Chapter 2 - Fundamentals of Data and Signals

A)      Introduction

a.       Possible data-to-signal conversion combinations

                                                               i.      Analog data-to-analog signal – amplitude and frequency modulation techniques

                                                             ii.      Digital data-to-square-wave digital signal – encoding techniques

                                                           iii.      Digital data-to-(a discrete) analog signal – modulation techniques

                                                           iv.      Analog data-to-digital signal – digitization techniques

1.       Digitization – converting analog data to digital signals

B)      Data and Signals

a.       Data – entities that convey meaning within a computer or system

                                                               i.      Example

1.       Computer file of names and addresses

b.       Signal – electric or electromagnetic impulses used to encode and transmit data

                                                               i.      Example

1.       Transmission of a telephone conversation over a telephone line

c.       Analog vs. Digital

                                                               i.      Analog data and analog signals are represented as continuous waveforms that can be at an infinite number of points between some given minimum and maximum. Usually presented as voltages

1.       Noise – unwanted electrical or electromagnetic energy that degrades the quality of signals and data

                                                             ii.      Digital data and digital signals are composed of a discrete or fixed number of values, rather than a continuous or infinite number of values

                                                           iii.      A look at how noise distorts digital signals

d.       Fundamentals of signals

                                                               i.      Amplitude – the height of the wave above (or below) a given reference point

1.       Denotes the voltage level of the signal (measured in volts), can also denote the current level of the signal (measured in amps), or the power level of the signal (measured in watts

                                                             ii.      Frequency – number of times a signal makes a complete cycle within a given time frame

                                                           iii.      Period – length, or time interval, of one cycle for frequency

                                                           iv.      Spectrum – range of frequencies that a signal spans from minimum to maximum

                                                             v.      Bandwidth – the absolute of the difference between the lowest and highest frequencies

                                                           vi.      Because extraneous noise degrades original signals, an electronic device usually has an effective bandwidth less than its bandwidth

                                                          vii.      Phase – the position of the waveform relative to a given moment of time, or relative to time zero

                                                        viii.      Attenuation – loss of power or loss of signal strength

1.       When traveling through any type of medium, a signal always experiences some loss of its power due to friction

                                                            ix.      Decibel (dB) – relative measure of signal loss or gain and is used to measure the logarithmic loss or gain of a signal

1.       Equation to measure signal loss or gain: 

a.       P2 = ending power level

b.       P1 = beginning power level

                                                             x.      Amplification – signal gains in decibel

C)      Converting Data into Signals

a.       Transmitting analog data with analog signals

                                                               i.      Modulation – process of sending data over a signal by varying its amplitude, frequency, or phase

b.       Transmitting digital data with square-wave digital signals: digital encoding schemes

                                                               i.      Nonreturn to zero digital encoding schemes

1.       Nonreturn to zero-level (NRZ-L) – transmits 1s as zero voltages and 0s as positive voltages

2.       Nonreturn to zero inverted (NRZI) – voltage change at the beginning of a 1 and no voltage change at the beginning of a zero

                                                             ii.      Manchester Digital Encoding Schemes

1.       Properties of Manchester encoding scheme

a.       To transmit a 1, the signal changes from low to high in the middle of the interval, and to transmit a 0, the signal changes from high to low in the middle of the interval

2.       Differential Manchester

a.       If there is a transition at the beginning of the interval, then a 0 is being transmitted, if there is no transition at the beginning of the interval, then a 1 is being transmitted

3.       Self-clocking – the occurrence of a regular transition is similar to second ticking on a clock

4.       Baud rate (baud) – the number of times a signal changes value per second

5.       Data rate is measured in bits per second (bps)

                                                           iii.      Bipolar-AMI encoding scheme – uses three voltage levels

1.       When transmitting a 0, a zero voltage is transmitted

2.       When transmitting a 1, either a negative or positive voltage is transmitted

                                                           iv.      4B/5B Digital encoding scheme – takes 4 bits of data, coverts the 4 bits into a unique 5-bit sequences, and encodes the 5 bits using NRZI

D)      Transmitting digital data with discrete analog signals

a.       Amplitude shift keying – amplitude is represented by two different amplitudes for a signal

                                                               i.      Can use more amplitudes in order to achieve two-bit representation

b.       Frequency shift keying – uses two different frequency ranges to represent data values of 0 and 1

                                                               i.      Intermodulation distortion – a phenomenon that occurs when the frequencies of two or more signals mix together and create new frequencies

c.       Phase shift keying – represents 0s and 1s by different changes in the phase of a waveform

                                                               i.      Quadrature phase shift keying – incorporates four different phase angles, each of which represents 2 bits

1.       a 45-degree phase shift represents 11

2.       a 135-degree phase shift represents 10

3.       a 225-degree phase shift represents 01

4.       a 315-degree phase shift represents 00

                                                             ii.      quadrature amplitude modulation – uses each signal to represent 4 bits

E)      Transmitting analog data with digital signals

a.       Pulse code modulation (PCM) – a codec, coverts the analog data to a digital signal by tracking the analog waveform and taking “snapshots” of the analog data at fixed intervals

                                                               i.      The binary value is then transmitted by means of a digital encoding format

                                                             ii.      Pulse amplitude modulation (PAM) – tracking an analog waveform and converting it to pulses that represent the wave’s height above a threshold

                                                           iii.      Sampling rate – frequency at which snapshots are taken

                              

b.       Delta modulation – a codec tracks the incoming analog data by assessing up or down “steps”. During each time period, the codec determines whether the waveform has risen one delta step or dropped one delta step. If the waveform rises on delta step, a 1 is transmitted, if the waveform drops, a 0 is transmitted

                                                               i.      Slope overload noise – when the analog waveform rises or drops too quickly, the

codec is not able to keep up with the change

F)       Data Codes – set of all textual characters or symbols and their corresponding binary patterns

a.       EBCDIC – 8 bit code allowed 256 (2⁸ = 256) possible combinations of textual symbols

b.       ASCII (American Standard Code for Information Interchange) – 7-bit version that allows for 128 (2⁷ = 128) possible combinations

                          

c.       Unicode – encoding technique that provides a unique coding value for every character in every language, no matter the platform

Chapter 1 – Introduction to Computer Networks and Data Communications Outline

A)      The Language of Computer Networks

a.       Computer network – an interconnected group of computers and computing equipment using either wires or radio waves that can share data and computing resources

                                                               i.      Wireless – computer networks that use radio waves. Can involve broadcast radio, microwaves, or satellite transmission

b.       Types of networks

                                                               i.      Personal area networks (PANs) – networks spanning an area of several meters around an individual. Include laptop, computers, smart cell phones, music players, and wireless connections

                                                             ii.      Local area networks (LANs) – networks spanning a room, a floor within a building, or an entire building

                                                           iii.      Campus area networks (CANs) – collections of local area networks that cover a campus (college campus or business campus)

                                                           iv.      Metropolitan area network (MANs) – networks that serve an area up to roughly 50 kilometers. They are high-speed networks that interconnect businesses with other businesses and the internet

                                                             v.      Wide area networks (WANs) – large networks encompassing parts of states, multiple states, countries, and the world

c.       Cloud

                                                               i.      Network cloud and cloud computing

d.       Data and signal

                                                               i.      Data – information that has been translated into a form more conductive to storage, transmission, and calculation.

                                                             ii.      Signal – used to transmit data

e.       Data communications – transfer of digital or analog data using digital or analog signals. Once created, these analog and signals are then transmitted over conducted media or wireless media

                                                               i.      Interfacing – sending one signal over a medium at one time

                                                             ii.      Multiplexing – the transmission of multiple signals on one medium. To transmit multiple signals simultaneously, they must be altered to not interfere with each other

                                                           iii.      Compression – squeezing data into a smaller package, thus reducing the amount of time needed to transmit the data

f.        Voice and data networks

                                                               i.      Merging of voice and data networks is an example of convergence

B)      The Big Picture of Networks

a.       Work stations – personal computers (microcomputers, desktops, laptops, or tablets) or smartphones

b.       Servers – computers that store network software and shared or private user files

c.       Switches – collection points for the wires that interconnect the workstations

d.       Routers – connecting devices between local area networks and wide area networks such as the internet

e.       Nodes – computing devices that allow workstations to connect to the network and that make the decisions about where to route a piece of data

f.        Subnetwork – consists of the nodes and transmission lines, collected into a cohesive unit

C)      Common Examples of Communications Networks

a.       The desktop computer and the internet

                                                               i.      Client/server system – client machines issues request for some form of data or service. Could be for database record from database server or request for a Web page from a Web server

b.       A laptop and a wireless connection

                                                               i.      Data communication protocols – sets of rules used by communication devices

c.       Cell phone system

d.       Other common network systems

         

                                                               i.      Computer terminal – a device that was essentially a keyboard and screen with no large hard drives, no gigabytes of memory, and little, if any, processing power

D)      Convergence – process of coming together toward a single point

E)      Network architectures

a.       Network architecture (communications model) – places the appropriate network pieces in layers. Each layer in the model defines what services either the hardware or software provides

                                                               i.      TCP/IP protocol suite – working model (currently used on the internet)

 

1.       Application layer – supports the network applications and in some cases include additional services such as encryption or compression

a.       Hypertext Transfer Protocol (HTTP) – allow Web browsers and servers to send and receive World Wide Web pages

b.       Simple Mail Transfer Protocol (SMTP) – allow users to send and receive electronic mail

c.       File Transfer Protocol (FTP) – transfer files from one computer system to another

d.       Telnet - allow a remote user to log in to another computer system

e.       Simple Network Management Protocol (SNMP) – the numerous elements within a computer network that are managed from a single point

2.       Transport layer – uses TCP to maintain an error-free end-to-end connection.

a.       Includes error control information in case one packet from a sequence of packets does not arrive at the final destination and package sequencing information so that all packets stay in the proper order.

b.       Performs end-to-end error control and end-to-end flow control

3.       Network layer (internet layer or IP layer) – used to transfer data within and between networks

a.       Internet protocol (IP) – software that prepares a packet of data so that it can move from one network to another on the internet or within a set of corporate networks

                                                                                                                                       i.      Generates the network addressing necessary for the system to recognize the next intended receiver

4.       Network access layer – layer that gets the data from the user workstation to the internet

a.       Prepares a data package (called a frame) for transmission from the user workstation to a router sitting between the local area network and the Internet

5.       Physical layer – layer in which the actual transmission of data occurs

a.       Physical layer handles voltage levels, plug and connector dimensions, pin configurations and other electrical and mechanical issues

b.       Also determines encoding or modulation technique to be used in the network

                                                             ii.      Open Systems Interconnection (OSI) model – originally designed to be a working model but has been used as a theoretical model

1.       Application layer – where the application using the network resides

2.       Presentation layer – performs a series of miscellaneous functions necessary for presenting the data package properly to the sender or receiver

3.       Session layer – responsible for establishing sessions between users

a.       Can support token management, a service that controls which user’s computer talks during the current sessions by passing a software token back and forth

b.       Also establishes synchronization points – backup points used in case of errors or failures

4.       Transport layer – ensures that the data packet that arrives at the final destination is identical to the data packet that left the originating stations

5.       Network layer – responsible for getting the data packets from router to router

6.       Data link layer – responsible for taking data from the network layer and transforming it into a frame

7.       Physical layer – handles the transmission of bits over a communications channel

                                                           iii.      Logical and physical connections

1.       Logical connection – nonphysical connection between sender and receiver that allows an exchange of commands and responses

2.       Physical connection – only direct connection between sender and receiver and is at the physical layer, where actual 1s and 0s – the digital content of the message – are transmitted over wires and airwaves

F)       Encapsulation – control information to a package as it moves through the layers