GEOPRIV M. Thomson Internet-Draft Andrew Intended status: Standards Track June 21, 2009 Expires: December 23, 2009 Expressing Confidence in a Location Object draft-thomson-geopriv-confidence-01 Status of This Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 23, 2009. Copyright Notice Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract A confidence element is described that expresses the estimated probability that the associated location information is correct. This element conveys information that might otherwise be lost about Thomson Expires December 23, 2009 [Page 1] Internet-Draft Confidence June 2009 the probability distribution represented by a region of uncertainty. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . . 4 2. Representation of Confidence in PIDF-LO . . . . . . . . . . . . 4 3. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Confidence Schema . . . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 5.1. URN Sub-Namespace Registration for urn:ietf:params:xml:ns:geopriv:conf . . . . . . . . . . . . 7 5.2. XML Schema Registration . . . . . . . . . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 8 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.1. Normative References . . . . . . . . . . . . . . . . . . . 8 7.2. Informative References . . . . . . . . . . . . . . . . . . 8 Thomson Expires December 23, 2009 [Page 2] Internet-Draft Confidence June 2009 1. Introduction Location information is often less than perfect. Two measures are used to quantify how imperfect the location information is: uncertainty and confidence. These terms, and their relationship with location information are explored in detail in [I-D.thomson-geopriv-uncertainty]. Standard forms for the expression of uncertainty are included in [RFC5491], but confidence is fixed to a value of 95%. On the whole, a fixed definition for confidence ensures consistency between implementations. Location generators that are aware of this constraint can generate location information at the required confidence. Location recipients are able to make sensible assumptions about the quality of the information that they receive. In some circumstances - particularly with pre-existing systems - location generators might provide location information with some other confidence. Common values include 38%, 67% and 90%; all of which are prevalent in current systems. Existing forms of expressing location information, such as that defined in [3GPP-TS-23_032], contain elements that express the confidence in the result. The addition of a confidence element provides information that was previously unavailable to recipients of location information. Without this information, a location server or generator that has access to location information with a confidence lower than 95% has two options: o The location server can scale regions of uncertainty in an attempt to acheive 95% confidence. This scaling process significantly degrades the quality of the information, because the location server might not have the necessary information; the assumptions that have to be made result in poor quality results. o The location server can ignore the confidence entirely, which results in giving the recipient of that information a false impression of its quality. Both of these choices degrade the quality of the information provided. The addition of a confidence element avoids this problem entirely if a location recipient supports and understands the element. A recipient that does not understand, and hence ignores, the confidence element is in no worse a position than if the location server ignored confidence. Thomson Expires December 23, 2009 [Page 3] Internet-Draft Confidence June 2009 1.1. Conventions used in this document 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]. This document relies on the definitions in [I-D.thomson-geopriv-uncertainty] and [RFC3693]. 2. Representation of Confidence in PIDF-LO The confidence element MAY be added to the "location-info" element of the Presence Information Data Format - Location Object (PIDF-LO) [RFC4119] document. This element expresses the confidence in the associated location information as a percentage. The confidence element optionally includes an attribute that indicates the shape of the probability density function (PDF) of the associated region of uncertainty. Three values are possible: unknown, normal and rectangular. Indicating a particular PDF only indicates that the distribution approximately fits the given shape based on the methods used to generate the location information. The PDF is normal if there are a large number of small, independent sources of error; rectangular if all points within the area have roughly equal probability of being the actual location of the Target; otherwise, the PDF MUST either be set to unknown or omitted. If a PIDF-LO does not include the confidence element, confidence is 95% [RFC5491]. A Point shape does not have uncertainty (or it has infinite uncertainty), so confidence is meaningless for a point; therefore, this element MUST be omitted if only a point is provided. Location generators SHOULD attempt to ensure that confidence is equal in each dimension when generating location information. This restriction, while not always possible, allows for more accurate scaling, if scaling is necessary. Confidence SHOULD NOT be included unless location information cannot be acquired with 95% confidence. Confidence SHOULD NOT be included with civic address information; civic addresses are less subject to variable errors than geodetic positions. 3. Example The PIDF-LO document in Figure 1 includes a representation of uncertainty as a circular area. The confidence element (on the line Thomson Expires December 23, 2009 [Page 4] Internet-Draft Confidence June 2009 marked with a comment) indicates that the confidence is 67% and that it follows a normal distribution. 42.5463 -73.2512 850.24 67 mac:010203040506 Figure 1: Example PIDF-LO with Confidence Thomson Expires December 23, 2009 [Page 5] Internet-Draft Confidence June 2009 4. Confidence Schema PIDF-LO Confidence This schema defines an element that is used for indicating confidence in PIDF-LO documents. Thomson Expires December 23, 2009 [Page 6] Internet-Draft Confidence June 2009 5. IANA Considerations 5.1. URN Sub-Namespace Registration for urn:ietf:params:xml:ns:geopriv:conf This section registers a new XML namespace, "urn:ietf:params:xml:ns:geopriv:conf", as per the guidelines in [RFC3688]. URI: urn:ietf:params:xml:ns:geopriv:conf Registrant Contact: IETF, GEOPRIV working group, (geopriv@ietf.org), Martin Thomson (martin.thomson@andrew.com). XML: BEGIN PIDF-LO Confidence Attribute

Namespace for PIDF-LO Confidence Attribute

urn:ietf:params:xml:ns:geopriv:conf

[[NOTE TO IANA/RFC-EDITOR: Please update RFC URL and replace XXXX with the RFC number for this specification.]]

See RFCXXXX.

END 5.2. XML Schema Registration This section registers an XML schema as per the guidelines in [RFC3688]. URI: urn:ietf:params:xml:schema:geopriv:conf Registrant Contact: IETF, GEOPRIV working group, (geopriv@ietf.org), Martin Thomson (martin.thomson@andrew.com). Schema: The XML for this schema can be found as the entirety of Section 4 of this document. Thomson Expires December 23, 2009 [Page 7] Internet-Draft Confidence June 2009 6. Security Considerations The security (and privacy) implications related to adding this information are not significant. 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. [RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object Format", RFC 4119, December 2005. 7.2. Informative References [RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J. Polk, "Geopriv Requirements", RFC 3693, February 2004. [I-D.thomson-geopriv-uncertainty] Thomson, M. and J. Winterbottom, "Representation of Uncertainty and Confidence in PIDF-LO", draft- thomson-geopriv-uncertainty-03 (work in progress), June 2009. [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. [3GPP-TS-23_032] "3GPP TS 23.032 V6.0.0 3rd Generation Partnership Project; Technical Specification Group Code Network; Universal Geographic Area Description (GAD)". Thomson Expires December 23, 2009 [Page 8] Internet-Draft Confidence June 2009 Author's Address Martin Thomson Andrew PO Box U40 Wollongong University Campus, NSW 2500 AU Phone: +61 2 4221 2915 EMail: martin.thomson@andrew.com URI: http://www.andrew.com/ Thomson Expires December 23, 2009 [Page 9]