03 communication methods

Question 1

what is serial data transmission

Answer 1

bits are sent one after another along the same data line​

This means that only one line is needed to transmit data in one direction. (Two lines are required for two-way communication, plus a common signal ground wire)​

Question 2

what is Parallel data transmission

Answer 2

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

This means that an 8-bit block of data will require 8 data channels, plus some extra for control information​

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Question 3

problems with parallel data transmission

Answer 3

as speeds of transmission get higher and higher, parallel connections developed problems

Question 4

the problem of skew

Answer 4

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​

Question 5

the problem of crosstalk

Answer 5

This refers to electromagnetic interference between two adjacent channels or parallel wires​

It gets more pronounced as the frequency (speed of transmission) increases​

Question 6

Serial vs parallel transmission​

Answer 6

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

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

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Question 7

serial vs parallel connectors​

Answer 7

Serial connectors such as USB (Universal Serial Bus) connectors are much smaller and cheaper than parallel connectors​

A PC has several USB ports for connecting peripherals​

Question 8

Synchronous transmission​

Answer 8

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 9

Asynchronous transmission​

Answer 9

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

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

Question 10

Latency

Answer 10

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 11

Protocol

Answer 11

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​

Question 12

Bit rate

Answer 12

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

Question 13

Baud rate

Answer 13

the rate at which the signal in a communications channel changes state​

It is usually measured in megabits per second (Mbit/s)​

Question 14

Relationship between bit rate and baud rate​

Answer 14

Bit rate = baud rate x number of bits per signal​

Question 15

Bandwidth

Answer 15

a measure of the maximum capacity of a communications channel​

In computer networks, the term bandwidth is used as a synonym for data transfer rate​