Computer Networks - Error Detection and Correction
- 1. COMPUTER NETWORKS BCA – VI SEMESTER SUB.CODE : 16SCCCA8 UNIT-II Error Detection and Correction Presented By S.Vijaya Lakshmi B.E(CSE) Assistant Professor, Department of Computer Science, Sri Sarada Niketan College for Women,Karur.
- 2. Error detection and correction • Networks must be able to transfer data from one device to another with complete accuracy. • Data can be corrupted during transmission. • For reliable communication, errors must be detected and corrected. • Error detection and correction are implemented either at the data link layer or the transport layer of the OSI model.
- 5. Cyclic Redundancy Check Given a k-bit frame or message, the transmitter generates an n-bit sequence, known as a frame check sequence (FCS), so that the resulting frame, consisting of (k+n) bits, is exactly divisible by some predetermined number. The receiver then divides the incoming frame by the same number and, if there is no remainder, assumes that there was no error.
- 6. Single-bit error • Single bit errors are the least likely type of errors in serial data transmission because the noise must have a very short duration which is very rare. • However this kind of errors can happen in parallel transmission. • Example: • If data is sent at 1Mbps then each bit lasts only 1/1,000,000 sec. or 1 μs. • For a single-bit error to occur, the noise must have a duration of only 1 μs, which is very rare.
- 7. Burst error
- 8. Burst error • Burst error is most likely to happen in serial transmission since the duration of noise is normally longer than the duration of a bit. • The number of bits affected depends on the data rate and duration of noise. • Example: • 🢂If data is sent at rate = 1Kbps then a noise of 1/100 sec can affect 10 bits. (1/100*1000)
- 9. Error detection • Error detection means to decide whether the received data is correct or not without having a copy of the original message. • Error detection uses the concept of redundancy, which means adding extra bits for detecting errors at the destination.
- 10. Redundancy
- 11. Error Correction It can be handled in two ways: receiver can have the sender retransmit the entire data unit. The receiver can use an error correcting code, which automatically corrects certain errors.
- 12. Error Correction
- 13. Single-bit error correction • To correct an error, the receiver reverses the value of the altered bit. To do so, it must know which bit is in error. • Number of redundancy bits needed • Let data bits = m • Redundancy bits = r • Total message sent = m+r 2r ≥ m+r+1
- 14. ThankYou 14