4,032 T-Berd A T-Berd is a T1 Bit Error Rate Detector. The generic term is used for any device that will perform BERT tests on a T1. If you have a T1 that's misbehaving, the provider will probably send out an engineer with a T-Berd to perform invasive testing. TDM stands for time-division multiplexing. A T1 link is a TDM link because its 24 channels are divided into time slots. A T1 link is a serial link, SO one bit is sent at a time. The channels are cycled through at a high rate of speed, with each channel being dedicated to a slice of time. Telecom Glossary CHAPTER 21 In the 1950s, the only method for connecting phone lines was with a pair of copper wires. For each phone line entering a building, there had to be a pair of copper wires. Wire congestion was a huge problem in central offices (COs) and under streets in met- ropolitan areas at the time. Imagine the CO of a large city, where tens of thousands of phone lines terminated, each requiring a pair of wires. These COs also needed to com- municate with each other, which required even more wiring. In 1961, Bell Labs in New Jersey invented the T1 as a means for digitally trunking multiple voice channels together between locations. The T1 delivered a 12:1 factor of relief from the congestion, as it could replace 24 two-wire phone lines with 4 wires. Back then, this was a major shift in thinking. Remember that at the time, digital tech- nology was practically nonexistent. The first T1 went into service in 1962, linking Illinois Bell's Dearborn office in Chicago with Skokie, Illinois. Today, you would be hard-pressed to find a company that doesn't deploy multiple T1s. In this chapter, I will go into detail about the design, function, and troubleshooting of T1s. While I usually try to simplify complex engineering topics, I feel that it's important to understand the principles of T1 operation. We live in a connected world, and much of that world is connected with T1s. Knowing how they work can save you countless hours of troubleshooting time when they break. Unders