This command is also used by the IMS-MGW to register with the MGCF entity. The MGCF entity can also use this command to request the IMS- MGW to disable a termination or a group of terminations. Most commands are reserved for the specific use of the MGCF entity to control the IMS-MGW gateway. The exceptions are NOTIFY and ServiceChange commands, the first being sent by the IMS-MGW and the second being able to be sent by one of the two entities. VoLTE and ViLTE 6.1.2.5. Interfaces The Mi interface is the reference point between the S-CSCF and BGCF entities. This interface supports SIP and SDP signaling. The Mj interface is the reference point between the BGCF and MGCF entities. This interface supports SIP and SDP signaling. The Mg interface is the reference point between the CSCF and MGCF entities. This interface supports SIP and SDP signaling. The Mn interface is the reference point between the MGCF and IMS- MGW entities. This interface supports H.248 signaling. The IMS-MGW performs the conversion of the transport protocols relating to the signaling exchanged between the MGCF, depending on signaling transport over IP (SIGTRAN) model, the PSTN and PLMN networks, depending on signaling system 7 (SS7) model (Figure 6.3). SS7 transport SIGTRAN transport Layer 2 Layer 2 Interconnection Layer 1 Layer 1 IMS / PSTN or PLMN Figure 6.3. Transport of ISUP signaling The IMS-MGW performs, in the case of the ISUP signaling, the conversion of protocols relating to the media flows between the two end- points, corresponding, firstly, to RTP flow, and, secondly, to TDM flow (Figure 6.4). Interconnections IMS-MGW G.711 G.711 Codec Codec Codec G.704 G.704 G.703 G.703 Telephone handset Network Layer 2 Interconnection IMS / PSTN or PLMN (CS mode) Layer 1 Interconnection IMS/EPS Figure 6.4. Voice transport 6.1.3. Session establishment 6.1.3.1. Session establishment initiated by IMS network The procedure for establishing the session corresponds to a call generated by the Alice's user agent (UA) connected to the IMS network to Bob's telep