The Port class is yet another abstract base class which forms the foundation for both the Input and Output classes. The Port class provides the means by which components communicate with the external world. After construction, each input port will know its external feeding connector and each output port will know which external connector to feed. As mentioned earlier, a linked list of input and output ports is maintained in the public interface of each component. These ports control signal flow to and from the component. The Port class is derived from the Connector class.