 the uplink and downlink components of a given data traffic flow are considered separately, and the link size is then estimated as the highest of the components. This approach makes sense in traditional bidirectional symmetric transport media, like E1/T1, which can still be used in the Iu-PS interface, for instance. In the case of network nodes handling IP traffic, it is more common to specify the throughput as combined uplink plus downlink components. This fact may also apply to the case of the SGSN, depending on the infrastructure vendor, although this is not explicitly mentioned. In that case, the interface traffic input should be properly modified to add the uplink and downlink components separately, if SO required. Secondly, the maximum number of simultaneous active PDP contexts is taken into account. This is calculated by multiplying the total amount of subscribers by the total number of simultaneous PDP contexts that are expected to be active during the busy hour. Once the total number of simultaneous PDP contexts needed is obtained, the total amount of GGSN nodes required according to this criterion would be calculated as the total amount of simultaneous PDP contexts divided by the maximum amount that can be handled in a single GGSN. In principle, session management and mobility management restrictions should also be taken into account, since the GGSN node may have dynamic limitations in terms of the maximum number of PDP context activation requests or PDP context modification requests. However, these limitations are rather difficult to characterise beforehand without having performance management measurements from a live network. Therefore, unless the node vendor provides explicit limitations that can be correlated with the traffic profiles of the dimensioning input, these aspects should be considered as part of the optimisation activities, to be dealt with later on. Dimensioning Similarly to the previous case, after these two aspects have been verified and the partial estimations of the number of GGSN n