 existing core network types will disappear overnight. Therefore interworking edge nodes are also necessary, for connection to legacy networks, such as PSTN/ISDN. Most of the required network conversions will take place in the edge nodes/media gateways. Seen from the access side the MGW could be called an access switch. Another name is multi-service gateways, where 'service' means network service (ATM, FR, PSTN) and not end-user service. MGW belongs to the access network with part of its functionality and to the backbone network with other functions. In IP networks with matching access and core networks, there is a limited need for MGW functionality. However, the IP network architecture often contains an edge node with QoS and aggregating functions at the border between access and backbone. For an IP-based core network two variants of the MGW exist, the edge-MGW towards the access network and the interworking-MGW towards other networks. Edge Nodes 11.2.3 LOCATION OF THE MEDIA GATEWAY The MGW is by definition located at the border between access and core connectivity, or at the border of other networks. To settle the access-core border point there is a need for a geographical partitioning into access areas. For traditional operators the location of the local exchange or mobile switching centre is acceptable as a partitioning point between access and core. If node locations and coverage areas of access switches are not given from the begin- ning, a first step is to study the forecast of traffic sources of various kinds in a selected area. Integrated access nodes or radio base stations are located close to the gravitational centre of their suitable coverage area. Then the access switch/MGW is positioned in a 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 sup