by means of the H.248 protocol, presented in Chapter 3. See Figure 11.3. Concluding this introduction, the 'all-access network architecture' with a common core interfacing a multitude of access types and other networks, is the basic reason for the use Voice or data Voice or data PSTN, ISDN, is packed is taken out PSTN, ISDN, PLMN, IP, FR, X.25 into ATM cells of ATM cells PLMN, IP, FR, X.25 Access node Access network Backbone network Access network (here ATM) AAL only at the gateway Figure 11.2 Illustration of a possible network structure: various access types, a gateway and a uniform ATM backbone. Layer 3 below AAL in the gateway is reserved for possible layer 3 signalling and addressing Edge Nodes SS7 ISUP ISUP/IP SIGTRAN Softswitch PSTN/ISDN switch network H.248 E1 speech Voice channels gateway RTP/UDP/IP Figure 11.3 A softswitch configuration Access Transport Service network Access transport = Optical rings Internet used when applicable server Other operator's server Large/medium network enterprises SGSN GGSN server control function IP packet backbone Access Access router Frame relay transport transport router Circuit mode, Ethernet (MGW), router (MGW) ATM, IP IP/VPN Access (MGW) transport (MGW) Access Access Access Access C transport transport DSLAM transport GSM/EDGE transport Homes & SMEs WLAN hot spot Resource sharing Copper xDSL Fibre Ethernet DSL WCDMA Figure 11.4 Edge nodes constitute the interface between access and core network of edge nodes. See Figure 11.4. When MGW and edge router are collocated the router is often called a site router. 11.2 ACCESS AND BACKBONE NETWORKS 11.2.1 ACCESS CONNECTIVITY During all processes of change, the expensive access network has been a conservative power. Let us mention the digitization, which by definition is not yet complete for PSTN in the access part. The convergence of the existing networks towards a packet network Understanding Changing Telecommunications - Building a Successful Telecom Business with broadband capability must be profitable with strict control o