5 General LCS architecture

23.1713GPPFunctional descriptionLocation Services (LCS)Release 1999Stage 2 (UMTS)TS

5.1 LCS access interfaces and reference points

There is one reference point between the LCS server and LCS client called Le, see Figure 5.1. Le is described in TSĀ 22.071 [4], however the protocol specifics are for further study. There may be more than a single LCS network interface to several different LCS clients or other networks. These networks may both differ in ownership as well as in communications protocol. The network operator should define and negotiate interconnect with each external LCS client or other network.

An interface differs from a reference point in that an interface is defined where specific LCS information is exchanges and needs to be fully recognized.

There is an interface called Lg that connects two independent LCS networks (different PLMNs) for message exchange.

Figure 5.1: LCS Access Interfaces and Reference Points

5.2 LCS Functional diagram, high level functions

TS 22.071 [4] describes LCS services from the LCS client point of view. In the present document, a more detailed description of LCS is given. The LCS functional diagram shown in Figure 5.2 depicts the interaction of the LCS client and the LCS server within the PLMN. The PLMN uses the various LCS components within the LCS server to provide the target UE Location Information to the LCS client.

Figure 5.2: UMTS LCS capability server Functional Diagram

The following list gives the logical functional entities for the LCS. Two main functional groupings are defined which encompass a number of smaller functions.

The LCS Functional entities are grouped as follows:

– The LCS Client functional group.

– The LCS Server functional group consists of functions in the UMTS PLMN supporting LCS:

– Client handling component;

– System handling component;

– Subscriber handling Component;

– Positioning component.

The functions of the LCS Client and the LCS Server in UMTS PLMN are described in more detail in this subclause.

The allocation of LCS functions to UMTS network elements is specified in clause 6.

5.3 LCS Client functional group

An LCS client contains an LCS component with one or more client(s), which by using location information can provide location, based services.

An LCS client is a logical functional entity that requests from the LCS server in the PLMN location information for one or more than one target UE within a specified set of parameters such as Quality of Service (QoS). The LCS Client may reside in an entity (including the UE) within the PLMN or in an entity external to the PLMN.

The specification of the LCS Client’s internal logic and its relation to the external use is outside the scope of the present document.

5.3.1 External Location Client Function (LCF)

The Location Client Function (LCF) provides a logical interface between the LCS client and the LCS server.

This function is responsible for requesting location information for one or more MEs/UEs, with a specified "QoS" and receiving a response, which contains either location information or a failure indicator.

[Editor’s note: this is only possible if the location request originates in the core network]

5.3.2 Internal Location Client Function (U-LCF)

The Location Client Function (LCF) provides a logical interface between the internal ACCESS NETWORK LCS applications and the ACCESS NETWORK LCS system handling entities (e.g. the Location System Control Function (U-LSCF) in the ACCESS NETWORK). This interface may be internal to one network element.

The ACCESS NETWORK may make use of location information for internal operations such as location assisted handover. In such a case, a U-LCF representing the internal ACCESS NETWORK LCS application may communicate with the U-LSCF to request and receive the location information.

For UTRAN, this interface is further described in [1].

5.4 LCS Server functional group in UMTS

The LCS server functional group consists of the UMTS functions that are needed for UMTS to support Location Services.

5.4.1 Client handling component

5.4.1.1 Location Client Control Function (LCCF)

The Location Client Control Function (LCCF) manages the external interface towards LCF. The LCCF identifies the LCS client by requesting client verification and authorization ( i.e. verifies that the LCS client is allowed to position the subscriber) through interaction with the Location Client Authorization Function (LCAF). The LCCF handles mobility management for location services (LCS) e.g., forwarding of positioning requests to 3G-VMSC. The LCCF determines if the final positioning estimate satisfies the QoS for the purpose of retry/reject. The LCCF provides flow control of positioning requests between simultaneous positioning requests. It may order the Location Client Co-ordinate Transformation Function (LCCTF) to perform a transformation to local co-ordinates. It also generates charging and billing related data for LCS via the Location System Billing Function (LSBF).

5.4.1.2 Location Client Authorization Function (LCAF)

The Location Client Authorization Function (LCAF) is responsible for providing access and subscription authorization to a client. Specifically, it provides authorization to a LCS client requesting access to the network and authorizes the subscription of a client. LCAF provides authorization to a LCS client requesting Location Information of a specific UE.

5.4.1.2.1 Access Subfunction

An Access Subfunction enables LCS clients to access LCS services. This subfunction provides verification and authorization of the requesting client.

When a LCS is requested, the Access Subfunction uses the information stored in the LCS client subscription profile to verify that:

– the LCS client is registered; and

– the LCS client is authorized to use the specified LCS request type;

– the LCS client is allowed to request location information for the subscriber(s) specified in the LCS request.

5.4.1.2.2 Subscription Subfunction

The LCS client Subscription profile shall contain a minimum set of parameters assigned on per LCS client basis for an agreed contractual period. The LCS client profile shall contain the following set of access parameters:

– LCS client identity;

– Allowed LCS request types (i.e. LIR, LDR or both); (see note)

– Maximum number of subscribers allowed in a single LCS request;

– Priority;

– Position override indicator;

– State(s);

– Event(s) (applicable to LDR requests only);

– Local coordinate system;

– LCS client access barring list (optional);

– PLMN access barring list applicability;

NOTE: LIR = Location Immediate Request; and LDR = Location Deferred Request.

For certain authorized LCS client internal to the PLMN, a subscription profile is unnecessary. These clients are empowered to access any defined service that is not barred for an UE subscriber. This permits positioning of emergency calls without the need for pre-subscription.

5.4.1.3 Location Client Co-ordinate Transformation Function (LCCTF)

The Location Client Co-ordinate Transformation Function (LCCTF) provides conversion of a location estimate expressed according to a universal latitude and longitude system into an estimate expressed according to a local geographic system understood by the LCF and known as location information. The local system required for a particular LCF will be either known from subscription information or explicitly indicated by the LCF.

5.4.1.4 Location Client Zone Transformation Function (LCZTF)

The Location Client Zone Transformation Function (LCZTF) performs transformations of a location (latitude and longitude) into a zone identity, which in North America identifies a particular emergency services zone.

5.4.2 System handling component

5.4.2.1 Location System Control Function in general (LSCF)

The Location System Control Function (LSCF) is responsible for co-ordinating location requests. This function manages call-related and non-call-related positioning requests of LCS and allocates network resources for handling them. The LSCF retrieves UE classmark for the purpose of determining a positioning method. The LSCF performs call setup if required as part of a LCS e.g., putting the ME on dedicated radio resources. It also caters for co-ordinating resources and activities with regard to requests related to providing assistance data needed for positioning. This function interfaces with the LCCF, LSPF, LSBF and PRCF. Using these interfaces, it conveys positioning requests to the PRCF, relays positioning data to the LCCF and passes charging related data to the LSBF.

5.4.2.2 Access Network Location System Control Function(U-LSCF)

The Access Network Location System Control Function is responsible for co-ordinating location requests. This function manages call-related and non-call-related location requests and allocates network resources for handling them. This function "insulates" the Location clients in the Core Network from the detailed operation of the location method in order that the Access Network may be used by several types of core network and with several location methods.

The U-LSCF for UTRAN is further described in [1].

5.4.2.3 Location System Billing Function (LSBF)

The Location System Billing Function (LSBF) is responsible for charging and billing activity within the network related to location services (LCS). This includes charging and billing of both clients and subscribers. Specifically, it collects charging related data and data for accounting between PLMNs.

5.4.2.4 Location System Operations Function (LSOF)

The Location System Operations Function (LSOF) is responsible for provisioning of data, positioning capabilities, data related to clients and subscription (LCS client data and UE data), validation, fault management and performance management of UMTS LCS.

An LSOF may be associated with each entity.

[Editor’s note: This is being studied in GSM. FFS in UMTS. Internal LCF may be part of O&M functions.]

5.4.2.5 Location System Broadcast Function (LSBcF)

The Location System Broadcast Function (LSBcF) provides broadcast capability. The LSBcF capability is only used when broadcast data is required for OTDOA or assisted GPS positioning methods.

5.4.3 Subscriber handling Component

5.4.3.1 Location Subscriber Authorization Function (LSAF)

The Location Subscriber Authorization Function (LSAF) is responsible for authorizing the provision of a location service (LCS) for a particular mobile station (UE with SIM/USIM). Specifically, this function validates that a LCS can be applied to a given subscriber. In case LCF is in the UE then LSAF verifies that the UE subscriber has subscribed to the requested LCS service.

5.4.3.2 Location Subscriber Privacy Function (LSPF)

The Location Subscriber Privacy function is responsible performs all privacy related authorizations. For a target UE it shall authorize the positioning request versus the privacy options of the target UE, if any.

5.4.4 Positioning components

The positioning components UMTS Access Network – Positioning Radio Co-ordination Function (U-PRCF), UMTS ACCESS NETWORK Positioning Calculation Function (U-PCF), UMTS Access Network – Positioning Signal Measurement Function (U-PSMF) and UMTS Access Network – Positioning Radio Resource Management (U-PRRM) are described in documents specific to each Access Network type.

For location services the Access Network shall send the result of the positioning to the core network in geographical co-ordinates as defined in TS 23.032. For UTRAN the SRNC shall map the cell(s) the Target UE is associated with into geographical co-ordinates, but this mapping is not standardized.

These entities are defined for UTRAN in [1].

5.5 Information Flows between Client and Server

Other types of national specific information flows may be supported in addition to the information flow specified here.

Any of the information flows here indicated may not be externally realized if the information does not flow over an open interface. On the other hand, if a flow goes over an open interface, it shall abide to a well-defined protocol, which will be further specified in other relevant specifications.

5.5.1 Location Service Request

Via the Location Service Request, the LCS client communicates with the LCS server to request for the location information of one or more than one UE within a specified quality of service. There exist two types of location service requests:

– Location Immediate Request (LIR); and

– Location Deferred Request (LDR).

The attributes for the information exchange between the LCS Client and the LCS Server have not been standardized for GSM. This information exchange may be standardized in later releases.

The following generic attributes are identified for Location Service Request information flow:

– Target UE identity;

– LCS Client identity;

– Number dialled by the target mobile user if the request is call related;

  • Requested Quality of Service information, if needed;
  • Type of location, i.e. current location or last known location
  • Priority, if needed
  • Local coordinate reference system, if needed;

Some of the information may be stored in GMLC and the LCS client does not need to include such information in the location service request.

5.5.2 Location Service Response

The LCS server (GMLC) sends the Location Service Response to the LCS client either as an:

– Immediate Response; or a

– Deferred Response, these deferred responses can be either single or periodic.

The following generic attributes are identified for the Location Service Response information flow:

  • Location indication of UE in geographical coordinates or local coordinate system;

In addition the information attributes of the location service request may be used also in the location service response.