L  IP-based Handover Interface for CC of CS Intercepts |R13|  Word‑p. 379

L.1  Background

Figure L.1 shows an overview of the architecture that shows using IP-based handover interface for CC of CS intercepts:

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Figure L.1: General Concepts of IP-based Handover Interface using an ASN.1 module for HI3

The call content (CC) from CS-MGW is delivered to the MF/DF3 over X3 reference point. In some implementations, the MSS may also have to be part of the CC interception to provide the signalling aspects of the CC-related call setup. The X3 reference point is not standardized in the present document.

L.2  Options for X3

This sub-clause provides a few options for realizing the X3 reference to support an IP-based handover interface. Figure L.2 shows three different possible options:

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Figure L.2: Three options for X3 reference point

The X3 reference point can be CS based in which case the MF/DF3 will have to convert the CS-based CC into RTP (RFC 3550 [86]) streams and then deliver the same over the HI3 reference point using the new ASN.1 object module (see TS 33.108) to the LEMF. The CS circuits that carry the content of intercepted call can be based on the dedicated direct links between the CS-MGW and the MF/DF3, or dynamic links setup via CS-based signalling (e.g. ISUP or ISDN).

The X3 reference point can also be a SIP-based in which case MSS will have to set up the SIP session and CS-MGW will have to deliver the CC in the form of RTP. The SIP-based signalling may use either SIP (RFC 3261 [88]) or SIP-I (RFC 3998 [87]). The MF/DF3 would have to deliver the received RTP streams to the LEMF using the the new ASN.1 object module (see TS 33.108) to the LEMF.

In another option, the MF/DF3 function can be integrated into the MSS/CS-GW and in this case, that integrated MF/DF3 will have to deliver the CC using the new ASN.1 object module (see TS 33.108) to the LEMF. However, realization of this approach can be complex since it will require the MSS/CS-MGW to have the capability to support the generation of RTP streams and then ASN.1 module based handover interface.

L.3  Information delivered along with the CC  Word‑p. 380

The CC delivered using the IP-based delivery interface should carry the following information at the minimum:

• Correlation information: to correlate the CC with the IRI messages
• Payload description: to decode the RTP streams
• Media direction: to indicate whether the payload belongs to target transmit or target receive or in a combined form.

The method used by the MF/DF3 in determining the above information is outside the scope of the present document. For example, the DF2 may pass the correlation information to the MF/DF3 or MSS may pass the correlation information to the MF/DF3. Since the RTP payload is constructed at the MF/DF3, the MF/DF3 may be able to derive the payload description on its own. The intercepted voice media stream may be delivered to the LEAs in a combined form (i.e. target transmit and receive as one stream) or in separated form (target transmit and target receive). The media direction may be provided by the MSS to the MF/DF3 or the MF/DF3 may derive the media direction using the other means.

M (Normative)  Virtualised Implementations |R15|  Word‑p. 381

M.1  General

The present document does not define functionality or architecture extensions to support virtualised implementation scenarios, equivalent to those provided by TS 33.127.

Where implementation scenarios require virtualisation of functions defined in the present document, the extensions defined in TS 33.127 clause 5.6 shall be applied. Where the architectural terminology (e.g. reference point names) of TS 33.127 differs from the present document, equivalent functionality and reference points in this specification shall be mapped to those in TS 33.127 (e.g. X2 interface in the present document shall be used in equivalence to LI_X2 defined in TS 33.127 and MF/DF used in equivalence to MDF in TS 33.127).

For all virtualised implementations based on the present document, the ADMF architectural decomposition extensions defined in TS 33.127 shall be used.

The general security and audit principles in TS 33.127 clause 8 shall be applied.

N  Change history  Word‑p. 382

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