The large and increasing quantity of pulse-code-modulation (p.c.m.) transmission circuits being installed in the national network means that the exchanges of the future will have to switch p.c.m. as well as analogue circuits. The paper analyses the problem of p.c.m. channel switching, and concludes that exchange switches using the simplest kind of crosspoints to provide analogue transmission of the channel digits serially within the basic 32-channel slot time, with a minimum slot changing, represent the simplest, cheapest and most reliable general solution.