ECRIT J. Winterbottom Internet-Draft M. Thomson Intended status: BCP Andrew Corporation Expires: April 16, 2009 October 13, 2008 Specifying Holes in LoST Service Boundaries draft-ietf-ecrit-specifying-holes-01.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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 April 16, 2009. Winterbottom & Thomson Expires April 16, 2009 [Page 1] Internet-Draft Service Boundary Holes October 2008 Abstract This document describes how holes can be specified in geodetic service boundaries. One means of implementing a search solution in a service database, such as one might provide with a LoST server, is described. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Specifying Holes . . . . . . . . . . . . . . . . . . . . . . . 5 4. GML Polygons . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Holes in GML Polygons . . . . . . . . . . . . . . . . . . . . 9 6. Service Boundary Specification and Selection Algorithm . . . . 10 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 10.1. Normative References . . . . . . . . . . . . . . . . . . 16 10.2. Informative References . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 Intellectual Property and Copyright Statements . . . . . . . . . . 18 Winterbottom & Thomson Expires April 16, 2009 [Page 2] Internet-Draft Service Boundary Holes October 2008 1. Introduction The LoST protocol [RFC5222] describes a protocol that's primary purpose is to map service and locations to destination addresses. LoST does this by provisioning boundary maps or areas against service URNs. The boundary is a polygon made up of sets of geodetic coordinates specifying an enclosed area. In some circumstances an area enclosed by a polygon, also known as an exterior polygon, may contain exception areas, or holes, that for the same service must yield a different destination to that described by the larger area. This document describes how holes SHOULD be specified in service boundaries defined using a GML encoding for the polygons and their internal elements (holes). GML polygons are based on elements defined in [ISO-19107]. o--------------o / \ / /\ \ / + +-----+ \ o | Hole \ o | | 1 / | | +-------+ |<--- Primary Polygon | +-------+ | | / Hole | | o \ 2 | o \ +-----+ + / \ \/ / \ / o--------------o Figure 1: Holes in a Polygon Winterbottom & Thomson Expires April 16, 2009 [Page 3] Internet-Draft Service Boundary Holes October 2008 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Winterbottom & Thomson Expires April 16, 2009 [Page 4] Internet-Draft Service Boundary Holes October 2008 3. Specifying Holes Holes related to an exterior boundary polygon MUST adhere to the following rules: Rule 1: Two holes MUST NOT have more than one point of intersection. If two or more holes share a common set of boundaries then to the primary polygon these represent a single hole in the service. The internal elements (holes) should have common boundaries removed and a single hole created irrespective of whether the excluded area is itself made up of multiple service boundaries. o--------------o o--------------o / \ / \ / /\ \ / /\ \ / + +-----+ \ / + +-----+ \ o | Hole \ o o | \ o | | 1 \ | | | One \ | | +-+-------+ | =========> | +-+ Hole + | | / Hole | | | / | | o \ 2 | o o \ | o \ +-----+ + / \ +-----+ + / \ \/ / \ \/ / \ / \ / o--------------o o--------------o Incorrect Correct Figure 2: Incorrect Hole Specification with Boundary Sharing Rule 2: A hole MUST NOT have more than one point of intersection with the outer-boundary of the primary (exterior) polygon. If more than one point of intersection occurs the primary polygon is either doesn't have a hole, it has an inlet as in Figure 3, or the primary polygon SHOULD be expressed as two polygons as in Figure 4. Winterbottom & Thomson Expires April 16, 2009 [Page 5] Internet-Draft Service Boundary Holes October 2008 +------- Inlet | v o---+-----+----o o---o o----o / |%%%%%| \ / | | \ / /%%%%%%| \ / / | \ / +%%%%%%%| \ / o o \ o |%%%%%%%%\ o o | \ o | |%%%%%%%%%\ | | | \ | | +-+%%%%%%%%+ | ========> | o-o o | | /%%%%%%%%| | | / | | o \%%%%%%%%| o o \ | o \ +-----+ + / \ o-----o o / \ \/ / \ \/ / \ / \ / o--------------o o--------------o Incorrect Correct Figure 3: Correct Specification of an Inlet A--q-----------B A-q q----------B / | | \ / | | \ / | | \ / | | \ / z r-----s \ / P z r-----s P \ H | \ C H o | \ o C | | One \ | | l | \ l | | y-x Hole t | ========> | y y-x t y | | / | | | g / | g | G \ | D G o \ | o D \ / v---u / \ n / v---u n / \ \ / / \ 1 \ / 2 / \ \ / / \ \ / / F-----w--------E F-----w w--------E 1 Polgon with a 2 Polygons that map Dividing Hole to the same service Figure 4: Correct Specification of Hole with Multiple Outer-Boundary Intersections Similarly, a polygon containing a hole with an island must be represented as two polygons mapping to the same service. Winterbottom & Thomson Expires April 16, 2009 [Page 6] Internet-Draft Service Boundary Holes October 2008 Rule 3: A hole MUST be a legal polygon in accordance with the geoshape specification [geoshape]. There is no restriction on the number of points that may be used to express the perimeter of the hole. Winterbottom & Thomson Expires April 16, 2009 [Page 7] Internet-Draft Service Boundary Holes October 2008 4. GML Polygons The GML encoding of a polygon defines a enclosed exterior boundary, with the first and last points of boundary being the same. Consider the example in Figure 5. B--------------C / \ / \ / \ A D \ / \ / \ / F--------------E 43.311 -73.422 43.111 -73.322 43.111 -73.222 43.311 -73.122 43.411 -73.222 43.411 -73.322 43.311 -73.422 Figure 5: Hexagon and Associated GML NOTE that polygon vertices in Figure 5 are expressed using elements for clarity. The vertices can also be expressed using a element. Winterbottom & Thomson Expires April 16, 2009 [Page 8] Internet-Draft Service Boundary Holes October 2008 5. Holes in GML Polygons A hole is specified in the polygon by defining an interior boundary. The points defining the internal boundary define the area represented by the hole in the primary (exterior) polygon. The shaded area in Figure 6 is represented by the 4 points of the interior boundary specified by (w,z,y,x). B-------------C / \ / w-------------x \ / |/////////////| \ A |/////////////| D \ |/////////////| / \ z-------------y / \ / F-------------E 43.311 -73.422 43.111 -73.322 43.111 -73.222 43.311 -73.122 43.511 -73.222 43.511 -73.322 43.311 -73.422 43.411 -73.322 43.211 -73.322 43.211 -73.222 43.411 -73.222 43.411 -73.322 Figure 6: Hexagon with Hole Winterbottom & Thomson Expires April 16, 2009 [Page 9] Internet-Draft Service Boundary Holes October 2008 6. Service Boundary Specification and Selection Algorithm A service boundary is represented by a polygon that may have many vertices. The enclosed area of the polygon represents the area in which a service, expressed as a service URN, maps to a single URI. Figure 6 shall be used to illustrate two service boundaries. The first service boundary A->F shall be referred to as area-A, and the second service boundary w->z shall be referred to as area-w. Further more area-A is directly represented by the GML encoding provided in Figure 6. Area-w is represented as a hole in area-A by the interior boundary. Since area-w is also a service boundary, a separate polygon describing this area is also required and is shown in Figure 7. 43.411 -73.322 43.211 -73.322 43.211 -73.222 43.411 -73.222 43.411 -73.322 Figure 7: GML for Area-w If this data were in a LoST server the data mappings may look similar to the example in Figure 8. This is an example only and does not represent actual LoST server provisioning or data transfer records. The example XML will not complie. Outer Area Police Department urn:service:sos.police 43.311 -73.422 43.111 -73.322 43.111 -73.222 Winterbottom & Thomson Expires April 16, 2009 [Page 10] Internet-Draft Service Boundary Holes October 2008 43.311 -73.122 43.511 -73.222 43.511 -73.322 43.311 -73.422 43.411 -73.322 43.211 -73.322 43.211 -73.222 43.411 -73.222 43.411 -73.322 sip:area-A-pd@example.com xmpp:area-A-pd@example.com 000 Inner Area Police Department urn:service:sos.police 43.411 -73.322 43.211 -73.322 43.211 -73.222 43.411 -73.222 43.411 -73.322 sip:area-w-pd@example.com xmpp:area-w-pd@example.com 000 Figure 8: Service Boundary Specifications It is considered likely that LoST servers will need to provide responses sufficiently quickly to allow real-time queries to be Winterbottom & Thomson Expires April 16, 2009 [Page 11] Internet-Draft Service Boundary Holes October 2008 performed as part of an emergency call routing flow. It is for this reason that databases supporting native geospatial query techniques are desirable and that service boundary specifications that are easily mapped to internal data structures are preferred. The format described in this memo makes support for this operation easy, while allowing an arbitrary number of holes in a service boundary to be specified. Each primary polygon is stored in the geospatial database and mapped to a service URN and destination URI. Holes may be stored as polygons in a separate table and mapped to the primary polygon. When a location is found to map to a polygon, the exceptions table can be checked to see if the primary polygon contains any coverage holes. In general no holes will exist for a service boundary, so this check results in almost no overhead and the service mapping can be returned. Where one or more holes are found to exist, the provided location is checked against each hole. If the location is found to exist in one of the specified holes then the primary polygon can be discarded, and searching of the service boundary database can continue. Winterbottom & Thomson Expires April 16, 2009 [Page 12] Internet-Draft Service Boundary Holes October 2008 7. Security Considerations This document does not introduce any security issues. Winterbottom & Thomson Expires April 16, 2009 [Page 13] Internet-Draft Service Boundary Holes October 2008 8. IANA Considerations There are no specific IANA considerations for this document. Winterbottom & Thomson Expires April 16, 2009 [Page 14] Internet-Draft Service Boundary Holes October 2008 9. Acknowledgements Thanks to Carl Reed for input provided to the list some months back and for reviewing this document. Thanks also to Michael Haberler for suggesting that such a specification is required. Winterbottom & Thomson Expires April 16, 2009 [Page 15] Internet-Draft Service Boundary Holes October 2008 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5222] Hardie, T., Newton, A., Schulzrinne, H., and H. Tschofenig, "LoST: A Location-to-Service Translation Protocol", RFC 5222, August 2008. [geoshape] Thomson, M. and C. Reed, "GML 3.1.1 PIDF-LO Shape Application Schema for use by the Internet Engineering Task Force (IETF)", Candidate OpenGIS Implementation Specification 06-142r1, Version: 1.0, April 2007. 10.2. Informative References [I-D.ietf-ecrit-lost-sync] Schulzrinne, H., "Synchronizing Location-to-Service Translation (LoST) Servers", draft-ietf-ecrit-lost-sync-00 (work in progress), July 2008. [ISO-19107] ISO, "Geographic information - Spatial Schema", ISO Standard 19107, First Edition, 5 2003. Winterbottom & Thomson Expires April 16, 2009 [Page 16] Internet-Draft Service Boundary Holes October 2008 Authors' Addresses James Winterbottom Andrew Corporation PO Box U40 University of Wollongong, NSW 2500 AU Email: james.winterbottom@andrew.com Martin Thomson Andrew Corporation PO Box U40 University of Wollongong, NSW 2500 AU Email: martin.thomson@andrew.com Winterbottom & Thomson Expires April 16, 2009 [Page 17] Internet-Draft Service Boundary Holes October 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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