ansmitters in fiber-optic systems are either Light-Emitting Diodes (LEDs) or lasers. There are several reasons for this: LEDs cost less than lasers. They are commonly used with multi-mode fiber. Lasers provide more power. Thus, less regeneration (amplification) is needed over long distances. At the receiving end, the light detector transducers (receivers) that change light pulses into electrical signals are either positive intrinsic negatives (PINs) or avalanche photodiodes (APDs). LEDs and PINs are used in applications with lower bandwidth and shorter distance requirements. Electrical Property-Disadvantage of Copper Cabling Signals transmitted via copper react to electrical interference or "noise" on the line. Power lines, lights, and electric machinery can all inject noise into the line in the form of electric energy. This is why interference from signals such as copiers, magnetic sources, manufacturing devices, and even radio stations can introduce noise and static into telephone calls and data transmissions. One way to protect copper cabling from noise and crosstalk introduced by nearby wires is to twist each insulated copper wire of a two-wire pair. Noise induced into one wire of the twisted pair cancels an equal amount of noise induced in the other wire of the pair. Crosstalk occurs when electrons that carry the conversations or data along www.TechnicalPDF.com a copper pair cross over, or "leak," on to other nearby wire pairs. Another electrical property of copper wire is resistance. Resistance causes signals to weaken as they are transmitted. This is referred to as attenuation. Attenuation is the reason signals on copper cable in the outside network need to be boosted on cable runs of more than approximately 1.5 miles. Thus, the dual inherent impairments of interference and resistance are the key factors that limit copper's performance. See Table 1-3 for the differences between copper and fiber cabling Copper Cabling Standards: Higher Capacity, Exacting Installation, and Connections Cabling standards have 