Flashcards
Data Link Layer & Error Detection and Correction
Flashcards do conjunto (14)
- 1Functionality of the Data Link Layer- Takes raw transmission (physical layer) and transform it into a connection which is free from errors, this is done via error detection and correction
- Creating frames from network layer packets
- Traffic regulation (stop fast sender swamping slower receiver) - 2What is error detection used for?Request re-transmission of corrupt packets
- 3What is error correction used for?Attempts to correct errors without the need for re-transmission
- 4What is redundant data?An overhead which eats into the available data transmission capacity of a channel
- 5What are the two main types of error detection/correction?- Backward Error Correction (BEC)
- Forward Error Correction (FEC) - 6What are the two stages involved with backward error correction (BEC)?1. Error Detection
2. Retransmission for correction - 7What are 3 common techniques used for backward error correction?1. Character parity bits
2. Longitudinal parity bits
3. Cyclic redundancy checks - 8What are character parity bits?Adding an additional bit to make a binary sequence either odd (odd parity) or even (even parity) when counting 1's
- 9What are longitudinal parity bits also know as and what do they do?Block Check Sum (BCS)
Block of octets (7 binary bits), odd parity horizontally if even parity vertically and vice versa - 10What are Cyclic Redundancy Checks also know as and how do they work?Frame Check Sequence (FCS)
- 11How is forward error correction different to backward error correction?- Provide more redundant data in header to enable error correction
- 12How do you calculate hamming distance?X = 1 0 1 1 0 0 0
Y = 1 0 0 1 0 0 0
-------------------------
D = 0 0 1 0 0 0 0
XOR
Distance = 1 - 13Give an example of backward error correctionHamming Code
- 14How many bit errors can a single hamming code correct?1