One Is NOT The Loneliest Number
Business and consumer demand for bandwidth-intensive services such as video streaming, VoIP, HDTV, and smart-device applications continues to grow rapidly with no end in sight. To address this growth, service providers are scrambling to quickly deploy, expand, and upgrade their broadband access networks.
Ensuring the healthiness of the fiber network and making sure that it performs well requires a number of tests. Before activating the network system, technicians and contractors have to measure a wide variety of network parameters including insertion loss, distance, and optical return loss to verify compliance with system-manufacturer specifications. To minimize deployment costs and testing times for both installation and network maintenance, providers must equip technicians with the right testing tools.
This article discusses practical test-and-measurement best practices using an all-in-one testing strategy. This solution combines tests such as bidirectional insertion loss (IL), optical return loss (ORL), and optical time domain reflectometry (OTDR), performing measurements automatically through a single connection port. The objective is to provide a technician with an improved system so he/she can perform all the tasks needed to install, turn up, and maintain metro and access point-to-point (P2P) and point-to-multipoint (PON) networks quickly.
Implementing an all-in-one test solution strategy has the potential to lower capital expenses (CapEx) by reducing the number of instruments that technicians must carry into the field. This reduces operational expenses (OpEx) by reducing testing time by more than 40% and facilitating faster resolution of optical link issues. This strategy could also help providers minimize training times, lessen testing time with fewer connections and disconnections, and optimize workflows.
Traditional fiber test strategies include the need for examination of the following: end-face inspection, optical power level, IL, ORL, and OTDR. These tests occur at different stages of the network lifecycle. Therefore, we’ll explore a better strategy that can be used during 3 phases of fiber deployment:
Phase 1: Construction/Splicing
Phase 2: Acceptance
Phase 3: Maintenance
Ideally, technicians would utilize an approach that would allow an all-in-one tool to flexibly span construction and troubleshooting applications. The technician could use it as a one-ended tester to do OTDR, power level measurement, video inspection, and source provisioning.
When the objective is to perform complete fiber-link acceptance testing, this improved strategy could also pair one technician with another technician. With one test connection on each end, the paired techs could automatically confirm continuity and perform a complete set of IL, ORL, and OTDR tests. Technicians could perform these tests uni- and bi-directionally, having the OTDR traces from both ends. This would allow them to instantly assess a problem in case IL or ORL tests fail.
During the construction phase of optical networks, installers and contractors commonly use an OTDR to characterize optical links and measure splices. Ideally, a single installer should be able to perform integrated testing functions that provide both averaged and real time results to instantaneously validate splice loss, connectors’ loss, and reflectance, as well as locate any undesired events such as bends.
Once a link is spliced and connectorized, the installer needs to provide a complete report that validates fiber-link performance. A loss test set (a light source and power meter) validates that the overall link loss meets network-equipment operational specifications.
An ORL meter is also often required if a link is expected to be operated at a high-speed data rate (10 G+) or with high-power RF video transmissions. If the back reflection for these networks is too high, ORL can affect the transmitted signal, creating a high rate of bit errors (BER) as well as damaging the transmitter itself.
Very often, installers need OTDR traces at 1310/1550 nm to record a “picture” of the network that proves proper cable installation. Some cases require bi-directional-OTDR analysis to get true and accurate splice values. The combination of bi-directional measurements, OTDR from both extremities of the optical fiber link, and analysis takes into account fiber-section performance differences such as core diameters, back-scattering coefficients, and other optical mismatches.
Even if an OTDR trace is not required, if IL or ORL tests do not meet specification requirements, an OTDR/fault finder must be used to determine why and where a problem or failure originates.
An improved approach would include an all-in-one tester that provides instantaneous troubleshooting without disconnection or reconnection. As soon as an IL and/or ORL value reaches a predefined threshold, the tester’s OTDR or fault finder would launch. The OTDR would provide a detailed view of the link with a table of all events. A fault finder would directly identify the worst issue (bend, connector, splice, and reflectance), avoiding a detailed interpretation of the trace.
For loss measurement, technicians usually work in pairs. One person is at each end of the fiber link. This improved testing strategy allows simultaneous IL, ORL, and OTDR tests either uni- or bi-directionally: one connection at each end. Auto-store and fiber incrementing adds more automation to further speed the acceptance process.
Maintenance and Troubleshooting
During the maintenance phase, technicians must check a transmitter’s output power and validate that the light at the receiver side is strong enough for the system to properly function.
Also, in case of high-BER issues, technicians should measure ORL from a central office or head end. If the power level at the receiver side and/or the ORL value is too low, then an improved strategy would have an OTDR that could locate and determine the extent of the problem (for example, a cable cut, macro-bend, or bad connector pair).
This all-in-one testing strategy would integrate a power meter, ORL meter, and an OTDR on a single port, enabling single-connection, one-button troubleshooting. This would greatly simplify and speed the troubleshooting process, enabling faster network recovery.
Test Strategies Should Not Test Providers’ Patience
CapEx and OpEx are major concerns for network operators. An all-in-one test strategy simplifies and speeds up fiber testing while improving productivity by offering the features and benefits that makes technicians’ day-to-day jobs easier.
An all-in-one testing strategy is an investment not only for today’s requirements, but also for future needs. One example of such a system is called FiberComplete™ from JDSU. This system also streamlines reporting capabilities -- an especially important feature with a large number of fiber deployments.
The bottom line is simple: Today’s providers must increase technician and installer efficiency while reducing their expenses AND delivering great service to their end user. Fiber-testing strategies have evolved to meet their needs and improve the productivity of their field teams. So, now ONE technician is not quite as lonely as he or she used to be in the OSP.
Figure 1. OTDR measurement.
Figure 2. Bi-directional loss, ORL and OTDR testing.
Figure 3. Typical link acceptance procedure vs. JDSU FiberComplete™ procedure.
Insertion Loss (IL)
Power loss, in dB, of lightwave passing through the optical fiber under test (FUT). It is defined as the ratio of transmitted power to incident power.
Optical Return Loss (ORL)
A measure of the reflectance of a FUT which represents, what fraction of the incident lightwave signal is scattered back to the source. It is defined as the ratio, in dB, of the reflected power to the incident power from FUT.
Charlène Roux is a Product Line Manager for JDSU specializing in fiber network test applications and solutions. She has been in the Fiber Communications Industry for 5 years, involved in field portables, from market analysis to development and production. For more information about JDSU, please visit www.jdsu.com.
Tim Yount is a Product Marketing Manager for JDSU, specializing in fiber network test applications and solutions. He has been in the Fiber Communications Industry for more than 25 years, involved in production and lab as well as field and monitoring applications. He lives in South Portland, Maine. He has been with JDSU since 2004. For more information about JDSU, please visit www.jdsu.com.
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