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. Nevertheless, by splitting the network into two stages, considerable economy could be affected.