2.1 Data Transmission

Question 1

Data transmission

Answer 1

The movement of data via a transmission medium between the sender and the receiver

Question 2

Simplex data transmission

Answer 2

Data travels in one direction only

Question 3

Half-duplex data transmission

Answer 3

Data can travel in both directions along a single cable, but not simultaneously

Question 4

Full-duplex data transmission

Answer 4

Data can travel in both directions simultaneously using 2 cables

Question 5

3 types of cable & their uses

Answer 5

1. Twisted pair cable (eg. Ethernet cable)
2. Coaxial cable (eg. television, electrical equipment)
3. Fibre-optic cable (eg. Internet cables)

Question 6

Serial data transmission

Application

Answer 6

Data is sent 1 bit at a time over a single wire

Application: connect computer to a modem

Question 7

Parallel data transmission

2 applications

Answer 7

1 byte of data is sent down 8 wires at the same time
Applications:
- sending data from a computer to a printer
- internal data transfer (buses)

Question 8

4 advantages of serial data transmission

Answer 8

1. SINGLE WIRE means there is less chance of interference/data corruption
2. SINGLE WIRE reduces costs
3. MORE reliable over greater distances
4. bits will still be synchronised after transmission

Question 9

Disadvantage of serial data transmission

Answer 9

Slower rate of data transmission

Question 10

Advantage of parallel data transmission

Answer 10

Faster rate of data transmission

Question 11

2 disadvantages of parallel data transmission

Answer 11

1. More expensive
2. Less reliable over long distances (bits can become ‘skewed’ where signals travel at different speeds due to differences in wires and may not all arrive at the same time)

Question 12

5 advantages of asynchronous transmission

Answer 12

1. Cheaper
2. If character is corrupted during transmission, successor & predecessor characters are not affected
3. Possible to transmit signals from sources with different bit rates
4. Transmission can start as soon as data byte is available
5. Easy to implement

Question 13

2 disadvantages of asynchronous transmission

Answer 13

1. Slower, less efficient

2. Successful transmission depends on recognition of start bits, which can be missed/corrupted

Question 14

Advantage of synchronous transmission

Answer 14

Faster

Question 15

2 disadvantages of synchronous transmission

Answer 15

1. Costly (needs local buffer storage to assemble blocks; needs accurately synchronised clocks at both ends)
2. Complicated (sender & receiver have to operate at same clock frequency)

Question 16

6 pros of using USB

Answer 16

1. Devices plugged into computer are automatically detected
2. USB connectors are shaped so that it is impossible to install devices incorrectly
3. Has become the industry standard; considerable support available to users
4. Supports multiple data transmission speeds
5. Latest USB standards are backward compatible with older standards
6. Faster transmission compared to wireless

Question 17

3 cons of using USB

Answer 17

1. Cable length is limited to 5m
2. Transmission speed limited to 480Mbps
3. Older USB standard may not be supported in the near future

Question 18

Integrated Circuit (IC)

Answer 18

An IC is a collection of microscopic electronic circuits, sealed into a plastic/ceramic package
*uses parallel data transmission

Question 19

When might a parity check not identify that a bit has been transmitted incorrectly?

Answer 19

• Even number of digits are changed

- A transposition error has occurred

Question 20

Explain how Automatic Repeat reQuests (ARQ) are used in data transmission and storage.

Answer 20

• It’s an error detection method
• Uses acknowledgement and timeout
• Request is sent (with data) requiring acknowledgement
• If no acknowledgment within certain time frame data package is resent
• When data received contains an error a request is sent (automatically) to resend the data
• The resend request is repeatedly sent until packet is received error free