The control unit performs three gen

The control unit performs three general tasks. First, it establishes connections.
This is generally done on demand, that is, at the request of an attached device.To establish the connection, the control unit must handle and acknowledge the request, determine if the intended destination is free, and construct a path through the switch.
Second, the control unit must maintain the connection. Because the digital switch uses
time division principles, this may require ongoing manipulation of the switching elements. However, the bits of the communication are transferred transparently (from the
point of view of the attached devices). Third, the control unit must tear down the connection, either in response to a request from one of the parties or for its own reasons