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CCNA1 Module 3. Topics. Objectives. Discuss the electrical properties of matter. Define voltage, resistance, impedance, current, and circuits. Describe the specifications and performances of different types of cable.
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Objectives • Discuss the electrical properties of matter. • Define voltage, resistance, impedance, current, and circuits. • Describe the specifications and performances of different types of cable. • Describe coaxial cable and its advantages and disadvantages over other types of cable. • Describe shielded twisted-pair (STP) cable and its uses. • Describe unshielded twisted-pair cable (UTP) and its uses.
Discuss the characteristics of straight-through, crossover, and rollover cables and where each is used. • Explain the basics of fiber-optic cable. • Describe how fibers can guide light for long distances. • Describe multimode and single-mode fiber. • Describe how fiber is installed. • Describe the type of connectors and equipment used with fiber-optic cable. • Explain how fiber is tested to ensure that it will function properly. • Discuss safety issues dealing with fiber-optics.
Periodic Table of Elements Copper(Cu),Silver(Ag), and Gold (Au)
Periodic Table The periodic table categorizes some groups of atoms by listing them in the form of columns. The atoms in each column belong to particular chemical families. Although they may have different numbers of protons, neutrons, and electrons, their outermost electrons have similar orbits and behave similarly when interacting with other atoms and molecules. The best conductors are metals, such as copper (Cu), silver (Ag), and gold (Au), because they have electrons that are easily freed. Other conductors include solder, a mixture of lead (Pb) and tin (Sn), and water with ions. An ion is an atom that has more electrons, or fewer electrons, than the number of protons in the nucleus of the atom. The human body is made of approximately 70% water with ions, which means that the human body is a conductor.
Atoms and Electrons • Electrons – Particles with a negative charge that orbit the nucleus • Nucleus – The center part of the atom, composed of protons and neutrons • Protons – Particles with a positive charge • Neutrons – Particles with no charge (neutral)
The protons and neutrons are bound together by a very powerful force. However, the electrons are bound to their orbit around the nucleus by a weaker force. Electrons in certain atoms, such as metals, can be pulled free from the atom and made to flow. This sea of electrons, loosely bound to the atoms, is what makes electricity possible. Electricity is a free flow of electrons. Loosened electrons that stay in one place, without moving, and with a negative charge, are called static electricity. If these static electrons have an opportunity to jump to a conductor, this can lead to electrostatic discharge (ESD).
ESD, though usually harmless to people, can create serious problems for sensitive electronic equipment. A static discharge can randomly damage computer chips, data, or both. The logical circuitry of computer chips is extremely sensitive to electrostatic discharge. Use caution when working inside a computer, router, and so on. Atoms, or groups of atoms called molecules, can be referred to as materials. Materials are classified as belonging to one of three groups depending on how easily electricity, or free electrons, flows through them. The basis for all electronic devices is the knowledge of how insulators, conductors and semiconductors control the flow of electrons and work together in various combinations.
Resistance and Impedance The term attenuation is important when learning about networks. Attenuation refers to the resistance to the flow of electrons and why a signal becomes degraded as it travels along the conduit. The letter R represents resistance. The unit of measurement for resistance is theohm. The symbol comes from the Greek letter omega.
Impedance is also measured in ohms, but takes into account the capacitive reactance and inductive reactance and resistive effects of the cable. This is a more realistic measurement of how a cable will respond to AC signals.
Current If amperage or current can be thought of as the amount or volume of electron traffic that is flowing, then voltage can be thought of as the speed of the electron traffic. The product of amperage and voltage equals wattage. Electrical devices such as light bulbs, motors and computer power supplies are rated in terms of watts. A watt is how much power a device consumes or produces.
For AC and DC electrical systems, the flow of electrons is always from a negatively charged source to a positively charged source. However, for the controlled flow of electrons to occur, a complete circuit is required. Remember, electrical current follows the path of least resistance.
Oscilloscope An oscilloscope is an electronic device used to measure electrical signals relative to time. An oscilloscope graphs the electrical waves, pulses, and patterns. An oscilloscope has an x-axis that represents time, and a y-axis that represents voltage. There are usually two y-axis voltage inputs so that two waves can be observed and measured at the same time.
Cables Specs 10BASE-T refers to the speed of transmission at 10 Mbps. The type of transmission is baseband, or digitally interpreted. The T stands for twisted pair. 10BASE5 refers to the speed of transmission at 10 Mbps. The type of transmission is baseband, or digitally interpreted. The 5 represents the capability of the cable to allow the signal to travel for approximately 500 meters before attenuation could disrupt the ability of the receiver to appropriately interpret the signal being received. 10BASE5 is often referred to as Thicknet. Thicknet is actually a type of network, while 10BASE5 is the cabling used in that network.
10BASE2 refers to the speed of transmission at 10 Mbps. The type of transmission is baseband, or digitally interpreted. The 2, in 10BASE2, represents the capability of the cable to allow the signal to travel for approximately 200 meters, before attenuation could disrupt the ability of the receiver to appropriately interpret the signal being received. 10BASE2 is often referred to as Thinnet. Thinnet is actually a type of network, while 10BASE2 is the cabling used in that network.
Unshielded twisted-pair cable has many advantages. It is easy to install and is less expensive than other types of networking media. In fact, UTP costs less per meter than any other type of LAN cabling. However, the real advantage is the size. Since it has such a small external diameter, UTP does not fill up wiring ducts as rapidly as other types of cable. This can be an extremely important factor to consider, particularly when installing a network in an older building. In addition, when UTP cable is installed using an RJ-45 connector, potential sources of network noise are greatly reduced and a good solid connection is practically guaranteed.
There are disadvantages in using twisted-pair cabling. UTP cable is more prone to electrical noise and interference than other types of networking media, and the distance between signal boosts is shorter for UTP than it is for coaxial and fiber optic cables. UTP was once considered slower at transmitting data than other types of cable. This is no longer true. In fact, today, UTP is considered the fastest copper-based media.
Wavelength The light used in optical fiber networks is one type of electromagnetic energy. When an electric charge moves back and forth, or accelerates, a type of energy called electromagnetic energy is produced. This energy in the form of waves can travel through a vacuum, the air, and through some materials like glass. An important property of any energy wave is the wavelength.
Visible Light Spectrum W= 300,000,000m/s / freq W=700 nm F=428.5 THz W=400 nm F=750 THz 1x10^12 Hz = 1 TeraHz
Human eyes were designed to only sense electromagnetic energy with wavelengths between 700 nanometers and 400 nanometers (nm). A nanometer is one billionth of a meter (0.000,000,001 meter) in length. Electromagnetic energy with wavelengths between 700 and 400 nm is called visible light. The longer wavelengths of light that are around 700 nm are seen as the color red. The shortest wavelengths that are around 400 nm appear as the color violet. This part of the electromagnetic spectrum is seen as the colors in a rainbow.
Wavelengths that are not visible to the human eye are used to transmit data over optical fiber. These wavelengths are slightly longer than red light and are called infrared light. Infrared light is used in TV remote controls. The wavelength of the light in optical fiber is either 850 nm, 1310 nm, or 1550 nm. These wavelengths were selected because they travel through optical fiber better than other wavelengths. 850nm light is called short wave (1000baseSX). 1550nm light is called long wave (1000baseLX).
Think of light rays as narrow beams of light like those produced by lasers. In the vacuum of empty space, light travels continuously in a straight line at 300,000 kilometers per second. However, light travels at different, slower speeds through other materials like air, water, and glass. When a light ray called the incident ray, crosses the boundary from one material to another, some of the light energy in the ray will be reflected back. That is why you can see yourself in window glass. The light that is reflected back is called the reflected ray.
The light energy in the incident ray that is not reflected will enter the glass. The entering ray will be bent at an angle from its original path. This ray is called the refracted ray. How much the incident light ray is bent depends on the angle at which the incident ray strikes the surface of the glass, and the different rates of speed at which light travels through the two substances A material with a large index of refraction is more optically dense and slows down more light than a material with a smaller index of refraction.
The Law of Reflection states that the angle of reflection of a light ray is equal to the angle of incidence. In other words, the angle at which a light ray strikes a reflective surface determines the angle that the ray will reflect off the surface.
If the incident ray strikes the glass surface at an exact 90-degree angle, the ray goes straight into the glass. The ray is not bent. However, if the incident ray is not at an exact 90-degree angle to the surface, then the transmitted ray that enters the glass is bent. The bending of the entering ray is called refraction. How much the ray is refracted depends on the index of refraction of the two transparent materials. If the light ray travels from a substance whose index of refraction is smaller, into a substance where the index of refraction is larger, the refracted ray is bent towards the normal. If the light ray travels from a substance where the index of refraction is larger into a substance where the index of refraction is smaller, the refracted ray is bent away from the normal.
Consider a light ray moving at an angle other than 90 degrees through the boundary between glass and a diamond. The glass has an index of refraction of about 1.523. The diamond has an index of refraction of about 2.419. Therefore, the ray that continues into the diamond will be bent towards the normal. When that light ray crosses the boundary between the diamond and the air at some angle other than 90 degrees, it will be bent away from the normal. The reason for this is that air has a lower index of refraction, about 1.000 than the index of refraction of the diamond.
Total Internal Refraction A design must be achieved for the fiber that will make the outside surface of the fiber act like a mirror to the light ray moving through the fiber. If any light ray that tries to move out through the side of the fiber were reflected back into the fiber at an angle that sends it towards the far end of the fiber, this would be a good “pipe” or “wave guide” for the light waves.
The following two conditions must be met for the light rays in a fiber to be reflected back into the fiber without any loss due to refraction: • The core of the optical fiber has to have a larger index of refraction (n) than the material that surrounds it. • The material that surrounds the core of the fiber is called the cladding. • The angle of incidence of the light ray must be greater than the critical angle for the core and its cladding. • When both of these conditions are met, the entire incident light in the fiber is reflected back inside the fiber.
