it can be composed of several sub-units, such as network termination, a set-top box and devices connected to a local area network. The CAU can also refer to a device shared by several end users, for example, a hub located in the basement of a multiple tenant building, a mobile radio base station or a WLAN access point. The mobile access points are widely segmented in a range from indoor picocell to 2G type coverage. Understanding Changing Telecommunications - Building a Successful Telecom Business Access concepts ANT = RNC, CAU = RBS for mobile Drop network Feeder network Access transport network When needed based on distance Radio Fibre Radio, fibre, CU CAU = Customer access unit ANT = Access network termination AN = Access node CPE = Customer premises equipment Access network Figure 13.12 A viable terminology in the access network A multi-service access node 2 (Figure 13.2) can be part of the access infrastructure, providing an interface for various types of CAUs. It multiplexes or concentrates traffic and can convert protocols between different types of traffic, for example between circuit mode and cell mode (ATM). The access node provides connection of customer access units, and connection to the access transport part of the network and to the edge node. It can be used by more than one operator. Internally the access node will be able to multiplex and/or switch circuit, packet (including Ethernet and IP) and cell mode. Conversion functions, such as circuit emulation, are normally not located here, but in media gateways/edge nodes. In the long run the media gateway and router function will probably migrate to the access node. Towards the edge node, the access node is often connected to a star point-to-point network structure, mainly over fibre with copper as an alternative. For reliability reasons, a connection to an optical access transport ring via an add/drop multiplexer is preferable but somewhat more expensive. The edge node, which connects the access network to backbone networks, provides variety of func