GeoPriv                                                 R. Marshall, Ed.
Internet-Draft                                                       TCS
Intended status: Informational                              July 9,                          November 3, 2008
Expires: January 10, May 7, 2009

           Requirements for a Location-by-Reference Mechanism
                draft-ietf-geopriv-lbyr-requirements-03
                draft-ietf-geopriv-lbyr-requirements-04

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Abstract

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

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5  6
   3.  Overview of Location-by-Reference  . . . . . . . . . . . . . .  6  7
   4.  High-Level Requirements  . . . . . . . . . . . . . . . . . . .  9 10
     4.1.  Requirements for a  Location Configuration Protocol  . . .  9 10
     4.2.  Requirements for a  Location Dereference Protocol  . . . . 11 12
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14 15
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15 16
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 17
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 18
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 17 18
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 17 18
   Appendix A.  Change log  . . . . . . . . . . . . . . . . . . . . . 18 19
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 20 22
   Intellectual Property and Copyright Statements . . . . . . . . . . 21 23

1.  Introduction

   Location-based

   Since all location-based services rely on ready access to location
   information,
   which this can be accomplished through a some direct means, or
   alternatively, through some indirect mechanism.  While there are
   mechanisms for providing location directly, (e.g., means as part of the SIP
   signaling protocol), an alternative mechanism has been developed for
   handling location indirectly, via a location reference, a pointer to
   the actual location
   information.  This reference is called a location
   URI, and is used by the mechanism  The direct vs. indirect approach we generally call the Location-by-
   Reference mechanism, characterize as
   either Location-by-Value (LbyV), or simply, LbyR.

   The use of Location-by-Reference (LbyR).

   While it is the case that within SIP, location can be handled in a
   direct manner, (i.e., passing the actual location URI is generally applied information around
   in one of the
   following ways:

   1.  Creation/allocation form of a PIDF-LO*), there are additional location URI,
   requirements which apply to certain applications and/or location
   architectures that are only satisfied by a specifying an indirect
   location server based
   on some request mechanism.

   2.  As part of a Location Configuration Protocol, between a target
   and location server*.

   3.  The location dereference process, (between  This document puts forth a dereference  client
   and dereference server).

   4.  Cancellation/expiration set of a requirements
   for such an indirect location URI, by a approach, namely, the LbyR location server
   based on either
   model.

   As justification for a direct target request or LbyR model, consider the following.  In some other action (e.g.,
   timer).

   *In this document, we make no differentiation between a LS, per
   RFC3693, and a LIS, but may refer
   mobile networks it is not efficient for the end host to either of them as a location
   server interchangeably.

   These four things fall under two general protocol mechanisms,
   location configuration protocols and location dereference protocols.

   A fifth use of periodically
   query the LIS for up-to-date location URI information.  This is within
   especially the context of what case when power is called a constraint or when a location conveyance.  Location conveyance
   update is defined 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 part to a presence server.
   Additionally, in some deployments, the network operator may not want
   to make location information widely available.  These kinds of
   location scenarios, and more, such as whether a Target is mobile and
   whether a mobile device needs to be located on demand or according to
   some pre-determined interval, together form the basis of motivation
   for the LbyR concept.

   The concept of an LbyR mechanism is simple.  It is made up of a
   pointer which makes reference to the actual location information by
   some combination of key value and fully qualified domain name.  This
   combination of data elements, in the form of a URI, is referred to
   specifically as a "location URI".

   The LbyR mechanism itself works according to an information
   lifecycle.  Within the LbyR mechanism, location URIs are temporary
   identifiers, each undergoing the following uses: Creation;
   Distribution; Conveyance; Dereference; and Termination.  The use of a
   location URI according to these various states is generally applied
   in one of the following ways:

   1.  Creation of a location URI, within a location server, based on
   some request for its creation.

   2.  Distribution of a location URI, via a Location Configuration
   Protocol, between a target and a location server**.

   3.  Conveyance, applied to LbyR, in SIP, is the transporting of the
   location URI, in this case, between any successive signaling
   nodes***.

   4.  Dereference of a location URI, a request/response between a
   client having a location URI and a location server holding the
   location  information that the location URI references.

   5.  Termination of a location URI, either due to expiration or
   cancellation within a location server, and which is based on a target
   cancellation  request or some other action, such as timer
   expiration.

   Location determination, different than location configuration or
   dereferencing, often includes topics related to manual provisioning
   processes, automated location calculations based on a variety of
   measurement techniques, and/or location transformations, (e.g., geo-
   coding), and is beyond the scope of this document.

   *The standard mechanism for LbyV has been defined around the use of
   the
   SIP protocol, PIDF-LO (Presence Information Document Format - Location Object
   [RFC4119]]), and is explicitly out of scope for in this document.

   **This document make no differentiation between a LS, per RFC3693,
   and a LIS [ref. draft-ietf-geopriv-l7-lcp-ps], but may refer to
   either of them as a location server interchangeably.

   ***Location Conveyance for either LbyR or LbyV, within SIP signaling
   is considered out of scope for this document (see
   [I-D.ietf-sip-location-conveyance] for an explanation of location
   conveyance
   of for either LbyR or LbyV scenarios.)

   Except for location using conveyance, the above stages in the LbyR
   lifecycle fall into one of two general categories of protocols,
   either a location URI. Location Configuration Protocol or a Location Dereference
   Protocol.  The stages of LbyR Creation, Distribution, and
   Termination, are each found within the set of Location Configuration
   Protocols (LCP).  The Dereference stage belongs solely to the set of
   Location Dereference Protocols.

   The issues around location configuration protocols have been
   documented in a location configuration protocol problem statement and
   requirements document [I-D.ietf-geopriv-l7-lcp-ps].  There are
   currently a several examples of a location configuration
   protocol.  These include protocols
   currently proposed, including, DHCP, LLDP-MED, and HELD
   [I-D.ietf-geopriv-http-location-delivery]) protocols.

   For dereferencing of a location URI, depending on the type of
   reference used, such as a 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 [I-D.ietf-geopriv-loc-filters].

   The structure of this document includes terminology, Section 2,
   followed by a discussion of the basic elements that surround how a
   location URI is used.  These elements, or actors, are discussed in an
   overview section, Section 3, accompanied by a graph and associated
   processing steps.

   Requirements are outlined accordingly, separated as location
   configuration requirements, Section 4.1, and location dereference
   requirements, Section 4.2.

   In contrast to using a location URI as the mechanism to support a
   Location-by-Reference model, it may be worth mentioning the common
   alternative model, that of Location-by-Value (LbyV), which provides
   location directly.  LbyV uses a location object, (e.g., a PIDF-LO,
   [RFC4119]) within SIP signaling.  Using the LbyV model for location
   configuration is considered out of scope for this document (see
   [I-D.ietf-sip-location-conveyance] for an explanation of location
   conveyance for either LbyR or LbyV scenarios.

   Location determination, different than a graph and associated
   processing steps.

   Requirements are outlined accordingly, separated as location
   configuration or
   dereferencing, often includes topics related to manual provisioning
   processes, automated measurements, and/or location transformations,
   (e.g., geo-coding), requirements, Section 4.1, and are beyond the scope of this document. location dereference
   requirements, Section 4.2.

2.  Terminology

   The key words "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 [RFC2119].

   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:

   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
      by means of a location URI for use in either a location
      configuration, conveyance, or dereferencing protocol, and which
      refers to a fully specified location.

   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
      client.

   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.

3.  Overview of Location-by-Reference

   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 section describes the task of retrieving entities and publishing location
   information to a third party, such as to a presence server.  Finally, interactions involved in some deployments, the network operator may not want to make
   location information widely available.

   Different location scenarios, such as whether a Target is mobile and
   whether a mobile device needs to be located on demand or according to
   some pre-determined interval 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
   [I-D.ietf-geopriv-loc-filters]. model.

                    +-----------+  Geopriv      +-----------+
                    |           |  Location     | Location  |
                    |    LIS    +---------------+ Recipient |
                    |           |  Dereference  |           |
                    +-+---+-----+  Protocol (3) +----+------+
                     *    |                        --
         Rulemaker  *     | Geopriv              --
         Policy    *      | Location           --
         Exchange *       | Configuration    --
            (1b) *        | Protocol       --
                *         | (1a)         --      Geopriv
               *          |            --        Using Protocol
     + - - - -*- - - - - -|- - - -+  --          (e.g., SIP)
     |+------+----+ +-----+-----+ |--            (2)
      | Rulemaker | | Target /  |--
     ||  / owner  | | End Host  + |
      |           | |           |
     |+-----------+ +-----------+ |

     |       User of Target       |
     + - - - - - - - - - - - - - -+

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

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

   (1a).  Target requests reference from server; and receives back, a
   location URI in server response

   (1b).  Rulemaker policy is consulted (interface out of scope)

   (2).  Target conveys reference to recipient (out of scope)

   (3).  Recipient dereferences location URI, by a choice of methods,
   including a request/response (e.g., HTTP) or publish/subscription
   (e.g., SIP SUBSCRIBE/NOTIFY)

   Note A. There is no requirement for using the same protocol in (1a)
   and (3).

   Note B. Figure 1 includes the interaction between the owner of the
   Target and the LIS to establish Rulemaker policies.  This is
   communications path (1b).  This interaction needs to be done before
   the LIS will authorize anything of other than default policies to a
   dereference request for location of the Target.

   Note C. that the The Target may take on the role of the Location Recipient
   whereby it would dereference the location URI to obtain its own
   location information.

   An example scenario of how this might work, is where the Target
   obtains a location URI in the form of a subscription URI (e.g., a SIP
   URI) via HELD, HELD (a Geopriv layer 7 location configuration protocol).
   Since, in
   In this case case, the Target equals is the same as the Recipient, then therefore the
   Target can subscribe to the URI in order to be notified of its
   current location based on subscription parameters.  In the example,
   parameters (see
   [I-D.ietf-geopriv-loc-filters]).  Additionally, are set up for a geospatial boundary
   can be specific Target/Recipient along with an
   expressed (ref.  [I-D.ietf-geopriv-policy]), geospatial boundary, so that the Target/Recipient will get its receives
   an updated location notification once it
   crosses the specified boundary. boundary is crossed (see
   [I-D.ietf-geopriv-loc-filters]).

   Location URIs may have an expiry associated to with them, primarily for
   security considerations, and generally so that the LIS is able to
   keep track of the location URIs that have been handed out, to know
   whether a location URI is still valid once the LIS receives it in a
   request, and in order for a recipient of such a URI from being able
   to (in some cases) permanently track a host.  Expiration of a
   location URI limits the time that accidental leaking of a location
   URI introduces.  Other justifications for expiration of location URIs
   include the ability for a LIS to do garbage collection.

   Because a location URI is a pointer to the Target's location, it is
   important that it be constructed in such a way that it does not
   unintentionally reveal any usable information about the Target it
   represents.  For example, it is important to prevent adversaries from
   obtaining any information that may be revealed about a Target by
   direct examination of the location URI itself, (e.g., names,
   identifiers, etc.), some determinable pattern or syntax (e.g.,
   sequence of numbers), or guessable codes (e.g., weak encryption).
   Therefore, each location URI must be constructed with security
   safeguards in mind.

   How a location URI is will ultimately be used within the dereference
   step is an important consideration at the time that the location URI
   is requested via a location configuration protocol.  Since
   dereferencing of location URIs could be done according to one of two
   authorization models, either an "access control" model control authorization model"
   or a "possession" model "possession authorization model" (see definitions, below), it is
   important that location configuration protocols indicate the type of
   a location URI that is being requested, (and also which type is
   returned).  Dereference protocols must support
   both types.

   1. Access control use type: authorization model:  Access to the location URI is
      limited by policy.  This is  In this case, the case where, for location configuration, Rule Maker (owner/Target) is
      able to provide authorization policies to the LIS applies (server side) authentication and access control at the
      location configuration step, and repeats authentication and
      authorization for each dereference operation of that during this
      stage, or through some other parallel mechanism (e.g., interface
      1b., Figure 1.).  Policies are attached to a location URI. URI through
      an (undisclosed) mechanism.

   2. Possession use type: authorization model:  The possession use type authorization
      model is described as having no authentication and/or
      authorization requirement aside from only possessing the location
      URI itself (in itself.  In this case, possession implies authorization). authorization.
      Access to the location URI is limited by distribution only.
      Whoever possesses the location URI has the ability to dereference
      it.  Possession use types authorization models may be used within specified
      domains only, or might be used across wide open public networks.

   In either of the above cases, a location URI needs to be constructed
   is such a way as to make it difficult to guess.  The form of the URI
   is constrained by the degree of randomness and uniqueness applied to
   it.  It is important to protect the actual location information from
   an intermediate node (despite the fact that in the possession model
   there would be nothing to prevent an interceptor from seeking to
   dereference the location URI).  Obfuscating the location URI
   safeguards against the undetected stripping off of what would
   otherwise be evident location information, since it forces a
   dereference operation by the location dereference server, an
   important step for the purpose of providing statistics, audit trails,
   and general logging for many different kinds of location based
   services.

4.  High-Level Requirements

   This document outlines the requirements for an Location by Reference
   mechanism which can be used by a number of underlying protocols.
   Requirements here address two general types of such protocols, a
   general location configuration protocol, and a general location
   dereferencing protocol.  Each of these two general protocols has
   multiple specific protocol implementations.  Location configuration
   protocols include, HELD, DHCP, and LLDP-MED, whereas current location
   dereferencing protocols include HELD Deref, HTTP GET, and SIP
   SUBSCRIBE/NOTIFY.  Because each of these specific protocol
   implementations has its own unique client and server interactions,
   the requirements here are not intended to state what a client or
   server is expected to do, but rather which requirements must be met
   separately by any location configuration protocol or location
   dereference protocol, for the purposes of using a location URI.

   The requirements are broken into two sections.

4.1.  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:  When a location URI has a limited
      validity interval, its lifetime MUST be indicated.

      Motivation: A location URI may not intend 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
      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 should be a way to nullify the
      location URI.

   C4. Location Information Masking:  The location URI form MUST,
      through randomization and uniqueness, ensure that any location
      specific information embedded within the location URI itself is
      kept obscure during location configuration.

      Motivation: It is important to keep any location information
      masked from a casual observing node.

   C5. User Identity Protection:  The location URI MUST NOT contain any
      user identifying information that identifies the user, device or
      address of record, (e.g., which includes phone extensions, badge
      numbers, first or last names, etc.), 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 only, or
      multiple times.

      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 URI Valid-for: Validity Interval Indication:  A location URI validity interval, if
      used, configuration protocol
      MUST include the validity time, in seconds, as provide an indication of how long the client can consider a location URI to be valid. validity interval
      (i.e., expiry time) when present.

      Motivation: It is important to be able to determine how long a
      location URI is to remain useful for, and when it must be
      refreshed.

   C8. Location URI Anonymous: only:  The location URI MUST NOT point to any
      information about the Target other than it's location.

      Motivation: A user should have the option to control how much
      information is revealed about them.  This provides that control by
      not forcing the inclusion of other information with location,
      (e.g., to not include any identification information in the
      location URI.)

   C9. Location URI Not guessable:  Where location URIs are used
      publicly, any location URI MUST be constructed using properties of
      uniqueness and cryptographically random sequences so that it is
      not guessable.  (Note that the number of bits depends to some
      extent on the number of active location URIs that might exist at
      the one time; 128-bit is most likely enough for the near term.)
      Motivation: Location URIs need to guard against any observing node
      or individual stripping off meaningful information about the
      Target.

   C10.  Location URI Optional:  In the case of user-provided
      authorization policies, where anonymous or non-guessable location
      URIs are not warranted, the location configuration protocol MAY
      support optional location URI forms.

      Motivation: Users don't always have such strict privacy
      requirements, but may opt to specify their own location URI, or
      components thereof.

   C11.  Location URI Use Type: Authorization Model:  The location configuration
      protocol
      MUST SHOULD indicate whether the requested location URI
      conforms to the access control authorization model or the
      possession authorization model.

      Motivation: Downstream dereference clients and servers need to
      know whether a location URI provided by the location configuration
      protocol conforms to an access control authorization model or a
      possession authorization model.

   C12.  Location URI Lifetime:  A location URI SHOULD have an
      associated expiration lifetime (i.e., validity interval), and MUST
      have an validity interval if used with the possession
      authorization model.

      Motivation: If a location URI is unintentionally leaked, then the
      amount of time that the reference can be potentially used by an
      unknown attacker (or, casual observer) needs to be limited.

4.2.  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 indicator:  The Validity Interval Indication:  A location dereference protocol
      MUST support provide an indicator showing that, if it is indication of the
      case, that a location URI validity interval
      (i.e., expiry time) when present.

      Motivation: It is no longer valid due important to expiration.

      Motivation: Location URIs are expected be able to expire, based on determine how long a
      location configuration protocol parameters, and it URI is therefore
      useful to convey the expired status of the location URI in the
      location dereference protocol. remain useful for, and what time it will no
      longer be usable.

   D3. Authentication:  The location dereference protocol MUST include
      mechanisms to authenticate both the client and the server.

      Motivation: Although the implementations must support
      authentication of both parties, any given transaction has the
      option not to authenticate one or both parties.

   D4.  Dereferenced Location Form:  The value returned by the
      dereference protocol MUST contain a well-formed PIDF-LO document.

      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. Location URI Repeated Use:  The location dereference protocol
      MUST support the ability for the same location URI to be resolved
      more than once, based on dereference server configuration.

      Motivation: Through dereference server configuration, for example,
      it may be useful to not only allow more than one dereference
      request, but, in some cases, to also limit the number of
      dereferencing attempts by a client.

   D6. Location URI Valid-for: Validity Interval Indication:  A location URI validity interval, if
      used, dereference protocol MUST include the validity time, in seconds, as
      provide an indication of how long the client can consider a location URI to be valid. validity interval (i.e.,
      expiry time) when present.

      Motivation: It is important to be able to determine how long a
      location URI is to remain useful for, and when dereferencing a location
      URI. it must be
      refreshed.

   D7. Location URI anonymized:  Any location URI whose dereference will
      not be subject to authentication and access control MUST be
      anonymized.

      Motivation: The dereference protocol must define an anonymized
      format for location URIs.  This format must identify the desired
      location information via a random token with at least 128 bits of
      entropy (rather than some kind of explicit identifier, such as an
      IP address).

   D8. Location Information Masking:  The location URI form MUST,
      through randomization and uniqueness, ensure that any location
      specific information embedded within the location URI itself is
      kept obscure during location URI dereferencing.

      Motivation: It is important to keep any location information
      masked from a casual observing node, requiring instead a discrete
      dereference operation in order to return location information.

   D9. Location Privacy:  The location dereference protocol MUST support
      the application of privacy rules to the dissemination of a
      requested location object.

      Motivation: The dereference server must obey all provisioned
      privacy rules that apply to a requested location object.

   D10.  Location Confidentiality:  The dereference protocol MUST
      support encryption of messages sent between the location
      dereference client and the location dereference server, and MAY
      alternatively provide messaging unencrypted.

      Motivation: Environmental and local configuration policy will
      guide the requirement for encryption for certain transactions.  In
      some cases, encryption may be the rule, in others, it may be
      acceptable to send and receive messages without encryption.

   D11.  Location URI Use Type: Authorization Model:  The location dereference
      protocol MUST SHOULD indicate whether the requested location URI
      conforms to the access control authorization model or the
      possession authorization model.

      Motivation: Downstream dereference clients need to know whether a
      location URI provided by the location configuration protocol
      conforms to an access control authorization model or a possession
      authorization model in order to save time processing dereference
      attempts.

5.  Security Considerations

   The LbyR mechanism currently addresses security issues as follows.

   A location URI, regardless of its construction, if public, by itself,
   implies no safeguard against anyone being able to dereference and get
   the location.  The method of constructing the location URI form to
   include randomization along with encryption does help prevent some
   potential pattern guessing.  In the case of one time use location
   URIs, (referred to as a pawn ticket), the argument can be made that
   possession implies permission, and location URIs that are public are
   protected only by privacy rules enforced at the dereference server.

   Any location URI, by necessity, indicates the server (name) that
   hosts the location information.  Knowledge of the server in some
   specific domain could therefore reveal something about the location
   of the Target.  This kind of threat may be mitigated somewhat by
   introducing another layer of indirection: namely the use of a
   (remote) presence server.

6.  IANA Considerations

   This document does not require actions by the IANA.

7.  Acknowledgements

   We

   I would like to thank the present IETF GEOPRIV working group chair
   for their continued support in progressing this document along, as
   well, I wish to thank past chairs, Andy Newton, Allison Mankin and
   Randall Gellens, for creating the design team which initiated this
   requirements work.  We'd  I'd also like to thank those original design team
   participants for their inputs, comments, and insightful 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.

8.  References

8.1.  Normative References

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

8.2.  Informative References

   [I-D.ietf-geopriv-http-location-delivery]
              Barnes, M., Winterbottom, J., Thomson, M., and B. Stark,
              "HTTP Enabled Location Delivery (HELD)",
              draft-ietf-geopriv-http-location-delivery-07
              draft-ietf-geopriv-http-location-delivery-10 (work in
              progress), April October 2008.

   [I-D.ietf-geopriv-l7-lcp-ps]
              Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7
              Location Configuration Protocol; Problem Statement and
              Requirements", draft-ietf-geopriv-l7-lcp-ps-08 (work in
              progress), June 2008.

   [I-D.ietf-geopriv-loc-filters]
              Mahy, R., R. and B. Rosen, "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
              draft-ietf-geopriv-loc-filters-02 (work in progress),
              March 2007.
              July 2008.

   [I-D.ietf-geopriv-policy]
              Schulzrinne, H., Tschofenig, H., Morris, J., Cuellar, J.,
              and J. Polk, "Geolocation Policy: A Document Format for
              Expressing Privacy Preferences for  Location Information",
              draft-ietf-geopriv-policy-17 (work in progress),
              June 2008.

   [I-D.ietf-sip-location-conveyance]
              Polk, J. and B. Rosen, "Location Conveyance for the
              Session Initiation Protocol",
              draft-ietf-sip-location-conveyance-10
              draft-ietf-sip-location-conveyance-11 (work in progress),
              February
              October 2008.

   [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.

Appendix A.  Change log

   Changes to this draft in comparison to the previous version (-04 vs.
   -03):

   1.  Changed wording of section 1 "Introduction", (Thompson ~ 7/09/08
   list comments).

   1.  Relocated text in section 3 "Overview of Location-by-Reference"
   to section 1 (Intro), (Thompson comments).

   2.  (Sect. 3, con't) Fixed Figure 1.  Label, based on (Thompson
   comments).

   3.  Fixed minor spelling errors, incl.  Note B., Note C., etc., based
   on (Thompson comments).

   4.  Added some qualifying text (security) around possession model,
   based on (Thompson comments).

   5.  Replaced "use type" labels with "authorization models", "access
   authorization model", and "possession authorization model", (Thompson
   comments).

   6.  Changed the entity role of applying security from LIS (Server-
   side authentication), to the Rule-Maker (owner/Target) providing
   policies to the LIS, (Thompson comments).

   7.  Changed requirement C3 to a MUST, (Thompson comments).

   8.  Added new requirement, C12, "C12.  Location URI Lifetime:" as a
   SHOULD for all, and MUST for possession auth model, (Thompson
   comments).

   9.  Changed name of requirement C8 to "Location Only", (Thompson
   comments).

   10.  Reworded C7 and D6 to be less implementation specific, (Thompson
   comments).

   11.  Changed requirements C11, D11 to SHOULD, (Thompson comments).

   12.  (Section 5:) Removed lead in sentence for readibility, (Thompson
   comments).

   13.  Remove "pawn ticket" reference - replaced with "possession
   authorization model", (Thompson comments).

   14.  Added new paragraph to the security section (Thompson, 7/09/08
   comments).

   15.  Corrected other minor spelling and wording errors and
   deficiencies (refer to diff 04/03) (-Editor).

   Changes to this draft in comparison to the previous version (-03 vs.
   -02):

   1.  Changed wording of section 3 "Overview of Location-by-Reference"
   (Polk, Thomson, Winterbottom ~ 4/1/08 list comments).

   2.  Added new requirement C4.  "Location Information Masking:", based
   on (Thomson ~4/1/08 list comment).

   3.  Added new requirement C11.  "Location URI Use Type:", based on
   (~4/1/08 list comments).

   4.  Added new requirement D11.  "Location URI Use Type:", for deref.
   based on (~4/1/08 list comments).

   5.  Replaced requirement D8.  "Location URI Non-Anonymized" with
   "Location Information Masking:".

   Changes to this draft in comparison to the previous version (-02 vs.
   -01):

   1.  Reworded Introduction (Barnes 12/6 list comments).

   2.  Changed name of "Basic Actors" section to "Overview of Location
   by Reference" (Barnes).

   3.  Keeping the LCP term away (for now) since it is used as Link
   Control Protocol elsewhere (IETF).

   4.  Changed formatting of Terminology section (Barnes).

   5.  Requirement C2. changed to indicate that if the URI has a
   lifetime, it has to have an expiry (Barnes)

   6.  C7.  Changed title and wording based on suggested text and dhcp-
   uri-option example (Polk).

   7.  The new C2 req. describing valid-for, was also added into the
   deref section, as D6

   8.  Changed C4 based on much list discussion - replaced by 3 new
   requirements...

   9.  Reworded C5 based on the follow-on C4 thread/discussion on list
   (~2/18).

   10.  Changed wording of D3 based on suggestion (Barnes).

   11.  Reworded D4 per suggestion (Barnes).

   12.  Changed D5 based on comment (Barnes), and additional title and
   text changes for clarity.

   13.  Added D9 and D10 per Richard Barnes suggestions - something
   needed in addition to his own security doc.

   14.  Deleted reference to individual Barnes-loc-sec draft per wg list
   suggestion (Barnes), but need more text for this draft's security
   section.

Author's Address

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

   Phone: +1 206 792 2424
   Email: rmarshall@telecomsys.com
   URI:   http://www.telecomsys.com

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