233 Questions
Data communications topologies are organized as ______
one-to-one (point-to-point), one-to-many (multi-drop), or many-to-many (networked)
The purpose of communication is to transmit ______ from the source to the destination(s)
data
In data communications, the media we use are: electrical conductors, light pipes, and electromagnetic transmission (usually referred to as ______)
wireless or radio
Point-to-point means just that, from one ______ to another, or directly from source to destination
point to another
Binary (Base 2) is used in data transmission systems due to its simplicity as a ______ signal
on-off
Analog signals, contrasting with binary digital signals, represent ______ quantities and are commonly used in industrial communications
continuous
4–20 mA current loop signal is a widely used industrial communications standard for representing 0% to 100% of a ______
range
Voltage is the difference in electrical potential, current performs the work, and resistance is the opposition a conductor offers to ______
current
Impedance is the opposition a conductor offers to a changing current value, and is measured in ______
Ohms
The ISA50 committee established the current loop as a standard due to its low impedance, greater noise immunity, and ability to power loop ______
instruments
All number systems are digital, including octal (Base 8) and hexadecimal (Base 16), used for human readability in coding and data ______
analysis
Bit patterns are organized into information through protocols or application programming ______
interfaces
Text is organized into codings, such as American Standard Code for Information Interchange ______
(ASCII)
Voltage is the difference in electrical ______, current performs the work, and resistance is the opposition a conductor offers to current
potential
Impedance is the opposition a conductor offers to a changing current value, and is ______ in Ohms
measured
The ISA50 committee established the current loop as a standard due to its low ______, greater noise immunity, and ability to power loop instruments
impedance
ASCII uses ______ bits with an eighth bit reserved for parity
7
EBCDIC uses ______ bits
8
Unicode uses ______ bits
16
EBCDIC uses ______ for special characters
blank spaces
Unicode has more than ______ characters
100,000
Morse code uses ______ for encoding
symbols
Error correction in data transmission uses ______ for error detection
CRC (Cyclic Redundancy Check)
ASCII has ______ characters, including uppercase and lowercase letters, digits, and some special characters
128
EBCDIC does not require a parity bit but instead uses ______ for error detection
CRC (Cyclic Redundancy Check)
Unicode is an industry standard for encoding that uses ______ bits
16
ASCII uses ______ for representation of a character
8 bits
EBCDIC is a proprietary system developed by ______
IBM
Multi-drop systems consist of a master station and slave stations, also classified as a ______.
network
In data communications, there are three modes of ______: simplex, half-duplex, and duplex.
transmission
Simplex, or uni______al mode, allows communication in one ______.
direction
Half-duplex mode allows communication in both directions but not at the same ______.
time
Duplex mode allows communication in both directions ______.
simultaneously
Serial transmission uses one ______ and sends bits one after the other.
channel
Parallel transmission uses multiple ______ and sends multiple bits at once.
channels
Parallel transmission has higher data ______ but faces challenges with logistics and simultaneous reception over distance.
throughput
Cross-talk increases with signaling ______, making it increasingly difficult to obtain faster data ______s.
rate
Most data ______ outside of computer cabinets are by serial transmission, while parallel transmission is used in computers.
transmissions
Parallel transmission is being replaced by serial transmission ______ like USB.
technologies
Digital signals have defined discrete ______, and binary digital signals have only two ______: a '1' or a '0'.
states
Standard signals in measurement and control allow users to pick and choose among vendors with confidence, and enable manufacturers to build instruments for a larger user base
standard
Digital Standard Signals include both open and proprietary standards in the telephone and ______ data communications area, but no open, all-______ standard has been established as an alternative to the analog 4–20 mA signal
digital
______ is an international standard for industrial fieldbuses, which defines eight different fieldbuses, four of which are primarily used in process control (PROFIBUS PA and FOUNDATION Fieldbus)
IEC 61158
______ is a physical and signal standard that continues to gain market share and acceptance in automation areas, and most fieldbuses and proprietary systems now provide networking services via ______
Ethernet
Data Organization: Communications Codes are the components of data organization designed for interface with humans. IBM designed one of the first digital communications codes: the ______ in 1947
IBM 4 of 8 Code
______, also known as International Telegraphic Alphabet (ITA) #5, is a 7-bit code that was designed in 1963 by the US government and gradually gained acceptance due to its numerically arranged code
ASCII
IBM 4 of ______ Code is a proprietary code with ______ bits for each character, which was used to detect character errors but carried a large overhead
8
______ does not make use of letter frequencies, but uses a numerically arranged code that permits sorting operations
ITA #5 (ASCII)
ITA #5 (ASCII) is usually transmitted as an ______ signal with the Most Significant Bit reserved for parity, but today when parity is used, another bit is added as the parity bit, making the signal 9 bits in length
8-bit
Data communications topologies are organized as one-to-one (point-to-point) or one-to-many (multi-drop) but not many-to-many (networked)
False
Multi-drop topology more closely resembles a network than it does point-to-point topology
True
In data communications, ASCII uses 7 bits for representation of a character
True
EBCDIC uses a parity bit for error detection
False
Multi-drop systems consist of a master station and slave stations, also classified as a network.
True
Simplex, or unidirectional mode, allows communication in one direction.
True
Parallel transmission uses multiple channels and sends multiple bits at once.
True
Parallel transmission has higher data throughput but faces challenges with logistics and simultaneous reception over distance.
True
Most data transmissions outside of computer cabinets are by serial transmission, while parallel transmission is used in computers.
False
Parallel transmission is being replaced by serial transmission technologies like USB.
True
Digital signals have defined discrete states, and binary digital signals have only two states: a '1' or a '0'.
True
Half-duplex mode allows communication in both directions but not at the same time.
True
Duplex mode allows communication in both directions simultaneously.
True
Serial transmission uses one channel and sends bits one after the other.
True
In data communications, there are three modes of transmission: simplex, half-duplex, and duplex.
True
Cross-talk increases with signaling rate, making it increasingly difficult to obtain faster data rates.
True
ASCII and EBCDIC are both based on fixed-length character representations and are still in use today
True
Unicode uses 7 bits for character representation
False
EBCDIC does not require a parity bit but instead uses CRC (Cyclic Redundancy Check) for error detection
True
Unicode allows users to represent ASCII characters without issue
True
ASCII, EBCDIC, and Unicode are all insufficient for representing multiple languages that require more than 128 patterns
False
Morse code is discussed in the text as a historical context of code representations
True
Error correction in data transmission uses CRC (Cyclic Redundancy Check) for error detection
False
The focus of the text is on specific examples and applications of encoding systems
False
EBCDIC uses 8 bits for character representation
False
ASCII uses 7 bits for character representation with an eighth bit reserved for parity
True
Unicode uses 16 bits for character representation
True
EBCDIC is an industry standard for encoding, representing, and handling text
False
Ethernet is a physical and signal standard that continues to lose market share and acceptance in automation areas
False
IEC 61158 defines four different fieldbuses, all of which are primarily used in process control
False
ASCII, also known as International Telegraphic Alphabet (ITA) #5, is an 8-bit code designed in 1963 by the US government
False
IBM 4 of 8 Code is a proprietary code with 8 bits for each character and is used to detect character errors with low overhead
False
ITA #5 (ASCII) is transmitted as a 9-bit signal with the Most Significant Bit reserved for parity
True
Digital Standard Signals include both open and proprietary standards in the telephone and digital data communications area, and an open, all-digital standard has been established as an alternative to the analog 4–20 mA signal
False
Standard signals in measurement and control do not allow users to pick and choose among vendors with confidence
False
Data Organization: Communications Codes are not designed for interface with humans
False
ASCII, also known as International Telegraphic Alphabet (ITA) #5, does not make use of letter frequencies, but uses a numerically arranged code that permits sorting operations
True
EBCDIC is a proprietary code with 7 bits for each character, used to detect character errors with low overhead
False
Ethernet is a physical and signal standard that continues to gain market share and acceptance in automation areas, and most fieldbuses and proprietary systems now provide networking services via Ethernet
True
IEC 61158 is an international standard for industrial fieldbuses, which defines eight different fieldbuses, four of which are primarily used in process control (PROFIBUS PA and FOUNDATION Fieldbus)
True
Binary (Base 2) is used in data transmission systems due to its complexity as a continuous signal
False
4–20 mA current loop signal is a widely used industrial communications standard for representing 0% to 100% of a range
True
Voltage is the difference in electrical potential, current performs the work, and resistance is the opposition a conductor offers to current
True
Impedance is the opposition a conductor offers to a changing current value, and is measured in Volts
False
The ISA50 committee established the current loop as a standard due to its high impedance, lower noise immunity, and inability to power loop instruments
False
Analog signals, contrasting with binary digital signals, represent discrete quantities and are commonly used in industrial communications
False
Bit patterns are organized into information through protocols or application programming interfaces
True
Text is organized into codings, such as American Standard Code for Information Interchange (ASCII)
True
All number systems are digital, including octal (Base 8) and hexadecimal (Base 16), used for human readability in coding and data analysis
True
Digital signals have defined discrete levels, and binary digital signals have only two states: a '1' or a '0'
True
Impedance is the opposition a conductor offers to a changing current value, and is measured in Ohms
True
Voltage is the difference in electrical potential, current performs the work, and resistance is the opposition a conductor offers to current
True
What are the three modes of transmission in data communications?
Simplex, half-duplex, and duplex
What are the media types used in data communications?
Electrical conductors, light pipes, and electromagnetic transmission
What are the two main topologies in data communications?
One-to-one (point-to-point) and one-to-many (multi-drop)
What are the defined relationships among members of a network?
Peers or ranked (master/slave)
What is the mode of transmission that allows communication in both directions but not at the same time?
Half-duplex
Which mode of transmission allows communication in both directions simultaneously?
Full-duplex
What type of transmission uses one channel and sends bits one after the other?
Serial transmission
Which transmission method uses multiple channels and sends multiple bits at once?
Parallel transmission
What is the primary challenge faced by parallel transmission over long distances?
Logistical challenges
Which number system is used for human readability in coding and data analysis?
Hexadecimal (Base 16)
What is the most widely used industrial communications standard for representing 0% to 100% of a range?
4–20 mA current loop signal
What is the unit of measurement for impedance?
Ohms
What did the ISA50 committee establish as a standard due to its low impedance, greater noise immunity, and ability to power loop instruments?
Current loop
'Bit patterns are organized into information through protocols or application programming interfaces' - What is used to organize bit patterns into information?
$j(x) = 4x + 9
What represents continuous quantities and is commonly used in industrial communications?
Analog signals
What is used for data transmission systems due to its simplicity as an on-off signal?
Binary (Base 2)
What is the purpose of communication?
To transmit data from the source to the destination(s)
What does ASCII stand for?
American Standard Code for Information Interchange
What does EBCDIC stand for?
Extended Binary Coded Decimal Interchange Code
What does Unicode use for character representation?
16 bits
'Digital signals have defined discrete states, and binary digital signals have only two states: a '1' or a '0'.' - What kind of signals have defined discrete states?
Digital signals
Which of the following is a standard for industrial fieldbuses that defines eight different fieldbuses, four of which are primarily used in process control?
PROFIBUS PA
What is the international standard for encoding, representing, and handling text that uses 8 bits for each character?
EBCDIC
Which code was designed in 1963 by the US government and gradually gained acceptance due to its numerically arranged code?
ASCII
Which signal standard has not been established as an alternative to the analog 4–20 mA signal?
Ethernet
'ITA #5' is another name for which encoding system?
ASCII
What is the opposition a conductor offers to a changing current value, measured in Volts?
Impedance
What type of signals have defined discrete states, with binary digital signals having only two states: '1' or '0'?
Digital signals
What type of transmission allows communication in both directions simultaneously?
Duplex
Which of these is an example of a digital communications code designed for interface with humans?
ASCII
What type of transmission allows communication in one direction only?
Simplex
What is used to convert current to voltage and provide the measurement signal in a current loop?
250-ohm resistor
How many characters does ASCII include?
128 characters
How many bits does Unicode use for character representation?
16 bits
What is the purpose of the eighth bit in ASCII?
To provide parity
What is the main limitation of ASCII and EBCDIC in representing multiple languages?
Limited to 256 patterns
Which encoding system does not require a parity bit but uses CRC for error detection?
EBCDIC
What is the total number of characters covered by Unicode?
>100,000 characters
How many bits are used by EBCDIC for character representation?
8 bits
What is the number of bits used by ASCII for character representation?
7 bits
What type of error detection is used by EBCDIC?
Cyclic Redundancy Check (CRC)
What is the main limitation of ASCII in representing multiple languages?
Limited to 128 patterns
Explain the concept of parity and its role in error detection in data communication systems.
Parity is a means of error detection in data communication systems. It involves adding an extra bit (parity bit) to the data structure to ensure a specific number of 1s in the character. The system can use 'odd' or 'even' parity, and the parity bit is chosen to make the total number of 1s in the character (including the parity bit) either odd or even. If the received data does not have the correct parity, an error is detected.
Describe the IBM 4 of 8 Code and its significance in error detection.
The IBM 4 of 8 Code is an early form of error detection used to detect errors in transmitted data. It checks if any character has more or less than four 1s in 8 bits. If an error is detected, the entire block of data (84 characters) is retransmitted. This code was significant in early data communication systems for ensuring more reliable data transmission.
What is block parity in the context of data communication, and how is it related to the format of transmitted data?
Block parity refers to the use of a vertical character format in data transmission systems, often based on the 80-column structure of punched cards. Due to historical data storage on punched cards, transmissions were organized in 80-character 'blocks.' If an error was detected in any character within the block, the entire block (84 characters) would be retransmitted, emphasizing the significance of error detection and retransmission in early data communication.
Discuss the relationship between the properties of the transmission medium, error probability, and the need for error detection in data communication systems.
The probability of error in data transmission depends on the properties of the transmission medium and the signal. Different media and signal properties can result in varying error probabilities. As a result, error detection mechanisms, such as parity and block parity, are crucial in identifying and correcting errors that occur during data transmission.
What is the main means of synchronizing the start-stop bits within each character in the old 'start-stop' teletypewriter signal?
motor speed
What is the baud rate?
the line modulation rate; that is, the number of signal changes per second that are placed on the communication medium in a given time
What is the difference between baud rate and bits per second?
Baud rate is the line modulation rate, while bits per second is the data transmission rate of the device that is transmitting or that a device is capable of receiving
What type of transmission uses bit timing and accounts for each bit of data?
synchronous transmission
What technique is used by modems running at 33.6 Kbps to achieve their higher data rate?
trellis encoding
What is the primary benefit of duplex operation in the Bi-Sync protocol?
eliminating the turnaround time, because the transmitter could do nothing else until it received a response to its transmitted block
What is the cost of data storage approximately in 1980 dollars when Bi-Sync was developed?
one US dollar per bit
What is the primary means of synchronizing the start-stop bits within each character in the old 'start-stop' teletypewriter signal?
motor speed
What is the clock signal typically transmitted along with in synchronous transmission?
the data, usually in the transition of data from one state to another
What is the data transmission rate of a device that is transmitting or that a device is capable of receiving?
bits per second
What is the term used to describe a change in a transmission medium signaling state?
baud per second
What technique is used to ensure data state transitions in most modern hardware?
scrambler
What is the purpose of Bi-Sync's transparent mode?
To allow control characters to be ignored until the receiver detects several data link escape characters.
What is the distinguishing feature of bit-oriented protocols in modern communications?
They make the protocol independent of the transmitted message type.
What is the purpose of the start delimiter in framing for bit-oriented protocols?
To indicate the beginning of the information frame.
What is the significance of the frame check sequence (FCS) in bit-oriented protocols?
It is used for error checking the user data.
What is the purpose of the flag characters in LAP-B protocol?
To 'frame' the data by indicating the beginning and end of each transmitted frame.
How does the LAP-B protocol ensure the use of the start and end pattern in frames?
By using a technique called zero insertion or bit stuffing.
What functionality does the LAP-B protocol provide for medium-induced errors?
Detection through the frame check sequence and identification by frame number.
What is the primary similarity between LAP-B, ADCCP, and HDLC protocols?
They are quite similar in structure and format.
What is the purpose of a stop delimiter in framing for bit-oriented protocols?
To indicate the end of the information frame.
In the context of bit-oriented protocols, what does it mean for user data to be encapsulated?
It means the user data is surrounded by the protocol, framing the data.
What is the significance of zero insertion in bit-oriented protocols?
It is used to ensure that five consecutive 1 bits in the data stream are followed by a 0.
What is the impact of medium-induced errors on the receiver in LAP-B protocol?
The receiver ignores an errored frame and notifies the transmitter upon receiving the next good frame that it is not the one it anticipated.
What is the purpose of a checksum in data communications?
A checksum is used for error detection in data communications.
What are the different error detecting codes mentioned in the text?
The text mentions checksum, CRCC, and various other cyclic, linear, quasi-cyclic, and polynomial codes for error detection.
Explain the Automatic Repeat Query (ARQ) method for error correction mentioned in the text.
The ARQ method involves the transmitter sending a frame, the receiver sending an ACK or NAK, and the transmitter retransmitting if an error is detected or if there is no response from the receiver.
What is the purpose of Forward Error Correction (FEC) in data communications?
FEC is used for simplex or noisy transmissions and requires analyzing and designing error-correcting algorithms, but it can have high error-detection and location overhead.
Define protocols in the context of data communications.
Protocols are accepted procedures used in personal interactions and data communications.
What is the significance of half-duplex mode in human communication?
Humans are effectively half-duplex and typically cannot multitask listening and speaking effectively.
What can result from frame corruption in data communications?
Frame corruption can result in the receiver not recognizing the frame, leading to no response.
How does a receiver detect duplicate frames in data communications?
The receiver can detect duplicate frames with the same frame number and drop one, sending another ACK.
Why is the efficiency of checksum lower compared to cyclic codes?
Checksum is less complex than cyclic codes, but its efficiency is not as high.
What happens when a timeout occurs in data communications?
When no response is received, the transmitter assumes an error and resends the frame.
What is the purpose of Modulo abbreviation in different programming languages?
The Modulo abbreviation varies by programming language, such as MOD in COBOL and % in C-style languages.
Why is Forward Error Correction (FEC) used for simplex or noisy transmissions?
FEC is used for simplex or noisy transmissions due to its high error-detection and location overhead.
What are the two types of parity used in parity checking for error detection in data communication?
Vertical and horizontal parity
What type of errors can parity checking detect?
Single-bit errors
What is the primary drawback of parity checking?
It is less effective for multiple-errored bits and adds significant overhead to data transmission
What is the purpose of Automatic Retransmission Queries (ARQ) in error correction?
To correct errors once they are detected by requiring the transmission device to store the last transmitted block and respond to the receiver's request to retransmit the block
How does Cyclic Redundancy Check (CRC) differ from parity checking in terms of efficiency?
CRC is a more efficient error detection scheme than parity checking
What does the pick-off point in CRC depend on?
The application and the error behavior of the communications channel
How does the overhead of CRC compare to parity checking?
CRC adds less overhead than parity checking, using only a few bits per character
What type of error does CRC excel at detecting compared to parity checking?
CRC is more effective than parity checking for detecting multiple-errored bits
What is the primary difference between Checksum and CRC?
Checksum is a linear code, while CRC is a cyclic code
What is the calculation process for generating a checksum?
Converting all bits in a block to their corresponding binary numbers and summing them using modulo addition
Why is CRC more widely used in modern data communications than checksum?
Due to its superior error detection capabilities
In what type of communication is CRC particularly used?
Industrial settings
What is the purpose of parity in error detection in data communication systems?
To ensure an even number of 1s in a character
What is the IBM 4 of 8 Code used for?
Detecting errors by checking for more or less than four 1s in 8 bits
What is the significance of the vertical character format based on punched cards?
It was based on the 80-column format of punched cards and was used for error detection and retransmission
What does the addition of a parity bit do to an 8-bit character?
Adds an extra bit to make it a 9-bit structure
What is the primary difference between Bi-Sync and LAP-B protocols?
Bi-Sync is character-oriented, while LAP-B is bit-oriented
What technique does LAP-B use to ensure that the frame starts and ends with the flag?
Bit stuffing
How are medium-induced errors detected and identified in bit-oriented protocols like LAP-B?
Through frame check sequence and frame number
What does it mean for user data to be encapsulated in framing for bit-oriented protocols?
User data is included within the framing structure
What is the primary reason for bit-oriented protocols being more commonly used than character-based protocols?
Independence from the data stream contents
What is the purpose of the eighth bit in ASCII?
Parity checking
What type of errors can be detected through parity checking?
Single-bit errors only
What does Bi-Sync protocol depend on?
Character-oriented codes
What does LAP-B use for framing?
Start and stop delimiters
What are bit-oriented protocols primarily used in?
Point-to-point and multi-drop systems
How many frames does LAP-B allow to be transmitted before the first frame must be acknowledged?
128
What is the primary difference between cyclic redundancy checks (CRC) and parity checking?
CRC uses a binary polynomial to generate a check character, while parity checking involves adding framing characters and a block parity character to each data block.
What is the main disadvantage of using parity checking for error detection in data communication?
Parity checking adds significant overhead to the data transmission, requiring an additional parity bit for each character.
What distinguishes checksum from cyclic redundancy checks (CRC) as an error-detection code?
Checksum is a linear code calculated by summing all bits in a block using modulo addition, while CRC uses vertical and horizontal parity bits for error detection.
What makes automatic retransmission queries (ARQ) an important method for error correction in data communication?
ARQ requires the transmission device to store the last transmitted block and respond to the receiver's request to retransmit the block.
Why is cyclic redundancy check (CRC) considered a more efficient error detection scheme than parity checking?
CRC adds less overhead than parity checking, using only a few bits per character.
What is the primary difference between asynchronous and synchronous transmission?
Asynchronous transmission uses start and stop bits per character, while synchronous transmission uses bit timing.
What is the difference between baud rate and bits per second?
Baud rate is the line modulation rate, while bits per second is the number of signal changes per second.
What is the purpose of trellis encoding in synchronous modems?
To achieve higher data rates by sending a signal state for each 56-bit combination.
What characterizes Binary Synchronous Communication (Bi-Sync) protocol?
It is a synchronous, character-based protocol developed for IBM systems and requires duplex transmission.
Why did efficient data transmission become crucial when Bi-Sync was developed?
As a result of the significant expense of data storage at that time.
What are communication protocols primarily used for?
Controlling electronic message handling and ensuring efficient data storage
Which statement accurately describes character-based protocols like Binary Synchronous Communication (Bi-Sync)?
They use control based on certain character combinations and require the transmitting terminal to store multiple blocks of data.
What distinguishes Bi-Sync as a synchronous, character-based protocol developed for IBM systems?
It requires duplex transmission for effective communication.
What coding technique does Trellis encoding employ in synchronous modems?
It achieves higher data rates by sending a signal state for each 56-bit combination.
Which statement accurately describes baud rate and bits per second?
Baud rate is the line modulation rate, while bits per second is the number of signal changes per second.
What is the purpose of Forward Error Correction (FEC) in data communications?
To correct errors in the received data without the need for retransmission
Which method is used for error correction in Automatic Repeat Query (ARQ) in data communications?
Transmitter retransmits if error detected or no response
What type of error detection code is checksum?
Block character used for error detection
What distinguishes Forward Error Correction (FEC) from Automatic Repeat Query (ARQ) in data communications?
FEC corrects errors without retransmission, while ARQ requests retransmission
What is the primary difference between checksum and Cyclic Redundancy Check (CRC) in terms of their error-detection capabilities?
CRC can detect a wider range of errors compared to checksum
What happens when a frame corruption occurs in data communications?
Receiver may not recognize the frame, leading to no response
What type of transmissions are suitable for Forward Error Correction (FEC)?
For simplex or noisy transmissions
What does Automatic Repeat Query (ARQ) rely on to determine whether a frame needs to be retransmitted?
Acknowledgment (ACK) or Negative Acknowledgment (NAK) from the receiver
Study Notes
-
The 250-ohm resistor in a current loop is used for converting current to voltage, which powers the loop instrument and provides the measurement signal.
-
Standard signals in measurement and control allow users to pick and choose among vendors with confidence, and enable manufacturers to build instruments for a larger user base.
-
Digital Standard Signals include both open and proprietary standards in the telephone and digital data communications area, but no open, all-digital standard has been established as an alternative to the analog 4–20 mA signal.
-
IEC 61158 is an international standard for industrial fieldbuses, which defines eight different fieldbuses, four of which are primarily used in process control (PROFIBUS PA and FOUNDATION Fieldbus).
-
Ethernet is a physical and signal standard that continues to gain market share and acceptance in automation areas, and most fieldbuses and proprietary systems now provide networking services via Ethernet.
-
Data Organization: Communications Codes are the components of data organization designed for interface with humans. IBM designed one of the first digital communications codes: the IBM 4 of 8 Code in 1947.
-
ASCII, also known as International Telegraphic Alphabet (ITA) #5, is a 7-bit code that was designed in 1963 by the US government and gradually gained acceptance due to its numerically arranged code.
-
IBM 4 of 8 Code is a proprietary code with 8 bits for each character, which was used to detect character errors but carried a large overhead.
-
ITA #5 (ASCII) does not make use of letter frequencies, but uses a numerically arranged code that permits sorting operations.
-
ITA #5 (ASCII) is usually transmitted as an 8-bit signal with the Most Significant Bit reserved for parity, but today when parity is used, another bit is added as the parity bit, making the signal 9 bits in length.
-
All number systems are digital, including octal (Base 8) and hexadecimal (Base 16), used for human readability in coding and data analysis
-
Binary (Base 2) is used in data transmission systems due to its simplicity as a on-off signal
-
Bit patterns are organized into information through protocols or application programming interfaces
-
Text is organized into codings, such as American Standard Code for Information Interchange (ASCII)
-
Analog signals, contrasting with binary digital signals, represent continuous quantities and are commonly used in industrial communications
-
4–20 mA current loop signal is a widely used industrial communications standard for representing 0% to 100% of a range
-
Voltage is the difference in electrical potential, current performs the work, and resistance is the opposition a conductor offers to current
-
Impedance is the opposition a conductor offers to a changing current value, and is measured in Ohms
-
The ISA50 committee established the current loop as a standard due to its low impedance, greater noise immunity, and ability to power loop instruments.
-
All number systems are digital, including octal (Base 8) and hexadecimal (Base 16), used for human readability in coding and data analysis
-
Binary (Base 2) is used in data transmission systems due to its simplicity as a on-off signal
-
Bit patterns are organized into information through protocols or application programming interfaces
-
Text is organized into codings, such as American Standard Code for Information Interchange (ASCII)
-
Analog signals, contrasting with binary digital signals, represent continuous quantities and are commonly used in industrial communications
-
4–20 mA current loop signal is a widely used industrial communications standard for representing 0% to 100% of a range
-
Voltage is the difference in electrical potential, current performs the work, and resistance is the opposition a conductor offers to current
-
Impedance is the opposition a conductor offers to a changing current value, and is measured in Ohms
-
The ISA50 committee established the current loop as a standard due to its low impedance, greater noise immunity, and ability to power loop instruments.
-
The text discusses various encoding systems for text representation, specifically ASCII, EBCDIC, and Unicode.
-
ASCII (American Standard Code for Information Interchange) uses 7 bits with an eighth bit reserved for parity; it has 128 characters, including uppercase and lowercase letters, digits, and some special characters.
-
To determine the binary representation of a character, trace its position vertically and obtain the first three bits, then travel horizontally to obtain the remaining bits.
-
EBCDIC (Extended Binary Coded Decimal Interchange Code) is a proprietary system developed by IBM and uses the blank spaces for special characters. It does not require a parity bit but instead uses CRC (Cyclic Redundancy Check) for error detection.
-
ASCII and EBCDIC are based on fixed-length character representations and are still in use today. However, they are insufficient for representing multiple languages that require more than 128 patterns.
-
Unicode is an industry standard for encoding, representing, and handling text, with more than 100,000 characters covering multiple symbol sets. It uses 16 bits and allows users to represent ASCII characters without issue.
-
The text discusses the historical context of code representations, from Morse code to fixed-length character representations. It also touches upon the issue of communication between systems using different encoding systems and the need for software or hardware translators.
-
The text briefly discusses the importance of error correction in data transmission, using the example of a scratch on a DVD causing alterations to the music.
-
Throughout the text, the focus is on the encoding systems themselves and their key features, rather than specific examples or applications.
-
The text discusses error detection and correction in data communication using vertical and horizontal parity checking and cyclic redundancy checks (CRC).
-
Parity checking involves adding framing characters and a block parity character to each data block for error detection. Vertical parity is determined for each character in the block, and horizontal parity is determined for each bit. The vertical and horizontal parity bits are used to check for parity errors in the block.
-
Parity checking can detect single-bit errors but is less effective for multiple-errored bits. It adds significant overhead to the data transmission, requiring an additional parity bit for each character.
-
Automatic retransmission queries (ARQ) are used to correct errors once they are detected. ARQ requires the transmission device to store the last transmitted block and respond to the receiver's request to retransmit the block.
-
Cyclic redundancy checks (CRC) are a more efficient error detection scheme than parity checking. CRC involves generating a check character from a data block using a binary polynomial. The receiver computes its own CRC and compares it to the transmitted CRC to detect errors.
-
The primary difference between various CRCs is the "pick-off point," which depends on the application and the error behavior of the communications channel.
-
CRC adds less overhead than parity checking, using only a few bits per character.
-
CRC is used in modern data communications, particularly in industrial settings, and is more effective than parity checking for detecting multiple-errored bits.
-
Checksum is an error-detection code that can be considered a type of CRC, but it is a linear code rather than a cyclic code. Checksum is calculated by converting all bits in a block to their corresponding binary numbers and summing them using modulo addition. The result is the checksum, which is added to the data block for error detection.
-
CRC is more widely used in modern data communications than checksum due to its superior error detection capabilities.
-
The text discusses error detection and correction in data communication using vertical and horizontal parity checking and cyclic redundancy checks (CRC).
-
Parity checking involves adding framing characters and a block parity character to each data block for error detection. Vertical parity is determined for each character in the block, and horizontal parity is determined for each bit. The vertical and horizontal parity bits are used to check for parity errors in the block.
-
Parity checking can detect single-bit errors but is less effective for multiple-errored bits. It adds significant overhead to the data transmission, requiring an additional parity bit for each character.
-
Automatic retransmission queries (ARQ) are used to correct errors once they are detected. ARQ requires the transmission device to store the last transmitted block and respond to the receiver's request to retransmit the block.
-
Cyclic redundancy checks (CRC) are a more efficient error detection scheme than parity checking. CRC involves generating a check character from a data block using a binary polynomial. The receiver computes its own CRC and compares it to the transmitted CRC to detect errors.
-
The primary difference between various CRCs is the "pick-off point," which depends on the application and the error behavior of the communications channel.
-
CRC adds less overhead than parity checking, using only a few bits per character.
-
CRC is used in modern data communications, particularly in industrial settings, and is more effective than parity checking for detecting multiple-errored bits.
-
Checksum is an error-detection code that can be considered a type of CRC, but it is a linear code rather than a cyclic code. Checksum is calculated by converting all bits in a block to their corresponding binary numbers and summing them using modulo addition. The result is the checksum, which is added to the data block for error detection.
-
CRC is more widely used in modern data communications than checksum due to its superior error detection capabilities.
-
Checksum: a block character used for error detection, less complex than cyclic codes, efficiency is not as high
-
Modulo abbreviation varies by programming language: MOD in COBOL, % in C-style languages
-
Error detecting codes include checksum, CRCC, and various other cyclic, linear, quasi-cyclic, and polynomial codes
-
Automatic Repeat Query (ARQ) method for error correction: transmitter sends frame, receiver sends ACK or NAK, transmitter retransmits if error detected or no response
-
Frame corruption can result in receiver not recognizing frame, leading to no response
-
Timeout occurs when no response is received, transmitter assumes error and resends frame
-
Receiver can detect duplicate frames with same frame number and drop one, sending another ACK
-
Forward error correction (FEC) used for simplex or noisy transmissions, requires analyzing and designing error-correcting algorithms, can have high error-detection and location overhead
-
Protocols are accepted procedures, used in personal interactions and data communications, humans are effectively half-duplex and typically cannot multitask listening and speaking effectively.
Test your knowledge of binary, decimal, octal, and hexadecimal number systems. Explore the significance of each system in coding, data analysis, and data transmission.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
