unit 10, chapter 6 & 8 data communications & transmission media

Network Introduction, Network Introduction, Overview and ClassificationOverview and Classification

Unit 10, Chapter 6 & 8Data Communications & Transmission Media

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.

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

Frequency Spectrum

Encoding Methods – Analog Methods: Amplitude Modulation

Decibels (dB)

Logarithmic ratio of signal input to output

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

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

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

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

Manchester Encoding

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

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)

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

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.

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

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

Null Modem

DTE-DCE Interfaces

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

RS-232 Pin Outs

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

Why is digital better

Better data integrityHigher CapacityEasier Integration – Voice, data and videoBetter security and privacyLower cost

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

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

Transmission Media - UTP

Unshielded Twisted PairShielded Twisted PairCoaxial CableOptical FiberWireless Media– Microwave– Satellite– Infrared– Wireless LANs

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


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


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

Shielded Twisted Pair

Ethernet Cables: Coaxial Cable Construction

Review Questions

1. The shielding on UTP wire is typically made from ____________.a. Kevlarb. Teflonc. PCBsd. none of the above

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

unit 10, chapter 6 & 8 data communications & transmission media

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