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IETF RFC 6444
Last modified on Wednesday, January 4th, 2012
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Internet Engineering Task Force (IETF) H. Schulzrinne
Request for Comments: 6444 Columbia University
Category: Informational L. Liess
ISSN: 2070-1721 Deutsche Telekom
H. Tschofenig
Nokia Siemens Networks
B. Stark
AT&T
A. Kuett
Skype
January 2012
Location Hiding: Problem Statement and Requirements
 Abstract
The emergency services architecture developed in the IETF Emergency
Context Resolution with Internet Technology (ECRIT) working group
describes an architecture where location information is provided by
access networks to endpoints or Voice over IP (VoIP) service
providers in order to determine the correct dial string and
information to route the call to a Public Safety Answering Point
(PSAP). To determine the PSAP Uniform Resource Identifier (URI), the
usage of the Location-to-Service Translation (LoST) protocol is
envisioned.
This document provides a problem statement and lists requirements for
situations where the Internet Access Provider (IAP) and/or the
Internet Service Provider (ISP) are only willing to disclose limited
or no location information.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
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/RFC 6444.
Schulzrinne, et al. Informational PAGE 1 
RFC 6444 Location Hiding Requirements January 2012
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
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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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material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction ....................................................3
1.1. Emergency Services Architecture ............................3
1.2. Location Hiding ............................................3
1.3. Location by Reference ......................................4
2. Terminology .....................................................5
3. Requirements ....................................................5
4. Security Considerations .........................................7
5. Acknowledgments .................................................7
6. Normative References ............................................7
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RFC 6444 Location Hiding Requirements January 2012
1. Introduction
1.1. Emergency Services Architecture
The emergency services architecture developed in the IETF Emergency
Context Resolution with Internet Technology (ECRIT) working group,
see [RFC 6443], describes an architecture where location information
is provided by access networks to endpoints or VoIP service providers
in order to determine the correct dial string and information to
route the call to a Public Safety Answering Point (PSAP). The
Location-to-Service Translation (LoST) protocol [RFC 5222] allows
callers and other call-routing entities to determine the PSAP Uniform
Resource Identifier (URI) for a specific geographical location
together with a service URN [RFC 5031]. The basic architecture is
shown in Figure 1 of [RFC 6443] and further detailed in the message
flow in Figure 2 of [RFC 6443].
For emergency services, location information is needed for three
purposes:
1. Emergency call routing to the PSAP that is responsible for a
specific geographical region.
2. Dispatch of the emergency personnel to the scene of an accident,
crime, or other type of incident.
3. Additionally, a Voice Service Provider (VSP) may need to verify
that a call is indeed an emergency call and may therefore require
location information to ensure that calls routed to a specific
URI point to a PSAP.
This document focuses on items (1) and (3). Providing location
information by the ISP to emergency authorities, including PSAPs,
regional emergency management association, and emergency personnel is
typically a legal obligation covered by regulatory frameworks.
1.2. Location Hiding
Internet Access Providers (IAPs) and Internet Service Providers
(ISPs) typically have little incentive to provide location
information to end hosts or independent VSPs (without monetary
compensation) for any purpose, including for emergency call routing.
The decision to deny disclosure of location information can be driven
by a number of technical and business concerns. Some providers may
perceive a risk that allowing users to access location information
for non-emergency purposes or prior to an emergency call will incur
additional server load and thus costs. Other providers may not want
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RFC 6444 Location Hiding Requirements January 2012
to make location information available without the ability to charge
for it. Yet, others fear problems with regard to privacy when
disclosing location information to potentially unknown third parties.
1.3. Location by Reference
The work on the Location Configuration Protocol (LCP) indicated the
need to provide the capability to obtain Location-by-References
(LbyRs) in addition to Location-by-Value (LbyV) from a Location
Information Server (LIS).
The LCP problem statement and requirements document is [RFC 5687].
The requirements for obtaining an LbyR via the LCP and the
corresponding dereferencing step can be found in [RFC 5808].
HTTP Enabled Location Delivery (HELD), see [RFC 5985], is an
instantiation of the LCP concept and allows LbyVs and LbyRs to be
requested.
A location reference may already satisfy the requirement for location
hiding if the PSAP has the appropriate credentials to resolve the
reference. These credentials allow the ISP/IAP to authenticate and
to authorize the party that would like to request location
information. The policy to obtain these credentials allows ISPs/IAPs
to put constraints under which these credentials are handed out.
ISPs/IAPs ideally might want to engage in a business relationship
with the VSP to receive a financial compensation for the service they
provide. On the Internet, the number of VSPs is potentially large
and the VSPs would not want to enter a business contract with
potentially every ISP/IAP worldwide. The number of potential
contracts between ISPs/IAPs and PSAPs is, however, relatively small
as they typically need to have a local relationship as PSAPs provide
their emergency services support in a certain geographical region for
which certain ISPs/IAPs have networks deployed.
Note that the requirement being met here is for delivery of location
information to the PSAP, not for LoST routing or for validation at
the VSP. Since LoST [RFC 5222] requires location by value, location
by reference cannot be used for location-based routing. Also, LoST
servers may be operated by independent parties, including VSPs, which
again may not be able to resolve the reference to location by value.
(Note that LoST is a protocol used for determining the location-
appropriate PSAP based on location information and a Service URN
[RFC 5031].)
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RFC 6444 Location Hiding Requirements January 2012
2. Terminology
The keywords "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], with the
important qualification that, unless otherwise stated, these terms
apply to the design of an solution supporting location hiding, not
its implementation or application.
This document reuses terminology from [RFC 5687].
3. Requirements
Req-1: There MUST be a way for the ISP/IAP to withhold precise
location information from the endpoint and from the VSP.
Req-2: The ISP/IAP MUST support the ability of the endpoint or the
VSP to route emergency calls.
Req-3: The VSP MUST be able to validate that a call purported to be
an emergency call is being routed to a bona fide URI, which
is denoted by being a URI in LoST for the designated
emergency service. This requirement is provided to deal
with potential security problems described in Section 5.1 of
[RFC 5069].
Req-4: The PSAP MUST receive precise location information (by
value) about emergency callers. As such, any solution MUST
be able to provide location information to the PSAP even
while withholding it from the emergency caller.
Req-5: The proposed solution MUST NOT assume a business or trust
relationship between the caller's VSP and the caller's ISP.
Req-6: A solution MUST consider deployment scenarios where a VSP
does not operate in the same jurisdiction as the PSAP.
Req-7: The solution MUST consider that service boundaries for the
various emergency services responsible for a particular
location may differ.
Req-8: The steps needed by the endpoint for emergency calling
SHOULD be no different when location is withheld versus when
location is not withheld. In particular, user agents cannot
require additional configuration to discover in which
particular environment (hiding or no hiding) they find
themselves.
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RFC 6444 Location Hiding Requirements January 2012
Req-9: The solution SHOULD work without the ISP/IAP having to
support SIP and without the need to utilize SIP between the
endpoint and the VSP.
Req-10: The solution MUST work if PSAP boundaries have holes. (For
a discussion about holes in PSAP boundaries and their
encoding, the reader is referred to [RFC 5964].)
Req-11: The solution MUST NOT assume the existence of Emergency
Service Routing Proxies (ESRPs) per country, state, and
city.
Req-12: The solution MUST consider that service boundaries for
different emergency services may differ, but they overlap at
the location of the caller.
Req-13: Though the solution MAY add steps to the emergency call
routing process described in [RFC 6443], these steps MUST NOT
significantly increase call setup latency. For example, the
revised process MUST NOT include "trial-and-error"
operations on its critical path, such as attempts at LbyR
resolutions that may take time to time out.
Req-14: The solution MUST allow the end host to determine PSAP/ESRP
URLs prior to the call, for all emergency services.
Req-15: The solution MUST allow user agents (UAs) to discover at
least their dial string ahead of the emergency call.
Req-16: The solution MUST have minimal impact on UAs, i.e., a
solution is preferred if it does not require a substantially
different emergency service procedure compared to the
procedure of dealing with emergency services where no
location hiding is applied.
Req-17: The solution MUST NOT interfere with the use of LoST for
non-emergency services.
Req-18: The solution MUST allow emergency calls to reach an IP-to-
PSTN gateway rather than the IP-based PSAP directly.
Req-19: The solution MUST NOT shift effort (externality), i.e., the
convenience of the location-hiding ISP MUST NOT impose a
burden on user agents or non-hiding ISPs/IAPs and SHOULD NOT
impose a burden on VSPs.
Req-20: The solution SHOULD minimize the impact on LoST, SIP
conveyance [RFC 6442], and DHCP.
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RFC 6444 Location Hiding Requirements January 2012
Req-21: The solution SHOULD NOT break in the presence of NATs and
SHOULD consider the presence of legacy devices, as described
in [RFC 5687].
4. Security Considerations
This document does not raise additional security consideration beyond
those mentioned in [RFC 5687] and discussed in this document.
5. Acknowledgments
We would like to thank the following ECRIT working group members (in
no particular order) for their contributions:
o Andrew Newton (andy@hxr.us)
o James Winterbottom (James.Winterbottom@andrew.com)
o Brian Rosen (br@brianrosen.net)
o Richard Barnes (rbarnes@bbn.com)
o Marc Linsner (mlinsner@cisco.com)
o Ted Hardie (hardie@qualcomm.com)
The authors would also like to thank Ben Campbell for his Gen-ART
review. Additionally, we would like to thank Jari Arkko, Alexey
Melnikov, Tim Polk, and Dan Romascanu for their IESG review.
6. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 5031] Schulzrinne, H., "A Uniform Resource Name (URN) for
Emergency and Other Well-Known Services", RFC 5031,
January 2008.
[RFC 5069] Taylor, T., Tschofenig, H., Schulzrinne, H., and M.
Shanmugam, "Security Threats and Requirements for
Emergency Call Marking and Mapping", RFC 5069,
January 2008.
[RFC 5222] Hardie, T., Newton, A., Schulzrinne, H., and H.
Tschofenig, "LoST: A Location-to-Service Translation
Protocol", RFC 5222, August 2008.
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RFC 6444 Location Hiding Requirements January 2012
[RFC 5687] Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7
Location Configuration Protocol: Problem Statement and
Requirements", RFC 5687, March 2010.
[RFC 5808] Marshall, R., "Requirements for a Location-by-Reference
Mechanism", RFC 5808, May 2010.
[RFC 5964] Winterbottom, J. and M. Thomson, "Specifying Holes in
Location-to-Service Translation (LoST) Service
Boundaries", RFC 5964, August 2010.
[RFC 5985] Barnes, M., "HTTP-Enabled Location Delivery (HELD)",
RFC 5985, September 2010.
[RFC 6442] Polk, J., Rosen, B., and J. Peterson, "Location Conveyance
for the Session Initiation Protocol", RFC 6442,
December 2011.
[RFC 6443] Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,
"Framework for Emergency Calling Using Internet
Multimedia", RFC 6443, December 2011.
Schulzrinne, et al. Informational PAGE 8
RFC 6444 Location Hiding Requirements January 2012
Authors' Addresses
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
Laura Liess
Deutsche Telekom Networks
Deutsche Telekom Allee 7
Darmstadt, Hessen 64295
Germany
Phone:
EMail: L.Liess@telekom.de
URI: http://www.telekom.de
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
Barbara Stark
AT&T
725 W Peachtree St, NE
Atlanta, GA 30308
USA
Phone: +1 404 499 7026
EMail: barbara.stark@att.com
Andres Kuett
Skype
EMail: andres.kytt@skype.net
Schulzrinne, et al. Informational PAGE 9
RFC TOTAL SIZE: 18495 bytes
PUBLICATION DATE: Wednesday, January 4th, 2012
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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