Location Hiding: Problem Statement and Requirements
RFC 6444

Document Type RFC - Informational (January 2012; No errata)
Authors Laura Liess  , Andres Kuett  , Henning Schulzrinne  , Hannes Tschofenig  , Barbara Stark 
Last updated 2018-12-20
Replaces draft-schulzrinne-ecrit-location-hiding-req
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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
                                                                A. Kuett
                                                            January 2012

          Location Hiding: Problem Statement and Requirements


   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

   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

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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
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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
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   Without obtaining an adequate license from the person(s) controlling
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   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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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 [RFC6443], 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 [RFC5222] 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 [RFC5031].  The basic architecture is
   shown in Figure 1 of [RFC6443] and further detailed in the message
   flow in Figure 2 of [RFC6443].

   For emergency services, location information is needed for three

   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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   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 [RFC5687].
   The requirements for obtaining an LbyR via the LCP and the
   corresponding dereferencing step can be found in [RFC5808].

   HTTP Enabled Location Delivery (HELD), see [RFC5985], is an
   instantiation of the LCP concept and allows LbyVs and LbyRs to be

   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 [RFC5222] 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

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2.  Terminology

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119], 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 [RFC5687].

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

   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

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   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 [RFC5964].)

   Req-11:  The solution MUST NOT assume the existence of Emergency
            Service Routing Proxies (ESRPs) per country, state, and

   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 [RFC6443], 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 [RFC6442], and DHCP.

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   Req-21:  The solution SHOULD NOT break in the presence of NATs and
            SHOULD consider the presence of legacy devices, as described
            in [RFC5687].

4.  Security Considerations

   This document does not raise additional security consideration beyond
   those mentioned in [RFC5687] 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

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

   [RFC5031]  Schulzrinne, H., "A Uniform Resource Name (URN) for
              Emergency and Other Well-Known Services", RFC 5031,
              January 2008.

   [RFC5069]  Taylor, T., Tschofenig, H., Schulzrinne, H., and M.
              Shanmugam, "Security Threats and Requirements for
              Emergency Call Marking and Mapping", RFC 5069,
              January 2008.

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

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   [RFC5687]  Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7
              Location Configuration Protocol: Problem Statement and
              Requirements", RFC 5687, March 2010.

   [RFC5808]  Marshall, R., "Requirements for a Location-by-Reference
              Mechanism", RFC 5808, May 2010.

   [RFC5964]  Winterbottom, J. and M. Thomson, "Specifying Holes in
              Location-to-Service Translation (LoST) Service
              Boundaries", RFC 5964, August 2010.

   [RFC5985]  Barnes, M., "HTTP-Enabled Location Delivery (HELD)",
              RFC 5985, September 2010.

   [RFC6442]  Polk, J., Rosen, B., and J. Peterson, "Location Conveyance
              for the Session Initiation Protocol", RFC 6442,
              December 2011.

   [RFC6443]  Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,
              "Framework for Emergency Calling Using Internet
              Multimedia", RFC 6443, December 2011.

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Authors' Addresses

   Henning Schulzrinne
   Columbia University
   Department of Computer Science
   450 Computer Science Building
   New York, NY  10027
   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
   EMail: L.Liess@telekom.de
   URI:   http://www.telekom.de

   Hannes Tschofenig
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  02600
   Phone: +358 (50) 4871445
   EMail: Hannes.Tschofenig@gmx.net
   URI:   http://www.tschofenig.priv.at

   Barbara Stark
   725 W Peachtree St, NE
   Atlanta, GA  30308
   Phone: +1 404 499 7026
   EMail: barbara.stark@att.com

   Andres Kuett
   EMail: andres.kytt@skype.net

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