for dimensioning interfaces (shown in Figure 3.59). The following assumptions are made at the beginning: U interface blocking = 2% This means that there is a modest chance left for any service request to be blocked by congestion in the air interface; 2% is commonly seen as a value that is both acceptable by subscribers and reduces costs for the operator. SHO = 40% Soft handover. This consists of assuming 50% mobile terminals without soft/softer handover, 15% with softer handover, 25% with soft handover, 5% with softer-soft handover and 5 % with soft-soft Transmission Network Planning and Optimisation handover. Studying all the legs of these user element connections, it can be found that there are 40% more connections in Iub due to a soft handover. VAF = 50% - Voice activity factor (VAAF). This is statistically easy to explain and the safe value is 50 %. Voice traffic = 12 mErl/sub, voice rate 12.2 kbps - This represents quite low subscriber activivity compared to current actual values in 2G networks, but this works here just as an example and could also be justified by lower voice service usage in the 3G network. (Voice services can be pushed to overlaying the 2G network.) CS data 10 mErl/subscrber, service class RT 64 kbps PS data 600 megabytes/month/user, service class NRT 128 kbps 200 BTSs (1 + + 1 configuration) 1000 subscribers/BTS The dimensioning is needed for Iub, I-cs, Iu-ps and Iur interfaces. Dimensioning is done for both circuit switched and packet switched traffic. In the following, to give some starting point, the dimensioning is done on the generic level to find out how much end user data are loaded on the system. The results must be revised later with information about vendor specific system features that affect the dimensioning. Those features can have a big impact on the results. Iub Interface Dimensioning For circuit switched traffic the inputs used are: Voice traffic: 12 mErl/subscriber CS data at 64 kbps: 10 mErl/subscriber 1000 subscribers/BTS Soft handover: 40% Voice activity factor: 50% Iu