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Content for  TS 33.107  Word version:  16.0.0

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G  Examples of CC interception for transcoded media |R12|Word‑p. 357

G.1  Introduction

This annex provides some illustrative examples of media transcoding scenarios and its implication on the CC interception.
In some situations, the media information known to the S-CSCF can be different from the media information associated with the CC delivered to the LEMF. For example, when transcoding is involved in the media path, the media information (e.g., codec used) can change at the time transcoding is done and the S-CSCF that normally provides the media information to the DF2 may not have the knowledge of media information associated with the CC delivered to the LEMF.
In a particular implementation, the CC interception point may be chosen in such a way that information associated with the intercepted CC always matches to the information known to the IRI ICE (e.g., S-CSCF). But, there may some deployment situations and/or regulations that may require having a need to perform the CC interception at the other points with the information known to S-CSCF not being aligned with the information associated with the intercepted CC.
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G.2  CC Interception of transcoded media

The Figure G.2-1 illustrates a case where the media is transcoded at the IMS-AGW. In this example, the media is not encrypted.
[not reproduced yet]
Figure G.2-1: Transcoded Media
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The Figure G.2-1 shows three different cases of CC interception points. In the illustrated example, Codec 1 is associated with the media from the Target to the Ingress point of IMS-AGW and Codec 2 is used from the Egress point of IMS-AGW and beyond. Therefore, Codec 1 is associated with the CC delivered to the LEMF when that CC is intercepted at the PDN-GW or at the Ingress point of IMS-AGW, and Codec 2 is associated with the media delivered to the LEMF when that CC is intercepted at the Egress point of IMS-AGW.
The Codec 2 is included within the SDP of SIP messages handled at the S-CSCF and therefore, if S-CSCF provides the codec information to the DF2 in all cases, then there would be a misalignment with the codec information delivered over the HI2 and codec information associated with the CC delivered over HI3 for Case 1 and Case 2.
Depending on which case is used for the CC interception, the P-CSCF can send either Codec 1 or Codec 2 to the DF2. With the DF2 using the codec information received from the P-CSCF for reporting purposes, the codec information reported in the HI2 and HI3 are now aligned. For case 3, the codec information would be aligned irrespective of who sends that information to the DF2. Therefore, for Case 3, P-CSCF sending the codec 2 information to the DF2 can be an implementation alternative.
In a scenario like this, an implementation can also be such that the CC interception is always done at the Egress point of IMS-AGW (i.e., only Case 3), but because of some deployment situations and regulations, there may also be a need to perform the CC interception at the Ingress point of IMS-AGW (Case 2) or at the PDN-GW (Case 1).
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G.3  CC Interception of transcoded media with e2ae encryptionWord‑p. 358
The Figure G.3-1 illustrates a case where the media is transcoded at IMS-AGW with e2ae encryption. In this example, media is encrypted e2ae (i.e. between the Target and the Ingress point of IMS-AGW). The CC is delivered to the LEMF in a decrypted form.
[not reproduced yet]
Figure G.3-1: Transcoded Media with e2ae encryption
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The Figure G.3-1 shows three different cases of CC interception points. In this example, Codec 1 is associated with the media from the Target to the Ingress point of IMS-AGW and Codec 2 is used from the Egress point of IMS-AGW and beyond. Therefore, Codec 1 is associated with the CC delivered to the LEMF when that CC is intercepted at the PDN-GW or at the Ingress point of IMS-AGW, and Codec 2 is associated with the media delivered to the LEMF when that CC is intercepted at the Egress point of IMS-AGW. The Codec 2 is included within the SDP of SIP messages handled at the S-CSCF and therefore, if S-CSCF provides the codec information to the DF2 in all cases, then there would be a misalignment with the codec information delivered over the HI2 and codec information associated with the CC delivered over HI3 for Case 1 and Case 2.
Depending on which case is used for the CC interception, the P-CSCF can send either Codec 1 or Codec 2 to the DF2. With the DF2 using the codec information received from the P-CSCF for reporting purposes, the codec information reported in the HI2 and HI3 are now aligned. For case 3, the codec information would be aligned irrespective of who sends that information to the DF2. Therefore, for Case 3, P-CSCF sending the codec 2 information to the DF2 can be an implementation alternative.
In this example, media is encrypted (with SDES keys in SDP) from Target to the Ingress point of IMS-AGW and not encrypted from the Egress point of IMS-AGW and beyond. Therefore, for Case 1 and Case 2, the DF2 has to provide the SDES keys to the DF3 (see clause 7A.1.A) to perform the decryption. The S-CSCF does not receive the SDES keys within the SDP of SIP messages. Therefore, P-CSCF shall send the SDES Keys to the DF2 and the DF2 shall use that for its handling (i.e., sending to the DF3). P-CSCF does not send any SDES Keys to the DF2 for Case 3 since the CC is intercepted in the Egress point of IMS-AGW in a decrypted form.
In a scenario like this, an implementation can also be such that the CC interception is always done at the Egress point of IMS-AGW (i.e., only Case 3), but because of some deployment situations and regulations, there may also be a need to perform the CC interception at the Ingress point of IMS-AGW (Case 2) or at the PDN-GW (Case 1).
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G.4  CC Interception of transcoded media with e2e hop-by-hop encryptionWord‑p. 359
The Figure G.4-1 illustrates a case where the media is transcoded at IMS-AGW with e2e hop-by-hop encryption. Different SDES keys are for the encryption.
[not reproduced yet]
Figure G.4-1: Transcoded Media with e2e encryption
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The Figure G.4-1 shows three different cases of CC interception points. In this example, Codec 1 is associated with the media from the Target to the Ingress point of IMS-AGW and Codec 2 is used from Egress point of IMS-AGW and beyond. Therefore, Codec 1 is associated with the CC delivered to the LEMF when that CC is intercepted at the PDN-GW or at the Ingress point of IMS-AGW, and Codec 2 is associated with the media delivered to the LEMF when that CC is intercepted at the Egress point of IMS-AGW. The Codec 2 is included within the SDP of SIP messages handled at the S-CSCF and therefore, if S-CSCF provides the codec information to the DF2 in all cases, then there would be a misalignment with the codec information delivered over the HI2 and codec information associated with the CC delivered over HI3 for Case 1 and Case 2.
Depending on which case is used for the CC interception, the P-CSCF can send either Codec 1 or Codec 2 to the DF2. With the DF2 using the codec information received from the P-CSCF for reporting purposes, the codec information reported in the HI2 and HI3 are now aligned. For case 3, the codec information would be aligned irrespective of who sends that information to the DF2. Therefore, for Case 3, P-CSCF sending the codec 2 information to the DF2 can be an implementation alternative.
The media is encrypted (with SDES keys in SDP) from Target to the Ingress point of IMS-AGW with SDES keyes-1 as the encryption keys and encrypted from Egress point of IMS-AGW to the other end using SDES keys-2 as the encryption keys. The S-CSCF is aware of only the SDES keys-2 as it sees that in the SDP of the SIP messages. For Case 1 and Case 2, the P-CSCF shall provide the SDES keys to the DF2. For Case 3, either of the two, S-CSCF or the P-CSCF, can send the SDES keys to the DF2. DF2 has to use the SDES keys received from the P-CSCF for its handling (i.e., sending it to DF3) to perform the decryption. For Case 3, if the P-CSCF does not send the SDES Keys to the DF2, then the DF2 will use the SDES keys received from the S-CSCF for its handling.
In a scenario like this, an implementation can also be such that the CC interception is always done at the Egress point of IMS-AGW (i.e., only Case 3), but because of some deployment situations and regulations, there may also be a need to perform the CC interception at the Ingress point of IMS-AGW (Case 2) or at the PDN-GW (Case 1).
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G.5  CC Interception of transcoded media at the TrGWWord‑p. 360
The Figure G.5-1 illustrates a case where the media is transcoded at TrGW. In this example, the TrGW provides the transcoding. This scenario can be see when an incoming call to the Target is forwarded (illustration assumes) or when Target is IMS roaming.
[not reproduced yet]
Figure G.5-1: TrGW Transcoded Media
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The Figure G.5-1 shows two different cases of CC interception points. In this example, Codec 1 is associated with the media from the first Other Party (e.g., calling party) to the Ingress point of TrGW and Codec 2 is used from Egress point of TrGW to the second Other Party (e.g., forwarded-to-party). Therefore, Codec 1 is associated with the CC delivered to the LEMF when that CC is intercepted at Ingress point of TrGW and Codec 2 is associated with the media delivered to the LEMF when that CC is intercepted at the Egress point of TrGW. The Codec 1 is included within the SDP of SIP messages handled at the S-CSCF and therefore, if S-CSCF provides that to the DF2 in both cases, there would be a misalignment with the codec information delivered over the HI2 and codec information associated with the CC delivered over HI3 for Case 2.
Depending on which case is used for the CC interception, the IBCF can send either Codec 1 or Codec 2 to the DF2. With the DF2 using the codec information received from the IBCF for reporting purposes, the codec information reported in the HI2 and HI3 are now aligned. For Case 1 the codec information would be aligned irrespective of who sends that information to the DF2. Therefore, for Case 1, IBCF sending the codec 1 information to the DF2 can be an implementation alternative.
In a scenario like this, an implementation can also be such that the CC interception is always done at the Ingress point of TrGW (i.e., only Case 1), but because of some deployment situations and/or regulations, there may also be a need to perform the CC interception at the Egress point of TrGW as well.
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