Adding revenue with fibre

Harley Lang III, marketing manager at Fluke Networks discusses the ways in which contractors can add to their revenue and profits by choosing an easy way to fibre certification.

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By  Harley Lang III Published  December 3, 2007

The growing need for network bandwidth means that many projects now have a fibre component. A requirement for fibre certifications is Optical Time Domain Reflectometery (OTDR) that goes beyond simple loss measurements to certify the workmanship of individual splices and connectors. But many legacy OTDR instruments are expensive and may require an expert to interpret the results.

As a result, many contractors are not able to bid on fibre installation projects even though the margins on fibre are substantially higher than the copper portion of the project. Other contractors handle fibre certification by hiring a subcontractor or use in-house technicians that specialise in fibre certification. Either of these approaches add costs, which makes it difficult to maintain the profitability.

Copper certification tools

Up to now, most contractors have focused on copper installation because it constituted such a large proportion of the available work. Analysers that integrate capabilities such as cable certification and link connectivity in a single instrument have enabled contractors to substantially reduce the cost of copper cable installation.

While copper has dominated the market, fibre will establish a larger market share soon in structured cabling applications for datacentres and campuses.

These instruments are typically used to certify the cable infrastructure by ensuring that it meets TIA/ISO standards requirements. They can also ensure that service can be activated by verifying network service availability and link connectivity to the network. Lastly, all test results are documented onto one consolidated report.

By providing a complete solution that streamlines every aspect of the certification job - setup, testing, troubleshooting, and reporting results - these integrated instruments substantially improve technician productivity. Instruments such as these can perform Cat 6 certification tests to full compliance to industry standards in as little as nine seconds. When a link fails, the new generation of testers provides quick and easy-to-understand directions to identify the point of failure in terms of distance on the link and the possible reasons for the failure. These directions identify corrective actions that test technicians can take to solve the problem quickly without having to consult the project manager.

Increasing role played by fibre

Over the same time period that these substantial improvements have been made in copper testing and certification, an increasing percentage of network installation contracts have come to include fibre as well as copper. While copper has dominated the market up to now, fibre will establish a larger market share in structured cabling system applications for datacentres, campuses and fibre-to-the-home. In addition, fibre will continue to be common in riser cabling systems.

However, fibre to the desktop (FTTD) will continue to amount to a very small percentage of the total horizontal cabling subsystem market in the future.

FTTD will be found mainly in niche applications in which gigabit speeds are required for applications such as computer aided design or computer aided manufacturing terminals or workstations handling video feeds. So it is expected that a significant mix of both copper and fibre media will remain in structured cabling systems.

Requirements of fibre certification

With fibre playing an increasing role in most projects, the subject of fibre certification is becoming increasingly important to cabling contractors in the region.

Certification recommendations such as TIA's TSB140 bulletin titled "Additional Guidelines for Field-Testing Length, Loss and Polarity of Optical Fibre Cabling Systems" provide guidelines on how to test fibre optic cabling systems in the field, offering two tiers of fibre network certification. Basic or Tier 1 fibre certification is required in all fibre optic cabling links.

The Tier 1 tests are attenuation (insertion loss), length and polarity. When conducting Tier 1 testing, each fibre link is measured for attenuation and results are documented. This test ensures that the fibre link exhibits less loss than the loss budget allows for the application.

Tier 2 fibre certification

Today, many network designers are including a requirement that Tier 2 fibre certification be performed by taking an OTDR trace of each fibre link. An OTDR trace is a graphical signature of a fibre's attenuation along its length. An OTDR transmits an optical pulse through the installed optical fibre and measures the fraction of light that is reflected due to Rayleigh scattering and Fresnel reflection. The OTDR displays the backscattered and reflected optical signal as a function of length.

By comparing the amount of light reflected back at different times, the OTDR can determine fibre and connection losses and reflectivity. By analysing the OTDR plot of trace, users can measure the attenuation and transmission loss between any two points along the cable plant. Technicians can also measure insertion loss and reflectance of any optical connection. The OTDR trace can also be used to locate fibre breaks or faults.

OTDR traces have several common characteristics. Most traces begin with an initial input pulse that is a result of a reflection occurring at the connection to the OTDR. Following this pulse, the ODTR trace is a gradual curve sloping downward that may be interrupted by gradual shifts. The gradual decline results from Rayleigh scattering as light travels along each fibre section. This decline is interrupted by sharp shifts that represent a local deviation of the trace in the upward or downward direction. These shifts or point defects are usually caused by connectors, splices or breaks. Finally the output pulse at the end of the OTDR trace results from a reflection occurring at the output fibre-end face.

Insight can be gained into the performance of the link components and the quality of the installation by examining non-uniformities in the trace. An OTDR trace does not replace the need for insertion loss measurement, but it complements the Tier 1 evaluation of the fibre link. Tier 2 testing makes it possible to certify that the workmanship and quality of the installation meets the design and warranty specifications for current and future applications.

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