Internet Engineering Task Force (IETF) M. Barnes, Ed.

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.

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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

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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].

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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

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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

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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.

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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).

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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].

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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.

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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.

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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.

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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.

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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.

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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

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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.

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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.

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<?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"/>


<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>


<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>

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<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>


<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>

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<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"/>


<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"/>


<xs:complexType name="locationRequestType">
<xs:complexContent>

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<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.

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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.

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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.

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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.

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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.

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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:[email protected]">
<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">

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<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:[email protected]

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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:[email protected]:
</locationURI>
</locationUriSet>
<presence xmlns="urn:ietf:params:xml:ns:pidf"
entity="pres:[email protected]">
<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>

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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, ([email protected]),
Mary Barnes ([email protected]).

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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, ([email protected]),
Mary Barnes ([email protected]).

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: [email protected]

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.

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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 <[email protected]>

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

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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, ([email protected]),
Mary Barnes ([email protected]).

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.

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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: [email protected]
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: [email protected]
URI: http://www.andrew.com/

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

EMail: [email protected]

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,

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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>.

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[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.

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[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.

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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.

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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."

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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."

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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: [email protected]

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