VAC was the first manufacturer of splitters, which achieve outstanding values for reflexion attenuation by adapting the POTS filter to the complex line resistance. A filter of the 10th order was needed to achieve a very good blocking attenuation of the ISDN filter.

When DTAG introduced ADSL , high demands were made of the POTS and ISDN splitters in order to ensure reliable operation.

Very high values were demanded for blocking attenuation and reflexion attenuation for the POTS filter (incl. the meter pulse at 16 kHz) and the ISDN filter (up to 90 kHz).

Thanks to further clear progress in the design of the POTS and ISDN filters, in the next stage VAC succeeded in halving the number of inductivities and capacities needed.

Extended application knowledge, to which VAC greatly contributed thanks to cooperation with DTAG and in standardisation bodies, as well as findings from the three years of operation of ADSL by DTAG enabled VAC to combine ISDN and POTS filters.