My 33.127 Notes

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5.4 LI Interfaces

5.4.13 Lawful Interception Identity Query Function (LI_IQF) Interface

LI_IQF is an interface between Lawful Interception Control Function (LICF) and Identity Query Function (IQF) and is used by the LICF to send management information related to Identity Event Functions (IEFs) and Identity Caching Function (ICF), to the IQF.

Further details about this interface is outside the scope of 33.127 V18.0.0 (2022-06) document.

5.4.14 Lawful Interception Internal Query Response (LI_XQR)

The LI_XQR interface is used by the IQF to send identifier association queries to the ICF and from the ICF to return identities associations to the IQF in response.

The following are examples of some of the information that may be passed over LI_XQR from the IQF to the ICF:

  • Information relating to the type of query.
  • Temporary or permanent identifier provided by the LEA.
  • Other information associated with identifier required for localisation provided by the LEA.
    • Cell identity.
    • Tracking area identifier.
  • Time that identifier provided by the LEA was observed by the LEA.
  • Location information request from the LEA for permanent to temporary identifier association.

The following are examples of some of the information that may be passed over LI_XQR from the ICF to the IQF:

  • Information relating to the type of query being responded to.
  • Temporary and permanent identifiers corresponding to identifier provided by LEA.
  • Identifier association validity start and end times.
  • Location information.

NOTE: The location information returned in the IQF response is the information associated at the time of the specific identifier association caching at the ICF.

5.4.15 Lawful Interception Handover Interface Query Response (LI_HIQR) Interface

The Lawful Interception Handover Interface Query Response (LI_HIQR) interface is used by the Law Enforcement Agency (LEA) to send identifier association queries to the IQF and from the IQF to return identities associations to the LEA in response.

The following are examples of some of the information that may be passed over LI_HIQR from LEA to the IQF:

  • Information relating to the type of query.
  • Warrant/authorization identifier.
  • Temporary or permanent identifier provided by the LEA.
  • Other information associated with identifier required for localisation provided by LEA.
    • Cell identity.
    • Tracking area identifier.
  • Time that identifier provided by LEA was observed by the LEA.
  • Location information request for permanent to temporary identifier association.

The following are examples of some of the information that may be passed over LI_HIQR from IQF to the LEA:

  • Information relating to the type of query being responded to.
  • Warrant/authorization identifier.
  • Temporary and permanent identifiers corresponding to identifier provided by LEA.
  • Identifier association validity start and end times.
  • Location information.

5.4.16 Lawful Interception Internal Event Record (LI_XER) Interface

The Lawful Interception Internal Event Record (LI_XER) interface is used by the IEF to send identifier association events to the ICF.

The following are examples of some of the information that may be passed over LI_XER from the IEF to the ICF:

  • Permanent identifier and temporary identifier association.
  • Permanent identifier and temporary identifier excommunication / de-association.
  • Time stamp of association observation.
  • Location information.

5.4.17 Lawful Interception Internal Event Management 1 (LI_XEM1) Interface

The LI_XEM1 interface is used by the LICF (proxied by the LIPF) to manage and control the activation state of the IEF(s) and ICF.

LI_XEM1 interfaces shall support the use of ETSI TS 103 221-1 for transport of XEM1 messages / information. However, the requirements specified in the present document shall apply regardless of generic default options specified in ETSI TS 103 221-1.

5.7 Identifier association and reporting

5.7.1 General

3GPP networks use temporary identifiers in place of permanent identifiers to ensure that identities which are visible on exposed interfaces (e.g. RAN) cannot be used to track or degrade the privacy of a subscriber. For LI purposes, CSPs are required to be able to provide real-time association between temporary and permanent identifiers where the use of such identifier associations impact the ability of the LEA to uniquely identify the UE, subscriber or true permanent identifiers associated with a service.

33.127 defines two sets of capabilities which allow CSPs to report such association to LEAs:

  • Real-time reporting of associations as observed by POIs as part of network access, target communications and service usage.
  • Dedicated real-time query, lookup and reporting of identifier associations.

For real-time reporting based on POI observation, associations are reported through a combination of dedicated event records sent from the POI to the MDF over LI_X2 and through inclusion of specific parameters in other communications service records reported over LI_X2.

For dedicated query, lookup and reporting, the following figure shows the high-level architecture used to support identifier association query and response requirements. The Identifier Event Function (IEF) provides the Identifier Caching Function (ICF) with the events necessary to answer the identifier association queries from the IQF. LEAs are able to issue real-time queries to the Identifier Query Function (IQF), which in turn queries the ICF.

High-level ID-Retrieval-via-Query-Response diagram

The IQF and ICF shall support the following query types:

  • Single query and response.
  • Single query and response followed by triggered real-time reporting of any subsequent changes reported to the ICF (see NOTE 2).

Within 33.127 V18.0.0 document, only a single ICF for all IEFs is supported.

Within 33.127 V18.0.0 document, interfaces and generic functionality for dedicated identifier query and response are defined in this clause, while specific instances of the IEFs are defined within clause 6 and the ICF in clause 7. For each request over LI_HIQR, the LEA shall provide a legal warrant/authorisation unique identifier. In addition, depending on the scenario, the LEA needs to provide, the observed identity (temporary or permanent), along with the serving cell identity, tracking area identifier, and time of observation by LEA.

The IQF shall obtain in real-time the identifier associations which match the LEA query from the ICF and provide a response to the LEA over LI_HIQR. In some cases, it may not be possible to establish a single unique identifier association given the information provided by the LEA. IQF handling in such a scenario is subject to the authorisation in the warrant and is outside the scope of the present document.

NOTE 1: If the LEA is unable to provide the tracking area associated with an observed temporary identifier this may prevent the CSP from uniquely associating the identifier to the correct UE.
NOTE 2: Single query and response followed by triggered real-time reporting of any subsequent changes detected by the IEF is only applicable to queries based on a permanent identifier where the changes reported are new temporary identifiers to which that permanent identifier has been associated.
NOTE 3: The terms identifier and identity are used interchangeably in clause 5.7. This also applies to the naming of functions like IQF.


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