1 / 58

Cisco CCNA

Cisco CCNA. Chapter 3. Electricity. Matter made up of Atoms Bohr Model of Atom Protons, Electrons, Neutrons. Electrical Properties of Matter. Insulators Electrons flow poorly if at all Plastic, Paper, Rubber, Glass, Air Conductors Easy flow of electrons Metals, water (ionized), humans

lexine
Télécharger la présentation

Cisco CCNA

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Cisco CCNA Chapter 3

  2. Electricity • Matter made up of Atoms • Bohr Model of Atom • Protons, Electrons, Neutrons

  3. Electrical Properties of Matter • Insulators • Electrons flow poorly if at all • Plastic, Paper, Rubber, Glass, Air • Conductors • Easy flow of electrons • Metals, water (ionized), humans • Semiconductors • Electron flow can be controlled precisely • Carbon (C), Germanium (Ge), Silicon (Si)

  4. Measuring Electricity • Voltage • Potential caused by separation in positive and negative charges. • Represented by letter V • Direct Current (DC) • Electron movement is in same direction • Alternating Current (AC) • Electrons move forwards and backwards

  5. Current • Flow of electrons • Represented by letter I • Unit of measurement is ampere (amp) • # charges / second past a point in a circuit

  6. Wattage • Basic unit of work done by electricity • Calculated by formula • W = V x I

  7. Resistance and Impedance • Resistance is property of material that resists electron movement • Represented by letter R • Unit of measure is Ohm (Ω) • Resistance generally refers to DC circuits • Impedance generally refers to AC circuits • Comprised of Capacitance, Resistance, Inductance

  8. Circuits • Electrons can only flow when they are in loops called circuits. • A closed loop will allow electrons to flow • An open loop prevents electrons from flowing • An open switch prevents electron flow • A closed switch allows electrons to flow

  9. Media • Twisted-pair Cable • Pair of wires forms circuit • Twisting prevents crosstalk • Ensures cancellation • Differential signaling • Two types • Shielded Twisted Pair (STP) • Unshielded Twisted Pair (UTP)

  10. Properties of STP • STP • Excellent protection from unwanted electrical noise • 10 – 100 Mbps • Moderately expensive • medium to large media and connector size • 100 m maximum cable length • RJ45 connector

  11. Properties of UTP • Susceptible to electrical noise • 10Mbps – 1Gbps speed and throughput • Inexpensive • Small media and connnector size • 100 m maximum cable length • RJ45 Connector

  12. Coaxial Cable • Consists of 4 main parts • Copper Conductor • Plastic Insulation • Braided copper shielding • Outer jacket • 1 cm diameter called thicknet • 0.35 cm called thinnet • BNC Connector

  13. Coaxial Cable • Used in bus topologies • IEEE no longer recommends this cable or topology as a standard • 10 – 100Mbps • Inexpensive • Medium size media and connector • 500 m maximum cable length

  14. Cable Specification and Termination Standards • Institute of Electrical and Electronic Engineers (IEEE) • IEEE 802.3 is Standard for Ethernet networks • IEEE 802.5 is Standard for Token Ring networks

  15. Telecommunications Industry Association (TIA) • 568-B : Commercial building cabling standard • 569-B : (Formerly 568-A) Commercial building standard for pathways and spaces • 570-A : Standard for residential and light commercial telecommunications • 606 : Administration standard for infrastructure of commercial buildings • 607 : Building grounding and bonding

  16. TIA/EIA 568-B • Includes standards for Horizontal & Backbone (Vertical) cabling. • 568-B calls for 2 cables to work area • Telephone cable for voice • 2 pair UTP with correct connectors • Network cable for data • 150 ohm STP 2-pair cable (Token Ring) • 100 ohm UTP 4-pair cable (Ethernet LAN’s) • 62.5/125 µ fiber-optic cable (Ethernet LAN’s)

  17. 568-B continued • Sets maximum cable lengths • 3 m patch cord from workstation to wall outlet • 90 m cable run from wall outlet to patch panel • 6 m patch cord from patch panel to horizontal cross connect in wiring closet

  18. Optical Media • Used for longer, high bandwidth point-to-point transmissions on backbone and WAN’s • Not susceptible to lightining, electromagnetic interference (EMI) or radio frequency interference (RFI) • Greater bandwidth capabilities • More secure than copper • Costs less than copper for long distance applications • No grounding concerns

  19. Electromagnetic Spectrum

  20. Ray Model of Light • Light travels from a source as a straight line called Rays • In a vacuum, light travels at 3x108 km/s • Light ray (incident ray) crosses boundary, some light is reflected back (reflected ray) • Light energy that is not reflected back enters the glass. The ray is bent from original path (refraction)

  21. Refracted Rays • Degree in which the Refracted Ray is bent depends on two factors • The angle at which the incident ray strikes glass • The different rate at which light moves through the two substances • The rate at which light moves through a substance depends on the optical density of the substance • This change allows light to bend in fiber optic cable

  22. Law of Reflection • Angle between an incident ray and a line perendicular (normal) to the surface of the glass is the angle of incidence • When reaches a critical angle, all light is reflected back to the original medium • Law of Reflection: angle of reflection is equal to angle of incidence

  23. Law of Refraction (Snell’s Law) • When light strikes glass, some of the light is reflected, while some is absorbed. • If light is at 90 degrees to the surface of the glass, the absorbed light is not bent • If other than 90 degrees, light is bent (refracted) • Amount of refraction depends on refraction index of the material • From small refraction index to large refraction index, light is bent to the normal • From large index to small index, light is bent away from normal

  24. Total Internal Reflection • Optical fiber must not lose light to surrounding in order to carry data • Two requirements • Core must have higher refractive index than material surrounding it (cladding) • Angle of incidence of the light ray is greater than the critical angle for core and cladding • If conditions met, all light is reflected back into fiber (total internal reflection)

  25. Total Internal Reflection (Cont) • Creating core with high refractive index is easy • Angle of Incidence is controlled by two factors • Numerical aperture of the fiber (range of angles that will be totally internally reflected) • Paths (modes) light can travel (wave path)

  26. Fiber Optic Cables • Superior to copper • Consists of: • Core -2 glass fibers encased in separate sheaths • One for Tx, One for Rx. Allows full duplex communication • Cladding • Buffer • Strengthening material • Outer Jacket

  27. Fiber Optic Cable (Cont) • Core • Carries light signals. Made from silica and other elements • Cladding • Reflect light back into core. Made from silica but with lower refractive index than core • Buffer • Usually made from plastic helps protect cladding and core • Strengthening material • Surroundsbuffer to prevent cable from being stretched • Outer Jacket • Protects against abrasion, solvents and other contaminants

  28. Single and Multimode Fiber • If only one wave path – Single Mode • Multiple paths – Multimode

  29. Multimode • Multiple paths propagate through fiber. • Multiple modes might travel different distances resulting in arriving at the end at different times – Modal Dispersion • Uses graded index glass • 62.5 or 50 µ core with 125 µ cladding • 62.5/125 or 50/125

  30. Single Mode Fiber • Core is 8-10 µ diameter • 9 µ is most common • Small diameter and Laser light entering at 90 degree angle – Rays transmitted in essentially straight line • Capable of higher data rate transmission

  31. Fiber Optic Cable • > 1 Gps speed and throughput • Expensive • Small media and connector size • >10 km single mode, 2 km multimode

  32. Fiber Cable Designs • Loose-Tube • Buffer material is not necessarily in direct contact with cladding • Primarily used in outside-building installations • Tight-Tube • Buffer material in direct contact with cladding • Primarily used inside buildings. • Most fiber used in LAN’s is tight-buffered multimode

  33. Other Components • Transmitters • Light Emitting Diodes (LED’s) • 850 or 1310 nm • Light amplification by stimulated emission radiation (Laser) • 1310 or 1550 nm. • Safety concerns • Used in WAN’s or campus backbones

  34. Other Components (contd) • Reciever • Functions as photovoltaic cell • Photons striking material free electrons to move – Current • P-intrinsic-n diodes (PIN photodiodes) • Designed to be sensitive to light at 850, 1310, 1550 nm

  35. Other Components (contd) • Connectors • Multimode uses SC connectors • Single mode uses ST connectors • Repeaters • Receive attenuating light and process back to original strength, timing etc and send back out • Patch Panels

  36. Signals and Noise • Not affected by external noise • As light travels through fiber, some light is lost – Attenuation • Scattering caused by microscopic non-uniformity (distortion) in the fiber • Absorption – Impurities in fiber absorb some light. • Irregularities in cladding-core boundary • Dispersion is the broadening of the pulse

  37. Installation, Care, Testing • Two types of bending • Macrobending – you can see this bend • Some light rays exceed critical angle and leak out • Microbending – Occurs on microscopic scale. • Same effect as macrobending • Prevent bending problems, fiber pulled through interducting

  38. Installation, Care, Testing (contd) • Ends must be finely finished to reduce attenuation of signal • Decibel (dB) is unit of power • Measure loss using two instruments • Optical Loss Meters • Optical Time Domain Reflectometers (OTDR’s) • Useful diagnostic info

  39. Wireless Communication • Signals use electromagnetic radiation traveling through air • Radio spectrum 300 kHz to 300 GHz

  40. Wireless Signal • How Fast? • What data rate can be achieved • How Far? • How far apart can units be placed and still get max data rate • How Many? • How many users without slowing data rate

  41. Signal Reliability • Type Modulation Used • More complex greater throughput • Distance • Attenuation – inverse square • Noise • Electronic noise and barriers affect RF

  42. Modulation • Amplitude Modulation (AM) • Modulates height of carrier wave • Frequency Modulation (FM) • Modulates frequency of wave • Phase Modulation (PM) • Modulates polarity (phase) of wave

  43. Radio Frequency Bands • 900 MHz – cordless and cell phones • 2.4 GHz – 802.11b • Most widely deployed • Max data rate 11 Mbps • 5 GHz – 802.11a • Max data rate 54 Mbps • Range limited • Inside 50 feet • Outside 2500 feet

  44. Spread-Spectrum Technology • Spread Spectrum developed in 40’s • Frequency-hopping spread spectrum • Direct-sequence spread spectrum

  45. Frequency-Hopping Spread Spectrum FHSS • Transmission hop from one frequency to another at random • Enables transmissions to hop around narrow band interference • Slower, and receiver must use same pattern to decode • Limited to 2 Mbps • Specific applications and watercraft

  46. Direct-sequence spectrum spread DSSS • Each data bit represented by string of 1s and 0s – chipping sequence • Will tolerate up to 40% loss of the string. • High throughput and range • Up to 11 Mbps data rate

  47. Wireless LAN Standards • 802.11 – DSSS up to 2 Mbps • 802.11b – FHSS up to 11 Mbps • Wi-FI • Backward compatible • 802.11a – up to 54 Mbps • 802.11g – Same as 802.11a but backwards compatible • Uses Othoganol Frequency Division Multiplexing

  48. Wireless Devices and Topologies • Access point (AP) – Hardwired to cabled LAN • Specific area called a cell • Range 20 feet to 25 miles • Typically 300 – 500 feet • Multiple AP’s can be overlapped to provide roaming between cells • 20% - 30% overlap is desirable

  49. Wireless Devices and Topologies (Contd) • When client is activated within LAN, starts listening for compatible device (AP or another host) to associate • Process is called scanning • Two types of scanning • Active scanning sends probe from device seeking to join network. Probe contains Service Set Identifier (SSID) of the network it wants to join. When AP with same SSID is found, authentication and association steps are completed • Passive scanning listens for beacon management frames (beacons) transmitted by AP’s or other hosts. When a node receives a beacon that contains SSID, authentication begins. • Continuous process allows nodes to associate and disassociate with changes in signal strength

  50. Wireless LAN’s Communicate • Once connected to WLAN, nodes pass frames. • Don’t use standard 802.3 frames • Three types of frames • Control • Management • Data

More Related