6.1 - Communication Methods

Question 1

What is serial data transmission?

Answer 1

Bits are sent one after another along the same data line
One line is required for data transmitted in one direction, two line needed for two way communication

Question 2

What is parallel data transmission?

Answer 2

Several bits are sent simultaneously along separate lines or channels
8 bit block of data will require 8 data channels plus some extra for control information

Question 3

What is an example of a serial data cable?

Answer 3

USB (universal serial bus)

Question 4

What are parallel cables used for?

Answer 4

Primarily used for connecting internal components as a ribbon of several smaller cables

Question 5

What is skew?

Answer 5

Problem with parallel data transmission data where bits travel at slightly different speeds along each wire as each individual wire has slightly different properties

Question 6

What is crosstalk?

Answer 6

EM interference between two adjacent channels or parallel wires
Becomes more pronounced as the frequency (speed of transmission) increases
Risk of corruption

Question 7

What are the differences between serial and parallel transmission?

Answer 7

Parallel can only be used only over very short distances aces (up to 2m), quick transmission
Serial is very reliable over very long dispatches at high frequencies, slower and cheaper

Question 8

What is synchronous data transmission?

Answer 8

All data transfers are timed to coincide with an internal clock pulse
Data is sent as one long stream or block of data, with no gaps in transmission
Receiver counts the bits and reconstructs bytes

Question 9

What is asynchronous transmission?

Answer 9

Each byte is sent separately the moment it is available instead of waiting for a clock signal
Each byte is preceded with a start bit and ends with a stop bit - a short time gap between each set of bits

Question 10

What is the parity bit used for?

Answer 10

Added as the 8th bit as a form of error detection

Question 11

What are the pros and cons of asynchronous transmission?

Answer 11

Pros:
- cheap
- effective form of serial transmission
- well suited to low speed connections (keyboard, mouse)
Cons:
- relatively slow flowing from increased number of bits sent

Question 12

What is latency?

Answer 12

Time delay between the moment the first byte or packet of communication starts and when it is received at its destination

Question 13

What is a protocol?

Answer 13

Set of rules relating to communication between devises

Question 14

What does the protocol need to define?

Answer 14

• standards for physical connections and cabling
• the rate of transmission (bit rate, baud rate)
• data format
• whether transmission is synchronous or asynchronous
• error checking procedures

Question 15

What is bit rate?

Answer 15

Number of bits transmitted in one second over a wired or wireless data link
Using baseband at each signal change one bit is transmitted
Faster signal change = greater number of bits per second

Question 16

What is baud rate?

Answer 16

Rate at which the signal in a communications channel changes state (megabits per second Mbit/s)

Question 17

What is baseband?

Answer 17

Carries one signal at a time
A bit is represented by either high or low voltage in the cable
In baseband, bit rate = baud rate

Question 18

What is broadband?

Answer 18

Carries multiple signals on a fixed carrier wave
Bits are sent as variations on the wave

Question 19

What is the formula for bit rate?

Answer 19

Bit rate = baud rate x number of bits per signal

Question 20

What is the bandwidth?

Answer 20

Measure of the maximum capacity of a communications channel
Synonym of data transfer rate
Bps, Mbps or Gbps

Question 21

What is the relationship between bandwidth and bit rate?

Answer 21

Direct relationship