3.9.1.1 Communication methods.

Question 1

Define serial transmission.

Answer 1

Data is sent one bit at a time over one communication line.

Could be fibre optic, metal wire or a wireless channel.

Question 2

What is serial transmission frequently used for?

Answer 2

Transmitting data over medium to long
distances (computationally speaking), such as from wired peripherals like mice and keyboards to your computer.

KEY PART: MEDIUM TO LONG DISTANCES.

Question 3

Define parallel data transmission.

Answer 3

Uses multiple communication lines and sends multiple bits at once.
The more lines the more data can be transferred simultaneously.

Question 4

Define data skew.

Answer 4

Data skew occurs as tiny differences in the length of time it takes for bits to travel down each of the wires means data can arrive unsynchronised.

Question 5

Define Crosstalk.

Answer 5

Crosstalk occurs between the wires causing data to become corrupt.

Question 6

When is skew worst?

Answer 6

Over long distances.`

Question 7

What can skew lead to?

Answer 7

can lead to bits from different pulses overlapping, causing corruption of data.

Question 8

State any other disadvantages of parallel.

Answer 8

Multiple lines = expensive.

Causes parallel to be most often used over short distances, such as between parts of the processor and within RAM.

Question 9

State the advantages of serial over parallel.

Answer 9

Serial doesn’t have crosstalk or skew - more reliable communication method, especially over long distances.
Serial - one line meaning cheaper to install.

Question 10

Define synchronous transmission.

Answer 10

Clock signal is used to time when signals are sent, aka controlling the transmission rate; this is done to ensure that both communicating devices transmit and receive data at the same speed.

Question 11

What happens if the devices are not synchronised?

Answer 11

Data could be lost/corrupted during transmission.

Question 12

Outline asynchronous transmission.

Answer 12

The shared clock signal is discarded and it instead uses start and stop bits to indicate the duration of a transmission.

Question 13

Outline the start and stop bits.

Answer 13

The start bit can either be a 0 or a 1 and the stop bit is always the opposite of the start bit.
Sender and receiver must use the same baud.
transmitter and receiver are not kept synchronised, they are only synchronised temporarily for the duration of each transmission e.g. when typing on a computer keyboard.

Question 14

Outline the different transmission medias.

Answer 14

Copper cable e.g. twisted pair, coaxial.

Fibre Optics.

Satellite.

Terrestrial microwave.

Radio.