4.1 Reference Model

29.2353GPPInterworking between SIP-I based circuit-switched core network and other networksRelease 17TS

Figure 4.1.1 shows the interworking reference model for the interworking between a SIP-I based circuit-switched core network and an external SIP-I based network:

Figure 4.1.1: interworking reference model

The IWU provides the control plane interworking between the external network and the SIP-I based circuit-switched core network. The IWU is a logical function within the GMSC Server (for incoming calls) and the MSC Server (for outgoing calls) that may reside with other 3GPP logical functions.

The user plane interworking is provided by the UP-IWU. The UP-IWU is a logical function within the MGW.

NOTE: In call scenarios without the need for the (G)MSC server to manipulate the bearer, the (G)MSC server may perform call control signalling without any associated MGW by not inserting a MGW in the bearer path during the call establishment. Call scenarios where the (G)MSC server needs to manipulate the bearer, e.g. scenarios with insertion of tones or announcements, lawful interception, CAMEL services do not allow this optimisation.

Nb reference point: The Nb reference point is defined in accordance with TS 29.414 [43].

Nc reference point: The Nc reference point is defined in accordance with TS 29.231 [4].