s calculated the number of access variants in its own portfolio at 7000. In general, public traffic needs a layer 3, which is intended for public addressing. Historically we have had E.163 for PSTN, E.164 for PSTN/ISDN, X.121 for X.25 and now IPv4 and IPv6 for the Internet. ATM and the upcoming Ethernet are both on layer 2. ATM can, however, also use E.164 addressing. For corporate private network traffic there is no need for layer 3 addressing, since layer 2 offers a sufficient addressing for limited networks, at least in frame relay, ATM Understanding Changing Telecommunications - Building a Successful Telecom Business Mobile access, GSM Multiplexing in the air Fixed access, cell mode ATM access node with statistical multiplexing Figure 13.14 Different methods but the same goal: traffic concentration Customer building MGW, LN, Edge node Access node (AN) Core media Feeder terminals Access transport terminals Core transport CUSTOMER ACCESS ACCESS NODE LOCAL NODE/MGW/EDGE NODE First network node, Second network node, typically located which typically does at main exchange, typically does Multiplexer access points (WLAN) Aggregation Concentration Concentration Switching/Routing Media conversion Basic services Control e.g. Narrowband switch Amplification e.g. ATM switch e.g. Fibre/coax hub (external) e.g. IP router e.g. DSLAM (in LE) e.g. Video distribution switch e.g. Narrowband access mux e.g. Extension point in WLAN e.g. Radio network controller Figure 13.15 Example of commonality in nodes and possibly also in Ethernet. Observe that the network is seen as limited to the public domain, where public numbering rules. More specific (tunnelled) private addresses or IP NAT addresses are used to find the end-user terminal within the private domain. In the case of public addressing using private networks there is a two-stage procedure. First the call is often routed in the private network to a point as close as possible to the public address. Where the connection leaves the private network and enters the public network, 