Data Transmission Methods

Question 1

What is serial transmission?

Answer 1

Where data is sent 1 bit after another, in sequence.

Question 2

What is parallel transmission?

Answer 2

Multiple data bits are sent at the same time, along side each other.

Question 3

What’s a downside of parallel transmission?

Answer 3

Skew and Crosstalk

Question 4

Define Skew.

Answer 4

Data from a each wire within a bus arrives at slightly different times and may not necessarily be synchronised with the clock.

Question 5

Define Crosstalk.

Answer 5

Electromagnetic interference from adjacent wires causes the wrong data to be interpreted.

Question 6

What’s advantageous about serial transmission?

Answer 6

• Larger distance
• Less wires => cheaper
• faster bit rates

Question 7

Define Bit Rate

Answer 7

The number of bits transmitted over a channel each second

Question 8

Units of Bit Rate

Answer 8

Bits per Second

Question 9

Define Baud Rate

Answer 9

The number of times a signal can change per second
Each signal is a Symbol that a number of bits can encode

Question 10

How does bit rate differ from baud rate?

Answer 10

Some transmission mediums such as RF will use frequency bands to encode different values which implies that a change in the signal doesn’t necessarily imply a single bit change.

Question 11

What equation links Bit rate, Baud rate and Bits per symbol

Answer 11

Bit rate = Baud Rate * Bits per Symbol

Question 12

Define Bandwidth

Answer 12

Bandwidth is the maximum rate of data transfer of a communication channel.

Question 13

What is the relationship between bandwidth and bit rate?
Hence or otherwise, what is bandwidth measured in?

Answer 13

Directly proportional ; The greater the bandwidth, The greater the maximum bit rate.
Measured in Bits per second.

Question 14

Define Latency.

Answer 14

The delay from the time that a signal is sent, to the time that it is received.

Question 15

What is synchronous data transmission?

Answer 15

Bits of data sent at a constant rate with a common clock signal. E.g. I2C

Question 16

What is asynchronous data transmission?

Answer 16

Data is transmitted when it is available, rather than at specific intervals with the addition of start and stop bits. E.g. RS232
Channels may be idle when data isn’t being sent.

Question 17

How does asynchronous data transmission work?

Answer 17

• Transmission channel is idle HIGH
• Start bit pulls channel LOW to indicate an incoming byte / packet
• Data bits of byte / packet are sent in series
• Receiver samples channel at regularly timed intervals and will stop recording after the predetermined number of characters is sent
• End bit resets channel idle HIGH

Question 18

Why are start AND stop bits required?

Answer 18

Start bit is used to indicate incoming data
End bit is used to return channel to idle HIGH so the next start bit can be recognised

Question 19

What is a parity bit?

Answer 19

An additional error checking bit that sets the number of ones in a transmission either odd or even, used to detect bit flipping. Parity is established between devices beforehand.