Unit 10, Chapter 6 & 8 Data 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 Hertz Megahertz – Millions of Hertz Gigahertz – 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 milliwatt Too much power on a circuit can create crosstalk Too 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 Db Phase – waves relative position measured in degrees

Attributes, Multiplexing and Modulation Analog voice circuits operate in the 300 – 3K Hz range Frequency 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 BAUD Maximum signaling rate is equal to the bandwidth in Hertz * 2 Circuit 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 equal Dibits = 2 bits of information are coded in on signal change Tribits = 3 bits/SC, Quadbits = 4 bits/signal change

Digital Signals Each pulse represents a 1 or a 0 Unipolar – 1 bit is represented by a positive voltage, 0 is represented by a negative voltage Bipolar, nonreturn to zero (NRZ) - 1 bit is represented by a positive voltage, 0 is represented by a negative voltage Bipolar, return-to-zero – Signal pulses are shorter and voltage always returns to zero Manchester 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 signal Code/Decoder - Name applied to an AD Converter / DA Converter Pulse Code Modulation – Encoding technique uses 256 integer values and samples signal 8000 times per second. Effective data rate is 8 bits * 8000 = 64Kbps Adaptive 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 transmissions Transmitter – Ensures digital signals being put on a line are properly shaped and timed. Can convert signal from DTE to a suitable signal for the carrier CSU – Protects carriers circuits from excess voltage Network Interface Card (NIC) – Simple transmitter/receiver Modems 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 end Half-duplex – transmit in one direction at a time Full-duplex – transmit in both directions at the same time Frequency 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 one Phase Modulation or Phase Shift Keying (PSK) – Shifts in the sine wave 90 degrees to show a one or a zero Quadrature Amplitude Modulation (QAM) – Shift in phase and amplitude to represent a one or zero Trellis Code Modulation(TCM) – Special form of QAM which can detect an invalid bit combination and determine the correct value

Modem Standards V.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.half-duplex 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.full-duplex 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 transferdata 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.Web pages 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 ConnectionBit Rate Modem 110 baud 0.1 kbit/s Modem 300 (300 baud) (Bell 103 or V.21)0.3 kbit/sBell 103V.21 Modem 1200 (600 baud) (Bell 212A or V.22)1.2 kbit/sBell 212AV.22 Modem 2400 (600 baud) (V.22bis)2.4 kbit/sV.22bis Modem 2400 (1200 baud) (V.26bis)2.4 kbit/sV.26bis Modem 4800 (1600 baud) (V.27ter)4.8 kbit/sV.27ter Modem 9600 (2400 baud) (V.32)9.6 kbit/sV.32 Modem 14.4 (2400 baud) (V.32bis)14.4 kbit/sV.32bis Modem 28.8 (3200 baud) (V.34)28.8 kbit/sV.34 Modem 33.6 (3429 baud) (V.34)33.6 kbit/sV.34 Modem 56k (8000/3429 baud) (V.90)56.0/33.6 kbit/sV.90 Modem 56k (8000/8000 baud) (V.92)56.0/48.0 kbit/sBondingV.92 Modem (two 56k modems)) (V.92)112.0/96.0 kbit/sV.92 Hardware compression (variable) (V.90/V.42bis) kbit/sV.90V.42bis Hardware compression (variable) (V.92/V.44) kbit/sV.92V.44

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 connector RS-449 – 37 Signal wires, added automatic modem testing, 100 Kbps up to 4000 feet or 10 Mbps up to 40 feet RS-336 – Allows automatic dialing of calls under modem control X.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 integrity Higher Capacity Easier Integration – Voice, data and video Better security and privacy Lower cost

Transmission Classification Simplex Half Duplex Full Duplex Parallel Mode – All bits transferred at the same time Serial Mode – One bit at a time is transferred Asynchronous (Asynch) – Each character is preceded by a start bit and ends with a stop bit Synchronous – 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 interception Frequency Hopping – Signal hops from frequency to frequency Direct Sequence – Constant frequency, radio station

Transmission Media - UTP Unshielded Twisted Pair Shielded Twisted Pair Coaxial Cable Optical Fiber Wireless 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

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

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

Shielded Twisted Pair

Ethernet Cables: Coaxial Cable Construction

Fiber Optic Cable Cisco Learning Institute Network+ Fundamentals and Certification Copyright ©2005 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Review Questions 1. The shielding on UTP wire is typically made from ____________. a. Kevlar b. Teflon c. PCBs d. none of the above

Review Questions 2. As of 2008, the most popular networking cable to install in new office buildings is ______________. a. optical fiber b. CAT 1 c. CAT 3 d. CAT 5