A method for determining the capacity that is needed on an lub link to fulfill Grade of Service (GoS) requirements in a Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN) for both Dedicated Channel (DCH) traffic and High-Speed Downlink Packet Access (HSDPA) traffic. The method includes determining the bandwidth demand of the HSDPA traffic (ElasticDim); calculating an average bandwidth of the DCH traffic on the lub interface (BW use,avg); setting an initial capacity (Capacity) to the capacity need of the DCH traffic (Capacity DCH), wherein at least the initial capacity will be provided for the DCH traffic in the dimensioned system; and, increasing the value of Capacity until a quality requirement of the HSDPA traffic is fulfilled, the maximum value of Capacity reached being the capacity that is needed for DCH and HSDPA traffic for the lub interface.