stablishment or modification, if it accepts the request; - CONFUSED message is sent by the MGCF entity in response to a media flow modification or establishment if it cannot deal with the received request message; - REJECTED message is sent by the MGCF entity in response to a request for media flow establishment or modification if it refuses the request. The bearer control tunnelling protocol (BCTP) protocol is used for the encapsulation of support control protocol for media flow. The header of the BCTP protocol contains the following indications: - the version of the BCTP protocol; - the type of support control protocol for media flow. 6.1.2.3. SIP-I signaling SIP-I signaling allows for the transport of ISUP messages encapsulated by SIP messages. The ISUP IAM message is carried by the SIP INVITE message. The ISUP ACM message is carried by the provisional response SIP 180 Ringing to the SIP INVITE request. The ISUP ANM message is carried by the SIP 200 OK response to the SIP INVITE request. The ISUP REL message is carried by the SIP BYE message. The ISUP RLC message is carried by the SIP 200 OK response to the SIP BYE request. 6.1.2.4. H.248 signaling The connection model describes the logical entities contained in the IMS- MGW entity that the MGCF entity can control. The main abstractions used in this connection model are contexts and terminations. 178 VoLTE and ViLTE A termination sends and/or collects several flows. The media flow parameters are encapsulated in the termination. A context is a package of allocated terminations. The NULL context contains all terminations which are not allocated to another termination, as is the case with idle time-slots on the TDM-mode interface. H.248 messages have a header which contains the identity of the transmitter and the version of the protocol. Several transactions can be concatenated in a H.248 message. The transactions contained in a message are dealt with independently and no order is predetermined. Each transaction is indicated by a transaction identifier and consis