Error detection and correction techniques are implemented either at the data link layer and the transport layer of the OSI model.
Data can be corrupted during transmission. for reliable communication, errors must be detected and corrected techniques.
- Bits lost
- Bits changed
- Bits added
Types of Error
- Single bit errors
- Burst errors
In information theory and techniques theory in computer science and telecommunication, error detection and correction techniques that enable reliable delivery of digital data over unreliable communication channels.
SINGLE BIT ERROR – The term single bit error means that only 1 bit of a given data unit (such as a byte, character, data unit, or packet) is changed from 1 to 0 or from 0 to 1.
BURST ERROR – The term burst error means two or more bits within the data unit have changed from 1 to 0 or from 0 to 1.
ERROR DETECTION AND CORRECTION TECHNIQUES
- Error Detection techniques concede the destination to detect errors.
- Sometimes undetected errors will still remain but the goal is to minimize these errors
- To detect and correct errors, sufficient redundancy bits need to be sent with data.
- Redundancy bits are the extra bits sent by the source to inform the destination about the data sent.
- Parity Check
- Cyclic Redundancy Check(based on binary division)
- Hamming Distance Check
BACKWORD ERROR CORRECTION
- Known as Automatic Repeat Request(ARR)
- The receiver device sends a request to the source device to re-send the data after detecting the error or errors
- More often used because it requires less bandwidth
- A return channel is required for backward error correction
Backward Error Correction
• There are two ways to overcome the errors
1 Positive acknowledgment
The receiver returns confirmation of every block received correctly. The transmitter-sends the block that is not acknowledged.
2 Negative acknowledgment
Receiverreturnsa request to retransmit only the data with error
FORWARD ERROR CORRECTION
- This technique allows the receiver to detect and correct errors without asking the send error retransmission
- The bandwidth requirements higher but the return channel is not needed
- Redundant data sent by transmitters also called error-correction code
Forward error correction
• Redundancy bits are added to the transmitted information using predetermined information
• Each redundancy bit is often a function of the many parts of original data or can also be nonsystematic
EXAMPLE OF forwarding ERROR CORRECTION
FORWARD ERROR CORRECTION
• Two main categories
1 BlockCoding: Reed-Solomon Coding, Hamming Codes, Binary BCH
2 Convolutional Coding: Viterbi algorithm
- Block Coding works on fixed-size packets of bits
- Mostly common used algorithmic Reed-Solomon
1. BLOCK CODING: REED-SOLOMON CODING
- A Reed-Solomon code is specified as RS(n,k) with s-bit symbols
- This means that the encoder takes k data symbols of s bits each and adds parity symbols to make any symbol codeword
- There are n-k parity symbols of s bits each. A Reed-Solomon decoder can correct up to t symbols that contain errors during a codeword, where 2t=n-k.
EXAMPLE OF REED-SOLOMON
- Example: A popular Reed-Solomon code is RS(255,223) with 8-bit symbols. Each codeword contains 255 code word bytes, of which 223 bytes are data and 32 bytes is parity. For this code:
- n = 255, k = 223, s = 8
- 2t = 32, t = 16
- The decoder can correct any 16 symbol errors within the code word
2. CONVOLUTIONAL CODING
Convolutional codes work on bitstreams
If desired convolutional code can be turned into a block code
Mostwidelyusedalgorithmis VitebiAlgorithmif desired
- Viterbi decoder examines a whole received data sequence of a given length at a time interval, then computes a metric for each path and makes a decision based on this metric
- One of the common metric used by the Viterbi Algorithm for paths comparison is the Hamming distance metric, which is a bit-wise comparison between the received codeword and the allowable codeword
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