Concept Exercise Chapter 4 Name: Date: Class: Cisco Exercises - Semester 1 - Networking Fundamentals Chapter 4 Electronics and Signals Introduction Electricity is a fact of modem life. We use it to perform a variety of tasks. It is brought to our homes, schools, and offices by power lines that carry it in the form of alternating current or AC. Another type of current called direct current, or DC, is the kind found in a flashlight, car battery, and on the motherboard of a computer. It is important to understand the difference between these two types of current flow. Direct current flows at a constant value when circuits are turned on. Alternating current rises and falls in current values as it is manufactured by power companies. Once it reaches our homes, schools, and offices, electricity is carried to appliances and machines via wires concealed in walls, floors, and ceilings. Consequently, inside these buildings, AC power line noise is all around us. If not properly addressed, power line noise can present problems for a network. In fact, as you will discover the more you work with networks, AC line noise coming from a nearby video monitor or hard disk drive can be enough to create errors in a computer system. It does this by burying the desired signals and preventing a computer's logic gates from detecting the leading and trailing edges of the square signal waves. This problem can be further compounded when a computer has a poor ground connection. The third type of electricity is static electricity. This most damaging uncontrollable form of electricity must be dealt with in order to protect sensitive electronic equipment. Such static discharges can destroy semiconductors and data in a seemingly random fashion as they shoot through a computer like bullets. As it can with problems related to AC line noise, good grounding can help solve problems that arise from electrostatic discharge. Concept Questions Demonstrate your knowledge of these concepts by answering the following questions in the space provided. Each wire in a cable can act like an antenna. When this happens, the wire actually absorbs electrical signals from other wires in the cable and from electrical sources outside the cable. If the resulting electrical noise reaches a high enough level, it can become difficult for NIC cards to discriminate the noise from the data signal. When electrical noise on the cable originates from signals on other wires in the cable, this is known as crosstalk. How can you minimize crosstalk? To ensure optimal performance, it is important for the network media to carry the signal from one device to another with as little degradation as possible. In networking, there are several factors that can cause the Signal to degrade. Some of these factors are internal. Others are external. Name some of the factors that can cause a signal to degrade and how to correct the problem. Inside copper wires, factors such as opposition to the flow of electrons (resistance), opposition to changes in voltage (capacitance), and opposition to changes in current (inductance), can cause signals to degrade. External sources of electrical impulses that can attack the quality of electrical signals on the cable include lighting, electrical motors, and radio systems. These types of interference are referred to as electromagnetic interference, or EMI, and radio frequency interference, or RFI. How can you protect your network from RFI?