F  Examples of IMS-based VoIP Lawful Interception (LI) call flows |R12|  Word‑p. 334

F.1  General remarks

All the call flows illustrate that the CC delivery begins once the SDP offer and answer is completed (i.e., when the media bearer is setup). In all the call flows, the first reliable response is SIP 200 OK.

In all the call flows, the originating end of the call sends the SDP offer and terminating end gives the SDP answer. Since, the first reliable response is SIP 200 OK, the SDP answer is always given in the SIP 200 OK message.

The call flows assume that per clause 7A, the IRI for VoIP is nothing but the delivery encapsulated SIP messages. The call flows do not show the method used for correlating the IRI with IRI and IRI with CC. It is presumed that those are stage 3 details.

All the call flows assume the presence of a Voice Application Server (shown as AS) that provides the voice services like digit translation, invoking the call forwarding, etc.

IRI in the visited CSP is intercepted by the P-CSCF and IRI in the home CSP is intercepted by the S-CSCF.

The call flows show that CC interception is done at the IP-CAN (and it should be interpreted to mean that the interception is done in the PDN-GW or GGSN depending on the packet core network), or at the TrGW or at the IM-MGW. The other possible CC interception options (e.g., IMS-AGW) are not shown.

Not all the functional elements are shown in the call flows. For example, the call flows do not show I-CSCF, HSS, PCRF.

All the call flows show a summary of SIP messages that are delivered to the LEA (not all SIP messages are shown). The term LEMF, used in some call flows, means it is an equivalent of LEA.

For each call flow, references are required to identify MMTEL service that it illustrates (for further study).

F.2  Call Originations from Target in Home CSP

F.2.0  Introduction

This clause gives 2 call flows to illustrate the call origination scenarios.

Figure F.1 illustrates the case where the Party_A (target) calls Party_B.

Figure F.2 illustrates the case where the Party_A (target) dials a special number (e.g., a speed call number or an 800-number), which is translated to Party_B by the AS.

F.2.1  Target Originated Call - Target (Party_A) Calls Party_B  Word‑p. 335

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Figure F.1: Target originated call - target calls Party_B

F.2.2  Target Originated Call - Target (Party_A) dials a Special Number  Word‑p. 336

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Figure F.2: Target originated call - target dials a special number

F.3  Call Terminations to Target - Home CSP

F.3.0  Introduction

This clause gives 1 call flow to illustrate the call termination scenario.

Figure F.3 illustrates the case where the Party_A calls target (Party_B).

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Figure F.3: Target receives an incoming call

F.4  Call Forwarding - Non Roaming  Word‑p. 337

F.4.0  Introduction

This clause gives 4 call flows to illustrate call forwarding scenarios.

Figure F.4 illustrates the case of an intra-CSP call forwarding unconditional. Here, the Party_A calls target (Party_B). The AS determines that all incoming calls to the target have to be forwarded to Party_C served by the same CSP.

Figure F.5 illustrates the case first part of an intra-CSP call forwarding no answer. Figure F.6 illustrate the second part of an intra-CSP call forwarding no answer. Here, the Party_A calls target (Party_B). . The target does not answer and the AS determines that target has a call forwarding no answer enabled to Party_C served by the same CSP.

Figure F.7 illustrates the case of inter-CSP call forwarding unconditional. Here, the Party_A calls target (Party_B). The AS determines that all incoming calls to the target have to be forwarded to Party_C served by a different CSP.

F.4.1  Intra-CSP Call Forwarding Unconditional  Word‑p. 338

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Figure F.4: Incoming call to target is forwarded within the CSP

F.4.2  Intra-CSP Call Forwarding No Answer  Word‑p. 339

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Figure F.5: Incoming call to target is forwarded due to call forwarding no answer within the CSP (flow 1 of 2)

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Figure F.6: Incoming call to target is forwarded due to call forwarding no answer within the CSP (flow 2 of 2)

F.4.3  Inter-CSP Call Forwarding Unconditional  Word‑p. 341

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Figure F.7: Incoming call to target is forwarded outside the CSP

F.5  IMS Roaming

F.5.0  General

This clause gives 3 call flows to illustrate the case of IMS roaming.

Figure F.8 illustrate the case where the roaming target originates a call. Here, roaming target (Party_A) calls Party_B who is served by the same CSP as that of target. Party_B is not roaming.

Figure F.8A illustrates the case where a roaming target originates a call with local breakout approach is used for roaming. In this case, home CSP of Party-B happens to be visited CSP where the target is roaming and hence, the media does not enter the HPLMN of target (i.e., Home CSP of target). A Home CSP reports the CC unavailability to the LEMF with "roaming" as the reason for CC unavailability.

Figure F.9 illustrates the case where a roaming target receives an incoming call. Here, non-roaming Party_A, who is served by the same CSP as that of target, calls the target (Party_B).

F.5.1  Roaming Target Originates a Call  Word‑p. 342

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Figure F.8: Roaming target originates a call

F.5.1A  CC Unvailable in Home CSP due to Optimal Media Routing |R13|  Word‑p. 343

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Figure F.8A: Roaming target originates a call and optimal media routing is applied

F.5.2  Call Termination to a Roaming Target  Word‑p. 344

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Figure F.9: Roaming target receives an incoming call

F.6  Interception in Visited CSP

F.6.0  General

This clause gives 3 call flows to illustrate the case of interception in the visited CSP. In all these flows, the IRI interception happens at the P-CSCF. Both IRI and CC interception happen in the visited CSP.

Figure F.10 illustrates the case where the target (Party_A) in the visited CSP originates a call dialing a special number. The special number is translated into Party_B in the home CSP. The flow also assumes that the interception is done only in the visited CSP.

Figure F.11 illustrates the case where the target (Party_B) in the visited CSP receives an incoming call from Party_A served by the same Home CSP. The flow assumes that the interception is done only in the visited CSP.

Figure F.12 illustrates the case where an incoming call to the target (Party_B) gets forwarded in the Home CSP due to call forwarding no answer. The flow also assumes that the interception is done only in the visited CSP.

F.6.1  Interception in Visited CSP - Target Originated Call  Word‑p. 345

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Figure F.10: Roaming target originates a call - interception in the visited CSP

F.6.2  Interception in Visited CSP - Target Terminating Calls.  Word‑p. 346

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Figure F.11: Roaming target receives a call - interception in the visited CSP

F.6.3  Incoming Call to Roaming Target is forwarded due to Call Forwarding No Answer  Word‑p. 347

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Figure F.12: Incoming call to target is forwarded in the home CSP due to Call Forwarding No Answer - interception in visited CSP

F.7  Ad-Hoc Conference Calls established by the Target |R13|

F.7.0  Introduction

This clause gives 9 call flows to illustrate the steps related to ad-hoc conference calling established by the target. The flows assume that the Party_A (target) has already made two calls, one to Party_B and one to Party_C, and placed both calls on hold so as to merge the two calls into a conference.

Figure F.7.1 illustrates the case where the Party_A (target) creates the conference.

Figure F.7.2 and Figure F.7.3 illustrate the case where the Party_A (target) brings the Party_C into the conference.

Figure F.7.4 and F.7.5 illustrate the case where the Party_A (target) brings the Party_B into the conference.

Figure F.7.6 illustrates the case where Party_C drops out of the conference call.

Figure F.7.7 illustrates the case where the call between two parties (Party_A (target) and Party_B) is converted back to a normal 2-party call.

Figure F.7.8 illustrates the case where Party_A (target) places the conference on hold.

Figure F.7.9 illustrates the case where Party_A (target) retrieves the held conference from hold.

Some of the steps may be executed by the target's UE automatically (in other words, no action is required by the target). For example, when the target tries to merge the call, the target's UE may execute the steps shown in Figure F.7.1, Figure F.7.2, Figure F.7.3, Figure F.7.4, Figure F.7.5 automatically in a serial fashion. The same way, the steps shown in Figure F.7.7 may be executed automatically after the steps shown in Figure F.7.6 when one of the conferees drop out of the conference.

The Figure F.7.8 and Figure F.7.9 are not really part of the conferencing steps, however, included here to show how the content of a held conference call (a requirement in some countries) is delivered to the LEAs.

F.7.1  Party_A (target) creates the conference  Word‑p. 348

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Figure F.7.1: Party_A (target) creates the conference

D1 and D10 represent the dialogue of the original call between the Party_A (target) and the Party_B. D2 and D20 represent the original the dialogue of the original call between Party_A (target) and the Party_C. D3 represents the new dialogue of call between Party_A and the conference.

The IRI/CC delivered for D1 and D10 use the Correlation Number 1. The IRI/CC delivered for D2 and D20 use the Correlation Number 2. The IRI/CC delivered for the conferencing (i.e., D3) uses the Correlation Number 3.

F.7.2  Party_C joins the conference

This flow is illustrated in two figures: Figure F.7.2 and Figure F.7.3.

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Figure F.7.2: Party_C joins the conference (flow 1 of 2)

D1 and D10 represent the dialogue of the original call between the Party_A (target) and the Party_B. D2 and D20 represent the original the dialogue of the original call between Party_A (target) and the Party_C. D3 represents the dialogue of the call between Party_A and the conference. D4 represents the dialogue that the Party_A (target) uses to refer Party_C to the conference.

The IRI/CC delivered for D1 and D10 use the Correlation Number 1. The IRI/CC delivered for D2 and D20 use the Correlation Number 2. The IRI/CC delivered for the conferencing (i.e., D3) uses the Correlation Number 3. The IRI for D4 uses the Correlation Number 4.

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Figure F.7.3: Party_C joins the conference (flow 2 of 2)

At the end of this flow, the Party_A (target) and Party_C are connected via the conference. Party_C is still on hold. Part of the original call between Party_A (target) and Party_C (D2) is released with D20 now representing the call between the Party_C and the conference.

F.7.3  Party_B joins the conference  Word‑p. 350

This flow is illustrated in two figures: Figure F.7.4 and Figure F.7.5.

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Figure F.7.4: Party_B joins the conference (flow 1 of 2)

D3 represents the dialogue of the call between the Party_A (target) and the conference. D20 represents the dialogue between the Party_C and the conference. D1 and D10 represent the original the dialogue of the original call between Party_A (target) and the Party_B. D5 represents the dialogue that the Party_A (target) uses to refer Party_B to the conference.

The IRI/CC delivered for D1 and D10 use the Correlation Number 1. The IRI/CC delivered for the conferencing (i.e., D3) uses the Correlation Number 3. The IRI for D5 uses the Correlation Number 5.

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Figure F.7.5: Party_B joins the conference (flow 2 of 2)

At the end of this flow, the Party_A (target), Party_B and Party_C are connected via the conference. Part of the original call between Party_A (target) and Party_B (D1) is released with D10 now representing the call between the Party_B and the conference.

F.7.4  Party_C drops out of the conference  Word‑p. 353

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Figure F.7.6: Party_C drops out of the conference

D3 represents the dialogue of the call between the Party_A (target) and the conference. D20 represents the dialogue between the Party_C and the conference. D10 represents the dialogue between the Party_B and the conference.

The IRI/CC delivered for the conferencing (i.e., D3) uses the Correlation Number 3.

At the end of this flow, Party_A (target) and Party_B are connected through the conference.

F.7.5  Reconfiguration from Conference to two-party call  Word‑p. 354

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Figure F.7.7: Conference is reconfigured to a two-party call

D3 represents the dialogue of the call between the Party_A (target) and the conference. D10 represents the dialogue between the Party_B and the conference.

The IRI/CC delivered for the conferencing (i.e., D3) uses the Correlation Number 3.

At the end of this flow, Party_A (target) and Party_B are connected directly (without the conference). The IRI/CC delivered for this call between Party_A (target) and Party_B (D3 and D10) uses the Correlation Number 3.

F.7.6  Party_A (target) places Conference on hold  Word‑p. 355

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Figure F.7.8: Party_A (target) retrieves conference on hold

D3 represents the dialogue of the call between the Party_A (target) and the conference. D20 represents the dialogue between the Party_C and the conference. D10 represents the dialogue between the Party_B and the conference.

The IRI/CC delivered for the conferencing (i.e., D3) uses the Correlation Number 3.

At the end of this flow, Party_B and Party_C can still communicate via the conference, but without the Party_A. The CC delivered from the MRFP contains the communication content of that conversation.

F.7.7  Party_A (target) retrieves Conference from hold  Word‑p. 356

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Figure F.7.9: Party_A (target) retrieves conference from hold

D3 represents the dialogue of the call between the Party_A (target) and the conference. D20 represents the dialogue between the Party_C and the conference. D10 represents the dialogue between the Party_B and the conference.

The IRI/CC delivered for the conferencing (i.e., D3) uses the Correlation Number 3.

At the end of this flow, Party_A (targt), Party_B and Party_C are communicating via the conference.

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