GEOPRIV WG                                                M. Barnes, Ed.
Internet-Draft                                                    Nortel
Intended status: Standards Track
Expires: March 12, May 2, 2009

                                                       September 8,

                                                        October 29, 2008

                 HTTP Enabled Location Delivery (HELD)

Status of this Memo

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   A Layer 7 Location Configuration Protocol (L7 LCP) is described that
   is used for retrieving location information from a server within an
   access network.  The protocol includes options for retrieving
   location information in two forms: by value and by reference.  The
   protocol is an extensible application-layer protocol that is
   independent of session-layer.  This document describes the use of
   HyperText Transfer Protocol (HTTP) and HTTP over Transport Layer
   Security (HTTP/TLS) as transports for the protocol.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Conventions & Terminology  . . . . . . . . . . . . . . . . . .  4
   3.  Overview and Scope . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Device Identifiers, NAT and VPNs . . . . . . . . . . . . .  7
       4.1.1.  Devices and VPNs . . . . . . . . . . . . . . . . . . .  7
       4.1.2.  LIS Handling of NATs and VPNs  . . . . . . . . . . . .  8
     4.2.  Location by Value  . . . . . . . . . . . . . . . . . . . .  8
     4.3.  Location by Reference  . . . . . . . . . . . . . . . . . .  8  9
   5.  Protocol Description . . . . . . . . . . . . . . . . . . . . .  9
     5.1.  Delivery Protocol  . . . . . . . . . . . . . . . . . . . . 10
     5.2.  Location Request . . . . . . . . . . . . . . . . . . . . . 10
     5.3.  Location Response  . . . . . . . . . . . . . . . . . . . . 10
     5.4.  Indicating Errors  . . . . . . . . . . . . . . . . . . . . 10 11
   6.  Protocol Parameters  . . . . . . . . . . . . . . . . . . . . . 11
     6.1.  "responseTime" Parameter . . . . . . . . . . . . . . . . . 11 12
     6.2.  "locationType" Parameter . . . . . . . . . . . . . . . . . 12
       6.2.1.  "exact" Attribute  . . . . . . . . . . . . . . . . . . 14
     6.3.  "code" Parameter . . . . . . . . . . . . . . . . . . . . . 14
     6.4.  "message" Parameter  . . . . . . . . . . . . . . . . . . . 15
     6.5.  "locationUriSet" Parameter . . . . . . . . . . . . . . . . 15
       6.5.1.  "locationURI" Parameter  . . . . . . . . . . . . . . . 15
       6.5.2.  "expires" Parameter  . . . . . . . . . . . . . . . . . 16
     6.6.  "Presence" Parameter (PIDF-LO) . . . . . . . . . . . . . . 16
   7.  XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 16 17
   8.  HTTP/HTTPS Binding . . . . . . . . . . . . . . . . . . . . . . 20
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 21
     9.1.  Assuring that the proper LIS has been contacted  . . . . . 21 22
     9.2.  Protecting responses from modification . . . . . . . . . . 22
     9.3.  Privacy and Confidentiality  . . . . . . . . . . . . . . . 22
   10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     10.1. HTTPS Example Messages . . . . . . . . . . . . . . . . . . 23 24
     10.2. Simple Location Request Example  . . . . . . . . . . . . . 26
     10.3. Location Request Example for Multiple Location Types . . . 27
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 28
     11.1. URN Sub-Namespace Registration for
           urn:ietf:params:xml:ns:geopriv:held  . . . . . . . . . . . 28
     11.2. XML Schema Registration  . . . . . . . . . . . . . . . . . 29
     11.3. MIME Media Type Registration for 'application/held+xml'  . 29
     11.4. Error code Registry  . . . . . . . . . . . . . . . . . . . 30
   12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 31
   13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 31
   14. Changes since last Version . . . . . . . . . . . . . . . . . . 32
   15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 37
     15.1. Normative References . . . . . . . . . . . . . . . . . . . 37
     15.2. Informative References . . . . . . . . . . . . . . . . . . 38
   Appendix A.  HELD Compliance to IETF LCP requirements  . . . . . . 39
     A.1.  L7-1: Identifier Choice  . . . . . . . . . . . . . . . . . 39
     A.2.  L7-2: Mobility Support . . . . . . . . . . . . . . . . . . 39 40
     A.3.  L7-3: ASP and Access Network Provider Relationship . . . . 40
     A.4.  L7-4: Layer 2 and Layer 3 Provider Relationship  . . . . . 40 41
     A.5.  L7-5: Legacy Device Considerations . . . . . . . . . . . . 41
     A.6.  L7-6: VPN Awareness  . . . . . . . . . . . . . . . . . . . 41
     A.7.  L7-7: Network Access Authentication  . . . . . . . . . . . 41 42
     A.8.  L7-8: Network Topology Unawareness . . . . . . . . . . . . 42
     A.9.  L7-9: Discovery Mechanism  . . . . . . . . . . . . . . . . 42
     A.10. L7-10: PIDF-LO Creation  . . . . . . . . . . . . . . . . . 42
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 42 43
   Intellectual Property and Copyright Statements . . . . . . . . . . 44 45

1.  Introduction

   The location of a Device is information that is useful for a number
   of applications.  The L7 Location Configuration Protocol (LCP)
   problem statement and requirements document
   [I-D.ietf-geopriv-l7-lcp-ps] provides some scenarios in which a
   Device might rely on its access network to provide location
   information.  The Location Information Server (LIS) service applies
   to access networks employing both wired technology (e.g.  DSL, Cable)
   and wireless technology (e.g.  WiMAX) with varying degrees of Device
   mobility.  This document describes a protocol that can be used to
   acquire Location Information (LI) from a LIS within an access

   This specification identifies two types of location information that
   may be retrieved from the LIS.  Location may be retrieved from the
   LIS by value, that is, the Device may acquire a literal location
   object describing the location of the Device.  The Device may also
   request that the LIS provide a location reference in the form of a
   location URI or set of location URIs, allowing the Device to
   distribute its LI by reference.  Both of these methods can be
   provided concurrently from the same LIS to accommodate application
   requirements for different types of location information.

   This specification defines an extensible XML-based protocol that
   enables the retrieval of LI from a LIS by a Device.  This protocol
   can be bound to any session-layer protocol, particularly those
   capable of MIME transport.  This document describes the use of
   HyperText Transfer Protocol (HTTP) and HTTP over Transport Layer
   Security (HTTP/TLS) as transports for the protocol.

2.  Conventions & Terminology

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

   This document uses the terms (and their acronym forms) Access
   Provider (AP), Location Information (LI), Location Object (LO),
   Device, Target, Location Generator (LG), Location Recipient (LR),
   Rule Maker (RM) and Rule Holder (RH) as defined in RFC 3693, GEOPRIV
   Requirements [RFC3693] .  The terms Location Information Server
   (LIS), Access Network, Access Provider (AP) and Access Network
   Provider are used in the same context as defined in the L7 LCP
   Problem statement and Requirements document
   [I-D.ietf-geopriv-l7-lcp-ps].  The usage of the terms, Civic
   Location/Address and Geodetic Location follows the usage in many of
   the referenced documents.

   In describing the protocol, the terms "attribute" and "element" are
   used according to their context in XML.  The term "parameter" is used
   in a more general protocol context and can refer to either an XML
   "attribute" or "element".

3.  Overview and Scope

   This document describes an interface between a Device and a Location
   Information Server (LIS).  This document assumes that the LIS is
   present within the same administrative domain as the Device (e.g.,
   the access network).  An Access Provider (AP) operates the LIS so
   that Devices (and Targets) can retrieve their LI.  The LIS exists
   because not all Devices are capable of determining LI, and because,
   even if a device is able to determine its own LI, it may be more
   efficient with assistance.  This document does not specify how LI is

   This document is based on the attribution of the LI to a Device and
   not specifically a person (end user) or Target, based on the premise
   that location determination technologies are generally designed to
   locate a device and not a person.  It is expected that, for most
   applications, LI for the device can be used as an adequate substitute
   for the end user's LI.  Since revealing the location of the device
   almost invariably reveals some information about the location of the
   user of the device, the same level of privacy protection demanded by
   a user is required for the device.  This approach may require either
   some additional assurances about the link between device and target,
   or an acceptance of the limitation that unless the device requires
   active user authentication, there is no guarantee that any particular
   individual is using the device at that instant.

   The following diagram shows the logical configuration of some of the
   functional elements identified in [RFC3693] and the LIS defined in
   [I-D.ietf-geopriv-l7-lcp-ps] and where this protocol applies, with
   the Rule Maker and Target represented by the role of the Device.
   Note that only the interfaces relevant to the Device are identified
   in the diagram.

                     | Access Network Provider                     |
                     |                                             |
                     |   +--------------------------------------+  |
                     |   | Location Information Server          |  |
                     |   |                                      |  |
                     |   |                                      |  |
                     |   |                                      |  |
                     |   |                                      |  |
                     |   +------|-------------------------------+  |
     Rule Maker   - _     +-----------+         +-----------+
           o          - - | Device    |         | Location  |
          <U\             |           | - - - - | Recipient |
          / \       _ - - |           |   APP   |           |
         Target - -       +-----------+         +-----------+

                        Figure 1: Significant Roles

   The interface between the Location Recipient (LR) and the Device
   and/or LIS is application specific, as indicated by the APP
   annotation in the diagram and it is outside the scope of the
   document.  An example of an APP interface between a device and LR can
   be found in the SIP Location Conveyance document

4.  Protocol Overview

   A device uses the HELD protocol to retrieve its location either
   directly in the form of a PIDF-LO document (by value) and indirectly
   as a Location URI (by reference).  The security necessary to ensure
   the accuracy, privacy and confidentiality of the device's location is
   described in the Security Considerations (Section 9).

   As described in the L7 LCP problem statement and requirements
   [I-D.ietf-geopriv-l7-lcp-ps], the Device must first discover the URI
   for the LIS for sending the HELD protocol requests.  The discovery
   methods are specified in [I-D.ietf-geopriv-lis-discovery].

   The LIS requires an identifier for the Device in order to determine
   the appropriate location to include in the location response message.
   In this document, the IP address of the Device, as reflected by the
   source IP address in the location request message, is used as the
   identifier.  Other identifiers are possible, but are beyond the scope
   of this document.

4.1.  Device Identifiers, NAT and VPNs

   Use of the HELD protocol is subject to the viability of the
   identifier used by the LIS to determine location.  This document
   describes the use of the source IP address sent from the Device as
   the identifier used by the LIS.  When Network Address Translation
   (NAT), a Virtual Private Network (VPN) or other forms of address
   modification occur between the Device and the LIS the location
   returned could be inaccurate.

   Not all cases of NATs introduce inaccuracies in the returned
   location.  For example, a NAT used in a residential Local Area
   Network (LAN) is typically not a problem.  The external IP address
   used on the Wide Area Network (WAN) side of the NAT is an acceptable
   identifier for all of the devices in the residence, on the LAN side
   of the NAT, since the covered geographical area is small.

   On the other hand, if there is a VPN between the Device and the LIS,
   for example for a teleworker, then the IP address seen by a LIS
   inside the enterprise network might not be the right address to
   identify the location of the Device.  Section 4.1.2 provides
   recommendations to address this issue.

4.1.1.  Devices and VPNs

   To minimize the impact of VPNs, connections or tunnels setup for security
   purposes or to traverse middleboxes, Devices that connect to servers
   such as VPN servers, SOCKS servers and HTTP proxy servers should
   perform their HELD query to the LIS prior to establishing a VPN tunnel.
   connection to other servers.  It is RECOMMENDED that discovery
   [I-D.ietf-geopriv-lis-discovery] and an initial query are performed
   before establishing the VPN. any connections to other servers.  If a Device
   performs the HELD query after establishing the VPN tunnel a connection to another
   server, the Device may receive inaccurate location information.

   Devices that establish VPN connections for use by other devices
   inside a LAN or other closed network could serve as a LIS, that
   implements the HELD protocol, for those other Devices.  Devices
   within the closed network are not necessarily able to detect the
   presence of the VPN and rely on the VPN device.  To VPN.  In this end, case, a VPN device should provide the
   address of the LIS server it provides, in response to discovery
   queries, rather than passing such queries through the VPN tunnel.
   Otherwise, the other devices would be totally unaware that they could
   receive inaccurate location information.

   It could also be useful for a VPN device to serve as a LIS for other
   location configuration options such as Dynamic Host Configuration
   Protocol (DHCP)[RFC3825] or Link Layer Discovery Protocol - Media
   Endpoint Discovery (LLDP-MED) [LLDP-MED].  For this case, the VPN
   device that serves as a LIS may first acquire its own location using

4.1.2.  LIS Handling of NATs and VPNs

   In the cases where the Device connects to the LIS through a VPN or a
   NAT that serves a large geographic area or multiple geographic
   locations (for example, a NAT used by an enterprise to connect their
   private network to the Internet), the LIS might not be able to return
   an accurate LI.  If the LIS cannot determine LI for the device, it
   should provide an error response to the requesting device.  The LIS
   needs to be configured to recognize identifiers that represent these

   LIS operators have a large role in ensuring the best possible
   environment for location determination.  The LIS operator needs to
   ensure that the LIS is properly configured with identifiers that fall
   within NATs and VPNs.  In order to serve a Device on a remote side of
   a NAT or VPN a LIS needs to have a presence on the side of the NAT or
   VPN nearest the Device.

4.2.  Location by Value

   Where a Device requires LI directly, it can request that the LIS
   create a PIDF-LO document.  This approach fits well with a
   configuration whereby the device directly makes use of the provided
   PIDF-LO document.  The details on the information that may be
   included in the PIDF-LO MUST follow the subset of those rules
   relating to the construction of the "location-info" element in the
   PIDF-LO Usage Clarification, Considerations and Recommendations
   document [I-D.ietf-geopriv-pdif-lo-profile].  Further detail is
   included in the detailed protocol section of this document Section 6

4.3.  Location by Reference

   Requesting location directly does not always address the requirements
   of an application.  A Device can request a location URI instead of
   literal location.  A Location URI is a URI [RFC3986] of any scheme,
   which a Location Recipient (LR) can use to retrieve LI.  A location
   URI provided by a LIS can be assumed to be globally-addressable; that
   is, anyone in possession of the URI can access the LIS.

   However, possession of the URI does not in any way suggest that the
   LIS indiscriminately reveals the location associated with the
   location URI.  The specific requirements associated with the
   dereference of the location are specified in
   [I-D.ietf-geopriv-lbyr-requirements].  The location dereference
   protocol details are out of scope of this document and are specified
   in [I-D.winterbottom-geopriv-deref-protocol].

   It should also be noted that while the lybr requirements document
   specifies a requirement that a client SHOULD be able to cancel
   location references, the protocol specified in this document does not
   provide that functionality.  The mechanism to provide this support in
   the protocol requires explicit management of Target state on the LIS.
   It is anticipated that extensions to HELD may support that

5.  Protocol Description

   As discussed in Section 4, this protocol provides for the retrieval
   of the device's location in the form of a PIDF-LO document and/or
   Location URI(s) from a LIS.  Three messages are defined to support
   the location retrieval: locationRequest, locationResponse and error.
   Messages are defined as XML documents.

   The Location Request (locationRequest) message is described in
   Section 5.2.  A Location Request message from a Device indicates
   whether location in the form of a PIDF-LO document (with specific
   type(s) of location) and/or Location URI(s) should be returned.  The
   LIS replies with a locationResponse message, including a PIDF-LO
   document and/or one or more Location URIs in case of success.  In the
   case of an error, the LIS replies with an error message.

   A MIME type "application/held+xml" is registered in Section 11.3 to
   distinguish HELD messages from other XML document bodies.  This
   specification follows the recommendations and conventions described
   in [RFC3023], including the naming convention of the type ('+xml'
   suffix) and the usage of the 'charset' parameter.

   Section 6 contains a more thorough description of the protocol
   parameters, valid values, and how each should be handled.  Section 7
   contains a more specific definition of the structure of these
   messages in the form of an XML Schema [W3C.REC-xmlschema-1-20041028].

5.1.  Delivery Protocol

   The HELD protocol is an application-layer protocol specified by an
   XML document.  The HELD protocol is defined independently of any
   lower layers used to transport messages from one host to another.
   This means that any protocol can be used to transport this protocol
   providing that it can provide a few basic features:

   o  The HELD protocol doesn't provide any mechanisms that enable
      detection of missing messages and retransmission, thus the
      protocol must have acknowledged delivery.
   o  The HELD protocol is a request/response protocol, thus the
      protocol must be able to correlate a response with a request.
   o  The HELD protocol REQUIRES that the underlying transport provide
      authentication, confidentiality, and protection against
      modification per Section 9.3.

   This document describes the use of a combination of HTTP [RFC2616],
   TLS [RFC4346] and TCP [RFC0793] in Section 8.

5.2.  Location Request

   A location request message is sent from the Device to the LIS when
   the Device requires its own LI.  The type of LI that a Device
   requests is determined by the type of LI that is included in the
   "locationType" element.

   The location request is made by sending a document formed of a
   "locationRequest" element.  The LIS uses the source IP address of the
   location request message as the primary source of identity for the
   requesting device or target.  It is anticipated that other Device
   identities may be provided through schema extensions.

   The LIS MUST ignore any part of a location request message that it
   does not understand, except the document element.

5.3.  Location Response

   A successful response to a location request MUST contain a PIDF-LO
   and/or location URI(s).  The response SHOULD contain location
   information of the requested "locationType".  The cases whereby a
   different type of location information MAY be returned are described
   in Section 6.2.

5.4.  Indicating Errors

   If the LIS is unable to provide location information based on the
   received locationRequest message, it MUST return an error message.
   The LIS may return an error message in response to requests for any

   An error indication document consists of an "error" element.  The
   "error" element MUST include a "code" attribute that indicates the
   type of error.  A set of predefined error codes are included in
   Section 6.3.

   Error responses MAY also include a "message" attribute that can
   include additional information.  This information SHOULD be for
   diagnostic purposes only, and MAY be in any language.  The language
   of the message SHOULD be indicated with an "xml:lang" attribute.

6.  Protocol Parameters

   This section describes in detail the parameters that are used for
   this protocol.  Table 1 lists the top-level components used within
   the protocol and where they are mandatory or optional for each of the

   | Parameter      |    Location    |    Location    |      Error     |
   |                |     Request    |    Response    |                |
   | responseTime   |        o       |                |                |
   | (Section 6.1)  |                |                |                |
   | locationType   |        o       |                |                |
   | (Section 6.2)  |                |                |                |
   | code           |                |                |        m       |
   | (Section 6.3)  |                |                |                |
   | message        |                |                |        o       |
   | (Section 6.4)  |                |                |                |
   | locationUriSet |                |        o       |                |
   | (Section 6.5)  |                |                |                |
   | Presence       |                |        o       |                |
   | (PIDF-LO)      |                |                |                |
   | (Section 6.6)  |                |                |                |

                     Table 1: Message Parameter Usage

6.1.  "responseTime" Parameter

   The "responseTime" attribute MAY be included in a location request
   message.  The "responseTime" attribute includes a time value
   indicating to the LIS how long the Device is prepared to wait for a
   response or a purpose for which the Device needs the location.

   In the case of emergency services, the purpose of obtaining the LI
   could be either for routing a call to the appropriate PSAP or
   indicating the location to which responders should be dispatched.
   The values defined for the purpose, "emergencyRouting" and
   "emergencyDispatch", will likely be governed by jurisdictional
   policies, and should be configurable on the LIS.

   The time value in the "responseTime" attribute is expressed as a non-
   negative integer in units of milliseconds.  The time value is
   indicative only and the LIS is under no obligation to strictly adhere
   to the time limit implied; any enforcement of the time limit is left
   to the requesting Device.  The LIS should provide the most accurate
   LI that can be determined within the specified interval for the
   specific service.

   The LIS may use the value of the time in the "responseTime" attribute
   as input when selecting the method of location determination, where
   multiple such methods exist.  If the "responseTime" attribute is
   absent, then the LIS should return the most precise LI it is capable
   of determining, with the time interval being implementation

6.2.  "locationType" Parameter

   The "locationType" element MAY be included in a location request
   message.  It contains a list of LI types that are requested by the
   Device.  The following list describes the possible values:

   any:  The LIS SHOULD attempt to provide LI in all forms available to
   geodetic:  The LIS SHOULD return a geodetic location for the Target.
   civic:  The LIS SHOULD return a civic address for the Target.
   locationURI:  The LIS SHOULD return a set of location URIs for the

   The LIS SHOULD return the requested location type or types.  The
   location types the LIS returns also depend on the setting of the
   optional "exact" attribute.  If the "exact" attribute is set to
   "true" then the LIS MUST return either the requested location type or
   provide an error response.  The "exact" attribute does not apply (is
   ignored) for a request for a location type of "any".  Further detail
   of the "exact" attribute processing is provided in the following
   Section 6.2.1.

   In the case of a request for specific locationType(s) and the "exact"
   attribute is false, the LIS MAY provide additional location types, or
   it MAY provide alternative types if the request cannot be satisfied
   for a requested location type.  The "SHOULD"-strength requirements on
   this parameter for specific location types are included to allow for
   soft-failover.  This enables a fixed client configuration that
   prefers a specific location type without causing location requests to
   fail when that location type is unavailable.  For example, a notebook
   computer could be configured to retrieve civic addresses, which is
   usually available from typical home or work situations.  However,
   when using a wireless modem, the LIS might be unable to provide a
   civic address and thus provides a geodetic address.

   The LIS SHOULD return location information in a form that is suited
   for routing and responding to an emergency call in its jurisdiction,
   specifically by value.  The LIS MAY alternatively or additionally
   return a location URI.  If the LIS believes that the Device is
   mobile, that is, its location may change over relatively short
   periods of time (i.e., several minutes), it SHOULD return a location
   URI.  If the "locationType" element is absent, a location URI MUST be
   assumed as the default.  A location URI provided by the LIS is a
   reference to the most current available LI and is not a stable
   reference to a specific location.

   It should be noted that the protocol does not support a request to
   just receive one of a subset of location types.  For example, in the
   case where a Device has a preference for just "geodetic" or "civic",
   it is necessary to make the request without an "exact" attribute,
   including both location types.  In this case, if neither is available
   a LIS SHOULD return a locationURI if available.

   The LIS SHOULD provide the locations in the response in the same
   order in which they were included in the "locationType" element in
   the request.  Indeed, the primary advantage of including specific
   location types in a request when the "exact" attribute is set to
   "false" is to ensure that one receives the available locations in a
   specific order.  For example, a locationRequest for "civic" could
   yield any of the following location types in the response:

   o  civic
   o  civic, geodetic
   o  civic, locationURI
   o  civic, geodetic, locationURI
   o  civic, locationURI, geodetic
   o  geodetic, locationURI (only if civic is not available)
   o  locationURI, geodetic (only if civic is not available)
   o  geodetic (only if civic is not available)
   o  locationURI (only if civic is not available)

   For the example above, if the "exact" attribute was "true", then the
   only possible response is either a "civic" location or an error

6.2.1.  "exact" Attribute

   The "exact" attribute MAY be included in a location request message
   when the "locationType" element is included.  When the "exact"
   attribute is set to "true", it indicates to the LIS that the contents
   of the "locationType" parameter MUST be strictly followed.  The
   default value of "false" allows the LIS the option of returning
   something beyond what is specified, such as a set of location URIs
   when only a civic location was requested.

   A value of "true" indicates that the LIS MUST provide a location of
   the requested type or types or MUST provide an error.  The LIS MUST
   provide the requested types only.  The LIS MUST handle an exact
   request that includes a "locationType" element set to "any" as if the
   "exact" attribute were set to "false".

6.3.  "code" Parameter

   All "error" responses MUST contain a response code.  All errors are
   application-level errors, and MUST only be provided in successfully
   processed transport-level responses.  For example where HTTP/HTTPS is
   used as the transport, HELD error messages MUST be accompanied by a
   200 OK HTTP/HTTPS response.

   The value of the response code MUST be one of the following tokens:

   requestError:  This code indicates that the request was badly formed
      in some fashion (other than the XML content).
   xmlError:  This code indicates that the XML content of the request
      was either badly formed or invalid.
   generalLisError:  This code indicates that an unspecified error
      occurred at the LIS.
   locationUnknown:  This code indicates that the LIS could not
      determine the location of the Device.

   unsupportedMessage:  This code indicates that an element in the XML
      document for the request, was not supported or understood by the
      LIS.  This error code is used when a HELD request contains a
      document element that is not supported by the receiver.
   timeout:  This code indicates that the LIS could not satisfy the
      request within the time specified in the "responseTime" parameter.
   cannotProvideLiType:  This code indicates that the LIS was unable to
      provide LI of the type or types requested.  This code is used when
      the "exact" attribute on the "locationType" parameter is set to
   notLocatable:  This code indicates that the LIS is unable to locate
      the Device, and that the Device MUST NOT make further attempts to
      retrieve LI from this LIS.  This error code is used to indicate
      that the Device is outside the access network served by the LIS;
      for instance, the VPN and NAT scenarios discussed in
      Section 4.1.2.

6.4.  "message" Parameter

   The "error" message MAY include a "message" attribute to convey some
   additional, human-readable information about the result of the
   request.  This message MAY be included in any language, which SHOULD
   be indicated by the "xml:lang", attribute.  The default language is
   assumed to be English.

6.5.  "locationUriSet" Parameter

   The "locationUriSet" element, received in a "locationResponse"
   message MAY contain any number of "locationURI" elements.  It is
   RECOMMENDED that the LIS allocate a Location URI for each scheme that
   it supports and that each scheme is present only once.  URI schemes
   and their secure variants, such as http and https, MUST be regarded
   as two separate schemes.

   If a "locationUriSet" element is received in a "locationResponse"
   message, it MUST contain an "expires" attribute, which defines the
   length of time for which the set of "locationURI" elements are valid.

6.5.1.  "locationURI" Parameter

   The "locationURI" element includes a single Location URI.  In order
   for a URI of any particular scheme to be included in a response,
   there MUST be a specification that defines how that URI can be used
   to retrieve location information.  The details of the protocol for
   dereferencing must meet the location dereference protocol
   requirements as specified in [I-D.ietf-geopriv-lbyr-requirements] and
   are outside the scope of this base HELD specification.

   Each Location URI that is allocated by the LIS is unique to the
   device that is requesting it.  At the time the location URI is
   provided in the response, there is no binding to a specific location
   type and the location URI is totally independent of the specific type
   of location it might reference.  The specific location type is
   determined at the time of dereference.

   A "locationURI" SHOULD NOT contain any information that could be used
   to identify the Device or Target.  Thus, it is RECOMMENDED that the
   "locationURI" element contain a public address for the LIS and an
   anonymous identifier, such as a local identifier or unlinked
   pseudonym.  Further guidelines to ensure the the privacy and
   confidentiality of the information contained in the
   "locationResponse" message, including the "locationURI", are included
   in Section 9.3.

6.5.2.  "expires" Parameter

   The "expires" attribute is only included in a "locationResponse"
   message when a "locationUriSet" element is included.  The "expires"
   attribute indicates the date/time at which the Location URIs provided
   by the LIS will expire.  The "expires" attribute does not define the
   length of time a location received by dereferencing the location URI
   will be valid.  The "expires" attribute is RECOMMENDED not to exceed
   24 hours and SHOULD be a minimum of several minutes.

   Location responses that contain a "locationUriSet" element MUST
   include the expiry time in the "expires" attribute.  If a Device
   dereferences a location URI after the expiry time, the dereference
   SHOULD fail.

6.6.  "Presence" Parameter (PIDF-LO)

   A "presence" parameter may be included in the "locationResponse"
   message when specific locationTypes (e.g., "geodetic" or "civic") are
   requested or a "locationType" of "any" is requested.  The LIS MUST
   follow the subset of the rules relating to the construction of the
   "location-info" element in the PIDF-LO Usage Clarification,
   Considerations and Recommendations document
   [I-D.ietf-geopriv-pdif-lo-profile] in generating the PIDF-LO for the
   presence parameter.

   Note that the presence parameter is not explicitly shown in the XML
   schema in Section 7 for a location response message, due to XML
   schema constraints, since PIDF is already defined and registered
   separately.  Thus, the "##other" namespace serves as a placeholder
   for the presence parameter in the schema.

7.  XML Schema

   This section gives the XML Schema Definition
   [W3C.REC-xmlschema-1-20041028], [W3C.REC-xmlschema-2-20041028] of the
   "application/held+xml" format.  This is presented as a formal
   definition of the "application/held+xml" format.  Note that the XML
   Schema definition is not intended to be used with on-the-fly
   validation of the presence XML document.  Whitespaces are included in
   the schema to conform to the line length restrictions of the RFC
   format without having a negative impact on the readability of the
   document.  Any conforming processor should remove leading and
   trailing white spaces.

  <?xml version="1.0"?>

        This document (RFC xxxx) defines HELD messages.
        <!-- [[NOTE TO RFC-EDITOR: Please replace XXXX
              with the RFC number for this specification.]] -->

    <xs:import namespace=""

    <!-- Return Location -->
    <xs:complexType name="returnLocationType">
        <xs:restriction base="xs:anyType">
            <xs:element name="locationURI" type="xs:anyURI"
          <xs:attribute name="expires" type="xs:dateTime"
    <!-- responseTime Type -->
    <xs:simpleType name="responseTimeType">
          <xs:restriction base="xs:token">
            <xs:enumeration value="emergencyRouting"/>
            <xs:enumeration value="emergencyDispatch"/>
          <xs:restriction base="xs:nonNegativeInteger">
            <xs:minInclusive value="0"/>

    <!-- Location Type -->
    <!-- Location Type -->
    <xs:simpleType name="locationTypeBase">
          <xs:restriction base="xs:token">
            <xs:enumeration value="any"/>
          <xs:restriction base="held:locationTypeList">
            <xs:minLength value="1"/>

    <xs:simpleType name="locationTypeList">
          <xs:restriction base="xs:token">
            <xs:enumeration value="civic"/>
            <xs:enumeration value="geodetic"/>
            <xs:enumeration value="locationURI"/>

    <xs:complexType name="locationTypeType">
        <xs:extension base="held:locationTypeBase">
          <xs:attribute name="exact" type="xs:boolean"
                        use="optional" default="false"/>

    <!-- Message Definitions -->
    <xs:complexType name="baseRequestType">
        <xs:restriction base="xs:anyType">
          <xs:attribute name="responseTime" type="held:responseTimeType"
          <xs:anyAttribute namespace="##any" processContents="lax"/>

    <xs:complexType name="errorType">
        <xs:restriction base="xs:anyType">
          <xs:attribute name="code" type="xs:token"
          <xs:attribute name="message" type="xs:string"
          <xs:attribute ref="xml:lang" use="optional"/>

    <xs:element name="error" type="held:errorType"/>

    <!-- Location Response -->
    <xs:complexType name="locationResponseType">
        <xs:restriction base="xs:anyType">
            <xs:element name="locationUriSet"
            <xs:any namespace="##other" processContents="lax"
                    minOccurs="0" maxOccurs="unbounded"/>

    <xs:element name="locationResponse"

    <!-- Location Request -->

    <xs:complexType name="locationRequestType">
        <xs:extension base="held:baseRequestType">
            <xs:element name="locationType"
            <xs:any namespace="##other" processContents="lax"
                    minOccurs="0" maxOccurs="unbounded"/>

    <xs:element name="locationRequest"


8.  HTTP/HTTPS Binding

   This section describes the use of HTTP [RFC2616] and HTTPS [RFC2818]
   as transport mechanisms for the HELD protocol, which all conforming
   implementations MUST support.

   The request is carried in the body of an HTTP/HTTPS POST request.
   The MIME type of both request and response bodies should be
   "application/held+xml".  This should be reflected in the HTTP
   Content-Type and Accept header fields.

   The LIS populates the HTTP/HTTPS headers so that they are consistent
   with the contents of the message.  In particular, the cache control
   header SHOULD be set to disable the HTTP/HTTPS caching of any PIDF-LO
   document or Location URIs.  Otherwise, there is the risk of stale
   locations and/or the unauthorized disclosure of the LI.  This also
   allows the LIS to control any caching with the "expires" parameter.
   The HTTP/HTTPS status code MUST indicate a 2xx series response for
   all HELD locationResponse and error messages.

   The use of HTTP/HTTPS also includes a default behaviour, which is
   triggered by a GET request, or a POST with no request body.  If
   either of these queries are received, the LIS MUST attempt to provide
   either a PIDF-LO document or a Location URI, as if the request was a
   location request.

   Implementation of HELD that implement HTTP transport MUST implement a
   transport over HTTPS [RFC2818].  TLS provides message integrity and
   confidentiality between Device and LIS.  The LIS MUST implement the
   server authentication method described in [RFC2818].  The device uses
   the URI obtained during LIS discovery to authenticate the server.
   The details of this authentication method are provided in section 3.1
   of [RFC2818].  When TLS is used, the Device SHOULD fail a request if
   server authentication fails, except in the event of an emergency.

9.  Security Considerations

   HELD is a location acquisition protocol whereby the a client requests
   its location from a LIS.  Specific requirements and security
   considerations for location acquisition protocols are provided in
   [I-D.ietf-geopriv-l7-lcp-ps].  An in-depth discussion of the security
   considerations applicable to the use of Location URIs and by
   reference provision of LI is included in

   By using the HELD protocol, the client and the LIS expose themselves
   to two types of risk:

   Accuracy:  Client receives incorrect location information
   Privacy:  An unauthorized entity receives location information

   The provision of an accurate and privacy/confidentiality protected
   location to the requestor depends on the success of five steps:

      1.  The client must determine the proper LIS.
      2.  The client must connect to the proper LIS.
      3.  The LIS must be able to identify the device by its identifier
      (IP Address).
      4.  The LIS must be able to return the desired location.
      5.  HELD messages must be transmitted unmodified between the LIS
      and the client.

   Of these, only the second, third and the fifth are within the scope
   of this document.  The first step is based on either manual
   configuration or on the LIS discovery defined in
   [I-D.ietf-geopriv-lis-discovery], in which appropriate security
   considerations are already discussed.  The fourth step is dependent
   on the specific positioning capabilities of the LIS, and is thus
   outside the scope of this document.

9.1.  Assuring that the proper LIS has been contacted

   This document assumes that the LIS to be contacted is identified
   either by an IP address or a domain name, as is the case for a LIS
   discovered as described in LIS Discovery
   [I-D.ietf-geopriv-lis-discovery].  When the HELD transaction is
   conducted using TLS [RFC4346], the LIS can authenticate its identity,
   either as a domain name or as an IP address, to the client by
   presenting a certificate containing that identifier as a
   subjectAltName (i.e., as an iPAddress or dNSName, respectively).  In
   the case of the HTTP binding described above, this is exactly the
   authentication described by TLS [RFC2818].  Any binding of HELD MUST
   be capable of being transacted over TLS so that the client can
   request the above authentication, and a LIS implementation for a
   binding MUST include this feature.  Note that in order for the
   presented certificate to be valid at the client, the client must be
   able to validate the certificate.  In particular, the validation path
   of the certificate must end in one of the client's trust anchors,
   even if that trust anchor is the LIS certificate itself.

9.2.  Protecting responses from modification

   In order to prevent that response from being modified en route,
   messages must be transmitted over an integrity-protected channel.
   When the transaction is being conducted over TLS (a required feature
   per Section 9.1), the channel will be integrity protected by
   appropriate ciphersuites.  When TLS is not used, this protection will
   vary depending on the binding; in most cases, without protection from
   TLS, the response will not be protected from modification en route.

9.3.  Privacy and Confidentiality

   Location information returned by the LIS must be protected from
   access by unauthorized parties, whether those parties request the
   location from the LIS or intercept it en route.  As in section Section 9.2,
   transactions conducted over TLS with appropriate ciphersuites are
   protected from access by unauthorized parties en route.  Conversely,
   in most cases, when not conducted over TLS, the response will be
   accessible while en route from the LIS to the requestor.

   Because HELD is an LCP and identifies clients and targets by IP
   addresses, a requestor is authorized to access location for an IP
   address only if it is the holder of that IP address.  The LIS MUST
   verify that the client is the target of the returned location, i.e.,
   the LIS MUST NOT provide location to other entities than the target.
   Note that this is a necessary, but not sufficient criterion for
   authorization.  A LIS MAY deny requests according to any local

   A prerequisite for meeting this requirement is that the LIS must have
   some assurance of the identity of the client.  Since the target of
   the returned location is identified by an IP address, simply sending
   the response to this IP address will provide sufficient assurance in
   many cases.  This is the default mechanism in HELD for assuring that
   location is given only to authorized clients; LIS implementations
   MUST support a mode of operation in which this is the only client

   Using IP return routability as an authenticator means that location
   information is vulnerable to exposure through IP address spoofing
   attacks.  A temporary spoofing of IP address could mean that a device
   could request a Location Object or Location URI that would result in
   another Device's location.  In addition, in cases where a Device
   drops off the network for various reasons, the re-use of the Device's
   IP address could result in another Device receiving the original
   Device's location rather than its own location.  These exposures are
   limited by the following:

   o  Location URIs MUST have a limited lifetime, as reflected by the
      value for the expires element in Section Section 6.5.2.  The lifetime of
      location URIs necessarily depends on the nature of the access.
   o  The network SHOULD have mechanisms that protect against IP address
      spoofing, such as those defined in [RFC3704].
   o  The LIS and network SHOULD be configured so that the LIS is made
      aware of Device movement within the network and addressing
      changes.  If the LIS detects a change in the network that results
      in it no longer being able to determine the location of the
      Device, then all location URIs for that Device SHOULD be

   The above measures are dependent on network configuration, which
   SHOULD be considered.  For instance, in a fixed internet access,
   providers may be able to restrict the allocation of IP addresses to a
   single physical line, ensuring that spoofing is not possible; in such
   an environment, additional measures may not be necessary.

10.  Examples

   The following sections provide basic HTTP/HTTPS examples, a simple
   location request example and a location request for multiple location
   types example along with the relevant location responses.  To focus
   on important portions of messages, the examples in Section 10.2 and
   Section 10.3 do not show HTTP/HTTPS headers or the XML prologue.  In
   addition, sections of XML not relevant to the example are replaced
   with comments.

10.1.   HTTPS Example Messages

   The examples in this section show a complete HTTPS message that
   includes the HELD request or response document.

   This example shows the most basic request for a LO.  This uses the
   GET feature described by the HTTP binding.

         GET /location HTTP/1.1
         Accept-Charset: UTF-8,*

   The GET request is exactly identical to a minimal POST request that
   includes an empty "locationRequest" element.

         POST /location HTTP/1.1
         Accept: application/held+xml,
         Accept-Charset: UTF-8,*
         Content-Type: application/held+xml
         Content-Length: 87

         <?xml version="1.0"?>
         <locationRequest xmlns="urn:ietf:params:xml:ns:geopriv:held"/>
   Since neither of these requests includes a "locationType" element,
   the successful response to either of these requests may contain any
   type of location.  The following shows a response containing a
   minimal PIDF-LO.


         HTTP/1.1 200 OK
         Server: Example LIS
         Date: Tue, 10 Jan 2006 03:42:29 GMT
         Expires: Tue, 10 Jan 2006 03:42:29 GMT
         Cache-control: private
         Content-Type: application/held+xml
         Content-Length: 594

         <?xml version="1.0"?>
         <locationResponse xmlns="urn:ietf:params:xml:ns:geopriv:held">
         <presence xmlns="urn:ietf:params:xml:ns:pidf"
           <tuple id="b650sf789nd">
            <geopriv xmlns="urn:ietf:params:xml:ns:pidf:geopriv10">
                <Point xmlns=""
                  <pos>-34.407 150.88001</pos>
   The error response to either of these requests is an error document.
   The following response shows an example error response.

         HTTP/1.1 200 OK
         Server: Example LIS
         Expires: Tue, 10 Jan 2006 03:49:20 GMT
         Cache-control: private
         Content-Type: application/held+xml
         Content-Length: 135

         <?xml version="1.0"?>
         <error xmlns="urn:ietf:params:xml:ns:geopriv:held"
                message="Unable to determine location"/>

10.2.  Simple Location Request Example

   The location request shown below doesn't specify any location types
   or response time.

   <locationRequest xmlns="urn:ietf:params:xml:ns:geopriv:held"/>

   The example response to this location request contains a list of
   Location URIs.

      <locationResponse xmlns="urn:ietf:params:xml:ns:geopriv:held">
        <locationUriSet expires="2006-01-01T13:00:00">
   An error response to this location request is shown below:

         <error xmlns="urn:ietf:params:xml:ns:geopriv:held"
                    message="Location not available"/>

10.3.  Location Request Example for Multiple Location Types

   The following Location Request message includes a request for
   geodetic, civic and any Location URIs.

         <locationRequest xmlns="urn:ietf:params:xml:ns:geopriv:held">
          <locationType exact="true">

   The corresponding Location Response message includes the requested
   location information, including two location URIs.

       <locationResponse xmlns="urn:ietf:params:xml:ns:geopriv:held">
          <locationUriSet expires="2006-01-01T13:00:00">
         <presence xmlns="urn:ietf:params:xml:ns:pidf:geopriv10"
         <tuple id="lisLocation">
              <gml:pos>-34.407242 150.882518</gml:pos>
              <gs:radius uom="urn:ogc:def:uom:EPSG::9001">30
              <ca:STS>Northfield Avenue</ca:STS>
              <ca:LMK>University of Wollongong</ca:LMK>
              <ca:NAM>Andrew Corporation</ca:NAM>

11.  IANA Considerations

   This document requires several IANA registrations detailed in the
   following sections.

11.1.  URN Sub-Namespace Registration for

   This section registers a new XML namespace,
   "urn:ietf:params:xml:ns:geopriv:held", per the guidelines in

      URI: urn:ietf:params:xml:ns:geopriv:held
      Registrant Contact: IETF, GEOPRIV working group,
      (, Mary Barnes (

           <?xml version="1.0"?>
           <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
           <html xmlns="" xml:lang="en">
               <title>HELD Messages</title>
               <h1>Namespace for HELD Messages</h1>
       [NOTE TO IANA/RFC-EDITOR: Please replace XXXX
       with the RFC number for this specification.]
               <p>See RFCXXXX</p>

11.2.  XML Schema Registration

   This section registers an XML schema as per the guidelines in

   URI:  urn:ietf:params:xml:schema:geopriv:held
   Registrant Contact:  IETF, GEOPRIV working group, (,
      Mary Barnes (
   Schema:  The XML for this schema can be found as the entirety of
      Section 7 of this document.

11.3.  MIME Media Type Registration for 'application/held+xml'

   This section registers the "application/held+xml" MIME type.

   Subject:  Registration of MIME media type application/held+xml
   MIME media type name:  application
   MIME subtype name:  held+xml
   Required parameters:  (none)
   Optional parameters:  charset
      Indicates the character encoding of enclosed XML.  Default is

   Encoding considerations:  Uses XML, which can employ 8-bit
      characters, depending on the character encoding used.  See RFC
      3023 [RFC3023], section 3.2.
   Security considerations:  This content type is designed to carry
      protocol data related to the location of an entity, which could
      include information that is considered private.  Appropriate
      precautions should be taken to limit disclosure of this
   Interoperability considerations:  This content type provides a basis
      for a protocol
   Published specification:  RFC XXXX [NOTE TO IANA/RFC-EDITOR: Please
      replace XXXX with the RFC number for this specification.]
   Applications which use this media type:  Location information
      providers and consumers.
   Additional Information:  Magic Number(s): (none)
      File extension(s): .xml
      Macintosh File Type Code(s): (none)
   Person & email address to contact for further information:  Mary
      Barnes <>
   Intended usage:  LIMITED USE
   Author/Change controller:  The IETF
   Other information:  This media type is a specialization of
      application/xml [RFC3023], and many of the considerations
      described there also apply to application/held+xml.

11.4.  Error code Registry

   This document requests that the IANA create a new registry for the
   HELD protocol including an initial registry for error codes.  The
   error codes are included in HELD error messages as described in
   Section 6.3 and defined in the schema in the 'codeType' token in the
   XML schema in (Section 7)

   The following summarizes the requested registry:

   Related Registry:   Geopriv HELD Registries, Error codes for HELD
   Defining RFC:  RFC XXXX [NOTE TO IANA/RFC-EDITOR: Please replace XXXX
      with the RFC number for this specification.]
   Registration/Assignment Procedures:  Following the policies outlined
      in [RFC5226], the IANA policy for assigning new values for the
      Error codes for HELD shall be Specification Required: values and
      their meanings must be documented in an RFC or in some other
      permanent and readily available reference, in sufficient detail
      that interoperability between independent implementations is

   Registrant Contact:  IETF, GEOPRIV working group, (,
      Mary Barnes (

   This section pre-registers the following seven initial error codes as
   described above in Section 6.3:

   requestError:  This code indicates that the request was badly formed
      in some fashion.
   xmlError:  This code indicates that the XML content of the request
      was either badly formed or invalid.
   generalLisError:  This code indicates that an unspecified error
      occurred at the LIS.
   locationUnknown:  This code indicates that the LIS could not
      determine the location of the Device.
   unsupportedMessage:  This code indicates that the request was not
      supported or understood by the LIS.  This error code is used when
      a HELD request contains a document element that is not supported
      by the receiver.
   timeout:  This code indicates that the LIS could not satisfy the
      request within the time specified in the "responseTime" parameter.
   cannotProvideLiType:  This code indicates that the LIS was unable to
      provide LI of the type or types requested.  This code is used when
      the "exact" attribute on the "locationType" parameter is set to
   notLocatable:  This code indicates that the LIS is unable to locate
      the Device, and that the Device MUST NOT make further attempts to
      retrieve LI from this LIS.  This error code is used to indicate
      that the Device is outside the access network served by the LIS;
      for instance, the VPN and NAT scenarios discussed in
      Section 4.1.2.

12.  Contributors

   James Winterbottom, Martin Thomson and Barbara Stark are the authors
   of the original document, from which this WG document was derived.
   Their contact information is included in the Author's address
   section.  In addition, they also contributed to the WG document,
   including the XML schema.

13.  Acknowledgements

   The author/contributors would like to thank the participants in the
   GEOPRIV WG and the following people for their constructive input and
   feedback on this document (in alphabetical order): Nadine Abbott,
   Eric Arolick, Richard Barnes (in particular the security section),
   Peter Blatherwick, Ben Campbell, Guy Caron, Eddy Corbett, Martin
   Dawson, Lisa Dusseault, Jerome Grenier, Ted Hardie, Cullen Jennings,
   Neil Justusson, Tat Lam, Marc Linsner, Patti McCalmont, Roger
   Marshall, Perry Prozeniuk, Carl Reed, Julian Reschke, Eric Rescorla,
   Brian Rosen, John Schnizlein, Shida Schubert, Henning Schulzrinne, Ed
   Shrum, Doug Stuard, Hannes Tschofenig and Karl Heinz Wolf.

14.  Changes since last Version

   NOTE TO THE RFC-Editor: Please remove this section prior to
   publication as an RFC.

   Changes from WG 09 to 10 (2nd WGLC):

   1) Updated text for Devices and VPNs (section 4.1.1) to include
   servers such as HTTP and SOCKs, thus changed the text to be generic
   in terms of locating LIS before connecting to one of these servers,

   2) Fixed (still buggy) HTTP examples.

   3) Added text explaining the whitespaces in XML schema are for
   readability/document format limitations and that they should be
   handled via parser/schema validation.

   4) Miscellaneous editorial nits

   Changes from WG 08 to 09 (Post-IETF LC: continued resolution of sec-
   dir and gen-art review comments, along with apps-area feedback):

   1) Removed heldref/heldrefs URIs, including fixing examples (which
   were buggy anyways).

   2) Clarified text for locationURI - specifying that the deref
   protocol must define or appropriately restrict and clarifying that
   requirements for deref must be met and that deref details are out of
   scope for this document.

   3) Clarified text in security section for support of both HTTP/HTTPS.

   4) Changed definition for Location Type to force the specification of
   at least one location type.

   Changes from WG 07 to 08 (IETF LC: sec-dir and gen-art review

   1) Fix editorial nits: rearranging sections in 4.1 for readibility,

   2) Added back text in Device and VPN section referencing DHCP and
   LLDP-MED when a VPN device serves as a LIS.

   3) Clarified the use of both HTTP and HTTPS.

   4) Defined two URIs related to 3 respectively - divided IANA
   registrations into sub-sections to accomodate this change.  (Note:
   LIS Discovery will now define that URI, thus this document defines
   the one associatied with a Location reference).

   5) Clarified the description of the location URI in Protocol Overview
   and Protocol parameter sections.  Note that these sections again
   reference location dereference protocol for completeness and
   clarification of issues that are out of scope for this base document.

   6) Defined new error code: notLocatable.

   7) Clarifications and corrections in security section.

   8) Clarified text for locationType, specifically removing extra text
   from "any" description and putting that in a separate paragraph.
   Also, provided an example.

   9) Added boundaries for "expires" parameter.

   10) Clarified that the HELD protocol as defined by this document does
   not allow for canceling location references.

   Changes from WG 06 to 07 (PROTO review comments):

   1) Fix nits: remove unused references, move requirements to
   Informational References section, fix long line in ABNF, fix ABNF
   (quotes around '?'), add schemaLocation to import namespace in XML

   2) Remove text in Device and VPN section referencing DHCP and LLDP-
   MED when a VPN device serves as a LIS, per Issue 1 resolution at
   IETF-71.  (Editorial oversight in producing version 06).

   Changes from WG 05 to 06 (2nd WGLC comments):

   1) Updated security section based on WG feedback, including
   condensing section 10.1.1 (Assuring the proper LIS has been
   contacted), restructuring sections by flattening, adding an
   additional step to the list that had been in the Accuracy section and
   removing summary section.

   2) Changed URI schema to "helds" to address concerns over referential
   integrity and for consistency with mandate of TLS for HELD.

   3) Editorial clarifications including fixing examples to match HELD
   URI definition (e.g., adding port, adding randomness to URI examples,

   4) Updated references removing unused references and moving
   requirements docs to Informational Reference section to avoid

   Changes from WG 04 to 05 (WGLC comments):

   1) Totally replaced the security section with the details provided by
   Richard Barnes so that we don't need a reference to the location
   security document.

   2) Fixed error codes in schema to allow extensibility.  Change the
   IANA registration to be "specification required".

   3) Cleaned up the HELD: URI description, per comments from Martin and
   James and partially addressing HELD-04 Issue 1.  Put the definition
   in a separate section and clarified the applicability (to also
   include being a results of the discovery process) and fixed examples.

   4) Updated the LocationURI section to be more accurate, address
   HELD-04 Issue 3, and include the reference to the new HELD:URI
   section.  Also, fixed an error in the doc in that the top level parm
   in the locationResponse is actually locationUriSet, which contains
   any number of locationURI elements and the "expires" parameter.  So,
   Table 1 was also updated and a new section for the LocationURISet was
   added that includes the subsections for the "locationURI" and
   "expires".  And, then clarified that "expires" applies to
   "locationURISet" and not per "locationURI".

   5) Editorial nits: pointed out offline by Richard (e.g., by-value ->
   by value, by-reference -> by reference, etc.) and onlist by James and
   Martin.  Please refer to the diff for a complete view of editorial

   6) Added text in HTTP binding section to disable HTTP caching
   (HELD-04 Issue 5 on the list).

   Changes from WG 03 to 04:

   1) Terminology: clarified in terminology section that "attribute" and
   "element" are used in the strict XML sense and "parameter" is used as
   a general protocol term Replaced term "HTTP delivery" with "HTTP
   transport".  Still have two terms "HTTP transport" and "HTTP
   binding", but those are consistent with general uses of HTTP.

   2) Editorial changes and clarifications: per Roger Marshall's and
   Eric Arolick's comments and subsequent WG mailing list discussion.

   3) Changed normative language for describing expected and recommended
   LIS behaviors to be non-normative recommendations in cases where the
   protocol parameters were not the target of the discussion (e.g., we
   can't prescribe to the LIS how it determines location or what it
   defines to be an "accurate" location).

   4) Clarified responseTime attribute (section 6.1).  Changed type from
   "decimal" to "nonNegativeInteger" in XML schema (section 7)

   5) Updated Table 1 in section 6 to only include top-level parameters
   and fixed some errors in that table (i.e., code for locationResponse)
   and adding PIDF-LO to the table.  Added a detailed section describing
   PIDF-LO (section 6.6), moving some of the normative text in the
   Protocol Overview to this section.

   6) Added schema and description for locationURI to section 6.5.
   Added IANA registration for HELD: URI schema.

   7) Added IANA registry for error codes.

   Changes from WG 02 to 03:

   1) Added text to address concern over use of IP address as device
   identifier, per long email thread - changes to section 3 (overview)
   and section 4 (protocol overview).

   2) Removed WSDL (section 8 updated, section 8.1 and 10.4 removed)

   3) Added extensibility to baseRequestType in the schema (an oversight
   from previous edits), along with fixing some other nits in schema
   (section 7)

   4) Moved discussion of Location URI from section 5.3 (Location
   Response) to where it rightly belonged in Section 6.5 (Location URI

   5) Clarified text for "expires" parameter (6.5.1) - it's an optional
   parm, but required for LocationURIs

   6) Clarified responseTime parameter: when missing, then the LCS
   provides most precise LI, with the time required being implementation

   7) Clarified that the MUST use in section 8 (HTTP binding) is a MUST

   8) Updated references (removed unused/added new).

   Changes from WG 01 to 02:

   1) Updated Terminology to be consistent with WG agreements and other
   documents (e.g., LCS -> LIS and removed duplicate terms).  In the
   end, there are no new terms defined in this document.

   2) Modified definition of responseTime to reflect WG consensus.

   3) Removed jurisdictionalCivic and postalCivic locationTypes (leaving
   just "civic").

   4) Clarified text that locationType is optional.  Fixed table 1 and
   text in section 5.2 (locationRequest description).  Text in section
   6.2 (description of locationType element) already defined the default
   to be "any".

   5) Simplified error responses.  Separated the definition of error
   response type from the locationResponse type thus no need for
   defining an error code of "success".  This simplifies the schema and

   6) Updated schema/examples for the above.

   7) Updated Appendix A based on updates to requirements document,
   specifically changes to A.1, A.3 and adding A.10.

   8) Miscellaneous editorial clarifications.

   Changes from WG 00 to 01:

   1) heldResponse renamed to locationResponse.

   2) Changed namespace references for the PIDF-LO geoShape in the
   schema to match the agreed GML PIDF-LO Geometry Shape Application

   3) Removed "options" element - leaving optionality/extensibility to
   XML mechanisms.

   4) Changed error codes to be enumerations and not redefinitions of
   HTTP response codes.

   5) Updated schema/examples for the above and removed some remnants of
   the context element.

   6) Clarified the definition of "Location Information (LI)" to include
   a reference to the location (to match the XML schema and provide
   consistency of usage throughout the document).  Added an additional
   statement in section 7.2 (locationType) to clarify that LCS MAY also
   return a Location URI.

   7) Modifed the definition of "Location Configuration Server (LCS)" to
   be consistent with the current definiton in the requirements

   8) Updated Location Response (section 6.3) to remove reference to
   context and discuss the used of a local identifier or unlinked
   pseudonym in providing privacy/security.

   9) Clarified that the source IP address in the request is used as the
   identifier for the target/device for the HELD protocol as defined in
   this document.

   10) Miscellaneous editorial clarifications.

15.  References

15.1.  Normative References

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

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346, April 2006.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed
              Networks", BCP 84, RFC 3704, March 2004.

              Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
              PIDF-LO Usage Clarification, Considerations and
              Recommendations", draft-ietf-geopriv-pdif-lo-profile-11 draft-ietf-geopriv-pdif-lo-profile-13
              (work in progress), February September 2008.

              Maloney, M.,
              Thompson, H., Mendelsohn, N., and D. Beech, D., and M. Maloney,
              "XML Schema Part 1: Structures Second Edition", World Wide
              Web Consortium Recommendation REC-xmlschema-1-20041028,
              October 2004,

              Biron, P. and A. Malhotra, "XML Schema Part 2: Datatypes
              Second Edition", World Wide Web Consortium
              Recommendation REC-xmlschema-2-20041028, October 2004,

              Thomson, M. and J. Winterbottom, "Discovering the Local
              Location Information Server (LIS)",
              draft-ietf-geopriv-lis-discovery-03 (work in progress),
              September 2008.

15.2.  Informative References

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, September 1981.

   [RFC3023]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media
              Types", RFC 3023, January 2001.

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

   [RFC3825]  Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host
              Configuration Protocol Option for Coordinate-based
              Location Configuration Information", RFC 3825, July 2004.

              TIA, "ANSI/TIA-1057 Link Layer Discovery Protocol - Media
              Endpoint Discovery".

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
              Registration Procedures for New URI Schemes", BCP 115,
              RFC 4395, February 2006.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

              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.

              Marshall, R., "Requirements for a Location-by-Reference
              Mechanism", draft-ietf-geopriv-lbyr-requirements-03 (work
              in progress), July 2008.

              Polk, J. and B. Rosen, "Location Conveyance for the
              Session Initiation Protocol",
              draft-ietf-sip-location-conveyance-10 (work in progress),
              September 2008.

              Winterbottom, J., Tschofenig, H., Schulzrinne, H.,
              Thomson, M., and M. Dawson, "An HTTPS Location
              Dereferencing Protocol Using HELD",
              draft-winterbottom-geopriv-deref-protocol-02 (work in
              progress), July 2008.

Appendix A.  HELD Compliance to IETF LCP requirements

   This appendix describes HELD's compliance to the requirements
   specified in the [I-D.ietf-geopriv-l7-lcp-ps].

A.1.  L7-1: Identifier Choice

   "The L7 LCP MUST be able to carry different identifiers or MUST
   define an identifier that is mandatory to implement.  Regarding the
   latter aspect, such an identifier is only appropriate if it is from
   the same realm as the one for which the location information service
   maintains identifier to location mapping."


   HELD uses the IP address of the location request message as the
   primary source of identity for the requesting device or target.  This
   identity can be used with other contextual network information to
   provide a physical location for the Target for many network
   deployments.  There may be network deployments where an IP address
   alone is insufficient to identify a Target in a network.  However,
   any necessary identity extensions for these networks is beyond the
   scope of this document.

A.2.  L7-2: Mobility Support

   "The GEOPRIV Layer 7 Location Configuration Protocol MUST support a
   broad range of mobility from devices that can only move between
   reboots, to devices that can change attachment points with the impact
   that their IP address is changed, to devices that do not change their
   IP address while roaming, to devices that continuously move by being
   attached to the same network attachment point."


   Mobility support is inherently a characteristic of the access network
   technology and HELD is designed to be access network agnostic.
   Consequently HELD complies with this requirement.  In addition HELD
   provides specific support for mobile environments by providing an
   optional responseTime attribute in location request messages.
   Wireless networks often have several different mechanisms at their
   disposal for position determination (e.g.  Assisted GPS versus
   location based on serving base station identity), each providing
   different degrees of accuracy and taking different amounts of time to
   yield a result.  The responseTime parameter provides the LIS with a
   criterion which it can use to select a location determination

A.3.  L7-3: ASP and Access Network Provider Relationship

   "The design of the L7 LCP MUST NOT assume a business or trust
   relationship between the Application Service Provider (ASP) and the
   Access Network Provider.  Requirements for resolving a reference to
   location information are not discussed in this document."


   HELD describes a location acquisition protocol between a Device and a
   LIS.  In the context of HELD, the LIS is within the Access Network.
   Thus, HELD is independent of the business or trust relationship
   between the Application Service Provider (ASP) and the Access Network
   Provider.  Location acquisition using HELD is subject to the
   restrictions described in Section 9.

A.4.  L7-4: Layer 2 and Layer 3 Provider Relationship

   "The design of the GEOPRIV Layer 7 Location Configuration Protocol
   MUST assume that there is a trust and business relationship between
   the L2 and the L3 provider.  The L3 provider operates the LIS and
   needs to obtain location information from the L2 provider since this
   one is closest to the end host.  If the L2 and L3 provider for the
   same host are different entities, they cooperate for the purposes
   needed to determine end system locations."


   HELD was specifically designed with this model in mind and readily
   allows itself to chaining requests between operators without a change
   in protocol being required.  HELD is a webservices protocol it which can
   be bound to transports other than HTTP. HTTP, such as BEEP.  Using o a
   protocol such as BEEP offers the option of high request throughput
   over a dedicated connection between an L3 provider and an L2 provider
   without incurring the serial restriction imposed by HTTP.  This is
   less easy to do with protocols that do not decouple themselves from
   the transport.

A.5.  L7-5: Legacy Device Considerations

   "The design of the GEOPRIV Layer 7 Location Configuration Protocol
   MUST consider legacy residential NAT devices and NTEs in an DSL
   environment that cannot be upgraded to support additional protocols,
   for example to pass additional information through DHCP."


   HELD is an application protocol and operates on top of IP.  A HELD
   request from a host behind a residential NAT will traverse the NAT
   acquiring the external address of the home router.  The location
   provided to the host therefore will be the address of the home router
   in this circumstance.  No changes are required to the home router in
   order to support this function, HELD was designed specifically to
   address this deployment scenario.

A.6.  L7-6: VPN Awareness

   "The design of the GEOPRIV Layer 7 Location Configuration Protocol
   MUST assume that at least one end of a VPN is aware of the VPN
   functionality.  In an enterprise scenario, the enterprise side will
   provide the LIS used by the client and can thereby detect whether the
   LIS request was initiated through a VPN tunnel."

   HELD does not preclude a LIS on the far end of a VPN tunnel being
   aware that the client request is occurring over that tunnel.  It also
   does not preclude a client device from accessing a LIS serving the
   local physical network and subsequently using the location
   information with an application that is accessed over a VPN tunnel.

A.7.  L7-7: Network Access Authentication

   "The design of the GEOPRIV Layer 7 Location Configuration Protocol
   MUST NOT assume prior network access authentication."


   HELD makes no assumptions about prior network access authentication.
   HELD strongly recommends the use of TLS with server-side certificates
   for communication between the end-point and the LIS.  There is no
   requirement for the end-point to authenticate with the LIS.

A.8.  L7-8: Network Topology Unawareness

   "The design of the GEOPRIV Layer 7 Location Configuration Protocol
   MUST NOT assume end systems being aware of the access network
   topology.  End systems are, however, able to determine their public
   IP address(es) via mechanisms such as STUN or NSIS NATFW NSLP."


   HELD makes no assumption about the network topology.  HELD doesn't
   require that the device know its external IP address, except where
   that is required for discovery of the LIS.

A.9.  L7-9: Discovery Mechanism

   "The L7 LCP MUST define a single mandatory to implement discovery


   HELD uses the discovery mechanism in

A.10.  L7-10: PIDF-LO Creation

   "When a LIS creates a PIDF-LO per RFC 4119 then it MUST put the
   <geopriv> element into the <device> element of the presence document
   (see RFC 4479).  This ensures that the resulting PIDF-LO document,
   which is subsequently distributed to other entities, conforms to the
   rules outlined in ". [I-D.ietf-geopriv-pdif-lo-profile]

   HELD protocol overview (Section 4 ) describes the requirements on the
   LIS in creating the PIDF-LO and prescribes that the PIDF-LO generated
   by the LIS MUST conform to [I-D.ietf-geopriv-pdif-lo-profile].

Authors' Addresses

   Mary Barnes (editor)
   2201 Lakeside Blvd
   Richardson, TX


   James Winterbottom
   PO Box U40
   Wollongong University Campus, NSW  2500

   Phone: +61 2 4221 2938

   Martin Thomson
   PO Box U40
   Wollongong University Campus, NSW  2500

   Phone: +61 2 4221 2915
   Barbara Stark
   Room 7A43
   725 W Peachtree St.
   Atlanta, GA  30308


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