Data Transmission Methods Flashcards
What is serial transmission?
Where data is sent 1 bit after another, in sequence.
What is parallel transmission?
Multiple data bits are sent at the same time, along side each other.
What’s a downside of parallel transmission?
Skew and Crosstalk
Define Skew.
Data from a each wire within a bus arrives at slightly different times and may not necessarily be synchronised with the clock.
Define Crosstalk.
Electromagnetic interference from adjacent wires causes the wrong data to be interpreted.
What’s advantageous about serial transmission?
- Larger distance
- Less wires => cheaper
- faster bit rates
Define Bit Rate
The number of bits transmitted over a channel each second
Units of Bit Rate
Bits per Second
Define Baud Rate
The number of times a signal can change per second
Each signal is a Symbol that a number of bits can encode
How does bit rate differ from baud rate?
Some transmission mediums such as RF will use frequency bands to encode different values which implies that a change in the signal doesn’t necessarily imply a single bit change.
What equation links Bit rate, Baud rate and Bits per symbol
Bit rate = Baud Rate * Bits per Symbol
Define Bandwidth
Bandwidth is the maximum rate of data transfer of a communication channel.
What is the relationship between bandwidth and bit rate?
Hence or otherwise, what is bandwidth measured in?
Directly proportional ; The greater the bandwidth, The greater the maximum bit rate.
Measured in Bits per second.
Define Latency.
The delay from the time that a signal is sent, to the time that it is received.
What is synchronous data transmission?
Bits of data sent at a constant rate with a common clock signal. E.g. I2C
What is asynchronous data transmission?
Data is transmitted when it is available, rather than at specific intervals with the addition of start and stop bits. E.g. RS232
Channels may be idle when data isn’t being sent.
How does asynchronous data transmission work?
- Transmission channel is idle HIGH
- Start bit pulls channel LOW to indicate an incoming byte / packet
- Data bits of byte / packet are sent in series
- Receiver samples channel at regularly timed intervals and will stop recording after the predetermined number of characters is sent
- End bit resets channel idle HIGH
Why are start AND stop bits required?
Start bit is used to indicate incoming data
End bit is used to return channel to idle HIGH so the next start bit can be recognised
What is a parity bit?
An additional error checking bit that sets the number of ones in a transmission either odd or even, used to detect bit flipping. Parity is established between devices beforehand.
