Panel Switch - Sender

Sender

While the non-director Strowger (step-by-step or SXS) switch moves synchronously with the dial pulses that come from the telephone dial, the more sophisticated Panel switch had senders, similar to the directors of later Director telephone system Strowger exchanges. The sender first translated the received digits into numbers appropriate for the selectors: District Brush, District Group, Office Brush, Office Group, Incoming Brush, Incoming Group, Final Brush, Final Tens, Final Units. Decoders helped by translating the first three digits of the phone number into four "District" and "Office" selecting numbers. Decoders also determined the proper rate at which to operate the message register and gave this information to the sender, which set this rate in the District Junctor. Auxiliary senders were added in the mid 20th century to implement Direct Distance Dialing.

When the selector had activated the correct brush or group, the sender sent a brief open circuit signal to command the selector to stop there and prepare for the next number for the next stage. District and Office parameters were variable translations supplied by the decoder, while Incoming parameters and Final Brush were a fixed translation from the Thousands and Hundreds digits of the phone number, merely to adapt efficiently to the capabilities of the Panel selector.

In the 1930s when the 1XB switch crossbar switching system was introduced, it used the same Revertive Pulse Register signaling system, not only to control panel selectors but to signal within itself and with similar exchanges. Later 5XB switch, 1ESS switch and other systems included RP equipment in order to maintain compatibility, in some cases decades after the last Panel switch in the city had been scrapped.