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An understanding of the following key points should have been achieved: Waves are energy traveling from one place to another, and are created by disturbances. All waves have similar attributes such as amplitude, period, and frequency. Sine waves are periodic, continuously varying functions. Analog signals look like sine waves. Square waves are periodic functions whose values remain constant for a period of time and then change abruptly. Digital signals look like square waves. Exponents are used to represent very large or very small numbers. The base of a number raised to a positive exponent is equal to the base multiplied by itself exponent times. For example, 103 = 10x10x10 = 1000. Logarithms are similar to exponents. A logarithm to the base of 10 of a number equals the exponent to which 10 would have to be raised in order to equal the number. For example, log10 1000 = 3 because 103 = 1000. Decibels are measurements of a gain or loss in the power of a signal. Negative values represent losses and positive values represent gains. Time-domain analysis is the graphing of voltage or current with respect to time using an oscilloscope. Frequency-domain analysis is the graphing of voltage or power with respect to frequency using a spectrum analyzer. Undesirable signals in a communications system are called noise. Noise originates from other cables, RFI, and EMI. White noise affects all frequencies, while narrowband interference affects only a certain subset of frequencies. Analog bandwidth is the frequency range that is associated with certain analog transmission, such as television or FM radio. Digital bandwidth measures how much information can flow from one place to another in a given amount of time. Its units are in various multiples of bits per second. Most LAN problems occur at the physical layer. The only way to prevent or troubleshoot many of these problems is through the use of cable testers. Proper cable installation according to standards increases LAN reliability and performance. Copper media is available in shielded and unshielded forms. Unshielded cable is more susceptible to noise. Signal degradation is due to various factors such as noise, attenuation, impedance mismatch, and several types of crosstalk. These factors cause decreased network performance. The TIA/EIA-568-B standard specifies ten tests that a copper cable must pass if it will be used for modern, high-speed Ethernet LANs. Optical fiber must also be tested according to networking standards. Category 6 cable must meet more rigorous frequency testing standards than Category 5 cable.