ll these trends will result in a steady decrease in cost per bit (as throughput rates increase) and capital cost (as fibre cost and component cost reduces over time). Installation cost remains more of a problem given that competitive access options have either been fully amortised (copper) or written down (cable). Delivery cost economics are therefore determined by the amount of legacy investment and physical reach of these competitive delivery options and the topology and demography serviced by those delivery systems. Service asymmetry is also a factor and cost per bit is only a valid comparison metric if the bits can be used efficiently, for example multiplexed over a sufficient numbers of users with capacity closely matched to user uplink and downlink requirements. Some first-order comparison can be achieved by analysing cost delivery economics in terms of addressable user density differentiated across five application domains, dense urban, urban, suburban, rural and remote rural as shown in Table 2.3. Self-evidently only wireless can deliver mobile or portable service, but as we will see later there is a delivery cost/benefit trade off in terms of signalling and coding overhead. With fixed service provision there is a choice of wireless that could be either radio frequency or free-space optical with point-to-multipoint offering a lower cost per subscriber but lower bit rate when compared with point-to-point. Fibre has a higher capacity/distance product than cable, which has a higher capacity/distance product than copper. However, cable and copper networks may have been amortised over a long period and installation costs have long since disappeared into the noise floor. Making Telecoms Work Table 2.3 Dense urban to remote rural teledensity Dense Urban Suburban Rural Remote urban rural Fibre Cable Copper Wireless Per bit cost reduces as fixed point- data rates to-point increase but Wireless subscriber fixed point- costs also to-multipoint increase Wireless portable Wireless mobile Investment cost per subscriber