CCNA1_M3_Networking_Media (1130689)
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CCNA – Semester1Module 3Networking MediaObjectives• Copper media and electronic signal• Optical media and light signal• Wireless media and waveCopper MediaElectricity BasicsThe basic unit of allmatter is an atom.– Protons – particles thathave positive charge– Neutrons – particles thathave no charge (neutral)– Electrons – particles thathave negative charge andorbit the nucleusStatic electricity• Electrons have beenloosened from the atomand stay in one place,without moving.• Electrostatic discharge(ESD).– ESD, though usuallyharmless to people, cancreate serious problems forsensitive electronicequipment.Measuring electricity: Current• The flow of charges that is created whenelectrons move.• Symbol: I.• Ampere (A).free electronElectrical definitions: AC and DC• Alternating Current (AC):– Electrical current flows in both directions; positive andnegative terminals continuously trade places (polarity).• Direct Current (DC):– Electrical current flows in one direction; negative topositive.Measuring electricity: Resistance•••••••Resistance: property of a material that opposes the electrical flow.Resistance consume electrical energy and cause attenuation.Symbol: R.Ohm (Ω).Impedance: total opposition to the current.Symbol: Z.Ohm (Ω).Measuring electricity: Voltage• Force or pressure caused by the separation ofelectrons and protons.• Symbol: U.• Volt (V).Basic Circuit• Source• Completepath• LoadOscilloscope• Graphs voltage over time• X-axis represents T, Y-axis represents VElectrical definitions: Ground• Ground can refer tothe place on theearth.• Ground can alsomean the referencepoint, or the 0 voltslevel, when makingelectricalmeasurements.Cable Specifications• What speeds for data transmission can beachieved using a particular type of cable?• What type of transmission is being considered?Will the transmissions be digital or will they beanalog-based?• How far can a signal travel through a particulartype of cable before attenuation of that signalbecomes a concern?Ethernet Specifications• 10BASE-T• 10BASE5• 10Base2Coaxial Cable••••If not properly grounded, shielding is very poor.Speed of transmission:10-100MpbsLonger cable runs than UTP & STP.Maximum cable length :– Thin cable : 185 m.– Thick cable : 500 m.•Impedance: 50Ω.Shielded Twisted-Pair Cable•Protection from all types of external interference, include EMI andRFI.– Cancellation: twisting of wires.– Shielding.•••Moderately expensive, quite difficult to install.Speed of transmission:10Mpbs-1GbpsMaximum cable length 100m.Screened Twisted-Pair CableCancellationUnshielded Twisted-Pair Cable••••More prone to EMI/RFI interference than any other cable types.Least expensive of all media– small diameter of cable (~ .43cm),– easy to install.Speed of transmission:10Mpbs-1GbpsMaximum cable length 100m.Straight-through cable• Station to hub/switch• Router to hub/switchCrossover cable• Switch/hub to switch/hub• Router/station to Router/stationConnecting devicesPWRWIC0ACT/CH0WIC0ACT/CH0ETHACTOKACT/CH1ACT/CH1COL123456789*8#iMac••Connecting devices of the same group: cross-overConnecting devices of different group: straight-through100Base-TX1: Transmit2: Transmit3: Receive4: Not used5: Not used6: Receive7: Not used8: Not used1: Transmit2: Transmit3: Receive4: Not used5: Not used6: Receive7: Not used8: Not usedRollover cable••PC requires an RJ45-to-DB9 or RJ45-to-DB25 adapterThis provide out-of-band console accessNote: only straigh-through and cross-over cable are used in making networkwhile rollover cable is used in making control connectionOptical MediaElectromagnetic Spectrum• Electromagnetic Energy––––––RadioMicrowavesRadarVisible lightX-raysGamma rays• If all the types of electromagnetic waves are arranged inorder from the longest wavelength down to the shortestwavelength, a continuum called the electromagneticspectrum is created.Reflection and refraction of lightTotal Internal Reflection• A light ray that is being turned on and off to senddata (1s and 0s) into an optical fiber must stay insidethe fiber until it reaches the far end.Laws of Total Reflection•The following two conditions must be met for the light rays ina fiber to be reflected back into the fiber with out any loss dueto refraction:– The core of the optical fiber has to have a larger index of refractionthan the material that surrounds it (the cladding).– The angle of incidence of the light ray is greater than the critical anglefor the core and its cladding.Single-Mode Fiber and Multimode FiberOther Optical Components• A transmitter is needed to convert theelectricity to light and at the receiver convertthe pulse of light at the proper wavelength backto electricity.Optical Connector• The type of connector most commonly usedwith multimode fiber is the SubscriberConnector (SC connector).
On single-modefiber, the Straight Tip (ST) connector isfrequently used.Advantages of optical signal• Fiber-optic cable is not affected by the sourcesof external noise like EMI• Transmission of light on one fiber in a cabledoes not generate interference that disturbstransmission on any other fiber• High speed, high security and long cable lengthSignals and Noise in Optical Fibers• The farther a light signal travels through a fiber, themore the signal loses strength. This attenuation isdue to several factors involving the nature of fiberitself.– Scattering of light in a fiber is caused by microscopic non-uniformity(distortions) in the fiber that reflects and scatters some of the lightenergy.– Absorption makes the light signal a little dimmer.– Another factor that causes attenuation of the light signal ismanufacturing irregularities or roughness in the core-to-claddingboundary.Installation of Optical Fiber•••If the fiber is stretched orcurved too tightly, it cancause tiny cracks in thecore that will scatter thelight rays.Bending the fiber in tootight a curve can changethe incident angle of lightrays striking the core-tocladding boundary.When the fiber has been pulled, the ends of the fiber must becleaved (cut) and properly polished to ensure that the ends aresmooth.Testing of Optical Fiber• When a fiber-optic link isbeing planned, theamount of signal powerloss that can be toleratedmust be calculated.
Thisis referred to as theoptical link loss budget.• Two of the most important testing instruments areOptical Loss Meters and Optical Time DomainReflectometers (OTDRs).Wireless MediaIEEE 802 Committees802.0 SEC802.1 High Level Interface (HILI)802.2 Logical Link Control (LLC)IEEE 802.11802.3 CSMA/CD Working GroupIEEE 802.11a802.4 Token BusIEEE 802.11b WiFi802.5 Token RingIEEE 802.11g802.6 Metropolitan Area Network (MAN)IEEE 802.15.1 Bluetooth802.7 BroadBand Technical Adv. Group (BBTAG)IEEE 802.11e802.8 Fiber Optics Technical Adv. Group (FOTAG)IEEE 802.11f802.9 Integrated Services LAN (ISLAN)IEEE 802.11h802.10 Standard for Interoperable LAN Security(SILS)IEEE 802.11i Security2004801.11 Wireless LAN (WLAN)IEEE 802.15 TG2802.12 Demand PriorityIEEE 802.15 TG3802.14 Cable-TV Based Broadband CommunicationNetwork802.15 Wireless Personal Area Network (WPAN)802.16 Broadband Wireless Access (BBWA)RPRSG Resilient Packet Ring Study Group (RPRSG)IEEE 802.15 TG4WLAN Organizations and StandardsStandardData RateModulationScheme802.11≤ 2Mbps2.4GHzFHSS orDSSS802.11a802.11b802.11gBluetoothPros/ConsThis specification has been extended into 802.11b.OFDM"Wi-Fi Certified." 8 available channels.
Less potentialfor RF interference than 802.11b and 802.11g. Betterthan 802.11b at supporting multimedia voice, videoand large-image applications in densely populateduser environments. Relatively shorter range than802.11b. Not interoperable with 802.11b.≤ 11Mbps2.4GHzDSSS withCCK"Wi-Fi Certified." 14 channels available.
Notinteroperable with 802.11a. Requires fewer accesspoints than 802.11a for coverage of large areas. Highspeed access to data at up to 300 feet from basestation.≤ 54Mbps2.4GHzOFDM >20MbpsDSSS +CCK <20MbpsUp to 2Mbps2.45GHzFHSS≤ 54Mbps5GHz"Wi-Fi Certified." 14 channels available. May replace802.11b. Improved security enhancements over802.11. Compatible with 802.11b.No native support for IP, so it does not support TCP/IP andwireless LAN applications well. Best suited for connectingPDAs, cell phones and PCs in short intervals.Wireless Devices and Topologies• A wireless network mayconsist of as few as twodevices.• Devices in WLAN arepeers• An access point (AP) iscommonly installed toact as a central hub forthe WLANHow WLANs Communicate• After establishingconnectivity to the WLAN, anode will pass framessimilarly to any other 802network.• WLANs use CSMA/CA• The receiving node returns apositive ACK, causing aconsumption of 50% of theavailable bandwidth, actualthroughput may reduce to 5 –5.5 Mbps• Adaptive Rate Selection (ARS)is used to set proper speedfor network nodes.Adaptive Rate Selection• Performance of thenetwork will also beaffected by signalstrength and degradationin signal quality due todistance or interference.• As the signal becomesweaker, Adaptive RateSelection (ARS) may beinvoked.Authentication and Association• IEEE 802.11 lists two types of authenticationprocesses.– Open system – only the SSID must match– Shared key – requires Wireless Equivalency Protocol (WEP)• Association permits a client to use the services ofthe AP to transfer data.Carrier Signal and Modulation• In a transmitter, the electrical (data) signals from acomputer or a LAN are not sent directly into the antennaof the transmitter.
Rather, these data signals are used toalter a second, strong signal called the carrier signal.Signals and Noise on a WLAN• The most obvious source of a signalproblem is the transmitting station andantenna type.• Leakage from a microwave of as little asone watt into the RF spectrum can causemajor network disruption. Wireless phonesoperating in the 2.4GHZ spectrum can alsocause network disorder.• Fog or high moisture conditions can affectwireless networks.• Lightning can also charge the atmosphereand alter the path of a transmitted signal.Wireless Security••••••VPNEAP-MD5 ChallengeLEAP (Cisco)User authenticationEncryptionData authenticationSummary••••••Electronic parametersEthernet cable typeLight and optical fiberOptical fiber installationWLAN communication and authenticationSignal modulation and WLAN security.
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