offices also provided the service.

The key to the new system was two-stage multi-frequency pulsing. The outgoing sender sent its Class 4 toll center an off-hook signal as usual, received a wink as usual as a "proceed to send" signal, and outpulsed only a special three-digit (later six-digit) access code. The toll center picked a trunk through the long-distance network to the gateway office, which sent a second wink to the originating office, which then sent the