Trunk Link

A trunk link frame (center) in the No. 5 Crossbar at Connections Museum, Seattle. The frame is comprised of two bays of equipment, each mostly full of crossbar switches.

A trunk linke frame (TLF or TL) is a frame on some telephone switches that provides inputs from, and outputs to trunks to other central offices. A trunk link frame is comprised of a number of crossbar switches, plus other relays used for control and logic.

One trunk link frame has between 100 and 160 trunk appearances. Because there are usually several hundred or several thousand trunks in an exchange, there are as many trunk link frames as required to serve the total number of trunks. Furthermore, spacing out trunks across several frames allows for redundancy, in case one trunk link frame is taken out of service.