Networks - Communication Basics

Question 1

Asynchronous Transmission (What it is, how it works, requirements)

Answer 1

• The transmission of data intermittently (at irregular intervals) between devices without the use of an external clock signal.
• The way of transmitting data that utilises start and stop bits to indicate the duration of a transmission.
• Start bit is either a 1 or 0, and the end bit is the opposite.
• Sender and receiver must use the same baud rate, and only need to synchronise their clocks for the duration of data transmission.

Question 2

What is a Start Bit?

Answer 2

• The bit used to indicate the beginning of a unit of data in asynchronous transmission.

Question 3

Stop Bit

Answer 3

• The bit used to indicate the end of a unit of data in asynchronous transmission.

Question 4

Synchronous Transmission + Example Of Usage

Answer 4

• The transmission of data which relies on a common clock signal (shared between the sender and recipient) to synchronise the time at which signals are sent.
• The signals are sent at regular intervals, and received in the same order they’re sent in.
• Hence, making this suitable for transmitting information in real-time systems.
• Used by the buses of the fetch-execute cycle.

Question 5

Bandwidth

Answer 5

• The amount of data that can a communication medium is capable of transmitting along a communication channel, measured in hertz.
• It relates to the range of frequencies available on the carrier wave that carries the data.
• There is a direct relationship between bandwidth and bit rate.
• Higher bandwidth = high bit rate

Question 6

Baud Rate

Answer 6

• The number of symbol changes, waveform changes, or signalling events across a channel per unit time.

Question 7

Bit Rate

Answer 7

• The speed of a particular transmission, which is the number of bits that are transmitted over a medium per second, often measured in bits per seconds (bps)
• A communication system’s bit rate = baud rate x no of bits per signal.
• Bit rate should > baud rate if more than one bit is sent per signal.

Question 8

Latency

Answer 8

• The time delay between an action being initiated and its effect being observed, often measured in milliseconds (ms).
• Usually increases with distance.

Question 9

Protocol

Answer 9

• A common set of rules relating to communication between devices which allow different computers to communicate with each other.
• These rules are followed during data transmission over a network to minimise inconsistencies.

Question 10

Symbol

Answer 10

• A symbol is a particular pattern of bits represented by a signal. For example, a symbol of four bits might be 1101.

Question 11

Serial Data Transmission

Answer 11

• In serial data transmission, data is sent one bit at a time over one communication line.
• Uses over medium to long distances (computationally speaking), such as for wired peripherals like keyboards connecting to a computer.

Question 12

Parallel Data Transmission

Answer 12

• Parallel data transmission uses numerous parallel communication lines at once in order to send multiple bits between components in a computer simultaneously.
• The more lines that a parallel communication medium uses, the more data that can be transferred simultaneously.

Question 13

Explain skewing in parallel tranmission

Answer 13

• Each of the communication lines that form part of a parallel communication medium have slightly different electrical properties, meaning that the time taken for one bit to be transferred will be slightly differ from line to line.
• This means bit sent together may not be received together, this is known as data skewing.
• It is worse over long distances, and can lead to bits from different pulses overlapping, causing data corruption.

Question 14

Where is parallel communication most commonly uses?

Answer 14

• Between internal components on a computer, such as parts of the CPU and RAM.

Question 15

Crosstalk

Answer 15

• Tightly packed communication lines can lead to signals leaking from one line into another, causing data corruption.

Question 16

Advantages of serial over parallel data transmission

Answer 16

• Serial data transmission doesn’t suffer from skew or crosstalk, making it more reliable.
• Hence, serial data transmission can be used over longer distances.
• Serial communication mediums use just one line, therefore making them cheaper to install than parallel mediums, which use more than one line.

Question 17

Difference between bandwidth and bit rate

Answer 17

• Bandwidth is the frequencies available on a carrier wave and therefore the capacity that is available, whereas bit rate is the actual speed of transfer.

Question 18

Describe how a start bit works with stop bits

Answer 18

• The start bit causes the receiver to synchronise its clock to the same rate as the sender.
• Both devices would have agreed beforehand on how many bits of data will follow, and whether a parity bit is used.
• The stop bit will then indicate that all data has arrived, so the processor can then begin handling the bits, ending the cycle.
• If another start bit is sent more data can be handles and the cycle continuous.