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Network Introduction, Network Introduction, Overview and ClassificationOverview and Classification
Unit 10, Chapter 6 & 8Data Communications & Transmission Media
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Objectives
Define the elements of a sine-wave.Define the elements of a digital signal.Identify key equipment for both transmission modes.Identify common ‘copper’ media.Define the two types of fiber optic cable and their attributes.Define key terms associated with managing copper and optical media.
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Analog Versus Digital
Analog – Signal amplitude or frequency modulation, continuous– Continuously Variable– Power 60hz
Digital – Discrete State– On = 1, Off = 0
Frequency – Number of vibrations per second, measured in Hertz (HZ). Human ear can hear from about 20 to 15K Hz.Sine Wave – One complete wave = 1 cycle or 1 Hertz
Kilohertz – Thousands of HertzMegahertz – Millions of HertzGigahertz – Billions of Hertz
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Frequency Spectrum
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Encoding Methods – Analog Methods: Amplitude Modulation
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Decibels (dB)
Logarithmic ratio of signal input to output
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Signals Attributes
Decibels and signal strength (amplitude) are of interest in telecommunications, 0 dB = 1 milliwatt, +3dB = 2 milliwatt, +6dB = 4 milliwattToo much power on a circuit can create crosstalkToo little power will affect signal attenuation (loss between to points on a line)A signal at the point of input will have a certain strength and will be reduced by attenuation, reduction is measured in DbPhase – waves relative position measured in degrees
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Attributes, Multiplexing and Modulation
Analog voice circuits operate in the 300 – 3K Hz rangeFrequency Division Multiplexing – Packing several analog signals onto one circuit. Each signal is assigned a different frequency (sub-channel)Modulation– Carrier wave generated in sub-channel frequency and
modulated to carry signal– Amplitude modulation (AM)– Frequency modulation (FM)– Phase Modulation (PM)– Demodulation = reading/interpreting the signal on the other
side
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Circuits
Signaling Rate – Number of times per second that a signal on a circuit changes. Signaling Rate is Measured in BAUD, signal changes 600 times per second = 600 BAUDMaximum signaling rate is equal to the bandwidth in Hertz * 2Circuit speed is in bits per second (bps)If signal rate changes at the same value as the bps then the 2 will be equal but normally they are not equalDibits = 2 bits of information are coded in on signal changeTribits = 3 bits/SC, Quadbits = 4 bits/signal change
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Digital Signals
Each pulse represents a 1 or a 0Unipolar – 1 bit is represented by a positive voltage, 0 is represented by a negative voltageBipolar, nonreturn to zero (NRZ) - 1 bit is represented by a positive voltage, 0 is represented by a negative voltageBipolar, return-to-zero – Signal pulses are shorter and voltage always returns to zeroManchester Encoding – Low – to –high transition during signaling period = 1, high-to-low = 0.– Allows synchronization on transition, predictable and known– Absence of transition indicates an error
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Manchester Encoding
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Analog/Digital Signals
Analog-to-digital Converter – Converts analog signals to digital. Samples analog stream at a set interval and converts reading to a number to be transmitted and ->Digital-to-analog converter – converts digital signals to analog. Uses the samples that were turned into a quantity (number) and recreates the signalCode/Decoder - Name applied to an AD Converter / DA ConverterPulse Code Modulation – Encoding technique uses 256 integer values and samples signal 8000 times per second. Effective data rate is 8 bits * 8000 = 64KbpsAdaptive Differential Pulse Code Modulation – Similar toe PCM but only transmits the difference from previous signal in 4 bits. Effective data rate = 4 bits * 8000 = 32K
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Transmission/Reception
Data Transmitter/Receiver or Data Service Unit/Channel Service Unit (CSU/DSU) used for digital transmissionsTransmitter – Ensures digital signals being put on a line are properly shaped and timed. Can convert signal from DTE to a suitable signal for the carrierCSU – Protects carriers circuits from excess voltageNetwork Interface Card (NIC) – Simple transmitter/receiverModems and CSU/DSUs are called Data Communication Equipment (DCE)
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Modems
Specialized digital-to-analog and analog-to-digital converter that modulates a signal onto a carrier wave and demodulating it at the other endHalf-duplex – transmit in one direction at a timeFull-duplex – transmit in both directions at the same timeFrequency Shift Keying – One bit turns on a oscillator which generates a wave form that is sent across the line, receiving end sees the wave form and generates a onePhase Modulation or Phase Shift Keying (PSK) – Shifts in the sine wave 90 degrees to show a one or a zeroQuadrature Amplitude Modulation (QAM) – Shift in phase and amplitude to represent a one or zeroTrellis Code Modulation(TCM) – Special form of QAM which can detect an invalid bit combination and determine the correct value
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Modem StandardsV.21: Capable of only 300 bps, it is an international standard used mainly outside of the U.S. V.22: Capable of 1200 bps at 600 baud. Used mainly outside the U.S. V.22bis: Used in the U.S. and out, it is capable of 2400 bps at 600 baud. V.23: Used mainly in Europe, it allows the modem to send and receive data at the same time at 75 bps. V.29: A one-way (half-duplex) standard that is used mostly for fax machines. Capable of 9600 bps. V.32: A full-duplex standard capable of 9600 bps at 2400 baud. V.32 modems automatically adjust their transmission speeds based on the quality of the lines. V.32bis: A second version of V.32, it is capable of 14,400 bps. It will also fallback onto V.32 if the phone line is impaired. V.32ter: The third version of V.32, capable of 19,200 bps. V.34: Capable of 28,000 bps or fallback to 24,000 and 19,200. This standard is backwards compatible with V.32 and V.32bis. V.34bis: Capable of 33,600 bps or fallback to 31,200. V.42: Same transfer rate as V.34 but is more reliable because of error correction. V.42bis: A data compression protocol that can enable modems to achieve a data transfer rate of 34,000 bps. V.44: Allows for compression of Web pages at the ISP end and decompression by the V.44-compliant modem, so transmitting the same information requires fewer data packets. V.90: The fastest transmissions standard available for analog transmission, it is capable of 56,000 bps. V.92: Transmits at the same speed as V.90 but offers a reduced handshake time and an on-hold feature.
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Modem Standards – Another Look
Connection Bit RateModem 110 baud 0.1 kbit/sModem 300 (300 baud) (Bell 103 or V.21) 0.3 kbit/sModem 1200 (600 baud) (Bell 212A or V.22) 1.2 kbit/sModem 2400 (600 baud) (V.22bis) 2.4 kbit/sModem 2400 (1200 baud) (V.26bis) 2.4 kbit/sModem 4800 (1600 baud) (V.27ter) 4.8 kbit/sModem 9600 (2400 baud) (V.32) 9.6 kbit/sModem 14.4 (2400 baud) (V.32bis) 14.4 kbit/sModem 28.8 (3200 baud) (V.34) 28.8 kbit/sModem 33.6 (3429 baud) (V.34) 33.6 kbit/sModem 56k (8000/3429 baud) (V.90) 56.0/33.6 kbit/sModem 56k (8000/8000 baud) (V.92) 56.0/48.0 kbit/sBonding Modem (two 56k modems)) (V.92) 112.0/96.0 kbit/sHardware compression (variable) (V.90/V.42bis) 56.0-220.0 kbit/sHardware compression (variable) (V.92/V.44) 56.0-320.0 kbit/s
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Modems
Cable Modem – Links a DTE to a cable television system cable– Speeds greater than 1Mbps– Speeds greater than 1Mbps are considered broadband
Null Modem allows 2 like devices to communicate
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Null Modem
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DTE-DCE Interfaces
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DTE-DCE Interface Standards
RS-232-C– 25 Pin / Wire Connector– Cable length 50 feet– Speed 20Kbps– 100 feet / 9600 bps– Most only use part of the standard, Pins 2,3 & 7
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RS-232 Pin Outs
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Other DCE-DTE Standards
RS-232-D – Upgraded RS-232-C, defined loopback pin, redefined protective ground, additional shield added, spec includes 25 pin connectorRS-449 – 37 Signal wires, added automatic modem testing, 100 Kbps up to 4000 feet or 10 Mbps up to 40 feetRS-336 – Allows automatic dialing of calls under modem controlX.21 and X.21 bis – Digital connections to a digital PSTN, 15 pin connector, X.21 bis is identical to RS-232-C and is used to connect analog devices to a packet switched circuit
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Why is digital better
Better data integrityHigher CapacityEasier Integration – Voice, data and videoBetter security and privacyLower cost
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Transmission Classification
SimplexHalf DuplexFull DuplexParallel Mode – All bits transferred at the same timeSerial Mode – One bit at a time is transferredAsynchronous (Asynch) – Each character is preceded by a start bit and ends with a stop bitSynchronous – Synchronization is by the senders clock and large amounts (blocks) of data are sent, use SYN character to synch the sender and receiver
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Spread Spectrum Transmission
Radio communication Signal is sent over a wide range of frequencies to avoid interceptionFrequency Hopping – Signal hops from frequency to frequency Direct Sequence – Constant frequency, radio station
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Transmission Media - UTP
Unshielded Twisted PairShielded Twisted PairCoaxial CableOptical FiberWireless Media– Microwave– Satellite– Infrared– Wireless LANs
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UTP Cabling Categories
Category 1– Two twisted pair (4 wires), voice grade( not rated for
data communications). Used with Plain Old Telephone System (POTS)
Category 2– 4 twisted pair (8 wires), suitable for up to 4Mbps
Category 3– Four twisted pair (8 wires), 3 twists per foot, and rated
for 16Mbps
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UTP Cabling Categories
Category 4–Two twisted pair (4 wires), voice and rated for 16Mbps
Category 5– 4 twisted pair (8 wires), suitable for up to 100 Mbps
Category 5e–Four twisted pair (8 wires) and rated for 1000 Mbps
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UTP Cabling Categories
Category 6 – Twice the bandwidth of Category 5e cabling and vastly
improved signal-to-noise margins – Category 6 cabling recognizes advances in cabling
technology and is designed to be backward compatible with categories 3, 5 and 5e. This ensures that any applications that operate on lower category cabling will be fully supported by category 6 cabling. When different category components are mixed with category 6 components, the resultant cabling will satisfy the category transmission requirements of the lower performing component
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Shielded Twisted Pair
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Shielded Twisted Pair
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Ethernet Cables: Coaxial Cable Construction
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Fiber Optic Cable
Cisco Learning InstituteNetwork+ Fundamentals and Certification
Copyright ©2005 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458
All rights reserved.
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Review Questions
1. The shielding on UTP wire is typically made from ____________.a. Kevlarb. Teflonc. PCBsd. none of the above
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Review Questions
2. As of 2008, the most popular networking cable to install in new office buildings is ______________.a. optical fiberb. CAT 1c. CAT 3d. CAT 5