Client-Server Approach to Mobile Location Services
Position Paper for the W3C/WAP Position Dependent Information Services Workshop
Steve Nowak, SignalSoft Corporation
Maureen O?Neill, SignalSoft Corporation
Over the last several years there have been significant technology developments for mobile location services support in wireless networks. GSM has developed a standard for location services in support of emergency services as well as support for a variety of commercial services. ANSI-41 has developed a standard in support of emergency services that will evolve to support commercial services as standards groups move the technology capabilities forward.
Previous WAP contributions have focused on handset-centric examples for obtaining location. It is desirable to enhance those contributions with network capabilities defined in the GSM and ANSI-41 work already in progress. This position paper describes these wireless network capabilities and presents opportunities for WAP to acquire position information from the wireless network.
Client-Server Approach to Mobile Location Services (MLS)
Wireless networks have utilized a client-server approach to the development of wireless network location services. The location services client is representative of location service applications that either reside within the wireless network (including MS) or may reside outside the wireless network. These clients are capable of requesting location information or network positioning assistance information from the wireless network. The location services server is a collection of wireless network and Mobile Station (MS) components that provide target MS location information to the location services client.
MLS Client
The mobile location services client is an entity that requests location information from the mobile location services server environment, for one or more target MS's within a specified set of interface parameters. The client may reside within the wireless network under the control of the wireless network operator, or outside the wireless network.
The client is expected to communicate and interface with the mobile location services server through a consistent set of parameters not limited to the following;
· Location request type (single, periodic update)
· Client Identity
· Target MS's (individual or list)
· Geographic location
· Quality of Service (accuracy, response time)
· Priority
· Timestamp
· Wireless network authorization of external clients
MLS Server
The mobile location services server is a collection of wireless network functions and bearer services responsible for responding to MLS Client requests for location information.
· The MLS server makes use of a positioning function to obtain the location information and furnish the information to the MLS client. Positioning is the basic function that performs the actual positioning of a specific target MS. The input to this function is a location request from a MLS client with a set of parameters such as Quality of Service (QoS) requirements. The end results of this function are the location information for the target MS provided back to the requesting MLS client.
· The particular requirements and characteristics of the MLS client are supported in the MLS server environment via a MLS client profile. The MLS restrictions associated with each target MS are supported in the target MS subscription profile. The MLS server may respond to a location request from a properly authorized MLS client with location information for the target MS's.
· The target MS is the object to be positioned by the MLS server environment. For network-based positioning methods no support is required in the MS. For mobile assisted and mobile-based positioning methods, the MS is actively involved in the procedures and support is required in the MS. For all positioning methods the ability to control privacy may be required by the MS user for each location request or through subscription to satisfy local regulatory requirements.
MLS Client-Server Interface
The MLS client and server communicate through a set of defined messages to exchange information. These messages contain a set of consistent parameters as described in the MLS client section above. In the case of MS-based positioning methods and the MLS client is in the MS, then an internal MLS client-server interface may be supported.
The MLS client performs a location service request to the MLS server within a specified set of QoS parameters to request location information for one or more target MS's. The location service request can ask for a single location estimate within a specific response time window (immediate) or can request periodic updates based on time duration or some event occurring in the wireless network (deferred). A location service response provides a result to the immediate request from the MLS server to the client. A location service request report provides the result of a deferred location service request from the server to the client.
Location Request Methods
There are two primary methods for MLS clients to request location information the first being network-based, and the second is mobile-originated.
Network-based location requests include requests initiated by MLS clients within the wireless network based on wireless user events (digits dialed, mobility, etc) or network operator events to request positioning to occur. Network-based location requests also includes MLS clients external to the wireless network requesting location information for specified target MS's (e.g. Internet MLS client). External MLS clients must be authorized before positioning can occur.
Mobile-originated location requests allow the MS to obtain its own geographical location or have its location information transferred to another MLS client. There are three classes of mobile-originated requests.
· Self Location - this is where the MS can determine its own location and needs to interact with the wireless network for each request.
· Autonomous Self Location - this allows a MS to interact with the network once for multiple location positionings. One interaction with the network allows the MS to obtain multiple locations over a predetermined time period.
· Transfer to Third Party - this allows the location of the MS to be transferred to another MLS client based on a request from the MS MLS client.
References
?Digital Cellular Telecommunications System (Phase 2+); Location Services (LCS); Service Description - Stage 1 (GSM 02.71 V 7.1.0 Release 1998)
?Digital Cellular Telecommunications System (Phase 2+); Location Services (LCS); Functional Description - Stage 2 (GSM 03.71 V 7.0.0)
Enhanced Wireless 911 Phase 2, (TR45.2.AHES PN-3890 Rev 10)