I  Interception of Targets with Non-Local IDs |R13|  Word‑p. 363

I.1  Introduction

This annex provides some informative illustrations on the interception of targets with Non-Local IDs. A target with a Non-Local ID means that the identity used for the target may not belong to the network that is providing the interception. However, in a roaming scenario, that subscriber with a Non-Local ID could as well be in the network where the interception is provided. For the lawful interception purpose, a target with a Non-Local ID is distinctly identified as a Non-Local target along with the nature of the interception that is required to be performed on that target.

This clause covers only the IRI aspects of interception capabilities since the capabilities to perform the CC interception do not change.

I.2  Interception of outgoing calls

I.2.1  General

In order to perform the interception of outgoing calls to a particular destination (identified as target with Non-Local ID for outgoing calls), called party information of the outgoing message is checked.

In the CS domain, this could be the Called Party Information present in the IAM message (as an example) that is sent from the switch that performs the interception.

In the case of IMS-based VoIP calls, this can be any of the SIP headers used to identify the called party information present in the outgoing SIP message. The examples are: Request URI and To headers. The interception functions may be provided by the S-CSCF or P-CSCF (optional in a non-roaming case, and mandatory in the roaming case when LBO approach is used as the roaming architecture). Alternatively, in another implementation, the interception functions may also be provided by the Egress IBCF or Egress MGCF for a non-roaming case. Of the two approaches S-CSCF/P-CSCF Vs IBCF/MGCF used for non-roaming case, only one approach is required to be supported within a CSP's network.

I.2.2  Interception at S-CSCF or P-CSCF

The Figure I.1 shows an example where the interception is done at the S-CSCF. The Figure I.2 shows an example where the interception is done at the P-CSCF in a roaming case with LBO as the roaming architecture. In both illustrations, Party-B is the target with Non-Local ID and the nature of the interception to be performed is for outgoing calls. In the call, the Request URI and To headers point to Party-B.

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Figure I.1: IRI ICE at S-CSCF - interception of a target with Non-Local ID for outgoing calls

Figure I.1 shows the case where S-CSCF is the IRI ICE and hence, the S-CSCF checks the Request URI and To headers of SIP message that it sends out toward IBCF/MGCF. Since a match is found, S-CSCF would perform the interception.

In the event, multiple S-CSCF are involved in the signalling path (due to call forwarding case), all S-CSCF are expected to do the same check and the S-CSCF closer to the Egress IBCF/MGCF will find a match. It is important to note that the S-CSCF checks the headers from the SIP message it sends out because the Request URI of the SIP message it receives will be pointing to the local ID (which may have the call forwarding activated).

As in the case of interception of target with Local ID, a P-CSCF may optionally provide the IRI ICE functions in a non-roaming case. However, in a roaming case with LBO as the roaming architecture, P-CSCF provides the IRI ICE functions.

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Figure I.2: IRI ICE at P-CSCF (roaming) - interception of a target with Non-Local ID for outgoing calls

In Figure I.2, the P-CSCF in the VPLMN checks the Request URI and To headers of SIP message that it sends out toward IBCF. Since a match is found, P-CSCF would perform the interception.

I.2.3  Interception at the IBCF/MGCF  Word‑p. 364

The Figure I.3 shows an example where the interception is done at the IBCF or MGCF in a non-roaming case. In the illustration, Party-B is the target with Non-Local ID and the nature of the interception to be performed is for outgoing calls. In the call, the Request URI and To headers point to Party-B.

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Figure I.3: IRI ICE at BCF - interception of a target with Non-Local ID for outgoing calls

Figure I.3 shows the case where the Egress IBCF or MGCF is the IRI ICE for intercepting when the target is identified with a Non-Local ID. Accordingly, the IBCF or MGCF checks the Request URI and To headers of SIP message. Since MGCF is providing signalling conversion (e.g., SIP to ISUP and Vice-Versa), the MGCF checks the headers of the SIP message it receives. IBCF could check the headers from either of the SIP messages (they have to be the same anyway). Alternatively, the MGCF could also check the Called Party Information present in the IAM it sends out.

I.3  Interception of incoming calls  Word‑p. 365

I.3.1  General

In order to perform the interception of incoming calls from a particular origination point (identified as target with Non-Local ID for incoming calls), calling party information and redirecting party information of the incoming message are checked. The redirecting information is checked because the call may have encountered a call forwarding before arriving at the CSP where the interception for Non-Local ID is performed.

In the CS domain, this could be the Calling Party Information and Redirecting Party Information present in the IAM message (as an example) that is received at the switch where the interception is performed.

In the case of IMS-based VoIP calls, this can be any of the SIP headers used to identify the calling party information and redirecting party information present in the incoming SIP message. The examples are: P-Asserted Id, From headers and History-Info, Diversion headers. The interception functions may be provided by the S-CSCF or P-CSCF (optional in a non-roaming case and mandatory in the roaming case when LBO approach is used as the roaming architecture). Alternatively, in another implementation, the interception functions may also be provided by the Ingress IBCF or Ingress MGCF for non-roaming case. Of the two approaches S-CSCF/P-CSCF Vs IBCF/MGCF used for non-roaming case, only one approach is required to be supported within a CSP's network.

I.3.2  Interception at S-CSCF or P-CSCF

The Figure I.4 shows an example where the interception is done at the S-CSCF. The Figure I.5 shows an example where the interception is done at the P-CSCF in a roaming case with LBO as the roaming architecture. In both illustrations, Party-A is the target with Non-Local ID and the nature of the interception to be performed is for incoming calls. In the call, the P-Asserted-Id, From headers point to Party-A. There are no History-Info or Diversion headers in the examples.

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Figure I.4: IRI ICE at S-CSCF - interception of a target with Non-Local ID for incoming calls

Figure I.4 shows the case where S-CSCF is the IRI ICE and hence, the S-CSCF checks the P-Asserted-Id and From headers of SIP message that it receives from the I-CSCF. Since a match is found, S-CSCF would perform the interception. In the event, multiple S-CSCF are involved in the signalling path (due to call forwarding case), all S-CSCFs may to do the same check and all S-CSCFs may end up finding a match to the target's Non-Local ID. Special care will have to be taken to suppress the duplicate interception of one LI request. When a call forwarding is involved, the subsequent S-CSCF may see History-Info or Diversion headers present, however, none of those are expected to match the Non-Local ID of the target. As in the case of interception of target with Local ID, a P-CSCF may optionally provide the IRI ICE functions in a non-roaming case. However, in a roaming case with LBO as the roaming architecture, P-CSCF provides the IRI ICE functions.

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Figure I.5: IRI ICE at P-CSCF (roaming) - interception of a target with Non-Local ID for incoming calls

In Figure I.5, the P-CSCF in the VPLMN checks the P-Asserted-Id, From headers and History-Info and Diversion headers of the SIP message that it receives. Since a match is found for P-Asserted-Id and From header values, P-CSCF would perform the interception.

I.3.3  Interception at the IBCF/MGCF  Word‑p. 366

The Figure I.6 shows an example where the interception is done at the IBCF or MGCF in a non-roaming case. In the illustration, Party-A is the target with Non-Local ID and the nature of the interception to be performed is for incoming calls. In the call, the P-Asserted-Id and From headers point to Party-A. There are no History-Info or Diversion headers in the example.

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Figure I.6: IRI ICE at BCF - interception of a target with Non-Local ID for incoming calls

Figure I.6 shows the case where the Ingress IBCF or MGCF is the IRI ICE for intercepting when the target is identified with a Non-Local ID. Accordingly, the IBCF or MGCF checks the P-Asserted-Id, From headers, and History-Info, Diversion headers of SIP message. Since MGCF is providing signalling conversion (e.g., ISUP to SIP and Vice-Versa), the MGCF checks the headers of the SIP message it sends out. IBCF could check the headers from either of the SIP messages (they have to be the same anyway). Alternatively, the MGCF could also check the Calling Party Information and Redirecting Information present in the IAM message that it receives.

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