r the access connections. The latter would be mainly microwave radios. Capacity increases will accumulate primarily around the controller sites, e.g. an area served by a 16 X 2M radio link will saturate as it takes 3G traffic. Thus, density will be a major challenge with radio links; consequently we will need traffic grooming in the field near the BSs. Mbit/s per Macro-cell BS site 900 GSM 1800 GSM WCDMA Figure 7.13 Macrocell traffic growth example. In a mixed environment, e.g. 2G and 3G, each BSC/RNC will concentrate capacity to the NSS and GPRS elements. Thus, even if the total volume is lower than in the access network, an integrated transport network will add efficiency and performance overall as illustrated in Figure 7.14. Consequently, a SDH based transport CN will provide flexi- ble capacity and a base for multi-protocol support as well as basic connectivity. The access network has more stringent delay requirements, e.g. WCDMA traffic needs ATM transport carried over TDM circuits. Thus, 3GPP technical specifications recom- mend ATM over semi-permanent point-to-point connection for the RAN network. On the other hand, in the CN transmission, efficiency gets more important. Thus, packet traffic can travel either on the top of ATM, or IP packets get carried directly over TDM infrastructure based on fibre, for example. Deploying 3G Networks 7.10.2 Transmission Reference Network Coming back to our field-study, we make the following assumptions: We assume that the transmission network will serve an existing 2G network (e.g. 1800 MHz GSM network). About 70% of existing BS sites can house a WCDMA BS. New UTRA sites will replace non-usable GSM sites and/or stand in for coverage where required, e.g. dense areas. Figure 7.15 illustrates a typical 2G-access network model, which will serve to pro- ject the links required in 2002 and 2005. In the model, 30% GSM BTSs connect through leased lines for the last mile access, 35% use MW radio links in cascaded structures, and 35% use MW radio links in hub structures. Internet 