IMS media gateway function
The IMS media gateway function (IMS-MGW) links the user planes in the circuit-switched domain (PSTN, GSM) and the IMS. To accomplish the linkage, the IMS-MGW terminates the bearer channels from the circuit-switched side and the media streams from the IMS backbone network. IMS-MGW can deal with RTP-based media streams of an IP backbone or the AAL2/ATM connections in an ATM backbone network. The ATM connections are implemented to deal with legacy backbone implementations.
In addition to the terminations, the IMS-MGW executes any conversion that might be required between the terminated sessions. Moreover, the IMS-MGW is capable of performing transcoding or user-plane signal processing when required by the terminated sessions. To better serve the circuit-switched domain, the IMS-MGW is capable of providing the traditional tones and announcements that are expected by circuit-switched domain users. The IMS-MGW is controlled by the MGCF.