【Lecture5】Computer Systems & Networks
Error Detection Method
- LRC (Longitudinal redundancy check)
- Checksum
- Hamming code
When information is stored in memory (either in RAM or disk) or sent via the network, the data can be corrupted with errors. Errors can occur randomly in single bits or in multiple bits at once (a burst error). That’s why both DRAM and disks implement methods to detect if an error has occurred.
LRC (Longitudinal redundancy check)
When we send the data, we don’t only send the data, we also send the BCC (Block Check Character) to determine when the date got broken while sending it to them. Additionally, this is basically used inside the LAN(Local Area Network).
Generating the BCC
Determin if the received data is correct
Checksum
This is basically used in HDD storage. Also, Checksum can only detect errors and cannot fix the errors. The reason that they use checksum and not the LRC for this HDD storage, is because for the LRC, there are too much additional information which you don’t use except for checking the data. Meaning, there are a lot of data that you cannot use when using the LRC.
Generate BCC
Determin if the received data is correct
Hamming code
This is mainly used on RAM and RAID.
Converting from binary code data to Hamming code
Detecting the error and fix it
- Your parity codes are as follows:
- Parity bit 1 = even
- Parity bit 2 = odd
- Parity bit 4 = odd
- Parity bit 8 = even
Q. Correct the following octal number: 0515 (Binary: 000101001101)
