GeoPriv                                                 R. Marshall, Ed.
Internet-Draft                                                       TCS
Intended status: Informational                          October 11, 2007
Expires: April 13, 2008

           Requirements for a Location-by-Reference Mechanism

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   Copyright (C) The IETF Trust (2007).

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   This document defines terminology and provides requirements relating
   to Location-by-Reference approach to handling location information
   within signaling and other Internet messaging.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements Terminology . . . . . . . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Terms  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Basic Actors . . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  High-Level Requirements  . . . . . . . . . . . . . . . . . . .  8
     5.1.  Requirements for a  Location Configuration Protocol  . . .  8
     5.2.  Requirements for a  Location Dereference Protocol  . . . .  9
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Appendix A.  Change log  . . . . . . . . . . . . . . . . . . . . . 15
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16
   Intellectual Property and Copyright Statements . . . . . . . . . . 17

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1.  Introduction

   Location-based services rely on ready access to location information,
   which can be through a direct or indirect mechanism.  While there is
   already a direct mechanism which exists to provide location as part
   of the SIP signaling protocol, an alternative mechanism has been
   developed for handling location indirectly, via a location reference,
   a reference which points to the actual location information.  This
   reference is called the location URI, and is used by the mechanism we
   call Location-by-Reference, or LbyR.

   Each of the actions by which a location URI can be used is
   represented by specific individual protocol.  For example, a Location
   Configuration Protocol, is used by a device or middlebox to acquire a
   location which already exists (examples of this protocol include
   DHCP, LLDP-MED, and HELD [I-D.ietf-geopriv-http-location-delivery]).
   The location configuration protocol problem statement and
   requirements document can be found in [I-D.ietf-geopriv-l7-lcp-ps].
   The action of conveying a location URI along from node to node
   according to specific rules in SIP, for example, is known as a
   conveyance protocol.  A location dereferencing protocol, is used by a
   client to resolve a location URI in exchange for location information
   from a dereference server (e.g., a LIS).

   The structure of this document first defines terminology, or points
   to the appropriate draft where defined, in Section 3.  Then a short
   discussion on the basic elements which show LbyR.  This section on
   actors, Section 4 includes a basic model, and describes the steps
   which the LbyR mechanism takes.

   Requirements are outlined separately for location configuration,
   Section 5.1, followed by those for a dereferencing protocol,
   Section 5.2.

   Location-by-Value, called LbyV, in contrast to LbyR, is a direct
   location conveyance approach and includes the location object, e.g.,
   a PIDF-LO [RFC4119] in the SIP signaling.  Location conveyance is out
   of scope for this document (see [I-D.ietf-sip-location-conveyance]
   for an explanation of conveyance of location including both LbyR and
   LbyV scenarios.

   Location determination, which may include the processes of manual
   provisioning, automated measurements, or location transformations,
   (e.g., geo-coding), are beyond the scope of this document.

   A detailed discussion of Identity information related to the caller,
   subscriber, or device, as associated to location or location URI, is
   also out of scope.

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2.  Requirements Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

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3.  Terminology

   This document reuses the terminology of [RFC3693], such as Location
   Server (LS), Location Recipient (LR), Rule Maker (RM), Target,
   Location Generator (LG), Location Object (LO), and Using Protocol:

3.1.  Terms

   Location-by-Value (LbyV):  The mechanism of representing location
      either in configuration or conveyance protocols, (i.e., the actual
      included location value).

   Location-by-Reference (LbyR):  The mechanism of representing location
      either in configuration, conveyance, or in dereferencing protocols
      as an identifier which refers to a fully specified location,
      (i.e., a pointer to the actual location value).

   Location Configuration Protocol:  A protocol which is used by a
      client to acquire either location or a location URI from a
      location configuration server, based on information unique to the

   Location Dereference Protocol:  A protocol which is used by a client
      to query a location dereference server, based on location URI
      input and which returns location information.

   Location URI:  An identifier which serves as a pointer to a location
      record on a remote host (e.g., LIS).  Used within an Location-by-
      Reference mechanism, a location URI is provided by a location
      configuration server, and is used as input by a dereference
      protocol to retrieve location from a dereference server.

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4.  Basic Actors

   In mobile wireless networks it is not efficient for the end host to
   periodically query the LIS for up-to-date location information.  This
   is especially the case when power is a constraint or a location
   update is not immediately needed.  Furthermore, the end host might
   want to delegate the task of retrieving and publishing location
   information to a third party, such as to a presence server.  Finally,
   in some deployments, the network operator may not want to make
   location information widely available.

   These use scenarios motivated the introduction of the LbyR concept.
   Depending on the type of reference, such as HTTP/HTTPS or SIP
   Presence URI, different operations can be performed.  While an HTTP/
   HTTPS URI can be resolved to location information, a SIP Presence URI
   provides further benefits from the SUBSCRIBE/NOTIFY concept that can
   additionally be combined with location filters

              +-----------+  Geopriv      +-----------+
              |           |  Location     | Location  |
              |    LIS    +---------------+ Recipient |
              |           |  Dereference  |           |
              +-----+-----+  Protocol (3) +----+------+
                    |                        --
                    | Geopriv              --
                    | Location           --
                    | Configuration    --
                    | Protocol       --
                    | (1)          --      Geopriv
                    |            --        Using Protocol
                    |          --          (e.g., SIP)
              +-----+-----+  --            (2)
              | Target /  |--
              | End Host  +
              |           |

    Figure 1: Shows the assumed communication  model for both a layer 7
       location configuration protocol and a dereference  protocol:

   Note that there is no requirement for using the same protocol in (1)
   and (3).

   The following list describes the location subscription approach:

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   1.  The end host discovers the LIS.

   2.  The target (end host) sends a request to the LIS asking for a
   location URI, as shown in (1) of Figure 1.

   3.  The LIS responds to the request and includes a location object
   along with a subscription URI.

   4.  The Target puts the subscription URI into a SIP message and
   forwards it to a Location Recipient via a using protocol, as shown in
   (2) of Figure 1.  The Location Recipient subscribes to the obtained
   subscription URI (see (3) of Figure 1) and potentially uses a
   location filter (see [I-D.ietf-geopriv-loc-filters]) to limit the
   notification rate.

   5.  If the Target moves outside a certain area, indicated by a
   location filter, the Location Recipient will receive a notification.

   Note that the Target may also act in the role of the Location
   Recipient whereby it would subscribe to its own location information.
   For example, the Target obtains a subscription URI from the Geopriv
   L7 Location Configuration Protocol.  It subscribes to the URI in
   order to obtain its current location information.  A service boundary
   indicates the bounded extent up to which the device can move without
   the need to have an updated location, since a re-query with any
   location within the boundary would result in the same answer returned
   from a location-based service.

   For LbyR, the LIS needs to maintain a list of randomized location
   URIs for each host, timing out each of these URIs after the reference
   expires.  Location URIs need to expire to prevent the recipient of
   such a URI from being able to (in some cases) permanently track a
   host.  Furthermore, an expiration mechanism also offers garbage
   collection capability for the LIS.

   Location URIs must be designed to prevent adversaries from obtaining
   a known Target's location.  There are at least two approaches: The
   location URI contains a random component which helps obscure
   sequential updates to location, yet still allows any holder of the
   location URI to obtain location information.  Alternatively, the
   location URI can remain public and the LIS performs access control
   via a separate authentication mechanism, such as HTTP digest or TLS
   client side authentication, when resolving the reference to a
   location object.

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5.  High-Level Requirements

   This document outlines only requirements for an LbyR mechanism which
   is used by two different protocols, a location configuration
   protocol, and a location dereferencing protocol.  Each of these
   protocols has its own unique client and server interactions, and the
   requirements here are not intended to state what a client or server
   is expected to do, but rather which requirements must be met by
   either the configuration or dereferencing protocol itself.

5.1.  Requirements for a  Location Configuration Protocol

   Below, we summarize high-level design requirements needed for a
   location-by-reference mechanism as used within the location
   configuration protocol.

   C1. Location URI support:  The configuration protocol MUST support a
      location reference in URI form.

      Motivation: It is helpful to have a consistent form of key for the
      LbyR mechanism.

   C2. Location URI expiration:  The lifetime of a location URI SHOULD
      be indicated.

      Motivation: Location URIs are not intended to represent a location
      forever, and the identifier eventually may need to be recycled, or
      may be subject to a specific window of validity, after which the
      location reference fails to yield a location, or the location is
      determined to be kept confidential.

   C3. Location URI cancellation:  The location configuration protocol
      SHOULD support the ability to request a cancellation of a specific
      location URI.

      Motivation: If the client determines that in its best interest to
      destroy the ability for a location URI to effectively be used to
      dereference a location, then there should be a way to nullify the
      location URI.

   C4. Random Generated:  The location URI MUST be hard to guess, i.e.,
      it MUST contain a cryptographically random component.

      Motivation: There is some benefit to the client if the location
      URI is generated in an obscured manner so that its sequence, for
      example in the case of a client's location update, can't be easy

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   C5. Identity Protection:  The location URI MUST NOT contain any
      information that identifies the user, device or address of record
      within the URI form.

      Motivation: It is important to protect caller identity or contact
      address from being included in the form of the location URI itself
      when it is generated.

   C6. Reuse indicator:  There SHOULD be a way to allow a client to
      control whether a location URI can be resolved once or multiple

      Motivation: The client requesting a location URI may request a
      location URI which has a 'one-time-use' only characteristic, as
      opposed to a location URI having multiple reuse capability.

   C7. Location timestamp:  There SHOULD be a way to allow a client to
      determine whether the dereferenced location information refers to
      the location of the Target at the time when the location URI was
      created or when it was dereferenced.

      Motivation: It is important to distinguish between an original and
      an updated location.

5.2.  Requirements for a  Location Dereference Protocol

   Below, we summarize high-level design requirements needed for a
   location-by-reference mechanism as used within the location
   dereference protocol.

   D1. Location URI support:  The location dereference protocol MUST
      support a location reference in URI form.

      Motivation: It is required that there be consistency of use
      between location URI formats used in an configuration protocol and
      those used by a dereference protocol.

   D2. Location URI expiration status:  The location dereference
      protocol MUST support a message indicating that for a location URI
      which is no longer valid, that the location URI has expired.

      Motivation: Location URIs are expected to expire, based on
      location configuration protocol parameters, and it is therefore
      useful to convey the expired status of the location URI in the
      location dereference protocol.

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   D3. Authentication:  The location dereference protocol MUST support
      either client-side and server-side authentication.

      Motivation: It is reasonable to expect implementations of
      authentication to vary.  Some implementations may choose to
      implement both client-side and server-side authentication, might
      implement one only, or may implement neither.

   D4.  Dereferenced Location Form:  The dereferenced location MUST
      result in a well-formed PIDF-LO.

      Motivation: This is in order to ensure that adequate privacy rules
      can be adhered to, since the PIDF-LO format comprises the
      necessary structures to maintain location privacy.

   D5. Repeated use:  The location dereference protocol MUST support the
      ability for the same location URI to be resolved more than once,
      based on server settings and configuration server parameters.

      Motivation: According to configuration server parameters, it may
      be necessary to have a limit on the number of dereferencing

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6.  Security Considerations

   The LbyR mechanism currently addresses security issues as follows.

      A location URI, regardless of its randomized construction, if
      public, implies no safeguard against anyone being able to
      dereference and get the location.  The randomization of a location
      URI in its naming does help prevent some potential guessing,
      according to some defined pattern.  In the instance of one-time-
      use location URIs, which function similarly to a pawn ticket, the
      argument can be made that with a pawn ticket, possession implies
      permission, and location URIs which are public are protected only
      by privacy rules enforced at the dereference server.

      Additional security issues will be discussed in the geopriv draft,

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7.  IANA Considerations

   This document does not require actions by the IANA.

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8.  Acknowledgements

   We would like to thank the IETF GEOPRIV working group chairs, Andy
   Newton, Allison Mankin and Randall Gellens, for creating the design
   team which initiated this requirements work.  We'd also like to thank
   those design team participants for their inputs, comments, and
   reviews.  The design team included the following folks: Richard
   Barnes; Martin Dawson; Keith Drage; Randall Gellens; Ted Hardie;
   Cullen Jennings; Marc Linsner; Rohan Mahy; Allison Mankin; Roger
   Marshall; Andrew Newton; Jon Peterson; James M. Polk; Brian Rosen;
   John Schnizlein; Henning Schulzrinne; Barbara Stark; Hannes
   Tschofenig; Martin Thomson; and James Winterbottom.

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9.  References

9.1.  Normative References

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

9.2.  Informative References

              Barnes, M., Winterbottom, J., Thomson, M., and B. Stark,
              "HTTP Enabled Location Delivery (HELD)",
              draft-ietf-geopriv-http-location-delivery-02 (work in
              progress), September 2007.

              Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7
              Location Configuration Protocol; Problem Statement and
              Requirements", draft-ietf-geopriv-l7-lcp-ps-05 (work in
              progress), September 2007.

              Mahy, R., "A Document Format for Filtering and Reporting
              Location Notications in the  Presence Information Document
              Format Location Object (PIDF-LO)",
              draft-ietf-geopriv-loc-filters-01 (work in progress),
              March 2007.

              Polk, J. and B. Rosen, "Location Conveyance for the
              Session Initiation Protocol",
              draft-ietf-sip-location-conveyance-08 (work in progress),
              July 2007.

   [RFC3693]  Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and
              J. Polk, "Geopriv Requirements", RFC 3693, February 2004.

   [RFC4119]  Peterson, J., "A Presence-based GEOPRIV Location Object
              Format", RFC 4119, December 2005.

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Appendix A.  Change log

   Changes to this draft in comparison to the -00 version:

   1.  Shortened Abstract and Introduction.

   2.  LDP term gone.  Expansion of Location Dereferencing Protocol,
   deletion of "LDP" acronym throughout, since LDP stands for Label
   Distribution Protocol elsewhere in the IETF.

   3.  LCP term is also gone.  LCP is used as Link Control Protocol
   elsewhere (IETF).

   4.  Reduced the number of terms in the doc.  Referenced other drafts
   or RFCs for repeated terms.

   5.  Requirement C2. changed to indicate that the URI has a lifetime.

   6.  C3.  Softened by changing from a MUST to a SHOULD.

   7.  C6.  Reworded for clarity.

   8.  C7.  Changed the MUST to a SHOULD to reflect a more appropriate

   9.  D6.  Replaced the text to make it clearer.

   10.  D7.  Deleted the requirement since it wasn't an appropriate task
   for the protocol.

   11.  Referenced Richard's security document

   12.  Cleaned up some text.

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Author's Address

   Roger Marshall (editor)
   TeleCommunication Systems, Inc.
   2401 Elliott Avenue
   2nd Floor
   Seattle, WA  98121

   Phone: +1 206 792 2424

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