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**

In this paragraph, we are going to talk about *Error Detection And Correction Techniques. But if you want to know about Transmission mode click this.*

**ERROR DETECTION**

- Error Detection techniques concede the destination to detect errors.
- Sometimes undetected errors will still remain but the goal is to minimize these errors

**ERROR DETECTION**

- 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.

**ERROR DETECTION**

- Parity Check
- Cyclic Redundancy Check(based on binary division)
- Checksum
- Hamming Distance Check

**ERROR CORRECTION**

**ERROR CORRECTION**

BackwardErrorCorrection

ForwardErrorCorrection

**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 CORRECTIO**N

**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

**conclusion**

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