GeoPriv                                                 R. Marshall, Ed.
Internet-Draft                                                       TCS
Intended status: Informational                         September 5, 2007
Expires: March 8, 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 a Location-by-Reference approach to handling location information
   within SIP signaling and other Internet messaging.  The key for a
   Location-by-Reference mechanism is the Location URI, which is a
   reference to a location, and is used by either an end-device or a
   middlebox to represent a location, and is used as a key by a
   dereferencing protocol to get a usable form of location.  An example
   application for which the Location-by-Reference mechanism is used is
   emergency call routing with voice-over-IP (VoIP) and general Internet
   multimedia systems, where Internet protocols are used end-to-end.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements Terminology . . . . . . . . . . . . . . . . . . .  5
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.1.  Definition of Terms  . . . . . . . . . . . . . . . . . . .  6
   4.  Basic Actors . . . . . . . . . . . . . . . . . . . . . . . . .  8
   5.  High-Level Requirements for a  Location Configuration
       Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   6.  High-Level Requirements for a  Location Dereference
       Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 17
     10.2. Informative References . . . . . . . . . . . . . . . . . . 17
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 18
   Intellectual Property and Copyright Statements . . . . . . . . . . 19

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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 Location-by-
   Reference mechanism.

   Since possessing the location URI alone is insufficient to perform
   location-based routing, the location URI must be dereferenced.  Once
   the actual location information is returned to a location recipient,
   it can then be used as input to some location-based service, such as
   in the case of routing a VoIP-based emergency call.

   This document lists a set of requirements for a Location-by-Reference
   (LbyR) mechanism, using a location URI within the SIP protocol for
   the purpose of executing a location-based service routing request.

   There are a variety of actions in which a location URI can be used.
   Included in this list is the action of 'location configuration', or
   the acquisition of the location into an end device or middlebox,
   'location conveyance', which is the shuttling of location between SIP
   signaling nodes, and, 'location dereferencing', which we define as
   the action of exchanging a location URI for the actual location
   information it points to at a dereference server, which we call a
   Location Information Server, or LIS.

   Each of these actions are represented by specific individual
   protocols.  A Location Configuration Protocol (LCP), is used by a
   device or middlebox to acquire a location which already exists
   (examples of this protocol include DHCP, LLDP-MED, and HELD).  By
   conveyance protocol, we mean a protocol which transports a location
   URI along from node to node according to specific rules (e.g., SIP).
   A Location Dereferencing Protocol (LDP), is used by a client to
   resolve a location URI in exchange for location information at a LIS.

   Though conveyance of a location URI may be discussed in general
   terms, any requirements for conveyance using LbyR are not included,
   and are considered out of scope.

   In our SIP example, the LbyR is setup, instead of having a content
   identifier (cid:) pointing to a location object within a SIP body, to
   have a location URI carried in the SIP Geolocation header.

   In constrast to LbyR, a direct access to location is equivalent to

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   having a location object included along with the signaling, (e.g., a
   PIDF-LO), is referred to as the Location-by-Value (LbyV) mechanism,
   and is treated as out of scope for this document.  A separate draft
   document exists which describes, for both LbyR and LbyV scenarios, a
   way to convey location within SIP [I-D.ietf-sip-location-conveyance].

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

   Requirements are outlined separately for the configuration step
   (LCP), (Section 5), followed by an additional list of requirements
   targeted toward the dereferencing step (LDP) (Section 6).

   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

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" in this document are to be interpreted as described in
   RFC 2119 [RFC2119].

   This document outlines only requirements for an LbyR mechanism which
   is used by two different protocols, a Location Configuration
   Protocol, and a Location Derferencing Protocol.  Each of these
   protocols has its own unique client and server interactions, and the
   requirements here are not intended to state what either an LCP or LDP
   host client or server is expected to do, but rather which
   requirements must be met by both the LCP and LDP interface protocols.

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3.  Terminology

3.1.  Definition of Terms

   Several of the terms presented below are based on Geopriv
   Requirements [RFC3693], and in some cases, extended to include
   additional language to support the LbyR model.

   Civic location:  A described location based on some understood
      location reference system, such a jurisdictions or postal delivery
      grid.  A street address valid within the USPS system is a common

   Coordinate location:  A reference to a geographic point which is able
      to be located as described by a set of defined coordinates within
      a geographic coordinate system, such as latitude and longitude,
      within the WGS-84 datum.  For example, 2-D geographic location is
      defined as an (x,y) coordinate value pair according to the
      distance north or south of the equator and east or west of the
      prime meridian.  A coordinate location may be absolute, or may
      have associated uncertainty related to it's exact position,
      depending on how it is represented.

   Location:  Either a geographic coordinate or feature representation
      based on a specific coordinate reference system, or by other
      identifiable information such as a street number and street name
      within a civic, postal, or abstract location reference system.

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

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

   Location Configuration Protocol (LCP):  A protocol which is used by a
      client to acquire location or a location URI from a location
      configuration server (e.g., (LIS)), based on information unique to
      the client.

   Location Dereference Protocol (LDP):  A protocol which is used by a
      client to query a location dereference server (e.g., (LIS)), based
      on location URI input and which returns location information
      (e.g., a PIDF-LO).

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   Location Information Server (LIS):  The entity which receives a
      client request for either location or a location reference.  In
      the latter case, also performs the dereference function for a
      Location Refernce Identifier, in the context of the Location-by-
      Reference model.  May also be referred to as a Location
      Information Server (LIS).  In the SIP Presence architecture, the
      LIS may be referred to as a Presence Server (PS).  In this
      document the LIS is an instance of an LS.

   Location Object (LO):  An object conveying location information (and
      possibly privacy rules) to which Geopriv security mechanisms and
      privacy rules are to be applied.

   Location Recipient (LR):  The entity that receives location
      information.  It may have asked for this location explicitly (by
      sending a query containing an location URI to a location
      configuration server), or it may receive this location

   Location Server (LS):  The entity to which a LG publishes location
      objects, the recipient of queries from location receivers, and the
      entity that applies rules designed by the rule maker.

   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 (LbyR) mechanism.  A location URI is provided by a
      location configuration server, based on a client request, and is
      the input used by the dereference protocol to retrieve the
      associated location from a dereference server.  It is assumed that
      a LIS can function both as a configuration server and dereference

   Rule Maker (RM):  The authority that creates rules governing access
      to location information for a target (typically, this it the
      target themselves).

   Target:  A person, end device, or other entity whose location is
      communicated by a Geopriv Location Object.

   Using Protocol:  A protocol (e.g., SIP) which carries a Location
      Object or an Location Reference Identifier.

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4.  Basic Actors

   LbyR with Location Subscription

   The LbyR mechanism can be used via a normal query/response mode, or
   alternatively, by using a subscription model to get updated location.

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

    Figure 1: Shows the assumed communication model  for a layer 7 (L7)
                               LCP and LDP:

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

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   and (3).

   The following list describes the location subscription approach:

   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 LCP 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 for a  Location Configuration Protocol

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

   C1. Location URI support - LCP:  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 LCP MUST support the ability to
      specify to the server, the length of time that a location URI will
      be valid.

      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.  A configurable carried in the
      LCP for a location URI ensures that the location reference becomes
      invalid based on some internal LIS settings.

   C3. Location URI cancellation:  The LCP MUST 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 has to be a way to nullify the
      location URI.  (This may be accomplished by setting the C2
      configurable to 'expire=now', for example.)

   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

   C5. Identity Protection - LCP :  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.

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   C6. Reuse flag default:  The LCP MUST support the default condition
      of a requested location URI being repeatedly reused.

      Motivation: The requestor of a location URI, shouldn't need to
      specify any special flag in order to receive a location URI which
      can later be used repeatedly, such as for an updated location.

   C7. One-time-use:  The LCP MUST support the ability for the client to
      request a 'one-time-use' location URI (e.g., via a reuse flag

      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.

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6.  High-Level Requirements for a  Location Dereference Protocol

   Below, we summarize high-level design requirements needed for a
   location-by-reference mechanism.

   D1. Location URI support - LDP:  The LDP 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 LCP and those used by a

   D2. Location URI expiration status:  The LDP 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 LCP
      parameters, and it is therefore useful to convey the expired
      status of the location URI in the LDP.

   D3. Authentication:  The LDP MUST support either client-side and
      server-side authentication between client and server.

      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:  Location URI dereferencing MUST
      result in a well-formed PIDF-LO.

      Motivation: This is in order to ensure both interoperation
      consistancy and 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 LDP MUST support the ability for the same
      location URI to be resolved more than once, based on server
      settings and LCP parameters.

      Motivation: According to LCP parameters, there may or may not be a
      limit on the number of dereferencing actions at the dereference

   D6. Updated location:  The LDP MUST support the ability for the same
      location URI to be resolved into a continuum of location values
      (e.g., location updates).

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      Motivation: A location URI when reused may not always result in
      the same location value, but may be a mixture of unchanged and
      changed location values.

   D7. Location form:  The LDP MUST support dereferenced location in
      both coordinate and civic forms.

      Motivation: It is important that the LDP not limit which type of
      location gets dereferenced, since it is assumed that some
      dereference servers may provide coordinate form of location only,
      others may provide civic only, while some may provide both forms
      of location.

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7.  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 a separate geopriv

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8.  IANA Considerations

   This document does not require actions by the IANA.

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9.  Acknowledgements

   I 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.

   I also would like to thank Andrew Newton; Martin Dawson; Henning
   Schulzrinne; Marc Linsner; Brian Rosen; Ted Hardie; James M. Polk;
   James Winterbottom; Martin Thomson; John Schnizlein; Barbara Stark;
   Jon Peterson; Allison Mankin; Randall Gellens; Cullen Jennings;
   Richard Barnes; Keith Drage; Rohan Mahy; and Hannes Tschofenig, for
   their individual contributions and comments.

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10.  References

10.1.  Normative References

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

10.2.  Informative References

              Barnes, M., "HTTP Enabled Location Delivery (HELD)",
              draft-ietf-geopriv-http-location-delivery-01 (work in
              progress), July 2007.

              Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7
              Location Configuration Protocol; Problem Statement and
              Requirements", draft-ietf-geopriv-l7-lcp-ps-04 (work in
              progress), August 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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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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