Core network Nb data transport and transport signalling
The present document specifies the bearer data transport and bearer control protocols used between MGWs within the CS core network across the Nb Interface. The present document assumes that the implementation of the split of the call control and the bearer transport and control, as specified in 3GPP TS 23.205 [1] with BICC-based Nc, and in 3GPP TS 23.231 [30] with SIP-I based Nc,, see figure 1. For BICC-based Nc, the User Plane protocol that uses this bearer data transport (Nb UP) is described in 3GPP TS 29.415 [3]. The transport format for the Nb interface with IP transport can optionally allow RTP multiplexing. Note that the present document does not preclude an implementation of a combined MSC Server and MGW.
Figure 1: CS core network logical architecture