n parameter set. Source and target cells are talked about specifically. Typically, the 'source-to-target' parameter set defines the handover criteria that will be used in commanding handovers from source to target and vice versa. Indeed, each cell should be able to recognise the other whether either the MSC or the BSC are handling the target cell. An adjacency is defined with a target cell location area code, cell identity, BCCH frequency, BSIC network colour code and BSIC broadcast colour code. In idle mode, the MS listens to the defined adjacent cells BCCH list. It is, however, possible to improve and optimise the number of target BCCHs by using the double BA (BCCH allocation) list parameters. A number of preferred BCCHs can be set as the BA list. Layers Cellular networks can be split into different layers, each one targeting a special traffic profile. To guarantee mobility for end users, the system should ensure interworking between cells of the same layer and also between cells of different layers. This interoperability is assumed according to predefined parameters. A layer can be continuous (in the case of macro sites) or discontinuous (in the case of hotspot micro sites). The layer concept does not only include macro/micro splitting; it also englobes dual-band (900- 1800 MHz) network interaction and multiradio access technologies (GSM-UMTS). Cells belonging to the same layer have a layer relationship 'SAME'. In normal conditions, they basically perform power budget handovers between them. Cells that are among different layers have either a 'LOWER' or an 'UPPER' relationship. The idea behind layer management is to keep slow-moving subscribers on micro cells (hotspot traffic) and redirect fast mobile traffic to macro cells (Figure 2.69). Concretely speaking, a mobile station will camp on a macro cell. Handover is triggered in the lower direction only if the mobile station is moving slowly. If the MS experiences some radio problems, a radio reason handover will be done in the upper direction urgently. Radio Ne