communication methods

Question 1

Serial data transmission

Answer 1

bits are sent one after another along the same data line

Serial connections were reliable but slow

Serial transmission is reliable over very long distances at very high frequencies

Question 2

Parallel data transmission

Answer 2

several bits (e.g. one byte of data) are sent simultaneously along separate lines or channels

For two-way communication, twice the number of lines are required

Parallel transmission can be used only over very short distances of up to about 2m

Question 3

problem of skew

Answer 3

As each individual wire has slightly different properties, bits travel at slightly different speeds along each of the wires. This produces a problem known as skew
bits arrive in a different order in which they were sent

Question 4

problem of crosstalk

Answer 4

This refers to electromagnetic interference between two adjacent channels or parallel wires
It gets more pronounced as the frequency (speed of transmission) increases
If the data is corrupted, it has to be retransmitted

Question 5

Synchronous transmission

Answer 5

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

Question 6

Asynchronous transmission

Answer 6

Using asynchronous data transmission, each byte is sent separately the moment it is available instead of waiting for a clock signal
Each byte is preceded by a start bit and ends with a stop bit or stop ‘period’ – a short time gap between each set of bits

Question 7

Asynchronous transmission + -

Answer 7

+
It is a cheap and effective form of serial transmission well suited to low-speed connections such as keyboard and mouse

-
Asynchronous transmission is relatively slow owing to the increased number of bits being sent

Question 8

latency

Answer 8

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

Question 9

protocol

Answer 9

All communications between devices require that the devices agree on the format of the data
The set of rules relating to communication between devices is called a protocol

Standards for physical connections and cabling
The rate of transmission (bit rate or baud rate)
Data format
Whether transmission is synchronous or asynchronous
Error checking procedures, e.g. odd or even parity

Question 10

Bit rate

Answer 10

number of bits (0’s and 1’s) transmitted in one second over a wired or wireless data link

Question 11

Baud rate

Answer 11

the rate at which the signal in a communications channel changes state
It is usually measured in megabits per second (Mbit/s)

Question 12

Relationship between bit rate and baud rate

Answer 12

Bit rate = baud rate x number of bits per signal

Question 13

Bandwidth

Answer 13

is a measure of the maximum capacity of a communications channel

synonym for data transfer rate