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Content for  TS 33.107  Word version:  16.0.0

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E  IMS-based VoIP Lawful Interception call scenarios |R12|Word‑p. 313

E.1  Overview

This informative annex provides the examples of call scenarios that illustrate the interception and delivery of CC interception for an IMS-based VoIP call.

E.2  Background

One of the use-cases of IMS-based VoIP service is VoLTE. The term "VoLTE" is used to refer to an IMS-based VoIP service when EPS (see TS 23.401) happens to be the access network. When EPS is not the access network, the lawful interception capabilities defined in this informative annex applies for any IMS-based VoIP service with the presumption that in those cases the media on the target's access goes through an IMS-AGW (see TS 29.334) or a PDN-GW (see TS 23.401 and TS 23.402) or a GGSN (UMTS network).
Even with the EPS-based access network, the media might still go through the IMS-AGW. And, in this case, a VoLTE shall be treated very similar to any other VoIP service.
Furthermore, it is presumed that an inter-CSP call enters or leaves an IMS network via an IBCF/TrGW or an MGCF/IM-MGW depending on whether the inter-working CSP network is an IMS-based network or a CS-based network (see TS 23.228). Also, for an IMS roaming scenario, it is presumed that the signalling and media enters or leaves the home CSP through the IBCF/TrGW.
The figure E.1 illustrates the VoIP configuration considered for the lawful interception capabilities defined in this clause:
[not reproduced yet]
Figure E.1: IMS-based VoIP Configuration
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In the remaining part of this informative annex, the PDN-GW/GGSN are shown in one box and is to be read as either the GGSN (UMTS) or the PDN-GW (EPS).
In figure E.1, the term "media node" is used to denote the network node present on media path and the term "signalling node" is used to denote the network node present on the signalling path.
The general concepts of VoIP LI is shown in figure E.2
[not reproduced yet]
Figure E.2: General Principles of VoIP Interception
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In clause 15, the SIP signalling nodes provide signalling information to the CC Interception Triggering Function. The CC Interception Triggering Function triggers the CC interception at a media node that implements the CC Intercept Function.
The following functional elements provide the CC Intercept Function in the example call scenarios:
  • PDN-GW/GGSN;
  • IMS-AGW;
  • TrGW;
  • IM-MGW
  • MRF.
The following functional elements provide the signalling to the CC Intercept Triggering Function:
  • P-CSCF for PDN-GW/GGSN and IMS-AGW;
  • IBCF for TrGW;
  • MGCF for IM-MGW
  • S-CSCF for MRF.
At any given time, for a specific target and for any given call, only one functional element is required to provide the CC interception. The functional element that provides the CC interception may vary, primarily, based on the CSP network implementation and the call scenario.
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E.3  Originating Call from the Target with CC Interception at the PDN-GW/GGSNWord‑p. 316

E.3.0  General

Figure E.3 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC, when a target originates a call with PDN-GW (or GGSN) providing the CC interception.
[not reproduced yet]
Figure E.3: VoIP lawful interception for an originating call with CC interception at the PDN-GW/GGSN
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The cloud shown with the label "voice services" is to indicate that the target is making a voice call and the called party can be within the same CSP's network or in another CSP's network.
Figure E.3 shows that the IRI interception is done at S-CSCF or AS. However, as specified in clause 7A, the IRI interception can also be done at the P-CSCF (not shown in figure E.3). The CC interception is done at the PDN-GW/GGSN. The P-CSCF sends the CC intercept trigger to the PDN-GW/GGSN.
The activation of intercept is done by the ADMF for IRI interception and CC interception using the same target identity (SIP URI, TEL URI or IMEI).
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E.3.1  Originating Call from the Target with CC Interception at the MRFWord‑p. 317
Figure E.3.1 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC when a target originates a call with an MRF providing the CC interception. The S-CSCF provides the CC Interception Triggering Function for the MRF.
[not reproduced yet]
Figure E.3.1: VoIP lawful interception for an originating call with CC interception at the MRF
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The cloud shown with the label "voice services" indicates that the target is making a voice call and the called party can be within the same CSP's network or in another CSP's network.
IRI interception is done at the S-CSCF. The CC interception is done at an MRF that functions as the CC ICE.
The MRF is deployed in a network configuration with an IP border access controller that serves to hide the presence of the MRF. The IP access border controller supports IP-level topology hiding for any voice media streams. Specifically, the border gateway supports NAT functionality; always presents its own IP address to the user; prevents ICMP Ping & ICMP Traceroute requests from being forwarded across the gateway; and, resets TTL field in the IP header.
The ADF activates interception at the S-CSCF for IRI interception and CC interception using the same target identity (SIP URI, TEL URI or IMEI). The S-CSCF dynamically triggers CC interception at the MRF for the call.
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E.4  Originating Call from the Target with CC Interception at the IMS-AGW

Figure E.4 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC, when a target originates a call with IMS-AGW providing the CC interception.
[not reproduced yet]
Figure E.4: VoIP lawful interception for an originating call with CC interception at the IMS-AGW
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The cloud shown with the label "voice services" is to indicate that the target is making a voice call and the called party can be within the same CSP's network or in another CSP's network.
Figure E.4 shows that the IRI interception is done at S-CSCF or AS. However, as specified in 7A, the IRI interception can also be done at the P-CSCF (not shown in figure E.4). The CC interception is done at the IMS-AGW. The P-CSCF sends the CC intercept trigger to the IMS-AGW.
The activation of intercept is done by the ADMF for IRI interception and CC interception using the same target identity (SIP URI, TEL URI or IMEI).
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E.5  Terminating Call to the Target with CC Interception at the PDN-GW/GGSNWord‑p. 319

E.5.0  General

Figure E.5 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC, when a target receives an incoming call with PDN-GW/GGSN providing the CC interception.
[not reproduced yet]
Figure E.5: VoIP lawful interception for a terminating call with CC interception at the PDN-GW/GGSN
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The cloud shown with the label "voice services" is to indicate that the target is receiving an incoming voice call and the calling party can be within the same CSP's network or in another CSP's network. The network nodes such as I-CSCF, HSS involved in the handling of an incoming call to the target are not shown for simplification of the drawing.
Figure E.5 shows that the IRI interception is done at S-CSCF or AS. However, as specified in 7A, the IRI interception can also be done at the P-CSCF (not shown in figure Z.5). The CC interception is done at the PDN-GW/GGSN. The P-CSCF sends the CC intercept trigger to the PDN-GW/GGSN.
The activation of intercept is done by the ADMF for IRI interception and CC interception using the same target identity (SIP URI, TEL URI or IMEI).
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E.5.1  Terminating Call to the Target with CC Interception at the MRF

Figure E.5.1 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC when the target receives an incoming call with an MRF providing the CC interception. The S-CSCF provides the CC Interception Triggering Function for the MRF.
The MRF is deployed in a network configuration with an IP border access controller that serves to hide the presence of the MRF. The IP access border controller supports IP-level topology hiding for any voice media streams. Specifically, the border gateway supports NAT functionality; always presents its own IP address to the user; prevents ICMP Ping & ICMP Traceroute requests from being forwarded across the gateway; and, resets TTL field in the IP header.
[not reproduced yet]
Figure E.5.1: VoIP lawful interception for a terminating call with CC interception at the MRF
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The cloud shown with the label "voice services" is to indicate that the target is receiving an incoming voice call and the calling party can be within the same CSP's network or in another CSP's network. The network nodes such as I-CSCF, HSS involved in the handling of an incoming call to the target are not shown for simplification of the figure.
IRI interception is done at the S-CSCF. The CC interception is done at an MRF that functions as the CC ICE.
The ADMF activates interception at the S-CSCF for IRI interception and CC interception using the same target identity (SIP URI, TEL URI or IMEI). The S-CSCF dynamically triggers CC interception at the MRF for the call.
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E.6  Terminating Call to the Target with CC Interception at the IMS-AGWWord‑p. 321
Figure E.6 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC, when a target receives an incoming call with IMS-AGW providing the CC interception.
[not reproduced yet]
Figure E.6: VoIP lawful interception for a terminating call with CC interception at the IMS-AGW
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The cloud shown with the label "voice services" is to indicate that the target is receiving an incoming voice call and the calling party can be within the same CSP's network or in another CSP's network. The network nodes such as I-CSCF, HSS involved in the handling of an incoming call to the target are not shown for simplification of the drawing.
Figure E.6 shows that the IRI interception is done at S-CSCF or AS. However, as specified in 7A, the IRI interception can also be done at the P-CSCF (not shown in figure E.6). The CC interception is done at the IMS-AGW. The P-CSCF sends the CC intercept trigger to the IMS-AGW.
The activation of intercept is done by the ADMF for IRI interception and CC interception using the same target identity (SIP URI, TEL URI or IMEI).
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E.7  Intra-CSP Forwarded Call with CC Interception at the PDN-GW/GGSNWord‑p. 322

E.7.0  General

Figure E.7 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC, when a target receives an incoming call with PDN-GW/GGSN providing the CC interception and the call is forwarded to another IMS subscriber within the CSP's network.
[not reproduced yet]
Figure E.7: VoIP lawful interception for an intra-CSP forwarded call with CC interception at the PDN-GW/GGSN
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The cloud shown with the label "voice services" is to indicate that the target is receiving an incoming voice call and the calling party can be within the same CSP's network or in another CSP's network. The network nodes such as I-CSCF, HSS involved in the handling of an incoming call to the target and to the forwarded-to-party are not shown for simplification of the drawing.
Figure E.7 shows that the IRI interception is done at S-CSCF or AS. In this scenario, the IRI interception cannot occur in the P-CSCF since the P-CSCF that provides the proxy functions to the target is not on the signalling path. The CC interception is done at the PDN-GW/GGSN. The P-CSCF (that provides the proxy functions to the forwarded-to-party) sends the CC intercept trigger to the PDN-GW/GGSN.
The activation of intercept is done by the ADMF for IRI interception and CC interception using the same target identity (SIP URI or TEL URI).
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E.7.1  Intra-CSP Forwarded Call with CC Interception at the MRF

Figure E.7.1 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC, when a target receives an incoming call with the MRF providing the CC interception and the call is forwarded to another IMS subscriber within the CSP's network. The S-CSCF provides the CC Interception Triggering Function for the MRF.
The MRF is deployed in a network configuration with an IP border access controller that serves to hide the presence of the MRF. The IP access border controller supports IP-level topology hiding for any voice media streams. Specifically, the border gateway supports NAT functionality; always presents its own IP address to the user; prevents ICMP Ping & ICMP Traceroute requests from being forwarded across the gateway; and, resets TTL field in the IP header.
[not reproduced yet]
Figure E.7.1: VoIP lawful interception for an intra-CSP forwarded call with CC interception at the MRF
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The cloud shown with the label "voice services" is to indicate that the target is receiving an incoming voice call and the calling party can be within the same CSP's network or in another CSP's network. The network nodes such as P-CSCF, IMS-AGW, HSS involved in the handling of an incoming call to the target and to the forwarded-to-party are not shown for simplification of the drawing.
Figure E.7.1 shows that the IRI interception is done at S-CSCF. The CC interception is done at the MRF that functions as the CC ICE.
The ADMF activates interception at the S-CSCF for IRI interception and CC interception using the same target identity (SIP URI or TEL URI). The S-CSCF dynamically activates CC interception at the MRF.
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E.8  Intra-CSP Forwarded Call with CC Interception at the IMS-AGWWord‑p. 324
Figure E.8 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC, when a target receives an incoming call with IMS-AGW providing the CC interception and the call is forwarded to another IMS subscriber within the CSP's network.
[not reproduced yet]
Figure E.8: VoIP lawful interception for an intra-CSP forwarded call with CC interception at the IMS-AGW
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The cloud shown with the label "voice services" is to indicate that the target is receiving an incoming voice call and the calling party can be within the same CSP's network or in another CSP's network. The network nodes such as I-CSCF, HSS involved in the handling of an incoming call to the target and to the forwarded-to-party are not shown for simplification of the drawing.
Figure E.8 shows that the IRI interception is done at S-CSCF or AS. In this scenario, the IRI interception cannot occur in the P-CSCF since the P-CSCF that provides the proxy functions to the target is not on the signalling path. The CC interception is done at the IMS-AGW. The P-CSCF (that provides the proxy functions to the forwarded-to-party) sends the CC intercept trigger to the IMS-AGW.
The activation of intercept is done by the ADMF for IRI interception and CC interception using the same target identity (SIP URI or TEL URI).
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E.9  Inter-CSP Forwarded Call to a CS DomainWord‑p. 325
Figure E.9 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC, when a target receives an incoming call and the call is forwarded to a subscriber on the CS domain of another CSP's network.
[not reproduced yet]
Figure E.9: VoIP lawful interception for an inter-CSP forwarded call to a CS Domain
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The cloud shown with the label "voice services" is to indicate that the target is receiving an incoming voice call and the calling party can be within the same CSP's network or in another CSP's network. The network nodes such as I-CSCF, HSS involved in the handling of an incoming call to the target are not shown for simplification of the drawing.
Figure E.9 shows that the IRI interception is done at S-CSCF or AS. In this scenario, the IRI interception cannot occur in the P-CSCF since the P-CSCF that provides the proxy functions to the target is not on the signalling path. The CC interception is done at the IM-MGW. The MGCF sends the CC intercept trigger to the IM-MGW.
The activation of intercept is done by the ADMF for IRI interception and CC interception using the same target identity (SIP URI or TEL URI).
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E.10  Inter-CSP Forwarded Call to an IMS DomainWord‑p. 326
Figure E.10 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC, when a target receives an incoming call and the call is forwarded to a subscriber on the IMS domain of another CSP's network.
[not reproduced yet]
Figure E.10: VoIP lawful interception for an inter-CSP forwarded call to an IMS Domain
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The cloud shown with the label "voice services" is to indicate that the target is receiving an incoming voice call and the calling party can be within the same CSP's network or in another CSP's network. The network nodes such as I-CSCF, HSS involved in the handling of an incoming call to the target are not shown for simplification of the drawing.
Figure E.10 shows that the IRI interception is done at S-CSCF or AS. In this scenario, the IRI interception cannot occur in the P-CSCF since the P-CSCF that provides the proxy functions to the target is not on the signalling path. The CC interception is done at the TrGW. IBCF sends the CC intercept trigger to the TrGW.
The activation of intercept is done by the ADMF for IRI interception and CC interception using the same target identity (SIP URI or TEL URI).
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E.11  Originating Call from the Target with IMS RoamingWord‑p. 327
Figure E.11 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC, when a target originates a call with IMS roaming.
[not reproduced yet]
Figure E.11: VoIP lawful interception for an originating call with IMS Roaming
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The cloud shown with the label "voice services" is to indicate that the target is making a voice call and the called party can be within the same CSP's network or in another CSP's network.
Figure E.11 shows that the IRI interception is done at S-CSCF or AS. The IRI interception at the P-CSCF does not apply to this configuration due to the fact that the P-CSCF resides at the visited CSP as a result of IMS roaming. The CC interception is done at the TrGW. The I-BCF sends the CC intercept trigger to the TrGW.
The activation of intercept is done by the ADMF for IRI interception and CC interception using the same target identity (SIP URI, TEL URI or IMEI).
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E.12  Terminating Call to the Target with IMS RoamingWord‑p. 328
Figure E.12 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC, when a target with IMS roaming receives an incoming call.
[not reproduced yet]
Figure E.12: VoIP lawful interception for a terminating call with IMS Roaming
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The cloud shown with the label "voice services" is to indicate that the target is receiving an incoming voice call and the calling party can be within the same CSP's network or in another CSP's network. The network nodes such as I-CSCF, HSS involved in the handling of an incoming call to the target are not shown for simplification of the drawing.
Figure E.12 shows that the IRI interception is done at S-CSCF or AS. The IRI interception at the P-CSCF does not apply to this configuration due to the fact that the P-CSCF resides at the visited CSP as a result of IMS roaming. The CC interception is done at the TrGW. The I-BCF sends the CC intercept trigger to the TrGW.
The activation of intercept is done by the ADMF for IRI interception and CC interception using the same target identity (SIP URI, or TEL URI or IMEI).
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E.13  Intra-CSP Forwarded Call with IMS RoamingWord‑p. 329
Figure E.13 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC, when an incoming call to a target gets forwarded to another subscriber who is IMS roaming. The target may or may not be IMS roaming.
[not reproduced yet]
Figure E.13: VoIP lawful interception for a intra-CSP forwarded call with IMS Roaming
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The cloud shown with the label "voice services" is to indicate that the target is receiving an incoming voice call and the calling party can be within the same CSP's network or in another CSP's network. The network nodes such as I-CSCF, HSS involved in the handling of an incoming call to the target are not shown for simplification of the drawing.
Figure E.13 shows that the IRI interception is done at S-CSCF or AS of the target. In this scenario, the IRI interception cannot occur in the P-CSCF since the P-CSCF that provides the proxy functions to the target is not on the signalling path. Since the forwarded-to-party is IMS roaming, the CC interception is done at the TrGW. IBCF sends the CC intercept trigger to the TrGW.
The activation of intercept is done by the ADMF for IRI interception and CC interception using the same target identity (SIP URI or TEL URI).
If the target is IMS roaming, but not the forwarded-to-party, then the CC interception for an intra-CSP forwarded call is done at the PDN-GW/GGSN (as illustrated in Z.9) or IMS-AGW (as illustrated in Z.8).
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E.14  Lawful interception in the VPLMN with IMS roaming |R13|

E.14.1  Local Breakout (LBO) with P-CSCF in VPLMN

E.14.1.1  General

This clause illustrates a few scenarios of lawful interception functions in the VPLMN for inbound roaming targets. The LI functions described address the IMS roaming scenarios. Local Breakout (LBO), roaming architecture used for VoLTE, is an example of IMS roaming.

E.14.1.2  Originating call from an Inbound Roaming Target with CC Interception at the PDN-GW/GGSNWord‑p. 330
Figure E.14 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC in the VPLMN, when an inbound roaming target originates a call with PDN-GW (or GGSN) providing the CC interception.
[not reproduced yet]
Figure E.14:VoIP lawful interception in VPLMN for an originating call with IMS Roaming with CC interception at the PDN-GW/GGSN
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The routing of call to the called party can vary based on the CSP policy and the network that serves the called party. The cloud shown with the label "voice services" is to indicate that the inbound roaming target is making a voice call and the called party can be within the same VPLMN, or at the HPLMN or served by another CSP's network. At the Egress point, an IBCF/TrGW is shown. There can be other scenarios where different network nodes (e.g., TRF, MGCF, IM-MGW) can be present. However, lawful interception of an inbound roaming target in the VPLMN is independent of topology that involves such network nodes.
Figure E.14 shows that the IRI interception is done at P-CSCF. The CC interception is done at the PDN-GW/GGSN. The P-CSCF sends the CC intercept trigger to the PDN-GW/GGSN.
The activation of intercept is done by the ADMF for IRI interception and CC interception using the same target identity (SIP URI or TEL URI).
Local Breakout (LBO) as a roaming architecture used for VoLTE is one of the examples of IMS roaming. Several call routing scenarios can happen with LBO. However, the lawful interception in the VPLMN is independent of all those call scenarios.
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E.14.1.3  Originating Call from an Inbound Roaming Target with CC Interception at the IMS-AGWWord‑p. 331
Figure E.15 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC in the VPLMN, when an inbound roaming target originates a call with IMS-AGW providing the CC interception.
[not reproduced yet]
Figure E.15: VoIP lawful interception in VPLMN for an originating call with IMS Roaming with CC interception at the IMS-AGW
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The routing of call to the called party can vary based on the CSP policy and the network that serves the called party. The cloud shown with the label "voice services" is to indicate that the inbound roaming target is making a voice call and the called party can be within the same VPLMN, or at the HPLMN or served by another CSP's network. At the Egress point, an IBCF/TrGW is shown. There can be other scenarios where different network nodes (e.g., TRF, MGCF, IM-MGW) can be present. However, lawful interception of an inbound roaming target in the VPLMN is independent of topology that involves such network nodes.
Figure E.15 shows that the IRI interception is done at P-CSCF. The CC interception is done at the IMS-AGW. The P-CSCF sends the CC intercept trigger to the IMS-AGW.
The activation of intercept is done by the ADMF for IRI interception and CC interception using the same target identity (SIP URI or TEL URI).
Local Breakout (LBO) as a roaming architecture used for VoLTE is one of the examples of IMS roaming. Several call routing scenarios can happen with LBO. However, the lawful interception in the VPLMN is independent of all those call scenarios.
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E.14.1.4  Terminating Call to an Inbound Roaming Target with the CC Interception at the PDN-GW/GGSNWord‑p. 332
Figure E.16 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC in the VPLMN, when an inbound target receives an incoming call with PDN-GW (or GGSN) providing the CC interception.
[not reproduced yet]
Figure E.16: VoIP lawful interception in the VPLMN for a terminating call with IMS Roaming with CC interception at the PDN-GW/GGSN
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A terminating call is always routed to the VPLMN via the HPLMN of the target. The cloud shown with the label "voice services" is to indicate the calling party can be within the same VPLMN, or in the HPLMN of the target, or in another CSP's network. At the Ingress point, an IBCF/TrGW is shown. Independent of where the call has originated from, a terminating call always enters the VPLMN through the IBCF/TrGW from the HPLMN.
Figure E.16-1 shows that the IRI interception is done at P-CSCF. The CC interception is done at the PDN-GW/GGSN. The P-CSCF sends the CC intercept trigger to the PDN-GW/GGSN.
The activation of intercept is done by the ADMF for IRI interception and CC interception using the same target identity (SIP URI or TEL URI).
Local Breakout (LBO) as a roaming architecture used for VoLTE is one of the examples of IMS roaming.
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E.14.1.5  Terminating Call to an Inbound Roaming Target with CC Interception at the IMS-AGWWord‑p. 333
Figure E.17 provides the lawful interception architecture to illustrate the interception and delivery of IRI and CC in the VPLMN, when an inbound target receives an incoming call with IMS-AGW providing the CC interception.
[not reproduced yet]
Figure E.17: VoIP lawful interception in the VPLMN for a terminating call with IMS Roaming with CC interception at the IMS-AGW
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A terminating call is always routed to the VPLMN via the HPLMN of the target. The loud shown with the label "voice services" is to indicate the calling party can be within the same VPLMN, or in the HPLMN of the target, or in another CSP's network. At the Ingress point, an IBCF/TrGW is shown. Independent of where the call has originated from, a terminating call always enters the VPLMN through the IBCF/TrGW from the HPLMN.
Figure E.17 shows that the IRI interception is done at P-CSCF. The CC interception is done at the IMS-AGW. The P-CSCF sends the CC intercept trigger to the IMS-AGW.
The activation of intercept is done by the ADMF for IRI interception and CC interception using the same target identity (SIP URI or TEL URI).
Local Breakout (LBO) as a roaming architecture used for VoLTE is one of the examples of IMS roaming.
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