A209 - Communication Methods Flashcards
What is Serial Data Transmission?
Data bits are sent in a sequence, one after the other, over a single line
What is Parallel Data transmission?
Several bits are sent at the same time over a set of parallel lines
What is a problem with Parallel Data transmission?
Crosstalk: electromagnetic interference between wires in close proximity results in transmitting corrupted data
Skew: bits transmitted across parallel links may travel at different speeds. In synchronous data transmission, this can result in data falling out of sync with the clock signal and therefore not being read correctly
What are the advantages of serial over parallel data transmission?
- Operates more efficiently at higher bit rates
- Not affected by skew
- Fewer wires in close proximity which minimises crosstalk
- Uses fewer wires and pins so are cheaper to implement
- Core infrastructure occupies less space
What is the bit rate?
The number of bits that are transmitted over a channel each second.
For broadband: bit rate = baud rate × number of bits encoded per symbol
What unit is bit rate measured in?
(SI prefix) bits per second / bps
What is the baud rate?
The number of times that a signal changes per second. Each signal is a symbol that can encode a certain number of bits
What unit is baud rate measured in?
(SI prefix) symbols per second / number signal changes per second
What is the relationship between bit rate and baud rate?
Symbol |-> 1 bit: bit rate = baud rate (baseband transmission)
Symbol |-> 2+ bits: bit rate > baud rate (broadband transmission)
What is bandwidth?
The maximum rate of data transfer of a communication channel
What unit is bandwidth measured in?
(SI prefix) bits per second / bps
What is latency?
The delay from the time that a signal is sent to the time that it is received
What is synchronous transmission?
Streams of bits are transferred over a communication channel at a constant rate. The transmitter and the receiver are synchronised using a common clock signal
What is asynchronous transmission?
No clock signal so start and stop bits are used to control the communication. Data is transmitted when it is available rather than at specific intervals
How are start and stop bits used in asynchronous transmission?
- Start bit sent at beginning of transmission so receiver can prepare for incoming data.
- Stop bit marks end of transmission.
- Stop bit must be opposite of start bit so receiver can recognise the next set of bits.
- Stop signal typically longer than one bit so receiver has time to get ready for arrival of the next set of data.
Why do you need both synchronous and asynchronous transmission?
Synchronous: faster and less data transferred because no transmission control bits
Asynchronous: more flexible and is able to transmit data as soon as it is available
What is a parity bit?
A bit added to data being sent across networks, used to check for transmission errors.
