site. At the switch sites BSC-to-MSC traffic would terminate to the MSC from the SDH DXC. The UTRAN traffic would terminate over the regional rings to the ATM switch located in the switch site, while aggregating traffic to the RNCs. As noted earlier, RNCs and CN nodes reside co-located at the switch sites hard-wired without requiring any transmission resources. Inter-site MSC traffic flow would use STM transport over the SDH backbone, and UMTS inter-switch site traffic would get routed over the ATM switching layer. The UMTS Network and Radio Access Technology Capacity projections show a higher bandwidth need in 2000 than in 2005 despite the higher number of subscriber in the latter. The reason lies in the better bandwidth utiliza- tion for UMTS traffic, e.g. codec at the edge for voice traffic means lower capacity re- quirement. For example, in 2000 we would need 160 E1s, about 210 E1s in 2002 and 118 Els 2005. This means that national ring capacity requirements, can drop to STM-4 capacity rather than STM-16. 7.10.3 Transmission Dimensioning Results In the following for completeness, we outline some dimensioning exercise results as- suming 750K UMTS subscribers and 900K GSM subscribers around 2002. We also assume about 1000K UMTS subscribers and 300K GMS subscribers by 2005. These assumptions are mainly to create enough margin and do not necessarily reflect the actual evolution of subscriber population. We do still use the traffic patterns shown in Table 7.5 and subscriber population in Table 7.2. The dimensioning exercise does in- clude the margins for unexpected subscriber growth [8]. 7.10.3.1 Traffic per Site Table 7.27 illustrates the reference number of sites for this transmission analysis, and the values in Table 7.28 indicate the average amount of bandwidth required per site on the Abis and lub interfaces for the different service areas. The values include frame OH and load factor, ready for mapping onto the payload on the physical PDH or SDH links. Table 7.27 Reference Number of Sites for 2002 and 2005 U/