 Packet data handler Edge Nodes Circuit/"ISUP"domain Signalling Control layer MSC, GMSC,TSC.. control interworking gateway control Packet domain IP multimedia domain SGSN, GGSN control CSCF, MGCF. ISDN/PSTN other PLMN UTRAN Circuit mode/ Internet intranets Control signaling User data (media) Connectivity layer Figure 11.8 A summary of the interfaces to the media gateways Real-time IP router Media stream handler Among framing components are ATM, AAL1, AAL2, AAL5, IP, UDP, RTP, L2TP (layer 2 tunnelling protocol), MPLS-LER (multi-protocol label switching-label edge router), GTP (gateway tunnelling protocol) and TDM. It should be stressed that it is important to distinguish between transfer mode and transmission system. A transmission system such as SDH can carry all types of transfer mode. In GPRS and UMTS there are two types of MGW on the access side: the MSC MGW and the SGSN MGW. Figures 11.9 and 11.10 give examples of their tasks. Obviously, the MSC MGW has many media stream functions. 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 t