest> and
<getMappingsResponse> . . . . . . . . . . . . . . . . . . . . 6
5. Synchronizing Mapping Stores via <syncMappingsRequest> and
<syncMappingsResponse> . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7.1. LoST Synchronization Namespace Registration . . . . . . . 9
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
9. RelaxNG . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. Introduction
The LoST (Location-to-Service Translation) protocol [2] maps
geographic locations to service URLs. As specified in the LoST
architecture description [3], there are a variety of LoST servers
that cooperate to provide a global, scalable and resilient mapping
service. The LoST protocol specification only describes the protocol
used for individual seeker-originated queries. This document adds
LoST operations that allow forest guides, resolver clusters and
authoritative servers to synchronize their database of mappings.
In the LoST architecture, servers can peer, i.e., have an on-going
data exchange relationship. Peering relationships are set up
manually, based on local policies. A server can peer with any number
of other servers. Forest guides peer with other forest guides;
resolvers peer with forest guides and other resolvers (in the same
cluster); authoritative mapping servers peer with forest guides and
other authoritative servers, either in the same cluster or above or
below them in the tree. If the type of LoST role does not matter, we
refer to LoST protocol participants as LoST nodes.
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.
The coverage regions of different authoritative servers can overlap.
This should only happen if the authoritative servers are
misconfigured or if there is a political dispute that involves
competing claims for the same region. A server MUST detect such
colliding claims and implement a policy to resolve the collision,
either through an automated policy mechanism or manual intervention.
This extension defines two new requests, <pushMappingsRequest> and
<getMappingsRequest>, that allow peering servers to exchange
mappings. These requests are used for all peering relationships and
always contain mapping entries, but naturally the content of the data
exchanged differs.
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 [1].
This document reuses terminology introduced by the mapping
architecture document [3].
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3. Distributing Mappings via <pushMappingsRequest>
When a LoST node obtains new information that is of interest to its
peers, it pushes the new mappings to its peers. This information
might arrive through non-LoST means, such as a manual addition to the
local mappings database, or through another LoST node, via a
<pushMappings> request or a <getMappingsResponse> described later.
Mappings in that request replace existing mappings with the same 'id'
parameter and a more recent 'created' parameter. (Enforcing the
latter avoids that a crashed node that wakes up injects outdated
information into the system.)
Each peer keeps track of which peer it has exchanged which mapping
elements with. Mapping elements are identified by the 'source',
'sourceID' and 'lastUpdated' parameters. A mapping is considered the
same if these three attributes match. Nodes never push the same
information to the same peer twice.
Instead of providing the mappings themselves, the LoST client can
include references to mappings that have changed since the last
request, by including <m> entries. The server then requests any out-
of-date or missing mappings by including a subset of that list as <m>
elements in a <getMappingsRequest> request.
To delete a mapping, the content of the mapping is left empty. The
node can delete the mapping from its internal mapping database, but
has to remember which peers it has distributed this update to. The
mapping is identified only by the 'sourceId' and 'source' parameters;
the other parameters are ignored if present. In other words, the
delete operation affects all versions of a mapping.
The response to <pushMappingsRequest> is <pushMappingsResponse>. It
only contains <errors> elements if there is an error condition. Only
the .... errors are defined (TBD).
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, giving the relatively low volume of data.)
An example is shown in Figure 1. In the example, the last mapping,
with source nj.us.example and mapping ID 'englewood', is being
removed.
<?xml version="1.0" encoding="UTF-8"?>
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<pushMappingsRequest xmlns="urn:ietf:params:xml:ns:lost1:sync">
<mappings>
<mapping sourceId="leonia.nj.us.example"
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="abc123">
<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>
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</mapping>
<mapping source="nj.us.example" sourceId="englewood"/>
</mappings>
</pushMappingsRequest>
<?xml version="1.0" encoding="UTF-8"?>
<pushMappingsResponse xmlns="urn:ietf:params:xml:ns:lost1:sync" />
</pushMappingsResponse>
Figure 1: Example pushMappingsRequest and pushMappingsResponse
4. Synchronizing Mapping Stores via <getMappingsRequest> and
<getMappingsResponse>
Get list of mappings identified by <m> elements. The server may not
be able to return all such mappings, but the client can easily tell
which mappings were unavailable since it can compare the mapping
identifiers to those returned in the mapping elements.
Errors TBD.
5. Synchronizing Mapping Stores via <syncMappingsRequest> and
<syncMappingsResponse>
While the <pushMappingsRequest> request allows new mappings to
propagate, it does not allow a newly-arriving node to acquire all
mappings maintained by another node. Therefore, we introduce
<syncMappingsRequest> and <syncMappingsResponse> to synchronize two
mapping stores. A LoST node wanting to synchronize its mapping store
with another node issues a <getMappingsRequest>, containing an
enumeration of the current mapping sources, source identifiers and
versions in <m> elements. The recipient of the request compares that
list to its own list of mappings. It then returns an unordered set
of mappings that are more recent than the ones identified in the
<getMappingsRequest>. It also returns any mappings that it knows
about that are not contained in the list at all. Thus, a querier can
get the complete listing of mappings by omitting 'm' elements
altogether.
The querier can limit the scope of the mappings returned by adding
'source', 'sourceId', and 'lastUpdated' attributes to
<getMappingsRequest>. If the 'source' attribute is specified, only
mappings with that particular source attribute are considered.
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Similarly, the 'sourceId' attribute restricts mappings to those
matching the attribute. If 'sourceId' is specified, the 'source'
attribute also needs to be provided, since the 'sourceId' attribute
is only defined for a particular source. Similarly, if 'lastUpdated'
is specified, 'source' and 'sourceId' need to be specified as well.
In other words, a querier cannot ask for all mappings last updated
today regardless of source, for example. 'm' elements that do not
match the <getMappingsRequest> attributes are silently ignored.
Errors TBD.
An example request and response is shown in Figure 2
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<?xml version="1.0" encoding="UTF-8"?>
<getMappingsRequest xmlns="urn:ietf:params:xml:ns:lost1:sync"
sourceId="authoritative.example">
<m sourceId="authoritative.example"
sourceId="abc123" version="1" />
<get sourceId="munich.example.de"
sourceId="xx" version="2" />
</getMappingsRequest>
<?xml version="1.0" encoding="UTF-8"?>
<getMappingsResponse xmlns="urn:ietf:params:xml:ns:lost1:sync"
xmlns:p2="http://www.opengis.net/gml">
<mappings>
<mapping
expires="2009-01-26T01:44:33Z"
lastUpdated="2008-11-26T01:00:00Z"
source="authoritative.example"
sourceId="abc123" version="2">
<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@ny.example.com</uri>
<uri>xmpp:nypd@example.com</uri>
<serviceNumber>911</serviceNumber>
</mapping>
</mappings>
</getMappingsResponse>
Figure 2: Example getMappingsRequest and getMappingsResponse
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6. Security Considerations
The LoST security considerations are discussed in [2]. The
operations described in this document involve mutually-trusting LoST
nodes. These nodes need to authenticate each other, using mechanisms
such as HTTP Digest, HTTP Basic over TLS or TLS client and server
certificates. Nodes implementing LoST MUST implement HTTP Basic
authentication over TLS and MAY implement other authentication
mechanisms.
7. IANA Considerations
7.1. LoST Synchronization Namespace Registration
URI: urn:ietf:params:xml:ns:lost1:sync
Registrant Contact: IETF ECRIT Working Group, Henning Schulzrinne
(hgs@cs.columbia.edu).
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:lost1:sync</h2>
<p>See <a href="[URL of published RFC]">RFCXXXX
[NOTE TO IANA/RFC-EDITOR:
Please replace XXXX with the RFC number of this
specification.]</a>.</p>
</body>
</html>
END
8. Acknowledgments
Andrew Newton and Cullen Jennings provided helpful input.
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9. RelaxNG
TBD
10. References
10.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Hardie, T., Newton, A., Schulzrinne, H., and H. Tschofenig,
"LoST: A Location-to-Service Translation Protocol",
draft-ietf-ecrit-lost-10 (work in progress), May 2008.
10.2. Informative References
[3] Schulzrinne, H., "Location-to-URL Mapping Architecture and
Framework", draft-ietf-ecrit-mapping-arch-03 (work in progress),
September 2007.
Author's Address
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
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