Topic 9.1 - Communication

Question 1

Define the serial transmission method

Answer 1

Data is sent over one bit at a time across one communication wire

Question 2

Define the parallel trasmission method

Answer 2

Multiple bits sent between components of a computer (RAM TO CPU) across multiple communication lines.
The more communication lines, the more bits can be transferred simultaneously

Question 3

When is Serial Transmission used

Answer 3

Usually for peripherals communicating with a computer (mouse and keyboard)

Question 4

When is Parallel Transmission used

Answer 4

Short range, high speed connections
Inside a computer
e.g. RAM comunicating with CPU

Question 5

Advantages of Serial over Parallel transmission

Answer 5

Much Cheaper -
communication lines are expensive and serial transmission only uses one

Travels longer distances -
Parallel can only travel between very small distances

Little data corruption (reliability) -
No risk of SKEW as there is only one bit of data being sent at a time.

Question 6

Advantages of Parallel over Serial transmission

Answer 6

Simpler hardware
Much higher speed of transmission

Question 7

What is SKEW

Answer 7

Occurs when all the bits are sent simultaneously but are not all received at the same time causing data corruption.
Only happens in Parallel transmission

Question 8

What are the 2 different types of Serial Transmission

Answer 8

Synchronous
Asynchronous

Question 9

Define synchronous transmission

Answer 9

Data is transferred at regular intervals
These are synchronised by a clock
Used within the busses of the processor during the fetch-execute cycle.

Users are in sync with each other so all data is received in the correct order, no need for start and stop bits
Useful for real time data
Enables whole blocks of data to be sent in timed sequences
Much faster

Question 10

What is Asynchronous transmission

Answer 10

Data is transferred one character at time
A start bit, stop bit and parity bit sent with each character in the packet
Generally for lower speed transmission (internet)
No need for users to be in sync with each other

Question 11

Advantages of Synchronous Transmission over Asynchronous

Answer 11

• Can send more bits since there is no need for stop, start and parity bits
• Reader and sender stay in sync over long periods, so all data is read at correct intervals, reducing chance of errors
• More suitable for long distance as there are more stable timings
• Lower latency or time-lags
• Can handle larger data volumes

Overall more efficient & reliable

Question 12

Advantages of Asynchronous transmission over Synchronous

Answer 12

Simpler & Cheaper - no need for synchronised clocks

Efficient for low data volumes being transmitted

Used in computer peripherals & the internet

Question 13

What are the purposes of the Start & Stop bits in Asynchronous Data Transmission

Answer 13

They indicate to the receiving device when a character that is being transmitted begins or ends.
No need for synchronised clocks.
Ensures accuracy when transmitting data.
The start bit is either a 0 or 1 and the stop bit is always the opposite.

Question 14

Define bandwidth

Answer 14

Range of frequencies that can be transmitted across a network connection

Question 15

Define bit rate

Answer 15

The number of bits that are transferred between devices per second

Question 16

Define baseband

Answer 16

The simplest form of data transmission, at each signal change just one bit is transmitted

Question 17

Define baud rate

Answer 17

Number of times a signal in a communications channel changes state in a second
1 Baud (Bd) = 1 symbol change per second.

Question 18

Equation for calculating bit rate

Answer 18

Bit rate =
baud rate * number of bits per signal

Question 19

Define Latency

Answer 19

The delay between an action being started and its effect being noticed
Increase with distance

Question 20

Define protocol

Answer 20

A strict set of rules for data transmission.
It covers common principles for physical connections.
Examples of protocols:
FTP - File transfer
HTTP/HTTPS - Website/ Secure website

Question 21

Define handshaking

Answer 21

When 2 devices exchange signals in order to set up a communication link.
For example Ready to send & Clear to send.

Question 22

What is the relationship between bit rate and bandwidth

Answer 22

As bandwidth increases, so does bit rate, since there are more channels that bits can be sent across.

Question 23

What is the difference between bit rate and baud rate

Answer 23

Bit rate is the total number of bits being transmitted in one second.

Baud rate is the number of times a signal changes (0 to 1)

Bit rate CAN be higher than baud rate if there is more than one bit per signal change
(001 to (010)