Tandem's Written By Forest Ranger The Tandem: ---------- Each tandem is a line with the capability of signaling any other tandem in any other toll switching office in North America. Tandems are programmed to route themselves to other tandems if all other direct routes are busy. If all other tandems are busy in one area then your tandem will route itself to the next nearest tandem that may be in another part of the continent. When a tandem is idle waiting for someone to use it sits there whistling 2600 Cycles per second facing all of thm numbers serviced by that exchange. This just means that the tandem is ready to be used. The other side of the the tandem is whistling 2600 cycles per second also into a number of trunk lines telling the phone system that the tandem has no outgoing or incoming calls. Dialing the Tandem: ------------------ You are automatically hooked into a tandem when you dial a long-distance phone number. The tandem then sends the number you dialed to the side facing away from you. The senling side stops whistling the 2600 cycles per second into the trunk line and at this point has been taken over. It will then carry the number dialed that will be converted to multi-frequency beep tones to a tandem in the NPA and centeral office you requested. FROM TARAN KING AT METAL SHOP (314)432-0756