EDAC

Question 1

What is Error Detection?

Answer 1

The ability to detect errors.

Question 2

Describe a Repetition scheme

Answer 2

Data is broken into blocks and sent multiple times. The Rx terminal can then determin the most likely data.

Question 3

What is a Parity Scheme?

Answer 3

A scheme that adds an extra binary digit (check bit). Two types are EVEN and ODD parity e.g. 011 an odd parity scheme would add an extra 1 to the data stream.

Question 4

Define Error Correction

Answer 4

Ability of the Rx Terminal to reconstruct original Tx Data error free

Question 5

Expand and Define ARQ

Answer 5

Automatic Repeat Request - A form of Error Correction, it uses Ack’s and Timeouts between the Rx and Tx terminals to inform when an error has been made.

Question 6

Name 3 types of ARQ

Answer 6

1) Stop/Wait
2) Go Back-N
3) Selective Repeat

Question 7

Explain Stop/Wait ARQ

Answer 7

It sends 1 frame at a time and won’t send another until there has been an Acknowledgement. Disadvantage = Inefficient

Question 8

Explain Go Back-N ARQ

Answer 8

The Tx Terminal will send a frame, the Rx Terminal will ask for a missed frame. The Tx terminal will then resend the whole block of data to include to missing frame.

Question 9

Explain Selective Repeat ARQ

Answer 9

The Rx terminal remembers the last missed bit and asks the Tx terminal to resend it. The Tx terminal sends the individual bit rather than the whole frame.

Question 10

What is Forward Error Correction?

Answer 10

The Rx terminal never sends back an acknowledgement. It decodes the most likely data and is used when a back channel is not required.