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Maintenance & Testing – Tools of the Trade (March 01, 2000)

A New Class of Tools for Multimode Fiber Lan Cable Testing Has Been Developed. These Testers Just Might Be the Most Productive to Date.


March 1, 2000  


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Fiber is beginning to appear in traditional ‘UTP territory’. And it is gaining in its share of premise LAN applications, due to its superior bandwidth and the ongoing improvements in fiber optic technology.

Premise LAN fiber is predominantly multimode, primarily 62.5/125 m and 50/125 m. Application and commercial building standards have been ratified to support common platforms for fiber LAN architectures. These standards specify optical power measurement equipment for measuring the loss of an installed multimode cable plant.

A new class of measurement equipment, optimized for testing multimode LAN cable in accordance with these industry standards, has been developed. These new tools are more productive, easier to use, and are more reliable than the tools traditionally used for fiber cable measurement.

COSTS COMING DOWN

Fiber has superior information carrying capacity compared to structured UTP cable, but the cost of optoelectronics previously made fiber cost-prohibitive for all but the most bandwidth-intensive or specialty applications. This is changing.

Fiber 100 Mbps Ethernet NICs are now available for under $100 and new economical VCSEL sources promise higher speed transmission. The costs of optical transceivers and fiber-based hub concentrators are steadily falling. There have also been continual improvements in fiber connectivity technology. New small form factor connectors offer high fiber density and an affordable approach to network design. And new multimode fiber designs are available for transmitting high data rates over long distances with laser-based light sources.

To support the use of optical fiber in LAN, various industry organizations are engaged in writing standards that define the performance requirements of installed fiber cable plants. Standards generally fall into one of two categories: application standards and commercial building standards. An application standard defines the performance requirements for a particular transmission protocol. Ethernet (IEEE 802.3), FDDI (ANSI) and Fiber Channel (ANSI) are examples. Commercial building standards, such as TIA/EIA-568-A and ISO/IEC 11801, provide generic performance criteria for a premise communications cabling system.

When evaluating the quality of an installed fiber optic LAN cabling network, the actual performance should be compared to the requirements of an industry standard to ensure that the cabling system will effectively support network communications. These standards define the maximum supportable distance and maximum channel attenuation at the appropriate operating wavelengths.

NEW CLASS OF EQUIPMENT

A new class of measurement equipment was developed to optimize premise multimode fiber LAN testing. These new tools measure length and channel attenuation as required by the standards, and they utilize the end-to-end technique to measure optical loss. This technique is accurate, reliable and conforms to the standards.

These tools feature a main and remote optical loss test set, each incorporating a dual wavelength 850/1300 nm source and meter, working in unison to test fiber links. This methodology allows the loss and length of the test jumpers to be excluded from the loss and length of the true fiber link. Two fibers, a Tx/Rx pair, are tested simultaneously to speed network testing. This is important in a fiber rich premise plant with many drops and branches. Bi-directional testing of each fiber is accomplished by swapping the Tx/Rx connectors at the cross connect, avoiding the walk to exchange source and meter units, which is required when using dedicated sources and meters. Time-of-flight techniques measure optical length, yielding an immediate, accurate result without interpretation or manipulation of cursors.

Not only do these new tools provide reliable loss and length measurements quickly, the tester compares the results against a standard selected by the user from a built-in LAN standards list. The tester immediately displays a ‘pass’ or ‘fail’ indication based upon the comparison. The new test tools and the supporting PC software enable the user to print summary or detailed certification reports.

The typical test procedure is as follows:

Daily Set-Up Procedure

1)Select the appropriate industry standard from the built-in list. Custom, user-defined standards can also be created.

2)Select one-way or bi-directional link testing.

3)Enter the job name and operator name.

4)Enter the group index of refraction for the fiber under test.

5)Select metric or English units for length measurement.

6)Select the language set for the user interface: English, French, German, Spanish or Italian.

7)Interconnect main and remote units with test jumpers and adapters (if any).

8)Make a reference measurement.

Fiber Measurement Procedure

1)Connect the main unit to a Tx/Rx fiber pair in the main cross connect facility and connect the remote unit to the corresponding fiber pair at the far end cross connect/outlet.

2)Push the Autotest button to initiate the test.

3)Save the results for each fiber by intelligent job and circuit ID names.

Repeat step until all fibers are tested.

Daily set-up tasks typically require less than five minutes. Only those items that differ from testing the previous day must be set.

The Autotest is completed in seven seconds. The test equipment measures the optical loss of two fibers (Rx and Tx) at two wavelengths (850 nm and 1300 nm) in one direction. It measures the optical length and calculates the optical loss budget if a formula-based standard was selected. The test tool internally compares results against the selected standard and calculates the margin. A ‘pass’ or ‘fail’ indication is provided for each fiber — all in only seven seconds. Results for both fibers can be saved in less than 30 seconds.

The speed in which you obtain an accurate, reliable result makes these new fiber LAN testers stand out from traditional fiber test equipment, particularly in terms of productivity and time savings. Test times are cut by 75 per cent over traditional power meter techniques.

THE REPORTING PROCESS

Network professionals require the presentation of test results in an easy-to-read format. A premise LAN test report includes the actual measured loss and length, the loss and length limits, and the margin between the two. Any individual test that exceeds the selected industry criteria is highlighted with a ‘fail’ notation. An intelligent circuit ID is assigned to each fiber. The report includes the applicable reference method, information specific to the project, fiber cable information and test equipment information.

The new LAN cable testers simplify the reporting process by including PC software written specifically for the LAN environment. A report showing that all fibers passed the selected criteria is proof that the network is “certified” for operation. The software prints summary or detailed certification reports. It provides the report in hard copy or electronic file format. The software is also capable of exporting the data in spreadsheet- and database-compatible format.

The new testers are hand-held, portable and designed for field use. Their compact size and lightweight is well suited for testing in communication closets and confined spaces. Temperature-compensated components permit stable, accurate operation over a wide temperature range. Long battery life assures hours of uninterrupted testing.

The use of fiber cable in premise LAN applications will continue to grow as associated network components continue to decline in price, improve in performance and are made easier to use. The new test tools, specifically designed to test premise multimode networks, make LAN cable testing simple, fast and accurate.CS

Eric Anderson is a Senior Product Manager at Microtest of Phoenix, AZ, where he is responsible for fiber optic cable test equipment. Anderson has 15 years of experience in the design, manufacture and application of fiber cable, passive optical components and test equipment.


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