Chapter 22: Fundamental Concepts of Data Communications – Review Notes

(Last Updated On: December 8, 2017)

Chapter 22: Fundamental Concepts of Data Communications

This is the summary notes of the important terms and concepts in Chapter 22 of the book "Electronic Communications System" by Wayne Tomasi. The notes are properly synchronized and concise for much better understanding of the book. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.


CHAPTER 22

FUNDAMENTAL CONCEPTS OF
DATA COMMUNICATIONS


Items

Definitions

Terms

1

Often used to represent characters and symbols such as
letters, digits and punctuation marks.
Another terms:
·        
character
codes
·        
character
sets
·        
symbol
codes
·        
character
languages

Data Communications Codes

2

Sometimes called the Telex Code, was the first fixed length
character developed for machines rather than for people.

Baudot Code

3

A French postal engineer who developed the baudot code in 1875
and named after Emile Baudot, an early pioneer in telegraph printing.

Thomas Murray

4

Fixed-length source code.

Fixed Length Block Code

5

Stands for United States of America Standard Code for
Information Exchange, better known as ASCII-63.

USASCII

6

The standard character set for source coding the alphanumeric
character set that humans understand but computers do not (computers only
understand 1s and 0s).
It is a seven bit fixed-length character set.

ASCII

7

Fixed-length source code.

Fixed Length Block Code

8

Extended binary coded decimal interchange-code, an eight bit
fixed length character developed in 1962 by International Business Machines
Corporation.

EBCDIC

9

Omnipresent block and white striped stickers that seem to
appear or virtually every consumer item in the US and most of the rest of the
world.

Bar Codes

10

It has spaces or gaps between characters. Each character is
independent of every other character.

Discrete Code

11

It does not include spaces between characters. An example is
Universal Product Code.

Continuous Code

12

It stores data in two dimensions in contrasts with
conventional linear bar codes which stores data along only one axis.

2D code

13

It uses an alphanumeric code similar to ASCII code. It
contains 9 vertical elements (5 bars & 4 spaces). It consists of 36
unique codes representing the 10 digits and 26 uppercase letters.
Other Names:
·        
Code
3 of 9
·        
3 of
9 code

Code-39

14

A continuous code since there are no interchangeable spaces.
Each UPC label contains a 12-digit number.

Universal Product Code

15

It consists of a 101 (bar-soace-bar) sequence, which is used
to frame the 12 digit UPC number.

Start & Stop Guard
Pattern

16

It separates the left and right halves of the label and
consists of two long bars in the center of the label.

Center Guard Frame

17

Caused by electrical interference from natural sources
Classification of Data Com Errors:
·        
single
bit
·        
multiple
bit
·        
burst

Categories of Error Control :
·        
Error
Detection
·        
Error
Correction


Transmission Errors

18

Errors with only one bit within a given a given string is in
error.

Single Bit Errors

19

Errors with two or more non-consecutive bits within a message.

Multiple-bit error

20

Errors when to or more consecutive bits within a given data
string are in error. It can affect one or more characters within a message.

Burst Error

21

The theoretical (Mathematical) expectation of the rate at
which errors will occur.

Probability of Error

22

The actual historical record of a system’s error performance.

Bit-Error Rate

23

The process of monitoring data transmission and deter mining
when errors have occurred. It neither correct errors nor identify which bits
are in error-they only indicate when an error has occurred.

Error Detection

24

Adding of bits for the sole purpose of detecting errors.
Types of redundancy checks:
·        
vertical
redundancy checking,
·        
checksum,

·        
longitudinal
redundancy checking
·        
cyclic
redundancy checking


Redundancy Checking

25

A form of error detection by duplicating each data unit for
the purpose of detecting errors.

Redundancy

26

An error detection bit.

Parity

27

The simplest error-detection scheme and is generally referred
to as character parity.

Vertical Redundancy Checking
(VRC)

28

An error detection bit in each character.

Parity Bit

29

The parity bit which is always a 1.

Marking Parity

30

The parity bit which is not sent or checked.

Ignored Parity

31

Form of redundancy error checking where each character has a
numerical value assigned to it.

Checksum

32

A redundancy error detection scheme that uses parity to
determine if a transmission error has occurred with n a message.

Longitudinal Redundancy Checking
(LRC)

33

An error occurred within a message.

Message Parity

34

The group pf characters that comprise a message.

Block or Frame of Data

35

The bit sequence for the LRC.

Block Check Sequence
(BCS)
or Frame Check Sequence
(FCS)

36

A convolution coding scheme that is most reliable redundancy
checking technique for error detection. Almost 99.999% of all transmission
errors are detected

Cyclic Redundancy Checking

37

Types of Error Messages.

Lost Message Damaged Message

38

One that never arrives at the destination or one that is
damaged to the extent that it is unrecognizable.

Lost message

39

One that is recognized at the destination but contains one or
more transmission errors.

Damaged Message

40

It includes enough redundant information with each transmitted
message to enable the receiver to determine when an error has occurred.
Examples:
·        
Parity
bits
·        
block
and frame check characters
·        
cyclic
redundancy characters

Error-Detecting Codes

41

It includes sufficient extraneous information along with each
message to enable the receiver to determine hen an error has occurred and
which bits is in error.
Two primary methods for error correction:
·        
Retransmission

·        
Forward
Error Correction


Error-correcting Codes

42

When a receive station requests the transmit station to resend
a message when the message is received in error.

Retransmission

43

A two-way radio term which automatically a retransmission f
the entire message.
Types of ARQ:
·        
Discrete

·        
Continuous


Automatic Repeat
Request (ARQ) or
Automatic Retransmission Request

44

The recipient of data sends a short message back to the sender
acknowledging receipt of the last transmission.
Types of acknowledgements:
·        
Positive

·        
Negative


Acknowledgement

45

A receive station becomes the transmit station such as when
acknowledgments are sent or when retransmission are sent in response to a
negative acknowledgment.

Line Turnarounds

46

It uses acknowledgments to indicate the successful or
unsuccessful reception of data.

Discrete ARQ

47

It can be used when messages are divided into smaller lock or
frames that are sequentially numbered and transmitted in succession, without
waiting for acknowledgments between blocks.

Continuous ARQ

48

The sending station does not receive an acknowledgment after a
predetermined length of time.

Retransmission Time-Out

49

The destination station asynchronously requests the
retransmission of specific frame of data and still be able to reconstruct the
entire message once all frames have been successfully transported through the
system.

Selective Repeat

50

The error-correction scheme that detects and corrects
transmission errors when they are received without requiring a
retransmission.

Forward Error Correction
(FEC)

51

A mathematician, who was an early pioneer in the development
of error-detection and correction procedures, developed the Hamming Code
while working at Bell Telephone Laboratories.

Richard W. Hamming

52

An error-correcting code used for correcting transmission
errors in synchronous data streams. It requires the addition of overhead to
the message, consequently increasing the length of a transmission.

Hamming Code

53

Inserted into a character at random locations.

Hamming Bits

54

The combination of the data bits and the hamming bits.

Hamming Code

55

It means to harmonize, coincide, or agree in time.

Synchronize

56

Involves identifying the beginning and end of a character with
in a message.

Character Synchronization

57

Its literal meaning is “without synchronism”. In Data Com, it
means “without a specific time reference”

Asynchronous

58

Asynchronous communications is called as such because each
data character is framed between start and stop bits.

Start-stop Transmission

59

A condition when the transmit and receive clocks are
substantially different.

Clock Slippage

60

It occurs when the transmit clock is substantially lower than
the receive clock.

Under slipping

61

Occurs when the transmit clock is substantially higher than
the receiver clock.

Overslipping

62

It involves transporting serial data at relatively high speeds
in groups pf characters.

Node

63

Interconnects digital computer equipment.

Synchronous Data

64

Plain old Telephone system

POTS

65

It is comprised of three basic elements:
·        
transmitter
(source)
·        
transmission
path (data channel)
·        
receiver
(destination)
3 fundamental components of endpoints:
·        
data
terminal equipment
·        
data
communications equipment
·        
serial
interface

Data Communications
System

66

It can be virtually any binary digital device that generates
transmits, receives, or interprets data messages. It is where information
originates or terminates.

Data Terminal
Equipment (DTE)

67

Devices used to input, output and display information such as
keyboards, printers and monitors

Terminal

68

Basically a modern-day terminal with enhance computing
capabilities

Client

69

High-powered, high capacity mainframe computers that support
terminals.

Hosts

70

It functions as modern-day host.

Servers

71

A general term use to describe equipment that interfaces data
terminal equipment to a transmission channel, such as a digital T1 carrier or
an analog telephone circuit. It is a signal conversion device, as it converts
signals from a DTE to a form more suitable to be transported over
transmission channel.
Types of DCE:
·        
channel
service units (CSUs)
·        
Digital
service units (DSUs)
·        
data
modems

Data Communications Equipment
(DCE)

72

Another term for DCE.

Data Circuit-terminating Equipment
(DCTE)

73

A DCE used to interface a DTE to an analog telephone circuit
commonly called POTS.

Data Modem

74

It controls data flow between several terminal devices and the
data communications channel.

Cluster Controller

75

Line control units at secondary stations.

Station Controllers
(STACOs)

76

Universal Asynchronous Receiver/transmitter it is designed for
asynchronous data transmission.

UART

77

A special purpose UART chip manufactured by Motorola.

Asynchronous
Communications
Interface Adapter
(ACIA)

78

It means that an asynchronous data format is used and no
clocking information transferred between the DTE and the DCE.

Asynchronous Data Transmission

79

An n-bit data register that keeps track of the status of the
UART’s transmits and receive buffer registers.

Status Word

80

Transmit shift register has completed transmission of data
character.

Transmit Buffer Empty
(TBMT)

81

Set when a received character has a parity error in it.

Receive Parity Error
(RPE)

82

Set when a character is received without any or with improper
number of stop bits.

Receive Framing Error
(RFE)

83

Set when a character in the receive buffer register is written
over by another receive character.

Receiver Overrun
(ROR)

84

A data character has been received and loaded
into the receive data register.

Receive Data Available
(RDA)

85

The difference in time between the beginning of a start bit
and when it is detected.

Detection Error

86

It is used for synchronous transmission of data between a DTE
and a DCE.
Functions of USRT:
·        
Serial
to parallel and parallel to serial data conversions
·        
Error
detection by inserting parity bits in the transmitter and checking parity
bits in the receiver.
·        
Insert
and detect unique data synchronization (SYN) characters
·        
Formatting
data in the transmitter and receiver.
·        
Provide
transmit and receive status information to the CPU.
·        
Voltage-level
conversion between the DTE and the serial interface and vice versa.
·        
Provide
a means of achieving bit and character synchronization.

Universal Synchronous Receiver/transmitter
(USRT)

87

It should provide the ff:
·        
A
specific range of voltages for transmit and receive signal levels
·        
Limitations
for the electrical parameters of the transmission line.
·        
Standard
cable and cable connectors
·        
Functional
description of each signal on the interface.

Serial Interface

88

In 1962, standardized the interface equipment between data
terminal equipment and data communications equipment.

Electronics Industries Association
(EIA)

89

It means “Recommended Standards”

RS

90

The official name of the RS-232 interface.

Interface Between Data
Terminal Equipment and
Data Communications
Equipment Employing
Data Communications
Equipment Employing
Serial Binary Interchange

91

In, 1969, the third revision which was published and remained
the industrial standard until 1987.

RS-232C

92

Sometimes referred to as the EIZ-232 standard Versions D and E
of the RS-232 standard changed some of the pin designations.

RS-232D

93

It is a sheath containing 25 wires with a DB25P-compatible
male connector (plug) on one end and a DB25S-compatible female connector
(receptacle) on the other end.
Two full-duplex channels:
·        
Primary
data-actual information
·        
secondary
data-diagnostic information and handshaking signals

Star Topology

94

It is designed for transporting asynchronous data between a
DTE and a DCE or between DTEs.

9-pin Version of RS-232

95

It is designed for transporting either synchronous or
asynchronous data between a DTE and a DCE.

25 pin Version

96

It is designed exclusively for dial-up telephone. It is used
for transporting asynchronous data between a DTE and a DCE when the DCE is
connected directly to a standard two-wire telephone line attached to the
public switched telephone network.

EIA-561

97

It converts the internal voltage levels from the DTE and DCE
to RS-232 values.

Voltage-Leveling Circuits

98

A voltage leveler wherein its output signals onto the cable.

Driver

99

It accepts signals from the cable.

Terminator

100

Protective ground, frame ground, or chassis ground.

FUNCTIONS OF RS-232 PINS
Pin 1

101

Transmit data or send data.

Pin 2

102

Receive data (RD or RxD).

Pin 3

103

Request to send (RS or RTS)

Pin 4

104

Clear to send.(CS or CTS)

Pin 5

105

Data set ready or modem ready.(DSR or MR)

Pin 6

106

Signal ground or reference ground.

Pin 7

107

Unassigned and non-EIA specified often held at +12V

Pin 8

108

Receive line signal detect, carrier detect or data carrier
detect (RLSD, CD or DCD)

Pin 9

109

Unassigned and often held at -12 Vdc for test purposes

Pin 10

110

Secondary receive line signal detect, secondary carrier detect
or secondary data carrier detect (SRLSD, SCD, or SDCD)

Pin 12

111

Secondary clear to send.

Pin 13

112

Secondary transmit data or secondary send data

Pin 14

113

Transmission signal element timing or serial Clock transmit.

Pin 15

114

Secondary received data

Pin 16

115

Receiver signal element timing or serial clock receive

Pin 17

116

Unassigned is used for local loopback signal

Pin 18

117

Secondary request to send

Pin 19

118

Data terminal ready.

Pin 20

119

Signal quality detector.

Pin 21

120

Ring indicator (RI)

Pin 22

121

Data signal rate selector (DSRS)

Pin 23

122

Transmit signal element timing or serial clock transmit-DTE

Pin 24

123

Unassigned. It is sometimes used as a control signal from the
DCE to the DTE to indicate that the DCE is in either the remote or local loop
back mode.

Pin 25

124

It specifies a 37-pin primary connector DB37 and a 9 pin
secondary connector DB9 for a total of 46 pins which provides more functions,
faster data transmission rates and spans greater distances than the RS-232.
Primary goals of RS-449:
·        
Compatibility
with the RS-232 interface standard
·        
Replace
the set of circuit names and mnemonics
·        
Provide
separate cables and connectors
·        
Reduce
crosstalk
·        
offer
higher data transmission
·        
longer
distances over twisted pair cables
·        
loopback
capable
·        
improve
performance and reliability specify a standard connector
Two categories:
·        
Category
I
·        
Category
II

RS-449 Serial Interface

125

Used by the DTE to request a local loopback from the DCE.

10 CIRCUITS IN RS-449
1.Local Loopback

126

Used by the DTE to request a remote loopback from the distant
DCE.

2.Remote Loopback

127

Allows the DTE to select the DCE’s transmit and receive
frequencies.

3. Select frequency

128

Used by DTE to signal the DCE that a test is in progress.

4.Test Mode

129

Common return wire for unbalanced signals propagating from the
DCE to the DTE

5. Receive Common

130

Used by the DTE to signal the DCE whether it is operational

6. Terminal in Service

131

Used by the DTE to request that the DCE switched to standby
equipment.

7. Select Standby

132

Used with a modem at the primary location of a multipoint data
circuit.

8. New Signal

133

It was intended to operate at data rates between 20 kbps and 2
Mbps using the same DB25 connector

RS-530 Serial Interface

134

It is used to interface computers, computer networks to analog
transmission media
Alternate names:
·        
datasets

·        
dataphones

·        
modems


Data Communications
Modem

135

A contraction derived from the words Modulator and
Demodulator.
Primary Block of a Modem:
·        
Serial
interface Circuit
·        
Modulator
Circuit
·        
Bandpass
filter and equalizer circuit
·        
telco
interface circuit
·        
demodulator
circuit
·        
carrier
and clock generation circuit

Modem

136

Data communications modems designed to operate over the
limited bandwidth of the PSTN.

Voice-band Modem

137

It is able of transporting higher bit rates.

Broadband Modem

138

Digital to analog converter.

DAC

139

Analog to digital converter.

ADC

140

It is a rate of change of signals on the transmission medium
after encoding and modulation have occurred

Baud

141

Refers to the rate of change of a digital information signal.

Bit Rate

142

It is classified as low-speed voice-band modems.

Asynchronous Modems

143

Synchronous data transported by asynchronous modems.

Isochronous Transmission

144

It uses PSK or quadrature amplitude modulation to transport
data.

Synchronous Modems

145

A special, internally generated bit pattern in transmit modem.

Training Sequence

146

Located in the transmit section of a modem and provide
pre-equalization

Compromise Equalizers

147

Located in the receiver section of a modem where they provide
post-equalization to the received signals

Adaptive Equalizer

148

The first internationally accepted standard for 9600bps data
transmission rate.

ITU-T V.29

149

It is intended to provide synchronous data transmission over
four-wire leased lines.

V.29 Standard

150

Five bits.

Quin bits

151

A technique for full-duplex operation over two wire switched
telephone lines.

Echo Cancellation

152

It address asynchronous-to synchronous transmission
conversions and error control that includes both detection and correction. It
specifies a new protocol called Link Access Procedures for Modems.

V.32 Specification

153

It is the next generation data transmission with data rates of
28.8 Kbps without compression possible using V.34.
V.34 Innovations:
·        
Nonlinear
coding
·        
multidimensional
coding and constellation shaping
·        
Reduced
complexity
·        
precoding
of data
·        
line
probing

V.fast

154

An enhanced standard adopted by ITU in 1996. It adds 31.2 kbps
and 33.6 kbps to the V.34 specification.

V.34+

155

Developed by ITU-T in February 1998 during a meeting in
Geneva, Switzerland. It defines an asymmetrical data transmission technology
where the upstream 33.6kbps and downstream of 56kbps.

V.90 Recommendation

156

A new modem standard in 2000 which offers 3 improvements over
V.90 that can be achieved only if both the transmit and receive modems and
the internet Service Provider (ISP) are compliant.
It offers:
·        
upstream
transmission rate of 48 kbps
·        
faster
call setup capabilities
·        
incorporation
of a hold option

V.92 Recommendation

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Chapter 22: Fundamental Concepts of Data Communications – Review Notes
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