1 Chapter 8 Data and Network Communication Technology.

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Chapter 8

Data and Network Communication Technology

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Systems Architecture Chapter 8

Chapter Goals

• Explain communication protocols.

• Describe signals and the media used to transmit digital signals

• Compare and contrast methods of encoding and transmitting data using analog and digital signals.

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Chapter Goals

• Describe methods for efficiently using communication channels.

• Describe methods for detecting and correcting data transmission errors.

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Chapter Topics

• Communication protocols• Encoding and transmitting bits• Transmission media• Channel organization• Clock synchronization• Error detection and correction

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Communication Protocols

• A message is a unit of data or information transmitted from a sender to one or more recipients.

• A communication protocol is a set of rules and conventions for communication.

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Communication Protocols

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Encoding and Transmitting Bits

• Carrier Waves• Modulation Methods• Analog Signals• Digital Signals• Signal Capacity Errors

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Carrier Waves

• Amplitude• Phase• Frequency

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Amplitude - is a measure of wave height or power. The maximum distance between a wave peak and its zero value.

Phase - a specific time point within a wave’s cycle.

Frequency - the number of cycles that occur in one second.

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• Bit are encoded within a wave by precisely manipulating or modulating.

• Data can be encoded as bits by any shared coding method. For example, text messages could be encoded with Morse code.

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Modulation Methods

• Amplitude Modulation• Frequency Modulation• Phase Modulation• Multilevel Coding

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Amplitude Modulation

• Represents bit values as specific wave amplitudes.

• Amplitude modulation holds frequency constant while varying amplitude to represent data.

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Frequency Modulation

• Represents bit values by varying carrier wave frequency while holding amplitude constant.

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Phase Modulation

The phase of a wave is used to represent data by making an instantaneous shift in the phase of a signal or switching quickly between two signals of different phases.

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Multilevel Coding

• A technique for embedding multiple bit values within a single wave characteristic.

• Groups of bits are treated as a single unit for the purposes of signal encoding.

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Analog Signals

• Uses the full range of a carrier wave characteristic to encode continuous data values.

• Analog signals are continuous in nature.

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Digital Signals

• Can contain one of a finite number of possible values.

• Digital signals can be generated using a square wave instead of a sine wave.

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Signal Capacity and Errors• Analog signals can carry a greater amount of

information than digital signals within a fixed time interval.

• Higher data carrying capacity results from the large number of possible messages that can be encoded within an analog signal during a period of time.

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• A digital signal is not as susceptible to noise and interference.

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Transmission Media

• Definition for transmission media• Characteristics of transmission media• Speed and Capacity• Frequency and Bandwidth• Signal-to-Noise Ratio• Electrical and Optical Cabling• Wireless Data Transmission

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Transmission Media

• Transmission medium – the communication path used to transport signals.

• Communication channel – consists of a sending device, receiving device and the transmission medium that connects them.

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Transmission Media

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Transmission Media

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Transmission Media

Characteristics of transmission media:

• Speed and capacity• Bandwidth• Noise, distortion, and susceptibility to external

interference

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Transmission Media

Speed and Capacity

• A raw data transfer rate is the maximum number of bits or bytes per second that the channel can carry.

• The effective data transfer rate describes the transmission capacity actually achieved with a particular communication protocol.

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Transmission Media

Frequency and Bandwidth

• Frequency is a measure of data carrying capacity.

• The difference between the maximum and minimum frequencies of a signal is the signal bandwidth.

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Transmission Media

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Transmission Media

Modulator-demodulator (modem) - technology is used to send digital signals over voice-grade telephone channels.

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Transmission Media

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Transmission Media

Signal-to-Noise Ratio

Noise – refers to any extraneous signals that might be interpreted incorrectly as data.

Attenuation – is a reduction in the strength of a signal as it passes through a transmission medium.

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Transmission Media

Signal-to-Noise Ratio

Signal to Noise Ratio – the effective speed limit of any given channel is determined by the power of the message-carrying signal in relation to the power of the noise in the channel.

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Transmission Media

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Transmission Media

Electrical and Optical Cabling

• Electrical signals usually are transmitted through copper wire.

• Optical cabling:– Fiber optic cable

• Electrical cabling:– Twisted Pair wire– Coaxial cable

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Transmission Media

Electrical and Optical Cabling - Twisted Pair Wire

• The most common transmission medium for telephone and local area network connections.

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Transmission Media

Electrical and Optical Cabling - Twisted Pair Wire

• Disadvantages:– High susceptibility to noise– Limited transmission capacity

• Advantages:– Low cost– Ease of installation

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Transmission Media

Electrical and Optical Cabling – Coaxial Cabling

Contains a single copper conductor surrounded by a thick plastic insulator, a metallic shield, and a tough outer plastic wrapping.

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Transmission Media


• Advantages:– Very resistant to EMI– High bandwidth– High data transmission capacity

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Transmission Media


• Disadvantages:– More costly than twisted pair– Harder to install

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Transmission Media

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Transmission Media

Fiber-optic cable

• Contains one or more strands of light-conducting filaments made of plastic or glass.

• Cable types – multimode and single mode.

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Transmission Media

Fiber-optic cable

• Advantages– Transmission speed– Low error rate

• Disadvantages– High cost– Difficult installation

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Transmission Media

Wireless Data Transmission

Uses short wave radio or infrared light waves to transmit data through the atmosphere or space.

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Channel Organization

• Simplex, Half Duplex and Full Duplex• Parallel and Serial Transmission• Channel Sharing

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Simplex, Half Duplex and Full Duplex

• A single communication channel requires two wires – signal wire (carries data), return wire (complete the electrical circuit between the sending and receiving devices)

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Simplex Mode

• Messages flow in one direction.• Used when data flows in one direction and

there is a small chance for transmission error.• The receiver can not notify the sender of the

error.• Used the send status messages from the host

computer.

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Half-Duplex Mode

• Uses a single shared channel.• Each node takes turns using the transmission

line to transmit and receive.• If an error is detected, the receiver can

request to have the message resent.

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Full-Duplex Mode

• The receiver can communicate with the sender at any time by using the second transmission line.

• If an error is sensed, the receiver immediately can notify the sender and halt the transmission.

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Simplex, Half-Duplex and Full-Duplex

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Parallel Transmission

• Uses a separate transmission line for each bit position.

• The number of lines is typically one word.• Parallel communication is relatively

expensive.

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Serial Transmission

• Uses only a single transmission line or line pair for electrical signals.

• Bits are sent sequentially through the single transmission line and reassembled by the receiver.


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Channel Sharing

• Transmission capacity typically is needed for short periods, or bursts.

• Channel sharing techniques combine the traffic of multiple.

• Result in more efficient utilization of available data transfer capacity.

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Channel Sharing

• Time Division Multiplexing (TDM)• Frequency Division Multiplexing (FDM)

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Time Division Multiplexing

• Describes any technique by which data transfer capacity is split into small time slices and allocated to multiple users and/or applications.

• Types of TDM – Packet Switching and Circuit Switching.

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Frequency Division Multiplexing (FDM)

• A single broadband channel is partitioned into multiple baseband subchannels.

• Each subchannel represents a single different frequency range (band).

• Signals are transmitted within each subchannel at a fixed frequency.

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Clock Synchronization

• Data must be sent using a common transmission rate.

• Senders place bits into a transmission line at precise intervals.

• Receivers examine the signal at or during specific time intervals.

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Two synchronization problems:

• Keeping sender and receiver clocks synchronized during transmission.

• Synchronizing the start of each message.

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Synchronous transmission – ensures that sender and receiver clocks are always synchronized by sending continuous data streams.

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Asynchronous transmission – messages are sent on an as-needed basis. Messages can be sent one after another or there can be periods of inactivity between messages.

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Error Detection and Correction

Methods of Error Detection:• Parity Checking• Block Checking• Cyclic Redundancy Checking

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• All error detection methods are based on some form of redundant transmission.

• A redundant message is transmitted after the original message.

• The receiver compares the two messages for a match.

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• If the two match, then the message is assumed to have been transmitted, received and interpreted correctly.

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Parity Checking (Vertical Redundancy Check)

• Used for character data.• One bit (parity bit) is appended to each

character.• Two parity schemes are used – Odd and

Even Parity.

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Parity Checking (Vertical Redundancy Check) – Odd Parity

• The parity bit is set to 0 if the number of 1 bits within the character is odd.

• The parity bit is set to 1 if the number of 1 bits within the character is even.

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Parity Checking (Vertical Redundancy Check) – Even Parity

• The parity bit is set to 0 if the number of 1 bits within the character is even.

• The parity bit is set to 1 if the number of 1 bits within the character is odd.

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Block Checking (Longitudinal Redundancy Checking)

• Used for blocks of characters.• The number of 1 bits is counted in a block of

characters by the sending computer.• The parity bits for each position are combined

into a Block Check Character (BCC) and appended to the end of the block.

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Block Checking (Longitudinal Redundancy Checking)

• The receiver counts the number of 1 bits in the block of characters and generates a Block Check Character.

• If the two Block Check Characters match,then the message is assumed to have been sent, transmitted and received correctly.

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Cyclic Redundancy Checking

• Most widely used error detection technique.• A block check character is produced. • A Cyclic Redundancy Checking character is

generated mathematically.

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Technology Focus

Wireless Network Standards

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Summary

• A communication protocol is a set of rules and conventions covering many communication aspects.

• Data bits can be encoded into analog or digital signals.

• Important characteristics of transmission media include raw data transfer rate, bandwidth, and susceptibility to noise, distortion, external interference, and attenuation.

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Summary

• The effective data transfer rate can be much less than the raw data transfer rate due to attenuation, distortion, and noise.

• Electrical cables are of two primary types – twisted pair and coaxial.

• Optical cables are of two types – multimode and single mode.

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Summary

• Data can be transmitted without wires via radio waves and infrared light.

• Channel organization describes the number of lines dedicated to a channel and the assignment of specific signals to those channels.

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Summary

• Parallel transmission uses multiple lines to send several bits per signal event. Serial transmission uses a single line to send one bit at a time.

• Channels often are shared among users and applications when no one user or application needs a continuous supply of data transfer capacity.

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Summary

• Sender and receiver must synchronize clocks to ensure that they use the same time periods and boundaries to encode and decode bit values.

• Error detection always is based on some form of redundant transmission.

1 Chapter 8 Data and Network Communication Technology.

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Transcript of 1 Chapter 8 Data and Network Communication Technology.