6.1 - Communication Methods

Question 1

What is serial data transmission?

Answer 1

Data is sent one bit at a time over one communication line (usually a metal wire but could be an optical fibre or wireless channel)
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

Multiple bits are sent simultaneously along numerous parallel communication lines
More lines = more data transferred simultaneously

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

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 electrical properties
Worse over long distances (corruption in extreme cases from overlapping of bits)

Question 6

What is crosstalk?

Answer 6

Occurs in parallel dat transmission when communication lines are tightly packed, signals can leak into another which can cause data corruption

Question 7

What are the differences between serial and parallel transmission?

Answer 7

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

Question 8

What is synchronous data transmission?

Answer 8

When a clock signal shared by both the sender and receiver is used to time when signals are sent
The signals are sent at regular intervals and received in the same order they are sent

Question 9

What is asynchronous transmission?

Answer 9

Uses start (either 0 or 1) and stop bits (opposite of start bit) instead of a shared clock signal to indicate duration of a transmission
Sender and receiver must use the same baud rate and need on,y for their clock signals to synchronise during transmission

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 an action being initiated and there being an observable effect

Question 13

What is a protocol?

Answer 13

Set of agreed rules relating to communication between devices (computer systems)

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 over the medium per second

Question 16

What is baud rate?

Answer 16

Number of signs, changes in the medium per second (1 baud = 1 symbol change per second)

Question 17

What is the formula for bit rate?

Answer 17

Bit rate (bps) = baud rate x number of bits per signal

Question 18

What is the bandwidth?

Answer 18

Range of frequencies a communication medium is capable of transmitting
Higher bandwidth (Hz) = higher bit rate (directly proportional)

Question 19

How can bit rate be higher than baud rate?

Answer 19

If more than one bit is encoded in each signal change

Question 20

What is synchronous transmission used in/for?

Answer 20

Within busses of a computers processor (fetch-execute cycle)
Suitable for transmitting information in real-time systems