1. Symptoms
A renowned cabling contractor and systems integrator used Category 6 cabling for the construction of a new telecommunications building in a city. While the number of points was not substantial, totaling 1,800 points, the project was completed quickly. However, they encountered some difficulties during the acceptance testing: the one-time acceptance rate was only 80%, with the remaining 20%, approximately 360 cable runs, failing to meet the standards. The cabling contractor used products from a reputable cable manufacturer, including a full set of cables and connectors, all of which had been quality-checked before construction. The construction team responsible had nearly four years of engineering experience, and they had successfully completed projects involving up to 100,000 cable runs in the past. This project was the first trial project using Category 6 cabling, and it proved to be a test for the company’s cabling construction team. Unfortunately, the results were not satisfactory. If the 360 cable runs had to be redone, it would result in significant losses. Consequently, the company decided to conduct a reevaluation of the remaining Category 6 cabling to determine whether the issue was with the products or whether they needed replacement or repair.
The results of the reevaluation are as follows: Ten rolls of products were sampled for evaluation, with each roll cut into 90-meter segments. These 90-meter Category 6 “Basic Link” segments were connected and subjected to on-site certification testing, resulting in 7 out of 10 rolls being noncompliant. Since the cabling contractor also served as a representative for the manufacturer, and the manufacturer’s sales representative couldn’t explain the test results, a second evaluation was conducted. The results showed that 6 out of 10 rolls of 90-meter simulated cables were still noncompliant, prompting them to seek help from the “Network Hospital” to identify the cause.
2. Diagnostic Process
Upon arrival at the site, a plan was developed to test a portion of the noncompliant cable runs, with a total of 20 runs sampled, all of which failed. The primary noncompliant parameters were reviewed, including Return Loss (RL), Power Sum Attenuation-to-Crosstalk Ratio (PSACR), and others, accounting for 80% of the failures, followed by Power Sum Equal Level Far-End Crosstalk (PSELFEXT), Power Sum Near-End Crosstalk (PSNEXT), and similar parameters. A recheck of the cable runs initially sampled by the contractor produced results that were mostly consistent with the previously mentioned findings. Relying solely on the manufacturer’s product certifications and quality certificates appeared to be insufficient in demonstrating that the products met the requirements of on-site certification testing during construction. To confirm whether the issue lay with the manufacturer’s cable products, connectors, and connecting modules, the suggestion was made for the cabling contractor to compare them with products from another cable manufacturer that they represented. The comparison method was as follows: Creating 10 cable runs using each of the products from the two cable manufacturers under the same testing conditions as the previous evaluation, and then comparing the results with the previous test results to determine whether the issue lay with the products themselves. One hour later, based on this recommendation, the cabling contractor produced two sets of 20 segments using cables from two other cable manufacturers, with 10 segments from each. Testing was conducted on these segments, with the results as follows: Segment pass rates were 80% for Product A and 70% for Product B. Each product had 20% of parameters that barely met the testing standards, generally with a margin of only 0.5-1.3. From this, it appeared that products from various cable manufacturers had similar pass rates. Did this not imply that products from all cable manufacturers were problematic? Based on logical analysis, there were only a few possible explanations: 1) Product quality might indeed be the issue, but why was the failure rate so consistent? This possibility seemed unlikely. 2) Issues might exist with testing equipment or the testing environment, such as instrument calibration errors or damage, or significant electromagnetic interference sources or signals. However, the construction site and the test location were about 400 meters apart, with a significantly different electromagnetic environment, and no neighboring properties or large electrical devices or high-power radiation sources nearby. This possibility also seemed unlikely. 3) There could be issues with construction methods, construction tools, and testing procedures. However, the construction team comprised employees with at least a year of construction experience, and the individual responsible for cable termination had worked with the company for over two and a half years, suggesting they had no technical issues. Visual inspections of termination tools showed no problems, and the termination tools used during construction were not the same as those used in the previously tested cable runs. They temporarily assumed that the products were not the issue and suggested using another DSP4000 cable tester that they had brought and the same model of cable tester owned by the cabling contractor for a comparative test. The results showed that the test results from both testers were quite consistent, indicating that there were no issues with the testers. To pinpoint the location of the problem, they used the DSP4000 cable tester’s “HDTDX” high-precision time-domain crosstalk analysis function and “HDTDR” high-precision time-domain reflection analysis function to analyze fault maps. The results revealed that the “hot spots” of noncompliant parameters were located at the connectors and connecting modules. This indicated that either the connectors and connecting modules had quality issues or there were problems with the construction process. They proceeded to reterminate the connectors and connecting modules in the noncompliant cable runs and tested them again. As a result, all three manufacturers’ products had all passed, with one manufacturer’s 10 cable runs being completely compliant, and the other two having only one noncompliant cable run. They reterminated the noncompliant cable runs once more and conducted a third test, with all of them passing. Subsequently, they diligently retested the 20% of cable runs with parameters close to the edge, and all of them passed. This suggested that the construction process for connectors and connecting modules might be a significant factor in the failure of certification testing.
3. Diagnostic Recommendations
The 360 noncompliant cable runs should be remade with strict quality controls to ensure the project’s quality. Additionally, comprehensive training for construction teams with a strong emphasis on the precision of construction processes should be implemented.
4. Afterword
One week later, the cabling contractor reported that after remaking the cable runs, all 1,800 cable runs had passed certification. In addition to remaking the 360 noncompliant cable runs, the 360 cable runs with parameters close to the edge were also redone. All parameters had margins of 2 dB or higher, and the company planned to use this project as a benchmark for their future work.