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Content for  TS 33.107  Word version:  16.0.0

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15  Invocation of Lawful Interception for IMS-based VoIP |R12|

15.1  Overview of VoIP Interception

The capabilities defined in this clause apply when the interception of content of communications for IMS-based VoIP is to be separated from the interception of content of communication at the packet data network. Non-Local ID targeting described in clause 7A is also valid in such case.
The network nodes, involved in providing the interception of an IMS-based VoIP call, shall be determined based on the deployment configuration and the call scenario. The scenarios where the media transport nodes and signalling nodes are handled by different CSPs are beyond the scope of this standard.
The interception of IRI for a VoIP call shall be done according to 15.3. The interception of VoIP CC shall be done according to 15.2.
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15.2  Provision of Content of CommunicationsWord‑p. 180

15.2.0  Overview |R13|

As the interception of CC needs to be done at a network node that has access to the voice media, and that interception of CC is required for all targeted calls, including forwarded calls and transferred calls, the CSP needs to support the capability to dynamically trigger CC interception for a call at a network node that has access to the voice media. Depending on the CSP's network configuration and the call scenario, different network elements will intercept the CC.
The interception and delivery of CC for VoIP may be done at the following functional element:
  1. PDN-GW/GGSN;
  2. IMS-AGW;
  3. TrGW;
  4. IM-MGW;
  5. MRF.
The functional elements that provide the signalling to generate the trigger for the CC interception may be any of the following functional elements:
  • P-CSCF, for PDN-GW/GGSN and IMS-AGW;
  • IBCF for TrGW;
  • MGCF for IM-MGW;
  • S-CSCF or AS 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 call scenario.
Annex E shows scenarios where the use of the above functional elements is applicable.
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15.2.1  General Principles of CC Interception

15.2.1.1  Intercept Trigger

As the interception of IRI and CC is required for all targeted VoIP calls, including forwarded and transferred calls, the CC shall be correlated with the IRI. The CC Interception Triggering Function triggers the CC interception for a call at the CC Intercept Function. The placement of the CC Interception Triggering Function is dependent on CSP network implementation, the call scenario, and the placement of network nodes that have access to the voice media.
The CC Interception Triggering Functions sends a CC intercept trigger to the CC Interception Function to activate CC interception for a call.
The intercept trigger, at the minimum, shall consist of the following:
  • Correlation Identifier;
  • Media Identifier
The Correlation Identifier is used correlate the CC with the corresponding IRI data and is delivered from the CC Intercept Function in the intercepted media packet (i.e., CC) over the X3 interface to the Delivery Function 3.
The Media Identifier is used to identify the media packets that have to be intercepted. The technique used in defining the Media Identifier is implementation specific.
The information passed in this CC intercept trigger shall adhere to the security requirements outlined in clause 8.
The mechanism used to provide the correlation between CC and IRI is implementation specific. For instance:
  • The CC Interception Triggering Function may send the correlation identifier value to the CC Interception Function that forwards it to DF3 onto X3 interface;
  • The CC Interception Triggering Function may send the correlation identifier (onto X2 interface) to the DF2 that forwards it to DF3. In this case the SDP information may be used to associate the CC packets with the IRI.
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15.2.1.2  X3-InterfaceWord‑p. 181
For the delivery of intercepted media packets, the following information shall be passed from the CC Intercept Function to the Delivery Function 3 in addition to the intercepted media packets:
  • target identity;
  • correlation identifier;
  • SDP information (optional);
  • time stamp (optional);
  • direction (indicates media is from or to the target) - optional;
The Delivery Function 3 delivers the information to the LEMF over the HI3 interface based on the national regulations.

15.2.2  VoIP CC Interception

The capabilities defined in this clause apply for the following cases:
  • When a target originates a call or receives an incoming call - the target's media passes through the indicated CC Intercept Function.
  • When an incoming call to the target is forwarded, the media of the forwarded call passes through the indicated CC Intercept Function.
The term "CC Intercept Function" is a generic term used to denote a network function that has access to the voice media of an intercepted call. The term "CC Interception Triggering Function" is a generic term used to denote a network function that provides a trigger to intercept the CC. The examples of CC Intercept Function and CC Interception Triggering Function are listed at the beginning of clause 15.2
Figure 15.1 illustrates the CC interception at the CC Intercept Function for a basic call. Figure 15.2 illustrates the CC interception at the CC Intercept Function for a forwarded call.
[not reproduced yet]
Figure 15.1: VoIP CC Interception for basic calls
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In figure 15.1, the Target is the target and the Other Party is the called party when the target originates a call; and the Other Party is the calling party when the target receives an incoming call. In both cases, the media passes through the CC Intercept Function present on the side of target's access network.
In figure 15.2 (below), there is no Target (i.e., target) shown because this is the scenario where an incoming call to a target gets forwarded. The figure 15.2 shows the calling party who originated call and the forwarded-to-party who receives the forwarded call. The media passes through the CC Intercept Function associated with the forwarded-to-party.
[not reproduced yet]
Figure 15.2: VoIP CC Interception for forwarded calls
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The CC Interception Triggering Function sends the CC intercept trigger to the CC Intercept Function according 15.2.1.1. The CC Intercept Function intercepts media packets for the call (identified based on the Media Identifier information received over the intercept trigger) and delivers the media packets as according to 15.2.1.2.
See Annex E and Annex F for details of Call Forwarding related scenarios and call flows.

15.2.3  Media Information Associated with the CC |R13|Word‑p. 183
When the media description known through the SDP offer and answer at the IRI ICE is different from the media description known to the CC Intercept Function, then CC Intercept Triggering Function may have to send the media description to the DF2 for reporting to the LEMF. See Annex G for illustrative examples.
The media description associated with the CC delivered to the LEMF over HI3 shall also be reported to the LEMF in case it is different from both of the above indicated media descriptions.
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15.2.4  CC Interception in HPLMN with IMS Roaming |R13|

For roaming targets who are physically not in the legal jurisdiction of the home network, depending on the roaming architecture deployed, media of the target may not enter the HPLMN for certain call scenarios. In such situations, based on the national option, the HPLMN served with the intercept order shall do the following:
  • Perform the interception without the CC and report to the LEMF that the CC is unavailable due to target's roaming situation. Note that the Evolved Serving System message (when EPS is part of the IP-CAN) also indicates to the LEMF that the target is roaming.
See TS 33.108 for the method used to report the CC unavailability indication.
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15.2.5  CC Interception with CUPS |R14|Word‑p. 184
With control and user plane separation of PDN-GW, the LI architecture defined in subclause 12.9 shall be used to provide the CC Intercept Function at the PDN-GW with the following extensions:
  • The PDN Gateway-C shall receive the CC intercept trigger from the CC Intercept Triggering Function.
  • The PDN Gateway-C shall use the target identity and correlation identifier received from the CC Intercept Triggering Function to notify the SX3LIF.
  • The PDN Gateway-C shall send the packet detection rules (as described in subclause 12.9.2) to intercept the user plane packets from the media bearer to the PDN Gateway-U.
The PDN Gateway-U shall forward user plane packets to the SX3LIF as described in subclause 12.9. The SX3LIF shall deliver the CC to the DF3 over X3 as described in subclause 12.9 and subclause 15.2.
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15.3  Provision of Intercept Related Information for VoIP

See clause 7A.

15.4  Lawful interception in the VPLMN with IMS roaming |R13|

15.4.1  Local breakout with P-CSCF in the VPLMN

LBO (as defined in TS 23.228) as a roaming architecture used for VoLTE is one of the examples of IMS roaming. Local Breakout architecture has several options (LBO Home Routing, LBO Visited Routing: the interception of IRI and CC in the VPLMN are independent of such options).
When an inbound roaming target originates a call or receives a terminating call, the P-CSCF present in the VPLMN provides IRI interception functions as described in clause 7A. The PDN-GW/GGSN or the IMS-AGW deployed in the VPLMN provides the CC interception as described in clause 15.2. The P-CSCF sends the CC intercept trigger to the PDN-GW/GGSN or to the IMS-AGW as described in clause 15.2.
Annex E illustrates a few scenarios of lawful interception in the VPLMN for inbound roaming target.
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15.5  Constraints for IMS VoIP Roaming Interception |R14|

National regulations may limit delivery of communications (CC and communications-associated IRI) of an outbound international roaming target by the HPLMN as described in clause 5.1.4 of TS 33.106.
If roaming interception is allowed, IMS VoIP interception and delivery to the LEMF by the HPLMN shall proceed normally as described elsewhere in this specification when the target is roaming outside the country as well as when the target is within the country.
If roaming interception is not allowed and it is determined that the target is outside the country, the HPLMN shall act as follows:
The HPLMN shall report IRI and CC for IMS VoIP sessions where the target is not participating in the IMS VoIP services which can be the result of the activation, invocation, or operation of any supplemental services that are performed entirely by the HPLMN. This can include invocation before an IMS VoIP session, at the beginning of an IMS VoIP session, mid IMS VoIP session, or at the end of an IMS VoIP session. Examples of such supplemental services include diversion services such as call forwarding (all calls, busy calls, etc.). Services where the target is still participating in the IMS VoIP session would not be reported (e.g., call hold, conferencing).
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