12
FLUKE NETWORKS
T IS THIS FIBRE LINK GOOD?
THAT’S A COMMON QUESTION, BUT THE RESPONSE MIGHT BE “GOOD FOR WHAT?” WERNER HEEREN, REGIONAL SALES DIRECTOR AT FLUKE NETWORKS, LOOKS AT HOW THE PERFORMANCE OF FIBRE LINKS CAN BE DETERMINED.
CABLING INSIGHT
HE ATTENUATION OR “LOSS” OF A FIBER link is the primary determinant of its ability to carry traffic. That sounds simple, but things quickly get more complicated than that. Let’s look at how the performance of fiber links is determined and how you determine if it’s “good”. When you put a signal into one end of a fiber, the signal that comes out the other end is smaller. The difference between the input and the output signals is called insertion loss. If there is too much loss, the signal coming out the end of the fiber will be too small for the receiver to interpret. Loss is expressed in decibels or dB, where every halving of the signal strength is represented by 3 dB. If the output signal is half of the input, that’s 3 dB of loss, ¼ is 6 dB of loss, etc. HOW MUCH LOSS IS TOO MUCH? The TIA and ISO define a loss limit or budget based on the length of the fiber and the number of connectors and splices. There are multiple versions of these parameters for different types of connectors and fiber, so for this example, we’ll use OM5 multimode fiber, which has the same limits in the TIA and ISO (Table 1). To calculate the loss budget of a link, just perform a calculation as shown:
