CCNA1 Module 3

Topics

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. Objectives

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.

Voltage

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 the ohm. 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.

Insulators, Conductors, and Semiconductors

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.

Water Analogy for Electricity

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.

Series Circuits

Cable Specifications

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. Cables Specs

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.

Coaxial Cable

Shielded Twisted Pair

ScTP Screened Twisted Pair

Unshielded Twisted Pair

UTP Cabling

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.

Straight-Through Cable Pinouts

Switch to Switch Connections

Cross-Over Cable

Connecting to a Console Port

Rollover Cable

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.

Electromagnetic Spectrum

Visible Light Spectrum W=700 nm F=428.5 THz W=400 nm F=750 THz W= 300,000,000m/s / freq 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).

Ray Model of Light

Index of Refraction

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.

Reflection

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.

Refraction

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 The diamond has an index of refraction of about 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 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: 1.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. 2.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.

Numerical Aperture (NA)

The numerical aperture of the fiber – The numerical aperture of a core is the range of angles of incident light rays entering the fiber that will be completely reflected. Modes – The paths which a light ray can follow when traveling down a fiber. By controlling both conditions, the fiber run will have total internal reflection. This gives a light wave guide that can be used for data communications.

Fiber Optics

Single Mode & Multimode Fiber

If the diameter of the core of the fiber is large enough so that there are many paths that light can take through the fiber, the fiber is called “multimode” fiber. Single-mode fiber has a much smaller core that only allows light rays to travel along one mode inside the fiber.

Duplex Fiber

Fiber Optic Cable Connector Usually, five parts make up each fiber-optic cable. The parts are the core, the cladding, a buffer, a strength material, and an outer jacket.

Dispersion Dispersion of a light flash also limits transmission distances on a fiber. Dispersion is the technical term for the spreading of pulses of light as they travel down the fiber.

Multimode uses a type of glass, called graded index glass for its core. This glass has a lower index of refraction towards the outer edge of the core. Therefore, the outer area of the core is less optically dense than the center and light can go faster in the outer part of the core. This design is used because a light ray following a mode that goes straight down the center of the core does not have as far to travel as a ray following a mode that bounces around in the fiber. All rays should arrive at the end of the fiber together. Then the receiver at the end of the fiber receives a strong flash of light rather than a long, dim pulse.

Optical Cable Design

Emitters Infrared Light Emitting Diodes (LEDs) or Vertical Cavity Surface Emitting Lasers (VCSELs) are two types of light source usually used with multimode fiber. Use one or the other. LEDs are a little cheaper to build and require somewhat less safety concerns than lasers. However, LEDs cannot transmit light over cable as far as the lasers. Multimode fiber (62.5/125) can carry data distances of up to 2000 meters (6,560 ft).

Single Mode Fiber

Warning: The laser light used with single-mode has a longer wavelength than can be seen. The laser is so strong that it can seriously damage eyes. Never look at the near end of a fiber that is connected to a device at the far end. Never look into the transmit port on a NIC, switch, or router. Remember to keep protective covers over the ends of fiber and inserted into the fiber-optic ports of switches and routers. Be very careful.

Transmission Devices

SC and ST Fiber Connectors

Connectors are attached to the fiber ends so that the fibers can be connected to the ports on the transmitter and receiver. The type of connector most commonly used with multimode fiber is the Subscriber Connector (SC connector). On single-mode fiber, the Straight Tip (ST) connector is frequently used.

There are two types of light sources used to encode and transmit the data through the cable: A light emitting diode (LED) producing infrared light with wavelengths of either 850nm or 1310 nm. These are used with multimode fiber in LANs. Lenses are used to focus the infrared light on the end of the fiber Light amplification by stimulated emission radiation (LASER) a light source producing a thin beam of intense infrared light usually with wavelengths of 1310nm or 1550 nm. Lasers are used with single-mode fiber over the longer distances involved in WANs or campus backbones. Extra care should be exercised to prevent eye injury

Signals and Noise in Fiber Optic Cable Although fiber is the best of all the transmission media at carrying large amounts of data over long distances, fiber is not without problems. When light travels through fiber, some of the light energy is lost. The farther a light signal travels through a fiber, the more the signal loses strength. This attenuation of the signal is due to several factors involving the nature of fiber itself. The most important factor is scattering. The scattering of light in a fiber is caused by microscopic non-uniformity (distortions) in the fiber that reflects and scatters some of the light energy.

Absorption is another cause of light energy loss. When a light ray strikes some types of chemical impurities in a fiber, the impurities absorb part of the energy. This light energy is converted to a small amount of heat energy. Absorption makes the light signal a little dimmer. Another factor that causes attenuation of the light signal is manufacturing irregularities or roughness in the core-to- cladding boundary. Power is lost from the light signal because of the less than perfect total internal reflection in that rough area of the fiber. Any microscopic imperfections in the thickness or symmetry of the fiber will cut down on total internal reflection and the cladding will absorb some light energy. Dispersion of a light flash also limits transmission distances on a fiber. Dispersion is the technical term for the spreading of pulses of light as they travel down the fiber.

Scattering

Bending

Fiber End Face Finishes