GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc5808

Internet Engineering Task Force (IETF) R. Marshall, Ed. Request for Comments: 5808 TCS Category: Informational May 2010 ISSN: 2070-1721

         Requirements for a Location-by-Reference Mechanism

Abstract

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

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc5808.

Copyright Notice

 Copyright (c) 2010 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Marshall Informational [Page 1] RFC 5808 GEOPRIV LbyR Requirements May 2010

 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Table of Contents

 1. Introduction ....................................................3
 2. Terminology .....................................................5
 3. Overview of Location-by-Reference ...............................6
    3.1. Location URI Usage .........................................7
    3.2. Location URI Expiration ....................................8
    3.3. Location URI Authorization .................................8
    3.4. Location URI Construction ..................................9
 4. High-Level Requirements .........................................9
    4.1. Requirements for a Location Configuration Protocol .........9
    4.2. Requirements for a Location Dereference Protocol ..........11
 5. Security Considerations ........................................12
 6. Acknowledgements ...............................................13
 7. References .....................................................13
    7.1. Normative References ......................................13
    7.2. Informative References ....................................13

Marshall Informational [Page 2] RFC 5808 GEOPRIV LbyR Requirements May 2010

1. Introduction

 All location-based services rely on ready access to location
 information.  Location information can be used in either a direct,
 Location-by-Value (LbyV) approach or an indirect, Location-by-
 Reference (LbyR) approach.
 For LbyV, location information is conveyed directly in the form of a
 Presence Information Data Format Location Object (PIDF-LO) [RFC4119].
 Using LbyV might be either infeasible or undesirable in some
 circumstances.  There are cases where LbyR is better able to address
 location requirements for a specific architecture or application.
 This document provides a list of requirements for use with the LbyR
 approach, and leaves the LbyV model explicitly out of scope.
 As justification for an LbyR model, consider the circumstance that in
 some mobile networks it is not efficient for the end host to
 periodically query the Location Information Server (LIS) for up-to-
 date location information.  This is especially the case when power
 availability is a constraint or when 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.  Additionally, in some
 deployments, the network operator may not want to make location
 information widely available.  These kinds of location scenarios form
 the basis of motivation for the LbyR model.
 The concept of an LbyR mechanism is simple.  An LbyR is made up of a
 URI scheme, a domain, and a randomized component.  This combination
 of data elements, in the form of a URI, is referred to specifically
 as a "location URI".
 A location URI is thought of as a reference to the current location
 of the Target, yet the location value might remain unchanged over
 specific intervals of time for several reasons.  The type of location
 information returned as part of the dereferencing step may, for
 example, be influenced by the following factors:
  1. Limitations in the process used to generate location information

mean that cached location might be used.

  1. Policy constraints may dictate that the location provided remains

fixed over time for specified Location Recipients. Without

   additional information, a Location Recipient cannot assume that the
   location information provided by any location URI is static, and
   will never change.

Marshall Informational [Page 3] RFC 5808 GEOPRIV LbyR Requirements May 2010

 The LbyR mechanism works according to an information life cycle.
 Within this life cycle, location URIs are considered 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, for example in SIP (Session
     Initiation Protocol), 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, due to either expiration or
     cancellation within a location server, and that is based on a
     Target cancellation request or some other action, such as timer
     expiration.
 Note that this document makes no functional differentiation between a
 Location Server (LS), per [RFC3693], and a Location Information
 Server (LIS), as shown in [RFC5687], but may refer to either of them
 as a location server interchangeably.
 Location determination, as distinct from 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.
 Location Conveyance for either LbyR or LbyV, as defined within SIP
 signaling is considered out of scope for this document.  (See
 [LOC-CONVEY] for an explanation of location conveyance for either
 LbyR or LbyV scenarios.)
 Except for location conveyance, the above stages in the LbyR life
 cycle fall into one of two general categories of protocols, either a
 Location Configuration Protocol or a Location Dereference Protocol.
 The stages of LbyR Creation, Distribution, and Termination, are each

Marshall Informational [Page 4] RFC 5808 GEOPRIV LbyR Requirements May 2010

 found within the set of Location Configuration Protocols (LCPs).  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 [RFC5687].  There are currently several
 examples of documented location configuration protocols, namely DHCP
 [DHCP-LOC-URI], LLDP-MED [LLDP-MED], and HELD [HELD].
 For dereferencing 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 [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, associated
 processing steps, and a brief discussion around the use, expiration,
 authorization, and construction of location URIs.
 Requirements are outlined accordingly, separated as location
 configuration requirements, Section 4.1, and 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],
 with the important qualification that, unless otherwise stated, these
 terms apply to the design of the Location Configuration Protocol and
 the Location Dereferencing Protocol, not its implementation or
 application.
 This document reuses the terminology of [RFC3693], such as Location
 Server (LS), Location Recipient (LR), Rule Maker (RM), Target, and
 Location Object (LO).  Furthermore, the following terms are defined
 in this document:
 Location-by-Value (LbyV): Using location information in the form of a
    location object (LO), such as a PIDF-LO.
 Location-by-Reference (LbyR): Representing location information
    indirectly using a location URI.

Marshall Informational [Page 5] RFC 5808 GEOPRIV LbyR Requirements May 2010

 Location Configuration Protocol: A protocol that is used by a Target
    to acquire either a location object or a location URI from a
    location configuration server, based on information unique to the
    Target.
 Location Dereference Protocol: A protocol that is used by a client to
    query a location server, based on the location URI input, and that
    returns location information.
 Location URI: As defined within this document, an identifier that
    serves as a reference to location information.  A location URI is
    provided by a location server, and is later used as input by a
    dereference protocol to retrieve location information.

3. Overview of Location-by-Reference

 This section describes the entities and interactions involved in the
 LbyR model.
          +---------+---------+   Location    +-----------+
          |         |         |  Dereference  | Location  |
          |      LIS/LS       +---------------+ Recipient |
          |         |         |   Protocol    |           |
          +----+----+----+----+      (3)      +-----+-----+
               |           *                        |
               |      Policy *                      |
      Location |      Exchange *                    |
 Configuration |        (*)      *                  | Location
      Protocol |              +----+----+           | Conveyance
         (1)   |              |  Rule   |           | Protocol
               |              |  Maker  |           |    (2)
          +----+----+         +---------+           |
          |         |                               |
          | Target  +-------------------------------+
          |         |
          +---------+
        Figure 1: Location Reference Entities and Interactions
 Figure 1 shows the assumed communication model for both a Layer 7
 location configuration protocol and a location dereference protocol.
 (1) The Target (an end device) uses a location configuration protocol
     to acquire a location reference from a LIS, which acts as (or is
     able to access) an LS.
     In the case where the Target is also a Rule Maker, the location
     configuration protocol can be used to convey policy information.

Marshall Informational [Page 6] RFC 5808 GEOPRIV LbyR Requirements May 2010

     In the case where possession of a location URI is the only
     required form of authorization (see Section 3.3), a policy is
     implied whereby any requester is granted access to location
     information.  This does not preclude other means of providing
     authorization policies.
     A Target could also acquire a location URI from the LS directly
     using alternative means, for example, the acquisition of a
     presence Address of Record (AoR) to be used for location
     information, in which case, it could be regarded as a location
     URI.
 (2) The Target conveys the location URI to the Location Recipient
     (interface out of scope).
 (3) The Location Recipient dereferences the location URI to acquire
     location information from the LS.
 The LS controls access to location information based on the policy
 provided by the Rule Maker.
 Note A.  There is no requirement for using the same protocol in (1)
          and (3).
 Note B.  Figure 1 includes the interaction between the owner of the
          Target and the LIS to obtain Rule Maker policies.  This
          interaction needs to happen before the LIS will authorize
          anything other than what is allowed based on default
          policies in order to dereference a location request of the
          Target.  This communication path is out of scope for this
          document.
 Note C.  The Target might take on the role of the Location Recipient,
          in which case, it could attempt to dereference the location
          URI itself, in order to obtain its own location information.

3.1. Location URI Usage

 An example scenario of how the above location configuration and
 location dereference steps might work using SIP is where a Target
 obtains a location URI in the form of a subscription URI (e.g., a SIP
 URI) via a location configuration protocol.  In this case, the Target
 is the same as the Recipient; 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 are set up for a
 specific Target/Recipient along with an expressed geospatial
 boundary, so that the Target/Recipient receives an updated location
 notification once the boundary is crossed (see [LOC-FILTERS]).

Marshall Informational [Page 7] RFC 5808 GEOPRIV LbyR Requirements May 2010

3.2. Location URI Expiration

 Location URIs may have an expiry associated with them, primarily for
 security considerations, and generally in order for the LIS 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 for preventing 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.

3.3. Location URI Authorization

 How a location URI will ultimately be used within the dereference
 step is an important consideration at the time the location URI is
 requested via a location configuration protocol.  The process of
 dereferencing location URIs will be influenced by the specific
 authorization model applied by the Location Information Server and
 the URI scheme that indicates the protocol to be used to resolve the
 reference to a location object.
 Location URIs manifest themselves in a few different forms.  The
 different ways that a location URI can be represented are based on
 local policy, and are depicted in the following four scenarios.
 1.  No location information included in the URI: As is typical, a
     location URI is used to get location information.  However, in
     this case, the URI representation itself does not need to reveal
     any specific information at all.  Location information is
     acquired by the dereferencing operation using a location URI.
 2.  URI does not identify a Target: By default, a location URI MUST
     NOT reveal any information about the Target other than location
     information.  This is true for the URI itself (or in the document
     acquired by dereferencing), unless policy explicitly permits
     otherwise.
 3.  Access control authorization model: If this model is used, the
     location URI MUST NOT include any location information in its
     representation.  Location URIs operating under this model could
     be widely published to recipients that are not authorized to
     receive this information.
 4.  Possession authorization model (the URI itself is a secret): If
     this model is used, the location URI is confidential information
     shared between the LIS/LS, the Target, and all authorized
     Location Recipients.  In this case, possession implies

Marshall Informational [Page 8] RFC 5808 GEOPRIV LbyR Requirements May 2010

     authorization.  Because knowledge of the location URI is used to
     authenticate and authorize access to location information, the
     URI needs to include sufficient randomness to make guessing its
     value difficult.  A possession model URI can include location
     information in its representation.

3.4. Location URI Construction

 Given scenarios 2 and 4, above, and depending on local policy, a
 location URI may be constructed in such a way as to make it difficult
 to guess.  Accordingly, the form of the URI is then constrained by
 the degree of randomness and uniqueness applied to it.  In this case,
 it may be important to protect the actual location information from
 inspection by an intermediate node.  Construction of a location URI
 in such a way as to not reveal any Target-specific information (e.g.,
 user or device information), with the goal of making the location URI
 appear bland, uninteresting, and generic, may be helpful to some
 degree in order to keep location information more difficult to
 detect.  Thus, obfuscating the location URI in this way may provide
 some level of safeguard against the undetected inspection and
 unintended use of what would otherwise be evident location
 information, since it forces a dereference operation at 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 a Location by Reference
 mechanism that 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.
 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 location configuration protocol MUST
     support a location reference in URI form.
     Motivation: A standardized location reference mechanism increases
     interoperability.

Marshall Informational [Page 9] RFC 5808 GEOPRIV LbyR Requirements May 2010

 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
     MUST support the ability to request a cancellation of a specific
     location URI.
     Motivation: If the Target determines that a location URI should
     no longer be used to dereference a location, then there should be
     a way to request that the location URI be nullified.
 C4. Location information masking: The location URI MUST ensure, by
     default, through randomization and uniqueness, that the location
     URI does not contain location-information-specific components.
     Motivation: It is important to keep any location information
     masked from a casual observing node.
 C5. Target identity protection: The location URI MUST NOT contain
     information that identifies the Target (e.g., user or device).
     Examples include phone extensions, badge numbers, and first or
     last names.
     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 Target to
     control whether a location URI can be resolved once only or
     multiple times.
     Motivation: The Target requesting a location URI may request a
     location URI that has a 'one-time-use' only characteristic, as
     opposed to a location URI having multiple reuse capability.  This
     would allow the server to return an error with or without
     location information during the subsequent dereference operation.
 C7. Selective disclosure: The location configuration protocol MUST
     provide a mechanism that allows the Rule Maker to control what
     information is being disclosed about the Target.

Marshall Informational [Page 10] RFC 5808 GEOPRIV LbyR Requirements May 2010

     Motivation: The Rule Maker has to be in control of how much
     information is revealed during the dereferencing step as part of
     the privacy features.
 C8. Location URI not guessable: As a default, the location
     configuration protocol MUST return location URIs that are random
     and unique throughout the indicated lifetime.  A location URI
     with 128 bits of randomness is RECOMMENDED.
     Motivation: Location URIs should be constructed in such a way
     that an adversary cannot guess them and dereference them without
     having previously obtained them from the Target.
 C9. Location URI options: In the case of user-provided authorization
     policies, where anonymous or non-guessable location URIs are not
     warranted, the location configuration protocol MAY support a
     variety of optional location URI conventions, as requested by a
     Target to a location configuration server (e.g., embedded
     location information within the location URI).
     Motivation: Users don't always have such strict privacy
     requirements, but may opt to specify their own location URI or
     components to be included within a location URI.

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 a configuration protocol and
     those used by a dereference protocol.
 D2. 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.
 D3. Dereferenced location form: The value returned by the dereference
     protocol MUST contain a well-formed PIDF-LO document.

Marshall Informational [Page 11] RFC 5808 GEOPRIV LbyR Requirements May 2010

     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.
 D4. 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.
 D5. Location confidentiality: The location dereference protocol MUST
     support confidentiality protection of messages sent between the
     Location Recipient and the location server.
     Motivation: The location URI indicates what type of security
     protocol has to be provided.  An example is a location URI using
     a HTTPS URI scheme.

5. Security Considerations

 The method of constructing the location URI to include randomized
 components helps to prevent adversaries from obtaining location
 information without ever retrieving a location URI.  In the
 possession model, a location URI, regardless of its construction, if
 made publicly available, implies no safeguard against anyone being
 able to dereference and get the location.  Care has to be paid when
 distributing such a location URI to the trusted location recipients.
 When this aspect is of concern, the authorization model has to be
 chosen.  Even in this model, care has to be taken on how to construct
 the authorization policies to ensure that only those parties have
 access to location information that are considered trustworthy enough
 to enforce the basic rule set that is attached to location
 information in a PIDF-LO document.
 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.
 A covert channel for protocol message exchange is an important
 consideration, given an example scenario where user A subscribes to
 location information for user B, then every time A gets a location
 update, an (external) observer of the subscription notification may

Marshall Informational [Page 12] RFC 5808 GEOPRIV LbyR Requirements May 2010

 know that B has moved.  One mitigation of this is to have periodic
 notification, so that user B may appear to have moved even when
 static.

6. Acknowledgements

 I would like to thank the present IETF GEOPRIV working group chairs,
 Alissa Cooper and Richard Barnes, past chairs, Robert Sparks, Andy
 Newton, Allison Mankin, and Randall Gellens, who established a design
 team that initiated this requirements work.  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, Andrew Newton, Jon Peterson, James M. Polk, Brian Rosen, John
 Schnizlein, Henning Schulzrinne, Barbara Stark, Hannes Tschofenig,
 Martin Thomson, and James Winterbottom.

7. References

7.1. Normative References

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

7.2. Informative References

 [DHCP-LOC-URI] Polk, J., "Dynamic Host Configuration Protocol (DHCP)
                IPv4 and IPv6 Option for a Location Uniform Resource
                Identifier (URI)", Work in Progress, March 2010.
 [HELD]         Barnes, M., Winterbottom, J., Thomson, M., and B.
                Stark, "HTTP Enabled Location Delivery (HELD)", Work
                in Progress, August 2009.
 [LLDP-MED]     Telecommunications Industry Association (TIA),
                "ANSI/TIA-1057 Link Layer Discovery Protocol - Media
                Endpoint Discovery", 2006.
 [LOC-FILTERS]  Mahy, R., Rosen, B., and H. Tschofenig, "Filtering
                Location Notifications in the Session Initiation
                Protocol (SIP)", Work in Progress, March 2010.
 [LOC-CONVEY]   Polk, J. and B. Rosen, "Location Conveyance for the
                Session Initiation Protocol", Work in Progress,
                February 2010.

Marshall Informational [Page 13] RFC 5808 GEOPRIV LbyR Requirements May 2010

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

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

Marshall Informational [Page 14]

/data/webs/external/dokuwiki/data/pages/rfc/rfc5808.txt · Last modified: 2010/05/11 17:04 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki