August
1997 QUESTION 5 Total Marks: 20 Marks |
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| 5. | (a) What is the purpose of parity checking? | [2] | ||||||||||
| (b) Assume that in a particular transmission protocol, bytes consist of seven bits of data, followed by one parity bit, using even parity. The following bytes are received. In which one has a transmission error occurred? | [3] | |||||||||||
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| Explain your answer. | ||||||||||||
| (c) Describe the VRC/LRC error-correcting scheme. Explain the limitations of this scheme. | [5] | |||||||||||
| (d) If the bytes of part (b) are followed by a check byte 00101101, determine which bit was wrong in the transmission, and give the correct form of the byte which was transmitted in error. | [4] | |||||||||||
| (e) Error-correction coding can entail high overheads. What is the alternative to the use of error-correcting codes? What factors determine which approach is appropriate? | [4] | |||||||||||
| (f) In the OSI model, error detection is a function performed by the data link level. Name two services provided by this layer, and two other functions it performs. | [2] |