A test system must provide uniform test results. Without uniformity in data, the technicians who rely on the data are unable to assess problems accurately. The only way to get uniformity is to use the same type of test head throughout a network (see Figure 3).

Figure 3. Multiple Vendor Equipment Precludes Uniformity

Different Test Heads Equal Variable Test Results

Using a variety of switches with different built-in test devices or combining different methods of testing, such as switch-based testing, copper pairs, and digitized bypass pairs, complicates the challenges of testing. Different test heads, for example, mean different measuring techniques, different applied voltages, and different transducer designs. The subsequent test results are, therefore, highly variable. This makes decision-making more difficult for workers, because they are uncertain of how to interpret the data.

There is more to uniformity in testing, however, than simply using uniform test heads (see Figure 4). Even if a service provider achieves a certain uniformity by using only copper bypass or only digitized bypass pairs, it will not be able to achieve true uniformity in its testing. The reason is that neither type can reproduce the exact characteristics of a test head, nor accurately pass a signal over the copper bypass pair. Line testing devices built into switches, remote switches, and DLCs have problems, too. Chiefly, they provide too simplistic a profile of the line both by conducting a limited number of tests and by failing to integrate the results. A properly designed line test system, however, provides a more sophisticated testing solution by integrating many more individual measurements into a comprehensive profile of the line.

Figure 4. Stand-Alone Test System Ensures Uniformity

Faults Caused by Water Conditions

Faults caused by water conditions illustrate the type of problems that can result from using different test heads. If different types of test heads are used to measure this type of fault, the variability in test results will be even greater than with other types of faults. This is because higher voltage applied during a resistance reading tends to make faults more unstable in water conditions. Because faults caused by water conditions are so common, a service provider that cannot accurately measure water faults can be swamped with service problems and unable to meet the needs of customers.

Stand-Alone Systems and Uniformity

Because of its ability to test at the source of dial tone, a stand-alone test system is able to provide the uniformity in testing needed for water faults and other types of problems. An additional advantage of this type of system is that it is independent of the switching and transmission equipment, so this equipment does not affect the system's measurements. Even if the switch is highly loaded, the test-system controller and test heads are able to talk to each other without affecting the switch. One of the most compelling reasons for maintaining test-head uniformity is that only then is it possible to maintain uniformity in the type of tests that can be run. Uniformity also makes it easier to train workers, because they only have to learn one set of commands and one type of equipment. Technicians who are familiar and comfortable with a test system and have confidence in it are more likely to use it.