Network Engineers

Preventing Problems – Qualification and Certification

Testing cables when installing them or when upgrading networks is the best way to prevent problems. There are two approaches to testing installed cabling.

Qualification testing is determining whether the cabling has the qualifications to do something—in other words, support a certain network speed or application. While a “Pass” on certification testing also ultimately indicates the ability to support a network speed or application per the standards, qualification testing does NOT officially recognize that a cabling link is standards compliant. Qualification testing might be used to determine if a link can support 1000BASE-T, 10GBASE-T, VoIP, PoE or other applications.

Certification testing is typically done by the original installer amd is typically required in order to receive the manufacturer’s warranty. This process determines if a link is compliant with a specific Category or Class of cable as determined by well-defined parameters outlined by relevant standard bodies. For instance, certification testing will determine if your link is compliant with Telecommunications Industry Association Category 6A or International Standards Organization Class EA standards. To certify a link to a standard, a certification tester must test for all of the specific parameters required by the standard. For copper, this includes parameters that go well beyond length, continuity and wiremap testing. We’re talking about parameters such as insertion loss, return loss, near-end crosstalk (NEXT), power sum NEXT, equal-level far-end crosstalk (ELFEXT), attenuation-to-crosstalk ration (ACR) and more. For fiber, it means testing for continuity, polarity, length and insertion loss (Tier 1) or backscatter, reflectance, optical return loss (Tier 2) and more.

Preventing Problems - Documentation and Reporting

Certifying a cabling installation doesn't mean anything without the burden of proof. Documenting the results is the only real way to ensure installation accountability and integrity, resolve disputes and facilitate more efficient troubleshooting.

Even if the customer or a manufacturer's warranty doesn't require documented test results, documentation is still a best practice and your best protection. If you certify a cabling installation that later fails and you don't have the documentation to prove it, how else do you provide evidence that the cable was functioning properly and that it met the specification when you were done with the job?

With today's documentation software, there is no excuse for skipping this critical last step. And it's a good idea to include plot data in your reports. Graphical depiction of measured test parameters is required for true certification testing and typically mandatory for a manufacturer's warranty. These graphs show valuable information about the cabling performance and can be a valuable tool for troubleshooting.

Preventing Problems – Labeling

Without labeling, your documentation will be of little use later on. The ANSI-TIA/EIA 606A labeling standard exists for a reason, and it goes hand in hand with documentation. That is why every work area outlet must be labeled with the floor, telecommunications room, patch panel and port from where it originates.

If you need to troubleshoot a specific link at a later date and check against its original test results, you will need the link's label at the customer location to correspond to the documentation. In fact the 606A standard says that documentation without labeling and labeling without documentation does not equal administration.

Troubleshooting Access Networks

With cabling being the leading cause of network failures, having the right tools and knowledge can keep network outages to a minimum. The right tool can make it easy for even non-experts to track down tough problems.

The most basic cable test tools perform verification - assuring that all wires in a cabling link are connected to the proper termination points and not to any other conductors. Better verification test tools also verify wire pairing and detect installation defects like “split pairs”. Verification test tools may also assist in troubleshooting by providing a toner to locate a cabling link or a Time Domain Reflectometer (TDR) to determine length of a cable or distance to a break or short circuit.

Next are Qualification test tools, such as the CableIQ™ Qualification Tester, which include all the capabilities of verification test tools but they are more powerful in that they perform an assessment of the cabling bandwidth and identify defects that affect the bandwidth.

Certification tools are the most sophisticated tools and provide “Pass” or “Fail” information in accordance with industry standards. They can also troubleshoot highly difficult problems such as unbalance, which can lead to PoE issues.

Preventing Problems - Fiber Cleaning and Inspection

Fiber optics inspection and cleaning is growing in importance as links with increasingly higher data rates are driving decreasingly small loss budgets. With less tolerance for overall light loss, the attenuation through adapters must be lower than ever before. This can be achieved by properly inspecting and cleaning fiber optic cables when they are installed or while making moves, or changes.

Both optical and video scopes can display the contamination or damage that can wreak havoc on fiber communications. Optical microscopes incorporate an objective lens and an eyepiece lens to allow you to view the end-face directly through the device. Video microscopes incorporate both an optical probe and a display for viewing the probe’s image. Probes are designed to be small so that they can reach ports in hard-to-access places

Many people have their own approaches for cleaning end-faces, including some suboptimal approaches such as blasting the fiber optic cable with canned air, or using Isopropyl alcohol (IPA). Fiber-specific solvents are superior at dissolving virtually any contaminate lurking on a fiber end-face and have tailored evaporation rates that give them time to work yet disappear before mating. Click cleaners make it easy for anyone to perform basic cleaning quickly.

Troubleshooting Fiber Networks

Troubleshooting fiber problems requires specialized equipment that ranges from very basic to highly sophisticated. Many network engineers don’t invest in the equipment due to its cost and complexity, instead hiring experts to troubleshoot fiber problems. However, newer tools are available that reduce costs, are simple enough for the occasional user, and can thereby eliminate the cost and wait for the expert.

The most common tool for testing fiber is the combination of Light Source and Power Meter. This pair is used to measure the loss of fiber optic power across the length of the link. If the loss is too great, the signal can’t get through with enough power to be “seen” at the far end.

Unfortunately, the Light Source / Power Meter combination can’t identify the cause of a fiber optic fault. Since connector contamination or damage are likely sources of fiber loss, a manual and time consuming inspection of each connection in the link may find the problem. Visual Fault Locators send a widely dispersed light down the cable, which can be used to find disconnected cables, breaks or even too-tight bends, but require a visual inspection of the entire length of the cable.

The ultimate fiber troubleshooting tool is the Optical Time Domain Reflectometer (OTDR). By sending a pulse of light down the cable and monitoring reflections, if can show the magnitude and distance to every imperfection in the link. Older models displayed complex traces which required a significant level of expertise to interpret. Newer models can interpret the traces and display simple diagrams indicating where the problems are. A recently introduced class of basic troubleshooters uses OTDR-like technology to display the distance to faults along the link.