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Content for  TS 33.127  Word version:  16.4.0

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5.4  LI interfaces

5.4.1  General

An LI architecture diagram showing point-to-point LI interfaces is shown in figure 5.4-1 below.
[not reproduced yet]
Figure 5.4-1: Architecture diagram with point-to-point LI interfaces
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5.4.2  Interface LI_SIWord‑p. 19
LI_SI is an interface between the SIRF and LIPF. SIRF uses this interface to provide the system information to the LIPF. The LIPF may request the SIRF for such information before sending the intercept provisioning information to the POIs. The SIRF may also notify the LIPF whenever the status of a system function changes (e.g. removed from service, migrating to another location, etc.).

5.4.3  Interface LI_HI1

LI_HI1 is used to send warrant and other interception request information from the LEA to the CSP. This interface may be electronic or may be an offline manual process depending on national warranty processes.
The following are some of the information elements sent over this interface:
  • Target identifier: used to identify the communications to be intercepted.
  • Type of intercept: used to indicate whether IRI only, CC only, or both IRI and CC, is to be delivered to the LEMF.
  • Service scoping: used to identify the service (e.g. voice, packet data, messaging, target positioning) to be intercepted.
  • Filtering criteria: used to provide additional specificity for the interception (e.g. for bandwidth optimization).
  • LEMF address: used to deliver the Interception Product.
  • Lawful Interception Indentifier (LIID) used to associate the issued warrant with the Interception Product.
LI_HI1 interfaces shall support the use of ETSI TS 103 120 [7] for communication of warrant information between the LEA and CSP. However, default configurations, information element formats and other parameters as defined in the present document shall apply regardless of generic default options specified in ETSI TS 103 120 [7].
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5.4.4  Interface LI_X1Word‑p. 20

5.4.4.1  General

LI_X1 interfaces are used to manage the POIs and TFs and to provision LI target information on the POIs and TFs in order to intercept target communications. LI_X1 interfaces are also used to manage and provision MDFs with the necessary information to deliver those communications in the correct format to LEMFs.
LI_X1 interfaces shall support the use of ETSI TS 103 221-1 [8] for transport of X1 messages / information. However, the requirements specified in the present document shall apply regardless of generic default options specified in TS 103 221-1 [8].
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5.4.4.2  LIPF and POI

The following are examples of some of the information that may be passed over LI_X1 to the POI as a part of intercept provisioning:
  • Information necessary to associate multiple xIRI/xCC at MDF2/MDF3.
  • Target identifier.
  • Type of intercept (IRI only; CC only; or IRI and CC).
  • Service scoping.
  • Further filtering criteria.
  • Address of MDF2 or MDF3.
The exact nature of the information passed depends on the role of the POI.
The LI_X1 interface between the LIPF (in the ADMF) and a Triggered POI shall be used only for audit and management purposes, and not for provisioning purposes.
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5.4.4.3  LIPF and TF

The following are examples of some of the information that may be passed over LI_X1 to the TF as a part of intercept provisioning:
  • Information necessary to associate multiple xIRI/xCC at MDF2/MDF3.
  • Target identifier.
  • Type of intercept (IRI only; CC only; or IRI and CC).
  • Service scoping.
  • Further filtering criteria.
  • Address of MDF2 or MDF3.
The exact nature of the information passed depends on the role of the TF.

5.4.4.4  LIPF and MDF2/MDF3Word‑p. 21
The following are examples of some of the information that may be passed over LI_X1 to the MDF2/MDF3 as a part of intercept provisioning:
  • Information necessary used to associate multiple xIRI/xCC at MDF2/MDF3.
  • Target identifier.
  • Lawful Interception identifier.
  • Type of intercept (IRI only; CC only; or IRI and CC).
  • Service scoping.
  • Further filtering criteria.
  • LEMF address.
The exact nature of the information passed depends on the role of the MDF.

5.4.5  Interface LI_X2

The LI_X2 interfaces are used to pass xIRI from IRI-POIs to the MDF2.
The following are some of the information passed over this interface to the MDF2 as a part of xIRI:
  • Target identifier.
  • Time stamp.
  • Correlation information.
  • IRI event resulting in xIRI.

5.4.6  Interface LI_X3

LI_X3 interfaces are used to pass real-time content of communications (i.e. xCC) and associated metadata from CC-POIs to MDF3.
The following are some of the information passed over this interface to the MDF3 as a part of xCC:
  • Target identifier.
  • Time stamp.
  • Correlation information.
  • User plane packets.

5.4.7  Interface LI_T

5.4.7.1  General

The LI_T interface is used to pass the triggering information from the Triggering Function to the POI. Depending on the POI type, two types of LI_T are defined:
  • LI_T2.
  • LI_T3.
LI_T2 is used when POI output is sent over LI_X2 and LI_T3 is used when POI output is sent over LI_X3.

5.4.7.2  Interface LI_T2Word‑p. 22
The LI_T2 interface is from IRI-TF to IRI-POI.
The following are some of the information passed over this interface to the IRI-POI:
  • Target identifier.
  • IRI interception rules.
  • MDF2 address.
  • Correlation information.
The IRI interception rules allow the IRI-POI to detect the target communication information to be intercepted.

5.4.7.3  Interface LI_T3

LI_T3 interface is from CC-TF to CC-POI.
The following are some of the information passed over this interface to CC-POI:
  • Target identifier.
  • CC interception rules.
  • MDF3 address.
  • Correlation information.
The CC interception rules allow the CC-POI to detect the target communication information to be intercepted.

5.4.8  Interface LI_HI2

LI_HI2 is used to send IRI from the MDF2 to the LEMF. This interface is defined in TS 33.128.

5.4.9  Interface LI_HI3

LI_HI3 is used to send CC from the MDF3 to the LEMF. This interface is defined in TS 33.128.

5.4.10  Interface LI_HI4

5.4.10.1  General

LI_HI4 is used by the MDF2 and MDF3 to report to the LEMF that the MDF2/3 have been provisioned as expected. This capability is mandatory to support but optional to use (subject to relevant national agreement) at both MDF2 and MDF3.

5.4.10.2  LI operation notification

The MDF2 and MDF3 shall support reporting to the LEMF changes to provisioning, including:
  • Activation of LI.
  • Modification of active LI.
  • Deactivation of LI.

5.4.10.3  Contents of the notificationWord‑p. 23
Each notification shall include at least the following:
  • The type of notification (e.g. activation, deactivation).
  • Relevant related information (LIID, time of change).

5.4.11  Interface LI_ADMF

LI_ADMF is an interface between LICF and LIPF and is used by the LICF to send the intercept provisioning information to the LIPF. Further details about this interface is outside the scope of the present document.

5.4.12  Interface LI_MDF

LI_MDF is an interface between MDF2 and MDF3 and is used for MDF2 and MDF3 to interact with each other in the generation of IRI and CC. Further details about this interface is outside the scope of the present document.

5.5  LI service discovery

In SBA as defined in TS 23.501 the NRF is a central repository of discoverable NFs. For NFs to be discoverable, they need to have been previously instantiated and undergone a degree of configuration (function identity allocated, IP addresses, certificates, network connectivity to NRF, etc.).
LI functions (e.g. ADMF, POIs and MDFs) exist within a separate security domain to the main network NF to which they are embedded. Furthermore, as with legacy networks, LI functions associated with NFs shall be configured and tested before the associated NF is allowed to enter active network user service (i.e. LI shall be configured and tested before an NF can handle live user traffic).
In the present document, all LI functions have dedicated LI_X interfaces and discovery of LI functions by the LIPF shall happen as part of the NF / LI function instantiation phase. POIs, TFs and MDFs shall not be subject to or within the scope of NRF service discovery as defined in TS 23.501. The SIRF is used to provide the LIPF with NF discovery information which shall be used to identify which NFs are applicable to intercept specific user sessions, as described in clause 5.3.6. However, the SIRF is not involved directly in LI service discovery.
The SIRF may be used to inform the LIPF that an NF has been registered / deregistered with the NRF and is now ready for use in a network user service. The LIPF is assumed to already have knowledge of which POIs and TFs are associated with which NFs.
POIs, TFs and MDFs may be discovered in virtualised deployments using the approach described in clause 5.6. The exact mechanisms for achieving this are out of scope of the present document.
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