A time division switching system having a time-space-time architecture is disclosed. The time-multiplexed communication links of this system comprise a plurality of channels certain of which are used to convey control information and the remaining ones of which are normally used to convey digital representations of subscriber signals. When a large quantity of control information must be exchanged, the system preempts selected channels from conveying digital representations of subscriber signals and uses these preempted channels to convey the large quantity of control information.