Issue link: https://www.e-digitaleditions.com/i/1386104
20 I ICT TODAY POLARITY TESTING IS ESSENTIAL For fiber links to properly send data, the transmit signal at one end of the cable must match the corresponding receiver at the other end. The purpose of any polarity scheme is to ensure this continuous connection. While it is straightforward with duplex connectivity, it becomes a bit more complex when dealing with MPO connec- tivity as now multiple transmitting fibers need to each correspond to their receive fiber. Industry standards on polarity include TIA-568 and ISO/IEC 14763-3 and call out three different polarity methods: Method A, Method B, and Method C. • Method A uses Type A straight-through MPO trunk cables with a key up connector on one end and a key down connector on the other end so that the fiber located in Position 1 arrives at Position 1 at the other end. When using Method A for duplex applications, making the transceiver-receiver flip is required in a patch cord at one end. • Method B uses key up connectors on both ends to achieve the transceiver-receiver flip so that the fiber located in Position 1 arrives at Position 12 at the opposite end, the fiber located in Position 2 arrives at Position 11 at the opposite end and so on. For duplex applications, Method B uses straight A-B patch cords on both ends. • Method C uses a key up connector on one end and a key down on the other end like Method A, but the flip happens within the cable itself where each pair of fibers is flipped so that the fiber in Position 1 arrives at Position 2 at the opposite end and the fiber in Position 2 arrives at Position 1. While this method works well for duplex applications, it does not support parallel optic applications and is, therefore, not recommended (Figure 1). With three different polarity methods and the need to use the correct type of patch cords for each, deploy- ment mistakes can be common. Today's data centers are also more complex with various concatenated links, which further complicates polarity. Therefore, having a fiber tester that can test individual patch cords, permanent links, and channels for correct polarity is essential for testing in today's data center. Key Up Key Down Type A (Straight) Key Up Key Up Type B (Reversed) Key Up Key Down Type C (Pairs Flipped) FIGURE 1: With the increase of MPO connectivity that encompasses three different polarity methods, using a fiber tester that can test for correct polarity is becoming essential.