A sender is a type of circuit and system module in 20th-century electromechanical telephone exchanges.
Once the sender received the translation, it directed the selectors in the switching fabric to the correct terminal, completing the connection to the called party.
As machine switching exchanges became commonplace, senders also played a critical role in communication between central offices of different types.
As technology improved, better signaling methods were devised, but backward compatibility with existing exchanges had to be maintained.
Common-channel signaling replaced senders after the development of stored program control (SPC).