1. Unit 1 Protocols Learning Objectives: 5.1.7 Understand the need to detect and correct errors in data transmission

2. Error Detection Errors can occur whenever information is stored or transmitted. Error detection techniques add extra parity bits to data to determine when errors have occurred. This activity uses a magic trick to show how to detect when data has been corrupted, and how to correct it.

3. Checksums A checksum is an algorithm used to check for errors in data transmission. It works by calculating a numerical value based on the number of bits in a packed of data. This value is attached to the packet. Now complete slide 12 of your Networks workbook. When the packet reaches its destination, the same checksum algorithm is applied to the data. If the two checksums don’t match it shows that an error has occurred and the receiving computer asks the sending computer to re-send that package. A match means that no transmission error has been detected.

4. Parity Checking Parity checking is a simple form of error detection. A parity bit is added to the end of a string of binary code to indicate whether the number of bits in the string with the value 1 is even or odd. There are two type of parity bits: Where the bit is set to 1 if the number of bits is odd. The extra parity bit will make the number of 1s even. Even Parity Where the parity bit is set to 1 if the number of bits is even. The extra parity bit will make the number of 1s odd. Odd Parity There are other more sophisticated methods of detecting errors, such as cyclic redundancy checks (CRC).

5. Example Work through these examples as a class. Data being transmitted Number of 1s Even parityOdd parity 01010103 0101010 1 0101010 0 00011114 0001111 0 10000012 Now complete slides 13-14 of your Networks workbook.