n increase in traffic would lead to an increase in the number of TRXs or the number of sites. In contrast, in 3G networks, capacity analysis is required more frequently because not only does traffic increase, the types of traffic (RT, NRT, etc.) change. An increase in traffic can lead to an increase in the number of signal processors/application managers and/or TRXs in a base station, and any increase in these will lead to an increase in link capacity. We have already seen that a base station site with a small number of users generates substantial traffic. Even if the increased number of users is small, the packet data might increase (i.e. a small number of users generates PS traffic), and then both the number of AMs and link capacity will need to be increased. An increase in link capacity will mean that RNC capacity has to be re-examined. Thus, capacity of the transmission network can be increased by: increasing the number of signal processors/application managers and/or TRXs increasing the number of base station sites increasing the number/capacity of RNCs. Quality Optimisation The asynchronous transfer mode was chosen for B-ISDN services SO that quality of service could be guaranteed. Thus, ATM will be a focus area in 3G optimisation. Performance of the physical layer is another area for scrutiny. 8.7.4 Analysis of the ATM layer Performance analysis of two ATM layers is of immediate interest: AAL2 and AAL5 (for CS and PS data respectively). The performance of these two layers can be monitored with the help of counters and performance indicators on management systems. These coun- ters/measurements are mainly observed to calculate the error ratios and delays. In most of cases of degradation, delay is the reason. Factors that may cause degradation in quality due to delay are as follows: Propagation: Variation in propagation conditions may force the physical media to cause delays in transporting the bits in ATM cells between ATM nodes and switches. Another probable cause may be the performance of the physical medi