





Internet Engineering Task Force (IETF)                    M. Barnes, Ed.
Request for Comments: 5985                                       Polycom
Category: Standards Track                                 September 2010
ISSN: 2070-1721


                 HTTP-Enabled Location Delivery (HELD)

Abstract

   This document defines a Layer 7 Location Configuration Protocol (L7
   LCP) and describes the use of HTTP and HTTP/TLS as transports for the
   L7 LCP.  The L7 LCP is used for retrieving location information from
   a server within an access network.  It 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 the session layer.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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/rfc5985.

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.





Barnes                       Standards Track                    [Page 1]

RFC 5985                          HELD                    September 2010


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions and Terminology  . . . . . . . . . . . . . . . . .  3
   3.  Overview and Scope . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . .  5
     4.1.  Device Identifiers, NAT and VPNs . . . . . . . . . . . . .  6
       4.1.1.  Devices and VPNs . . . . . . . . . . . . . . . . . . .  6
       4.1.2.  LIS Handling of NATs and VPNs  . . . . . . . . . . . .  7
     4.2.  Location by Value  . . . . . . . . . . . . . . . . . . . .  7
     4.3.  Location by Reference  . . . . . . . . . . . . . . . . . .  8
   5.  Protocol Description . . . . . . . . . . . . . . . . . . . . .  8
     5.1.  Location Request . . . . . . . . . . . . . . . . . . . . .  9
     5.2.  Location Response  . . . . . . . . . . . . . . . . . . . .  9
     5.3.  Indicating Errors  . . . . . . . . . . . . . . . . . . . .  9
   6.  Protocol Parameters  . . . . . . . . . . . . . . . . . . . . . 10
     6.1.  "responseTime" Parameter . . . . . . . . . . . . . . . . . 10
     6.2.  "locationType" Parameter . . . . . . . . . . . . . . . . . 11
       6.2.1.  "exact" Attribute  . . . . . . . . . . . . . . . . . . 13
     6.3.  "code" Parameter . . . . . . . . . . . . . . . . . . . . . 13
     6.4.  "message" Parameter  . . . . . . . . . . . . . . . . . . . 14
     6.5.  "locationUriSet" Parameter . . . . . . . . . . . . . . . . 14
       6.5.1.  "locationURI" Parameter  . . . . . . . . . . . . . . . 14
       6.5.2.  "expires" Parameter  . . . . . . . . . . . . . . . . . 15
     6.6.  "Presence" Parameter (PIDF-LO) . . . . . . . . . . . . . . 16
   7.  XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 16
   8.  HTTP Binding . . . . . . . . . . . . . . . . . . . . . . . . . 20
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 22
     9.1.  Assuring That the Proper LIS Has Been Contacted  . . . . . 23
     9.2.  Protecting Responses from Modification . . . . . . . . . . 23
     9.3.  Privacy and Confidentiality  . . . . . . . . . . . . . . . 23
   10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     10.1. Examples of HTTPS Messages . . . . . . . . . . . . . . . . 25
     10.2. Example of a Simple Location Request . . . . . . . . . . . 26
     10.3. An Example of a Location Request 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 . . . . . . . . . . . . . . . . . . . . . . . . . 32
   13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 32
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33
     14.1. Normative References . . . . . . . . . . . . . . . . . . . 33
     14.2. Informative References . . . . . . . . . . . . . . . . . . 34




Barnes                       Standards Track                    [Page 2]

RFC 5985                          HELD                    September 2010


   Appendix A.  HELD Compliance to IETF LCP Requirements  . . . . . . 36
     A.1.  L7-1: Identifier Choice  . . . . . . . . . . . . . . . . . 36
     A.2.  L7-2: Mobility Support . . . . . . . . . . . . . . . . . . 36
     A.3.  L7-3: ASP and Access Network Provider Relationship . . . . 37
     A.4.  L7-4: Layer 2 and Layer 3 Provider Relationship  . . . . . 37
     A.5.  L7-5: Legacy Device Considerations . . . . . . . . . . . . 37
     A.6.  L7-6: VPN Awareness  . . . . . . . . . . . . . . . . . . . 38
     A.7.  L7-7: Network Access Authentication  . . . . . . . . . . . 38
     A.8.  L7-8: Network Topology Unawareness . . . . . . . . . . . . 38
     A.9.  L7-9: Discovery Mechanism  . . . . . . . . . . . . . . . . 39
     A.10. L7-10: PIDF-LO Creation  . . . . . . . . . . . . . . . . . 39

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 [RFC5687] 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 network.

   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 HTTP
   and HTTP/TLS as transports for the protocol.

2.  Conventions and 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 [RFC2119].





Barnes                       Standards Track                    [Page 3]

RFC 5985                          HELD                    September 2010


   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), and
   Rule Maker (RM) and Rule Holder (RH) as defined in 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 [RFC5687].  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).  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 determined.  An Access Provider
   (AP) operates the LIS so that Devices (and Targets) can retrieve
   their LI.  This document assumes that the Device and Access Provider
   have no prior relationship other than what is necessary for the
   Device to obtain network access.

   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
   [RFC5687].  It also shows where this protocol applies, with the Rule




Barnes                       Standards Track                    [Page 4]

RFC 5985                          HELD                    September 2010


   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          |  |
                     |   |                                      |  |
                     |   |                                      |  |
                     |   |                                      |  |
                     |   |                                      |  |
                     |   +------|-------------------------------+  |
                     +----------|----------------------------------+
                                |
                                |
                               HELD
                                |
     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 [LOC-CONVEY].

4.  Protocol Overview

   A Device uses the HTTP-Enabled Location Delivery (HELD) protocol to
   retrieve its location either directly in the form of a Presence
   Information Data Format Location Object (PIDF-LO) document (by value)
   or 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
   document [RFC5687], the Device MUST first discover the URI for the
   LIS for sending the HELD protocol requests.  The URI for the LIS
   SHOULD be obtained from an authorized and authenticated entity.  The
   details for ensuring that an appropriate LIS is contacted are



Barnes                       Standards Track                    [Page 5]

RFC 5985                          HELD                    September 2010


   provided in Section 9 and in particular Section 9.1.  The LIS
   discovery protocol details are out of scope of this document and are
   specified in [RFC5986].  The type of URI provided by LIS discovery is
   RECOMMENDED to be an HTTPS URI.

   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 connections or tunnels setup for security
   purposes or for traversing middleboxes, Devices that connect to
   servers such as VPN servers, SOCKS servers, and HTTP proxy servers
   should perform their HELD query on the LIS prior to establishing a
   connection to other servers.  It is RECOMMENDED that discovery
   [RFC5986] and an initial query be performed before establishing any
   connections to other servers.  If a Device performs the HELD query
   after establishing a connection to another server, the Device may
   receive inaccurate location information.





Barnes                       Standards Track                    [Page 6]

RFC 5985                          HELD                    September 2010


   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.  In this 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].  For this case, the VPN Device that
   serves as a LIS may first acquire its own location using HELD.

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
   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
   conditions.

   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
   indicate Devices on the remote side of a NAT or VPN.  In order to
   serve the Devices on the 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 [RFC5491].  Further detail is included in "Protocol
   Parameters" (Section 6).






Barnes                       Standards Track                    [Page 7]

RFC 5985                          HELD                    September 2010


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 [RFC5808].  The location
   dereference protocol details are out of scope of this document.  As
   such, many of the requirements in [RFC5808] (e.g., canceling of
   location references) are not intended to be supported by this
   specification.  It is anticipated that future specifications may
   address these requirements.

5.  Protocol Description

   As discussed in Section 4, the HELD 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.

   The Location Request (locationRequest) message is described in
   Section 5.1.  A Location Request message from a Device indicates
   whether location should be returned in the form of a PIDF-LO document
   (with specific type(s) of location) and/or Location URI(s).  In case
   of success, the LIS replies with a locationResponse message,
   including a PIDF-LO document and/or one or more Location URIs.  In
   the case of an error, the LIS replies with an error message.

   The HELD protocol messages are defined as XML documents that MUST be
   encoded in UTF-8.  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.
   The 'charset' parameter MUST be included with the XML document.

   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].




Barnes                       Standards Track                    [Page 8]

RFC 5985                          HELD                    September 2010


   Section 8 describes the use of a combination of HTTP [RFC2616], TLS
   [RFC5246], and TCP [RFC0793] for transporting the HELD messages.

5.1.  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.  If the document
   element of a request is not supported, the LIS MUST return an error
   with the unsupportedMessage error code.

5.2.  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.

5.3.  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
   "locationType".

   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.






Barnes                       Standards Track                    [Page 9]

RFC 5985                          HELD                    September 2010


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 (m) or optional (o) for
   each of the messages.

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

                     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 Public Safety
   Answering Point (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 provides the most accurate
   LI that can be determined within the specified interval for the
   specific service.



Barnes                       Standards Track                   [Page 10]

RFC 5985                          HELD                    September 2010


   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
   dependent.

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
      it.

   geodetic:  The LIS SHOULD return a location by value in the form of a
      geodetic location for the Target.

   civic:  The LIS SHOULD return a location by value in the form of a
      civic address for the Target.

   locationURI:  The LIS SHOULD return a set of Location URIs for the
      Target.

   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.

   When there is 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.




Barnes                       Standards Track                   [Page 11]

RFC 5985                          HELD                    September 2010


   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 "locationType" element is absent, a
   value of "any" 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
   message.







Barnes                       Standards Track                   [Page 12]

RFC 5985                          HELD                    September 2010


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 carried by a
   200 OK HTTP/HTTPS response.

   The value of the response code MUST be an IANA-registered value.  The
   following tokens are registered by this document:

   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.  The same request can be
      sent by the Device at a later time.  Devices MUST limit any
      attempts to retry requests.

   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.



Barnes                       Standards Track                   [Page 13]

RFC 5985                          HELD                    September 2010


   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
      "true".

   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 one or more "message" attributes to
   convey some additional, human-readable information about the result
   of the request.  The message MAY be included in any language, which
   SHOULD be indicated by the "xml:lang", attribute.  The default
   language is assumed to be English ("en") [RFC5646].

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 [RFC5808] 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





Barnes                       Standards Track                   [Page 14]

RFC 5985                          HELD                    September 2010


   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.

   When a LIS returns a "locationURI" element to a Device, the policy on
   the "locationURI" is set by the LIS alone.  This specification does
   not include a mechanism for the HELD client to set access control
   policies on a "locationURI".  Conversely, there is no mechanism, in
   this protocol as defined in this document, for the LIS to provide a
   Device the access control policy to be applied to a "locationURI".
   Since the Device is not aware of the access controls to be applied to
   (subsequent) requests to dereference a "locationURI", the client
   SHOULD protect a "locationURI" as if it were a Location Object --
   i.e., the Device SHOULD send a "locationURI" over encrypted channels
   and only to entities that are authorized to have access to the
   location.

   Further guidelines to ensure 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 30 minutes.

   All date-time values used in HELD MUST be expressed in Universal
   Coordinated Time (UTC) using the Gregorian calendar.  The XML schema
   allows use of time zone identifiers to indicate offsets from the zero
   meridian, but this option MUST NOT be used with HELD.  The extended
   date-time form using upper case "T" and "Z" characters defined in
   [W3C.REC-xmlschema-2-20041028] MUST be used to represent date-time
   values.







Barnes                       Standards Track                   [Page 15]

RFC 5985                          HELD                    September 2010


   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 single "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 [RFC5491]
   in generating the PIDF-LO for the presence parameter.

   The LIS MUST NOT include any means of identifying the Device in the
   PIDF-LO unless it is able to verify that the identifier is correct
   and inclusion of identity is expressly permitted by a Rule Maker.
   Therefore, PIDF parameters that contain identity are either omitted
   or contain unlinked pseudonyms [RFC3693].  A unique, unlinked
   presentity URI SHOULD be generated by the LIS for the mandatory
   presence "entity" attribute of the PIDF document.  Optional
   parameters such as the "contact" and "deviceID" elements [RFC4479]
   are not used.

   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.








Barnes                       Standards Track                   [Page 16]

RFC 5985                          HELD                    September 2010


  <?xml version="1.0"?>
  <xs:schema
      targetNamespace="urn:ietf:params:xml:ns:geopriv:held"
      xmlns:xs="http://www.w3.org/2001/XMLSchema"
      xmlns:held="urn:ietf:params:xml:ns:geopriv:held"
      xmlns:xml="http://www.w3.org/XML/1998/namespace"
      elementFormDefault="qualified"
      attributeFormDefault="unqualified">

    <xs:annotation>
      <xs:documentation>
        This document (RFC 5985) defines HELD messages.
      </xs:documentation>
    </xs:annotation>

    <xs:import namespace="http://www.w3.org/XML/1998/namespace"/>

    <!-- Return Location -->
    <xs:complexType name="returnLocationType">
      <xs:complexContent>
        <xs:restriction base="xs:anyType">
          <xs:sequence>
            <xs:element name="locationURI" type="xs:anyURI"
                        maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="expires" type="xs:dateTime"
                        use="required"/>
        </xs:restriction>
      </xs:complexContent>
    </xs:complexType>

    <!-- responseTime Type -->
    <xs:simpleType name="responseTimeType">
      <xs:union>
        <xs:simpleType>
          <xs:restriction base="xs:token">
            <xs:enumeration value="emergencyRouting"/>
            <xs:enumeration value="emergencyDispatch"/>
          </xs:restriction>
        </xs:simpleType>
        <xs:simpleType>
          <xs:restriction base="xs:nonNegativeInteger">
            <xs:minInclusive value="0"/>
          </xs:restriction>
        </xs:simpleType>
      </xs:union>
    </xs:simpleType>




Barnes                       Standards Track                   [Page 17]

RFC 5985                          HELD                    September 2010


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

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

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

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



Barnes                       Standards Track                   [Page 18]

RFC 5985                          HELD                    September 2010


    <xs:complexType name="errorType">
      <xs:complexContent>
        <xs:restriction base="xs:anyType">
          <xs:sequence>
            <xs:element name="message" type="held:errorMsgType"
                        minOccurs="0" maxOccurs="unbounded"/>
            <xs:any namespace="##other" processContents="lax"
                    minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="code" type="xs:token"
                        use="required"/>
          <xs:anyAttribute namespace="##any" processContents="lax"/>
        </xs:restriction>
      </xs:complexContent>
    </xs:complexType>

    <xs:complexType name="errorMsgType">
      <xs:simpleContent>
        <xs:extension base="xs:token">
          <xs:attribute ref="xml:lang"/>
          <xs:anyAttribute namespace="##any" processContents="lax"/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>

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

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

    <xs:element name="locationResponse"
                type="held:locationResponseType"/>

    <!-- Location Request -->
    <xs:complexType name="locationRequestType">
      <xs:complexContent>



Barnes                       Standards Track                   [Page 19]

RFC 5985                          HELD                    September 2010


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

    <xs:element name="locationRequest"
                type="held:locationRequestType"/>

  </xs:schema>

8.  HTTP Binding

   This section describes the use of HTTP [RFC2616] and HTTP over TLS
   [RFC2818] as transport mechanisms for the HELD protocol, which a
   conforming LIS and Device MUST support.

   Although HELD uses HTTP as a transport, it uses a strict subset of
   HTTP features, and due to the restrictions of some features, a LIS is
   not a fully compliant HTTP server.  It is intended that a LIS can
   easily be built using an HTTP server with extensibility mechanisms
   and that a HELD Device can trivially use existing HTTP libraries.
   This subset of requirements helps implementors avoid ambiguity with
   the many options that the full HTTP protocol offers.

   A Device that conforms to this specification MAY choose not to
   support HTTP authentication [RFC2617] or cookies [RFC2965].  Because
   the Device and the LIS may not necessarily have a prior relationship,
   the LIS SHOULD NOT require a Device to authenticate, either using the
   above HTTP authentication methods or TLS client authentication.
   Unless all Devices that access a LIS can be expected to be able to
   authenticate in a certain fashion, denying access to location
   information could prevent a Device from using location-dependent
   services, such as emergency calling.  Extensions to this protocol
   might result in the addition of request parameters that a LIS might
   use to decide to request Device authentication.

   A HELD request is carried in the body of an HTTP POST request.  The
   Device MUST include a Host header in the request.






Barnes                       Standards Track                   [Page 20]

RFC 5985                          HELD                    September 2010


   The MIME type of HELD request and response bodies is
   "application/held+xml".  LIS and Device MUST provide this value in
   the HTTP Content-Type and Accept header fields.  If the LIS does not
   receive the appropriate Content-Type and Accept header fields, the
   LIS SHOULD fail the request, returning a 406 (not acceptable)
   response.  HELD responses SHOULD include a Content-Length header.

   Devices MUST NOT use the "Expect" header or the "Range" header in
   HELD requests.  The LIS MAY return 501 (not implemented) errors if
   either of these HTTP features are used.  In the case that the LIS
   receives a request from the Device containing an If-* (conditional)
   header, the LIS SHOULD return a 412 (precondition failed) response.

   The POST method is the only method REQUIRED for HELD.  If a LIS
   chooses to support GET or HEAD, it SHOULD consider the kind of
   application doing the GET.  Since a HELD Device only uses a POST
   method, the GET or HEAD MUST be either an escaped URL (e.g., somebody
   found a URL in protocol traces or log files and fed it into their
   browser) or somebody doing testing/debugging.  The LIS could provide
   information in the HELD response indicating that the URL corresponds
   to a LIS server and only responds to HELD POST requests, or the LIS
   could instead try to avoid any leak of information by returning a
   very generic HTTP error message such as 404 (not found).

   The LIS populates the HTTP headers of responses so that they are
   consistent with the contents of the message.  In particular, the
   "CacheControl" header SHOULD be set to disable caching of any PIDF-LO
   document or Location URIs by HTTP intermediaries.  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
   HELD "expires" parameter.  The HTTP status code MUST indicate a 2xx
   series response for all HELD locationResponse and HELD error
   messages.

   The LIS MAY redirect a HELD request.  A Device MUST handle redirects
   by using the Location header provided by the server in a 3xx
   response.  When redirecting, the Device MUST observe the delay
   indicated by the Retry-After header.  The Device MUST authenticate
   the server that returns the redirect response before following the
   redirect, if a Device requires that the server is authenticated.  A
   Device SHOULD authenticate the LIS indicated in a redirect.

   The LIS SHOULD support persistent connections and request pipelining.
   If pipelining is not supported, the LIS MUST NOT allow persistent
   connections.  The Device MUST support termination of a response by
   the closing of a connection.





Barnes                       Standards Track                   [Page 21]

RFC 5985                          HELD                    September 2010


   Implementations of HELD that implement HTTP transport MUST implement
   transport over TLS [RFC2818].  TLS provides message integrity and
   confidentiality between the Device and LIS.  The Device MUST
   implement the server authentication method described in Section 3.1
   of [RFC2818], with an exception in how wildcards are handled.  The
   leftmost label MAY contain the wildcard string "*", which matches any
   single domain name label.  Additional characters in this leftmost
   label are invalid (that is, "f*.example.com" is not a valid name and
   does not match any domain name).

   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 HTTPS [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 client requests
   its location from a LIS.  Specific requirements and security
   considerations for location acquisition protocols are provided in
   [RFC5687].  An in-depth discussion of the security considerations
   applicable to the use of Location URIs and by-reference provision of
   LI is included in [RFC5808].

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

   Accuracy:  The client receives incorrect location information.

   Privacy:  An unauthorized entity receives location information.

   The provision of an accurate and privacy- and 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.




Barnes                       Standards Track                   [Page 22]

RFC 5985                          HELD                    September 2010


   Of these, only steps 2, 3, and 5 are within the scope of this
   document.  Step 1 is based on either manual configuration or on the
   LIS discovery defined in [RFC5986], in which appropriate security
   considerations are already discussed.  Step 4 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 [RFC5986].  When the HELD
   transaction is conducted using TLS [RFC5246], 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].  If the
   client has external information as to the expected identity or
   credentials of the proper LIS (e.g., a certificate fingerprint),
   these checks MAY be omitted.  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 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.



Barnes                       Standards Track                   [Page 23]

RFC 5985                          HELD                    September 2010


   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
   policy.

   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
   authentication.

   Using IP return routability as an authenticator means that location
   information is vulnerable to exposure through IP address spoofing
   attacks.  A temporary spoofing of an IP address could mean that when
   a Device requests a Location Object or Location URI, it receives
   another Device's location because the attacker is able to receive
   packets sent to the spoofed address.  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 6.5.2.  The lifetime of
      Location URIs necessarily depends on the nature of the access.

   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
      invalidated.

   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.






Barnes                       Standards Track                   [Page 24]

RFC 5985                          HELD                    September 2010


10.  Examples

   The following sections provide examples of basic HTTP/HTTPS, a simple
   location request, and a location request for multiple location types,
   along with the relevant location responses.  To focus on important
   portions of messages, the examples in Sections 10.2 and 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.  Examples of HTTPS Messages

   The examples in this section show complete HTTP/HTTPS messages that
   include the HELD request or response document.

   This example shows the most basic request for a LO.  The POST
   includes an empty "locationRequest" element.

         POST /location HTTP/1.1
         Host: lis.example.com:49152
         Content-Type: application/held+xml;charset=utf-8
         Content-Length: 87

         <?xml version="1.0"?>
         <locationRequest xmlns="urn:ietf:params:xml:ns:geopriv:held"/>

   Since the above request does not include a "locationType" element,
   the successful response to the request 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;charset=utf-8
   Content-Length: 856

   <?xml version="1.0"?>
    <locationResponse xmlns="urn:ietf:params:xml:ns:geopriv:held">
     <presence xmlns="urn:ietf:params:xml:ns:pidf"
      entity="pres:3650n87934c@ls.example.com">
      <tuple id="b650sf789nd">
       <status>
        <geopriv xmlns="urn:ietf:params:xml:ns:pidf:geopriv10">
         <location-info>
          <Point xmlns="http://www.opengis.net/gml"
           srsName="urn:ogc:def:crs:EPSG::4326">



Barnes                       Standards Track                   [Page 25]

RFC 5985                          HELD                    September 2010


           <pos>-34.407 150.88001</pos>
          </Point>
         </location-info>
         <usage-rules
          xmlns:gbp="urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy">
          <gbp:retention-expiry>2006-01-11T03:42:28+00:00
          </gbp:retention-expiry>
         </usage-rules>
         <method>Wiremap</method>
        </geopriv>
       </status>
       <timestamp>2006-01-10T03:42:28+00:00</timestamp>
      </tuple>
     </presence>
    </locationResponse>

   The error response to the request 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;charset=utf-8
         Content-Length: 182

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

10.2.  Example of a Simple Location Request

   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="2006-01-01T13:00:00.0Z">
       <locationURI>https://ls.example.com:9768/357yc6s64ceyoiuy5ax3o
       </locationURI>
       <locationURI>sip:9769+357yc6s64ceyoiuy5ax3o@ls.example.com



Barnes                       Standards Track                   [Page 26]

RFC 5985                          HELD                    September 2010


       </locationURI>
     </locationUriSet>
   </locationResponse>

   An error response to this location request is shown below:

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

10.3.  An Example of a Location Request 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">
            geodetic
            civic
            locationURI
          </locationType>
          </locationRequest>

   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="2006-01-01T13:00:00.0Z">
       <locationURI>https://ls.example.com:9768/357yc6s64ceyoiuy5ax3o
       </locationURI>
       <locationURI>sip:9769+357yc6s64ceyoiuy5ax3o@ls.example.com:
       </locationURI>
      </locationUriSet>
      <presence xmlns="urn:ietf:params:xml:ns:pidf"
        entity="pres:ae3be8585902e2253ce2@10.102.23.9">
      <tuple id="lisLocation">
       <status>
        <geopriv xmlns="urn:ietf:params:xml:ns:pidf:geopriv10">
        <location-info>
         <gs:Circle xmlns:gs="http://www.opengis.net/pidflo/1.0"
           xmlns:gml="http://www.opengis.net/gml"
           srsName="urn:ogc:def:crs:EPSG::4326">
          <gml:pos>-34.407242 150.882518</gml:pos>
          <gs:radius uom="urn:ogc:def:uom:EPSG::9001">30
          </gs:radius>
         </gs:Circle>



Barnes                       Standards Track                   [Page 27]

RFC 5985                          HELD                    September 2010


         <ca:civicAddress
           xmlns:ca="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
           xml:lang="en-au">
          <ca:country>AU</ca:country>
          <ca:A1>NSW</ca:A1>
          <ca:A3>Wollongong</ca:A3>
          <ca:A4>Gwynneville</ca:A4>
          <ca:STS>Northfield Avenue</ca:STS>
          <ca:LMK>University of Wollongong</ca:LMK>
          <ca:FLR>2</ca:FLR>
          <ca:NAM>Andrew Corporation</ca:NAM>
          <ca:PC>2500</ca:PC>
          <ca:BLD>39</ca:BLD>
          <ca:SEAT>WS-183</ca:SEAT>
          <ca:POBOX>U40</ca:POBOX>
        </ca:civicAddress>
       </location-info>
       <usage-rules
         xmlns:gbp="urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy">
        <gbp:retransmission-allowed>false
        </gbp:retransmission-allowed>
        <gbp:retention-expiry>2007-05-25T12:35:02+10:00
        </gbp:retention-expiry>
       </usage-rules>
       <method>Wiremap</method>
      </geopriv>
     </status>
     <timestamp>2007-05-24T12:35:02+10:00</timestamp>
    </tuple>
   </presence>
   </locationResponse>

11.  IANA Considerations

   IANA has made the registrations detailed in the following sections.

11.1.  URN Sub-Namespace Registration for
       urn:ietf:params:xml:ns:geopriv:held

   This section registers a new XML namespace,
   "urn:ietf:params:xml:ns:geopriv:held", per the guidelines in
   [RFC3688].

   URI: urn:ietf:params:xml:ns:geopriv:held

   Registrant Contact: IETF, GEOPRIV working group, (geopriv@ietf.org),
   Mary Barnes (mary.ietf.barnes@gmail.com).




Barnes                       Standards Track                   [Page 28]

RFC 5985                          HELD                    September 2010


      XML:

         BEGIN
           <?xml version="1.0"?>
           <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
             "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
           <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
             <head>
               <title>HELD Messages</title>
             </head>
             <body>
               <h1>Namespace for HELD Messages</h1>
               <h2>urn:ietf:params:xml:ns:geopriv:held</h2>
               <p>See RFC 5985</p>
             </body>
           </html>
         END

11.2.  XML Schema Registration

   This section registers an XML schema as per the guidelines in
   [RFC3688].

   URI:  urn:ietf:params:xml:schema:geopriv:held

   Registrant Contact:  IETF, GEOPRIV working group, (geopriv@ietf.org),
      Mary Barnes (mary.ietf.barnes@gmail.com).

   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.

   To:  ietf-types@iana.org

   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
      Same as the charset parameter of "application/xml" as specified in
      RFC 3023 [RFC3023], Section 3.2.



Barnes                       Standards Track                   [Page 29]

RFC 5985                          HELD                    September 2010


   Encoding considerations:  Same as the encoding considerations of
      "application/xml" as specified in 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
      information.

   Interoperability considerations:  This content type provides a basis
      for a protocol.  There are multiple interoperable implementations
      of this protocol.

   Published specification:  RFC 5985

   Applications which use this media type:  Location information
      providers and consumers.

   Additional Information:
      Magic Number(s): (none)
      File extension(s): .heldxml
      Macintosh File Type Code(s): "TEXT"

   Person & email address to contact for further information:
      Mary Barnes <mary.ietf.barnes@gmail.com>

   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

   As defined in this document, IANA created 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 is a summary of the registry:

   Related Registry:   Geopriv HELD Registries, Error codes for HELD

   Defining RFC:  RFC 5985




Barnes                       Standards Track                   [Page 30]

RFC 5985                          HELD                    September 2010


   Registration/Assignment Procedures:  Following the policies outlined
      in [RFC5226], the IANA policy for assigning new values for the
      Error codes for HELD is Standards Action: Values are assigned only
      for Standards Track RFCs approved by the IESG.

   Registrant Contact:  IETF, GEOPRIV working group, (geopriv@ietf.org),
      Mary Barnes (mary.ietf.barnes@gmail.com).

   This section registers the following eight initial error codes as
   described 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
      "true".

   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.









Barnes                       Standards Track                   [Page 31]

RFC 5985                          HELD                    September 2010


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 below.  They made additional
   contributions to the WG document, including the XML schema.

      James Winterbottom
      Andrew
      Andrew Building (39)
      University of Wollongong
      Northfields Avenue
      Wollongong, NSW  2522
      AU

      Phone: +61 2 4221 2938
      EMail: james.winterbottom@andrew.com
      URI:   http://www.andrew.com/


      Martin Thomson
      Andrew
      Andrew Building (39)
      University of Wollongong
      Northfields Avenue
      Wollongong, NSW  2522
      AU

      Phone: +61 2 4221 2915
      EMail: martin.thomson@andrew.com
      URI:   http://www.andrew.com/

      Barbara Stark
      BellSouth
      Room 7A43
      725 W Peachtree St.
      Atlanta, GA  30308
      US

      EMail: barbara.stark@att.com

13.  Acknowledgements

   The author and 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,
   Bernard Aboba, Eric Arolick, Richard Barnes (in particular, the
   security considerations section), Peter Blatherwick, Ben Campbell,



Barnes                       Standards Track                   [Page 32]

RFC 5985                          HELD                    September 2010


   Guy Caron, Eddy Corbett, Martin Dawson, Lisa Dusseault, Robins
   George, Jerome Grenier, Ted Hardie, Cullen Jennings, Neil Justusson,
   Tat Lam, Marc Linsner, Patti McCalmont, Alexey Melnikov, Roger
   Marshall, Tim Polk, Perry Prozeniuk, Carl Reed, Julian Reschke, Eric
   Rescorla, Dan Romascanu, Brian Rosen, John Schnizlein, Shida
   Schubert, Henning Schulzrinne, Ed Shrum, Doug Stuard, Hannes
   Tschofenig, and Karl Heinz Wolf.

14.  References

14.1.  Normative References

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

   [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.

   [RFC2965]  Kristol, D. and L. Montulli, "HTTP State Management
              Mechanism", RFC 2965, October 2000.

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

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5491]  Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
              Presence Information Data Format Location Object (PIDF-LO)
              Usage Clarification, Considerations, and Recommendations",
              RFC 5491, March 2009.

   [RFC5646]  Phillips, A. and M. Davis, "Tags for Identifying
              Languages", BCP 47, RFC 5646, September 2009.

   [RFC5986]  Thomson, M. and J. Winterbottom, "Discovering the Local
              Location Information Server (LIS)", RFC 5986,
              September 2010.

   [W3C.REC-xmlschema-1-20041028]
              Thompson, H., Mendelsohn, N., Beech, D., and M. Maloney,
              "XML Schema Part 1: Structures Second Edition", World Wide
              Web Consortium Recommendation REC-xmlschema-1-20041028,
              October 2004,
              <http://www.w3.org/TR/2004/REC-xmlschema-1-20041028>.



Barnes                       Standards Track                   [Page 33]

RFC 5985                          HELD                    September 2010


   [W3C.REC-xmlschema-2-20041028]
              Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes
              Second Edition", World Wide Web Consortium
              Recommendation REC-xmlschema-2-20041028, October 2004,
              <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028>.

14.2.  Informative References

   [LLDP-MED]
              TIA, "ANSI/TIA-1057 Link Layer Discovery Protocol - Media
              Endpoint Discovery".

   [LOC-CONVEY]
              Polk, J., Rosen, B., and J. Peterson, "Location Conveyance
              for the Session Initiation Protocol", Work in Progress,
              July 2010.

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

   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, June 1999.

   [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.

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

   [RFC4479]  Rosenberg, J., "A Data Model for Presence", RFC 4479,
              July 2006.

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






Barnes                       Standards Track                   [Page 34]

RFC 5985                          HELD                    September 2010


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

   [RFC5808]  Marshall, R., "Requirements for a Location-by-Reference
              Mechanism", RFC 5808, May 2010.













































Barnes                       Standards Track                   [Page 35]

RFC 5985                          HELD                    September 2010


Appendix A.  HELD Compliance to IETF LCP Requirements

   This appendix describes HELD's compliance to the requirements
   specified in [RFC5687].

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."

   COMPLY

   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."

   COMPLY

   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
   determining the location based on the identity of the serving base
   station), 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 technique.




Barnes                       Standards Track                   [Page 36]

RFC 5985                          HELD                    September 2010


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."

   COMPLY

   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."

   COMPLY

   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 which can
   be bound to transports other than HTTP, such as BEEP.  Using 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 Network Termination
   Equipment (NTE) in an DSL environment that cannot be upgraded to
   support additional protocols, for example to pass additional
   information through DHCP."






Barnes                       Standards Track                   [Page 37]

RFC 5985                          HELD                    September 2010


   COMPLY

   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."

   COMPLY

   HELD does not preclude a LIS on the far end of a VPN tunnel from
   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."

   COMPLY

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






Barnes                       Standards Track                   [Page 38]

RFC 5985                          HELD                    September 2010


   COMPLY

   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
   mechanism."

   COMPLY

   HELD uses the discovery mechanism in [RFC5986].

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 [now RFC 5941]."

   COMPLY

   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 [RFC5491].

Author's Address

   Mary Barnes (editor)
   Polycom

   EMail: mary.ietf.barnes@gmail.com
















Barnes                       Standards Track                   [Page 39]

