Efficient fiber optic restoration depends on finding the problem, knowing how to fix it, having the right parts, and getting it all done quickly. Like any type of emergency, planning ahead will minimize the problems encountered.
Documentation is the most helpful thing you can have when trying to troubleshoot a fiber network. Start with the manufacturer’s datasheets on every component you use: electronics; cables; connectors; hardware, such as patch panels; splice closures; and even mounting hardware. Along with the data, one should have the manufacturer’s helpline contact information, which will be of immense value during restoration (for more on documentation, see the October 2008 Fiber Optics column).
During installation, mark every fiber in every cable at every connection, and keep records using cable plant documentation software or a simple spreadsheet of where every fiber goes. When tested, add loss data taken with an optical loss test set (OLTS) and optical time domain reflectometer (OTDR) data when available. Someone must be in charge of this data and keep it up-to-date.
Next, you must have proper test equipment available. An OLTS also should have a power meter to test the power of the signals to determine if the problem is in the electronics or cable plant. Total failure of all fibers in the cable plant means a break or cut in the cable. For premises cables, finding the location often is simple if you have a visual fault locator (VFL), which is a bright red laser coupled into the optical fiber that allows testing continuity, tracing fibers or finding bad connectors at patch panels.
For longer cables, an OTDR will be useful. Outside plant networks should use the OTDR to document the cable plant during installation, so during restoration, a simple comparison of installation data with current traces will usually find problems. OTDRs also can find noncatastrophic problems, e.g., when a cable is kinked or stressed, so it only has higher loss, which also can cause network problems.
Once you find the problem, you have to repair it. Repair requires having the right tools, supplies and trained personnel available. Besides the test equipment needed for troubleshooting, you need tools for splicing and termination, which may include a fusion splicer for outside plant cables. You also need matching components. For every installation, a reasonable amount of excess cable and installation hardware should be set aside in storage for restoration. Some users store the restoration supplies along with documentation in a sealed container ready for use. Remember the fiber optic patchcords that connect the electronics to the cable plant can be damaged and are not considered repairable. Just keep replacements available.
One big problem is pulling the two cable ends close enough to allow splicing them together. You need about 1 meter of cable on each end to strip the cable, splice the fibers and to place them in a splice closure. Designing the cable plant with local service loops is recommended. If the cable ends are too short, you have to splice in a new section of cable, which should be kept from the leftovers after installation.
What else besides cables and cable plant hardware should be in a restoration kit? You should have a termination or mechanical splice kit and proper supplies. For splices, you need splice closures with adequate space for a number of splices equal to the fiber count in the cable. All these should be placed in a clearly marked box with a copy of the cable plant documentation and stored in a safe place where those who will eventually need it can find it fast.
Personnel must be properly trained to use this equipment and do the troubleshooting and restoration. And, of course, they must be available on a moment’s notice. The biggest delay in restoring a fiber optic communications link is often the chaos that ensues while personnel figures out what to do. Having a plan that is known to the responsible person is the most important issue.
Major users of fiber optics have restoration plans in place, personnel trained and kits of supplies ready for use. It’s doubtful that most premises users are ready for such contingencies. Users may find that the cost of owning all this expensive equipment is not economic. It may be preferable to keep an inexpensive test set consisting of a VFL and OLTS at each end of the link and have an experienced contractor on call for restoration.
HAYES is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at www.JimHayes.com.