Module 6 Chapter 1 Communication Methods

Question 1

What is meant by data communication?

Answer 1

Sending and receiving data from one computer or device to another.

Question 2

Give three common applications of data communication.

Answer 2

• Sending and receiving e-mails
• Making and receiving calls on mobile phones
• Requesting and fetching data from a server

Question 3

Is data communication limited to data transferred across separate computer systems?

Answer 3

No, data communication takes place with all computer systems, between the CPU and its peripheral devices such as a disk drive.

Question 4

What are the two alternative methods of data transmission we use?

Answer 4

• Serial data transmission

- Parallel data transmission

Question 5

What is serial data transmission?

Answer 5

When data is sent from source to destination over a single cable, one bit at a time.

Question 6

What is parallel data transmission?

Answer 6

When several bits are sent simultaneously over a number of parallel wires to transmit data from source to destination.

Question 7

What are the advantages of serial data transmission over parallel data transmission?

Answer 7

• Very high bit rates can be achieved (depending on the type of cable, fibre-optic cables being very fast)
• Data can be easily transmitted over longer distances
• No problem with skew or crosstalk as found in parallel data transmission
• Serial cables are cheaper in general
• Serial connectors typically take up less space

Question 8

What is the typical range of data transfer rates achieved by serial data transmission?

Answer 8

50 Megabits per second (Mbs) to 100 Gigabits per second (Gbs)

Question 9

Where is parallel data transmission normally used?

Answer 9

Within a computer system. Parallel cables are often used for computer buses. Parallel cables can also be used to transmit data over short distances ,a couple of metres at most, connecting devices such as a PC and a nearby printer.

Question 10

What is the advantage of using parallel data transmission?

Answer 10

More bits can be transferred at once, which can lead to a faster transfer rate, but not always as the baud rate can be severely limited.

Question 11

What two problems with parallel data transmission can cause corrupted data at higher signal frequencies?

Answer 11

• Crosstalk: interference between parallel lines

- Skew: bits travelling parallel lines at different rates

Question 12

What is crosstalk?

Answer 12

A problem that occurs in parallel data transmission where parallel lines interfere with each other, corrupting the data. This is worsened by higher signal frequencies and transmitting data over longer distances.

Question 13

What is skew?

Answer 13

When variations in the exact properties of individual wires in a parallel connection cause bits to travel across them at different speeds and arrive at their destination out of order, causing data to be corrupted. For this reason, parallel data transmission is only reliable over short distances and signal frequencies are limited.

Question 14

When would you use serial data transmission?

Answer 14

When you need to transfer data across distances over about two metres.

Question 15

What is protocol?

Answer 15

A set of rules relating to communication between devices.
In order to allow equipment from different suppliers to be networked, a standardised set of rules (protocols) has to be implemented, covering standards for physical connectors, cabling, mode of transmission, speed, data format, error detection and correction methods. Any pieces of equipment which use the same communication protocol can be networked.

Question 16

What is bit rate?

Answer 16

The speed at which data is transmitted, measured in bits per second.

Question 17

What is baud rate?

Answer 17

The rate at which the signal changes, so how quickly the signal can go from 1 to 0 or 0111 to 0100. It is measured in ‘units’ per second.

Question 18

How do you calculate bit rate?

Answer 18

bit rate = baud rate * number of bits per signal

Question 19

What is baseband?

Answer 19

Baseband is when bit rate is equal to baud rate. In other words, the number of bits per signal is one.

Question 20

What is bandwidth?

Answer 20

The amount of data that can be transmitted in a fixed amount of time. It is usually expressed in bits per second (bps). Bandwidth is essentially the maximum bit rate of a signal.

Question 21

What is latency?

Answer 21

Latency is the time delay between the moment the first byte of a communication leaves the source and when it arrives at its destination.

Question 22

What is a parity bit?

Answer 22

The last bit in a byte, used for error checking.

Question 23

What are the two types of parity?

Answer 23

• Odd parity, where the number of 1’s must be odd

- Even parity, where the number of 1’s must be even

Question 24

Assuming no error has occurred, does the following byte use even or odd parity?
00010110

Answer 24

Odd parity.

Question 25

Assuming no error has occurred, does the following byte use even or odd parity? 01010110

Answer 25

Even parity.

Question 26

A computer system is using an even parity system and needs to transmit the following seven digit binary number: 0011101 What would the parity bit be?

Answer 26

0

Question 27

A computer system is using an even parity system and needs to transmit the following seven digit binary number: 1011101 What would the parity bit be?

Answer 27

1

Question 28

A computer system is using an odd parity system and needs to transmit the following seven digit binary number: 0011101 What would the parity bit be?

Answer 28

1

Question 29

A computer system is using an odd parity system and needs to transmit the following seven digit binary number: 1011101 What would the parity bit be?

Answer 29

0

Question 30

A computer system is using an odd parity system and transmits the following byte: 01101001 Has an error occurred?

Answer 30

Yes; there's an even number of 1's.

Question 31

A computer system is using an odd parity system and transmits the following byte: 11101001 Has an error occurred?

Answer 31

No; there's an odd number of 1's.

Question 32

A computer system is using an even parity system and transmits the following byte: 01101001 Has an error occurred?

Answer 32

No; there's an even number of 1's.

Question 33

A computer system is using an even parity system and transmits the following byte: 01101011 Has an error occurred?

Answer 33

Yes; there's an odd number of 1's.

Question 34

How does parity checking work?

Answer 34

When a byte is transmitted, the first seven bits are used to store the data and the eighth bit is used to give the entire byte either and odd or even number of 1's, depending on the parity system being used. When the byte is received, the number of 1's in each byte is checked and if they're not correct (odd or even) then the data is discarded as corrupted and the receiving computer requests the source to resend it.

Question 35

What is synchronous transmission?

Answer 35

When data is transferred at regular intervals that are timed by a clocking signal. This allows for a constant and reliable transmission of time-sensitive data.

Question 36

Where is synchronous transmission typically used?

Answer 36

When using parallel data transmission such as a computer bus.

Question 37

What is asynchronous transmission?

Answer 37

When bytes are sent one after another as soon as they're available. Bytes are encased in stop and start bits to prevent bytes overlapping.

Question 38

What is significant about the relationship between stop and start bits?

Answer 38

They're always opposite. If the start bit is 1, the stop bit will be 0 and vice verse.