This unit is responsible for operation and management functions and carrier control. From the transmission network planning perspective, the AM takes the same place as a TRX in BASICS OF TRANSMISSION NETWORK PLANNING GSM transmission network planning. The number of AMs is dependent on the traffic that is carried by the base station and is in no way dependent upon the number of cells or number of TRXs. ATM Cross-connect (AXC) This is responsible for cross-connection at the ATM (asynchronous transfer mode) level. It also acts as an interface between the AM and the interface units. AXC can be a standalone unit. Interface Unit (IFU) This is the interface between the base station and Iub interface. It may vary depending on the type of transmission - E1/T1/JT1 or PDH/SDH, etc. Radio Network Controller (RNC) As noted in earlier chapters, the radio network controller in WCDMA 3G networks is equiv- alent to BSC of a radio network. Apart from similar functions, there is one main addition in RNC, which is an interface, Iur, between two RNCs. The RNC is a very complicated network element, but a simplified block diagram is shown in Figure 8.3. Switching & Multiplexing Control Unit (RRM) Figure 8.3 Block diagram of radio network controller (RNC) Interface Unit (IFU) There are mainly two kinds of interface unit, PDH and SDH. On either of the interfaces (Lub/Iur/Iu), a PDH or SDH interface can be configured. Switching and Multiplexing Unit Asynchronous transfer mode (ATM) forms the backbone of WCDMA networks. In the RNC, the functionalities of the switching unit include providing the required support for the ATM traffic, ATM cell switching, AAL2 switching, and multiplexing of traffic. Control Unit (RRM) Radio resource management is considered to be the most important function of the RNC. All three network planning entities - radio, transmission and core - are affected by it. 3G TRANSMISSION NETWORK PLANNING AND OPTIMISATION The control unit is responsible for RRM functions such as handovers, admission control, power control and 