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Content for  TR 23.842  Word version:  11.0.0

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1  Scopep. 6

The present document investigates architecture solutions for making the Network Provided Location Information (NPLI) related to the access network that the UE is camped on available to the IMS nodes whenever the IMS operator needs to record this information either to fulfil legal obligations, for charging or for other purposes.
This study will gather the various existing regulatory and operator requirements that the solution needs to fulfil, in particular:
  • whether the provision of the Network Provided Location (NPLI) Information and local time are applicable to all the users served by a network (i.e. "non-roaming" subscribers and inbound roamers) or only to the network operator subscribers;
  • whether Network Provided Location (NPLI) and local time need to be made available also if EPS/GPRS and IMS services of a subscriber are provided by different networks;
  • what events trigger the need to retrieve the Network Provided Location (NPLI) and local time.
The study is then expected to produce solution candidates which detail the necessary Stage 2 message flows, architecture enhancements and new functionality needed in the EPS and GPRS networks. The solution candidates will also describe what IP Multimedia Subsystem elements are affected in order to obtain the Network Provided Location (NPLI).
The solutions produced will then be assessed against the criteria identified in section 7 where recommendations for normative work will also be made.

2  Referencesp. 6

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
  • References are either specific (identified by date of publication, edition number, version number, etc.) or non specific.
  • For a specific reference, subsequent revisions do not apply.
  • For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
TR 21.905: "Vocabulary for 3GPP Specifications".
[2]  Void.
TS 23.167: "IP Multimedia Subsystem (IMS) emergency sessions".
TS 23.292: "IP Multimedia Subsystem (IMS) centralized services; Stage 2".
TS 29.328: "IP Multimedia (IM) Subsystem Sh interface; Signalling flows and message contents".
TS 23.271: "Functional stage 2 description of Location Services (LCS)".
TS 23.228: "IP Multimedia Subsystem (IMS); Stage 2".
TS 23.078: "Customized Applications for Mobile network Enhanced Logic (CAMEL) Phase 4; Stage 2".
TS 23.401: "General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access".
TS 24.229: "IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3".

3  Definitions and abbreviationsp. 7

3.1  Definitionsp. 7

For the purposes of the present document, the terms and definitions given in TR 21.905 and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905.
Network Provided Location Information:
Information provided by the network. Specifically, this can be the Cell Global Identity (CGI), CSG Identity (CSGID), Geographical Identifier (GI) and/or PLMN ID, depending on the type of access network that the UE is camped on and on the level of granularity that is provided. Based on operator policy and/or roaming agreement, local time of visited network is included.
Geographical Identifier:
Identifier of a geographical area defined within a country or territory. The Geographical Identifier may be described in a geospatial manner (e.g. geodetic coordinates) or as civic location information (e.g. a postcode), or use an operator-specific format. It may be generated by the access network, or by an IMS node. It is assumed that a given cell cannot belong to more that one area identified by a Geographical Identifier.

3.2  Abbreviationsp. 7

For the purposes of the present document, the abbreviations given in TR 21.905 and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905.
Geographical Identifier
Network Provided Location Information

4  Scenarios for Network Provided Location Information Provisionp. 7

4.1  Lawful interceptionp. 7

A legal obligation exists for network operators to record the Cell-ID when lawful interception is applied. Though the UE currently provides the Cell-ID information, some regulators do not to trust this information because it may have been tampered with, therefore they require a network provided Cell-ID.
For an originating or terminating IMS session involving an intercepted UE, both the Cell-ID where intercepted UE has initiated the session and the Cell-ID where the session was released are required. There is no requirement to be able to track the changes in the Cell-ID value during the session.

4.2  Chargingp. 7

The CDRs generated within IMS have to contain Network Provided Location Information (NPLI) in order to guarantee correct billing. This applies for all CDRs from any user/session regardless of whether the session is successfully established or not.
In case the UE to be located is camped on a visited network (that is not an equivalent PLMN to the HPLMN), the level of granularity of the NPLI (Cell ID, CSG ID, GI, PLMN ID) provided between PLMNs depends on roaming agreements. In all cases, the Cell-ID or CSGID needs to be provided to IMS nodes in the VPLMN when the UE to be located is camped on that same VPLMN or equivalent PLMN to the VPLMN.
In the case of an IMS voice session, for example, the NPLI of the UE needs to be recorded for an originating or terminating IMS session establishment. The NPLI need to be provided when the session is successfully connected/released and when the session is dropped due to, for instance, radio condition changes.
When an IMS Session is modified, e.g. when a new media component is added to an MMTel call, the NPLI also needs to be stored as the location of the user at the time when the session is modified may generate a charging event.
NPLI is also needed to correctly charge for localized services. NPLI needs to be available to any IMS node that generates charging records. The network that the IMS node is located in will determine if Cell-ID, CSGID, GI or PLMN ID is needed. For example, on an IMS session origination where the P-CSCF is in a VPLMN and the S-CSCF is in the Home or equivalent PLMN, the Cell-ID or CSGID would be in the P-CSCF CDR and the PLMN ID would be in the S-CSCF CDR.
The NPLI of the serving cell is likewise needed by IMS elements involved in online charging. In the case of online charging, it is needed at the time of the IMS service request, or when the IMS service request being processed form mobile terminated services, because it may be taken into consideration for service authorization.
The local time of the serving cell is likewise needed for both offline and online charging, to be provided to the IMS elements in either case at the same time as the NPLI.

4.3  IMS Emergency Calls Routingp. 8

In order to be able to route an emergency call to the appropriate PSAP, the NPLI is required. The NPLI shall be provided to the E-CSCF before it performs PSAP selection. The Cell-ID of the cell where the emergency call is originated is considered to provide sufficient accuracy for a correct routeing of the call. In some instances, depending on the specific PSAP configuration and based on regulatory requirements, a lower level of accuracy than that provided by the Cell-ID may be preferable, e.g. GI.
If local regulation requires support for UEs which have insufficient credentials (e.g. UICC-less), network provided Cell-ID must also be obtained for these UEs.
Existing mechanisms as defined in TS 23.167 may be used for the PSAP selection, those can be LCS based if the operator supports LCS or non-LCS based if the operator does not support LCS.
In all cases, minimal impact on the session set-up time for obtaining the network provided location information is important as in some countries stringent requirements exist on emergency call set up time.

4.4  Retention of Location Information Datap. 8

Network operators have a legal obligation to record and store for a certain amount of time information about their subscribers such as events, services used as well as location where the service was consumed. It is expected that when a service is provided by IMS the same requirements that exist today for CS services will continue to apply.

4.5  Special Call Routing for Localised Servicesp. 8

For localised services and for routeing of originating or terminating sessions dependent on the current location of the UE, the NPLI needs to be available to the IMS before deciding on whether or where to route the session. It is expected that localised services are provided by IMS with minimal impact regarding session set-up time and in the same way as provided by the CS domain today.

4.6  Location-based service triggeringp. 8

Network operators implement services that need to be triggered based on the location of the user. For example, an anti-fraud AS may be triggered when a user is roaming. In order to allow this for IMS services, certified location information needs to be available at the time of triggering Application Servers, with at least the granularity of a PLMN ID, while processing requests for originating or terminating session establishment and requests for SMS.

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