Location Services

LoCation Services (LCS) on the MME and SGSN is a 3GPP standards-compliant feature that enables the system (MME or SGSN) to collect and use or share location (geographical position) information for connected UEs in support of a variety of location services.

Location Services - Feature Description

The Location Services (LCS) feature enables the EPC MME and the GPRS/UMTS SGSN to use the SLg (MME) or Lg (SGSN) interface which provides the mechanisms to support specialized mobile location services for operators, subscribers, and third party service providers. Use of this feature and the SLg/Lg interface is license controlled.

The location information is reported in standard geographical co-ordinates (longitude and latitude) together with the time-of-day and the estimated errors (uncertainty) of the location of the UE. For external use, the location information may be requested by and reported to a client application associated with the UE, or a client within or attached to the core network. For internal use, the location information can be utilized by the SGSN for functions such as location assisted handover or to support other features.

Location information is intended to be used for

  • location-based charging (e.g., home-location billing, roaming-location billing),
  • location-based services (e.g., lawful interception, emergency calls),
  • positioning services offered to the subscribers (e.g., mobile yellow pages, navigation applications on mobiles), and
  • by the operator for service provider services such as network planning and enhanced call routing.

Relationship to Other SGSN Functions

The Location Services feature utilizes several of the existing SGSN functionalities:

  • Mobility Management module
  • MAP Service module

How Location Services Works

The MME/SGSN LCS responsibilities center around UE subscription authorization and managing LCS positioning requests. The LCS functions of the MME/SGSN are related to charging and billing, LCS co-ordination, location request, authorization and operation of the LCS services.

When using the Iu interface, before the SGSN can request location information of a target UE from the radio access network (RAN), an Iu signaling connection must have been established between the SGSN and the RAN. The SGSN sends a Location Request message to the RAN. The RAN determines the location of the target UE related to this Iu signaling connection and sends a Location Report to the SGSN over the same Iu signaling connection. On the Iu interface, only one location request for a geographic location estimate can be ongoing at any time.

The pre-requisite for LCS procedures on the Gb interface is that the UE is in “ready state”. On the Gb interface, only one location request can be ongoing at any time.

The operation begins with a LCS Client requesting location information for a UE from the LCS server. The LCS server will pass the request to the LCS functional entities (MME/SGSN) in the core network. The LCS functional entities (MME/SGSN) in the core network then:

  1. verifies that the LCS Client is authorized to request the location of the UE or subscriber;
  2. verify that location services are supported by the UE;
  3. establish whether it (the MME/SGSN) is allowed to locate the UE or subscriber, for privacy or other reasons;
  4. establish which network element in the radio access network ( GERAN or UTRAN or E-UTRAN ) should receive the Location Request;
  5. request the access network (via the A, Gb, Iu or S1 interface) to provide location information for an identified UE, with indicated QoS;
  6. receive information about the location of the UE from the Access Network and forward it to the Client;
  7. send appropriate accounting information to an accounting function.

Architecture

The MME is accessible to the Gateway Mobile Location Center (GMLC) via the SLg interface.

The SGSN is accessible to the GMLC via the Lg interface.


Figure 1. LCS Architecture

The MME may inform the HLR/HSS about a UE's location services capabilities for an EPC network.

The SGSN may inform the HLR/HSS regarding the LCS capabilities of UE in GPRS (2G) or UMTS (3G) networks. The SGSN may include the IP address of the B-GMLC associated with the SGSN in the MAP_UPDATE_GPRS_LOCATION message during Attach and ISRAU procedures.

Limitations

MME

Currently, MME support is limited to:

  1. Immediate Mobile-Terminating Location Requests [TS 3GPP 23.271]
  2. Location reporting granularity is at the E-UTRAN Cell Global Identifier (EGCI) level only.
  3. Only Provide Subscriber Location messages with the id as IMSI are supported.

SGSN

Currently, SGSN support is limited to:

  1. Immediate Mobile-Terminating Location Requests [TS 3GPP 23.271]
    • Limited support for GPRS.
  2. A single Location Request at one time.

Flows

Location Services call flows are standards compliant for both the MME and the SGSN.

MME


Figure 2. 4G LCS - Mobile Terminated Location Request Call Flow - Connected Mode
  1. The MME receives a Provide Location Request from the GMLC. The UE is in Connected mode.
  2. The MME sends Location Report Control message with request-type as 'Direct'.
  3. The eNodeB (ENB) sends the current location of the UE (ECGI) in the Location report message.
  4. The MME sends Provide Location Answer to GMLC with ECGI received in the location Report Message

Figure 3. 4G LCS - Mobile Terminated Location Request Call Flow - Idle Mode
  1. The MME receives a Provide Location Request from the GMLC. The UE is in idle mode.
  2. The MME pages the UE.
  3. If the UE does not respond to the page, the MME responds with the last known location and sets the age of location report accordingly if the Location Type requested by the GMLC was “current or last known location”.
  4. If paging is successful, the UE responds with Service request/TAU request.
  5. The MME uses the ECGI in the S1 message and sends Provide Location Answer message to the GMLC.

SGSN


Figure 4. 2G Mobile Terminating Location Request

Figure 5. 3G Mobile Terminating Location Request

Standards Compliance

The Location Services feature complies with the following standards:

MME

  • TS 3GPP 23.271, v9.6.0
  • TS 3GPP 24.080, v9.2.0
  • TS 3GPP 24.171, v9.0.0
  • TS 3GPP 29.172, v9.4.0

SGSN

  • TS 3GPP 23.271, v9.6.0
  • TS 3GPP 24.030, v9.0.0
  • TS 3GPP 24.080, v9.2.0
  • TS 3GPP 25.413, v9.8.0 (sections 8.19.2 and 8.20.2)
  • TS 3GPP 29.002, v9.7.0

Configuring Location Services (LCS) on the MME

This section provides a high-level series of steps and the associated configuration examples to configure Location Services on the MME.

The commands could be issued in a different order, but we recommend that you follow the outlined order for an initial LCS configuration. All listed configuration steps are mandatory unless otherwise indicated.

IMPORTANT:

For all the required configuration commands to be available and to implement the configuration, the MME must have loaded the license for the Lg interface.

  1. Create a location service configuration on the MME.
  2. Associate the location service with the appropriate Diameter endpoint.
  3. Associate the MME service with this location service.
  4. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide.
  5. Verify the configuration for each component by following the instructions provided in the Verifying the Feature Configuration section.

Creating and Configuring a Location Service on the MME

A location service must be created within a context. Up to 16 separate location services can be created.

config

   context <context_name> -noconfirm

      location-service  <location_svc_name> -noconfirm

      associate
diameter endpoint <endpoint>

      end

Notes:

  • This series of commands creates a Location service and associates the service with a diameter endpoint.

Associate the MME Service with the Location Service

Once the location service is created and configured, the MME service must be associated with it. The steps below assume the MME service has already been created.

config

   context <context_name> -noconfirm

      mme-service  <mme_svc_name>

      associate
location-service <location_svc_name>

      end

Notes:

  • This series of commands associates an MME service with the new location service.

Verifying the LCS Configuration for the MME

The following command displays configuration information for all Location services configured on the MME.

show location-service
service all

The following command displays the location service to which each MME service is associated.

show mme-service all

Monitoring and Troubleshooting LCS on the MME

LCS Show Command(s) and/or Outputs

The following command displays statistics for all Location services activity on the MME.

show location-service
statistics all

Use the following command to clear the LCS statistics for a specific Location service on the MME.

clear location-service
statistics service location_svc_name

Configuring Location Services (LCS) on the SGSN

This section provides a high-level series of steps and the associated configuration examples to configure Location Services on the 2G or 3G SGSN -- or for both.

The commands could be issued in a different order, but we recommend that you follow the outlined order for an initial LCS configuration. All listed configuration steps are mandatory unless otherwise indicated.

IMPORTANT:

For all the required configuration commands to be available and to implement the configuration, the SGSN must have loaded the license for the Lg interface.

  1. Enable Location Services on the SGSN.
  2. Identify the GMLC (in the MAP service) to which the SGSN connects for LCS access to the external LCS client.
  3. Configure the MAP service’s M1 timer.

    IMPORTANT:

    Step 3 is not mandatory but it is recommended.

  4. Create a location services configuration and associate the MAP service.
  5. Fine-tune LCS configuration per UE by defining LCS-related restrictions.
  6. Associate the location services configuration with the appropriate SGSN - GPRS (2G) service and/or UMTS (3G) service.
  7. Associate the location services configuration with an operator policy.
  8. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide.
  9. Verify the configuration for each component by following the instructions provided in the Verifying the Feature Configuration section.

Enabling LCS on the SGSN

Location Services functionality is enabled globally for the SGSN.

config

   sgsn-global

      location-services

      end

Notes:

  • This command enables and ‘starts’ LCS on the SGSN.
  • This command also enables support for the Lg interface on the SGSN.
  • Using the ‘no’ keyword stops LCS.

Identifying the GMLC

Use the MAP service configuration to identify the GMLC to which the SGSN connects for LCS access to the external LCS client. We recommend that you also configure the MAP service’s M1 timer, however, this is option.

config

   context <context_name>

      map-service <map_service_name>

         gmlc { isdn E.164# | point-code <point_code> } gsn-address <ipv4_address> [ source-ssn <ssn> ] 

         timeout
m1 seconds 

         end

Notes:

  • Only one GMLC can be configured per MAP service.
  • isdn is the 1-15 digit E.164 number that identifies the GMLC.
  • point-code is the address for the GMLC in dotted-decimal ###.###.### or decimal ######## SS7 point-code format
  • gsn-address is the IPv4 address for the GMLC
  • source-ssn optionally identifies the source SSN value to be used.

Creating the Location Service Configuration for the SGSN

This set of configuration commands creates a location service configuration and associates the MAP service with the location service. Up to 16 separate location services can be created.

config

   context context_name

      location-service loc_serv_name

         associate
map-service map_serv_name

         end

Notes:

  • The SGSN supports a maximum of 16 location service configuration. It should be noted that this number, 16, is not part of the SGSN’s service configuration limit of 256.
  • Associate the MAP Service configuration in which the GMLC is defined.

Fine-tuning the Location Service Configuration

Fine-tune the location service configuration per UE by defining LCS-related restrictions. The following commands will be used to configure the LCSN timer (location notification invoke procedures timer). This is an optional timer.

config

   context context_name

      location-service loc_serv_name

         timeout
lcsn seconds

Notes:

LCSN timer range is 10 - 20 with a default of 15. seconds.

Associating the Location Service Config with the SGSN

Location service functionality can be associated with either the 3G SGSN via commands in the SGSN Service configuration mode or with the 2G SGSN via commands in the GPRS Service configuration mode.

The following associates the location service configuration with a 3G SGSN:

config

   context context_name

      sgsn-service service-name

         associate
location-service loc_serv_name

Notes:

  • To associate with a 2G SGSN, enter the GPRS service configuration mode in place of the SGSN service configuration mode.

Associating the Location Service Config with an Operator Policy

Location service functionality can be associated with an operator policy to provide granular control.

The following associates the location service configuration with a call-control profile by IMSI and these CLIs will disable/enable Mobile Terminating, Mobile Originating and/or Network Induced location requests by access-type.

config

   call-control-profile
 ccprofile_name

      location-service service-name

         lcs-mo { allow | restrict } access-type { gprs | umts }

Notes:

  • lcs-mo enables mobile-originating location requests.
  • replace lcs-mo with lcs-mt to enable the mobile-terminating Location Requests or with lcs-ni to enable network-induced Location Requests.
  • Default for the 3 lcs commands is allow

Verifying the LCS Configuration for the SGSN

View the location service configuration to verify the configurations created for the Location Service functionality, by using the following commands:

show location-service
service { all | name loc_serv_name

View the MAP configuration to verify the MAP configurations created for the Location Service functionality, by using the following commands:

show map-service { all | name map_serv_name

View the call-control profile configuration to verify the configurations created for the Location Service functionality, by using the following commands:

show call-control-profile
full name ccprof_name

Monitoring and Troubleshooting the LCS on the SGSN

Use the commands listed below to monitor and/or troubleshoot the operation of the Location Services on the SGSN.

  • show map statistics name map-service-name
  • clear map statistics name map-service-name
  • show gmm-sm statistics
  • show subscribers sgsn-only summary
  • show subscribers gprs-only summary