the same amount of time (with 17 occurring). The signal on the right can be described as having more bits per second (bps) of throughput. When someone says that a DS3 has more bandwidth than a T1, what he's really saying is that the DS3 will deliver higher throughput in that it is capable of 45 million bits per second (Mbps), as opposed to the T1's paltry (by comparison) 1.54 Mbps. In common usage, the terms bandwidth and throughput are Telecom Glossary One bit Three bits Figure 20-2. Digital state changes over time interchangeable. A more accurate term to refer to links might be data rate, as a DS3 can deliver the same number of bits in a shorter amount of time than a T1. In simplest terms, a DS3 is faster than a T1. BERT stands for Bit Error Rate Test. You'll often hear "BERT test," although this is technically redundant because the T in BERT stands for test. Still, saying, "We're going to run some BERTs on the T1" will make everyone look at you funny. BERT tests are disruptive tests run on a link to validate the data integrity of the circuit. You usually run a BERT test by putting the remote end of the link in loop- back and sending out a special pattern of ones and zeros. How the data is returned from the far-end loopback can help you determine whether certain types of prob- lems exist in the line. Some of the common types of BERT tests you may hear mentioned include QRSS (Quasi-Random Signal Source), 3 in 24, 1:7 or 1 in 8, Min/Max, All Ones, and All Zeros. Each of these patterns stresses a link in a certain predictable way. A device used to perform BERT testing on a T1 is called a T-Berd. Central Office (CO) The central office is where phone lines from residences or businesses physically terminate. COs have the necessary switching equipment to route calls locally or to another carrier as needed. When you make a call that is destined for somewhere other than your premises, the CO is the first stop. With technology like T1, the copper connection from your location will probably terminate at a CO, where it may