 star the preferred topology in 3G transmission networks. For real-time traffic, especially data, delay will be the basis of quality. Longer chains mean more time required for the traffic to reach the RNC/SGSN, which will degrade the quality of the call. A star topology is used to reduce the delays. 8.6 DETAILED PLANNING As shown in Figure 8.4, detailed planning has four major aspects: 2 Mb plans, parameter planning (ATM), synchronisation, and network management system planning. The princi- ples of 2 Mb and NMS planning are the same as described in Chapter 3. Parameter planning is different. 8.6.1 Parameter Planning Due to the involvement of ATM, parameter planning has now become an essential part of transmission network planning. Due to this, transmission planning in 3G networks has become a more complicated and challenging task as compared to transmission planning in GSM networks. We have seen the basics of ATM in sections above. Now there are two main aspects to be focused upon in this part: ATM configuration parameters, and ATM performance (related) parameters. However, before we venture into parameter planning for the services provided by ATM network, let us understand the traffic management on the ATM itself. 8.6.2 Traffic Management on the ATM Apart from virtual channels and virtual paths, as explained earlier, there are also PVCs and SVCs. A PVC (permanent virtual connection) is set up on a permanent basis. PVCs are set up by the NMS or element managers, while SVCs (switched virtual connections) require a signalling protocol (UNI/NNI) to set up the connection. ATM signalling is used to set up the virtual connections, allowing the switching and end station to communicate and exchange various management and QoS information for these connections. Signalling in ATM is always considered to be outband as there is always a dedicated pair of VCI/VPI values to send the signalling messages to an end station from a station requesting a virtual connection. How does this process take place? When one ATM device wants t