n the access switch/MGW is positioned in suitable available building. Provided most of the subscriber traffic comes from access nodes and not from direct access lines the exact position of the access node is not very critical. However, it must be located close to a high capacity optical ring. The capacity of the access switch must be dimensioned to support all the access nodes in addition to own possible direct access lines. 11.3 MGW INTERFACES 11.3.1 ACCESS On the access side there is an abundance of interfaces. Using reference architecture makes the situation much simpler. See Figure 11.5. 11.3.2 BACKBONE Although the backbone converges towards IP/ATM over DWDM, it can still take many different shapes. See Figure 11.6. 11.3.3 INTERFACE TO THE MEDIA GATEWAY CONTROL H.248 This interface is described in the key enabler part in chapter 3, section 3.14. See also Figure 11.7. Access node Edge node from access side Gateways ex. media conversion, servers Routing Access Transfer Backbone transport ATM, FR, Ethernet & TDM Transmission SDH, SONET, PDH BSC, RNC Aggregate router Figure 11.5 The access side of the edge node Understanding Changing Telecommunications - Building a Successful Telecom Business Call control (not part of the backbone) Media handling Telephony (IP) VPN (IP) MM Transfer modes Carries everything over anything Transfer mode conversion Frame relay IP shim Transmission PDH/SDH/SONET PDH/SDH/SONET Connectivity/Transmission conversion Fiber Figure 11.6 The backbone stack Control server Control server Figure 11.7 Decoupled media gateway and media gateway control - initially the server and the gateway were integrated in the same unit 11.3.4 INTERFACES TO OTHER NETWORKS Common interfaces to other networks are the ones towards Internet and PSTN/ ISDN/PLMN. See Figure 11.8. 11.4 MEDIA GATEWAY TASKS Referring to Figure 11.1 some main MGW tasks are media handling, framing and con- nectivity, including switching and/or routing. The MGW can for example function as one or any combination of the following: ATM switch