4.2 - Error Control Flashcards
These kinds of errors (ex: mistake in typing a number) are usually controlled through the app or program (through app validation and error messages)
Human errors
These kinds of errors are controlled by the network hardware and software (ex: transmission error)
Network errors
Two categories of network errors:
- Corrupted data
- Lost data
Networks should be designed to ________, ________, and _________ both corrupted data and lost data
prevent…detect…correct
Introduced by equipment or natural disturbances, and it degrades the performance of a communication circuit
Noise
Noise manifests itself as:
- Extra bits
- Missing bits
- Bits that have been “flipped”
Sources of error:
- White Noise
- Impluse Noise
- Crosstalk
- Echo
- Attenuation
- Intermodulation Noise
Movement of electrons
Cause of white noise:
Sudden increases in electricity (e.g., lightning, surges)
Cause of impulse noise:
Multiplexer guardbands too small or wires too close together
Cause of crosstalk:
Poor connections
Cause of echo:
Gradual decrease in signal over distance
Cause of attenuation:
Signals from several circuits combine
Cause of intermodulation noise:
Techniques to prevent errors:
- Shielding
- Moving Cables
- Use of Repeaters/Amplifiers
______________ is the process of protecting wires by covering them with an insulating coating
Shielding
Shielding is one of the best ways to prevent:
- Impulse noise
- Crosstalk
- Intermodulation noise
______________ away from sources of noise can also reduce impulse noise, crosstalk, and intermodulation noise
Moving cables
For _____________ — avoiding lights and heavy machinery
impulse noise
For ___________ — physically separating the cables from other communication cables
crosstalk
For ______, ________ —- tune transmission equipment and redo connections
echoes….white noise
To avoid ______________, telephone circuits have repeaters or amplifiers spaced throughout their length
attentuation
The only way to do error detection is to send ______________ with each message
extra data
These error-detection data are added to each message by the ______________ layer of the sender on the basis of some mathematical calculations performed on the message
data link
The ___________ performs the same mathematical calculations on the message it receives and matches its results with the message
receiver
The rate at which a system, process, or operation can produce, process, or deliver units of output within a given time period
Thoroughput
One of the oldest and simplest error-detection methods is ___________
parity
The ______________ is to make the total number of 1s in the byte (including the parity bit) either an even number or an odd number
parity bit
The value of this additional ______________ is based on the number of 1s in each byte transmitted
parity bit
Parity can detect errors only when an ______ number of bits have been switched; any even number of errors cancel one another out
odd
The probability of detecting an error is only about 50%
Parity checking
With a checksum technique, a ____________ (typically 1 byte) is added to the end of the message
checksum
______________ is calculated by adding the decimal value of each character in the message, dividing the sum by 255, and using the remainder as the checksum
Checksum
Use of ______________ detects close to 95% of the errors for multiple-bit burst errors
checksum
With ______________, a message is treated as one long binary number, which is divided by a preset number, and the remainder is used as the CRC code
cyclic redundancy check (CRC)
It adds 8, 16, 24, or 32 bits to the message
cyclic redundancy check (CRC)
Probability of detecting error is 99 - 100%
cyclic redundancy check (CRC)
The simplest, most effective, least expensive, and most commonly used method for error correction is ______________
retransmission
