Transmission errors

• External electromagnetic signals can cause incorrect delivery of data
  • Data can be received incorrectly
  • Data can be lost
  • Unwanted data can be generated
• Any of these problems are called transmission errors

• Error detection - send additional information so incorrect data can be detected and rejected
• Error correction - send additional information so incorrect data can be corrected and accepted

Error Detecting Codes (Implemented either at Data link layer or Transport Layer of OSI Model)Whenever a message is transmitted, it may get scrambled by noise or data may get corrupted. To avoid this, we use error-detecting codes which are additional data added to a given digital message to help us detect if any error has occurred during transmission of the message.


Some popular techniques for error detection are:
1. Simple Parity check

• 1 is added to the block if it contains odd number of 1’s, and
• 0 is added if it contains even number of 1’s

2. Checksum


all received segments are added using 1’s complement arithmetic to get the sum. 




3. cyclic redundancy check(CRC)
In CRC, a sequence of redundant bits, called cyclic redundancy check bits, are appended to the end of data unit so that the resulting .