Media stream Coding/decoding server Echo cancellation Tone handling Conference calls Announcement machine Data transmission interworking Transport Exchange terminals for TDM transport Bearer control ATM link interface Figure 11.9 Example of MSC MGW functions Understanding Changing Telecommunications - Building a Successful Telecom Business Capabilities server MGW control execution (within MGW) Charging capabilities QoS protocols RAB mapping GTP-U termination Security protocols Figure 11.10 Example of SGSN MGW functions Example of media stream components are: Voice coder. For UMTS the adaptive multi-rate (AMR) voice codec is the default coding/decoding algorithm. Echo canceller. Echo cancellers attenuate echo generated from the conversion between four-wire and two-wire transmission in the PSTN, and reduce mobile crosstalk (see Book 2 Part b, Chapter 4.3). Circuit-switched data. (See Book 2, Chapters 1.3.3 and 4.3.2). Multiparty call. Multiparty call supports the conversation between more than two parties. Tone sender/receiver. The tone sender/receiver provides tones to be sent to and received from end users. DTMF tones can be sent to the far end of the connection as requested by a mobile station. DTMF tones can also be used with interactive messaging applications. Interactive messaging. The interactive messaging application provides subscribers with information messages on special conditions in the network or conditions that pertain to the service in use. To reduce the footprint, the signalling gateway application, which provides signalling interworking between IP, ATM and TDM networks, can be co-located with the media gateway node. See Figure 11.11. 11.4.1 QoS FUNCTIONS Quality of service (QoS) is supported by the media gateway through a combination of ATM traffic management, multi-protocol label switching (MPLS) and differentiated ser- vices (Diffserv) for IP. The selection of the AAL framing component is also QoS related as well as the protocols RTP, RTCP and RTSP. The MGC level controls the QoS handling in the