Issue link: https://www.e-digitaleditions.com/i/1066130
January/February 2019 I 49 FIGURE 13: Tier 2 testing of an MPO characterizes individual events, making it an excellent trouble shooting tool. it would be to have the MPO source on the left hand side and then work the way through that cassette with a simplex MPO power meter. That introduces a lot of complexity in terms of referencing and values, and it can get very manual and time consuming. Doing it the first way is very quick and easy. Many of the 24-fiber systems deployed are in the backbone or trunk cabling as opposed to being end-to- end systems. There are 24-fiber end-to-end systems such as 100GBASE-SR10, which is a 100 Gig multimode system using the 24-fiber MPO connector at the optics at the QSFPs. The ICT industry may see more 24-fiber systems come into play where technicians need to be testing those links and channels as 24-fiber. Testing 24-fiber MPO cables requires use of a 2x12 fanout cable. The red and the purple are the 12-fiber ends, and the green is the 24-fiber end (see Figure 12). Connect everything together using a three cord reference method, because the technician cannot plug into the tester with a 24-fiber connector. Connect that all up with the first leg, shown with the red fibers. Set a reference to get to zero dB on the power meter and then work the way through all the trunks, testing one trunk at a time and testing fibers 1 through 12 while working the way through all the trunks that need completed. Once all the trunks for the links or channels have been tested, switch and connect the other side—in this case the purple side or the second leg to the tester. Set another reference. Then, work the way through all the Testing 24f Systems with 12f Tester FIGURE 12: When testing 24-fiber systems with a 12-fiber tester, it is not necessary to test the trunks alone for length/loss. Test the links or channels instead. • Trunks alone do not need to be tested for loss/strength - Test links or channels instead (typically 12f or LC) • Test all trunks (fibers 13-24) MPO Bulkhead Trunk 2x12f to 24f MPO Test Cords MPO Bulkhead trunks again testing fibers 13 to 24 for loss, length and polarity. In this case, work through the set-up with a 12-fiber tester; it is still much faster than using a duplex tester where the technician would have to be doing 12 tests instead of two. For systems, such as the SR4, only the outside eight fibers are used, so 5, 6, 7, and 8 are not used. Again, look at some of the architectures and designs where a 24-fiber trunk cabling is used with cassettes. Those cassettes break down to three eights that go out the equipment. If testing from the front of the cassette, there are really only eight fibers populated on each of the three connectors. The entire 24-fiber trunk is utilized, which is what makes a 24-fiber trunk so efficient. In this case, test from the front of those cassettes. If all of those fibers were turned on, the system would fail from excess loss. What technicians want to have the ability to do on testers is to turn those fibers off, so they do not even test them. They are just completely ignored in terms of the testing and the technician only tests the fibers that are populated. Likewise, in an SR10 system turn off fibers 1 and 12, because those outside fibers may not be used, or in fact, populated. Use the selecting in channels to reflect the typology. TIER 2 TESTING Tier 2 testing offers an optional additional test to Tier 1. Technicians always need to do loss, length and polarity with an optical loss test set (OLTS) including the MPO light sourcing power meters. The advantage of doing a Tier 2 test is that it characterizes each individual event whether it is a splice or a connection, or if it is the cable attenuation (dB per kilometer). Simplex Fiber - connect OTDR module to switch module Launch Cable Receiving Cable Cable Under Test