 The switching network was composed of reed relay cross-points arranged to give three (A, B and C) stages of switching on either side of a number of linking circuits.The A-stage switches concentrate traffic from the peripheral terminals on to B-C-stage arrays, which are internally connected to provide full accessibility between every B-switch terminal and every C-switch terminal of the array.A simple switch enabling two subscribers to be connected to two others can be constructed, but extending this to larger sizes becomes increasingly uneconomic.