Spirits Working Group J. Voelker Internet draft Lucent Technologies Expires June 2001 SPIRITS Support for Location Services Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. Abstract SPIRITS services are those originating in the PSTN and involving interactions between the PSTN and the Internet. This document describes how SPIRITS supports those aspects of location services whereby the PSTN wireless network provides location related events to internet applications requesting them. An example of such an event is a mobile station entering a pre-specified geographic zone. 1. Introduction SPIRITS [1] services are those originating in the PSTN and involving interactions between the PSTN and the Internet. This document describes how SPIRITS can support those aspects of location services whereby the PSTN wireless network provides location related events; for example, when a mobile station (MS - aka a cell phone) enters a pre-specified geographic zone. Because the PSTN tracks its MS customers in its conventional role of delivering telephone calls, it can potentially Voelker Internet Draft [Page 1] Spirits Support for Location Services Expires June 2001 leverage that capability to efficiently assist with certain aspects of providing advanced location services. [2] also addresses the use of SPIRITS/PINT for location. 2. Location Services Location services report or utilize the geographic location of one or more mobile stations (i.e. cell phones). Location can be obtained from the PSTN wireless network (henceforth called the PSTN), from GPS equipped MSs, or via hybrids of these two mechanisms whereby information from the PSTN is delivered to a GPS equipped MS to improve the efficiency of the GPS calculations. Examples of location services are: a) Tell party A the location of party B. b) Determine and deliver to a MS the location of some restaurants nearest its current location. c) Push advertisements for a particular retail store to all MS subscribed to the service and within a half mile of that store's location. d) Notify party A of that party B has just landed at a particular airport and turned on his/her cell phone. e) When party B arrives at a particular airport and turns on his cell phone, ring that phone and play an announcement giving updated hotel reservation and meeting time information. Then notify party A, the source of the announcement, that it has been delivered. f) Report the identity of every MS entering or leaving a particular specified geographic region. This is hopefully subject to appropriate privacy protections. g) Periodically report the count of MS entering or leaving a particular specified geographic region. h) Track a particular MS. 3. Wireless PSTN role in providing location services The wireless PSTN is ideally situated to contribute to location services under certain circumstances which we discuss below. 3.1 Location Regions Native to the PSTN In typical cellular PSTN networks, at any given time, a MS with service available is associated with several PSTN network entities. It is served by a particular cell site. In particular, the MS is served by a particular sector of that cell site indicating which of three Voelker Internet Draft [Page 2] Spirits Support for Location Services Expires June 2001 directional antennae is used to communicate with the MS. The cell site is served by an mobile switching center (MSC) which does call processing. The MSC is among a set served by a Visitor Location Register (VLR). The Home Location Register(HLR) has an association with the MS independent of the MS's current location. For these entities to work together, there is distributed within the cellular network information to track the MS as it moves across cell-sectors, across MSCs, and across VLRs. This tracking can be leveraged to assist with location services. For example, to recognize when a MS has been turned on at a particular airport (and presuming the MS will be initially turned at the airport after it arrived by plane while turned off), it generally suffices to recognize when that airport's local cell site or MSC begins to serve that MS. So, normal operation of the cellular PSTN provides, as a side effect, a trap for location discovery that can be efficiently used for location services. Most natural to the PSTN are location regions defined by cell/sector, MSC control area, and VLR control area. SPIRITS interworking has the greatest potential benefit for location services which based on the entry/exit of MS from these natural (i.e. already monitored for MS presence) wireless PSTN regions. (This is not to say that other location services may not also benefit from the use of a SPIRITS interface.) For completeness, note that the PSTN, when augmented with Mobile Positioning Centers (MPC) and Positioning Determining Equipment (PDE) can locate a MS with great precision not restricted to these "natural" regions. To accomplish this the radio signals received at multiple cell/sectors in the vicinity of the MS are compared. Also, GPS information collected at the MS itself can be used. In addition there are hybrid technologies utilizing cell site's radio reception of the MS's radio transmissions to supplement GPS calculations performed within the MS. 3.2 Triggered location events vs. polling If the PSTN is asked (say via PINT mechanism) to notify some entity when one of a set of MS enters a particular cell site, the PSTN need only perform a low overhead check when an MS enters that cell site. That is, it would need to check to see whether the entering MS is on the list of MS that it is monitoring. In contrast, a polling mechanism would need to undertake what is likely to be a relatively more expensive operation. Polling involves querying for the location of each MS on the list at periodic intervals. Most of these polling queries may apply to a MS not powered up, not moving, or distant from the region of interest. So, to identify when an MS enters a cell site or some other region natural to the PSTN, asking the PSTN to provide a trap or trigger based mechanism may be more efficient than polling the MS. As the number of MS whose entry to region is of interest increases, the relative advantages of a trap mechanism relative to polling increases. Hybrid usage of trigger and polling methods may sometimes be appropriate. For example, entry of an MS into a region that is not Voelker Internet Draft [Page 3] Spirits Support for Location Services Expires June 2001 natural to the PSTN could be monitored in a two stage manner. First use a PSTN trigger mechanism to determine when the MS entered one a set of (say) cell sites that together overlay the desired region. When this trigger occurs, use polling to determine when the MS enters the actual target region. Such polling may be controlled from within the PSTN or be controlled from the IP world with the individual polling queries using PINT protocol. 4. SPIRITS and Location Services SPIRITS provides a means for the PSTN to signal entities in the IP world that a PSTN monitored trigger has occurred. See Figure 1 in the appendix for the SPIRITS architecture. Note that what we are here calling triggers are not included among the the set of triggers conventionally defined for the intelligent network. The conventional triggers are based upon telephone call events whereas entry/exit from a region is a trigger having no necessary relation to a telephone call. 4.1 Operation We use the term "application" to refer to the end-user of the location information. The operational sequence would be the following: a) The application, via PINT mechanisms, registers with the PSTN to be notified when a location trigger is encountered. The location trigger is defined in terms of a location region and some set of MS. (The nature of a location trigger is discussed further below.) Alternatively, but of likely less utility, the registration information can be provisioned in the PSTN network. b) The PSTN, using means outside the scope of SPIRITS (and perhaps not yet implemented in real PSTN networks) arranges to test the identity of each MS observed to enter (or perhaps exit from) from the registration defined region against the registration defined set of MS. If the registration permits (see section 4.2), prune MS from the monitored set once they have met the entry/exit criterion. c) When a MS on the list is observed meeting a trigger criterion, the PSTN transfers the identity of that MS, with a reference to the particular registration, to the SPIRITS client. Note that transfer may be delayed if batch reporting is in effect. d) The SPIRITS client transfer the identity of the MS, with a reference to the particular registration, to SPIRITS server. e) The SPIRITS server transfers the identity of the MS, with a reference to the particular registration, to the application that generated the registration. Note that the application thusly notified that a particular MS has entered the registered region, may next elect to poll for the location Voelker Internet Draft [Page 4] Spirits Support for Location Services Expires June 2001 of the MS (now known to be in the vicinity of the desired region) to determine when it enters a more tightly defined region. In general, this polling will not involve Spirits. 4.2 Registration data Registration data may include a) Reference to a specification of location region. This must be understood by the PSTN in terms such as cell site or MSC area or a union of such natural regions. If a more general location region is defined, the PSTN would need additional capabilities to map that region to natural regions and to poll once entry to the natural region has been triggered. b) Set of MS. This can be an explicit list or can be an implicit definition of a set based on specifying some characteristics of the MS to be monitored. Can also reference a provisioned set. c) Whether the trigger involves entry, exit, or both from the region. d) Reporting criterion. Batch or single event. If batch, what delimits a batch; e.g. periodic reporting interval, number of accumulated events, whichever of the above occurs first, etc. e) For a particular MS, should multiple entry (or exits) from the region be reported. Note that requiring this places extra load on the PSTN trigger monitoring function. Being able to prune the set of monitored MS as they trigger events reduces the cost of matching a triggering MS against the contracting list of monitored MS. f) Time to live. If the TTL=0, then an explicit registration cancellation is needed. If the registration was done via provisioning, cancellation is probably also via provisioning. 4.3 Returned data The data returned may be some subset of the following: a) set of MS (perhaps only a single member in set) meeting the trigger criterion b) for each reported MS, whether entry or exit event c) time stamp for each MS trigger event d) count of MS meeting trigger criterion within some time period. In this case, probably not include the identities of particular MS. Has privacy advantages in some uses. e) report of audio message (as specified by registration) when that audio message is played in response to the MS entering the target region. E.g. when passenger lands at airport, phone rings and message Voelker Internet Draft [Page 5] Spirits Support for Location Services Expires June 2001 is played providing updated hotel reservations. The requesting application is then notified via Spirits that the audio message was delivered. 4.4. Privacy Privacy is obviously of great importance in location services. It is not clear where in the architecture the Policy Enforcement Point (PEP) should be located. The PEP must permit the location of a user to be delivered only in accordance with the user's (or subscriber's) wishes expressed as a function of the particular application receiving the user's location and whether that application can associate the location with the identity of the user. (In some cases, government requirements or carrier policy may override user/subscriber preference.) Upon initial processing of a registration by the PSTN, the list of monitored MS should be pruned to conform to privacy policy. In other words, filter for privacy before investing in the work of collecting location information that is not allowed to be delivered to the requesting application. 5. Services provided by SPIRITS architecture The following aspects of location services using SPIRITS can and should use the same mechanisms as other kinds of services using SPIRITS: security (including authentication and confidentiality), billing, accounting, transport of messages, binding of trigger firing reports to the associated registered request. 6. Acknowledgments Bill Opdyke, Margaret Ervin-Willis, and especially Kumar Vemuri provided helpful feedback on this draft. Jack Kozik suggested location as a potential SPIRITS contribution. 6. Reference [1] L. Slutsman (Ed.), I. Faynberg, H. Lu, M. Weissman, "The SPIRITS Architecture". , Work in Progress. October 2000. [2] I. Faynberg, J. Gato, H. Lu, "IN and PINT-related Requirements for SPIRITS Protocol", , work in progress. November 2000. Voelker Internet Draft [Page 6] Spirits Support for Location Services Expires June 2001 Appendix Subscriber's IP Network IP Host _______________ .................... | _____________ | A . ________________ . | |PINT Client|*******| PINT Server |******** | |___________| | : |______________| : * | ____________ | : * : * | | SPIRITS | | B . _______*________ : * | | Server |*******|SPIRITS Proxy | : * | |___________| | : |______________| : * |_______________| .........*.......... * *C * _________________ ______*________ * | Subscriber | |SPIRITS Client | * | Telephone | | | * |_________________| |_______________| * * * * E * Line * D * ++++++++++*+++++++++++ PSTN +++*+++++++++++++++*++ * * * +-------------------+ +-----------------+ | Service Switching |*****| Service Control | | Function | SS7 | Function | +-------------------+ +-----------------+ Figure 1: SPIRITS Architecture Voelker Internet Draft [Page 7] Spirits Support for Location Services Expires June 2001 Author's Address John Voelker Lucent Technologies Room 1A-417 263 Shuman Blvd Naperville, Il. 60566-7050 E-mail: jvoelker@lucent.com Telephone: +1 630 713 5538 Full Copyright Statement Copyright (C) The Internet Society (1998). 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