![]() The extra time taken with the loopback approach to continuity check, OTDR test, disconnect, inspect, reconnect and then test again was more or less the same as the time taken by FiberComplete to perform the automatic exchange of setup data between near- and far-end devices, perform bi-dir testing, and retrieve test results from the far-end unit. There was only a marginal difference in the total test time (which includes all the setup, fiber inspection and actual testing time). ![]() VIAVI has tested both approaches: our fully-automated FiberComplete solution versus the loopback mode on our regular OTDR. With option 1, you do not need to do this as there is an OTDR connected at both ends of the fiber plus there are solutions available (such as the VIAVI FiberComplete application) that will automatically handle testing in both directions to remove any delays that come from manually starting each part of the bi-dir test. You have to run an OTDR test in one direction, pause testing while you disconnect from fiber 1, inspect and connect to fiber 2, then manually restart testing, plus (critically) you have to perform an additional continuity test before the main OTDR test to make sure the loopback device is connected properly. With option 3, there is a manual element to the process. You would be forgiven for immediately choosing option 3. Also, with option 3 you can effectively test two fibers at once – the first fiber from the OTDR at one end and loopback device at the far end, plus the second fiber (obviously using the same ducting or in the same fiber bundle) coming from the far end loopback device to the OTDR location. The first and obvious thing about option 1 is potential cost due to requiring two OTDR versus just one for option 3. The only realistic and practical options, at least in terms of total time to complete testing which includes travel time, are 1 and 3. One unit – that stays put and employs a loopback device to enable bi-dir testing.One unit – that is moved from one end of the link to the other to test both directions.Two units – a true bi-dir approach with one at each end of a link under test.Bi-dir OTDR testing allows you to average out these manufacturing/ backscattering/ measurement differences to give true event loss, helping you diagnose whether a splice, connector or section of fiber really is a problem and needs to be replaced, potentially saving you time and money or stopping you from abandoning a good fiber link.Īs there is a clear benefit to bi-dir OTDR testing, the question is: what’s the best way to go about it and are there any limitations? You can generally choose between three use cases: Testing from the other end (far end) of the fiber link would reveal that second event so you have a more accurate view of what is in the real/actual fiber link.ĭifferences between fiber manufacturers or even manufacturing batches can lead to variances in the backscatter coefficient of a fiber and when spliced to another fiber results in a ‘gainer’. There are a number of reasons to perform bi-dir test and when it comes to the OTDR piece the basics are that it gives more accurate measurements, can reveal more detail and correctly diagnose issues (or non-issues), for example:īi-dir OTDR fiber tests can reveal events hidden by OTDR dead zones where events that are close together could be missed and shown as a single event, the reflected (or backscattered) light from the first event means that the light reflected by a nearby event, just after the first, is swamped or missed by the OTDR. We’ve touched on bi-directional (bi-dir) fiber testing in previous blogs where we looked at bi-dir fiber testing and how to cut test times in half. ![]() The most thorough approach in these cases is to check and certify fibers bi-directionally, but as the saying goes there is more than one way to crack an egg, leading to many questions: do different bi-directional (bi-dir) test methods achieve the same end-goal, do they perform the same in terms of total testing time, is one approach better than another, or is one approach more suited for a specific application? ![]() If it’s existing networks, that means checking that fibers are still in good shape and that nothing has changed significantly since original deployment (remember that accidents and damage do occur and sections may have been replaced/repaired). If it’s a new link or network, that means verifying that fibers have been laid and spliced correctly in the first place. One thing that is critical for these new or upgraded services to function to their peak and with maximum reliably is that the physical layer fiber networks they are built on have no flaws. There are any number of things you can point to that demonstrate what is driving growth in fiber deployment, regional FTTH/PON initiatives, national high-speed broadband growth, core network 100/400G upgrades, or preparation for new services such as 5G.
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