Location Hiding: Problem Statement and Requirements
draft-ietf-ecrit-location-hiding-req-01.txt

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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 end points 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). For determining the PSAP Uniform Resource Identifier (URI) the usage of the Location-to-Service Translation (LoST) Protocol is envisioned.

This document explores the architectural impact for the IETF emergency services architecture 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.

This document provides a problem statement and lists requirements.

Table of Contents

1.  Introduction
    1.1.  Emergency Services Architecture
    1.2.  Location Hiding
    1.3.  Location by Reference
2.  Terminology
3.  Requirements
    3.1.  High-Level Requirements
    3.2.  Detailed Requirements
    3.3.  Desirable Properties
4.  IANA Considerations
5.  Security Considerations
6.  Acknowledgments
7.  References
    7.1.  Normative References
    7.2.  Informative References
§  Authors' Addresses
§  Intellectual Property and Copyright Statements

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 [I‑D.ietf‑ecrit‑framework] (Rosen, B., Schulzrinne, H., Polk, J., and A. Newton, “Framework for Emergency Calling using Internet Multimedia,” July 2009.), describes an architecture where location information is provided by access networks to end points 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] (Hardie, T., Newton, A., Schulzrinne, H., and H. Tschofenig, “LoST: A Location-to-Service Translation Protocol,” August 2008.) allows callers and other call-routing entities to determine the PSAP Uniform Resource Identifier (URI) for a specific geographical location together with a service URI [RFC5031] (Schulzrinne, H., “A Uniform Resource Name (URN) for Emergency and Other Well-Known Services,” January 2008.). The basic architecture is shown in Figure 1 of [I‑D.ietf‑ecrit‑framework] (Rosen, B., Schulzrinne, H., Polk, J., and A. Newton, “Framework for Emergency Calling using Internet Multimedia,” July 2009.) and further detailed in the message flow in Figure 2 of [I‑D.ietf‑ecrit‑framework] (Rosen, B., Schulzrinne, H., Polk, J., and A. Newton, “Framework for Emergency Calling using Internet Multimedia,” July 2009.).

For emergency services, location information is needed in three ways:

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 types of incidents
3. Additionally, a VSP may need to verify that an 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.

It is very important to note that this document only discusses location hiding in the context of location information that is need for call routing. ISPs have no interest or even legal basis for hiding location information from emergency services personnel.

1.2.  Location Hiding

In some cases, location providers (e.g., Internet Access Providers (IAPs) and/or the Internet Service Providers (ISPs)) are unwilling to provide precise location information to end points or VSPs, as is called for in the above model. The decision to deny location 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 to make location information available without the ability to charge for it.

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 can be found in [I‑D.ietf‑geopriv‑l7‑lcp‑ps] (Tschofenig, H. and H. Schulzrinne, “GEOPRIV Layer 7 Location Configuration Protocol; Problem Statement and Requirements,” July 2009.). The requirements for obtaining an LbyR via the LCP and the corresponding dereferencing step can be found in [I‑D.ietf‑geopriv‑lbyr‑requirements] (Marshall, R., “Requirements for a Location-by-Reference Mechanism,” November 2009.).

HTTP Enabled Location Delivery (HELD), see [I‑D.ietf‑geopriv‑http‑location‑delivery] (Barnes, M., Winterbottom, J., Thomson, M., and B. Stark, “HTTP Enabled Location Delivery (HELD),” August 2009.), 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. This requires a trust relationship between the PSAP and the ISP. 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.

Unfortunately, a location reference is not compatible with LoST, as LoST requires an information value rather than a reference. Also, LoST servers may be operated by the VSP, which may not have a trust relationship with the ISP.

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 [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.), 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 [I‑D.ietf‑geopriv‑l7‑lcp‑ps] (Tschofenig, H. and H. Schulzrinne, “GEOPRIV Layer 7 Location Configuration Protocol; Problem Statement and Requirements,” July 2009.).

3.  Requirements

3.1.  High-Level Requirements

Req-A:

There MUST be a way an access network can withhold detailed location information from any entity it wishes to, and specifically, the endpoint, and a VSP.

Req-B:

The ISP/IAP MUST support the ability of the endpoint or the VSP to route emergency calls.

Req-C:

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.

Req-D:

The PSAP MUST be provided precise location information (by value) for emergency callers. The endpoint and/or VSP may provide this information either by value or by reference.

3.2.  Detailed Requirements

Req-1:

The proposed solution MUST NOT assume a business or trust relationship between the caller's VSP and the caller's ISP.

Req-2:

A solution MUST consider deployment scenarios where a VSP is outside the jurisdiction of the PSAP.

Req-3:

The solution MUST offer automated discovery of servers and other behavior, i.e., no manual configuration can be assumed.

Req-4:

The steps needed by the endpoint for emergency calling SHOULD be no different when location is withheld vs. when location is not withheld. In particular, user agents cannot require additional configuration to discover which particular environment (hiding or no hiding) they find themselves in.

Req-5:

The solution SHOULD work for non-SIP entities, without the ISP/IAP having to support these protocols.

Req-6:

The solution MUST work if PSAP boundaries have holes.

Req-7:

The solution MUST NOT assume the existence of Emergency Service Routing Proxies (ESRPs) per country, state and city.

Req-8:

The solution MUST consider that service boundaries for different emergency services may differ, but they overlap at the location of the caller.

Req-9:

Though the solution MAY add steps to the emergency call routing process described in [framework], 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-10:

The solution MUST allow the end host to determine PSAP/ESRP URLs prior to the call, for all emergency services.

Req-11:

The solution MUST allow UAs to discover at least their dial string ahead of the emergency call.

Req-12:

The solution MUST have minimal impact on UAs.

Req-13:

The solution MUST NOT interfere with the use of LoST for non-emergency services.

Req-14:

Deleted

Req-15:

Calls may reach a PSTN gateway, rather than the PSAP directly.

3.3.  Desirable Properties

• 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.
  
  
• The solution SHOULD minimize the impact on LoST, SIP conveyance [I‑D.ietf‑sip‑location‑conveyance] (Polk, J. and B. Rosen, “Location Conveyance for the Session Initiation Protocol,” March 2009.) and DHCP.
  
  
• The solution SHOULD NOT rely on DHCP for LoST configuration, as the information in the DHCP server provided by the ISP may not reach the UA, due to NATs.

4.  IANA Considerations

This document does not require actions by IANA.

5.  Security Considerations

This document does not raise additional security consideration beyond those mentioned in [I‑D.ietf‑geopriv‑l7‑lcp‑ps] (Tschofenig, H. and H. Schulzrinne, “GEOPRIV Layer 7 Location Configuration Protocol; Problem Statement and Requirements,” July 2009.) and discussed in this document.

6.  Acknowledgments

We would like to thank the following ECRIT working group members (in no particular order) for their contributions:

• Andrew Newton (andy@hxr.us)
• James Winterbottom (James.Winterbottom@andrew.com)
• Brian Rosen (br@brianrosen.net)
• Richard Barnes (rbarnes@bbn.com)
• Marc Linsner (mlinsner@cisco.com)
• Ted Hardie (hardie@qualcomm.com)

7.  References

7.1. Normative References

7.2. Informative References

Authors' Addresses

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