ECRIT H. Schulzrinne
Internet-Draft Columbia U.
Expires: April 26, 2006 October 23, 2005
Location-to-URL Mapping Protocol (LUMP)
draft-schulzrinne-ecrit-lump-01
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
LUMP (Location-to-URL Mapping Protocol) maps geographic locations,
described as PIDF-LO objects containing civic or geospatial
information, to one or more URLs. It is based on a standard RPC
mechanism and supports updates. This document describes the message
formats, while a companion document describes the overall system
architecture.
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Introductory Example . . . . . . . . . . . . . . . . . . . . 5
5. Overview of System Operation . . . . . . . . . . . . . . . . 6
6. Resolver Discovery . . . . . . . . . . . . . . . . . . . . . 7
7. Messages . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Configuring Emergency Dial Strings . . . . . . . . . . . . . 11
9. Security . . . . . . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1 Normative References . . . . . . . . . . . . . . . . . . 13
10.2 Informative References . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . 14
A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . 15
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1. Terminology
In this document, the key words "MUST", "MUSTNOT", "REQUIRED",
"SHALL", "SHALLNOT", "SHOULD", "SHOULDNOT", "RECOMMENDED", "MAY", and
"OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
indicate requirement levels for compliant implementations.
2. Definitions
In addition to the terms defined in [11], this document uses the
following terms to describe LUMP:
authoritative resolver: Resolver that can provide the authoritative
answer to a particular set of queries, e.g., covering a set of
PIDF-LO civic labels or a particular region described by a
geometric shape. In some (rare) cases of territorial disputes,
two resolvers may be authoritative for the same region.
child: A child is a resolver that is authoritative for a subregion of
a particular server. A child can in turn be parent.
cluster: A cluster is a group of resolver (servers) that all share
the same mapping information and return the same results for
queries. Clusters provide redundancy and share query load.
Clusters are fully-meshed, i.e., they all exchange updates with
each other.
complete: A civic mapping region is considered complete if it covers
a set of hierarchical labels in its entirety, i.e., there is no
other resolver that covers parts of the same region. (A complete
mapping may have children that cover strict subsets of this
region.) For example, a region spanning the whole country is
complete, but a region spanning only some of the streets in a city
is not.
hint: A hint provides a mapping from a region to a server name, used
to short-cut mapping operations.
first resolver: The first resolver is the resolver contacted directly
by the ESRP or end system to obtain a mapping. Architecturally,
all resolvers can serve as first resolvers, although local policy
may disallow this.
leaf: A resolver that has no children.
mapping: A mapping is a short-hand for 'mapping from a location
object to one or more URLs describing either another mapping
server or the desired PSAP URLs.
parent: A resolver that covers the region of all of its children. A
resolver without a parent is a root resolver.
peer: A resolver maintains associations other resolvers, called
peers. Peers synchronize their region maps.
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querier: The resolver, ESRP or end system requesting a mapping.
region map: A data object describing a contiguous area covered by a
resolver, either as a subset of a civic address or a geometric
object.
root region map: A data object describing a contiguous area covered
by a resolver, with no parent map.
resolver: The server providing (part of) the mapping service.
Resolvers cooperate to offer the mapping service to queriers.
root resolver: A resolver without parents is a root resolver.
3. Introduction
The location-to-URL mapping protocol (LUMP) maps a tuple consisting
of a service URN and a civic or geospatial location, typically
specified as a PIDF-LO object, to a set of URLs that describe the
services available for that location. The initial application is the
mapping of locations to the appropriate Public Safety Answering Point
(PSAP) for emergency calling. LUMP uses a common RPC protocol for
its operations.
LUMP has the following properties, described more fully later in this
document:
Satisfies the requirements [11] for mapping protocols.
LUMP supportes lookup as well as address validation for civic
addresses.
LUMP allows separate hierarchies and geographic service boundaries
for each type of service.
LUMP re-uses of the most commonly used RPC protocol, SOAP, with a
variety of transport and security options. (Other mechanisms,
such as XML-RPC or REST-style HTTP, may also work.) The choice is
motivated by the availability of numerous well-tested
implementations, both open and closed source, in just about any
conceivable language framework (with the possible exception of
Fortran and Cobol).
LUMP uses a robust clustering and replication architectures that
distributes load as widely as possible, with every resolver as an
entry point.
LUMP fully specifies mechanisms for distributing coverage-region
information.
Mapping can be based on either civic or geospatial location
information, with no performance penalty for either.
Service regions can overlap.
LUMP supports split responsibility for a single civic hierarchy
level. (Example: A city has three public safety agencies, with
three PSAPs and independent mapping databases, each covering a
subset of the streets in the city.)
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LUMP can be deployed bottom-deployment as well as top-down, with
no need for a global coordinating body or the management of a
global namespace or DNS name. The mechanism described does not
require a country-level mapping server or a set of "root" servers.
Mapping services can be offered close to the access network, by
the multimedia service provider (MSP), including voice service
providers (VSPs), or by independent third parties.
LUMP supports a mechanism for updates and synchronization.
LUMP uses automated cluster replication with guaranteed
convergence properties for maximum robustness [7].
LUMP can be extended to additional operations and data types.
Scalable both horizontally and vertically, i.e., any number of
servers can support each subset of the mapping information and the
number of levels is not bounded.
LUMP minimizes round trips by caching individual mappings as well
as coverage regions ("hinting"). Unless otherwise desired, there
is only one message exchange (roundtrip delay) between the ESRP or
end system requesting a mapping and the designated resolver. This
also facilitates reuse of TLS or other secure transport
association across multiple queries.
LUMP supports both exact and approximate (best-guess) matching,
controllable by the querier.
Mapping servers require only limited mutual trust.
The overall mapping architecture employed by LUMP is described in a
companion [12] document. This document assumes that the reader has
consulted that document, as this document only describes the basic
request-response message mechanism.
4. Introductory Example
For this example, assume that there is a SIP-based VSPs V that offers
a first resolver service to its customers. The VSP operates a
cluster of such LUMP servers, advertised to their customers via DHCP.
For simplicity, we only look at resolution by civic address;
resolution by geo coordinates work exactly in the same fashion.
Assume that in the United States, each state operates a resolver,
covering the counties or parishes in the state. In our example,
there is no server covering all of the United States or larger
regions. Each county in the state in turn has a list of coverage
regions, typically consisting of one or more PSAPs. The state
servers have their own database that is not shared with the rest of
country. Assume that the caller is located at 123 Broad Avenue,
Bergen County, Leonia, New Jersey.
An end user affiliated with V1 needs to place an emergency call and
dials "9-1-1". The end device translates this into an "sos" URI,
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which reaches the outbound proxy operated by V1, acting as an ESRP
here. The ESRP issues a LUMP request to the local first resolver,
RV1. RV1 has stored the coverage regions for all the states and
matches the request to the New Jersey server, using the PIDF-LO
location information contained in the SIP INVITE request for the
lookup operation. Since it operates in recursive mode, it in turn
queries the New Jersey server, say, lump:state.nj.example.gov. That
server does not want to reveal more detailed information to the
caller and simple returns a URL for the state-wide emergency services
proxy, say sip:sos@emergency.nj.example.gov.
The ESRP routes the call to sip:sos@emergency.nj.example.gov, a SIP
proxy server. In one or more resolution steps, that proxy server in
turn consults a local LUMP server with the same PIDF-LO location
information. Assume that the town of Leonia is served by two PSAPs,
which do not share the same database. Streets south of a main road
are served by one, those north by another. The state LUMP server
only knows that Leonia has two such servers and issues a request to
both, i.e., lump:north.leonianj.example.gov and lump:
south.leonianj.example.gov. Broad Avenue is divided by this street,
with 124 Broad Avenue happening to fall north of the dividing line.
Both LUMP servers get the request and the northern server returns an
answer, while the southern server indicates that this address is
outside of its coverage region. The northern server returns the PSAP
address, say, sip:police@leonianj.example.gov. The proxy simply
routes the call to that location, including the location information.
This is only one of many possible deployment scenarios. As noted
elsewhere, the area served by each server does not have to correspond
to a particular civic address level or can span multiple levels. The
referral graph can differ between civic and geospatial addresses and
can utilize completely different servers, beyond the first resolver.
5. Overview of System Operation
A querier, such as an ESRP or end system, desiring to obtain a
location mapping follows the steps below:
Identify a resolver: Using either DHCP [2], a service location
protocol such as DNS-SD [9] or SLP [6], a using-protocol
configuration protocol (e.g., [10] for SIP) or another
configuration mechanism, the querier obtains one DNS name for a
LUMP resolver.
Determine the resolver: The domain name obtained in the previous step
is resolved using the associated SRV [3] resource record. The
querier chooes the highest-priority server, and continues down the
list if that server does not respond. As detailed in the SRV
specification, a querier chooses randomly among multiple entries
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with the same weight. The use of DNSsec is RECOMMENDED.
Send query to resolver: The querier sends a LUMP query to the
resolver identified in the previous step, using an existing or
newly-established secure transport association. The query
contains a PIDF-LO [4] object. The resolver either determines
that it is authoritative for the location contained in the query,
recursively queries other servers or it provides an indication
whom to ask next.
In principle, the protocols between querier and resolvers and between
LUMP servers do not have to be the same. We leave this for future
study.
In the next section, we describe how LUMP works "behind the scenes"
to perform this resolution.
6. Resolver Discovery
LUMP services may be operated by a variety of organizations and
entities, including Internet service providers, Internet access
providers, voice service providers, and specialized LUMP service
providers, such as public safety agencies or commercial database
vendors. Each of these can either advertise their own servers or
servers operated by other entities.
LUMP supports a range of resolver discovery mechanisms. Essentially,
any discovery protocol may be used, including SLP [6], DNS-based [9]
or UDDI. If the Internet service provider offers LUMP services, it
may advertise these via DHCP. If the voice service provider offers
LUMP services, it may include those in the SIP device configuration
[10].
In general, it is advantageous to use a resolver that is close, in
both a network topology and geographic sense, to the querier. Such
proximity reduces the query latency due to reduced round-trip times
and, in many cases, such servers will already have the necessary
results cached, or at least pointers to appropriate authoritative
resolvers and may already have established security associations with
the appropriate resolver.
7. Messages
LUMP currently defines two request/response interactions: the first
one requests a mapping from a geo or civic location and the second
one asks the server for its coverage region.
The mapping and coverage region query indicate the desired service.
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Results returned by both queries indicate their validity (expiration)
time.
If a civic-location query for a mapping does not contain a precise
mapping, it contains a civic location object that indicates which
parts of the civic address have been used in the mapping. If there
is no precise match, zero or more civic location objects are returned
indicating possible alternatives that do exist within the mapping
database.
Region queries are only meaningful if addressed to authoritative
servers. These servers respond with a list of polygons and/or civic
address descriptions indicating their coverage region.
LUMP uses web services as its protocol substrate. The schema for the
LUMP messages is shown in Figure 1, while the web services definition
is shown in Figure 2.
<schema targetNamespace="urn:ietf:params:xml:ns:lump"
xmlns:ca="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns="http://www.w3.org/2000/10/XMLSchema">
<include schemaLocation="civic.xsd"/>
<include schemaLocation="geopriv.xsd"/>
<complexType name="empty"/>
<element name="mappingRequest" type="mappingRequestType"/>
<element name="mappingResponse" type="mappingResponseType"/>
<element name="regionRequest" type="mappingRequestType"/>
<element name="regionResponse" type="mappingResponseType"/>
<complexType name="mappingRequestType">
<sequence>
<element name="service" type="anyURI"/>
<choice>
<element name="recurse" type="empty"/>
<element name="redirect" type="empty"/>
</choice>
<choice>
<element name="civic" type="ca:civicAddress"/>
<element name="geo" type="ca:civicAddress"/>
</choice>
</sequence>
</complexType>
<complexType name="mappingResponseType">
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<sequence>
<element name="URI" type="anyURI"
minOccurs="0" maxOccurs="unbounded"/>
<element name="civicMatch" type="ca:civicAddress"
minOccurs="0" maxOccurs="1"/>
<element name="civicAlternate" type="ca:civicAddress"
minOccurs="0" maxOccurs="unbounded"/>
</sequence>
<attribute name="expires" type="dateTime" use="required"/>
</complexType>
<complexType name="regionRequestType">
<sequence>
<element name="service" type="anyURI"/>
</sequence>
</complexType>
<complexType name="regionResponseType">
<sequence>
<element name="civicRegion" type="ca:civicAddress"
minOccurs="0" maxOccurs="unbounded"/>
<element name="geoRegion" type="ca:locInfoType"
minOccurs="0" maxOccurs="unbounded"/>
</sequence>
<attribute name="expires" type="dateTime" use="required"/>
</complexType>
</schema>
Schema for LUMP
Figure 1
<?xml version="1.0" encoding="UTF-8"?>
<definitions name="LUMP"
xmlns="http://schemas.xmlsoap.org/wsdl/"
xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"
xmlns:http="http://schemas.xmlsoap.org/wsdl/http/"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:civic="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xmlns:lump="urn:ietf:params:xml:ns:lump"
xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/"
xmlns:mime="http://schemas.xmlsoap.org/wsdl/mime/"
xmlns:tns="urn:ietf:params:xml:ns:lump:proto"
targetNamespace="urn:ietf:params:xml:ns:lump:proto">
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<import namespace="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
location="http://www.cs.columbia.edu/~hgs/tmp/civic.xsd"/>
<import namespace="urn:ietf:params:xml:ns:pidf:geopriv10"
location="http://www.cs.columbia.edu/~hgs/tmp/geopriv.xsd"/>
<import namespace="urn:ietf:params:xml:ns:lump"
location="http://www.cs.columbia.edu/~hgs/tmp/lump.xsd"/>
<message name="mappingRequestMessage">
<part name="body" element="lump:mappingRequest"/>
</message>
<message name="mappingReponseMessage">
<part name="body" element="lump:mappingResponse"/>
</message>
<wsdl:portType name="mappingPortType">
<wsdl:operation name="mapping" parameterOrder="body">
<wsdl:input message="tns:mappingRequestMessage"/>
<wsdl:output message="tns:mappingResponseMessage"/>
</wsdl:operation>
</wsdl:portType>
<wsdl:binding name="lumpSoapBinding" type="tns:mappingPortType">
<wsdlsoap:binding style="rpc"
transport="http://schemas.xmlsoap.org/soap/http"/>
<wsdl:operation name="mapping">
<wsdlsoap:operation soapAction=""/>
<wsdl:input>
<wsdlsoap:body
encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"
use="encoded"/>
</wsdl:input>
<wsdl:output>
<wsdlsoap:body
encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"
use="encoded"/>
</wsdl:output>
</wsdl:operation>
</wsdl:binding>
<wsdl:service name="lump">
<wsdl:port binding="tns:lumpSoapBinding" name="mappingPortType">
<wsdlsoap:address location="http://www.example.com"/>
</wsdl:port>
</wsdl:service>
</definitions>
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Schema for LUMP
Figure 2
8. Configuring Emergency Dial Strings
For the foreseeable future, some user devices and software will
emulate the user interface of a telephone, i.e., the only way to
enter call address information is via a 12-button keypad. Also,
emergency numbers are likely to used until essentially all
communication devices feature IP connectivity and an alphanumeric
keyboard. Unfortunately, more than 60 emergency numbers are in use
throughout the world, with many of those numbers serving non-
emergency purposes elsewhere, e.g., identifying repair or directory
services. Countries also occasionally change their emergency
numbers, for example, by selecting a number already in use in other
countries of a region (such as 112 in Europe).
Thus, a system that allows devices to be used internationally to
place emergency calls needs to allow devices to discover emergency
numbers automatically. In the system proposed, these numbers are
strictly of local significance and are generally not visible in call
signaling messages.
For simplicity of presentation, this section assumes that emergency
numbers are valid throughout a country, rather than, say, be
restricted to a particular city. This appears likely to be true in
countries likely to deploy IP-based emergency calling solutions. In
addition, the solution proposed also works if certain countries do
not use a national emergency number. There is no requirement that a
country uses a single emergency number for all emergency services,
such as fire, police, or rescue.
For the best user experience, systems should be able to discover two
sets of numbers, namely those used in the user's home country and in
the country the user is currently visiting. The user is most likely
to remember the former, but a companion borrowing a device in an
emergency may only know the local emergency numbers.
Determining home and local emergency numbers is a configuration
problem, but unfortunately, existing configuration mechanisms are
ill-suited for this purpose. For example, a DHCP server might be
able to provide the local emergency number, but not the home numbers.
Similarly, SIP configuration would be able to provide the numbers
valid at the location of the SIP service provider, but even a SIP
service provider with national footprint may serve customers that are
visiting any number of other countries.
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Since dial strings are represented as URLs [5], the problem of
determining local and home emergency numbers is a problem of mapping
locations to a set of URLs, i.e., exactly the problem that LUMP is
solving already.
The mapping operation is almost exactly the same as for determining
the emergency service URL. The only difference is that if a querier
knows the civic location at least to the country level, it will use a
query where the PIDF-LO only includes the country code. If it only
knows its geospatial location, it has to include that longitude and
latitude. The querier uses the service identifiers "dialstring.sos",
"dialstring.sos.fire", etc. The resolver returns the appropriate set
of URLs and, if a geospatial location was used in the query, the
current region map for the country.
Within the LUMP system, emergency calling regions are global
information, i.e., they are distributed using the peer broadcast
mechanism described earlier. Thus, every resolver has access to all
region mappings. This makes it possible that a querier can ask any
resolver for this information, reducing the privacy threat of
revealing its location outside of an emergency call. The privacy
threat is further reduced by the long-lived nature of the
information, i.e., in almost all cases, the querier will have already
cached the national boundary information or country information on
its first visit to the country, using the normal LUMP hinting
mechanism. (Given the modest storage needs, a querier could even
cache all boundary maps.)
9. Security
LUMP addresses the following security issues, usually through the
underlying transport security associations:
Server impersonation: Queriers, cluster members and peers can assure
themselves of the identity of the remote party by using the
facilities in the underlying channel security mechanism, such as
TLS.
Query or query result corruption: To avoid that an attacker can
modify the query or its result, LUMP RECOMMENDS the use of channel
security, such as TLS.
Region corruption: To avoid that a third party or an untrustworthy
member of the LUMP server population introduces a region map that
it is not authorized for, any peer introducing a new region map
MUST sign the object by encapsulating the data into a CMS wrapper.
A recipient MUST verify, through a local policy mechanism, that
the signing entity is indeed authorized to speak for that region.
Determining who can speak for a particular region is inherently
difficult unless there is a small set of authorizing entities that
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resolvers can trust. Receiving resolvers should be particularly
suspicious if an existing region map is replaced with a new one
with a new resolver address.
Additional threats that need to be addressed by operational measures
include denial-of-service attacks.
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] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.
[3] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[4] Peterson, J., "A Presence-based GEOPRIV Location Object Format",
draft-ietf-geopriv-pidf-lo-03 (work in progress),
September 2004.
[5] Rosen, B., "Dialstring parameter for the sip URI",
draft-rosen-iptel-dialstring-02 (work in progress), July 2005.
10.2 Informative References
[6] Guttman, E., Perkins, C., Veizades, J., and M. Day, "Service
Location Protocol, Version 2", RFC 2608, June 1999.
[7] Zhao, W., Schulzrinne, H., and E. Guttman, "Mesh-enhanced
Service Location Protocol (mSLP)", RFC 3528, April 2003.
[8] Newton, A. and M. Sanz, "IRIS: The Internet Registry
Information Service (IRIS) Core Protocol", RFC 3981,
January 2005.
[9] Krochmal, M. and S. Cheshire, "DNS-Based Service Discovery",
draft-cheshire-dnsext-dns-sd-03 (work in progress), July 2005.
[10] Petrie, D., "A Framework for Session Initiation Protocol User
Agent Profile Delivery", draft-ietf-sipping-config-framework-07
(work in progress), July 2005.
[11] Schulzrinne, H. and R. Marshall, "Requirements for Emergency
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Context Resolution with Internet Technologies",
draft-schulzrinne-ecrit-requirements-01 (work in progress),
July 2005.
[12] Schulzrinne, H., "Location-to-URL Mapping Architecture and
Framework", draft-schulzrinne-ecrit-mapping-arch-00 (work in
progress), October 2005.
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
Appendix A. Acknowledgments
Richard Stastny, ... provided helpful comments.
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Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
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