Switch designs vary, but typically, a repeating counter is incremented with an internal clock.
The RAM location chosen for the incoming data is taken from a small memory indexed by the counter.
That is, a new switch set-up is shifted-in, and then a single pulse applies the new configuration instantly to all the connected ICs.
In a time-slot interchange (TSI) switch, two memory accesses are required for each connection (one to read and one to store).
If there are n connections and t is the operation time for n lines, then t=2nT which givesn=t/2T t and n normally come from a higher-level system design of the switching fabric.
The SLICs serve as the outer space-division switches of a modern wired telephone system.