Chapter 8 Data and Network Communication Technology

Chapter Goals Explain communication protocols. 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.

Systems Architecture Chapter 8 Chapter Goals Describe methods for efficiently using communication channels. Describe methods for detecting and correcting data transmission errors.

Chapter Topics Communication protocols Encoding and transmitting bits Systems Architecture Chapter 8 Chapter Topics Communication protocols Encoding and transmitting bits Transmission media Channel organization Clock synchronization Error detection and correction

Communication Protocols Systems Architecture Chapter 8 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.

Communication Protocols Systems Architecture Chapter 8 Communication Protocols

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits Carrier Waves Modulation Methods Analog Signals Digital Signals Signal Capacity Errors

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits Carrier Waves Amplitude Phase Frequency

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits 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.

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits 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.

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits Modulation Methods Amplitude Modulation Frequency Modulation Phase Modulation Multilevel Coding

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits Amplitude Modulation Represents bit values as specific wave amplitudes. Amplitude modulation holds frequency constant while varying amplitude to represent data.

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits Frequency Modulation Represents bit values by varying carrier wave frequency while holding amplitude constant.

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits 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.

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits 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.

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits Analog Signals Uses the full range of a carrier wave characteristic to encode continuous data values. Analog signals are continuous in nature.

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits 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.

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits 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.

Encoding and Transmitting Bits Systems Architecture Chapter 8 Encoding and Transmitting Bits A digital signal is not as susceptible to noise and interference.

Transmission Media Definition for transmission media Systems Architecture Chapter 8 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

Systems Architecture Chapter 8 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.

Systems Architecture Chapter 8 Transmission Media

Systems Architecture Chapter 8 Transmission Media

Transmission Media Characteristics of transmission media: Systems Architecture Chapter 8 Transmission Media Characteristics of transmission media: Speed and capacity Bandwidth Noise, distortion, and susceptibility to external interference

Transmission Media Speed and Capacity Systems Architecture Chapter 8 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.

Transmission Media Frequency and Bandwidth Systems Architecture Chapter 8 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.

Systems Architecture Chapter 8 Transmission Media

Systems Architecture Chapter 8 Transmission Media Modulator-demodulator (modem) - technology is used to send digital signals over voice-grade telephone channels.

Systems Architecture Chapter 8 Transmission Media

Transmission Media Signal-to-Noise Ratio Systems Architecture Chapter 8 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.

Transmission Media Signal-to-Noise Ratio Systems Architecture Chapter 8 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.

Systems Architecture Chapter 8 Transmission Media

Transmission Media Electrical and Optical Cabling Systems Architecture Chapter 8 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

Transmission Media Electrical and Optical Cabling - Twisted Pair Wire Systems Architecture Chapter 8 Transmission Media Electrical and Optical Cabling - Twisted Pair Wire The most common transmission medium for telephone and local area network connections.

Transmission Media Electrical and Optical Cabling - Twisted Pair Wire Systems Architecture Chapter 8 Transmission Media Electrical and Optical Cabling - Twisted Pair Wire Disadvantages: High susceptibility to noise Limited transmission capacity Advantages: Low cost Ease of installation

Transmission Media Electrical and Optical Cabling – Coaxial Cabling Systems Architecture Chapter 8 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.

Transmission Media Electrical and Optical Cabling – Coaxial Cabling Systems Architecture Chapter 8 Transmission Media Electrical and Optical Cabling – Coaxial Cabling Advantages: Very resistant to EMI High bandwidth High data transmission capacity

Transmission Media Electrical and Optical Cabling – Coaxial Cabling Systems Architecture Chapter 8 Transmission Media Electrical and Optical Cabling – Coaxial Cabling Disadvantages: More costly than twisted pair Harder to install

Systems Architecture Chapter 8 Transmission Media

Transmission Media Fiber-optic cable Systems Architecture Chapter 8 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.

Transmission Media Fiber-optic cable Advantages Disadvantages Systems Architecture Chapter 8 Transmission Media Fiber-optic cable Advantages Transmission speed Low error rate Disadvantages High cost Difficult installation

Transmission Media Wireless Data Transmission Systems Architecture Chapter 8 Transmission Media Wireless Data Transmission Uses short wave radio or infrared light waves to transmit data through the atmosphere or space.

Channel Organization Simplex, Half Duplex and Full Duplex Systems Architecture Chapter 8 Channel Organization Simplex, Half Duplex and Full Duplex Parallel and Serial Transmission Channel Sharing

Channel Organization Simplex, Half Duplex and Full Duplex Systems Architecture Chapter 8 Channel Organization 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)

Systems Architecture Chapter 8 Channel Organization

Systems Architecture Chapter 8 Channel Organization

Channel Organization Simplex Mode Messages flow in one direction. Systems Architecture Chapter 8 Channel Organization 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.

Channel Organization Half-Duplex Mode Uses a single shared channel. Systems Architecture Chapter 8 Channel Organization 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.

Channel Organization Full-Duplex Mode Systems Architecture Chapter 8 Channel Organization 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.

Channel Organization Simplex, Half-Duplex and Full-Duplex Systems Architecture Chapter 8 Channel Organization Simplex, Half-Duplex and Full-Duplex

Channel Organization Parallel Transmission Systems Architecture Chapter 8 Channel Organization Parallel Transmission Uses a separate transmission line for each bit position. The number of lines is typically one word. Parallel communication is relatively expensive.

Systems Architecture Chapter 8 Channel Organization

Channel Organization Serial Transmission Systems Architecture Chapter 8 Channel Organization 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.

Systems Architecture Chapter 8 Channel Organization

Channel Organization Channel Sharing Systems Architecture Chapter 8 Channel Organization 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.

Channel Organization Channel Sharing Time Division Multiplexing (TDM) Systems Architecture Chapter 8 Channel Organization Channel Sharing Time Division Multiplexing (TDM) Frequency Division Multiplexing (FDM)

Channel Organization Time Division Multiplexing Systems Architecture Chapter 8 Channel Organization 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.

Systems Architecture Chapter 8 Channel Organization

Channel Organization Frequency Division Multiplexing (FDM) Systems Architecture Chapter 8 Channel Organization 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.

Systems Architecture Chapter 8 Channel Organization

Clock Synchronization Systems Architecture Chapter 8 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.

Clock Synchronization Systems Architecture Chapter 8 Clock Synchronization Two synchronization problems: Keeping sender and receiver clocks synchronized during transmission. Synchronizing the start of each message.

Clock Synchronization Systems Architecture Chapter 8 Clock Synchronization

Clock Synchronization Systems Architecture Chapter 8 Clock Synchronization Synchronous transmission – ensures that sender and receiver clocks are always synchronized by sending continuous data streams.

Clock Synchronization Systems Architecture Chapter 8 Clock Synchronization

Clock Synchronization Systems Architecture Chapter 8 Clock Synchronization 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.

Clock Synchronization Systems Architecture Chapter 8 Clock Synchronization

Error Detection and Correction Systems Architecture Chapter 8 Error Detection and Correction Methods of Error Detection: Parity Checking Block Checking Cyclic Redundancy Checking

Error Detection and Correction Systems Architecture Chapter 8 Error Detection and Correction 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.

Error Detection and Correction Systems Architecture Chapter 8 Error Detection and Correction If the two match, then the message is assumed to have been transmitted, received and interpreted correctly.

Error Detection and Correction Systems Architecture Chapter 8 Error Detection and Correction 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.

Error Detection and Correction Systems Architecture Chapter 8 Error Detection and Correction 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.

Error Detection and Correction Systems Architecture Chapter 8 Error Detection and Correction 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.

Error Detection and Correction Systems Architecture Chapter 8 Error Detection and Correction 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.

Error Detection and Correction Systems Architecture Chapter 8 Error Detection and Correction 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.

Error Detection and Correction Systems Architecture Chapter 8 Error Detection and Correction

Error Detection and Correction Systems Architecture Chapter 8 Error Detection and Correction Cyclic Redundancy Checking Most widely used error detection technique. A block check character is produced. A Cyclic Redundancy Checking character is generated mathematically.

Technology Focus Wireless Network Standards Systems Architecture Chapter 8 Technology Focus Wireless Network Standards

Systems Architecture Chapter 8 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.

Systems Architecture Chapter 8 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.

Systems Architecture Chapter 8 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.

Systems Architecture Chapter 8 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.

Systems Architecture Chapter 8 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.