etc. The data layer also controls the physical layer. The network layer basically contains functions that are required for the transport control plane. The control plane contains signalling related to the services that are handled by the network. The Iub interface is maintained by NBAP; in the I interface it is RANAP; while in Iur it is RNSAP. For signalling between the application and the destination on the physical layer, user plane signalling is utilised; for example on the U interface it is DPDCH. User Data Control Data Application Layer Application Layer User Plane Control Plane Presentation Layer Presentation Layer Session Layer Session Layer Transport Layer Transport Layer Network Layer Transport Plane Data Layer Physical Layer Figure 1.7 The OSI model in 3G Second-generation Network Planning and Optimisation (GSM) Fundamentals of Cellular Neocork Planning di Optimisation A.R. Mishra e 2004 John Wiley & Sons, Ltd. ISBN: 0-470-86267-X Radio Network Planning and Optimisation Since the early days of GSM development, GSM system network planning has undergone extensive modification SO as to fulfill the ever-increasing demand from operators and mobile users with issues related to capacity and coverage. Radio network planning is perhaps the most important part of the whole design process owing to its proximity to mobile users. Before going into details of the process, we first look at some fundamental issues. 2.1 BASICS OF RADIO NETWORK PLANNING 2.1.1 The Scope of Radio Network Planning The radio network is the part of the network that includes the base station (BTS) and the mobile station (MS) and the interface between them, as shown in Figure 2.1. As this is the part of the network that is directly connected to the mobile user, it assumes considerable importance. The base station has a radio connection with the mobile, and this base station should be capable of communicating with the mobile station within a certain coverage area, and of maintaining call quality standards. The radio network should be able to off