Async, Sync and Line Coding

Question 1

What is an Asynchronous system?

Answer 1

Requires extra elements added to a Tx data stream to inform Rx terminal where a word begins and ends. This system does not require a linked timing device.

Question 2

What is a Synchronous system?

Answer 2

Requires extra elements added to a Tx data stream to inform Rx terminal where a block of data starts and ends. Clocking devices at both Tx and Rx must be synchronised to avoid errors.

Question 3

Disadvantages of an Asynchronous system?

Answer 3

1) No large amount of data
2) Large amount of overhead
3) Terminal clocks are independent which can result in corrupt data

Question 4

Disadvantages of a Synchronous system?

Answer 4

1) Potential to send a long run of 1s or 0s

2) Start/Stop Flag could be recreated in the data stream

Question 5

Describe a Character Oriented Transmission:

Answer 5

A sequence of data, usually 8 bits in length with all control data in character form. Each frame begins with a SYN which signals the Rx terminal at the beginning of a block.

Question 6

Describe a Bit Oriented Transmission:

Answer 6

A transmission where the block of data is treated as a sequence of bits. Uses a flag to indicate the beginning and end of a block.

Question 7

What is Zero Bit Insertion?

Answer 7

To ensure flags are not repeated in the data, after every five 1s a zero is automatically added. E.g 01111110 = a flag, 0111110 = Zero bit insertion to stop the data being mistaken for a flag.